# A Comprehensive Review on Pharmacotherapeutics of Herbal Bioenhancers

Authors: Ghanshyam B. Dudhatra; Shailesh K. Mody; Madhavi M. Awale; Hitesh B. Patel; Chirag M. Modi; Avinash Kumar; Divyesh R. Kamani; Bhavesh N. Chauhan
Journal: The Scientific World Journal
 (2012)

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## Abstract

In India, Ayurveda has made a major contribution to the drug discovery process with new means of identifying active compounds. Recent advancement in bioavailability enhancement of drugs by compounds of herbal origin has produced a revolutionary shift in the way of therapeutics. Thus, bibliographic investigation was carried out by analyzing classical text books and peer-reviewed papers, consulting worldwide-accepted scientific databases from last 30 years. Herbal bioenhancers have been shown to enhance bioavailability and bioefficacy of different classes of drugs, such as antibiotics, antituberculosis, antiviral, antifungal, and anticancerous drugs at low doses. They have also improved oral absorption of nutraceuticals like vitamins, minerals, amino acids, and certain herbal compounds. Their mechanism of action is mainly through absorption process, drug metabolism, and action on drug target. This paper clearly indicates that scientific researchers and pharmaceutical industries have to give emphasis on experimental studies to find out novel active principles from such a vast array of unexploited plants having a role as a bioavailability and bioefficacy enhancer. Also, the mechanisms of action by which bioenhancer compounds exert bioenhancing effects remain to be explored.


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## Body

## 1. Introduction

Modern pharmaceutical research is concerned with all aspects of identifying new chemical substances with new modes of action. Particularly, economics of treatment linked to drug dosage has led to new drug development technologies. As a result, treatments are now becoming more affordable for wide sections of society, including the financially challenged. One way to achieve reduction in drug dosage, and therefore drug toxicity and cost, is to increase drug bioavailability [1]. The consumption of antibiotics and drugs by man is increasing at an alarming rate. Out of the total drugs and chemicals, 20–50% of that use is unnecessary depending on the class of antibiotic. In addition, indiscriminate use of antibiotics promotes antibiotic resistance leading to multiple drug resistance and makes it difficult to control the diseases. The infected individuals have to consume more amount of antibiotics; this may be due to (1) reduced absorption in gut membrane when taken orally, (2) restrictive uptake by target microbe, and (3) operation of efflux pump leading to indiscriminate extrusion of the antibiotics or therapeutic molecules. So, the major amount of the applied drug is wasted and only a minor amount is being targeted to the site of infection [2].In addition, the unutilized drug/antibiotics amount remains as a load in the body and environment acting as a selection pressure facilitating emergence of drug resistance, ultimately leading to failure of antibiotics against resistant infections. This is also responsible for side effects, illness, and reduction in life expectancy. One of the possible ways to reduce drug dosage is synergism between two therapeutic agents, that is, combination therapy. However, if both drugs used concurrently have antimicrobial property, the problem of selection pressure and drug toxicity will continue. Thus, there is need of molecules, which are not antimicrobial or target drugs but enhance activity and availability of main drugs in combination therapy, that is, bioenhancers. These molecules by their presence will not exert any selection pressure for mutants to emerge resistant against them and on that their ill effects can be minimized. The resistance development process will be substantially delayed, ultimately leading to enhanced life-span of the novel and existing antibiotics. Such drugs/molecule facilitators should have novel properties such as (1) nontoxic to humans or animals, (2) they should be effective at a very low concentration in a combination, (3) they should be easy to formulate, and (4) most importantly enhance uptake/absorption and activity of the drug molecules. This can lead to developing judicious and strategic concentrations of antibiotic with specific bioenhancers to improve availability of the drug for controlling the infectious organisms effectively [2].Herbal bioenhancer is an agent of herbal origin or any phytomolecule, which is capable of enhancing bioavailability and bioefficacy of a particular drug or nutrient with which it is combined, without any typical pharmacological activity of its own at the dose used. In the 1920’s, Bose, an acknowledged author of “Pharmacographia Indica,” reported an enhanced antiasthmatic effect of an Ayurvedic formula containingvasaka (Adhatoda vasica) when administered with long pepper [3]. The term bioavailability enhancer was first coined by Indian Scientists at the Regional Research laboratory, Jammu (RRL, now known as Indian Institute of Integrative Medicine) discovered and scientifically validated piperine as the world’s first bioavailability enhancer in 1979 [4].The concept of bioenhancers of herbal origin can be tracked back from the ancient knowledge of Ayurveda system of medicine. Use of ayurvedic preparation “Trikatu” from the period between the 7th century B.C. and the 6th century A.D., which is a Sanskrit, word meaning three acrids. It refers to a combination of black pepper (Piper nigrumLinn.), long pepper (Piper longumLinn.), and ginger (Zingiber officinaleRosc.), which contains active component piperine, which enhances the bioavailability of drugs, nutrients, and vitamins [2].


## 2. Bioavailability/Bioefficacy-Enhancing Activity

The term bioavailability or bioenhancing activity is defined as “a substance at a lower dosage level, which in combination with a drug or nutrient provides more availability of the drug by reducing the consumption of the drug or nutrient resulting in enhanced efficacy of the drugs.”The great interests for the improvement of bioavailability of a large number of drugs are (1) poorly available, (2) administered for long periods, (3) toxic, and (4) expensive. Maximizing bioavailability is therapeutically important because the extent of bioavailability directly influences plasma concentrations and consequently therapeutic efficacy. Bioavailability enhancement can make the expensive drugs affordable and reduce the toxic effects by reducing the required dose of drugs.Poorly bioavailable drugs remain subtherapeutic because a major portion of a dose never reaches the plasma or exerts its pharmacological effect unless and until very large doses are given which may lead to serious side effects. Any significant improvement in bioavailability will result in lowering the dose or the dose frequency of that particular drug. Intersubject variability is particularly of concern for a drug with a narrow safety margin. Incomplete oral bioavailability includes poor dissolution or low aqueous solubility, poor intestinal membrane permeation, degradation of the drug in gastric or intestinal fluids, and presystemic intestinal or hepatic metabolism. Many therapeutic treatments are also accompanied by loss of essential nutraceuticals in the course of therapy. The bioenhancers improve nutritional status by increasing bioavailability/bioefficacy of various nutraceuticals including metals and vitamins [5].Bioavailability enhancement can be done by the following [5].(a)
Promoting the absorption of the drugs from GIT.(b)
Inhibiting or reducing the rate of biotransformation of drugs in the liver or intestines.(c)
Modifying the immune system in such a way that the overall requirement of the drug is reduced substantially.(d)
Increasing the penetration or the entry into the pathogens even where they become persistors within the macrophages such as forMycobacterium tuberculosisand such others. This eventually ensures the enhanced killing of these organisms is well secured within the places otherwise inaccessible to the active drug.(e)
Inhibiting the capability of pathogens or abnormal tissue to reject the drug, for example, efflux mechanisms frequently encountered with antimalarial, anticancer and antimicrobial drugs.(f)
Modifying the signaling process between host and pathogen ensuring increased accessibility of the drugs to the pathogens.(g)
Enhancing the binding of the drug with the target sites such as receptors, proteins, DNA, RNA, and the like in the pathogen, thus potentiating and prolonging its effect leading to enhanced antibiotic activity against pathogens.(h)
Besides above mode of action, the bioenhancer agents may also be useful for promoting the transport of nutrients and the drugs across the blood brain barrier, which could be of immense help in the control of diseases like cerebral infections, epilepsy, and other CNS problems.Modern drug development processes achieve oral bioavailability enhancement by a number of approaches.(a)
Increasing the polarity of the drug through chemical modification.(b)
Salt preparation or complexation.(c)
Prodrug formation.(d)
Micronization and nanonization.(e)
Specific polymorphic form selection.(f)
Targeted delivery of the drug to the site of action.(g)
Controlled drug delivery through film coating.(h)
Sustained drug release through polymorphic matrices formation.(i)
Liposomal microencapsulation and so forth.(j)
Application of P-glycoprotein inhibitors [6, 7].However, bioavailability enhancement through the supplementation of the main therapeutic agent with a secondary agent gained wide popularity since the traditional times. However, based on Ayurvedic literature, a new approach is increasing bioavailability of drugs including poorly bioavailable drugs by using herbal bioenhancers [5].Major categories of drugs that have shown increased bioenhancement include cardiovascular, respiratory, CNS, GIT, antibiotics, and anticancerous. Some examples include tetracyclines, sulfadiazine, vasicine, rifampicin, pyrazinamide, ethambutol, phenytoin, phenobarbitone, carbamazepine, nimesulide, indomethacinβ-carotene, coenzyme Q10, ciprofloxacin, curcumin, dapsone, amino acids, glucose, and several other classes of drugs [8].


## 3. Mechanisms of Action

Herbal bioenhancers act through several mechanisms of action. Different herbal bioenhancers may have same or different mechanisms of action. They increase bioavailability of nutraceuticals by acting on gastrointestinal tract to enhance absorption, whereas they increase bioavailability of drugs by acting on drug metabolism process. Various mechanisms of action postulated for herbal bioenhancers are shown in Table1.Table 1
Mechanisms of action of herbal bioenhancers.
Mechanisms of action
References
Bioenergetic properties
Reanmongkol et al. [9], Jamwal and Singh [10]
Increases gastrointestinal blood supply and reduces hydrochloric acid secretion
Annamalai and Manavalan [11]
Stimulation ofγ-glutamyl transpeptidase (GGT) activity which enhances uptake of amino acids
Johri et al. [12]
Cholagogues effect
Majeed et al. [13]
Thermogenic and bioenergetics properties
Majeed et al. [13]
Inhibition of gastric emptying time, gastrointestinal transit
Bajad et al. [14]
Inhibition of drug metabolizing enzymes and suppression of first pass metabolism
Atal et al. [15], Reen et al. [16], and Bhardwaj et al. [17]
Modifications in GIT epithelial cell membrane permeability
Khajuria et al. [18]They cause inhibition of gastric emptying (GE) of solids/liquids in rats and gastrointestinal transit (GT) in mice in a dose- and time-dependent manners was studied. It significantly inhibited GE of solids and GT at the doses extrapolated from humans (1 mg/kg and 1.3 mg/kgp.o. in rats and mice, resp.). However, at the same dose the effect was insignificant for GE of liquids. One-week oral treatment of 1 mg/kg and 1.3 mg/kg in rats and mice, respectively, did not produce a significant change in activity as compared to single-dose administration. GE inhibitory activity is independent of gastric acid and pepsin secretion [14].Thermogenic and bioenergetic mechanisms are believed to be triggered by activation of thermoreceptors and release of catecholamines and/or direct action as beta 1, 2, 3-adrenoceptor agonist. Secretion of catecholamines can also be mediated by ATP via P2-type purinergic receptors and through a direct or indirect stimulation by the compositions of the invention of dopaminergic and serotinergic systems. It is known that stimulation of β-3 adrenoceptors results in increased thermogenesis, decrease in the amount of white adipose tissue without food intake being affected, increased levels of insulin receptors, and decreased levels of serum insulin and blood glucose. This may possess antiobesity and antidiabetic effects, which by themselves contribute to the mechanism of thermogenesis and the increase in lean body mass. The thermogenic effect may also be mediated by an increase in the activity of thyroid peroxidase, an important enzyme in thyroid hormone synthesis, an increase in the plasma levels of triiodothyronine (T3) and thyroxine (T4) with simultaneous increase in tissue oxygen uptake, and increase in thermogenesis [19].Piperine mediated changes in the permeability of rat intestinal epithelial cells: the status ofγ-glutamyl transpeptidase activity, uptake of amino acids, and lipid peroxidation was studied. The effect of piperine on the absorptive function of the intestine were studied. In vitro experiments showed that piperine (25–100 μM) significantly stimulated γ-glutamyl transpeptidase activity, enhanced the uptake of radiolabelled l-leucine, l-isoleucine, and l-valine, and increased lipid peroxidation in freshly isolated epithelial cells of rat jejunum. In the presence of benzyl alcohol, an enhanced γ-glutamyl transpeptidase activity due to piperine was maintained. These results suggested that piperine may interact with the lipid environment to produce effects which lead to increased permeability of the intestinal cells [12].


## 4. Herbal Bioenhancers

### 4.1. Piperine

Piperine, the major plant alkaloid present inP. nigrumLinn (Black pepper) and P. longumLinn (Long pepper), has bioavailability enhancing activity for some nutritional substances and for some drugs [20]. It has been used extensively as a condiment and flavoring for all types of savory dishes. Piper species have been used in folklore medicine for the treatment of various diseases, including seizure disorders [21]. Piperine is known to exhibit a variety of biological activities which include anti-inflammatory activity [22, 23], antipyretic activity [24], fertility enhancement [25], antifungal activity [26], antidiarrhoeal activity [27], antioxidant activity [28–33], antimetastatic activity [34], antithyroid activity [35, 36], antimutagenic activity [37–40], antitumor activity [39, 41, 42], antidepressant activity [43–45], antiplatelet activity [46], analgesic activity [47], hepatoprotective activity [48], antihypertensive activity [49], and antiasthmatic activity [50]. Piperine exhibits a toxic effect against hepatocytes [51] and cultured hippocampal neurons [52], reproductive toxicity in swiss albino mice [53], and immunotoxicity [54].Piperine reduces the aflatoxin B1-induced cytotoxicity and micronuclei formation in rat hepatoma cells in concentration-dependent manner. It is capable of counteracting aflatoxin B1 toxicity by suppressing cytochromes P450-mediated bioactivation of the mycotoxin [55]. Inhibition of aflatoxin B1-induced cytotoxicity and genotoxicity in chinese hamster cells by piperine was reported by Reen et al. [56]. A significant suppression (33.9–66.5%) in the micronuclei formation induced by benzo(a)pyrene and cyclophosphamide was reduced following oral administration of piperine at doses of 25, 50, and 75 mg/kg in mice [32].Piperine modulates the oxidative changes by inhibiting lipid peroxidation and mediating enhanced synthesis or transport of glutathione thereby replenishing thiol redox [57]. Simultaneous supplementation with black pepper or piperine in rats fed high fat diet lowered thiobarbituric acid reactive substances (TBARS) and conjugated dienes levels and maintained superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione-S-transferase (GST), and glutathione (GSH) levels close to controls in rats [30]. Piperine could effectively inhibit benzo(a)pyrene-induced lung carcinogenesis in albino mice by offering protection from protein damage and also by suppressing cell proliferation [58]. It produces chemopreventive effect by modulating lipid peroxidation and augmenting antioxidant defense system [59, 60]. Supplementation of piperine causes inhibition of Phase I and II enzymes, elevation of glutathione metabolizing enzymes, reduction in DNA damage, and DNA protein cross-links in benzo(a)pyrene-induced lung carcinogenesis in mice [38, 61].The antiapoptotic efficacy of piperine has been demonstrated against cisplatin-induced apoptosis via heme oxygenase-1 induction in auditory cells [62]. Piperine can reverse the corticosterone induced reduction of brain-derived neurotrophic factor mRNA expression in cultured hippocampal neurons [44]. Gallic acid exerts a synergistic effect when administered with piperine and provides a more pronounced therapeutic potential in reducing beryllium-induced hepatorenal dysfunction and oxidative stress consequences [63]. Piperine contains pentacyclic oxindole group which is effective for immunomodulation. This immunomodulation activity is due to its multifaceted activities such as antioxidative, antiapoptotic, and restorative ability against cell proliferative mitogenic response, thymic and splenic cell population, and cytokine release [64].Daily supplement taken with a nutrient or nutrients by an average healthy adult, piperine is effective and safe in a broad dose range. A preferred effective dose range of piperine for oral use to enhance gastrointestinal nutrient absorption is 0.0004–0.15 mg/kg/day. The recommended dose of piperine for a healthy individual for oral use is approximately 5 mg/person/day. Black pepper contains approximately 5–9% piperine, listed by the Food and Drug Administration (FDA) as an herb which is generally recognized as safe (GRAS) for its intended use as spice, seasoning, or flavoring. The bioenhancing dose of piperine is approximately 15 mg/person/day and no more than 20 mg/day in divided doses, which corresponds to from several thousands to up to 40,000 times less than the LD50 dose of piperine, as established in various experiments on rodents. The effective bioenhancing dose of piperine for drug compounds varies, but the prior art studies indicated that a dose of approximately 10% (w/w) of the active drug could be regarded as an appropriate bioenhancing dose for most drugs [19]. LD50 of piperine has been found to be 330 and 514 mg/kg in mice and rats, respectively. In subacute toxicity tests, piperine in a dosage of 100 mg/kg was found to be nontoxic [65].There are two possible explanations for the role of piperine in drug bioavailability: (a) nonspecific mechanisms mainly promoting rapid absorption of drugs and nutrients, for example, increased blood supply to the gastrointestinal tract, decreased hydrochloric acid secretion which prevents breakdown of some drugs, increased emulsifying content of the gut, and increased enzymes likeγ-glutamyl transpeptidase which participate in active and passive transport of nutrients to the intestinal cells, and (b) nonspecific mechanisms inhibiting enzymes participating in biotransformation of drugs, preventing their inactivation and elimination [19].


#### 4.1.1. Drug Metabolizing Enzymes Inhibited by Piperine (Shown in Table2)

Table 2
Drug metabolizing enzymes inhibited by piperine.
Drug metabolizing enzymes
References
Arylhydrocarbon hydroxylase (AHH)
Atal et al. [15], Singh et al. [66]
Uridine diphosphate- (UDP-) glucuronyl transferase
Atal et al. [15], Singh et al. [66]
Ethylmorphine-N-demethylase
Atal et al. [15], Singh et al. [66]
7-Ethoxycoumarin-O-deethylase
Atal et al. [15], Singh et al. [66]
3-Hydroxy-benzo(a)pyrene glucuronidation
Atal et al. [15], Singh et al. [66]
UDP-glucose dehydrogenase (UDP-GDH)
Reen et al. [16]
5-lipoxygenase
Stöhret al. [67]
Cyclooxygenase-1
Stöhret al. [67]
Cytochrome P450
Atal et al. [15], Singh et al. [66], Bhardwaj et al. [17]The interaction of piperine with enzymatic drug biotransforming reactions in hepatic tissue has been studiedin vitro and in vivo. Piperine inhibited arylhydrocarbon hydroxylation, ethylmorphine-N-demethylation, 7-ethoxycoumarin-O-deethylation, and 3-hydroxy-benzo(a)pyrene glucuronidation in rat postmitochondrial supernatant in vitro in a dose-dependent manner. Piperine inhibition of these reactions in postmitochondrial supernatant from 3-methylcholanthrene and phenobarbital treated rats was similar to the controls. Inhibition by piperine of arylhydrocarbon hydroxylase (AHH) from 3-methylcholanthrene treated rats was comparable to that observed with 7, 8-benzoflavone. Piperine caused noncompetitive inhibition of hepatic microsomal AHH from the untreated and 3-methylcholanthrene-treated rats with a Ki=30μM which was close to the apparent Km of AHH observed in the controls. Similarly, the kinetics of inhibition of ethylmorphine-N-demethylase from control rat liver microsomes exhibited noncompetitive inhibition with an apparent Km=0.8mM and Ki=35μM. These studies demonstrated that piperine is a nonspecific inhibitor of drug metabolism. Oral administration of piperine in rats strongly inhibited the hepatic AHH and Uridine diphosphate-(UDP-) glucuronyltransferase (UGT) activities. The maximal inhibition of AHH observed within 1 h restored to normal value in 6 h. These results demonstrate that piperine is a potent inhibitor of drug metabolism [15]. Piperine modified the rate of glucuronidation by lowering the endogenous UDP-glucuronic acid (UDP-GA) content and also by inhibiting the transferase activity [66].The effects of piperine on UDP-glucose dehydrogenase (UDP-GDH) and glucuronidation potentials of rat and guinea pig liver and intestine were studiedin vitro. Piperine caused a concentration-related strong inhibition of UDP-GDH (50% at 10 μM) reversibly and equipotently, in both tissues. Partially purified rat liver UDP-GDH was used to obtain the kinetic values at pH optima of 9.4 and 8.6. At pH 9.4, Km=15 μM, Vmax=5.2 nmol, with NADH—Ki=6μM, with NAD—Ki=16 μM were obtained. At pH 8.6, Km=35 μM, Vmax=7.5 nmol, and Ki=15 μM. In all of these cases, piperine caused noncompetitive inhibition. Data from structure activity comparisons of piperine analogs indicated that the presence of conjugated double bonds in the side chain of the molecule is a factor in piperine inhibition. However, the UDP-GA contents were decreased less effectively by piperine in isolated rat hepatocytes compared with enterocytes of guinea pig small intestine. Piperine at 50 μM caused a marginal decrease of UDP-GA in hepatocytes when the rate of glucuronidation of 3-hydroxybenzo(a)pyrene (3-OH-BP) decreased by about 40%. The decrease obtained at 10 μM piperine in intestinal cells was comparable to that obtained at 50–100 μM in hepatocytes. UGT activities towards 3-OH-BP (UGT1A1) and 4-OH-biphenyl (UGT2B1) were also determined. Piperine did not affect the rate of glucuronidation of 4-OH-biphenyl in rat liver, whereas that of 3-OH-BP was impaired significantly. In guinea pig small intestine, both these activities were inhibited significantly requiring less than 25 μM piperine to produce more than 50% inhibition of UGT(s). The results suggested that (i) piperine is a potent inhibitor of UDP-GDH, (ii) inhibition is offered exclusively by the conjugated double bonds of the molecule, and (iii) piperine exerts stronger effects on intestinal glucuronidation than in rat liver [16].Piperine inhibits human P-glycoprotein and CYP3A4 (CYP: Cytochrome P450). Both the proteins are expressed in enterocytes and hepatocytes and contribute to a major extent to first-pass elimination of many drugs. This indicates that dietary piperine could affect plasma concentrations of P-glycoprotein and CYP3A4 substrates in humans, in particular if these drugs are administered orally. Some of the metabolizing enzymes inhibited or induced by piperine include CYP1A1, CYP1B1, CYP1B2, CYP2E1, and CYP3A4. Most of the drugs metabolized by these enzymes will therefore be influenced by bioenhancers [17].


#### 4.1.2. Drugs/Nutraceuticals Bioenhanced by Piperine

Piperine acts as an antimicrobial bioenhancer which enhances bioavailability and bioefficacy of drugs by acting on drug metabolism. It also acts as a nutritional bioenhancer which enhances bioavailability and absorption of nutrients by acting on gastrointestinal tract. Allameh et al. [68] reported that piperine enhances bioavailability of aflatoxin B1 in rat tissues. A 10 mg dose of piperine causes a marked increase in serum gonadotropins and a decrease in intratesticular testosterone concentration, despite normal serum testosterone titres in adult male albino rats [69]. However, some of the experimental findings also indicated the ability to decrease the bioavailability of drugs, like rifampicin [70, 71], isoniazid [72], and Diclofenac sodium [73].Piperine has been shown to inhibit several cytochrome P450-mediated pathways and phase II reactions in animal models. Piperine, or mixtures containing piperine, has been shown to increase the bioavailability, blood levels, and efficacy of many of drugs (Table3) and nutraceuticals (Table 4). Administration of piperinesignificantly increased plasma concentrations of rifampicin,phenytoin, spartein, sulfadiazine, tetracycline, propranolol, and theophylline in humans.Table 3
Drugs bioenhanced by piperine.
Drugs
Experimental model
References
Vasicine
Rats
Zutshi and Kaul [74]
Pyrazinamide
In vitro
Zutshi [75]
Phenytoin, propranolol, theophyllin, spartein, sulphadiazine, and tetracycline
Human volunteers
Bano et al. [76, 77]
Pentobarbitone
Human volunteers
Mujumdar et al. [78]
Curcumin
Human volunteers and rats
Shoba et al. [79]
In vivo
Shaikh et al. [80]
Rats
Suresh and Srinivasan [81]
Nimesulide
Mice
Gupta et al. [82]
Indomethacin
Rabbits
Karan et al. [83]
Oxyphenylbutazone
Rats
Mujumdar et al. [84]
Phenytoin
Human volunteers
Velpandian et al. [85], Pattanaik et al. [86]
Rifampicin
Human
Zutshi et al. [87]
In vitro
Balakrishnan et al. [88]
Amoxycillin trihydrate and cefotaxime
Rats
Hiwale et al. [89]
EGCG [(−)-epigallocatechin-3-gallate]
Mice
Lambert et al. [90]
Oxytetracycline
WLH hens
Singh et al. [91]
Ciprofloxacin
Rabbits
Balkrishna and Yogesh [92]
In vitro
Khan et al. [8]
Nevirapine
Human
Kasibhatta and Naidu [93]
Diclofenac sodium and pentazocine
Albino mice
Pooja et al. [47]
Pefloxacin
Gaddi goats
Dama et al. [94]
Ampcilllin and norloxacin
Rabbits
Janakiraman and Manavalan [95]
Carbamazepine
In vitro
Pattanaik et al. [96]
Fexofenadine
Rats
Jin and Han [97]
Metronidazole
Rabbits
Singh et al. [98]
Ampicillin trihydrate
Human
Janakiraman and Manavalan [99]
Resveratrol
Mice
Johnson et al. [100]
Gatifloxacin
Layer birds
Patel et al. [101]
Broiler birds
Devada et al. [102]
Atenolol
Rats
Singh and Chand [103]
Ibuprofen
In vitro
Venkatesh et al. [104]
Losartan potassium
Rats
Singh et al. [105]Table 4
Nutraceuticals bioenhanced by piperine [13, 19].
Class
Examples
Water soluble vitamins
Vitamin B1, Vitamin B2, niacinamide, Vitamin B6, Vitamin B12, folic acid, and Vitamin C
Fat soluble vitamins
Vitamin A,β-carotene (provitamin), Vitamin D, Vitamin E, and Vitamin K
Amino acids
Lysine, isoleucine, leucine, threonine, valine, tryptophan, phenylalanine, and methionine
Minerals
Iodine, calcium, iron, zinc, copper, selenium, magnesium, potassium, and manganese
Herbal compounds
Boswellic acid (Boswellia serrata), Ginsenosides (Gingko biloba), Withanaloids (Withania somnifera), Curcuminoides (Curcuma longa), and Pycnogenol (Pinus pinaster)Piperine and Phenytoin
Effect of piperine on pharmacokinetics of phenytoin was studied in healthy volunteers. In a crossover study, five volunteers received either a single oral dose (300 mg) of phenytoin alone or in combination with multiple doses of piperine (20 mg × 7 days) followed by an oral dose of phenytoin. Blood samples were collected at 0.5, 1, 2, 3, 4, 8, 12, 24, and 48 h after drug administration and analyzed for phenytoin by the enzyme-multiplied immunoassay technique. The results showed that a single daily dose of piperine for 7 days decreased thet1/2α (P<0.05), prolonged the t1/2 (P<0.01), and produced a higher AUC (P<0.05) in comparison to phenytoin alone. It is therefore concluded that piperine on multiple-dose administration alters the pharmacokinetic parameters of the antiepileptic [76].
A preliminary pharmacokinetic study was carried out in mice by administering phenytoin (10 mg) orally, with or without piperine (0.6 mg). Subsequently, oral pharmacokinetics of phenytoin was carried out in six healthy volunteers in a crossover design. Phenytoin tablet (300 mg) was given 30 minutes after ingestion of a soup (Melahu rasam) with or without black pepper. A further study of intravenous pharmacokinetics of phenytoin (1 mg) in rats with or without oral pretreatment with piperine (10 mg) was also conducted. The phenytoin concentration in the serum was analyzed by HPLC. The study showed a significant increase in the kinetic estimates of Ka, AUC0-10 and AUC0-∞ in the piperine fed mice. Similarly, in human volunteers piperine increased Ka, AUC0-48, AUC0-∞ and delayed elimination of phenytoin. Intravenous phenytoin in the oral piperine-treated rat group showed a significant alteration in the elimination phase indicating its metabolic blockade [85].
The effect of piperine on oral bioavailability of phenytoin was studied in human volunteers. The objective of this study was to explore the effect of a single dose of piperine in patients with uncontrolled epilepsy on the steady-state pharmacokinetics of phenytoin. Two groups of 10 patients each receiving either a 150 mg or 200 mg twice daily dose of phenytoin were selected. 12 h after the night dose, venous blood samples were collected at 0, 0.5, 1, 2, 4, 6, 9, and 12 h after administration of phenytoin. On the next study day, piperine 20 mg was administered along with phenytoin and samples were collected similarly. There was a significant increase inAUC0-12h (P<0.01), Cmax (P<0.001), and Ka (P<0.05), whereas the changes in Kel and tmax were not significant. The results showed that piperine enhanced the bioavailability of phenytoin significantly, possibly by increasing the absorption [86].Piperine and Pentobarbitone
Effect of piperine on pentobarbitone-induced hypnosis in rats was studied. Piperine treatment in rats, treated chronically with phenobarbitone, significantly potentiated pentobarbitone sleeping time, as compared to the controls. There was no alteration in barbital sodium sleeping time. It is possible that piperine inhibits liver microsomal enzyme system and thereby potentiates the pentobarbitone sleeping time [78].Piperine with Propranolol and Theophylline
The effects of piperine on the bioavailability and pharmacokinetics of propranolol and theophylline were studied. Six subjects in each group received a single oral dose of propranolol (40 mg) or theophylline (150 mg) alone or in combination with piperine (20 mg) daily for 7 days. An earliertmax and a higher Cmax and AUC were observed in the subjects who received piperine and propranolol. It produced a higher Cmax, longer t1/2, and a higher AUC with theophylline. In clinical practice, the enhanced systemic availability of oral propranolol and theophylline could be exploited to achieve better therapeutic control and improved patient compliance [77].Piperine and Nimesulide
Influence of piperine on nimesulide-induced antinociception was studied in mice. The plasma concentration after oral administration of nimesulide (10 mg/kg) alone was8.03±0.99 μg/mL. However, when it was administered with piperine (10 mg/kg), the plasma concentration of nimesulide increased to 11.9±0.23 μg/mL. This indicates that piperine inhibits the biotransformation and metabolism of nimesulide leading to significantly (P<0.05) higher levels of drug in the systemic circulation. The findings of this study suggest that piperine could be used as a biological enhancer when coadministered with nimesulide [82].Piperine and Curcumin
Influence of piperine on the pharmacokinetics of curcumin in animals and human volunteers was studied. The medicinal properties of curcumin obtained fromCurcuma longa Linn. cannot be utilized because of poor bioavailability due to its rapid metabolism in the liver and intestinal wall. The effect of combining piperine, a known inhibitor of hepatic and intestinal glucuronidation, was evaluated on the bioavailability of curcumin in rats and healthy human volunteers. When curcumin was given alone, at dose 2 g/kg to rats, moderate serum concentrations were achieved over a period of 4 h. Concomitant administration of piperine 20 mg/kg increased the serum concentration of curcumin for a short period of 1-2 h after drug. tmax was significantly increased (P<0.02) while t1/2 and ClB significantly decreased (P<0.02), and the bioavailability was increased by 154%. On the other hand, in humans after a dose of 2 g curcumin alone, serum levels were either undetectable or very low (Table 5). Concomitant administration of piperine 20 mg produced much higher concentrations from 0.25 to 1 h after drug (P<0.01 at 0.25 and 0.5 h; P<0.001 at 1 h); the increase in bioavailability was 200%. The study shows that in the dosages used, piperine enhances the serum concentration, extent of absorption, and bioavailability of curcumin in both rats and humans with no adverse effects [79].Table 5
Comparative pharmacokinetic parameters after oral supplementation of curcumin and curcumin + piperine in human volunteers [79].
Parameters
Curcumin
Curcumin (2g/kg) + piperine
(2g/kg)
(20mg/kg)
C
max (μg/mL)
1.35
±
0.23
1.80
±
0.16
t
max (h)
0.83
±
0.05
1.29
±
0.23
t
1
/
2 (h)
1.70
±
0.58
1.05
±
0.18
AUC (μg·h/mL)
2.36
±
0.28
3.64
±
0.31
Cl
B (L/h)
713
±
12
495.90
±
193.90Piperine andβ-Carotene
The effectiveness of piperine was evaluated for its ability to improve serum response ofβ-carotene during oral supplementation using a double-blind, crossover study design. Subjects were randomly selected to ingest a daily β-carotene dose (15 mg) either with 5 mg of piperine or placebo during each of two 14-day supplementation periods. Intersubject variability in presupplementation serum β-carotene levels was minimized by limiting the selection of volunteers to healthy, adult males with fasting serum β-carotene values <20 pg/dL. The results indicate that significantly greater increases (P<0.0001) in serum β-carotene occurred during supplementation with β-carotene plus piperine (49.8±9.6 pg/dL versus 30.9±5.4 pg/dL) compared to β-carotene plus placebo. Supplementation with betacarotene plus piperine for 14 days produced a 60% greater increase AUC than was observed during supplementation with β-carotene plus placebo (Table 6). Study suggests that the serum response during oral β-carotene supplementation is improved through the nonspecific, thermogenic property of piperine, described in this paper as thermonutrient in action [20].Table 6
Effect of piperine on the serumβ-carotene levels during a 14-day supplementation in human volunteers [20].
Treatment (n=6)
β-carotene (μg/dL)
AUC (μg/dL) × (time in days)
Day 0
Day 14
Change
β-carotene + placebo
16.3 ± 2.6
47.2 ± 6.4
30.9 ± 5.4
272 ± 47.6
β-carotene + piperine
16.0 ± 3.1
65.8 ± 9.7
49.8 ± 9.6
435 ± 74.2Piperine and Coenzyme Q10
An extract from the fruits of black pepper consisting of a minimum of 98% pure piperine was evaluated in a clinical study using a double-blind design. The relative bioavailability of 90 mg and 120 mg of coenzymeQ10 administered in a single-dose experiment or in separate experiments for 14 and 21 days with placebo or with 5 mg of piperine was determined by comparing measured changes in plasma concentration. The intersubject variability was minimized by limiting the selection of individuals to healthy adult male volunteers with (presupplementation) fasting coenzyme Q10 values between 0.30 and 0.60 mg/L. The results of the single-dose study and the 14-day study indicate smaller, but not significant, increases in plasma concentrations of coenzyme Q10 in the control group compared with the group receiving coenzyme Q10 with a supplement of piperine. Supplementation of 120 mg coenzyme Q10 with piperine for 21 days produced approximately 30% greater AUC than was observed during supplementation with coenzyme Q10 plus placebo. It is postulated that the bioenhancing mechanism of piperine to increase plasma levels of supplemental coenzyme Q10 is nonspecific and possibly based on its description in the literature as a thermonutrient [106].Piperine and Rifampicin
Piperine augments transcription inhibitory activity of rifampicin by several folds againstMycobacterium smegmatis. A 24 : 1 (w/w) mixture of antibiotic rifampicin and piperine shows remarkable growth inhibitory effect on M. smegmatis, and this inhibition is higher than that of rifampicin alone. Interestingly, piperine alone, even at higher concentration, does not inhibit the growth of Mycobacterium. As RNA polymerase is the site of action of rifampicin, the enzyme was purified from M. smegmatis and the mixture of rifampicin and piperine was found to abrogate nonspecific transcription catalyzed by M. smegmatisRNA polymerase. The effect is higher than rifampicin alone and piperine shows no effect independently. When RNA polymerase was purified from a rifampicin-resistant strain of M. smegmatis, the enzymatic activity, otherwise resistant to rifampicin, significantly decreases in the presence of piperine along with rifampicin. Piperine enhances the binding ability of rifampicin to RNA polymerase [88].
The amount of piperine used in the range of 0.4–0.9% by weight of the antituberculosis and antileprosy drugs. Antituberculosis composition contains rifampicin (100–300 mg), isoniazid (100–300 mg) and pyrazinamide (500–1000 mg) (combination of any two), and piperine (5–29 mg). Antileprosy composition contains rifampicin (100–300 mg), dapsone (50–100 mg), and piperine (5–20 mg). Effect of piperine on pharmacokinetic parameters of rifampicin, isoniazid, and pyrazinamide combination was studied in human volunteers. The results from Table7 indicate that piperine significantly increases the bioavailability of antituberculosis drugs like rifampicin, isoniazid, and pyrazinamide [107, 108].Table 7
Effect of piperine on pharmacokinetics of rifampicin, isoniazid, and pyrazinamide combination in human volunteers [107, 108].
Kineticparameters
Formulation A
Formulation B
Rifampicin
Isoniazid
Pyrazinamide
Rifampicin**
Isoniazid**
Pyrazinamide**
t
1
/
2 (h)
0.67 ± 0.008
0.64 ± 0.01
0.60 ± 0.03
0.40 ± 0.04
0.42 ± 0.04
0.37 ± 0.008
t
1
/
2
(el) (h)
8.40 ± 0.06
7.90 ± 0.10
9.50 ± 0.14
11.1 ± 0.18
8.15 ± 0.26*
11.0 ± 0.17
C
max (μg/mL)
8.20 ± 0.46
2.56 ± 0.17
27.0 ± 2.0
17.6 ± 1.09
10.07 ± 0.90
40.0 ± 1.64
AUC0–∞ (μg·h/mL)
104.6 ± 4.38
41.0 ± 1.72
318.6 ± 8.05
143.95 ± 5.85
94.95 ± 3.98
435.41 ± 9.7
*Not significant (P > 0.05), **highly significant (P < 0.001).
Formulation A: rifampicin—450 mg, isoniazid—300 mg, pyrazinamide—1500 mg.
Formulation B: rifampicin—450 mg, isoniazid-300 mg, pyrazinamide—1500 mg, piperine—20 mg.Risorine is a formulation developed by the Indian Institute of Integrative Medicine, Jammu, and marketed in India in November 2009 in public—private partnership with Cadila Pharmaceutical Ltd, Ahmedabad. Risorine has been approved for marketing by Drug Controller General of India, after successful completion of all the phased clinical trials. It contains rifampicin (200 mg), isoniazid (300 mg), and piperine (10 mg). It has been found to be bioequivalent with commercially available rifampicin preparations. This is due to enhanced uptake of the drug by body cells, and also because the drug remains available in blood for longer durations. Combining piperine with rifampicin decreases the dose of rifampicin from 450 to 200 mg [109].Piperine with Amoxicillin Trihydrate and Cefotaxime
Effect of coadministration of piperine on pharmacokinetics ofβ-lactam antibiotics was studied in rats. Coadministration of piperine enhanced bioavailability of β-lactam antibiotics like amoxicillin trihydrate and cefotaxime sodium significantly in rats. The improved bioavailability is reflected in various pharmacokinetic parameters, namely tmax, Cmax, t1/2, and AUC of these antibiotics. The increased bioavailability could be attributed to the effect of piperine on microsomal metabolizing enzymes or enzymes system [89].Piperine and Epigallocatechin Gallate (EGCG)
Piperine enhanced the bioavailability of the tea polyphenol EGCG in Mice. EGCG, from green tea (Camellia sinensis), has demonstrated chemopreventive activity in animal models of carcinogenesis. Cotreatment with piperine enhanced the bioavailability of EGCG in mice. Intragastric coadministration of 163.8 μmol/kg EGCG and 70.2 μmol/kg piperine to male CF-1 mice increased the plasma Cmax and AUC by 1.3-fold compared to mice treated with EGCG only. Piperine appeared to increase EGCG bioavailability by inhibiting glucuronidation and gastrointestinal transit. Piperine (100 μmol/L) inhibited EGCG glucuronidation in mouse small intestine (by 40%) but not in hepatic microsomes. Piperine (20 μmol/L) also inhibited production of EGCG-3′′-glucuronide in human HT-29 colon adenocarcinoma cells. Small intestinal EGCG levels in CF-1 mice following treatment with EGCG alone had a Cmax=37.50±22.50 nmol/g at 60 min that then decreased to 5.14±1.65 nmol/g at 90 min; however, cotreatment with piperine resulted in a Cmax=31.60±15.08 nmol/g at 90 min, and levels were maintained above 20 nmol/g until 180 min. This resulted in a significant increase in the small intestine EGCG AUC (4621.80±1958.72 nmol/g/min versus 1686.50±757.07 nmol/g/min). EGCG appearance in the colon and the feces of piperine-cotreated mice was slower than in mice treated with EGCG alone [90].Piperine and Oxytetracycline (OTC)
The pharmacokinetic profile of orally administered oxytetracycline (10 mg/kg body weight) was studied 7 days after oral treatment ofP. longum (15 mg equivalent/kg) in White Leghorn birds (WLH) (2.0–2.8 kg). On day 8, oxytetracycline (OTC) was administered orally and blood samples were collected from the wing vein in heparinized vials for plasma separation at 0 (before treatment), 15, 30, 60, 120, 240, 360, 480, and 600 min after OTC administration. Plasma OTC concentrations were determined by microbial assay technique using Bacillus cereus var. mycoides (ATCC 11778) as test organism. The plasma levels of OTC against time were adequately described by one compartment open model (Table 8). The pharmacokinetic data (Table 9) revealed that P. longum-treated animals had significantly higher AUC, AUMC, and MRT. Prior treatment of P. longum significantly reduced β and increased t1/2. The ClB reduced by 21%, whereas td increased by 29%. The treatment with P. longum reduced loading and maintenance dose by 33.3% and 39%, respectively [91].Table 8
Comparison of mean plasma levels of oxytetracycline (μg/mL) at different time intervals following oral administration in control and P. longum-treated WLH birds [91].
Time (Min)
Control
Treated
15
0.23 ± 0.024
0.30 ± 0.022*
30
0.34 ± 0.025
0.45 ± 0.029**
60
0.72 ± 0.051
0.77 ± 0.046
120
0.58 ± 0.037
0.63 ± 0.030
240
0.37 ± 0.015
0.47 ± 0.034**
360
0.26 ± 0.017
0.38 ± 0.021****
480
0.23 ± 0.015
0.31 ± 0.019***
600
0.19 ± 0.005
0.25 ± 0.015***
n = 8, mean ± SE; *P < 0.1, **P < 0.05, ***P < 0.01, ****P < 0.001.Table 9
Comparative pharmacokinetic parameters of oxytetracycline administered orally (10 mg/kg) in control andP. longum treated birds [91].
Parameters
Control OTC
Treated OTC + piperine
β
(/h)
0.147 ± 0.011
0.112 ± 0.006*
t
1
/
2
β (h)
4.934 ± 0.422
6.370 ± 0.438**
AUC (μg·h/mL)
5.055 ± 0.689
6.417 ± 0.317*
AUMC (μg·h2/mL)
43.62 ± 11.15
63.58 ± 7.042*
MRT (h)
7.98 ± 0.744
9.77 ± 0.644**
t
d (h)
16.38 ± 1.4
21.142 ± 1.453**
Cl
B (mL/kg/h)
184.63 ± 7.7
145.97 ± 14.42**
n = 8, mean ± SE; *P < 0.01, **P < 0.05.Piperine and Ciprofloxacin
The influence of coadministration of piperine on pharmacokinetic profile of ciprofloxacin in rabbits was studied. The study reveals that piperine has affected statically to the pharmacokinetics of the ciprofloxacin which is significant with change inCmax, tmax, AUC, and Kel. The results obtained are the combined effect of piperine on the absorption kinetics and the inhibition of the metabolism of the ciprofloxacin. This leads to increase bioavailability of ciprofloxacin when administered with piperine [92].
The potentiating effect of piperine with ciprofloxacin inin vitro combination against Staphylococcus aureusATCC 29213 was studied and its suggestive role as an efflux pumps inhibitor. Piperine, in combination with ciprofloxacin, markedly reduced the MIC and mutation prevention concentration of ciprofloxacin for S. aureus, including methicillin resistant S. aureus. In vitro combination studies, the final concentrations ranged from 0.03 to 64 μg/mL for ciprofloxacin and from 0.8 to 50 μg/mL for piperine. The final bacterial inoculum in each well was 5×105 CFU/mL. The plates were incubated at 37°C for 24 h. Piperine did not show any antibacterial activity when tested up to 100 μg/mL. Table 10 is showing that there was a 2-fold reduction in the MIC of ciprofloxacin (from 0.25 to 0.12 μg/mL) for S. aureus ATCC 29213 when tested in combination with piperine at 12.5 and 25 μg/mL. The MIC was further reduced to 4-fold with 50 μg/mL piperine [8]. Piperine inhibits the efflux of ethidium bromide and ciprofloxacin from bacterial cells (Table 11). It is a P-glycoprotein inhibitor that inhibits ciprofloxacin efflux [8].Table 10
MIC of ciprofloxacin forS. aureus ATCC 29213 at different concentrations of piperine [8].
Piperine conc.
MIC (μg) of ciprofloxacin for S. aureus
(μg/mL)
ATCC 29213
0.0
0.25
12.5
0.12
25
0.12
50
0.06Table 11
Drug susceptibilities ofS. aureusATCC 29213 and the ciprofloxacin selected mutant (CIPr-1) [8].
Compound
MIC (μg/mL)
S. aureusATCC 29213
CIPr-1
Ethidium bromide
4
8
Ethidium bromide + piperine
1
2
Ciprofloxacin
0.25
128
Ciprofloxacin + piperine
0.12
8Piperine and Nevirapine
Influence of piperine on the pharmacokinetics of nevirapine under fasting conditions was studied. This was a crossover, placebo-controlled pilot study conducted in a total of eight healthy adult males aged 20–40 years. Subjects were randomly assigned to receive piperine 20 mg or placebo each morning for 6 days, and on day 7, nevirapine (200 mg) plus piperine (20 mg) or nevirapine plus placebo in a crossover fashion. Blood samples were collected from 1–144 h after dose for pharmacokinetic analysis. MeanCmax, AUCt, AUC0-∞, and Clast values of nevirapine were increased by approximately 120%, 167%, 170%, and 146%, respectively, when coadministered with piperine. This pilot study provided evidence for enhanced bioavailability of nevirapine when administered with piperine [93].Piperine with Diclofenac Sodium and Pentazocine
The analgesic activity ofP. nigrum extract per se and its interaction with diclofenac sodium and pentazocine in albino mice was studied. Healthy albino mice of either sex weighing 25–30 grams were taken and divided into 4 groups of 8 animals each. Peripheral analgesic activity was evaluated by acetic acid-induced writhing test, using diclofenac sodium (5 mg/kg), P. nigrum extract (10 mg/kg), and their combination (5+10 mg/kg) orally. Similarly central analgesic activity was studied using tail flick method and pentazocine (5 mg/kg) orally was used instead of diclofenac sodium. P. nigrum extract alone did not show any significant analgesic activity in tail flick and writhing methods. However, results of acetic acid-induced writhing model showed that diclofenac sodium reduces writhing 54.90% with respect to control when administered alone, but showed significant decrease in writhes 78.43% with respect to control when P. nigrum extract was coadministered with diclofenac sodium. When P. nigrum extract combined with pentazocine showed significant increase in tail flick latency in comparison with pentazocine alone and control group (P<0.05), the results suggest that the P. nigrum extract significantly increased the analgesic activity of diclofenac sodium and pentazocine [47].Piperine and Pefloxacin
The pharmacokinetics of orally administered pefloxacin were studied to evaluate the bioenhancing effect of the herbal bioenhancer, trikatu, in mountain Gaddi goats (n=6). The findings of the study revealed a decreased plasma concentration (P>0.05) of pefloxacin following trikatu administration during the absorption phase (10, 15, and 20 min after pefloxacin administration). In contrast, the plasma concentrations of pefloxacin were significantly higher at 4, 6, 8, and 12 h (during the elimination phase) of the pefloxacin administration. The findings of the investigation revealed higher values for AUC, AUMC, MRT, td, and bioavailability. Trikatu treatment, however, significantly reduced t1/2 and zero time intercept of the elimination phase. The Vd(area) and Vd(B) were significantly higher in trikatu-treated animals indicating a better penetration of the drug. Based on the MIC of 0.8 μg/mL of pefloxacin; a priming dose of 6.0 mg/kg and a maintenance dose of 2.21 mg/kg are required to be administered at 8 h intervals. For practical purposes in goats this would mean a priming dose of 6 mg/kg and a maintenance dose of 2 mg/kg given by the oral route to be repeated at 8 h intervals [94].Piperine with Ampicillin and Norfloxacin
Effect of piperine on oral bioavailability of ampicillin and norfloxacin was studied in rabbits. Coadministration of piperine (20 mg/kg), an alkaloid fromP. nigrum, enhanced oral bioavailability of ampicillin and norfloxacin in animal model. This is reflected in various pharmacokinetic measurements like Cmax, tmax, AUC, and t1/2 of the above antibiotics in animal model shown in Tables 12, 13, and 14 [95].Table 12
Effect of piperine on plasma concentration of ampicillin in rabbits [95].
Time (h)
Ampicillin (μg/mL)
Ampicillin + piperine (μg/mL)
0.0
0
0
0.5
30.584 ± 0.38
35.481 ± 0.26
1.0
44.668 ± 0.32
251.188 ± 0.27
1.5
31.672 ± 0.49
188.364 ± 0.31
2.0
26.607 ± 0.37
84.139 ± 0.31
2.5
18.836 ± 0.38
66.834 ± 0.26
3.0
17.782 ± 0.32
35.481 ± 0.27
3.5
12.589 ± 0.31
33.496 ± 0.26
4.0
12.589 ± 0.32
26.607 ± 0.27
4.5
9.441 ± 0.26
26.607 ± 0.27
n = 6, mean ± SD, P < 0.05.Table 13
Effect of piperine on plasma concentration of norfloxacin in rabbits [95].
Time (h)
Norfloxacin (μg/mL)
Norfloxacin + piperine (μg/mL)
0.0
0
0
1.0
10.593 ± 0.26
14.125 ± 0.27
2.0
7.079 ± 0.26
17.783 ± 0.32
3.0
5.623 ± 0.32
14.963 ± 0.27
4.0
5.011 ± 0.38
11.885 ± 0.32
5.0
4.732 ± 0.26
10.592 ± 0.37
6.0
3.981 ± 0.26
8.414 ± 0.25
7.0
3.548 ± 0.21
8.414 ± 0.26
8.0
3.349 ± 0.26
7.079 ± 0.26
9.0
3.162 ± 0.27
7.079 ± 0.27
10.0
2.512 ± 0.27
5.623 ± 0.27
11.0
2.238 ± 0.26
5.011 ± 0.27
12.0
1.778 ± 0.26
4.467 ± 0.27
n = 6, mean ± SD, P < 0.Table 14
Pharmacokinetic parameters of ampicillin, norfloxacin, and in combination with piperine after oral treatment in rabbit [95].
Treatment
t
max (h)
C
max (μg/mL)
t
1
/
2 (h)
AUC (μg·h/mL)
Ampicillin (150mg/kg)
1 ± 0.31
44.6 ± 0.27
1.3 ± 0.46
103.7 ± 0.52
Ampicillin (150mg/kg) + piperine (20mg/kg)
1.1 ± 0.3
251.2 ± 0.28
1.9 ± 0.57
350.49 ± 0.47
Norfloxacin (150mg/kg)
3.1 ± 0.32
11 ± 0.26
1.75 ± 0.38
63.98 ± 0.51
Norfloxacin (150mg/kg) + piperine (20mg/kg)
3.2 ± 0.31
16.1 ± 0.27
2.97 ± 0.38
111.69 ± 0.54
n = 6, mean ± SD, P < 0.05.Piperine and Carbamazepine
The effect of piperine on the steady-state pharmacokinetics of a single dose of carbamazepine in poorly controlled epilepsy patients on carbamazepine monotherapy was studied. Patients (n=10 each) receiving either 300 mg or 500 mg dose of carbamazepine twice a day were selected. After administration of carbamazepine, venous blood samples were collected at 0, 0.5, 1, 2, 4, 6, 9, and 12 h. Subsequently, piperine (20 mg p.o.) was administered along with carbamazepine and samples were collected similarly. Piperine significantly increased the mean plasma concentrations of carbamazepine at most of the time points in both dose groups. There was a significant increase in AUC0-12h (P<0.001), average Css (P<0.001), t1/2 (P<0.05), and a decrease in Kel (P<0.05), in both the dose groups, whereas changes in Ka and t1/2α were not significant. Cmax (P<0.01) and tmax (P<0.01) were increased significantly following piperine administration in the 500 mg dose group; however, these parameters were not significant in the lower dose group. Piperine could significantly enhance the oral bioavailability of carbamazepine, possibly by decreasing the elimination or by increasing its absorption [96].Piperine and Fexofenadine
Effect of piperine, a major component of black pepper, on the oral exposure of fexofenadine in rats was studied. Pharmacokinetic parameters of fexofenadine were determined in rats following an oral (10 mg/kg) administration of fexofenadine in the presence and absence of piperine (10 or 20 mg/kg). Compared to the control group given fexofenadine alone, the combined use of piperine increased the AUC offexofenadine by 180% to 190% while there was no significant change in Cmax and t1/2 of fexofenadine in rats. The bioavailability of fexofenadine was increased by approximately 2-fold via the concomitant use of piperine. Furthermore, tmax tends to be increased which might be attributed to the delayed gastric emptying in the presence of piperine. In conclusion, piperine significantly enhanced the oral exposure of fexofenadine in rats likely by the inhibition of P-glycoprotein-mediated cellular efflux during the intestinal absorption, suggesting that the combined use of piperine or piperine-containing diet with fexofenadine may require close monitoring for potential drug-diet interactions [97].Piperine and Metronidazole
Effect of piperine on bioavailability of metronidazole was studied in rabbits. Male New Zealand white rabbits (2.0–2.5 kg body weight) used for pharmacokinetic and bioavailability study. Three groups of rabbits were formed from which one group was considered as control and received only vehicle (distilled water) orally. The remaining two groups were treated with metronidazole and combination of metronidazole and piperine, respectively. About 1 mL of blood sample was collected at the different time intervals and analyzed spectrophotometrically by HPLC. Different pharmacokinetic parameters have shown to enhance bioavailability of metronidazole in combination with piperine than metronidazole alone (Table15). So, it is concluded that bioavailability of metronidazole was significantly enhanced in the presence of piperine [98].Table 15
Comparative pharmacokinetic parameters after oral administration of metronidazole and in combination with piperine in rabbits [98].
Pharmacokinetic
Metronidazole
Metronidazole + piperine
parameters
C
max (ng/mL)
3,805.89 ± 233.8
6,007.07 ± 348.8
AUC0–24 (ng·h/mL)
45,073.75 ± 713.7
84,980.98 ± 345.6
t
max (h)
1.66 ± 0.57
1.66 ± 0.57
K
el (mL/h)
0.06 ± 0.02
0.04 ± 0.02
t
1
/
2 (h)
1.48 ± 1.23
12.24 ± 1.04
V
d (L)
2.69 ± 0.23
1.48 ± 0.65Piperine and Resveratrol
Effect of piperine on oral bioavailability of resveratrol was studied in mice. Employing a standardized LC-MS assay, the effect of piperine coadministration with resveratrol on serum levels resveratrol and resveratrol-3-O-β-D-glucuronide in C57BL mice was determined. Mice were administered resveratrol (100 mg/kg) or resveratrol (100 mg/kg) + piperine (10 mg/kg), and the serum levels of resveratrol and resveratrol-3-O-β-D-glucuronide were analyzed at different times. The AUC to resveratrol was enhanced to 229% and the Cmax was increased to 1544% with the addition of piperine. Study demonstrated that piperine significantly improves the in vivo bioavailability of resveratrol [100].Piperine and Gatifloxacin
Influence of coadministration of piperine on pharmacokinetic profile of gatifloxacin was studied in layer birds. The pharmacokinetic profile (Tables16 and 17) of gatifloxacin (10 mg/kg body weight) along with piperine coadministration (15 mg/kg) via single oral dose in layer birds showed t1/2, Cmax, and AUC of 4.03±0.097 h, 2.14±0.019 μg/mL, and 17.54±0.204 μg·h/mL, respectively, which is found significantly higher than gatifloxacin alone (3.74±0.073 h, 1.74±0.023 μg/mL, and 15.25±0.219 μg·h/mL, resp.). This study reveals that piperine has significant effect on the pharmacokinetics of the gatifloxacin. There is enhancement in bioavailability (F) from 74.52±1.021% to 85.74±0.956% in piperine + gatifloxacin-treated group. The results obtained are the combined effect of piperine on the absorption kinetics and the inhibition of the metabolism of gatifloxacin [101].Table 16
Comparison of plasma concentrations (μg/mL) of gatifloxacin- and gatifloxacin + piperine-treated birds after single oral administration (10 mg/kg) [101].
Time (h)
Gatifloxacin
Gatifloxacin + piperine
0.5
0.48 ± 0.013
0.53 ± 0.009**
0.75
1 ± 0.014
1.16 ± 0.029**
1
1.35 ± 0.016
1.46 ± 0.021*
2
1.74 ± 0.023
2.14 ± 0.020
4
1.35 ± 0.02
1.47 ± 0.034*
8
0.97 ± 0.009
1.08 ± 0.019**
12
0.46 ± 0.01
0.54 ± 0.008
n = 6, *Significant at P < 0.05, **Highly significant at P < 0.01.Table 17
Comparison of pharmacokinetic parameters of gatifloxacin- and gatifloxacin + piperine-treated layer birds after single oral administration (10 mg/kg) [101].
Pharmacokinetic
Gatifloxacin
Gatifloxacin + piperine
parameters
C
max (μg/mL)
1.74 ± 0.023
2.14 ± 0.019*
AUC (μg·h/mL)
15.25 ± 0.219
17.54 ± 0.204*
t
max (h)
2 ± 0.0
2 ± 0.0
t
1
/
2 (h)
3.74 ± 0.073
4.03 ± 0.097*
V
d (L/kg)
3.54 ± 0.038
3.33 ± 0.083*
F (%)
74.52 ± 1.021
85.74 ± 0.956*
n = 6, mean ± SE; **Highly significant at P < 0.01, *Significant at P < 0.05.The influence of coadministration of piperine on pharmacokinetic profile of gatifloxacin was studied in broiler birds. The pharmacokinetic profile of gatifloxacin (10 mg/kg body weight) along with piperine coadministration (15 mg/kg) via single dose oral administration in broiler birds showedt1/2, Cmax, and AUC of 4.1±0.092 h, 2.14±0.02 μg/mL, and 17.58±0.17 μg·h/mL, respectively, which is found significantly higher than t1/2, Cmax and AUC of 3.81±0.07 h, 1.74±0.024 μg/mL, and 15.24±0.23 μg·h/mL, respectively, obtained after single oral administration of gatifloxacin (10 mg/kg body weight) alone. This study reveals that piperine has significant effect on the pharmacokinetics of the gatifloxacin. There is significant enhancement of bioavailability (F) in piperine-treated group (81.95±1.56%) compared to gatifloxacin alone treated group (72.96±1.10%). The results obtained are the combined effect of piperine on the absorption kinetics and the inhibition of the metabolism of gatifloxacin [102].Piperine and Atenolol
A bioavailability of atenolol in presence of piperine was studied in male New Zealand white rats. All rats were divided in three groups. First group was considered as control and received only vehicle (distilled water) orally. The remaining two groups were treated with atenolol and combination of atenolol and piperine, respectively. About 2 mL of blood sample was collected at the different time intervals and analyzed spectrophotometrically by HPLC. The pharmacokinetic parameters obtained after administration of atenolol (100 mg/kg) and combination of atenolol (100 mg/kg) and piperine (10 mg/kg). So, from Table18 it can be concluded that bioavailability of atenolol was significantly enhanced in presence of piperine [103].Table 18
Comparison of pharmacokinetic parameters of atenolol- and atenolol + piperine-treated male New Zealand white rats after single oral administration (100 mg/kg) [103].
Pharmacokinetic
Atenolol
Atenolol + piperine
parameters
C
max (pg/mL)
22,453 ± 233
37,860 ± 348
AUC0–24 (pg·h/mL)
1,07,189 ± 1615
1,52,011 ± 2354
t
max (h)
2.0 ± 0.0
2.0 ± 0.0
K
el (mL/h)
0.27 ± 0.005
0.25 ± 0.010
t
1
/
2 (h)
6.27 ± 0.057
6.72 ± 0.100
V
d (L)
4.54 ± 0.786
2.88 ± 0.305
n = 3, mean ± SE.Piperine and Ibuprofen
Influence of piperine on ibuprofen-induced antinociception and its pharmacokinetics was studied. Piperine (10 mg/kg) significantly increased the dose-dependent antinociceptive activity of ibuprofen evaluated by both acetic acid writhing and formalin test, when it was administered with ibuprofen. Ibuprofen plasma concentration was also increased when it was administered with piperine. The synergistic antinociception activity of ibuprofen when administered with piperine can be attributed to increased plasma concentration of ibuprofen. From this study it can be concluded that piperine can be used as a bioenhancer along with ibuprofen [104].Piperine and Losartan Potassium
Effect of piperine on bioavailability of losartan potassium was studied in male New Zealand white rats. All rats were divided in three groups. First group received only mineral water orally. Second group received losartan potassium (100 mg/kg). Third group received losartan potassium (100 mg/kg) and piperine (10 mg/kg). About 2 mL of blood sample was collected at the different time intervals and analyzed by HPLC. The pharmacokinetic parameters obtained after administration of losartan potassium (100 mg/kg) and combination of losartan potassium (100 mg/kg) and piperine (10 mg/kg). So, from Table19 it can be concluded that bioavailability of losartan potassium was significantly enhanced in presence of piperine [105].Table 19
Comparison of pharmacokinetic parameters of losartan potassium- and losartan potassium + piperine-treated male New Zealand white rats after single oral administration (100 mg/kg) [105].
Pharmacokinetic
Losartan potassium
Losartan potassium
parameters
+ piperine
C
max (pg/mL)
32,461 ± 1436
48,399 ± 6060
AUC0–24 (pg·h/mL)
1,10,441 ± 5280
1,69,924 ± 14,343
t
max (h)
1.0 ± 0.0
1.0 ± 0.0
K
el (mL/h)
0.295 ± 0.002
0.283 ± 0.022
t
1
/
2 (h)
2.34 ± 0.01
2.44 ± 0.195
V
d (L)
3.0 ± 0.15
2.0 ± 0.25
n = 3, mean ± SE.


### 4.2.Zingiber officinale

The major pungent compounds inZingiber officinale (Ginger) of rhizome extract contain potentially active gingerols, which can be converted to shogaols, zingerone, and paradol [110, 111]. The odor of ginger depends mainly on its volatile oil, the yield of which varies from 1 to 3% [112]. In laboratory animals, the gingerols increase the motility of the gastrointestinal tract and have analgesic, sedative, antipyretic, and antibacterial properties [113]. [6]-gingerol is the major pungent principle of ginger. The chemopreventive potentials of [6]-gingerol present a promising future alternative to expensive and toxic therapeutic agents [114]. Ginger exhibits activities like antiulcer activity [115, 116], antithrombotic activity [117], antimicrobial activity [118], antifungal activity [119], anti-inflammatory activity [117, 120–122], antidiabetic activity [123], antiemetic activity [124, 125], anthelmintic activity [126], analgesic and antipyretic activity [121], antioxidant and antiapoptotic activity [122], and anticancer activity [127].Ginger acts powerfully on GIT mucous membrane. The role of ginger is to regulate intestinal function to facilitate absorption. The composition containingZ. officinale alone provides bioavailability/bioenhancing activity in the range of 30–75%, and piperine and Z. officinale, and provides the bioavailability of drugs in the range of 10–85%. The dosage of bioenhancer from Z. officinale as extract is in the range of 10–30 mg/kg body weight and piperine is in the range of 4–12 mg/kg body weight. The dosage of bioenhancer from Z. officinale as bioactive fraction is in the range of 5–15 mg/kg body weight, preferably 30 mg/kg body weight and piperine is in the range of 6–10 mg/kg body weight, preferably 8 mg/kg body weight. The extracts or its fractions either in presence or absence of piperine have been found to be highly selective in their bioavailability enhancing activity (Table 20). It varies from almost nearly significant (20%) to highly significant (200%) [128, 129].Table 20
Percent enhancement in bioavailability of different drugs/compounds by supplementation of bioactive fractions fromZ. officinaleand its combination with piperine [128, 129].
Category
Compound
Percent enhancement
BE fromZ. officinale
BE fromZ. officinale + piperine
Macrolides
Azithromycin
78
85
Erythromycin
68
105
Roxithromycin
72
93
Cephalosporins
Cefalexin
75
85
Cefadroxil
68
65
Penicillins
Amoxycillin
80
90
Cloxacillin
76
90
Aminoglycosides
Kanamycin
65
92
Fluoroquinolones
Ciprofloxacin
68
70
Pefloxacin
53
69
Antifungal
Fluconazole
120
110
Ketoconazole
125
100
Antiviral
Acyclovir
82
85
Zidovudine
105
126
CNS drugs
Alprazolam
76
70
Anticancer
Methotrexate
87
49
5-Fluorouracil
110
93
Doxorubicin
72
75
Cisplatin
56
45
Cardiovascular
Amlodipine
68
95
Propranolol
76
104
Lisinopril
76
100
Anti-inflammatory/Antiarthritic
Diclofenac
90
140
Nimesulide
144
165
Piroxicam
86
134
Antituberculosis/Antileprosy
Rifampicin
65
98
Dapsone
46
55
Ethionamide
56
48
Cycloserine
71
70
Antihistamines
Salbutamol
78
92
Theophylline
76
80
Bromhexine
46
75
Corticosteroids
Dexamethasone
76
80
Betamethasone
75
70
Immunosuppressants
Cyclosporin A
116
120
Tacrolimus
75
117
Antiulcer
Ranitidine
147
165
Cimetidine
98
76
Vitamins
Vitamin A (1 mg/kg)
30
40
Vitamin E (40 mg/kg)
27
25
Vitamin C (50 mg/kg)
25
24
Folic acid (50μg/kg)
34
35
Antioxidants
β-Carotene (15 mg/kg)
36
55
Silymarin (5 mg/kg)
28
43
Herbal products
Curcumin (50 mg/kg)
43
70
Rutin (40 mg/kg)
21
78
Herbal plants
Echinacea
66
82
Tinospora cordifolia
67
112
Picrorhiza kurroa
56
87
Andrographis paniculata
55
70
Emblica ribes
65
72
Asparagus racemosus
44
60
Withania somnifera
64
48
Amino acids
Methionine (20 mg/kg)
25
45
Lysine (40 mg/kg)
15
40
Leucine (50 mg/kg)
17
34
Valine (25 mg/kg)
25
46
Isoleucine (25 mg/kg)
31
35
Essential elements
Zinc (0.1 mg/kg)
19
20
Potassium (25 mg/kg)
21
19


### 4.3.  Niaziridin

Niaziridin is a nitrile glycoside that has been isolated from the leaves, pods, and bark of Drumstick (Moringa oleifera) [130]. M. oleifera has shown to exhibit activities like antifertility effect [131], antimicrobial activity [132], diuretic activity [133], anticancer activity [134, 135], anti-inflammatory activity [133, 135], hypotensive and spasmolytic activity [136], antifungal activity [137], antiulcer activity [138], antioxidant activity [139, 140], hepatoprotective activity [141], hypolipidaemic activity [142], antiteratogenic activity [143], and antiarthritic activity [144].It enhances bioactivity of commonly used antibiotics such as rifampicin, ampicillin, tetracycline, and nalidixic acid against Gram-positive bacteria likeM. smegmatisand Bacillus subtilisand Gram-negative bacteria like E. coli (Table 21). It enhances activity of commonly used antibiotics such as rifampicin, ampicillin, tetracycline, and nalidixic acids against E. coli Gram-negative bacteria. It enhances activity of rifampicin, ampicillin, tetracycline, and nalidixic acids by 1.2–19-fold against the Gram-positive strains. It enhances the activity of azole antifungal drugs such as clotrimazole against Candida albicans by 5-6-fold. However, the antifungal activity enhancement was observed only at a relatively higher concentration (10 μg/mL) of the compound. It also facilitates the uptake of nutrients like Vitamin B12 through the intestinal gut membrane in combination, thus also functioning as bioavailability enhancer [145, 146].Table 21
Enhancement of antibiotic activity by niaziridin* in combination with antibiotics against different organisms [145, 146].
Organisms
Antibiotics
Concentration (μg/mL)
Fold enhancement of activity
E. coli (CA8000)
Rifampicin
20.0
38.8
Rifampicin
30.0
12.6
Ampicillin
6.0
5.3
Tetracycline
1.0
2.3
Tetracycline
2.0
5.2
Nalidixic acid
6.0
50.0
B. subtilis (MTCC121)
Rifampicin
0.05
19.4
Ampicillin
0.01
5.1
Tetracycline
1.0
3.5
Nalidixic acid
2.0
7.0
M. smegmatis (MC2 155)
Rifampicin
0.05
1.9
Ampicillin
0.01
4.7
Tetracycline
1.0
4.0
Nalidixic acid
2.0
1.2
*Dose:E. coli = 0.1 μg/kg; B. subtilisand M. smegmatis= 1.0 μg/kg.


### 4.4.  Glycyrrhizin

Glycyrrhizin is a glycoside obtained from roots and stolon of Liquorice (Glycyrrhiza glabra). It has expectorant action to treat bronchitis and can also reduce inflammation, allergies, asthma, gastritis, peptic ulcers, rheumatism, and sore throat. It helps the liver to detoxify drugs and is used for treatment of liver disease. It strengthens the immune system, stimulates the adrenal gland, and is diuretic and laxative. Glycyrrhizin is 50 times sweeter than sugar. Primary uses include treatment for peptic ulcers and stomach ailments, respiratory, and intestinal passages. Glycyrrhizin exhibits activities like antihepatotoxic activity [147, 148], anti-inflammatory activity [149, 150], anticancer activity [151], and antiviral activity [152, 153].The concentration of glycyrrhizin ranges from 0.05 to 50% of the weight of the antibacterial compounds. The concentration of glycyrrhizin ranges from 0.10 to 10% of the weight of the nutraceutical compounds. The concentration of glycyrrhizin ranges from 0.25 to 20% of the weight of the antifungal agents. The level of glycyrrhizin ranges from 10 to 10,000-fold of the weight of the anticancer compound used [154, 155].Glycyrrhizin-mediated enhancement in the cell division inhibitory action of anticancer agent “Taxol” (paclitaxel) in the animal cell culture experiments using cancerous cell line MCF-7. The anticancerous activity of Taxol in terms of inhibiting the growth and multiplication of MCF-7 cancer cells was markedly enhanced by 5-fold. The cancerous cells growth inhibition by Taxol (0.01μg/mL) in presence of glycyrrhizin (1 μg/mL) was higher than even the treatment with Taxol (0.05 μg/mL) alone [154, 155].It enhances bioactivity of commonly used antibiotics such as rifampicin, ampicillin, tetracycline, and nalidixic acids against Gram-positive bacteria likeM. smegmatisand Bacillus subtilisand Gram-negative bacteria like E. coli(Table 22). It enhances activity of commonly used antibiotics such as rifampicin, ampicillin, tetracycline, and nalidixic acids against E. coli Gram-negative bacteria. It enhances activity of rifampicin, tetracycline, and nalidixic acids against the Gram-positive strains. It enhances the activity of azole antifungal drugs such as clotrimazole against Candida albicans[154, 155].Table 22
Enhancement of antibiotic activity by glycyrrhizin (1μg/mL) in combination with antibiotics against different organisms [154, 155].
Organisms
Antibiotics
Concentration (μg/mL)
Fold enhancement of activity
E. coli (ATCC 10536)
Rifampicin
10.0
3.8
Rifampicin
20.0
14.0
Nalidixic acid
8.0
9.5
Ampicillin
6.0
12.6
Ampicillin
8.0
2.1
Tetracycline
2.0
1.9
Tetracycline
4.0
9.0
B. subtilis (ATCC 6015)
Nalidixic acid
6.0
4.5
Nalidixic acid
8.0
6.75
Tetracycline
1.0
5.0
M. smegmatis (ATCC 14468)
Rifampicin
0.5
6.5
Nalidixic acid
4.0
7.7
Tetracycline
0.5
1.5


### 4.5.Cuminum cyminum

The main components ofC. cyminum oil are p-mentha-1,4-dien-7-al, cumin aldehyde, γ-terpinene, and β-pinene [156]. C. cyminumexhibits activities like estrogenic activity [157], hypolipidaemic activity [158], antinociceptive and anti-inflammatory activity [159], anticonvulsant effect [160], anticancer activity [161], antimicrobial activity [156, 162], antitussive effect [163], antioxidant activity [164], and antifungal activity [165]. The doses of its fractions responsible for the bioavailability enhancement activity ranged from 0.5 to 25 mg/kg body weight. The dosage level of the composition comprising C. cyminumextract is in the range of 10–30 mg/kg body weight and composition comprising bioactive fraction is in the range of 2–20 mg/kg body weight. The composition contain C. cyminumextract or the fractions there of which provides bioavailability/bioenhancing activity in the range of 25–335% (Table 23). Polar and nonpolar extract of parts of C. cyminumand piperine increased bioavailability in the range of 25–435% [166, 167].Table 23
Percent enhancement in bioavailability of different compounds by supplementation of bioactive fractions fromC. cyminum and its combination with piperine [166, 167].
Category
Compound
Percent enhancement
BE fromC. cyminum
BE fromC. cyminum + piperine
Macrolides
Azithromycin
83
97
Erythromycin
75
95
Roxithromycin
67
103
Cephalosporins
Cefalexin
60
75
Cefadroxil
90
79
Penicillins
Amoxycillin
75
98
Cloxacillin
94
95
Aminoglycosides
Kanamycin
95
110
Fluoroquinolones
Ciprofloxacin
52
47
Pefloxacin
47
57
Ofloxacin
61
73
Antifungal
Fluconazole
170
126
Ketoconazole
136
156
Antiviral
Acyclovir
110
98
Zidovudine
330
415
CNS drugs
Alprazolam
60
104
Anticancer
Methotrexate
125
30
5-Fluorouracil
335
435
Doxorubicin
85
103
Cisplatin
70
79
Cardiovascular
Amlodipine
55
103
Propranolol
135
210
Lisinopril
83
98
Anti-inflammatory/Antiarthritic
Diclofenac
65
108
Nimesulide
168
150
Piroxicam
70
107
Antituberculosis/Antileprosy
Rifampicin
250
365
Dapsone
60
75
Ethionamide
78
65
Cycloserine
89
90
Antihistamines
Salbutamol
110
85
Theophylline
87
75
Bromhexine
50
90
Corticosteroids
Dexamethasone
85
105
Betamethasone
95
82
Immuno-suppressants
Cyclosporin A
156
275
Tacrolimus
75
117
Antiulcer
Ranitidine
117
89
Cimetidine
123
105
Vitamins
Vitamin A (1 mg/kg)
26
18
Vitamin B1 (10 mg/kg)
37
33
Antioxidants
β-Carotene (15 mg/kg)
45
53
Silymarin (5 mg/kg)
32
41
Herbal products
Curcumin (50 mg/kg)
39
29
Herbal plants
Echinacea
72
90
Tinospora cordifolia
98
152
Picrorhiza kurroa
78
115
Andrographis paniculata
72
68
Emblica ribes
72
60
Asparagus racemosus
35
72
Withania somnifera
55
65
Amino acids
Methionine (20 mg/kg)
27
30
Lysine (40 mg/kg)
35
29
Leucine (50 mg/kg)
31
32
Valine (25 mg/kg)
25
24
Isoleucine (25 mg/kg)
40
22
Essential elements
Iron (0.5 mg/kg)
23
29


### 4.6.Carum carvi

Carum carvi (Caraway) contains caraway oil obtained from dried and crushed seeds. Carvone and limonene are the chief constituents of the oil and its odour and flavour are mainly attributed to them [168]. C. carvi exhibits activities like antiulcer effects [169], hypoglycemic effect [170], antimicrobial activity [156, 171], diuretic activity [172], antioxidant activity [171, 173], antiaflatoxigenic activity [174], and antifungal activity [171]. The effective dose of the bioenhancer extract is in the range of 5–100 mg/kg body weight and the dose bioactive fraction of bioenhancer is in the range of 1–55 mg/kg body weight. It has been reported to enhance bioavailability of antibiotics, antifungal, antiviral, and anticancerous drug. The extract or its fractions were found to be 20–110% more active and when used in combination with Z. officinale, it was found to be more effective, in the range of 10–150 mg/kg body weight. C. carviin different combinations showed pronounced activity ranging from 25 to 95% in presence of piperine and amount of piperine in formulations ranged from 3 to 15 mg/kg body weight [5, 175]. The percent enhancement of bioavailability of different class of drugs by fractions of C. carvi and in combination with piperine and Z. officinaleis shown in Table 24.Table 24
Percent enhancement in bioavailability of different drugs/compounds by supplementation of bioactive fractions fromC. carvi and its combination with piperine and Z. officinale[5, 175].
Category
Compound
Dose (mg/kg)
Percent enhancement
BE fromC. carvi
C. carvi+ piperine
C. carvi+ Z. officinale
Macrolides
Azithromycin
25
55
90
86
Erythromycin
45
70
100
105
Roxithromycin
15
65
95
98
Cephalosporins
Cefalexin
45
Nil
90
79
Cefadroxil
45
67
95
85
Ceftrioxone
25
72
78
75
Cefixime
40
80
79
82
Cefidinir
40
89
95
130
Penicillins
Amoxicillin
45
75
115
100
Cloxacillin
25
110
95
110
Aminoglycosides
Amikacin
50
85
100
92
Kanamycin
50
Nil
87
68
Fluoroquinolones
Ciprofloxacin
45
78
110
133
Pefloxacin
40
Nil
70
75
Ofloxacin
20
65
167
170
Norfloxacin
40
55
65
60
Antifungal
Fluconazole
65
65
98
110
Amphotericin B
78
78
90
80
Ketoconazole
55
55
100
96
Antiviral
Acyclovir
40
78
100
90
Zidovudine
10
92
95
87
CNS drugs
Alprazolam
0.1
Nil
70
80
Haloperidol
0.5
95
90
85
Anticancer
Methotrexate
5
76
89
102
5-Fluorouracil
25
90
110
100
Doxorubicin
5
Nil
70
69
Cisplatin
5
Nil
Nil
55
Cardiovascular
Amlodipine
1
Nil
50
65
Lisinopril
1
79
95
90
Atenolol
5
100
93
97
Propranolol
8
68
90
75
Anti-inflammatory/antiarthritic
Diclofenac
5
Nil
100
95
Piroxicam
2
Nil
98
76
Nimesulide
10
100
140
145
Rofecoxib
2.5
75
70
80
Antituberculosis/antileprosy
Rifampicin
40
110
170
140
Pyrazinamide
12.5
45
50
55
Dapsone
10
56
67
68
Ethionamide
25
68
65
70
Cycloserine
40
70
80
75
Antihistamines
Salbutamol
0.8
75
89
80
Theophylline
30
70
79
89
Bromhexine
25
Nil
70
71
Loratidine
1
76
70
80
Corticosteroids
Prednisolone
4
65
67
60
Dexamethasone
0.05
72
77
73
Betamethasone
0.1
80
89
77
Immuno-suppressants
Cyclosporin A
10
100
105
120
Tacrolimus
5
90
95
114
Antiulcer
Ranitidine
30
67
70
150
Cimetidine
40
72
84
100
Omeprazole
2
76
70
75
Vitamins
Vitamin A
1
19
16
27
Vitamin B1
10
42
26
55
Antioxidants
β-Carotene
15
55
59
72
Silymarin
5
38
45
41
Herbal products
Curcumin
50
48
51
52
Rutin
40
45
40
42
Herbal plants
Echinacea agustifolia
10
Nil
76
65
Tinospora cordifolia
50
76
90
71
Picrorhiza kurroa
50
80
110
76
Aegles marmelos
1000
65
65
60
Andrographis paniculata
50
68
72
54
Asparagus racemosus
50
Nil
55
45
Terminalia chebula
50
92
87
91
Withania somnifera
60
76
70
76
Centella asiatica
30
68
65
62
Amino acids
Methionine
20
28
30
37
Lysine
40
29
38
43
Leucine
50
21
32
40
Valine
25
19
29
38
Isoleucine
25
34
44
50


### 4.7. Allicin

Allicin is an allyl sulfur containing compound obtained from Garlic (Allium sativum). Allicin exhibits activities like antiplatelet activity [176], antioxidant activity [177, 178], antibacterial activity [179, 180], anticancer activity [181], Immunomodulating effect [182], antidiabetic activity [183, 184], antiparasitic activity [185], antifungal activity [186–188], antioxidant and anti-inflammatory activity [189, 190], and antiviral activity [191].


#### 4.7.1. Allicin and Cu2+

Cu2+ showed a dose-dependent fungicidal activity against Saccharomyces cerevisiae cells, and its lethal effect was extremely enhanced in the presence of allicin, an allyl sulfur compound from garlic. The fungicidal activity of Cu2+ was unaffected or rather attenuated by other sulfur-containing compounds such as N-acetyl-cysteine, l-cysteine, or dithiothreitol. Ca2+ could absolutely protect against the lethal effect of Cu2+ itself, but showed no protection against the fungicidal activity of Cu2+ newly generated in combination with allicin. Cu2+ accelerated an endogenous generation of reactive oxygen species (ROS) in S. cerevisiae cells at a lethal concentration, but such intracellular oxidative stress induction was not observed during cell death progression upon treatment with Cu2+ and allicin. A surfactant, sodium N-lauroyl sarcosinate (SLS), enhanced the solubilization of a few proteins including alkyl hydroperoxide reductase 1 (AHP1) in intact cells, accounting for the absence of this protein in the extract from allicin-treated cells. Allicin-treated cells were rendered extremely sensitive to the subsequent Cu2+ treatment as in the case of SLS-treated cells. Allicin-treated cells and SLS-treated cells similarly showed an increased sensitivity to exogenously added tert-butyl hydroperoxide (t-BOOH), organic peroxide that is detoxified by the action of AHP1. Our study suggests that allicin influences the mode of cell surface localization or the related function of AHP1 as a defense against phospholipid peroxidation by the external action of Cu2+ [192].


#### 4.7.2.  Allicin and Amphotericin B

Enhancement of the fungicidal activity of amphotericin B (AmB) by allicin, an allyl-sulfur compound from garlic, against the yeastSaccharomyces cerevisiae as a model system was studied. AmB is a representative antibiotic for the control of serious fungal infections, and its fungicidal activity was greatly enhanced by allicin (Table 25). In addition to the plasma membrane permeability change, AmB induced vacuole membrane damage so that the organelles were visible as small discrete particles. Although allicin was ineffective in promoting AmB-induced plasma membrane disability, this compound enhanced AmB-induced structural damage to the vacuolar membrane even at a nonlethal dose of the antibiotic. Allicin could also enhance the antifungal activity of AmB against the pathogenic fungus C. albicansand againstAspergillus fumigatus. In contrast, allicin did not enhance the cytotoxic activity of AmB against cells of human promyelocytic leukemia (HL-60), a vacuole-less organism [187].Table 25
Enhancement of fungicidal activity of AmB by Allicin againstS. cerevisiae [187].
Drug/compound
Conc. (μg)
Action againstS. cerevisiae
AmB alone
1
Mostly resistance to action
AmB alone
5
Subjected to lethal damage
Allicin alone
120
Not lethal
AmB + allicin
0.5 + 120
More susceptible to fungicidal activity of AmBAllicin was found to inhibit ergosterol transport from the plasma membrane to the cytoplasm, which is considered to be a cellular protective response to AmB-induced vacuole disruption inS. cerevisiae. The study suggests that AmB lethality against C. albicans depends at least in part on its vacuole disruptive activity under the physiological condition permissive for invasive growth of the fungus [188].Ogita et al. [193] reported that allicin enhances AmB-induced vacuole membrane damage by inhibiting ergosterol trafficking from the plasma membrane to the vacuole membrane. Ogita et al. [194] suggested that the fungicidal activity of AmB combined with allicin is involved in vacuole disruption but not in potassium ion efflux, and that the expression of allicin-mediated activity of AmB requires the presence of ergosterol in the plasma membrane.


### 4.8.  Lysergol

Lysergol, a phytomolecule, is obtained from Morning Glory Plant (Ipomoea spp.) which enhances the killing activities of different antibiotics on bacteria and is a promising herbal bioenhancer. It has been isolated from higher plants like Rivea corymbosa, Ipomoea violacea,andIpomoea muricata. Bioenhancing activities of lysergol are under investigation. The effective amount of lysergol as a bioenhancer and bioavailability enhancer is in the range of 1–10 μg/mL but preferable dosage level is 10 μg/mL. It enhances bioavailability of different drugs like rifampicin, tetracycline, and ampicillin. Lysergol enhances the antimicrobial effect of the antibiotic compound in the range of 2–12-fold (Table 26). It is effective against broad spectrum microbes, Gram-positive and Gram-negative, consisting E. coli(ATCC 10536), B. subtilis(ATCC 6051),M. smegmatis(ATCC 14468), and other similar microbes [2]. Patil et al. [195] reported that lysergol improved the bioavailability of berberine after oral administration in Sprague-Dawley rats.Table 26
Enhancement of antibiotic activity by lysergol (10μg/mL) in combination with rifampicin against different organisms [2].
Organisms
Antibiotics
Concentration (μg/mL)
Fold enhancement of activity
E. coli (ATCC 10536)
Rifampicin
10
6–12
Rifampicin
20
3–5
B. subtilis(ATCC 6051)
Rifampicin
0.4
3–4.6
M. smegmatis (ATCC 14468)
Rifampicin
0.2
4.5–6


### 4.9.Aloe Vera Gel and Whole Leaf Extract

Aloe vera had a salutary effect on both vitamin C and vitamin E. Aloe vera gel and whole leaf extracts shown increased plasma concentration and improved absorption of both, vitamin C and vitamin E. The Aloe vera gel extract was especially effective in slowing down and increasing the absorption of ascorbate. It prolonged its plasma concentration significantly, even for 24 h, and following an overnight fast. Both the gel and whole leaf extracts improved the absorption of vitamin E and prolonged its plasma concentration, especially after 8 h. AUC for vitamin C and vitamin E with Aloe gel and whole leaf extract is shown in Table 27. Aloe vera is unique in its ability to increase bioavailability of both of these vitamins and should be considered as a future nutritional herbal bioenhancer [196].Table 27
AUC of vitamins C and E alone or with Aloe gel or Aloe whole leaf extract [196].
Supplement
AUC (μMh)
Vitamin C (500 mg)
339 ± 124
Vitamin C + Aloe whole leaf extract
272 ±144
Vitamin C + Aloe gel
1031 ± 513
Vitamin E (420 mg)
19.3 ± 23.2
Vitamin E + Aloe whole leaf extract
38.3 ± 17.0
Vitamin E + Aloe gel
71.3 ± 22.5
mean ± SE.


### 4.10.Stevia rebaudiana

Stevia rebaudiana(Stevia) is known as honey leaf which has been used as sweetener in South America. The chief constituent of stevia is stevioside, the glycoside which is 200 times sweeter than sucrose. Other constituents include steviol, austroinulin, rebaudioside, and dulcoside A. Extracts/fractions/pure isolates of stevia either alone or in combination with piperine are selective in enhancing the bioavailability/bioefficacy of drugs, nutraceuticals, and herbal drugs/formulations. The percentage of stevia in the bioenhancing composition varies from 0.01 to 80%. The dosage of bioenhancer derived from stevia extract is in the range of 0.01–50 mg/kg body weight and piperine is in the range of 0.01–12 mg/kg body weight. The dosage of bioenhancer derived from stevia bioactive fraction or pure compound is in the range of 0.01–40 mg/kg body weight, preferably 30 mg/kg body weight and piperine is in the range of 0.01–10 mg/kg body weight, preferably 8 mg/kg body weight. The dosage of bioenhancer derived from stevia leaf is in the range of 0.01–250 mg/dose of the drug, nutraceutical, or herbal extract. The dosage of bioenhancer derived from stevia fraction or pure compound is in the range of 0.01–75 mg irrespective of the amount of drug in the composition, preferably 1–30 mg/dose of the drug, nutraceutical, or herbal extract. Stevia enhanced bioavailability of different groups like antibiotics, antiobese drugs, antidiabetic drugs, antifungal drugs, antiviral drugs, anticancer drugs, cardiovascular drugs, anti-inflammatory, antiarthritic agents, antituberculosis/antileprosy drugs, anthelmintic/respiratory drugs, immune-modulators, antiulcer drugs, and herbal products or drugs [197].


### 4.11. Curcumin

Curcumin is the principal curcuminoid of the popular Indian spice turmeric (Curcuma longa). Curcumin suppresses drug metabolizing enzymes (CYP3A4) in the liver [198] as well as inducing changes in the drug transporter P-glycoprotein, hence increasing the Cmax and AUC of celiprolol and midazolam in rats [199]. The influence of curcumin before treatment on pharmacokinetic disposition of norfloxacin was studied in rabbits after single oral administration. The pharmacokinetic data revealed that curcumin-treated animals had significantly (P≤0.05) higher AUC and AUMC. Prior treatment of curcumin significantly (P≤0.05) increased t1/2β and Vd of norfloxacin. Further treatment with curcumin reduced loading and maintenance doses by 26% and 24%, respectively [200].


### 4.12. Sinomenine

Sinomenine is an alkaloid obtained fromSinomenium acutum,widely used for treatment of rheumatic and arthritic diseases in China and Japan.A single dose of paeoniflorin (150 mg/kg) alone and with sinomenine hydrochloride (90 mg/kg) was administered by gastric gavage to unrestrained conscious male Sprague-Dawley rats (250–300 g). A Blood sample was collected periodically via a jugular vein before and after dosing from 10 min to 12 h. HPLC assay was developed to determine the plasma concentrations of paeoniflorin. After coadministration of sinomenine, theCmax of paeoniflorin was elevated, tmax was delayed, AUC0-∞was increased, MRT was prolonged, CLB was decreased, and Vd was reduced. These results from Table 28 indicate that sinomenine hydrochloride significantly improved the bioavailability of paeoniflorin in rats [201].Table 28
Pharmacokinetic parameters of paeoniflorin (150 mg/kg) and in combination with sinomenine (90 mg/kg) after oral administration in rats [201].
Parameters
Paeoniflorin
Sinomenine + paeoniflorin
AUC0–∞ (μg·h/mL)
124.62 ± 36.91
1540.43 ± 548.96**
C
max (μg/mL)
1.26 ± 0.23
6.03 ± 2.45*
t
max (min)
45.00 ± 5.00
77.30 ± 17.50*
t
1
/
2 (min)
19.58 ± 9.01
53.78 ± 22.17***
Cl
B (mL/kg/min)
1301.83 ± 429.03
110.44 ± 45.61*
V
d (mL/kg)
102044.14 ± 46608.43
16064.25 ± 17189.33***
MRT (min)
133.12 ± 38.63
224.07 ± 26.62*
n = 6, mean ± SD; *P < 0.01, **P < 0.001, ***P < 0.05.Sinomenine at 16 and 136μM concentrations could significantly enhance the absorption of paeoniflorin (20 μM) by 1.5- and 2.5-fold, respectively, and subsequently improve the bioavailability of paeoniflorin in rats. The mechanism underlying the improvement of paeoniflorin’s bioavailability was proposed that sinomenine could decrease the efflux transport of paeoniflorin by P-glycoprotein [202].


### 4.13. Genistein

Genistein is an isoflavone found in a number of dietary plants like soybean (Glycine max) and kudzu (Pueraria lobata) and has been studied for a number of potential health effects including anticancer and anti-inflammatory activity [203]. It is a well-known phytoestrogen [204].


#### 4.13.1. Genistein and Paclitaxel

The effect of orally administered genistein on the pharmacokinetics of paclitaxel administered through oral and intravenous route in rats was studied. A single dose of paclitaxel was administered orally (30 mg/kg) or intravenous route (3 mg/kg) alone or 30 min after oral administration of genistein (3.3 mg/kg or 10 mg/kg). The presence of 10 mg/kg genistein significantly (P<0.05) increased the AUC (54.7%) of orally administered paclitaxel, which was due to the significantly (P<0.05) decreased CLF of paclitaxel (35.2%). Genistein also increased Cmax of paclitaxel significantly (P<0.05 by 3.3 mg/kg, 66.8%; P<0.01 by 10 mg/kg, 91.8%). Consequently, the AB of paclitaxel in the presence of genistein was 0.020–0.025, which was elevated more than the control group (0.016); the RB of orally administered paclitaxel was increased from 1.26 to 1.55-fold. 10 mg/kg genistein also significantly (P<0.05) increased the AUC (40.5%) and reduced the CLB (30%) of intravenously administered paclitaxel. The presence of genistein improved the systemic exposure of paclitaxel in this study [205].


#### 4.13.2.  Genistein and Epigallocatechin Gallate

Cotreatment of HT-29 human colon cancer cells with genistein increased cytosolic EGCG by 2-5-fold compared with treatment with EGCG only. Intragastric coadministration of EGCG (75 mg/kg) and genistein (200 mg/kg) to CF-1 mice resulted in an increase int1/2 (148.7±16.4 versus 111.5±23.4 min) and AUC (183.9±20.2 versus 125.8±26.4 mg/mL at 3 min) of EGCG. Cotreatment with genistein also increased the Cmax, 6 h exposure AUC, and t1/2 of EGCG in the small intestine by 2.0-, 4.7-, and 1.4-fold, respectively, compared with mice treated with EGCG only. This study demonstrates that genistein can enhance EGCG bioavailability [206].


### 4.14.Ammannia multiflora

The methanolic extract ofAmmannia multiflora (Lythraceae) showed significant bioenhancing activity with the antibiotic nalidixic acid. A. multiflora contains a novel compound ammaniol along with other compounds. The methanolic extract of Ammannia multiflora bioenhancing activity in combination with nalidixic acid against the two strains, CA8000 and DH5α of Escherichia coli. The results showed that the methanolic extract of A. multiflora possessed significant bioenhancing activity and reduced the dose of nalidixic acid fourfold. The methanolic extract of Ammannia multiflora was also tested for antimycobacterial activity against Mycobacterium H37Rv and was found to show moderate activity (MIC 25 μg/mL) against this pathogen [207].


### 4.15. Capsaicin

Capsaicin is the active component of chili peppers (Capsicum annum). It is an irritant for mammals, including humans, and produces a sensation of burning in any tissue with which it comes into contact. Cruz et al. [208] reported that Capsicum annum reduces bioavailability of aspirin after oral administration in rats. Lopez et al. [209] have shown that capsaicin has little or no impact on bioavailability of ciprofloxacin.Absorption and bioavailability of theophylline from a sustained release gelatin capsule were investigated in 10 male rabbits after oral administration (20 mg/kg), with and without a ground capsicum fruit suspension. Comparison of pharmacokinetic parameters showed that the concomitant absorption of capsicum increases AUC from86.06±9.78 mg·h/L to 138.32±17.27 mg·h/L, P<0.001, Cmax from 6.65±0.76 to 8.78±0.98 mg/L, P<0.01, and MRT from 14.94±2.97 h to 20.98±5.75 h, P<0.001. A second administration of the capsicum suspension, 11 hours after dosing, produced a new rise of theophylline plasma levels in every rabbit. This indicated that due to action of capsaicin bioavailability of theophylline was enhanced [210].


## 4.1. Piperine

Piperine, the major plant alkaloid present inP. nigrumLinn (Black pepper) and P. longumLinn (Long pepper), has bioavailability enhancing activity for some nutritional substances and for some drugs [20]. It has been used extensively as a condiment and flavoring for all types of savory dishes. Piper species have been used in folklore medicine for the treatment of various diseases, including seizure disorders [21]. Piperine is known to exhibit a variety of biological activities which include anti-inflammatory activity [22, 23], antipyretic activity [24], fertility enhancement [25], antifungal activity [26], antidiarrhoeal activity [27], antioxidant activity [28–33], antimetastatic activity [34], antithyroid activity [35, 36], antimutagenic activity [37–40], antitumor activity [39, 41, 42], antidepressant activity [43–45], antiplatelet activity [46], analgesic activity [47], hepatoprotective activity [48], antihypertensive activity [49], and antiasthmatic activity [50]. Piperine exhibits a toxic effect against hepatocytes [51] and cultured hippocampal neurons [52], reproductive toxicity in swiss albino mice [53], and immunotoxicity [54].Piperine reduces the aflatoxin B1-induced cytotoxicity and micronuclei formation in rat hepatoma cells in concentration-dependent manner. It is capable of counteracting aflatoxin B1 toxicity by suppressing cytochromes P450-mediated bioactivation of the mycotoxin [55]. Inhibition of aflatoxin B1-induced cytotoxicity and genotoxicity in chinese hamster cells by piperine was reported by Reen et al. [56]. A significant suppression (33.9–66.5%) in the micronuclei formation induced by benzo(a)pyrene and cyclophosphamide was reduced following oral administration of piperine at doses of 25, 50, and 75 mg/kg in mice [32].Piperine modulates the oxidative changes by inhibiting lipid peroxidation and mediating enhanced synthesis or transport of glutathione thereby replenishing thiol redox [57]. Simultaneous supplementation with black pepper or piperine in rats fed high fat diet lowered thiobarbituric acid reactive substances (TBARS) and conjugated dienes levels and maintained superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione-S-transferase (GST), and glutathione (GSH) levels close to controls in rats [30]. Piperine could effectively inhibit benzo(a)pyrene-induced lung carcinogenesis in albino mice by offering protection from protein damage and also by suppressing cell proliferation [58]. It produces chemopreventive effect by modulating lipid peroxidation and augmenting antioxidant defense system [59, 60]. Supplementation of piperine causes inhibition of Phase I and II enzymes, elevation of glutathione metabolizing enzymes, reduction in DNA damage, and DNA protein cross-links in benzo(a)pyrene-induced lung carcinogenesis in mice [38, 61].The antiapoptotic efficacy of piperine has been demonstrated against cisplatin-induced apoptosis via heme oxygenase-1 induction in auditory cells [62]. Piperine can reverse the corticosterone induced reduction of brain-derived neurotrophic factor mRNA expression in cultured hippocampal neurons [44]. Gallic acid exerts a synergistic effect when administered with piperine and provides a more pronounced therapeutic potential in reducing beryllium-induced hepatorenal dysfunction and oxidative stress consequences [63]. Piperine contains pentacyclic oxindole group which is effective for immunomodulation. This immunomodulation activity is due to its multifaceted activities such as antioxidative, antiapoptotic, and restorative ability against cell proliferative mitogenic response, thymic and splenic cell population, and cytokine release [64].Daily supplement taken with a nutrient or nutrients by an average healthy adult, piperine is effective and safe in a broad dose range. A preferred effective dose range of piperine for oral use to enhance gastrointestinal nutrient absorption is 0.0004–0.15 mg/kg/day. The recommended dose of piperine for a healthy individual for oral use is approximately 5 mg/person/day. Black pepper contains approximately 5–9% piperine, listed by the Food and Drug Administration (FDA) as an herb which is generally recognized as safe (GRAS) for its intended use as spice, seasoning, or flavoring. The bioenhancing dose of piperine is approximately 15 mg/person/day and no more than 20 mg/day in divided doses, which corresponds to from several thousands to up to 40,000 times less than the LD50 dose of piperine, as established in various experiments on rodents. The effective bioenhancing dose of piperine for drug compounds varies, but the prior art studies indicated that a dose of approximately 10% (w/w) of the active drug could be regarded as an appropriate bioenhancing dose for most drugs [19]. LD50 of piperine has been found to be 330 and 514 mg/kg in mice and rats, respectively. In subacute toxicity tests, piperine in a dosage of 100 mg/kg was found to be nontoxic [65].There are two possible explanations for the role of piperine in drug bioavailability: (a) nonspecific mechanisms mainly promoting rapid absorption of drugs and nutrients, for example, increased blood supply to the gastrointestinal tract, decreased hydrochloric acid secretion which prevents breakdown of some drugs, increased emulsifying content of the gut, and increased enzymes likeγ-glutamyl transpeptidase which participate in active and passive transport of nutrients to the intestinal cells, and (b) nonspecific mechanisms inhibiting enzymes participating in biotransformation of drugs, preventing their inactivation and elimination [19].


### 4.1.1. Drug Metabolizing Enzymes Inhibited by Piperine (Shown in Table2)

Table 2
Drug metabolizing enzymes inhibited by piperine.
Drug metabolizing enzymes
References
Arylhydrocarbon hydroxylase (AHH)
Atal et al. [15], Singh et al. [66]
Uridine diphosphate- (UDP-) glucuronyl transferase
Atal et al. [15], Singh et al. [66]
Ethylmorphine-N-demethylase
Atal et al. [15], Singh et al. [66]
7-Ethoxycoumarin-O-deethylase
Atal et al. [15], Singh et al. [66]
3-Hydroxy-benzo(a)pyrene glucuronidation
Atal et al. [15], Singh et al. [66]
UDP-glucose dehydrogenase (UDP-GDH)
Reen et al. [16]
5-lipoxygenase
Stöhret al. [67]
Cyclooxygenase-1
Stöhret al. [67]
Cytochrome P450
Atal et al. [15], Singh et al. [66], Bhardwaj et al. [17]The interaction of piperine with enzymatic drug biotransforming reactions in hepatic tissue has been studiedin vitro and in vivo. Piperine inhibited arylhydrocarbon hydroxylation, ethylmorphine-N-demethylation, 7-ethoxycoumarin-O-deethylation, and 3-hydroxy-benzo(a)pyrene glucuronidation in rat postmitochondrial supernatant in vitro in a dose-dependent manner. Piperine inhibition of these reactions in postmitochondrial supernatant from 3-methylcholanthrene and phenobarbital treated rats was similar to the controls. Inhibition by piperine of arylhydrocarbon hydroxylase (AHH) from 3-methylcholanthrene treated rats was comparable to that observed with 7, 8-benzoflavone. Piperine caused noncompetitive inhibition of hepatic microsomal AHH from the untreated and 3-methylcholanthrene-treated rats with a Ki=30μM which was close to the apparent Km of AHH observed in the controls. Similarly, the kinetics of inhibition of ethylmorphine-N-demethylase from control rat liver microsomes exhibited noncompetitive inhibition with an apparent Km=0.8mM and Ki=35μM. These studies demonstrated that piperine is a nonspecific inhibitor of drug metabolism. Oral administration of piperine in rats strongly inhibited the hepatic AHH and Uridine diphosphate-(UDP-) glucuronyltransferase (UGT) activities. The maximal inhibition of AHH observed within 1 h restored to normal value in 6 h. These results demonstrate that piperine is a potent inhibitor of drug metabolism [15]. Piperine modified the rate of glucuronidation by lowering the endogenous UDP-glucuronic acid (UDP-GA) content and also by inhibiting the transferase activity [66].The effects of piperine on UDP-glucose dehydrogenase (UDP-GDH) and glucuronidation potentials of rat and guinea pig liver and intestine were studiedin vitro. Piperine caused a concentration-related strong inhibition of UDP-GDH (50% at 10 μM) reversibly and equipotently, in both tissues. Partially purified rat liver UDP-GDH was used to obtain the kinetic values at pH optima of 9.4 and 8.6. At pH 9.4, Km=15 μM, Vmax=5.2 nmol, with NADH—Ki=6μM, with NAD—Ki=16 μM were obtained. At pH 8.6, Km=35 μM, Vmax=7.5 nmol, and Ki=15 μM. In all of these cases, piperine caused noncompetitive inhibition. Data from structure activity comparisons of piperine analogs indicated that the presence of conjugated double bonds in the side chain of the molecule is a factor in piperine inhibition. However, the UDP-GA contents were decreased less effectively by piperine in isolated rat hepatocytes compared with enterocytes of guinea pig small intestine. Piperine at 50 μM caused a marginal decrease of UDP-GA in hepatocytes when the rate of glucuronidation of 3-hydroxybenzo(a)pyrene (3-OH-BP) decreased by about 40%. The decrease obtained at 10 μM piperine in intestinal cells was comparable to that obtained at 50–100 μM in hepatocytes. UGT activities towards 3-OH-BP (UGT1A1) and 4-OH-biphenyl (UGT2B1) were also determined. Piperine did not affect the rate of glucuronidation of 4-OH-biphenyl in rat liver, whereas that of 3-OH-BP was impaired significantly. In guinea pig small intestine, both these activities were inhibited significantly requiring less than 25 μM piperine to produce more than 50% inhibition of UGT(s). The results suggested that (i) piperine is a potent inhibitor of UDP-GDH, (ii) inhibition is offered exclusively by the conjugated double bonds of the molecule, and (iii) piperine exerts stronger effects on intestinal glucuronidation than in rat liver [16].Piperine inhibits human P-glycoprotein and CYP3A4 (CYP: Cytochrome P450). Both the proteins are expressed in enterocytes and hepatocytes and contribute to a major extent to first-pass elimination of many drugs. This indicates that dietary piperine could affect plasma concentrations of P-glycoprotein and CYP3A4 substrates in humans, in particular if these drugs are administered orally. Some of the metabolizing enzymes inhibited or induced by piperine include CYP1A1, CYP1B1, CYP1B2, CYP2E1, and CYP3A4. Most of the drugs metabolized by these enzymes will therefore be influenced by bioenhancers [17].


### 4.1.2. Drugs/Nutraceuticals Bioenhanced by Piperine

Piperine acts as an antimicrobial bioenhancer which enhances bioavailability and bioefficacy of drugs by acting on drug metabolism. It also acts as a nutritional bioenhancer which enhances bioavailability and absorption of nutrients by acting on gastrointestinal tract. Allameh et al. [68] reported that piperine enhances bioavailability of aflatoxin B1 in rat tissues. A 10 mg dose of piperine causes a marked increase in serum gonadotropins and a decrease in intratesticular testosterone concentration, despite normal serum testosterone titres in adult male albino rats [69]. However, some of the experimental findings also indicated the ability to decrease the bioavailability of drugs, like rifampicin [70, 71], isoniazid [72], and Diclofenac sodium [73].Piperine has been shown to inhibit several cytochrome P450-mediated pathways and phase II reactions in animal models. Piperine, or mixtures containing piperine, has been shown to increase the bioavailability, blood levels, and efficacy of many of drugs (Table3) and nutraceuticals (Table 4). Administration of piperinesignificantly increased plasma concentrations of rifampicin,phenytoin, spartein, sulfadiazine, tetracycline, propranolol, and theophylline in humans.Table 3
Drugs bioenhanced by piperine.
Drugs
Experimental model
References
Vasicine
Rats
Zutshi and Kaul [74]
Pyrazinamide
In vitro
Zutshi [75]
Phenytoin, propranolol, theophyllin, spartein, sulphadiazine, and tetracycline
Human volunteers
Bano et al. [76, 77]
Pentobarbitone
Human volunteers
Mujumdar et al. [78]
Curcumin
Human volunteers and rats
Shoba et al. [79]
In vivo
Shaikh et al. [80]
Rats
Suresh and Srinivasan [81]
Nimesulide
Mice
Gupta et al. [82]
Indomethacin
Rabbits
Karan et al. [83]
Oxyphenylbutazone
Rats
Mujumdar et al. [84]
Phenytoin
Human volunteers
Velpandian et al. [85], Pattanaik et al. [86]
Rifampicin
Human
Zutshi et al. [87]
In vitro
Balakrishnan et al. [88]
Amoxycillin trihydrate and cefotaxime
Rats
Hiwale et al. [89]
EGCG [(−)-epigallocatechin-3-gallate]
Mice
Lambert et al. [90]
Oxytetracycline
WLH hens
Singh et al. [91]
Ciprofloxacin
Rabbits
Balkrishna and Yogesh [92]
In vitro
Khan et al. [8]
Nevirapine
Human
Kasibhatta and Naidu [93]
Diclofenac sodium and pentazocine
Albino mice
Pooja et al. [47]
Pefloxacin
Gaddi goats
Dama et al. [94]
Ampcilllin and norloxacin
Rabbits
Janakiraman and Manavalan [95]
Carbamazepine
In vitro
Pattanaik et al. [96]
Fexofenadine
Rats
Jin and Han [97]
Metronidazole
Rabbits
Singh et al. [98]
Ampicillin trihydrate
Human
Janakiraman and Manavalan [99]
Resveratrol
Mice
Johnson et al. [100]
Gatifloxacin
Layer birds
Patel et al. [101]
Broiler birds
Devada et al. [102]
Atenolol
Rats
Singh and Chand [103]
Ibuprofen
In vitro
Venkatesh et al. [104]
Losartan potassium
Rats
Singh et al. [105]Table 4
Nutraceuticals bioenhanced by piperine [13, 19].
Class
Examples
Water soluble vitamins
Vitamin B1, Vitamin B2, niacinamide, Vitamin B6, Vitamin B12, folic acid, and Vitamin C
Fat soluble vitamins
Vitamin A,β-carotene (provitamin), Vitamin D, Vitamin E, and Vitamin K
Amino acids
Lysine, isoleucine, leucine, threonine, valine, tryptophan, phenylalanine, and methionine
Minerals
Iodine, calcium, iron, zinc, copper, selenium, magnesium, potassium, and manganese
Herbal compounds
Boswellic acid (Boswellia serrata), Ginsenosides (Gingko biloba), Withanaloids (Withania somnifera), Curcuminoides (Curcuma longa), and Pycnogenol (Pinus pinaster)Piperine and Phenytoin
Effect of piperine on pharmacokinetics of phenytoin was studied in healthy volunteers. In a crossover study, five volunteers received either a single oral dose (300 mg) of phenytoin alone or in combination with multiple doses of piperine (20 mg × 7 days) followed by an oral dose of phenytoin. Blood samples were collected at 0.5, 1, 2, 3, 4, 8, 12, 24, and 48 h after drug administration and analyzed for phenytoin by the enzyme-multiplied immunoassay technique. The results showed that a single daily dose of piperine for 7 days decreased thet1/2α (P<0.05), prolonged the t1/2 (P<0.01), and produced a higher AUC (P<0.05) in comparison to phenytoin alone. It is therefore concluded that piperine on multiple-dose administration alters the pharmacokinetic parameters of the antiepileptic [76].
A preliminary pharmacokinetic study was carried out in mice by administering phenytoin (10 mg) orally, with or without piperine (0.6 mg). Subsequently, oral pharmacokinetics of phenytoin was carried out in six healthy volunteers in a crossover design. Phenytoin tablet (300 mg) was given 30 minutes after ingestion of a soup (Melahu rasam) with or without black pepper. A further study of intravenous pharmacokinetics of phenytoin (1 mg) in rats with or without oral pretreatment with piperine (10 mg) was also conducted. The phenytoin concentration in the serum was analyzed by HPLC. The study showed a significant increase in the kinetic estimates of Ka, AUC0-10 and AUC0-∞ in the piperine fed mice. Similarly, in human volunteers piperine increased Ka, AUC0-48, AUC0-∞ and delayed elimination of phenytoin. Intravenous phenytoin in the oral piperine-treated rat group showed a significant alteration in the elimination phase indicating its metabolic blockade [85].
The effect of piperine on oral bioavailability of phenytoin was studied in human volunteers. The objective of this study was to explore the effect of a single dose of piperine in patients with uncontrolled epilepsy on the steady-state pharmacokinetics of phenytoin. Two groups of 10 patients each receiving either a 150 mg or 200 mg twice daily dose of phenytoin were selected. 12 h after the night dose, venous blood samples were collected at 0, 0.5, 1, 2, 4, 6, 9, and 12 h after administration of phenytoin. On the next study day, piperine 20 mg was administered along with phenytoin and samples were collected similarly. There was a significant increase inAUC0-12h (P<0.01), Cmax (P<0.001), and Ka (P<0.05), whereas the changes in Kel and tmax were not significant. The results showed that piperine enhanced the bioavailability of phenytoin significantly, possibly by increasing the absorption [86].Piperine and Pentobarbitone
Effect of piperine on pentobarbitone-induced hypnosis in rats was studied. Piperine treatment in rats, treated chronically with phenobarbitone, significantly potentiated pentobarbitone sleeping time, as compared to the controls. There was no alteration in barbital sodium sleeping time. It is possible that piperine inhibits liver microsomal enzyme system and thereby potentiates the pentobarbitone sleeping time [78].Piperine with Propranolol and Theophylline
The effects of piperine on the bioavailability and pharmacokinetics of propranolol and theophylline were studied. Six subjects in each group received a single oral dose of propranolol (40 mg) or theophylline (150 mg) alone or in combination with piperine (20 mg) daily for 7 days. An earliertmax and a higher Cmax and AUC were observed in the subjects who received piperine and propranolol. It produced a higher Cmax, longer t1/2, and a higher AUC with theophylline. In clinical practice, the enhanced systemic availability of oral propranolol and theophylline could be exploited to achieve better therapeutic control and improved patient compliance [77].Piperine and Nimesulide
Influence of piperine on nimesulide-induced antinociception was studied in mice. The plasma concentration after oral administration of nimesulide (10 mg/kg) alone was8.03±0.99 μg/mL. However, when it was administered with piperine (10 mg/kg), the plasma concentration of nimesulide increased to 11.9±0.23 μg/mL. This indicates that piperine inhibits the biotransformation and metabolism of nimesulide leading to significantly (P<0.05) higher levels of drug in the systemic circulation. The findings of this study suggest that piperine could be used as a biological enhancer when coadministered with nimesulide [82].Piperine and Curcumin
Influence of piperine on the pharmacokinetics of curcumin in animals and human volunteers was studied. The medicinal properties of curcumin obtained fromCurcuma longa Linn. cannot be utilized because of poor bioavailability due to its rapid metabolism in the liver and intestinal wall. The effect of combining piperine, a known inhibitor of hepatic and intestinal glucuronidation, was evaluated on the bioavailability of curcumin in rats and healthy human volunteers. When curcumin was given alone, at dose 2 g/kg to rats, moderate serum concentrations were achieved over a period of 4 h. Concomitant administration of piperine 20 mg/kg increased the serum concentration of curcumin for a short period of 1-2 h after drug. tmax was significantly increased (P<0.02) while t1/2 and ClB significantly decreased (P<0.02), and the bioavailability was increased by 154%. On the other hand, in humans after a dose of 2 g curcumin alone, serum levels were either undetectable or very low (Table 5). Concomitant administration of piperine 20 mg produced much higher concentrations from 0.25 to 1 h after drug (P<0.01 at 0.25 and 0.5 h; P<0.001 at 1 h); the increase in bioavailability was 200%. The study shows that in the dosages used, piperine enhances the serum concentration, extent of absorption, and bioavailability of curcumin in both rats and humans with no adverse effects [79].Table 5
Comparative pharmacokinetic parameters after oral supplementation of curcumin and curcumin + piperine in human volunteers [79].
Parameters
Curcumin
Curcumin (2g/kg) + piperine
(2g/kg)
(20mg/kg)
C
max (μg/mL)
1.35
±
0.23
1.80
±
0.16
t
max (h)
0.83
±
0.05
1.29
±
0.23
t
1
/
2 (h)
1.70
±
0.58
1.05
±
0.18
AUC (μg·h/mL)
2.36
±
0.28
3.64
±
0.31
Cl
B (L/h)
713
±
12
495.90
±
193.90Piperine andβ-Carotene
The effectiveness of piperine was evaluated for its ability to improve serum response ofβ-carotene during oral supplementation using a double-blind, crossover study design. Subjects were randomly selected to ingest a daily β-carotene dose (15 mg) either with 5 mg of piperine or placebo during each of two 14-day supplementation periods. Intersubject variability in presupplementation serum β-carotene levels was minimized by limiting the selection of volunteers to healthy, adult males with fasting serum β-carotene values <20 pg/dL. The results indicate that significantly greater increases (P<0.0001) in serum β-carotene occurred during supplementation with β-carotene plus piperine (49.8±9.6 pg/dL versus 30.9±5.4 pg/dL) compared to β-carotene plus placebo. Supplementation with betacarotene plus piperine for 14 days produced a 60% greater increase AUC than was observed during supplementation with β-carotene plus placebo (Table 6). Study suggests that the serum response during oral β-carotene supplementation is improved through the nonspecific, thermogenic property of piperine, described in this paper as thermonutrient in action [20].Table 6
Effect of piperine on the serumβ-carotene levels during a 14-day supplementation in human volunteers [20].
Treatment (n=6)
β-carotene (μg/dL)
AUC (μg/dL) × (time in days)
Day 0
Day 14
Change
β-carotene + placebo
16.3 ± 2.6
47.2 ± 6.4
30.9 ± 5.4
272 ± 47.6
β-carotene + piperine
16.0 ± 3.1
65.8 ± 9.7
49.8 ± 9.6
435 ± 74.2Piperine and Coenzyme Q10
An extract from the fruits of black pepper consisting of a minimum of 98% pure piperine was evaluated in a clinical study using a double-blind design. The relative bioavailability of 90 mg and 120 mg of coenzymeQ10 administered in a single-dose experiment or in separate experiments for 14 and 21 days with placebo or with 5 mg of piperine was determined by comparing measured changes in plasma concentration. The intersubject variability was minimized by limiting the selection of individuals to healthy adult male volunteers with (presupplementation) fasting coenzyme Q10 values between 0.30 and 0.60 mg/L. The results of the single-dose study and the 14-day study indicate smaller, but not significant, increases in plasma concentrations of coenzyme Q10 in the control group compared with the group receiving coenzyme Q10 with a supplement of piperine. Supplementation of 120 mg coenzyme Q10 with piperine for 21 days produced approximately 30% greater AUC than was observed during supplementation with coenzyme Q10 plus placebo. It is postulated that the bioenhancing mechanism of piperine to increase plasma levels of supplemental coenzyme Q10 is nonspecific and possibly based on its description in the literature as a thermonutrient [106].Piperine and Rifampicin
Piperine augments transcription inhibitory activity of rifampicin by several folds againstMycobacterium smegmatis. A 24 : 1 (w/w) mixture of antibiotic rifampicin and piperine shows remarkable growth inhibitory effect on M. smegmatis, and this inhibition is higher than that of rifampicin alone. Interestingly, piperine alone, even at higher concentration, does not inhibit the growth of Mycobacterium. As RNA polymerase is the site of action of rifampicin, the enzyme was purified from M. smegmatis and the mixture of rifampicin and piperine was found to abrogate nonspecific transcription catalyzed by M. smegmatisRNA polymerase. The effect is higher than rifampicin alone and piperine shows no effect independently. When RNA polymerase was purified from a rifampicin-resistant strain of M. smegmatis, the enzymatic activity, otherwise resistant to rifampicin, significantly decreases in the presence of piperine along with rifampicin. Piperine enhances the binding ability of rifampicin to RNA polymerase [88].
The amount of piperine used in the range of 0.4–0.9% by weight of the antituberculosis and antileprosy drugs. Antituberculosis composition contains rifampicin (100–300 mg), isoniazid (100–300 mg) and pyrazinamide (500–1000 mg) (combination of any two), and piperine (5–29 mg). Antileprosy composition contains rifampicin (100–300 mg), dapsone (50–100 mg), and piperine (5–20 mg). Effect of piperine on pharmacokinetic parameters of rifampicin, isoniazid, and pyrazinamide combination was studied in human volunteers. The results from Table7 indicate that piperine significantly increases the bioavailability of antituberculosis drugs like rifampicin, isoniazid, and pyrazinamide [107, 108].Table 7
Effect of piperine on pharmacokinetics of rifampicin, isoniazid, and pyrazinamide combination in human volunteers [107, 108].
Kineticparameters
Formulation A
Formulation B
Rifampicin
Isoniazid
Pyrazinamide
Rifampicin**
Isoniazid**
Pyrazinamide**
t
1
/
2 (h)
0.67 ± 0.008
0.64 ± 0.01
0.60 ± 0.03
0.40 ± 0.04
0.42 ± 0.04
0.37 ± 0.008
t
1
/
2
(el) (h)
8.40 ± 0.06
7.90 ± 0.10
9.50 ± 0.14
11.1 ± 0.18
8.15 ± 0.26*
11.0 ± 0.17
C
max (μg/mL)
8.20 ± 0.46
2.56 ± 0.17
27.0 ± 2.0
17.6 ± 1.09
10.07 ± 0.90
40.0 ± 1.64
AUC0–∞ (μg·h/mL)
104.6 ± 4.38
41.0 ± 1.72
318.6 ± 8.05
143.95 ± 5.85
94.95 ± 3.98
435.41 ± 9.7
*Not significant (P > 0.05), **highly significant (P < 0.001).
Formulation A: rifampicin—450 mg, isoniazid—300 mg, pyrazinamide—1500 mg.
Formulation B: rifampicin—450 mg, isoniazid-300 mg, pyrazinamide—1500 mg, piperine—20 mg.Risorine is a formulation developed by the Indian Institute of Integrative Medicine, Jammu, and marketed in India in November 2009 in public—private partnership with Cadila Pharmaceutical Ltd, Ahmedabad. Risorine has been approved for marketing by Drug Controller General of India, after successful completion of all the phased clinical trials. It contains rifampicin (200 mg), isoniazid (300 mg), and piperine (10 mg). It has been found to be bioequivalent with commercially available rifampicin preparations. This is due to enhanced uptake of the drug by body cells, and also because the drug remains available in blood for longer durations. Combining piperine with rifampicin decreases the dose of rifampicin from 450 to 200 mg [109].Piperine with Amoxicillin Trihydrate and Cefotaxime
Effect of coadministration of piperine on pharmacokinetics ofβ-lactam antibiotics was studied in rats. Coadministration of piperine enhanced bioavailability of β-lactam antibiotics like amoxicillin trihydrate and cefotaxime sodium significantly in rats. The improved bioavailability is reflected in various pharmacokinetic parameters, namely tmax, Cmax, t1/2, and AUC of these antibiotics. The increased bioavailability could be attributed to the effect of piperine on microsomal metabolizing enzymes or enzymes system [89].Piperine and Epigallocatechin Gallate (EGCG)
Piperine enhanced the bioavailability of the tea polyphenol EGCG in Mice. EGCG, from green tea (Camellia sinensis), has demonstrated chemopreventive activity in animal models of carcinogenesis. Cotreatment with piperine enhanced the bioavailability of EGCG in mice. Intragastric coadministration of 163.8 μmol/kg EGCG and 70.2 μmol/kg piperine to male CF-1 mice increased the plasma Cmax and AUC by 1.3-fold compared to mice treated with EGCG only. Piperine appeared to increase EGCG bioavailability by inhibiting glucuronidation and gastrointestinal transit. Piperine (100 μmol/L) inhibited EGCG glucuronidation in mouse small intestine (by 40%) but not in hepatic microsomes. Piperine (20 μmol/L) also inhibited production of EGCG-3′′-glucuronide in human HT-29 colon adenocarcinoma cells. Small intestinal EGCG levels in CF-1 mice following treatment with EGCG alone had a Cmax=37.50±22.50 nmol/g at 60 min that then decreased to 5.14±1.65 nmol/g at 90 min; however, cotreatment with piperine resulted in a Cmax=31.60±15.08 nmol/g at 90 min, and levels were maintained above 20 nmol/g until 180 min. This resulted in a significant increase in the small intestine EGCG AUC (4621.80±1958.72 nmol/g/min versus 1686.50±757.07 nmol/g/min). EGCG appearance in the colon and the feces of piperine-cotreated mice was slower than in mice treated with EGCG alone [90].Piperine and Oxytetracycline (OTC)
The pharmacokinetic profile of orally administered oxytetracycline (10 mg/kg body weight) was studied 7 days after oral treatment ofP. longum (15 mg equivalent/kg) in White Leghorn birds (WLH) (2.0–2.8 kg). On day 8, oxytetracycline (OTC) was administered orally and blood samples were collected from the wing vein in heparinized vials for plasma separation at 0 (before treatment), 15, 30, 60, 120, 240, 360, 480, and 600 min after OTC administration. Plasma OTC concentrations were determined by microbial assay technique using Bacillus cereus var. mycoides (ATCC 11778) as test organism. The plasma levels of OTC against time were adequately described by one compartment open model (Table 8). The pharmacokinetic data (Table 9) revealed that P. longum-treated animals had significantly higher AUC, AUMC, and MRT. Prior treatment of P. longum significantly reduced β and increased t1/2. The ClB reduced by 21%, whereas td increased by 29%. The treatment with P. longum reduced loading and maintenance dose by 33.3% and 39%, respectively [91].Table 8
Comparison of mean plasma levels of oxytetracycline (μg/mL) at different time intervals following oral administration in control and P. longum-treated WLH birds [91].
Time (Min)
Control
Treated
15
0.23 ± 0.024
0.30 ± 0.022*
30
0.34 ± 0.025
0.45 ± 0.029**
60
0.72 ± 0.051
0.77 ± 0.046
120
0.58 ± 0.037
0.63 ± 0.030
240
0.37 ± 0.015
0.47 ± 0.034**
360
0.26 ± 0.017
0.38 ± 0.021****
480
0.23 ± 0.015
0.31 ± 0.019***
600
0.19 ± 0.005
0.25 ± 0.015***
n = 8, mean ± SE; *P < 0.1, **P < 0.05, ***P < 0.01, ****P < 0.001.Table 9
Comparative pharmacokinetic parameters of oxytetracycline administered orally (10 mg/kg) in control andP. longum treated birds [91].
Parameters
Control OTC
Treated OTC + piperine
β
(/h)
0.147 ± 0.011
0.112 ± 0.006*
t
1
/
2
β (h)
4.934 ± 0.422
6.370 ± 0.438**
AUC (μg·h/mL)
5.055 ± 0.689
6.417 ± 0.317*
AUMC (μg·h2/mL)
43.62 ± 11.15
63.58 ± 7.042*
MRT (h)
7.98 ± 0.744
9.77 ± 0.644**
t
d (h)
16.38 ± 1.4
21.142 ± 1.453**
Cl
B (mL/kg/h)
184.63 ± 7.7
145.97 ± 14.42**
n = 8, mean ± SE; *P < 0.01, **P < 0.05.Piperine and Ciprofloxacin
The influence of coadministration of piperine on pharmacokinetic profile of ciprofloxacin in rabbits was studied. The study reveals that piperine has affected statically to the pharmacokinetics of the ciprofloxacin which is significant with change inCmax, tmax, AUC, and Kel. The results obtained are the combined effect of piperine on the absorption kinetics and the inhibition of the metabolism of the ciprofloxacin. This leads to increase bioavailability of ciprofloxacin when administered with piperine [92].
The potentiating effect of piperine with ciprofloxacin inin vitro combination against Staphylococcus aureusATCC 29213 was studied and its suggestive role as an efflux pumps inhibitor. Piperine, in combination with ciprofloxacin, markedly reduced the MIC and mutation prevention concentration of ciprofloxacin for S. aureus, including methicillin resistant S. aureus. In vitro combination studies, the final concentrations ranged from 0.03 to 64 μg/mL for ciprofloxacin and from 0.8 to 50 μg/mL for piperine. The final bacterial inoculum in each well was 5×105 CFU/mL. The plates were incubated at 37°C for 24 h. Piperine did not show any antibacterial activity when tested up to 100 μg/mL. Table 10 is showing that there was a 2-fold reduction in the MIC of ciprofloxacin (from 0.25 to 0.12 μg/mL) for S. aureus ATCC 29213 when tested in combination with piperine at 12.5 and 25 μg/mL. The MIC was further reduced to 4-fold with 50 μg/mL piperine [8]. Piperine inhibits the efflux of ethidium bromide and ciprofloxacin from bacterial cells (Table 11). It is a P-glycoprotein inhibitor that inhibits ciprofloxacin efflux [8].Table 10
MIC of ciprofloxacin forS. aureus ATCC 29213 at different concentrations of piperine [8].
Piperine conc.
MIC (μg) of ciprofloxacin for S. aureus
(μg/mL)
ATCC 29213
0.0
0.25
12.5
0.12
25
0.12
50
0.06Table 11
Drug susceptibilities ofS. aureusATCC 29213 and the ciprofloxacin selected mutant (CIPr-1) [8].
Compound
MIC (μg/mL)
S. aureusATCC 29213
CIPr-1
Ethidium bromide
4
8
Ethidium bromide + piperine
1
2
Ciprofloxacin
0.25
128
Ciprofloxacin + piperine
0.12
8Piperine and Nevirapine
Influence of piperine on the pharmacokinetics of nevirapine under fasting conditions was studied. This was a crossover, placebo-controlled pilot study conducted in a total of eight healthy adult males aged 20–40 years. Subjects were randomly assigned to receive piperine 20 mg or placebo each morning for 6 days, and on day 7, nevirapine (200 mg) plus piperine (20 mg) or nevirapine plus placebo in a crossover fashion. Blood samples were collected from 1–144 h after dose for pharmacokinetic analysis. MeanCmax, AUCt, AUC0-∞, and Clast values of nevirapine were increased by approximately 120%, 167%, 170%, and 146%, respectively, when coadministered with piperine. This pilot study provided evidence for enhanced bioavailability of nevirapine when administered with piperine [93].Piperine with Diclofenac Sodium and Pentazocine
The analgesic activity ofP. nigrum extract per se and its interaction with diclofenac sodium and pentazocine in albino mice was studied. Healthy albino mice of either sex weighing 25–30 grams were taken and divided into 4 groups of 8 animals each. Peripheral analgesic activity was evaluated by acetic acid-induced writhing test, using diclofenac sodium (5 mg/kg), P. nigrum extract (10 mg/kg), and their combination (5+10 mg/kg) orally. Similarly central analgesic activity was studied using tail flick method and pentazocine (5 mg/kg) orally was used instead of diclofenac sodium. P. nigrum extract alone did not show any significant analgesic activity in tail flick and writhing methods. However, results of acetic acid-induced writhing model showed that diclofenac sodium reduces writhing 54.90% with respect to control when administered alone, but showed significant decrease in writhes 78.43% with respect to control when P. nigrum extract was coadministered with diclofenac sodium. When P. nigrum extract combined with pentazocine showed significant increase in tail flick latency in comparison with pentazocine alone and control group (P<0.05), the results suggest that the P. nigrum extract significantly increased the analgesic activity of diclofenac sodium and pentazocine [47].Piperine and Pefloxacin
The pharmacokinetics of orally administered pefloxacin were studied to evaluate the bioenhancing effect of the herbal bioenhancer, trikatu, in mountain Gaddi goats (n=6). The findings of the study revealed a decreased plasma concentration (P>0.05) of pefloxacin following trikatu administration during the absorption phase (10, 15, and 20 min after pefloxacin administration). In contrast, the plasma concentrations of pefloxacin were significantly higher at 4, 6, 8, and 12 h (during the elimination phase) of the pefloxacin administration. The findings of the investigation revealed higher values for AUC, AUMC, MRT, td, and bioavailability. Trikatu treatment, however, significantly reduced t1/2 and zero time intercept of the elimination phase. The Vd(area) and Vd(B) were significantly higher in trikatu-treated animals indicating a better penetration of the drug. Based on the MIC of 0.8 μg/mL of pefloxacin; a priming dose of 6.0 mg/kg and a maintenance dose of 2.21 mg/kg are required to be administered at 8 h intervals. For practical purposes in goats this would mean a priming dose of 6 mg/kg and a maintenance dose of 2 mg/kg given by the oral route to be repeated at 8 h intervals [94].Piperine with Ampicillin and Norfloxacin
Effect of piperine on oral bioavailability of ampicillin and norfloxacin was studied in rabbits. Coadministration of piperine (20 mg/kg), an alkaloid fromP. nigrum, enhanced oral bioavailability of ampicillin and norfloxacin in animal model. This is reflected in various pharmacokinetic measurements like Cmax, tmax, AUC, and t1/2 of the above antibiotics in animal model shown in Tables 12, 13, and 14 [95].Table 12
Effect of piperine on plasma concentration of ampicillin in rabbits [95].
Time (h)
Ampicillin (μg/mL)
Ampicillin + piperine (μg/mL)
0.0
0
0
0.5
30.584 ± 0.38
35.481 ± 0.26
1.0
44.668 ± 0.32
251.188 ± 0.27
1.5
31.672 ± 0.49
188.364 ± 0.31
2.0
26.607 ± 0.37
84.139 ± 0.31
2.5
18.836 ± 0.38
66.834 ± 0.26
3.0
17.782 ± 0.32
35.481 ± 0.27
3.5
12.589 ± 0.31
33.496 ± 0.26
4.0
12.589 ± 0.32
26.607 ± 0.27
4.5
9.441 ± 0.26
26.607 ± 0.27
n = 6, mean ± SD, P < 0.05.Table 13
Effect of piperine on plasma concentration of norfloxacin in rabbits [95].
Time (h)
Norfloxacin (μg/mL)
Norfloxacin + piperine (μg/mL)
0.0
0
0
1.0
10.593 ± 0.26
14.125 ± 0.27
2.0
7.079 ± 0.26
17.783 ± 0.32
3.0
5.623 ± 0.32
14.963 ± 0.27
4.0
5.011 ± 0.38
11.885 ± 0.32
5.0
4.732 ± 0.26
10.592 ± 0.37
6.0
3.981 ± 0.26
8.414 ± 0.25
7.0
3.548 ± 0.21
8.414 ± 0.26
8.0
3.349 ± 0.26
7.079 ± 0.26
9.0
3.162 ± 0.27
7.079 ± 0.27
10.0
2.512 ± 0.27
5.623 ± 0.27
11.0
2.238 ± 0.26
5.011 ± 0.27
12.0
1.778 ± 0.26
4.467 ± 0.27
n = 6, mean ± SD, P < 0.Table 14
Pharmacokinetic parameters of ampicillin, norfloxacin, and in combination with piperine after oral treatment in rabbit [95].
Treatment
t
max (h)
C
max (μg/mL)
t
1
/
2 (h)
AUC (μg·h/mL)
Ampicillin (150mg/kg)
1 ± 0.31
44.6 ± 0.27
1.3 ± 0.46
103.7 ± 0.52
Ampicillin (150mg/kg) + piperine (20mg/kg)
1.1 ± 0.3
251.2 ± 0.28
1.9 ± 0.57
350.49 ± 0.47
Norfloxacin (150mg/kg)
3.1 ± 0.32
11 ± 0.26
1.75 ± 0.38
63.98 ± 0.51
Norfloxacin (150mg/kg) + piperine (20mg/kg)
3.2 ± 0.31
16.1 ± 0.27
2.97 ± 0.38
111.69 ± 0.54
n = 6, mean ± SD, P < 0.05.Piperine and Carbamazepine
The effect of piperine on the steady-state pharmacokinetics of a single dose of carbamazepine in poorly controlled epilepsy patients on carbamazepine monotherapy was studied. Patients (n=10 each) receiving either 300 mg or 500 mg dose of carbamazepine twice a day were selected. After administration of carbamazepine, venous blood samples were collected at 0, 0.5, 1, 2, 4, 6, 9, and 12 h. Subsequently, piperine (20 mg p.o.) was administered along with carbamazepine and samples were collected similarly. Piperine significantly increased the mean plasma concentrations of carbamazepine at most of the time points in both dose groups. There was a significant increase in AUC0-12h (P<0.001), average Css (P<0.001), t1/2 (P<0.05), and a decrease in Kel (P<0.05), in both the dose groups, whereas changes in Ka and t1/2α were not significant. Cmax (P<0.01) and tmax (P<0.01) were increased significantly following piperine administration in the 500 mg dose group; however, these parameters were not significant in the lower dose group. Piperine could significantly enhance the oral bioavailability of carbamazepine, possibly by decreasing the elimination or by increasing its absorption [96].Piperine and Fexofenadine
Effect of piperine, a major component of black pepper, on the oral exposure of fexofenadine in rats was studied. Pharmacokinetic parameters of fexofenadine were determined in rats following an oral (10 mg/kg) administration of fexofenadine in the presence and absence of piperine (10 or 20 mg/kg). Compared to the control group given fexofenadine alone, the combined use of piperine increased the AUC offexofenadine by 180% to 190% while there was no significant change in Cmax and t1/2 of fexofenadine in rats. The bioavailability of fexofenadine was increased by approximately 2-fold via the concomitant use of piperine. Furthermore, tmax tends to be increased which might be attributed to the delayed gastric emptying in the presence of piperine. In conclusion, piperine significantly enhanced the oral exposure of fexofenadine in rats likely by the inhibition of P-glycoprotein-mediated cellular efflux during the intestinal absorption, suggesting that the combined use of piperine or piperine-containing diet with fexofenadine may require close monitoring for potential drug-diet interactions [97].Piperine and Metronidazole
Effect of piperine on bioavailability of metronidazole was studied in rabbits. Male New Zealand white rabbits (2.0–2.5 kg body weight) used for pharmacokinetic and bioavailability study. Three groups of rabbits were formed from which one group was considered as control and received only vehicle (distilled water) orally. The remaining two groups were treated with metronidazole and combination of metronidazole and piperine, respectively. About 1 mL of blood sample was collected at the different time intervals and analyzed spectrophotometrically by HPLC. Different pharmacokinetic parameters have shown to enhance bioavailability of metronidazole in combination with piperine than metronidazole alone (Table15). So, it is concluded that bioavailability of metronidazole was significantly enhanced in the presence of piperine [98].Table 15
Comparative pharmacokinetic parameters after oral administration of metronidazole and in combination with piperine in rabbits [98].
Pharmacokinetic
Metronidazole
Metronidazole + piperine
parameters
C
max (ng/mL)
3,805.89 ± 233.8
6,007.07 ± 348.8
AUC0–24 (ng·h/mL)
45,073.75 ± 713.7
84,980.98 ± 345.6
t
max (h)
1.66 ± 0.57
1.66 ± 0.57
K
el (mL/h)
0.06 ± 0.02
0.04 ± 0.02
t
1
/
2 (h)
1.48 ± 1.23
12.24 ± 1.04
V
d (L)
2.69 ± 0.23
1.48 ± 0.65Piperine and Resveratrol
Effect of piperine on oral bioavailability of resveratrol was studied in mice. Employing a standardized LC-MS assay, the effect of piperine coadministration with resveratrol on serum levels resveratrol and resveratrol-3-O-β-D-glucuronide in C57BL mice was determined. Mice were administered resveratrol (100 mg/kg) or resveratrol (100 mg/kg) + piperine (10 mg/kg), and the serum levels of resveratrol and resveratrol-3-O-β-D-glucuronide were analyzed at different times. The AUC to resveratrol was enhanced to 229% and the Cmax was increased to 1544% with the addition of piperine. Study demonstrated that piperine significantly improves the in vivo bioavailability of resveratrol [100].Piperine and Gatifloxacin
Influence of coadministration of piperine on pharmacokinetic profile of gatifloxacin was studied in layer birds. The pharmacokinetic profile (Tables16 and 17) of gatifloxacin (10 mg/kg body weight) along with piperine coadministration (15 mg/kg) via single oral dose in layer birds showed t1/2, Cmax, and AUC of 4.03±0.097 h, 2.14±0.019 μg/mL, and 17.54±0.204 μg·h/mL, respectively, which is found significantly higher than gatifloxacin alone (3.74±0.073 h, 1.74±0.023 μg/mL, and 15.25±0.219 μg·h/mL, resp.). This study reveals that piperine has significant effect on the pharmacokinetics of the gatifloxacin. There is enhancement in bioavailability (F) from 74.52±1.021% to 85.74±0.956% in piperine + gatifloxacin-treated group. The results obtained are the combined effect of piperine on the absorption kinetics and the inhibition of the metabolism of gatifloxacin [101].Table 16
Comparison of plasma concentrations (μg/mL) of gatifloxacin- and gatifloxacin + piperine-treated birds after single oral administration (10 mg/kg) [101].
Time (h)
Gatifloxacin
Gatifloxacin + piperine
0.5
0.48 ± 0.013
0.53 ± 0.009**
0.75
1 ± 0.014
1.16 ± 0.029**
1
1.35 ± 0.016
1.46 ± 0.021*
2
1.74 ± 0.023
2.14 ± 0.020
4
1.35 ± 0.02
1.47 ± 0.034*
8
0.97 ± 0.009
1.08 ± 0.019**
12
0.46 ± 0.01
0.54 ± 0.008
n = 6, *Significant at P < 0.05, **Highly significant at P < 0.01.Table 17
Comparison of pharmacokinetic parameters of gatifloxacin- and gatifloxacin + piperine-treated layer birds after single oral administration (10 mg/kg) [101].
Pharmacokinetic
Gatifloxacin
Gatifloxacin + piperine
parameters
C
max (μg/mL)
1.74 ± 0.023
2.14 ± 0.019*
AUC (μg·h/mL)
15.25 ± 0.219
17.54 ± 0.204*
t
max (h)
2 ± 0.0
2 ± 0.0
t
1
/
2 (h)
3.74 ± 0.073
4.03 ± 0.097*
V
d (L/kg)
3.54 ± 0.038
3.33 ± 0.083*
F (%)
74.52 ± 1.021
85.74 ± 0.956*
n = 6, mean ± SE; **Highly significant at P < 0.01, *Significant at P < 0.05.The influence of coadministration of piperine on pharmacokinetic profile of gatifloxacin was studied in broiler birds. The pharmacokinetic profile of gatifloxacin (10 mg/kg body weight) along with piperine coadministration (15 mg/kg) via single dose oral administration in broiler birds showedt1/2, Cmax, and AUC of 4.1±0.092 h, 2.14±0.02 μg/mL, and 17.58±0.17 μg·h/mL, respectively, which is found significantly higher than t1/2, Cmax and AUC of 3.81±0.07 h, 1.74±0.024 μg/mL, and 15.24±0.23 μg·h/mL, respectively, obtained after single oral administration of gatifloxacin (10 mg/kg body weight) alone. This study reveals that piperine has significant effect on the pharmacokinetics of the gatifloxacin. There is significant enhancement of bioavailability (F) in piperine-treated group (81.95±1.56%) compared to gatifloxacin alone treated group (72.96±1.10%). The results obtained are the combined effect of piperine on the absorption kinetics and the inhibition of the metabolism of gatifloxacin [102].Piperine and Atenolol
A bioavailability of atenolol in presence of piperine was studied in male New Zealand white rats. All rats were divided in three groups. First group was considered as control and received only vehicle (distilled water) orally. The remaining two groups were treated with atenolol and combination of atenolol and piperine, respectively. About 2 mL of blood sample was collected at the different time intervals and analyzed spectrophotometrically by HPLC. The pharmacokinetic parameters obtained after administration of atenolol (100 mg/kg) and combination of atenolol (100 mg/kg) and piperine (10 mg/kg). So, from Table18 it can be concluded that bioavailability of atenolol was significantly enhanced in presence of piperine [103].Table 18
Comparison of pharmacokinetic parameters of atenolol- and atenolol + piperine-treated male New Zealand white rats after single oral administration (100 mg/kg) [103].
Pharmacokinetic
Atenolol
Atenolol + piperine
parameters
C
max (pg/mL)
22,453 ± 233
37,860 ± 348
AUC0–24 (pg·h/mL)
1,07,189 ± 1615
1,52,011 ± 2354
t
max (h)
2.0 ± 0.0
2.0 ± 0.0
K
el (mL/h)
0.27 ± 0.005
0.25 ± 0.010
t
1
/
2 (h)
6.27 ± 0.057
6.72 ± 0.100
V
d (L)
4.54 ± 0.786
2.88 ± 0.305
n = 3, mean ± SE.Piperine and Ibuprofen
Influence of piperine on ibuprofen-induced antinociception and its pharmacokinetics was studied. Piperine (10 mg/kg) significantly increased the dose-dependent antinociceptive activity of ibuprofen evaluated by both acetic acid writhing and formalin test, when it was administered with ibuprofen. Ibuprofen plasma concentration was also increased when it was administered with piperine. The synergistic antinociception activity of ibuprofen when administered with piperine can be attributed to increased plasma concentration of ibuprofen. From this study it can be concluded that piperine can be used as a bioenhancer along with ibuprofen [104].Piperine and Losartan Potassium
Effect of piperine on bioavailability of losartan potassium was studied in male New Zealand white rats. All rats were divided in three groups. First group received only mineral water orally. Second group received losartan potassium (100 mg/kg). Third group received losartan potassium (100 mg/kg) and piperine (10 mg/kg). About 2 mL of blood sample was collected at the different time intervals and analyzed by HPLC. The pharmacokinetic parameters obtained after administration of losartan potassium (100 mg/kg) and combination of losartan potassium (100 mg/kg) and piperine (10 mg/kg). So, from Table19 it can be concluded that bioavailability of losartan potassium was significantly enhanced in presence of piperine [105].Table 19
Comparison of pharmacokinetic parameters of losartan potassium- and losartan potassium + piperine-treated male New Zealand white rats after single oral administration (100 mg/kg) [105].
Pharmacokinetic
Losartan potassium
Losartan potassium
parameters
+ piperine
C
max (pg/mL)
32,461 ± 1436
48,399 ± 6060
AUC0–24 (pg·h/mL)
1,10,441 ± 5280
1,69,924 ± 14,343
t
max (h)
1.0 ± 0.0
1.0 ± 0.0
K
el (mL/h)
0.295 ± 0.002
0.283 ± 0.022
t
1
/
2 (h)
2.34 ± 0.01
2.44 ± 0.195
V
d (L)
3.0 ± 0.15
2.0 ± 0.25
n = 3, mean ± SE.


## 4.1.1. Drug Metabolizing Enzymes Inhibited by Piperine (Shown in Table2)

Table 2
Drug metabolizing enzymes inhibited by piperine.
Drug metabolizing enzymes
References
Arylhydrocarbon hydroxylase (AHH)
Atal et al. [15], Singh et al. [66]
Uridine diphosphate- (UDP-) glucuronyl transferase
Atal et al. [15], Singh et al. [66]
Ethylmorphine-N-demethylase
Atal et al. [15], Singh et al. [66]
7-Ethoxycoumarin-O-deethylase
Atal et al. [15], Singh et al. [66]
3-Hydroxy-benzo(a)pyrene glucuronidation
Atal et al. [15], Singh et al. [66]
UDP-glucose dehydrogenase (UDP-GDH)
Reen et al. [16]
5-lipoxygenase
Stöhret al. [67]
Cyclooxygenase-1
Stöhret al. [67]
Cytochrome P450
Atal et al. [15], Singh et al. [66], Bhardwaj et al. [17]The interaction of piperine with enzymatic drug biotransforming reactions in hepatic tissue has been studiedin vitro and in vivo. Piperine inhibited arylhydrocarbon hydroxylation, ethylmorphine-N-demethylation, 7-ethoxycoumarin-O-deethylation, and 3-hydroxy-benzo(a)pyrene glucuronidation in rat postmitochondrial supernatant in vitro in a dose-dependent manner. Piperine inhibition of these reactions in postmitochondrial supernatant from 3-methylcholanthrene and phenobarbital treated rats was similar to the controls. Inhibition by piperine of arylhydrocarbon hydroxylase (AHH) from 3-methylcholanthrene treated rats was comparable to that observed with 7, 8-benzoflavone. Piperine caused noncompetitive inhibition of hepatic microsomal AHH from the untreated and 3-methylcholanthrene-treated rats with a Ki=30μM which was close to the apparent Km of AHH observed in the controls. Similarly, the kinetics of inhibition of ethylmorphine-N-demethylase from control rat liver microsomes exhibited noncompetitive inhibition with an apparent Km=0.8mM and Ki=35μM. These studies demonstrated that piperine is a nonspecific inhibitor of drug metabolism. Oral administration of piperine in rats strongly inhibited the hepatic AHH and Uridine diphosphate-(UDP-) glucuronyltransferase (UGT) activities. The maximal inhibition of AHH observed within 1 h restored to normal value in 6 h. These results demonstrate that piperine is a potent inhibitor of drug metabolism [15]. Piperine modified the rate of glucuronidation by lowering the endogenous UDP-glucuronic acid (UDP-GA) content and also by inhibiting the transferase activity [66].The effects of piperine on UDP-glucose dehydrogenase (UDP-GDH) and glucuronidation potentials of rat and guinea pig liver and intestine were studiedin vitro. Piperine caused a concentration-related strong inhibition of UDP-GDH (50% at 10 μM) reversibly and equipotently, in both tissues. Partially purified rat liver UDP-GDH was used to obtain the kinetic values at pH optima of 9.4 and 8.6. At pH 9.4, Km=15 μM, Vmax=5.2 nmol, with NADH—Ki=6μM, with NAD—Ki=16 μM were obtained. At pH 8.6, Km=35 μM, Vmax=7.5 nmol, and Ki=15 μM. In all of these cases, piperine caused noncompetitive inhibition. Data from structure activity comparisons of piperine analogs indicated that the presence of conjugated double bonds in the side chain of the molecule is a factor in piperine inhibition. However, the UDP-GA contents were decreased less effectively by piperine in isolated rat hepatocytes compared with enterocytes of guinea pig small intestine. Piperine at 50 μM caused a marginal decrease of UDP-GA in hepatocytes when the rate of glucuronidation of 3-hydroxybenzo(a)pyrene (3-OH-BP) decreased by about 40%. The decrease obtained at 10 μM piperine in intestinal cells was comparable to that obtained at 50–100 μM in hepatocytes. UGT activities towards 3-OH-BP (UGT1A1) and 4-OH-biphenyl (UGT2B1) were also determined. Piperine did not affect the rate of glucuronidation of 4-OH-biphenyl in rat liver, whereas that of 3-OH-BP was impaired significantly. In guinea pig small intestine, both these activities were inhibited significantly requiring less than 25 μM piperine to produce more than 50% inhibition of UGT(s). The results suggested that (i) piperine is a potent inhibitor of UDP-GDH, (ii) inhibition is offered exclusively by the conjugated double bonds of the molecule, and (iii) piperine exerts stronger effects on intestinal glucuronidation than in rat liver [16].Piperine inhibits human P-glycoprotein and CYP3A4 (CYP: Cytochrome P450). Both the proteins are expressed in enterocytes and hepatocytes and contribute to a major extent to first-pass elimination of many drugs. This indicates that dietary piperine could affect plasma concentrations of P-glycoprotein and CYP3A4 substrates in humans, in particular if these drugs are administered orally. Some of the metabolizing enzymes inhibited or induced by piperine include CYP1A1, CYP1B1, CYP1B2, CYP2E1, and CYP3A4. Most of the drugs metabolized by these enzymes will therefore be influenced by bioenhancers [17].


## 4.1.2. Drugs/Nutraceuticals Bioenhanced by Piperine

Piperine acts as an antimicrobial bioenhancer which enhances bioavailability and bioefficacy of drugs by acting on drug metabolism. It also acts as a nutritional bioenhancer which enhances bioavailability and absorption of nutrients by acting on gastrointestinal tract. Allameh et al. [68] reported that piperine enhances bioavailability of aflatoxin B1 in rat tissues. A 10 mg dose of piperine causes a marked increase in serum gonadotropins and a decrease in intratesticular testosterone concentration, despite normal serum testosterone titres in adult male albino rats [69]. However, some of the experimental findings also indicated the ability to decrease the bioavailability of drugs, like rifampicin [70, 71], isoniazid [72], and Diclofenac sodium [73].Piperine has been shown to inhibit several cytochrome P450-mediated pathways and phase II reactions in animal models. Piperine, or mixtures containing piperine, has been shown to increase the bioavailability, blood levels, and efficacy of many of drugs (Table3) and nutraceuticals (Table 4). Administration of piperinesignificantly increased plasma concentrations of rifampicin,phenytoin, spartein, sulfadiazine, tetracycline, propranolol, and theophylline in humans.Table 3
Drugs bioenhanced by piperine.
Drugs
Experimental model
References
Vasicine
Rats
Zutshi and Kaul [74]
Pyrazinamide
In vitro
Zutshi [75]
Phenytoin, propranolol, theophyllin, spartein, sulphadiazine, and tetracycline
Human volunteers
Bano et al. [76, 77]
Pentobarbitone
Human volunteers
Mujumdar et al. [78]
Curcumin
Human volunteers and rats
Shoba et al. [79]
In vivo
Shaikh et al. [80]
Rats
Suresh and Srinivasan [81]
Nimesulide
Mice
Gupta et al. [82]
Indomethacin
Rabbits
Karan et al. [83]
Oxyphenylbutazone
Rats
Mujumdar et al. [84]
Phenytoin
Human volunteers
Velpandian et al. [85], Pattanaik et al. [86]
Rifampicin
Human
Zutshi et al. [87]
In vitro
Balakrishnan et al. [88]
Amoxycillin trihydrate and cefotaxime
Rats
Hiwale et al. [89]
EGCG [(−)-epigallocatechin-3-gallate]
Mice
Lambert et al. [90]
Oxytetracycline
WLH hens
Singh et al. [91]
Ciprofloxacin
Rabbits
Balkrishna and Yogesh [92]
In vitro
Khan et al. [8]
Nevirapine
Human
Kasibhatta and Naidu [93]
Diclofenac sodium and pentazocine
Albino mice
Pooja et al. [47]
Pefloxacin
Gaddi goats
Dama et al. [94]
Ampcilllin and norloxacin
Rabbits
Janakiraman and Manavalan [95]
Carbamazepine
In vitro
Pattanaik et al. [96]
Fexofenadine
Rats
Jin and Han [97]
Metronidazole
Rabbits
Singh et al. [98]
Ampicillin trihydrate
Human
Janakiraman and Manavalan [99]
Resveratrol
Mice
Johnson et al. [100]
Gatifloxacin
Layer birds
Patel et al. [101]
Broiler birds
Devada et al. [102]
Atenolol
Rats
Singh and Chand [103]
Ibuprofen
In vitro
Venkatesh et al. [104]
Losartan potassium
Rats
Singh et al. [105]Table 4
Nutraceuticals bioenhanced by piperine [13, 19].
Class
Examples
Water soluble vitamins
Vitamin B1, Vitamin B2, niacinamide, Vitamin B6, Vitamin B12, folic acid, and Vitamin C
Fat soluble vitamins
Vitamin A,β-carotene (provitamin), Vitamin D, Vitamin E, and Vitamin K
Amino acids
Lysine, isoleucine, leucine, threonine, valine, tryptophan, phenylalanine, and methionine
Minerals
Iodine, calcium, iron, zinc, copper, selenium, magnesium, potassium, and manganese
Herbal compounds
Boswellic acid (Boswellia serrata), Ginsenosides (Gingko biloba), Withanaloids (Withania somnifera), Curcuminoides (Curcuma longa), and Pycnogenol (Pinus pinaster)Piperine and Phenytoin
Effect of piperine on pharmacokinetics of phenytoin was studied in healthy volunteers. In a crossover study, five volunteers received either a single oral dose (300 mg) of phenytoin alone or in combination with multiple doses of piperine (20 mg × 7 days) followed by an oral dose of phenytoin. Blood samples were collected at 0.5, 1, 2, 3, 4, 8, 12, 24, and 48 h after drug administration and analyzed for phenytoin by the enzyme-multiplied immunoassay technique. The results showed that a single daily dose of piperine for 7 days decreased thet1/2α (P<0.05), prolonged the t1/2 (P<0.01), and produced a higher AUC (P<0.05) in comparison to phenytoin alone. It is therefore concluded that piperine on multiple-dose administration alters the pharmacokinetic parameters of the antiepileptic [76].
A preliminary pharmacokinetic study was carried out in mice by administering phenytoin (10 mg) orally, with or without piperine (0.6 mg). Subsequently, oral pharmacokinetics of phenytoin was carried out in six healthy volunteers in a crossover design. Phenytoin tablet (300 mg) was given 30 minutes after ingestion of a soup (Melahu rasam) with or without black pepper. A further study of intravenous pharmacokinetics of phenytoin (1 mg) in rats with or without oral pretreatment with piperine (10 mg) was also conducted. The phenytoin concentration in the serum was analyzed by HPLC. The study showed a significant increase in the kinetic estimates of Ka, AUC0-10 and AUC0-∞ in the piperine fed mice. Similarly, in human volunteers piperine increased Ka, AUC0-48, AUC0-∞ and delayed elimination of phenytoin. Intravenous phenytoin in the oral piperine-treated rat group showed a significant alteration in the elimination phase indicating its metabolic blockade [85].
The effect of piperine on oral bioavailability of phenytoin was studied in human volunteers. The objective of this study was to explore the effect of a single dose of piperine in patients with uncontrolled epilepsy on the steady-state pharmacokinetics of phenytoin. Two groups of 10 patients each receiving either a 150 mg or 200 mg twice daily dose of phenytoin were selected. 12 h after the night dose, venous blood samples were collected at 0, 0.5, 1, 2, 4, 6, 9, and 12 h after administration of phenytoin. On the next study day, piperine 20 mg was administered along with phenytoin and samples were collected similarly. There was a significant increase inAUC0-12h (P<0.01), Cmax (P<0.001), and Ka (P<0.05), whereas the changes in Kel and tmax were not significant. The results showed that piperine enhanced the bioavailability of phenytoin significantly, possibly by increasing the absorption [86].Piperine and Pentobarbitone
Effect of piperine on pentobarbitone-induced hypnosis in rats was studied. Piperine treatment in rats, treated chronically with phenobarbitone, significantly potentiated pentobarbitone sleeping time, as compared to the controls. There was no alteration in barbital sodium sleeping time. It is possible that piperine inhibits liver microsomal enzyme system and thereby potentiates the pentobarbitone sleeping time [78].Piperine with Propranolol and Theophylline
The effects of piperine on the bioavailability and pharmacokinetics of propranolol and theophylline were studied. Six subjects in each group received a single oral dose of propranolol (40 mg) or theophylline (150 mg) alone or in combination with piperine (20 mg) daily for 7 days. An earliertmax and a higher Cmax and AUC were observed in the subjects who received piperine and propranolol. It produced a higher Cmax, longer t1/2, and a higher AUC with theophylline. In clinical practice, the enhanced systemic availability of oral propranolol and theophylline could be exploited to achieve better therapeutic control and improved patient compliance [77].Piperine and Nimesulide
Influence of piperine on nimesulide-induced antinociception was studied in mice. The plasma concentration after oral administration of nimesulide (10 mg/kg) alone was8.03±0.99 μg/mL. However, when it was administered with piperine (10 mg/kg), the plasma concentration of nimesulide increased to 11.9±0.23 μg/mL. This indicates that piperine inhibits the biotransformation and metabolism of nimesulide leading to significantly (P<0.05) higher levels of drug in the systemic circulation. The findings of this study suggest that piperine could be used as a biological enhancer when coadministered with nimesulide [82].Piperine and Curcumin
Influence of piperine on the pharmacokinetics of curcumin in animals and human volunteers was studied. The medicinal properties of curcumin obtained fromCurcuma longa Linn. cannot be utilized because of poor bioavailability due to its rapid metabolism in the liver and intestinal wall. The effect of combining piperine, a known inhibitor of hepatic and intestinal glucuronidation, was evaluated on the bioavailability of curcumin in rats and healthy human volunteers. When curcumin was given alone, at dose 2 g/kg to rats, moderate serum concentrations were achieved over a period of 4 h. Concomitant administration of piperine 20 mg/kg increased the serum concentration of curcumin for a short period of 1-2 h after drug. tmax was significantly increased (P<0.02) while t1/2 and ClB significantly decreased (P<0.02), and the bioavailability was increased by 154%. On the other hand, in humans after a dose of 2 g curcumin alone, serum levels were either undetectable or very low (Table 5). Concomitant administration of piperine 20 mg produced much higher concentrations from 0.25 to 1 h after drug (P<0.01 at 0.25 and 0.5 h; P<0.001 at 1 h); the increase in bioavailability was 200%. The study shows that in the dosages used, piperine enhances the serum concentration, extent of absorption, and bioavailability of curcumin in both rats and humans with no adverse effects [79].Table 5
Comparative pharmacokinetic parameters after oral supplementation of curcumin and curcumin + piperine in human volunteers [79].
Parameters
Curcumin
Curcumin (2g/kg) + piperine
(2g/kg)
(20mg/kg)
C
max (μg/mL)
1.35
±
0.23
1.80
±
0.16
t
max (h)
0.83
±
0.05
1.29
±
0.23
t
1
/
2 (h)
1.70
±
0.58
1.05
±
0.18
AUC (μg·h/mL)
2.36
±
0.28
3.64
±
0.31
Cl
B (L/h)
713
±
12
495.90
±
193.90Piperine andβ-Carotene
The effectiveness of piperine was evaluated for its ability to improve serum response ofβ-carotene during oral supplementation using a double-blind, crossover study design. Subjects were randomly selected to ingest a daily β-carotene dose (15 mg) either with 5 mg of piperine or placebo during each of two 14-day supplementation periods. Intersubject variability in presupplementation serum β-carotene levels was minimized by limiting the selection of volunteers to healthy, adult males with fasting serum β-carotene values <20 pg/dL. The results indicate that significantly greater increases (P<0.0001) in serum β-carotene occurred during supplementation with β-carotene plus piperine (49.8±9.6 pg/dL versus 30.9±5.4 pg/dL) compared to β-carotene plus placebo. Supplementation with betacarotene plus piperine for 14 days produced a 60% greater increase AUC than was observed during supplementation with β-carotene plus placebo (Table 6). Study suggests that the serum response during oral β-carotene supplementation is improved through the nonspecific, thermogenic property of piperine, described in this paper as thermonutrient in action [20].Table 6
Effect of piperine on the serumβ-carotene levels during a 14-day supplementation in human volunteers [20].
Treatment (n=6)
β-carotene (μg/dL)
AUC (μg/dL) × (time in days)
Day 0
Day 14
Change
β-carotene + placebo
16.3 ± 2.6
47.2 ± 6.4
30.9 ± 5.4
272 ± 47.6
β-carotene + piperine
16.0 ± 3.1
65.8 ± 9.7
49.8 ± 9.6
435 ± 74.2Piperine and Coenzyme Q10
An extract from the fruits of black pepper consisting of a minimum of 98% pure piperine was evaluated in a clinical study using a double-blind design. The relative bioavailability of 90 mg and 120 mg of coenzymeQ10 administered in a single-dose experiment or in separate experiments for 14 and 21 days with placebo or with 5 mg of piperine was determined by comparing measured changes in plasma concentration. The intersubject variability was minimized by limiting the selection of individuals to healthy adult male volunteers with (presupplementation) fasting coenzyme Q10 values between 0.30 and 0.60 mg/L. The results of the single-dose study and the 14-day study indicate smaller, but not significant, increases in plasma concentrations of coenzyme Q10 in the control group compared with the group receiving coenzyme Q10 with a supplement of piperine. Supplementation of 120 mg coenzyme Q10 with piperine for 21 days produced approximately 30% greater AUC than was observed during supplementation with coenzyme Q10 plus placebo. It is postulated that the bioenhancing mechanism of piperine to increase plasma levels of supplemental coenzyme Q10 is nonspecific and possibly based on its description in the literature as a thermonutrient [106].Piperine and Rifampicin
Piperine augments transcription inhibitory activity of rifampicin by several folds againstMycobacterium smegmatis. A 24 : 1 (w/w) mixture of antibiotic rifampicin and piperine shows remarkable growth inhibitory effect on M. smegmatis, and this inhibition is higher than that of rifampicin alone. Interestingly, piperine alone, even at higher concentration, does not inhibit the growth of Mycobacterium. As RNA polymerase is the site of action of rifampicin, the enzyme was purified from M. smegmatis and the mixture of rifampicin and piperine was found to abrogate nonspecific transcription catalyzed by M. smegmatisRNA polymerase. The effect is higher than rifampicin alone and piperine shows no effect independently. When RNA polymerase was purified from a rifampicin-resistant strain of M. smegmatis, the enzymatic activity, otherwise resistant to rifampicin, significantly decreases in the presence of piperine along with rifampicin. Piperine enhances the binding ability of rifampicin to RNA polymerase [88].
The amount of piperine used in the range of 0.4–0.9% by weight of the antituberculosis and antileprosy drugs. Antituberculosis composition contains rifampicin (100–300 mg), isoniazid (100–300 mg) and pyrazinamide (500–1000 mg) (combination of any two), and piperine (5–29 mg). Antileprosy composition contains rifampicin (100–300 mg), dapsone (50–100 mg), and piperine (5–20 mg). Effect of piperine on pharmacokinetic parameters of rifampicin, isoniazid, and pyrazinamide combination was studied in human volunteers. The results from Table7 indicate that piperine significantly increases the bioavailability of antituberculosis drugs like rifampicin, isoniazid, and pyrazinamide [107, 108].Table 7
Effect of piperine on pharmacokinetics of rifampicin, isoniazid, and pyrazinamide combination in human volunteers [107, 108].
Kineticparameters
Formulation A
Formulation B
Rifampicin
Isoniazid
Pyrazinamide
Rifampicin**
Isoniazid**
Pyrazinamide**
t
1
/
2 (h)
0.67 ± 0.008
0.64 ± 0.01
0.60 ± 0.03
0.40 ± 0.04
0.42 ± 0.04
0.37 ± 0.008
t
1
/
2
(el) (h)
8.40 ± 0.06
7.90 ± 0.10
9.50 ± 0.14
11.1 ± 0.18
8.15 ± 0.26*
11.0 ± 0.17
C
max (μg/mL)
8.20 ± 0.46
2.56 ± 0.17
27.0 ± 2.0
17.6 ± 1.09
10.07 ± 0.90
40.0 ± 1.64
AUC0–∞ (μg·h/mL)
104.6 ± 4.38
41.0 ± 1.72
318.6 ± 8.05
143.95 ± 5.85
94.95 ± 3.98
435.41 ± 9.7
*Not significant (P > 0.05), **highly significant (P < 0.001).
Formulation A: rifampicin—450 mg, isoniazid—300 mg, pyrazinamide—1500 mg.
Formulation B: rifampicin—450 mg, isoniazid-300 mg, pyrazinamide—1500 mg, piperine—20 mg.Risorine is a formulation developed by the Indian Institute of Integrative Medicine, Jammu, and marketed in India in November 2009 in public—private partnership with Cadila Pharmaceutical Ltd, Ahmedabad. Risorine has been approved for marketing by Drug Controller General of India, after successful completion of all the phased clinical trials. It contains rifampicin (200 mg), isoniazid (300 mg), and piperine (10 mg). It has been found to be bioequivalent with commercially available rifampicin preparations. This is due to enhanced uptake of the drug by body cells, and also because the drug remains available in blood for longer durations. Combining piperine with rifampicin decreases the dose of rifampicin from 450 to 200 mg [109].Piperine with Amoxicillin Trihydrate and Cefotaxime
Effect of coadministration of piperine on pharmacokinetics ofβ-lactam antibiotics was studied in rats. Coadministration of piperine enhanced bioavailability of β-lactam antibiotics like amoxicillin trihydrate and cefotaxime sodium significantly in rats. The improved bioavailability is reflected in various pharmacokinetic parameters, namely tmax, Cmax, t1/2, and AUC of these antibiotics. The increased bioavailability could be attributed to the effect of piperine on microsomal metabolizing enzymes or enzymes system [89].Piperine and Epigallocatechin Gallate (EGCG)
Piperine enhanced the bioavailability of the tea polyphenol EGCG in Mice. EGCG, from green tea (Camellia sinensis), has demonstrated chemopreventive activity in animal models of carcinogenesis. Cotreatment with piperine enhanced the bioavailability of EGCG in mice. Intragastric coadministration of 163.8 μmol/kg EGCG and 70.2 μmol/kg piperine to male CF-1 mice increased the plasma Cmax and AUC by 1.3-fold compared to mice treated with EGCG only. Piperine appeared to increase EGCG bioavailability by inhibiting glucuronidation and gastrointestinal transit. Piperine (100 μmol/L) inhibited EGCG glucuronidation in mouse small intestine (by 40%) but not in hepatic microsomes. Piperine (20 μmol/L) also inhibited production of EGCG-3′′-glucuronide in human HT-29 colon adenocarcinoma cells. Small intestinal EGCG levels in CF-1 mice following treatment with EGCG alone had a Cmax=37.50±22.50 nmol/g at 60 min that then decreased to 5.14±1.65 nmol/g at 90 min; however, cotreatment with piperine resulted in a Cmax=31.60±15.08 nmol/g at 90 min, and levels were maintained above 20 nmol/g until 180 min. This resulted in a significant increase in the small intestine EGCG AUC (4621.80±1958.72 nmol/g/min versus 1686.50±757.07 nmol/g/min). EGCG appearance in the colon and the feces of piperine-cotreated mice was slower than in mice treated with EGCG alone [90].Piperine and Oxytetracycline (OTC)
The pharmacokinetic profile of orally administered oxytetracycline (10 mg/kg body weight) was studied 7 days after oral treatment ofP. longum (15 mg equivalent/kg) in White Leghorn birds (WLH) (2.0–2.8 kg). On day 8, oxytetracycline (OTC) was administered orally and blood samples were collected from the wing vein in heparinized vials for plasma separation at 0 (before treatment), 15, 30, 60, 120, 240, 360, 480, and 600 min after OTC administration. Plasma OTC concentrations were determined by microbial assay technique using Bacillus cereus var. mycoides (ATCC 11778) as test organism. The plasma levels of OTC against time were adequately described by one compartment open model (Table 8). The pharmacokinetic data (Table 9) revealed that P. longum-treated animals had significantly higher AUC, AUMC, and MRT. Prior treatment of P. longum significantly reduced β and increased t1/2. The ClB reduced by 21%, whereas td increased by 29%. The treatment with P. longum reduced loading and maintenance dose by 33.3% and 39%, respectively [91].Table 8
Comparison of mean plasma levels of oxytetracycline (μg/mL) at different time intervals following oral administration in control and P. longum-treated WLH birds [91].
Time (Min)
Control
Treated
15
0.23 ± 0.024
0.30 ± 0.022*
30
0.34 ± 0.025
0.45 ± 0.029**
60
0.72 ± 0.051
0.77 ± 0.046
120
0.58 ± 0.037
0.63 ± 0.030
240
0.37 ± 0.015
0.47 ± 0.034**
360
0.26 ± 0.017
0.38 ± 0.021****
480
0.23 ± 0.015
0.31 ± 0.019***
600
0.19 ± 0.005
0.25 ± 0.015***
n = 8, mean ± SE; *P < 0.1, **P < 0.05, ***P < 0.01, ****P < 0.001.Table 9
Comparative pharmacokinetic parameters of oxytetracycline administered orally (10 mg/kg) in control andP. longum treated birds [91].
Parameters
Control OTC
Treated OTC + piperine
β
(/h)
0.147 ± 0.011
0.112 ± 0.006*
t
1
/
2
β (h)
4.934 ± 0.422
6.370 ± 0.438**
AUC (μg·h/mL)
5.055 ± 0.689
6.417 ± 0.317*
AUMC (μg·h2/mL)
43.62 ± 11.15
63.58 ± 7.042*
MRT (h)
7.98 ± 0.744
9.77 ± 0.644**
t
d (h)
16.38 ± 1.4
21.142 ± 1.453**
Cl
B (mL/kg/h)
184.63 ± 7.7
145.97 ± 14.42**
n = 8, mean ± SE; *P < 0.01, **P < 0.05.Piperine and Ciprofloxacin
The influence of coadministration of piperine on pharmacokinetic profile of ciprofloxacin in rabbits was studied. The study reveals that piperine has affected statically to the pharmacokinetics of the ciprofloxacin which is significant with change inCmax, tmax, AUC, and Kel. The results obtained are the combined effect of piperine on the absorption kinetics and the inhibition of the metabolism of the ciprofloxacin. This leads to increase bioavailability of ciprofloxacin when administered with piperine [92].
The potentiating effect of piperine with ciprofloxacin inin vitro combination against Staphylococcus aureusATCC 29213 was studied and its suggestive role as an efflux pumps inhibitor. Piperine, in combination with ciprofloxacin, markedly reduced the MIC and mutation prevention concentration of ciprofloxacin for S. aureus, including methicillin resistant S. aureus. In vitro combination studies, the final concentrations ranged from 0.03 to 64 μg/mL for ciprofloxacin and from 0.8 to 50 μg/mL for piperine. The final bacterial inoculum in each well was 5×105 CFU/mL. The plates were incubated at 37°C for 24 h. Piperine did not show any antibacterial activity when tested up to 100 μg/mL. Table 10 is showing that there was a 2-fold reduction in the MIC of ciprofloxacin (from 0.25 to 0.12 μg/mL) for S. aureus ATCC 29213 when tested in combination with piperine at 12.5 and 25 μg/mL. The MIC was further reduced to 4-fold with 50 μg/mL piperine [8]. Piperine inhibits the efflux of ethidium bromide and ciprofloxacin from bacterial cells (Table 11). It is a P-glycoprotein inhibitor that inhibits ciprofloxacin efflux [8].Table 10
MIC of ciprofloxacin forS. aureus ATCC 29213 at different concentrations of piperine [8].
Piperine conc.
MIC (μg) of ciprofloxacin for S. aureus
(μg/mL)
ATCC 29213
0.0
0.25
12.5
0.12
25
0.12
50
0.06Table 11
Drug susceptibilities ofS. aureusATCC 29213 and the ciprofloxacin selected mutant (CIPr-1) [8].
Compound
MIC (μg/mL)
S. aureusATCC 29213
CIPr-1
Ethidium bromide
4
8
Ethidium bromide + piperine
1
2
Ciprofloxacin
0.25
128
Ciprofloxacin + piperine
0.12
8Piperine and Nevirapine
Influence of piperine on the pharmacokinetics of nevirapine under fasting conditions was studied. This was a crossover, placebo-controlled pilot study conducted in a total of eight healthy adult males aged 20–40 years. Subjects were randomly assigned to receive piperine 20 mg or placebo each morning for 6 days, and on day 7, nevirapine (200 mg) plus piperine (20 mg) or nevirapine plus placebo in a crossover fashion. Blood samples were collected from 1–144 h after dose for pharmacokinetic analysis. MeanCmax, AUCt, AUC0-∞, and Clast values of nevirapine were increased by approximately 120%, 167%, 170%, and 146%, respectively, when coadministered with piperine. This pilot study provided evidence for enhanced bioavailability of nevirapine when administered with piperine [93].Piperine with Diclofenac Sodium and Pentazocine
The analgesic activity ofP. nigrum extract per se and its interaction with diclofenac sodium and pentazocine in albino mice was studied. Healthy albino mice of either sex weighing 25–30 grams were taken and divided into 4 groups of 8 animals each. Peripheral analgesic activity was evaluated by acetic acid-induced writhing test, using diclofenac sodium (5 mg/kg), P. nigrum extract (10 mg/kg), and their combination (5+10 mg/kg) orally. Similarly central analgesic activity was studied using tail flick method and pentazocine (5 mg/kg) orally was used instead of diclofenac sodium. P. nigrum extract alone did not show any significant analgesic activity in tail flick and writhing methods. However, results of acetic acid-induced writhing model showed that diclofenac sodium reduces writhing 54.90% with respect to control when administered alone, but showed significant decrease in writhes 78.43% with respect to control when P. nigrum extract was coadministered with diclofenac sodium. When P. nigrum extract combined with pentazocine showed significant increase in tail flick latency in comparison with pentazocine alone and control group (P<0.05), the results suggest that the P. nigrum extract significantly increased the analgesic activity of diclofenac sodium and pentazocine [47].Piperine and Pefloxacin
The pharmacokinetics of orally administered pefloxacin were studied to evaluate the bioenhancing effect of the herbal bioenhancer, trikatu, in mountain Gaddi goats (n=6). The findings of the study revealed a decreased plasma concentration (P>0.05) of pefloxacin following trikatu administration during the absorption phase (10, 15, and 20 min after pefloxacin administration). In contrast, the plasma concentrations of pefloxacin were significantly higher at 4, 6, 8, and 12 h (during the elimination phase) of the pefloxacin administration. The findings of the investigation revealed higher values for AUC, AUMC, MRT, td, and bioavailability. Trikatu treatment, however, significantly reduced t1/2 and zero time intercept of the elimination phase. The Vd(area) and Vd(B) were significantly higher in trikatu-treated animals indicating a better penetration of the drug. Based on the MIC of 0.8 μg/mL of pefloxacin; a priming dose of 6.0 mg/kg and a maintenance dose of 2.21 mg/kg are required to be administered at 8 h intervals. For practical purposes in goats this would mean a priming dose of 6 mg/kg and a maintenance dose of 2 mg/kg given by the oral route to be repeated at 8 h intervals [94].Piperine with Ampicillin and Norfloxacin
Effect of piperine on oral bioavailability of ampicillin and norfloxacin was studied in rabbits. Coadministration of piperine (20 mg/kg), an alkaloid fromP. nigrum, enhanced oral bioavailability of ampicillin and norfloxacin in animal model. This is reflected in various pharmacokinetic measurements like Cmax, tmax, AUC, and t1/2 of the above antibiotics in animal model shown in Tables 12, 13, and 14 [95].Table 12
Effect of piperine on plasma concentration of ampicillin in rabbits [95].
Time (h)
Ampicillin (μg/mL)
Ampicillin + piperine (μg/mL)
0.0
0
0
0.5
30.584 ± 0.38
35.481 ± 0.26
1.0
44.668 ± 0.32
251.188 ± 0.27
1.5
31.672 ± 0.49
188.364 ± 0.31
2.0
26.607 ± 0.37
84.139 ± 0.31
2.5
18.836 ± 0.38
66.834 ± 0.26
3.0
17.782 ± 0.32
35.481 ± 0.27
3.5
12.589 ± 0.31
33.496 ± 0.26
4.0
12.589 ± 0.32
26.607 ± 0.27
4.5
9.441 ± 0.26
26.607 ± 0.27
n = 6, mean ± SD, P < 0.05.Table 13
Effect of piperine on plasma concentration of norfloxacin in rabbits [95].
Time (h)
Norfloxacin (μg/mL)
Norfloxacin + piperine (μg/mL)
0.0
0
0
1.0
10.593 ± 0.26
14.125 ± 0.27
2.0
7.079 ± 0.26
17.783 ± 0.32
3.0
5.623 ± 0.32
14.963 ± 0.27
4.0
5.011 ± 0.38
11.885 ± 0.32
5.0
4.732 ± 0.26
10.592 ± 0.37
6.0
3.981 ± 0.26
8.414 ± 0.25
7.0
3.548 ± 0.21
8.414 ± 0.26
8.0
3.349 ± 0.26
7.079 ± 0.26
9.0
3.162 ± 0.27
7.079 ± 0.27
10.0
2.512 ± 0.27
5.623 ± 0.27
11.0
2.238 ± 0.26
5.011 ± 0.27
12.0
1.778 ± 0.26
4.467 ± 0.27
n = 6, mean ± SD, P < 0.Table 14
Pharmacokinetic parameters of ampicillin, norfloxacin, and in combination with piperine after oral treatment in rabbit [95].
Treatment
t
max (h)
C
max (μg/mL)
t
1
/
2 (h)
AUC (μg·h/mL)
Ampicillin (150mg/kg)
1 ± 0.31
44.6 ± 0.27
1.3 ± 0.46
103.7 ± 0.52
Ampicillin (150mg/kg) + piperine (20mg/kg)
1.1 ± 0.3
251.2 ± 0.28
1.9 ± 0.57
350.49 ± 0.47
Norfloxacin (150mg/kg)
3.1 ± 0.32
11 ± 0.26
1.75 ± 0.38
63.98 ± 0.51
Norfloxacin (150mg/kg) + piperine (20mg/kg)
3.2 ± 0.31
16.1 ± 0.27
2.97 ± 0.38
111.69 ± 0.54
n = 6, mean ± SD, P < 0.05.Piperine and Carbamazepine
The effect of piperine on the steady-state pharmacokinetics of a single dose of carbamazepine in poorly controlled epilepsy patients on carbamazepine monotherapy was studied. Patients (n=10 each) receiving either 300 mg or 500 mg dose of carbamazepine twice a day were selected. After administration of carbamazepine, venous blood samples were collected at 0, 0.5, 1, 2, 4, 6, 9, and 12 h. Subsequently, piperine (20 mg p.o.) was administered along with carbamazepine and samples were collected similarly. Piperine significantly increased the mean plasma concentrations of carbamazepine at most of the time points in both dose groups. There was a significant increase in AUC0-12h (P<0.001), average Css (P<0.001), t1/2 (P<0.05), and a decrease in Kel (P<0.05), in both the dose groups, whereas changes in Ka and t1/2α were not significant. Cmax (P<0.01) and tmax (P<0.01) were increased significantly following piperine administration in the 500 mg dose group; however, these parameters were not significant in the lower dose group. Piperine could significantly enhance the oral bioavailability of carbamazepine, possibly by decreasing the elimination or by increasing its absorption [96].Piperine and Fexofenadine
Effect of piperine, a major component of black pepper, on the oral exposure of fexofenadine in rats was studied. Pharmacokinetic parameters of fexofenadine were determined in rats following an oral (10 mg/kg) administration of fexofenadine in the presence and absence of piperine (10 or 20 mg/kg). Compared to the control group given fexofenadine alone, the combined use of piperine increased the AUC offexofenadine by 180% to 190% while there was no significant change in Cmax and t1/2 of fexofenadine in rats. The bioavailability of fexofenadine was increased by approximately 2-fold via the concomitant use of piperine. Furthermore, tmax tends to be increased which might be attributed to the delayed gastric emptying in the presence of piperine. In conclusion, piperine significantly enhanced the oral exposure of fexofenadine in rats likely by the inhibition of P-glycoprotein-mediated cellular efflux during the intestinal absorption, suggesting that the combined use of piperine or piperine-containing diet with fexofenadine may require close monitoring for potential drug-diet interactions [97].Piperine and Metronidazole
Effect of piperine on bioavailability of metronidazole was studied in rabbits. Male New Zealand white rabbits (2.0–2.5 kg body weight) used for pharmacokinetic and bioavailability study. Three groups of rabbits were formed from which one group was considered as control and received only vehicle (distilled water) orally. The remaining two groups were treated with metronidazole and combination of metronidazole and piperine, respectively. About 1 mL of blood sample was collected at the different time intervals and analyzed spectrophotometrically by HPLC. Different pharmacokinetic parameters have shown to enhance bioavailability of metronidazole in combination with piperine than metronidazole alone (Table15). So, it is concluded that bioavailability of metronidazole was significantly enhanced in the presence of piperine [98].Table 15
Comparative pharmacokinetic parameters after oral administration of metronidazole and in combination with piperine in rabbits [98].
Pharmacokinetic
Metronidazole
Metronidazole + piperine
parameters
C
max (ng/mL)
3,805.89 ± 233.8
6,007.07 ± 348.8
AUC0–24 (ng·h/mL)
45,073.75 ± 713.7
84,980.98 ± 345.6
t
max (h)
1.66 ± 0.57
1.66 ± 0.57
K
el (mL/h)
0.06 ± 0.02
0.04 ± 0.02
t
1
/
2 (h)
1.48 ± 1.23
12.24 ± 1.04
V
d (L)
2.69 ± 0.23
1.48 ± 0.65Piperine and Resveratrol
Effect of piperine on oral bioavailability of resveratrol was studied in mice. Employing a standardized LC-MS assay, the effect of piperine coadministration with resveratrol on serum levels resveratrol and resveratrol-3-O-β-D-glucuronide in C57BL mice was determined. Mice were administered resveratrol (100 mg/kg) or resveratrol (100 mg/kg) + piperine (10 mg/kg), and the serum levels of resveratrol and resveratrol-3-O-β-D-glucuronide were analyzed at different times. The AUC to resveratrol was enhanced to 229% and the Cmax was increased to 1544% with the addition of piperine. Study demonstrated that piperine significantly improves the in vivo bioavailability of resveratrol [100].Piperine and Gatifloxacin
Influence of coadministration of piperine on pharmacokinetic profile of gatifloxacin was studied in layer birds. The pharmacokinetic profile (Tables16 and 17) of gatifloxacin (10 mg/kg body weight) along with piperine coadministration (15 mg/kg) via single oral dose in layer birds showed t1/2, Cmax, and AUC of 4.03±0.097 h, 2.14±0.019 μg/mL, and 17.54±0.204 μg·h/mL, respectively, which is found significantly higher than gatifloxacin alone (3.74±0.073 h, 1.74±0.023 μg/mL, and 15.25±0.219 μg·h/mL, resp.). This study reveals that piperine has significant effect on the pharmacokinetics of the gatifloxacin. There is enhancement in bioavailability (F) from 74.52±1.021% to 85.74±0.956% in piperine + gatifloxacin-treated group. The results obtained are the combined effect of piperine on the absorption kinetics and the inhibition of the metabolism of gatifloxacin [101].Table 16
Comparison of plasma concentrations (μg/mL) of gatifloxacin- and gatifloxacin + piperine-treated birds after single oral administration (10 mg/kg) [101].
Time (h)
Gatifloxacin
Gatifloxacin + piperine
0.5
0.48 ± 0.013
0.53 ± 0.009**
0.75
1 ± 0.014
1.16 ± 0.029**
1
1.35 ± 0.016
1.46 ± 0.021*
2
1.74 ± 0.023
2.14 ± 0.020
4
1.35 ± 0.02
1.47 ± 0.034*
8
0.97 ± 0.009
1.08 ± 0.019**
12
0.46 ± 0.01
0.54 ± 0.008
n = 6, *Significant at P < 0.05, **Highly significant at P < 0.01.Table 17
Comparison of pharmacokinetic parameters of gatifloxacin- and gatifloxacin + piperine-treated layer birds after single oral administration (10 mg/kg) [101].
Pharmacokinetic
Gatifloxacin
Gatifloxacin + piperine
parameters
C
max (μg/mL)
1.74 ± 0.023
2.14 ± 0.019*
AUC (μg·h/mL)
15.25 ± 0.219
17.54 ± 0.204*
t
max (h)
2 ± 0.0
2 ± 0.0
t
1
/
2 (h)
3.74 ± 0.073
4.03 ± 0.097*
V
d (L/kg)
3.54 ± 0.038
3.33 ± 0.083*
F (%)
74.52 ± 1.021
85.74 ± 0.956*
n = 6, mean ± SE; **Highly significant at P < 0.01, *Significant at P < 0.05.The influence of coadministration of piperine on pharmacokinetic profile of gatifloxacin was studied in broiler birds. The pharmacokinetic profile of gatifloxacin (10 mg/kg body weight) along with piperine coadministration (15 mg/kg) via single dose oral administration in broiler birds showedt1/2, Cmax, and AUC of 4.1±0.092 h, 2.14±0.02 μg/mL, and 17.58±0.17 μg·h/mL, respectively, which is found significantly higher than t1/2, Cmax and AUC of 3.81±0.07 h, 1.74±0.024 μg/mL, and 15.24±0.23 μg·h/mL, respectively, obtained after single oral administration of gatifloxacin (10 mg/kg body weight) alone. This study reveals that piperine has significant effect on the pharmacokinetics of the gatifloxacin. There is significant enhancement of bioavailability (F) in piperine-treated group (81.95±1.56%) compared to gatifloxacin alone treated group (72.96±1.10%). The results obtained are the combined effect of piperine on the absorption kinetics and the inhibition of the metabolism of gatifloxacin [102].Piperine and Atenolol
A bioavailability of atenolol in presence of piperine was studied in male New Zealand white rats. All rats were divided in three groups. First group was considered as control and received only vehicle (distilled water) orally. The remaining two groups were treated with atenolol and combination of atenolol and piperine, respectively. About 2 mL of blood sample was collected at the different time intervals and analyzed spectrophotometrically by HPLC. The pharmacokinetic parameters obtained after administration of atenolol (100 mg/kg) and combination of atenolol (100 mg/kg) and piperine (10 mg/kg). So, from Table18 it can be concluded that bioavailability of atenolol was significantly enhanced in presence of piperine [103].Table 18
Comparison of pharmacokinetic parameters of atenolol- and atenolol + piperine-treated male New Zealand white rats after single oral administration (100 mg/kg) [103].
Pharmacokinetic
Atenolol
Atenolol + piperine
parameters
C
max (pg/mL)
22,453 ± 233
37,860 ± 348
AUC0–24 (pg·h/mL)
1,07,189 ± 1615
1,52,011 ± 2354
t
max (h)
2.0 ± 0.0
2.0 ± 0.0
K
el (mL/h)
0.27 ± 0.005
0.25 ± 0.010
t
1
/
2 (h)
6.27 ± 0.057
6.72 ± 0.100
V
d (L)
4.54 ± 0.786
2.88 ± 0.305
n = 3, mean ± SE.Piperine and Ibuprofen
Influence of piperine on ibuprofen-induced antinociception and its pharmacokinetics was studied. Piperine (10 mg/kg) significantly increased the dose-dependent antinociceptive activity of ibuprofen evaluated by both acetic acid writhing and formalin test, when it was administered with ibuprofen. Ibuprofen plasma concentration was also increased when it was administered with piperine. The synergistic antinociception activity of ibuprofen when administered with piperine can be attributed to increased plasma concentration of ibuprofen. From this study it can be concluded that piperine can be used as a bioenhancer along with ibuprofen [104].Piperine and Losartan Potassium
Effect of piperine on bioavailability of losartan potassium was studied in male New Zealand white rats. All rats were divided in three groups. First group received only mineral water orally. Second group received losartan potassium (100 mg/kg). Third group received losartan potassium (100 mg/kg) and piperine (10 mg/kg). About 2 mL of blood sample was collected at the different time intervals and analyzed by HPLC. The pharmacokinetic parameters obtained after administration of losartan potassium (100 mg/kg) and combination of losartan potassium (100 mg/kg) and piperine (10 mg/kg). So, from Table19 it can be concluded that bioavailability of losartan potassium was significantly enhanced in presence of piperine [105].Table 19
Comparison of pharmacokinetic parameters of losartan potassium- and losartan potassium + piperine-treated male New Zealand white rats after single oral administration (100 mg/kg) [105].
Pharmacokinetic
Losartan potassium
Losartan potassium
parameters
+ piperine
C
max (pg/mL)
32,461 ± 1436
48,399 ± 6060
AUC0–24 (pg·h/mL)
1,10,441 ± 5280
1,69,924 ± 14,343
t
max (h)
1.0 ± 0.0
1.0 ± 0.0
K
el (mL/h)
0.295 ± 0.002
0.283 ± 0.022
t
1
/
2 (h)
2.34 ± 0.01
2.44 ± 0.195
V
d (L)
3.0 ± 0.15
2.0 ± 0.25
n = 3, mean ± SE.


## 4.2.Zingiber officinale

The major pungent compounds inZingiber officinale (Ginger) of rhizome extract contain potentially active gingerols, which can be converted to shogaols, zingerone, and paradol [110, 111]. The odor of ginger depends mainly on its volatile oil, the yield of which varies from 1 to 3% [112]. In laboratory animals, the gingerols increase the motility of the gastrointestinal tract and have analgesic, sedative, antipyretic, and antibacterial properties [113]. [6]-gingerol is the major pungent principle of ginger. The chemopreventive potentials of [6]-gingerol present a promising future alternative to expensive and toxic therapeutic agents [114]. Ginger exhibits activities like antiulcer activity [115, 116], antithrombotic activity [117], antimicrobial activity [118], antifungal activity [119], anti-inflammatory activity [117, 120–122], antidiabetic activity [123], antiemetic activity [124, 125], anthelmintic activity [126], analgesic and antipyretic activity [121], antioxidant and antiapoptotic activity [122], and anticancer activity [127].Ginger acts powerfully on GIT mucous membrane. The role of ginger is to regulate intestinal function to facilitate absorption. The composition containingZ. officinale alone provides bioavailability/bioenhancing activity in the range of 30–75%, and piperine and Z. officinale, and provides the bioavailability of drugs in the range of 10–85%. The dosage of bioenhancer from Z. officinale as extract is in the range of 10–30 mg/kg body weight and piperine is in the range of 4–12 mg/kg body weight. The dosage of bioenhancer from Z. officinale as bioactive fraction is in the range of 5–15 mg/kg body weight, preferably 30 mg/kg body weight and piperine is in the range of 6–10 mg/kg body weight, preferably 8 mg/kg body weight. The extracts or its fractions either in presence or absence of piperine have been found to be highly selective in their bioavailability enhancing activity (Table 20). It varies from almost nearly significant (20%) to highly significant (200%) [128, 129].Table 20
Percent enhancement in bioavailability of different drugs/compounds by supplementation of bioactive fractions fromZ. officinaleand its combination with piperine [128, 129].
Category
Compound
Percent enhancement
BE fromZ. officinale
BE fromZ. officinale + piperine
Macrolides
Azithromycin
78
85
Erythromycin
68
105
Roxithromycin
72
93
Cephalosporins
Cefalexin
75
85
Cefadroxil
68
65
Penicillins
Amoxycillin
80
90
Cloxacillin
76
90
Aminoglycosides
Kanamycin
65
92
Fluoroquinolones
Ciprofloxacin
68
70
Pefloxacin
53
69
Antifungal
Fluconazole
120
110
Ketoconazole
125
100
Antiviral
Acyclovir
82
85
Zidovudine
105
126
CNS drugs
Alprazolam
76
70
Anticancer
Methotrexate
87
49
5-Fluorouracil
110
93
Doxorubicin
72
75
Cisplatin
56
45
Cardiovascular
Amlodipine
68
95
Propranolol
76
104
Lisinopril
76
100
Anti-inflammatory/Antiarthritic
Diclofenac
90
140
Nimesulide
144
165
Piroxicam
86
134
Antituberculosis/Antileprosy
Rifampicin
65
98
Dapsone
46
55
Ethionamide
56
48
Cycloserine
71
70
Antihistamines
Salbutamol
78
92
Theophylline
76
80
Bromhexine
46
75
Corticosteroids
Dexamethasone
76
80
Betamethasone
75
70
Immunosuppressants
Cyclosporin A
116
120
Tacrolimus
75
117
Antiulcer
Ranitidine
147
165
Cimetidine
98
76
Vitamins
Vitamin A (1 mg/kg)
30
40
Vitamin E (40 mg/kg)
27
25
Vitamin C (50 mg/kg)
25
24
Folic acid (50μg/kg)
34
35
Antioxidants
β-Carotene (15 mg/kg)
36
55
Silymarin (5 mg/kg)
28
43
Herbal products
Curcumin (50 mg/kg)
43
70
Rutin (40 mg/kg)
21
78
Herbal plants
Echinacea
66
82
Tinospora cordifolia
67
112
Picrorhiza kurroa
56
87
Andrographis paniculata
55
70
Emblica ribes
65
72
Asparagus racemosus
44
60
Withania somnifera
64
48
Amino acids
Methionine (20 mg/kg)
25
45
Lysine (40 mg/kg)
15
40
Leucine (50 mg/kg)
17
34
Valine (25 mg/kg)
25
46
Isoleucine (25 mg/kg)
31
35
Essential elements
Zinc (0.1 mg/kg)
19
20
Potassium (25 mg/kg)
21
19


## 4.3.  Niaziridin

Niaziridin is a nitrile glycoside that has been isolated from the leaves, pods, and bark of Drumstick (Moringa oleifera) [130]. M. oleifera has shown to exhibit activities like antifertility effect [131], antimicrobial activity [132], diuretic activity [133], anticancer activity [134, 135], anti-inflammatory activity [133, 135], hypotensive and spasmolytic activity [136], antifungal activity [137], antiulcer activity [138], antioxidant activity [139, 140], hepatoprotective activity [141], hypolipidaemic activity [142], antiteratogenic activity [143], and antiarthritic activity [144].It enhances bioactivity of commonly used antibiotics such as rifampicin, ampicillin, tetracycline, and nalidixic acid against Gram-positive bacteria likeM. smegmatisand Bacillus subtilisand Gram-negative bacteria like E. coli (Table 21). It enhances activity of commonly used antibiotics such as rifampicin, ampicillin, tetracycline, and nalidixic acids against E. coli Gram-negative bacteria. It enhances activity of rifampicin, ampicillin, tetracycline, and nalidixic acids by 1.2–19-fold against the Gram-positive strains. It enhances the activity of azole antifungal drugs such as clotrimazole against Candida albicans by 5-6-fold. However, the antifungal activity enhancement was observed only at a relatively higher concentration (10 μg/mL) of the compound. It also facilitates the uptake of nutrients like Vitamin B12 through the intestinal gut membrane in combination, thus also functioning as bioavailability enhancer [145, 146].Table 21
Enhancement of antibiotic activity by niaziridin* in combination with antibiotics against different organisms [145, 146].
Organisms
Antibiotics
Concentration (μg/mL)
Fold enhancement of activity
E. coli (CA8000)
Rifampicin
20.0
38.8
Rifampicin
30.0
12.6
Ampicillin
6.0
5.3
Tetracycline
1.0
2.3
Tetracycline
2.0
5.2
Nalidixic acid
6.0
50.0
B. subtilis (MTCC121)
Rifampicin
0.05
19.4
Ampicillin
0.01
5.1
Tetracycline
1.0
3.5
Nalidixic acid
2.0
7.0
M. smegmatis (MC2 155)
Rifampicin
0.05
1.9
Ampicillin
0.01
4.7
Tetracycline
1.0
4.0
Nalidixic acid
2.0
1.2
*Dose:E. coli = 0.1 μg/kg; B. subtilisand M. smegmatis= 1.0 μg/kg.


## 4.4.  Glycyrrhizin

Glycyrrhizin is a glycoside obtained from roots and stolon of Liquorice (Glycyrrhiza glabra). It has expectorant action to treat bronchitis and can also reduce inflammation, allergies, asthma, gastritis, peptic ulcers, rheumatism, and sore throat. It helps the liver to detoxify drugs and is used for treatment of liver disease. It strengthens the immune system, stimulates the adrenal gland, and is diuretic and laxative. Glycyrrhizin is 50 times sweeter than sugar. Primary uses include treatment for peptic ulcers and stomach ailments, respiratory, and intestinal passages. Glycyrrhizin exhibits activities like antihepatotoxic activity [147, 148], anti-inflammatory activity [149, 150], anticancer activity [151], and antiviral activity [152, 153].The concentration of glycyrrhizin ranges from 0.05 to 50% of the weight of the antibacterial compounds. The concentration of glycyrrhizin ranges from 0.10 to 10% of the weight of the nutraceutical compounds. The concentration of glycyrrhizin ranges from 0.25 to 20% of the weight of the antifungal agents. The level of glycyrrhizin ranges from 10 to 10,000-fold of the weight of the anticancer compound used [154, 155].Glycyrrhizin-mediated enhancement in the cell division inhibitory action of anticancer agent “Taxol” (paclitaxel) in the animal cell culture experiments using cancerous cell line MCF-7. The anticancerous activity of Taxol in terms of inhibiting the growth and multiplication of MCF-7 cancer cells was markedly enhanced by 5-fold. The cancerous cells growth inhibition by Taxol (0.01μg/mL) in presence of glycyrrhizin (1 μg/mL) was higher than even the treatment with Taxol (0.05 μg/mL) alone [154, 155].It enhances bioactivity of commonly used antibiotics such as rifampicin, ampicillin, tetracycline, and nalidixic acids against Gram-positive bacteria likeM. smegmatisand Bacillus subtilisand Gram-negative bacteria like E. coli(Table 22). It enhances activity of commonly used antibiotics such as rifampicin, ampicillin, tetracycline, and nalidixic acids against E. coli Gram-negative bacteria. It enhances activity of rifampicin, tetracycline, and nalidixic acids against the Gram-positive strains. It enhances the activity of azole antifungal drugs such as clotrimazole against Candida albicans[154, 155].Table 22
Enhancement of antibiotic activity by glycyrrhizin (1μg/mL) in combination with antibiotics against different organisms [154, 155].
Organisms
Antibiotics
Concentration (μg/mL)
Fold enhancement of activity
E. coli (ATCC 10536)
Rifampicin
10.0
3.8
Rifampicin
20.0
14.0
Nalidixic acid
8.0
9.5
Ampicillin
6.0
12.6
Ampicillin
8.0
2.1
Tetracycline
2.0
1.9
Tetracycline
4.0
9.0
B. subtilis (ATCC 6015)
Nalidixic acid
6.0
4.5
Nalidixic acid
8.0
6.75
Tetracycline
1.0
5.0
M. smegmatis (ATCC 14468)
Rifampicin
0.5
6.5
Nalidixic acid
4.0
7.7
Tetracycline
0.5
1.5


## 4.5.Cuminum cyminum

The main components ofC. cyminum oil are p-mentha-1,4-dien-7-al, cumin aldehyde, γ-terpinene, and β-pinene [156]. C. cyminumexhibits activities like estrogenic activity [157], hypolipidaemic activity [158], antinociceptive and anti-inflammatory activity [159], anticonvulsant effect [160], anticancer activity [161], antimicrobial activity [156, 162], antitussive effect [163], antioxidant activity [164], and antifungal activity [165]. The doses of its fractions responsible for the bioavailability enhancement activity ranged from 0.5 to 25 mg/kg body weight. The dosage level of the composition comprising C. cyminumextract is in the range of 10–30 mg/kg body weight and composition comprising bioactive fraction is in the range of 2–20 mg/kg body weight. The composition contain C. cyminumextract or the fractions there of which provides bioavailability/bioenhancing activity in the range of 25–335% (Table 23). Polar and nonpolar extract of parts of C. cyminumand piperine increased bioavailability in the range of 25–435% [166, 167].Table 23
Percent enhancement in bioavailability of different compounds by supplementation of bioactive fractions fromC. cyminum and its combination with piperine [166, 167].
Category
Compound
Percent enhancement
BE fromC. cyminum
BE fromC. cyminum + piperine
Macrolides
Azithromycin
83
97
Erythromycin
75
95
Roxithromycin
67
103
Cephalosporins
Cefalexin
60
75
Cefadroxil
90
79
Penicillins
Amoxycillin
75
98
Cloxacillin
94
95
Aminoglycosides
Kanamycin
95
110
Fluoroquinolones
Ciprofloxacin
52
47
Pefloxacin
47
57
Ofloxacin
61
73
Antifungal
Fluconazole
170
126
Ketoconazole
136
156
Antiviral
Acyclovir
110
98
Zidovudine
330
415
CNS drugs
Alprazolam
60
104
Anticancer
Methotrexate
125
30
5-Fluorouracil
335
435
Doxorubicin
85
103
Cisplatin
70
79
Cardiovascular
Amlodipine
55
103
Propranolol
135
210
Lisinopril
83
98
Anti-inflammatory/Antiarthritic
Diclofenac
65
108
Nimesulide
168
150
Piroxicam
70
107
Antituberculosis/Antileprosy
Rifampicin
250
365
Dapsone
60
75
Ethionamide
78
65
Cycloserine
89
90
Antihistamines
Salbutamol
110
85
Theophylline
87
75
Bromhexine
50
90
Corticosteroids
Dexamethasone
85
105
Betamethasone
95
82
Immuno-suppressants
Cyclosporin A
156
275
Tacrolimus
75
117
Antiulcer
Ranitidine
117
89
Cimetidine
123
105
Vitamins
Vitamin A (1 mg/kg)
26
18
Vitamin B1 (10 mg/kg)
37
33
Antioxidants
β-Carotene (15 mg/kg)
45
53
Silymarin (5 mg/kg)
32
41
Herbal products
Curcumin (50 mg/kg)
39
29
Herbal plants
Echinacea
72
90
Tinospora cordifolia
98
152
Picrorhiza kurroa
78
115
Andrographis paniculata
72
68
Emblica ribes
72
60
Asparagus racemosus
35
72
Withania somnifera
55
65
Amino acids
Methionine (20 mg/kg)
27
30
Lysine (40 mg/kg)
35
29
Leucine (50 mg/kg)
31
32
Valine (25 mg/kg)
25
24
Isoleucine (25 mg/kg)
40
22
Essential elements
Iron (0.5 mg/kg)
23
29


## 4.6.Carum carvi

Carum carvi (Caraway) contains caraway oil obtained from dried and crushed seeds. Carvone and limonene are the chief constituents of the oil and its odour and flavour are mainly attributed to them [168]. C. carvi exhibits activities like antiulcer effects [169], hypoglycemic effect [170], antimicrobial activity [156, 171], diuretic activity [172], antioxidant activity [171, 173], antiaflatoxigenic activity [174], and antifungal activity [171]. The effective dose of the bioenhancer extract is in the range of 5–100 mg/kg body weight and the dose bioactive fraction of bioenhancer is in the range of 1–55 mg/kg body weight. It has been reported to enhance bioavailability of antibiotics, antifungal, antiviral, and anticancerous drug. The extract or its fractions were found to be 20–110% more active and when used in combination with Z. officinale, it was found to be more effective, in the range of 10–150 mg/kg body weight. C. carviin different combinations showed pronounced activity ranging from 25 to 95% in presence of piperine and amount of piperine in formulations ranged from 3 to 15 mg/kg body weight [5, 175]. The percent enhancement of bioavailability of different class of drugs by fractions of C. carvi and in combination with piperine and Z. officinaleis shown in Table 24.Table 24
Percent enhancement in bioavailability of different drugs/compounds by supplementation of bioactive fractions fromC. carvi and its combination with piperine and Z. officinale[5, 175].
Category
Compound
Dose (mg/kg)
Percent enhancement
BE fromC. carvi
C. carvi+ piperine
C. carvi+ Z. officinale
Macrolides
Azithromycin
25
55
90
86
Erythromycin
45
70
100
105
Roxithromycin
15
65
95
98
Cephalosporins
Cefalexin
45
Nil
90
79
Cefadroxil
45
67
95
85
Ceftrioxone
25
72
78
75
Cefixime
40
80
79
82
Cefidinir
40
89
95
130
Penicillins
Amoxicillin
45
75
115
100
Cloxacillin
25
110
95
110
Aminoglycosides
Amikacin
50
85
100
92
Kanamycin
50
Nil
87
68
Fluoroquinolones
Ciprofloxacin
45
78
110
133
Pefloxacin
40
Nil
70
75
Ofloxacin
20
65
167
170
Norfloxacin
40
55
65
60
Antifungal
Fluconazole
65
65
98
110
Amphotericin B
78
78
90
80
Ketoconazole
55
55
100
96
Antiviral
Acyclovir
40
78
100
90
Zidovudine
10
92
95
87
CNS drugs
Alprazolam
0.1
Nil
70
80
Haloperidol
0.5
95
90
85
Anticancer
Methotrexate
5
76
89
102
5-Fluorouracil
25
90
110
100
Doxorubicin
5
Nil
70
69
Cisplatin
5
Nil
Nil
55
Cardiovascular
Amlodipine
1
Nil
50
65
Lisinopril
1
79
95
90
Atenolol
5
100
93
97
Propranolol
8
68
90
75
Anti-inflammatory/antiarthritic
Diclofenac
5
Nil
100
95
Piroxicam
2
Nil
98
76
Nimesulide
10
100
140
145
Rofecoxib
2.5
75
70
80
Antituberculosis/antileprosy
Rifampicin
40
110
170
140
Pyrazinamide
12.5
45
50
55
Dapsone
10
56
67
68
Ethionamide
25
68
65
70
Cycloserine
40
70
80
75
Antihistamines
Salbutamol
0.8
75
89
80
Theophylline
30
70
79
89
Bromhexine
25
Nil
70
71
Loratidine
1
76
70
80
Corticosteroids
Prednisolone
4
65
67
60
Dexamethasone
0.05
72
77
73
Betamethasone
0.1
80
89
77
Immuno-suppressants
Cyclosporin A
10
100
105
120
Tacrolimus
5
90
95
114
Antiulcer
Ranitidine
30
67
70
150
Cimetidine
40
72
84
100
Omeprazole
2
76
70
75
Vitamins
Vitamin A
1
19
16
27
Vitamin B1
10
42
26
55
Antioxidants
β-Carotene
15
55
59
72
Silymarin
5
38
45
41
Herbal products
Curcumin
50
48
51
52
Rutin
40
45
40
42
Herbal plants
Echinacea agustifolia
10
Nil
76
65
Tinospora cordifolia
50
76
90
71
Picrorhiza kurroa
50
80
110
76
Aegles marmelos
1000
65
65
60
Andrographis paniculata
50
68
72
54
Asparagus racemosus
50
Nil
55
45
Terminalia chebula
50
92
87
91
Withania somnifera
60
76
70
76
Centella asiatica
30
68
65
62
Amino acids
Methionine
20
28
30
37
Lysine
40
29
38
43
Leucine
50
21
32
40
Valine
25
19
29
38
Isoleucine
25
34
44
50


## 4.7. Allicin

Allicin is an allyl sulfur containing compound obtained from Garlic (Allium sativum). Allicin exhibits activities like antiplatelet activity [176], antioxidant activity [177, 178], antibacterial activity [179, 180], anticancer activity [181], Immunomodulating effect [182], antidiabetic activity [183, 184], antiparasitic activity [185], antifungal activity [186–188], antioxidant and anti-inflammatory activity [189, 190], and antiviral activity [191].


### 4.7.1. Allicin and Cu2+

Cu2+ showed a dose-dependent fungicidal activity against Saccharomyces cerevisiae cells, and its lethal effect was extremely enhanced in the presence of allicin, an allyl sulfur compound from garlic. The fungicidal activity of Cu2+ was unaffected or rather attenuated by other sulfur-containing compounds such as N-acetyl-cysteine, l-cysteine, or dithiothreitol. Ca2+ could absolutely protect against the lethal effect of Cu2+ itself, but showed no protection against the fungicidal activity of Cu2+ newly generated in combination with allicin. Cu2+ accelerated an endogenous generation of reactive oxygen species (ROS) in S. cerevisiae cells at a lethal concentration, but such intracellular oxidative stress induction was not observed during cell death progression upon treatment with Cu2+ and allicin. A surfactant, sodium N-lauroyl sarcosinate (SLS), enhanced the solubilization of a few proteins including alkyl hydroperoxide reductase 1 (AHP1) in intact cells, accounting for the absence of this protein in the extract from allicin-treated cells. Allicin-treated cells were rendered extremely sensitive to the subsequent Cu2+ treatment as in the case of SLS-treated cells. Allicin-treated cells and SLS-treated cells similarly showed an increased sensitivity to exogenously added tert-butyl hydroperoxide (t-BOOH), organic peroxide that is detoxified by the action of AHP1. Our study suggests that allicin influences the mode of cell surface localization or the related function of AHP1 as a defense against phospholipid peroxidation by the external action of Cu2+ [192].


### 4.7.2.  Allicin and Amphotericin B

Enhancement of the fungicidal activity of amphotericin B (AmB) by allicin, an allyl-sulfur compound from garlic, against the yeastSaccharomyces cerevisiae as a model system was studied. AmB is a representative antibiotic for the control of serious fungal infections, and its fungicidal activity was greatly enhanced by allicin (Table 25). In addition to the plasma membrane permeability change, AmB induced vacuole membrane damage so that the organelles were visible as small discrete particles. Although allicin was ineffective in promoting AmB-induced plasma membrane disability, this compound enhanced AmB-induced structural damage to the vacuolar membrane even at a nonlethal dose of the antibiotic. Allicin could also enhance the antifungal activity of AmB against the pathogenic fungus C. albicansand againstAspergillus fumigatus. In contrast, allicin did not enhance the cytotoxic activity of AmB against cells of human promyelocytic leukemia (HL-60), a vacuole-less organism [187].Table 25
Enhancement of fungicidal activity of AmB by Allicin againstS. cerevisiae [187].
Drug/compound
Conc. (μg)
Action againstS. cerevisiae
AmB alone
1
Mostly resistance to action
AmB alone
5
Subjected to lethal damage
Allicin alone
120
Not lethal
AmB + allicin
0.5 + 120
More susceptible to fungicidal activity of AmBAllicin was found to inhibit ergosterol transport from the plasma membrane to the cytoplasm, which is considered to be a cellular protective response to AmB-induced vacuole disruption inS. cerevisiae. The study suggests that AmB lethality against C. albicans depends at least in part on its vacuole disruptive activity under the physiological condition permissive for invasive growth of the fungus [188].Ogita et al. [193] reported that allicin enhances AmB-induced vacuole membrane damage by inhibiting ergosterol trafficking from the plasma membrane to the vacuole membrane. Ogita et al. [194] suggested that the fungicidal activity of AmB combined with allicin is involved in vacuole disruption but not in potassium ion efflux, and that the expression of allicin-mediated activity of AmB requires the presence of ergosterol in the plasma membrane.


## 4.7.1. Allicin and Cu2+

Cu2+ showed a dose-dependent fungicidal activity against Saccharomyces cerevisiae cells, and its lethal effect was extremely enhanced in the presence of allicin, an allyl sulfur compound from garlic. The fungicidal activity of Cu2+ was unaffected or rather attenuated by other sulfur-containing compounds such as N-acetyl-cysteine, l-cysteine, or dithiothreitol. Ca2+ could absolutely protect against the lethal effect of Cu2+ itself, but showed no protection against the fungicidal activity of Cu2+ newly generated in combination with allicin. Cu2+ accelerated an endogenous generation of reactive oxygen species (ROS) in S. cerevisiae cells at a lethal concentration, but such intracellular oxidative stress induction was not observed during cell death progression upon treatment with Cu2+ and allicin. A surfactant, sodium N-lauroyl sarcosinate (SLS), enhanced the solubilization of a few proteins including alkyl hydroperoxide reductase 1 (AHP1) in intact cells, accounting for the absence of this protein in the extract from allicin-treated cells. Allicin-treated cells were rendered extremely sensitive to the subsequent Cu2+ treatment as in the case of SLS-treated cells. Allicin-treated cells and SLS-treated cells similarly showed an increased sensitivity to exogenously added tert-butyl hydroperoxide (t-BOOH), organic peroxide that is detoxified by the action of AHP1. Our study suggests that allicin influences the mode of cell surface localization or the related function of AHP1 as a defense against phospholipid peroxidation by the external action of Cu2+ [192].


## 4.7.2.  Allicin and Amphotericin B

Enhancement of the fungicidal activity of amphotericin B (AmB) by allicin, an allyl-sulfur compound from garlic, against the yeastSaccharomyces cerevisiae as a model system was studied. AmB is a representative antibiotic for the control of serious fungal infections, and its fungicidal activity was greatly enhanced by allicin (Table 25). In addition to the plasma membrane permeability change, AmB induced vacuole membrane damage so that the organelles were visible as small discrete particles. Although allicin was ineffective in promoting AmB-induced plasma membrane disability, this compound enhanced AmB-induced structural damage to the vacuolar membrane even at a nonlethal dose of the antibiotic. Allicin could also enhance the antifungal activity of AmB against the pathogenic fungus C. albicansand againstAspergillus fumigatus. In contrast, allicin did not enhance the cytotoxic activity of AmB against cells of human promyelocytic leukemia (HL-60), a vacuole-less organism [187].Table 25
Enhancement of fungicidal activity of AmB by Allicin againstS. cerevisiae [187].
Drug/compound
Conc. (μg)
Action againstS. cerevisiae
AmB alone
1
Mostly resistance to action
AmB alone
5
Subjected to lethal damage
Allicin alone
120
Not lethal
AmB + allicin
0.5 + 120
More susceptible to fungicidal activity of AmBAllicin was found to inhibit ergosterol transport from the plasma membrane to the cytoplasm, which is considered to be a cellular protective response to AmB-induced vacuole disruption inS. cerevisiae. The study suggests that AmB lethality against C. albicans depends at least in part on its vacuole disruptive activity under the physiological condition permissive for invasive growth of the fungus [188].Ogita et al. [193] reported that allicin enhances AmB-induced vacuole membrane damage by inhibiting ergosterol trafficking from the plasma membrane to the vacuole membrane. Ogita et al. [194] suggested that the fungicidal activity of AmB combined with allicin is involved in vacuole disruption but not in potassium ion efflux, and that the expression of allicin-mediated activity of AmB requires the presence of ergosterol in the plasma membrane.


## 4.8.  Lysergol

Lysergol, a phytomolecule, is obtained from Morning Glory Plant (Ipomoea spp.) which enhances the killing activities of different antibiotics on bacteria and is a promising herbal bioenhancer. It has been isolated from higher plants like Rivea corymbosa, Ipomoea violacea,andIpomoea muricata. Bioenhancing activities of lysergol are under investigation. The effective amount of lysergol as a bioenhancer and bioavailability enhancer is in the range of 1–10 μg/mL but preferable dosage level is 10 μg/mL. It enhances bioavailability of different drugs like rifampicin, tetracycline, and ampicillin. Lysergol enhances the antimicrobial effect of the antibiotic compound in the range of 2–12-fold (Table 26). It is effective against broad spectrum microbes, Gram-positive and Gram-negative, consisting E. coli(ATCC 10536), B. subtilis(ATCC 6051),M. smegmatis(ATCC 14468), and other similar microbes [2]. Patil et al. [195] reported that lysergol improved the bioavailability of berberine after oral administration in Sprague-Dawley rats.Table 26
Enhancement of antibiotic activity by lysergol (10μg/mL) in combination with rifampicin against different organisms [2].
Organisms
Antibiotics
Concentration (μg/mL)
Fold enhancement of activity
E. coli (ATCC 10536)
Rifampicin
10
6–12
Rifampicin
20
3–5
B. subtilis(ATCC 6051)
Rifampicin
0.4
3–4.6
M. smegmatis (ATCC 14468)
Rifampicin
0.2
4.5–6


## 4.9.Aloe Vera Gel and Whole Leaf Extract

Aloe vera had a salutary effect on both vitamin C and vitamin E. Aloe vera gel and whole leaf extracts shown increased plasma concentration and improved absorption of both, vitamin C and vitamin E. The Aloe vera gel extract was especially effective in slowing down and increasing the absorption of ascorbate. It prolonged its plasma concentration significantly, even for 24 h, and following an overnight fast. Both the gel and whole leaf extracts improved the absorption of vitamin E and prolonged its plasma concentration, especially after 8 h. AUC for vitamin C and vitamin E with Aloe gel and whole leaf extract is shown in Table 27. Aloe vera is unique in its ability to increase bioavailability of both of these vitamins and should be considered as a future nutritional herbal bioenhancer [196].Table 27
AUC of vitamins C and E alone or with Aloe gel or Aloe whole leaf extract [196].
Supplement
AUC (μMh)
Vitamin C (500 mg)
339 ± 124
Vitamin C + Aloe whole leaf extract
272 ±144
Vitamin C + Aloe gel
1031 ± 513
Vitamin E (420 mg)
19.3 ± 23.2
Vitamin E + Aloe whole leaf extract
38.3 ± 17.0
Vitamin E + Aloe gel
71.3 ± 22.5
mean ± SE.


## 4.10.Stevia rebaudiana

Stevia rebaudiana(Stevia) is known as honey leaf which has been used as sweetener in South America. The chief constituent of stevia is stevioside, the glycoside which is 200 times sweeter than sucrose. Other constituents include steviol, austroinulin, rebaudioside, and dulcoside A. Extracts/fractions/pure isolates of stevia either alone or in combination with piperine are selective in enhancing the bioavailability/bioefficacy of drugs, nutraceuticals, and herbal drugs/formulations. The percentage of stevia in the bioenhancing composition varies from 0.01 to 80%. The dosage of bioenhancer derived from stevia extract is in the range of 0.01–50 mg/kg body weight and piperine is in the range of 0.01–12 mg/kg body weight. The dosage of bioenhancer derived from stevia bioactive fraction or pure compound is in the range of 0.01–40 mg/kg body weight, preferably 30 mg/kg body weight and piperine is in the range of 0.01–10 mg/kg body weight, preferably 8 mg/kg body weight. The dosage of bioenhancer derived from stevia leaf is in the range of 0.01–250 mg/dose of the drug, nutraceutical, or herbal extract. The dosage of bioenhancer derived from stevia fraction or pure compound is in the range of 0.01–75 mg irrespective of the amount of drug in the composition, preferably 1–30 mg/dose of the drug, nutraceutical, or herbal extract. Stevia enhanced bioavailability of different groups like antibiotics, antiobese drugs, antidiabetic drugs, antifungal drugs, antiviral drugs, anticancer drugs, cardiovascular drugs, anti-inflammatory, antiarthritic agents, antituberculosis/antileprosy drugs, anthelmintic/respiratory drugs, immune-modulators, antiulcer drugs, and herbal products or drugs [197].


## 4.11. Curcumin

Curcumin is the principal curcuminoid of the popular Indian spice turmeric (Curcuma longa). Curcumin suppresses drug metabolizing enzymes (CYP3A4) in the liver [198] as well as inducing changes in the drug transporter P-glycoprotein, hence increasing the Cmax and AUC of celiprolol and midazolam in rats [199]. The influence of curcumin before treatment on pharmacokinetic disposition of norfloxacin was studied in rabbits after single oral administration. The pharmacokinetic data revealed that curcumin-treated animals had significantly (P≤0.05) higher AUC and AUMC. Prior treatment of curcumin significantly (P≤0.05) increased t1/2β and Vd of norfloxacin. Further treatment with curcumin reduced loading and maintenance doses by 26% and 24%, respectively [200].


## 4.12. Sinomenine

Sinomenine is an alkaloid obtained fromSinomenium acutum,widely used for treatment of rheumatic and arthritic diseases in China and Japan.A single dose of paeoniflorin (150 mg/kg) alone and with sinomenine hydrochloride (90 mg/kg) was administered by gastric gavage to unrestrained conscious male Sprague-Dawley rats (250–300 g). A Blood sample was collected periodically via a jugular vein before and after dosing from 10 min to 12 h. HPLC assay was developed to determine the plasma concentrations of paeoniflorin. After coadministration of sinomenine, theCmax of paeoniflorin was elevated, tmax was delayed, AUC0-∞was increased, MRT was prolonged, CLB was decreased, and Vd was reduced. These results from Table 28 indicate that sinomenine hydrochloride significantly improved the bioavailability of paeoniflorin in rats [201].Table 28
Pharmacokinetic parameters of paeoniflorin (150 mg/kg) and in combination with sinomenine (90 mg/kg) after oral administration in rats [201].
Parameters
Paeoniflorin
Sinomenine + paeoniflorin
AUC0–∞ (μg·h/mL)
124.62 ± 36.91
1540.43 ± 548.96**
C
max (μg/mL)
1.26 ± 0.23
6.03 ± 2.45*
t
max (min)
45.00 ± 5.00
77.30 ± 17.50*
t
1
/
2 (min)
19.58 ± 9.01
53.78 ± 22.17***
Cl
B (mL/kg/min)
1301.83 ± 429.03
110.44 ± 45.61*
V
d (mL/kg)
102044.14 ± 46608.43
16064.25 ± 17189.33***
MRT (min)
133.12 ± 38.63
224.07 ± 26.62*
n = 6, mean ± SD; *P < 0.01, **P < 0.001, ***P < 0.05.Sinomenine at 16 and 136μM concentrations could significantly enhance the absorption of paeoniflorin (20 μM) by 1.5- and 2.5-fold, respectively, and subsequently improve the bioavailability of paeoniflorin in rats. The mechanism underlying the improvement of paeoniflorin’s bioavailability was proposed that sinomenine could decrease the efflux transport of paeoniflorin by P-glycoprotein [202].


## 4.13. Genistein

Genistein is an isoflavone found in a number of dietary plants like soybean (Glycine max) and kudzu (Pueraria lobata) and has been studied for a number of potential health effects including anticancer and anti-inflammatory activity [203]. It is a well-known phytoestrogen [204].


### 4.13.1. Genistein and Paclitaxel

The effect of orally administered genistein on the pharmacokinetics of paclitaxel administered through oral and intravenous route in rats was studied. A single dose of paclitaxel was administered orally (30 mg/kg) or intravenous route (3 mg/kg) alone or 30 min after oral administration of genistein (3.3 mg/kg or 10 mg/kg). The presence of 10 mg/kg genistein significantly (P<0.05) increased the AUC (54.7%) of orally administered paclitaxel, which was due to the significantly (P<0.05) decreased CLF of paclitaxel (35.2%). Genistein also increased Cmax of paclitaxel significantly (P<0.05 by 3.3 mg/kg, 66.8%; P<0.01 by 10 mg/kg, 91.8%). Consequently, the AB of paclitaxel in the presence of genistein was 0.020–0.025, which was elevated more than the control group (0.016); the RB of orally administered paclitaxel was increased from 1.26 to 1.55-fold. 10 mg/kg genistein also significantly (P<0.05) increased the AUC (40.5%) and reduced the CLB (30%) of intravenously administered paclitaxel. The presence of genistein improved the systemic exposure of paclitaxel in this study [205].


### 4.13.2.  Genistein and Epigallocatechin Gallate

Cotreatment of HT-29 human colon cancer cells with genistein increased cytosolic EGCG by 2-5-fold compared with treatment with EGCG only. Intragastric coadministration of EGCG (75 mg/kg) and genistein (200 mg/kg) to CF-1 mice resulted in an increase int1/2 (148.7±16.4 versus 111.5±23.4 min) and AUC (183.9±20.2 versus 125.8±26.4 mg/mL at 3 min) of EGCG. Cotreatment with genistein also increased the Cmax, 6 h exposure AUC, and t1/2 of EGCG in the small intestine by 2.0-, 4.7-, and 1.4-fold, respectively, compared with mice treated with EGCG only. This study demonstrates that genistein can enhance EGCG bioavailability [206].


## 4.13.1. Genistein and Paclitaxel

The effect of orally administered genistein on the pharmacokinetics of paclitaxel administered through oral and intravenous route in rats was studied. A single dose of paclitaxel was administered orally (30 mg/kg) or intravenous route (3 mg/kg) alone or 30 min after oral administration of genistein (3.3 mg/kg or 10 mg/kg). The presence of 10 mg/kg genistein significantly (P<0.05) increased the AUC (54.7%) of orally administered paclitaxel, which was due to the significantly (P<0.05) decreased CLF of paclitaxel (35.2%). Genistein also increased Cmax of paclitaxel significantly (P<0.05 by 3.3 mg/kg, 66.8%; P<0.01 by 10 mg/kg, 91.8%). Consequently, the AB of paclitaxel in the presence of genistein was 0.020–0.025, which was elevated more than the control group (0.016); the RB of orally administered paclitaxel was increased from 1.26 to 1.55-fold. 10 mg/kg genistein also significantly (P<0.05) increased the AUC (40.5%) and reduced the CLB (30%) of intravenously administered paclitaxel. The presence of genistein improved the systemic exposure of paclitaxel in this study [205].


## 4.13.2.  Genistein and Epigallocatechin Gallate

Cotreatment of HT-29 human colon cancer cells with genistein increased cytosolic EGCG by 2-5-fold compared with treatment with EGCG only. Intragastric coadministration of EGCG (75 mg/kg) and genistein (200 mg/kg) to CF-1 mice resulted in an increase int1/2 (148.7±16.4 versus 111.5±23.4 min) and AUC (183.9±20.2 versus 125.8±26.4 mg/mL at 3 min) of EGCG. Cotreatment with genistein also increased the Cmax, 6 h exposure AUC, and t1/2 of EGCG in the small intestine by 2.0-, 4.7-, and 1.4-fold, respectively, compared with mice treated with EGCG only. This study demonstrates that genistein can enhance EGCG bioavailability [206].


## 4.14.Ammannia multiflora

The methanolic extract ofAmmannia multiflora (Lythraceae) showed significant bioenhancing activity with the antibiotic nalidixic acid. A. multiflora contains a novel compound ammaniol along with other compounds. The methanolic extract of Ammannia multiflora bioenhancing activity in combination with nalidixic acid against the two strains, CA8000 and DH5α of Escherichia coli. The results showed that the methanolic extract of A. multiflora possessed significant bioenhancing activity and reduced the dose of nalidixic acid fourfold. The methanolic extract of Ammannia multiflora was also tested for antimycobacterial activity against Mycobacterium H37Rv and was found to show moderate activity (MIC 25 μg/mL) against this pathogen [207].


## 4.15. Capsaicin

Capsaicin is the active component of chili peppers (Capsicum annum). It is an irritant for mammals, including humans, and produces a sensation of burning in any tissue with which it comes into contact. Cruz et al. [208] reported that Capsicum annum reduces bioavailability of aspirin after oral administration in rats. Lopez et al. [209] have shown that capsaicin has little or no impact on bioavailability of ciprofloxacin.Absorption and bioavailability of theophylline from a sustained release gelatin capsule were investigated in 10 male rabbits after oral administration (20 mg/kg), with and without a ground capsicum fruit suspension. Comparison of pharmacokinetic parameters showed that the concomitant absorption of capsicum increases AUC from86.06±9.78 mg·h/L to 138.32±17.27 mg·h/L, P<0.001, Cmax from 6.65±0.76 to 8.78±0.98 mg/L, P<0.01, and MRT from 14.94±2.97 h to 20.98±5.75 h, P<0.001. A second administration of the capsicum suspension, 11 hours after dosing, produced a new rise of theophylline plasma levels in every rabbit. This indicated that due to action of capsaicin bioavailability of theophylline was enhanced [210].


## 5. Other Bioenhancers

### 5.1. Quercetin

Quercetin is a plant-derived flavonoid found in fruits, vegetables, leaves, and grains. Quercetin has exhibited activities including antioxidant, radical scavenging, anti-inflammatory, antiatherosclerotic, anticancer, and antiviral effects [211]. Quercetin is an inhibitor of CYP3A4 and a modulator of P-glycoprotein [212–215]. It has been shown to decrease bioavailability of cyclosporin in pigs and rats [212]. Wang et al. [216] reported that coadministration of quercetin with digoxin leads to lethal effects in pigs.


#### 5.1.1. Quercetin and Paclitaxel

The effect of quercetin on the bioavailability of paclitaxel was studied after oral administration in rats. Paclitaxel (40 mg/kg) and prodrug (280 mg/kg, 40 mg/kg as the paclitaxel) were administered orally to rats pretreated with quercetin (2, 10, 20 mg/kg). The pharmacokinetic parameters shown in Table29 indicated that quercetin increases bioavailability of paclitaxel in rats [217].Table 29
Pharmacokinetic parameters of paclitaxel (40 mg/kg) and in combination with pretreated quercetin rats after oral administration [218].
Parameters
Paclitaxel control
Quercetin pretreatment
2 mg/kg
10 mg/kg
20 mg/kg
3 days, 10 mg/kg
3 days, 20 mg/kg
AUC (ng·h/mL)
1605 ± 409
2835 ± 721*
4205 ± 1103**
4978 ± 1211**
5123 ± 1263**
5301 ± 1328**
C
max (ng/mL)
104 ± 27
161 ± 31*
248 ± 63**
279 ± 71**
288 ± 74**
299 ± 76**
t
max (h)
2.0 ± 0.6
1.6 ± 0.5
1.5 ± 0.4
1.5 ± 0.5
1.5 ± 0.4
1.5 ± 0.4
t
1
/
2 (h)
9.9 ± 2.5
13.9 ± 3.5
16.6 ± 4.4*
17.5 ± 4.5*
17.6 ± 4.6*
17.9 ± 4.7*
MRT (h)
15 ± 3.8
22 ± 5.6
25 ± 6.4*
26 ± 6.5*
26 ± 6.4*
26 ± 6.5*
AB (%)
2.0
3.5*
5.3**
6.2**
6.4**
6.6**
RB (%)
100
176
261
309
318
329
n = 8, mean ± SD; *P < 0.05; **P < 0.01, significant difference compared to control.


#### 5.1.2. Quercetin and Verapamil

Pharmacokinetic parameters of verapamil and norverapamil were determined after the oral administration of verapamil (10 mg/kg) to rabbits in the presence and absence of quercetin (5.0 and 15 mg/kg). While coadministration of quercetin concurrently was not effective to enhance the oral exposure of verapamil, pretreatment of quercetin 30 min before verapamil administration significantly altered the pharmacokinetics of verapamil. Compared with the control group, theCmax and AUC of verapamil increased approximately 2-fold in the rabbits pretreated with 15 mg/kg quercetin. There was no significant change in tmax and t1/2 of verapamil in the presence of quercetin. Consequently, absolute and relative bioavailability values of verapamil in the rabbits pretreated with quercetin were significantly higher (P<0.05) than those from the control group. In conclusion, pretreatment of quercetin significantly enhanced the oral exposure of verapamil [218].


#### 5.1.3. Quercetin and Diltiazem

The effect of quercetin (2, 10, 20 mg/kg) pretreatment on the bioavailability of diltiazem (15 mg/kg) was studied in rabbits after oral administration. The plasma concentrations of diltiazem in the rabbits pretreated with quercetin were increased significantly (P<0.05, at 2 mg/kg; P<0.01, at 10 and 20 mg/kg) compared with the control, but the plasma concentrations of diltiazem coadministered with quercetin were not significant. The AUC and Cmax of the diltiazem in the rabbits pretreated with quercetin were significantly higher (P<0.05, at 2 mg/kg; P<0.01, at 10 and 20 mg/kg) than the control. The AB of diltiazem in the rabbits pretreated with quercetin was significantly (P<0.05 at 2 mg/kg, P<0.01 at 10 and 20 mg/kg) higher (9.10–12.81%) than the control (4.64%). The bioavailability of diltiazem in the rabbits pretreated with quercetin is increased significantly compared with the control, but not in the rabbits coadministered with quercetin [213].


#### 5.1.4. Quercetin and Tamoxifen

The pharmacokinetic parameters of tamoxifen in plasma were determined after oral administration of tamoxifen (10 mg/kg) with or without quercetin (2.5, 7.5 and 15 mg/kg). The coadministration of quercetin (2.5 and 7.5 mg/kg) significantly (P<0.05) increased the Ka, Cmax, and AUC of tamoxifen. The AB of tamoxifen with 2.5 and 7.5 mg/kg quercetin ranged from 18.0 to 24.1%, which was significantly higher than the control group, 15.0% (P<0.05). The RB of tamoxifen coadministered with quercetin was 1.20–1.61 times higher than the control group. The coadministration of quercetin caused no significant changes in the terminal t1/2 and tmax of tamoxifen. The enhanced bioavailability of tamoxifen as a result of its coadministration with quercetin might be due to the effect of quercetin promoting the intestinal absorption and reducing the first-pass metabolism of tamoxifen [214].


#### 5.1.5. Quercetin and Fexofenadine

Short-term effect of quercetin on the pharmacokinetics of fexofenadine was studied in 12 healthy volunteers. Subjects were treated daily for 7 days with 500 mg quercetin or placebo 3 times a day. On day 7, a single dose of 60 mg fexofenadine was administered orally. Effects on AUC,Cmax, t1/2, Kel, and ClR are shown in Table 30 after administration of fexofenadine and in combination with quercetin. The results showed that short-term use of quercetin elevated the plasma concentrations of fexofenadine in humans [219].Table 30
Pharmacokinetic parameters of fexofenadine (60 mg) and in combination quercetin (500) mg after a single-dose administration [50].
Parameters
Fexofenadine
Fexofenadine + quercetin
AUC0–∞ (ng·h/mL)
2,075.5 ± 461.7
3,227.1 ± 665.9
C
max (ng/mL)
295.3 ± 135.4
480.3 ± 163.7
t
max (h)
2.0 (0.5–5)
2 (1.5–3)
K
el
(/h)
0.16 ± 0.02
0.16 ± 0.05
t
1
/
2 (h)
4.5 ± 0.8
4.7 ± 1.5
Cl
R (L/h)
4.72 ± 1.13
4.29 ± 1.40
Data are expressed as mean ± SD except fortmax, which is expressed as median (range).


#### 5.1.6. Quercetin and Etoposide

The effect of quercetin on the pharmacokinetics of etoposide was studied in rats. Etoposide was administered to rats orally (9 mg/kg) or intravenous (3 mg/kg) without or with quercetin (1, 5, or 15 mg/kg). The plasma concentration of etoposide was determined by HPLC with fluorescence detector. In the presence of quercetin, the pharmacokinetic parameters of etoposide were significantly altered in the oral group, but not in the intravenous group. The presence of quercetin significantly (5 mg/kg,P<0.05; 15 mg/kg, P<0.01) increased the AUC of orally administered etoposide from 43.0–53.2%. The presence of 5 or 15 mg/kg of quercetin significantly (P<0.05) decreased the CLB of oral etoposide. Consequently, compared to the control group (8.87%), the presence of quercetin significantly (5 mg/kg, P<0.05; 15 mg/kg, P<0.01) increased the AB of etoposide to 12.7 or 13.6%. The results from Table 31 indicated that oral bioavailability of etoposide was enhanced by quercetin [220].Table 31
Pharmacokinetic parameters of etoposide (9 mg/kg) and in combination with quercetin after oral administration in rats [220].
Parameters
Etoposide control
Quercetin + etoposide
1 mg/kg
5 mg/kg
15 mg/kg
AUC (ng·h/mL)
1226 ± 154
1419 ± 222
1753 ± 315*
1878 ± 364**
C
max (ng/mL)
484 ± 74.7
455 ± 80.5
586 ± 89.5*
673 ± 93.3*
Cl
B (mL/kg/h)
8265 ± 1566
7178 ± 1391
5980 ± 1292*
5481 ± 1167*
t
max (h)
0.500 ± 0.158
0.667 ± 0.129
0.693 ± 0.154
0.708 ± 0.188
K
el (/h)
0.255 ± 0.031
0.230 ± 0.027
0.225 ± 0.025
0.221 ± 0.018
t
1
/
2 (h)
2.75 ± 0.32
3.05 ± 0.37
3.11 ± 0.39
3.16 ± 0.41
AB (%)
8.87 ± 1.33
10.3 ± 1.55
12.7 ± 1.96*
13.6 ± 2.24**
RB (%)
100
116
143
153
n = 6, mean ± SD; *P < 0.05, **P < 0.01 compared to control.


#### 5.1.7. Quercetin and Epigallocatechin Gallate

Epigallocatechin gallate (EGCG) is a main anticancer component in green tea. The pharmacokinetic parameters after oral administration of green tea extract (GTE) and GTE + quercetin (Q). In rat, supplementations of GTE and GTE + Q raised the plasmaCmax were 55.29±1.70 and 94.44±1.59 ng/mL, respectively. The corresponding t1/2 elimination was 2.04±0.2 h and 2.28±0.049 h. The AUC0-24h was 510.16±9.88 ng·h/mL and 794.08±15.27 ng·h/mL (P≤0.05), respectively. The results showed that quercetin increased bioavailability of EGCG in rats [221].


#### 5.1.8. Quercetin and Doxorubicin

The pharmacokinetic parameters of doxorubicin were determined in rats after oral (50 mg/kg) or intravenous (10 mg/kg) administration in the presence and absence of quercetin (0.6, 3 or 15 mg/kg). Compared to control, quercetin significantly increased the AUC andCmax of oral doxorubicin, while there was no significant change in tmax and t1/2 of doxorubicin. Consequently, the AB of doxorubicin was increased by quercetin compared to control, and the RB of oral doxorubicin was increased by 1.32–2.36-fold (Table 32). In contrast, the pharmacokinetics of intravenous doxorubicin was not affected by quercetin [215].Table 32
Pharmacokinetic parameters of doxorubicin (50 mg/kg) and in the presence or absence (control) of quercetin (0.6, 3, and 15 mg/kg) after oral administration [215].
Parameters
Doxorubicin (control)
Doxorubicin + quercetin
0.6 mg/kg
3 mg/kg
15 mg/kg
AUC0–∞ (ng·h/mL)
186 ± 44.6
244 ± 63.2*
344 ± 98.6**
439 ± 107.3**
C
max (ng/mL)
20.2 ± 5.13
27.3 ± 6.42*
38.0 ± 9.28*
45.6 ± 11.16**
t
max (h)
0.25
0.25
0.25
0.25
V
ss (L/min)
6.54 ± 1.45
5.06 ± 1.13
2.88 ± 0.64*
2.23 ± 0.52*
t
1
/
2 (h)
13.5 ± 3.32
13.7 ± 3.41
13.8 ± 3.51
13.9 ± 3.82
AB (%)
3.04 ± 0.74
4.01 ± 0.94*
5.58 ± 1.32**
7.12 ± 1.71**
RB (%)
100
132
185
236
n = 7, mean ± SD; *P < 0.05, **P < 0.01 significant difference compared to control.Park et al. [223] reported that quercetin did not affect the in vivo pharmacokinetics of intravenously administered doxorubicin.


### 5.2. Naringin

Naringin is the major flavonoid glycoside found in grapefruit, apples, onions, and tea [224]. Naringin exerts a variety of pharmacological effects such as antioxidant activity, antiulcer activity, antiallergic activity and anticancer activity [211], and blood lipid lowering. Naringin has been reported as a CYP3A4 inhibitor [225, 226] as well as a P-glycoprotein modulator [226, 227]. Park et al. [223] reported that naringin did not affect the in vivo pharmacokinetics of intravenously administered doxorubicin.


#### 5.2.1. Naringin and Diltiazem

Pharmacokinetic parameters of diltiazem were determined in rats following an oral administration of diltiazem (15 mg/kg) to rats in the presence and absence of naringin (5 and 15 mg/kg). Compared to the control given diltiazem alone, theCmax and AUC of diltiazem increased by 2-fold in rats pretreated with naringin, while there was no significant change in tmax and terminal t1/2 of diltiazem. Consequently, AB and RB values of diltiazem in the presence of naringin were significantly higher (P<0.05) than those from the control group. Metabolite-parent AUC ratio in the presence of naringin decreased by 30% compared to the control group, implying that naringin could be effective to inhibit the metabolism of diltiazem. In conclusion, the concomitant use of naringin significantly enhanced the oral exposure of diltiazem in rats [228].


#### 5.2.2. Naringin and Paclitaxel

The effect of oral naringin on the pharmacokinetics of intravenous paclitaxel was studied in rats. Oral naringin (3.3 and 10 mg/kg) was pretreated 30 min before intravenous (3 mg/kg) administration of paclitaxel. After intravenous administration of paclitaxel, the AUC was significantly greater (40.8% and 49.1% for naringin doses of 3.3 and 10 mg/kg, resp.), andClB was significantly slower (29.0% and 33.0% decrease, resp.) than controls. The significantly greater AUC could be due mainly to an inhibition of metabolism of paclitaxel via CYP3A1/2 by oral naringin. The inhibition of hepatic P-glycoprotein by oral naringin could also contribute to the significantly greater AUC of intravenous paclitaxel by oral naringin [229].


#### 5.2.3. Naringin and Verapamil

The effect of naringin on the pharmacokinetics of verapamil was studied in rabbits. The pharmacokinetic parameters of verapamil were determined after administering verapamil (9 mg/kg) orally to rabbits in the pretreated with naringin (1.5, 7.5, and 15 mg/kg). Naringin pretreatment significantly altered the pharmacokinetic parameters of verapamil. Compared with the control group (given verapamil alone), theKa, Cmax, and AUC of verapamil were significantly increased in the pretreatment of naringin. However, there were no significant change in tmax and t1/2 of verapamil. Consequently, pretreatment of naringin significantly increased the AB of verapamil significantly in a dose-dependent manner and elevated the RB of verapamil by 1.26–1.69-fold (Table 33). In conclusion, pretreatment of naringin enhanced the oral bioavailability of verapamil [222].Table 33
Pharmacokinetic parameters of verapamil (9 mg/kg) and in combination with naringin pretreated rabbits after oral administration [222].
Parameters
Verapamil control
Naringin pretreatment
1.5 mg/kg
7.5 mg/kg
15 mg/kg
AUC (ng·h/mL)
291 ± 75.7
370 ± 96.1*
445 ± 1025**
494 ± 142**
C
max (ng/mL)
55.3 ± 14.4
66.5 ± 17.3
86.9 ± 53.3**
92.6 ± 54.5**
t
max (h)
0.25 ± 0.07
0.25 ± 0.08
0.25 ± 0.06
0.25 ± 0.08
K
a(/h)
3.8 ± 0.99
5.1 ± 1.30
6.1 ± 1.59*
6.8 ± 1.72*
t
1
/
2 (h)
12.0 ± 3.12
13.4 ± 3.46
13.6 ± 3.51
13.9 ± 3.61
AB (%)
8.8 ± 2.3
11.2 ± 2.8*
13.5 ± 3.2**
15.0 ± 3.4**
RB (%)
100
126
153
169
n = 6, mean ± SD; *P < 0.05, **P < 0.01, significant difference compared to control.


### 5.3. Capmul

Capmul is a glyceryl caprate produced from edible fats and oils. It is commonly used in lip products. Cho et al. [230] reported that capmul MCM C10 enhanced the bioavailability of ceftriaxone by 55–79% in rats.


### 5.4. Cow Urine Distillate

Cow urine distillate is more effective as bioenhancer than cow urine, to increase the effectiveness of antimicrobial, antifungal, and anticancer drugs [231].Cow urine has antitoxic activity against the cadmium chloride toxicity and it can be used as a bioenhancer of zinc. Mature male mice exposed to cadmium chloride only showed 0% fertility rate. However, the animals exposed to cadmium chloride + cow urine distillate + zinc sulfate showed 90% fertility rate with 100% viability and lactation indices. Fertility index was also found to be 88% in group treated with cadmium chloride + cow urine distillate. Thus, these results indicate that cow urine distillate works as an antitoxic against the cadmium chloride toxicity and it can be used as a bioenhancer of zinc [232].Cow urine distillate increased the activity of rifampicin by about 5–7 times againstEscherichia coli and 3–11 times against Gram-positive bacteria. It probably acts by enhancing the transport of antibiotics across the membrane of gastrointestinal tract. The enhancement in transport is approximately 2–7 times [109].Cow urine distillate enhanced the gonadotropin releasing hormone conjugate on the reproductive hormones and estrous cycle of female mice [233]. Cow urine distillate significantly enhanced the effect of gonadotropin releasing hormone on the gonadosomatic indices, sperm motility, sperm count, and sperm morphology, especially in 90- and 120-day-treated groups (P<0.05) in male mice.Cow urine distillate enhanced these effects because of its immunomodulatory properties [234].


## 5.1. Quercetin

Quercetin is a plant-derived flavonoid found in fruits, vegetables, leaves, and grains. Quercetin has exhibited activities including antioxidant, radical scavenging, anti-inflammatory, antiatherosclerotic, anticancer, and antiviral effects [211]. Quercetin is an inhibitor of CYP3A4 and a modulator of P-glycoprotein [212–215]. It has been shown to decrease bioavailability of cyclosporin in pigs and rats [212]. Wang et al. [216] reported that coadministration of quercetin with digoxin leads to lethal effects in pigs.


### 5.1.1. Quercetin and Paclitaxel

The effect of quercetin on the bioavailability of paclitaxel was studied after oral administration in rats. Paclitaxel (40 mg/kg) and prodrug (280 mg/kg, 40 mg/kg as the paclitaxel) were administered orally to rats pretreated with quercetin (2, 10, 20 mg/kg). The pharmacokinetic parameters shown in Table29 indicated that quercetin increases bioavailability of paclitaxel in rats [217].Table 29
Pharmacokinetic parameters of paclitaxel (40 mg/kg) and in combination with pretreated quercetin rats after oral administration [218].
Parameters
Paclitaxel control
Quercetin pretreatment
2 mg/kg
10 mg/kg
20 mg/kg
3 days, 10 mg/kg
3 days, 20 mg/kg
AUC (ng·h/mL)
1605 ± 409
2835 ± 721*
4205 ± 1103**
4978 ± 1211**
5123 ± 1263**
5301 ± 1328**
C
max (ng/mL)
104 ± 27
161 ± 31*
248 ± 63**
279 ± 71**
288 ± 74**
299 ± 76**
t
max (h)
2.0 ± 0.6
1.6 ± 0.5
1.5 ± 0.4
1.5 ± 0.5
1.5 ± 0.4
1.5 ± 0.4
t
1
/
2 (h)
9.9 ± 2.5
13.9 ± 3.5
16.6 ± 4.4*
17.5 ± 4.5*
17.6 ± 4.6*
17.9 ± 4.7*
MRT (h)
15 ± 3.8
22 ± 5.6
25 ± 6.4*
26 ± 6.5*
26 ± 6.4*
26 ± 6.5*
AB (%)
2.0
3.5*
5.3**
6.2**
6.4**
6.6**
RB (%)
100
176
261
309
318
329
n = 8, mean ± SD; *P < 0.05; **P < 0.01, significant difference compared to control.


### 5.1.2. Quercetin and Verapamil

Pharmacokinetic parameters of verapamil and norverapamil were determined after the oral administration of verapamil (10 mg/kg) to rabbits in the presence and absence of quercetin (5.0 and 15 mg/kg). While coadministration of quercetin concurrently was not effective to enhance the oral exposure of verapamil, pretreatment of quercetin 30 min before verapamil administration significantly altered the pharmacokinetics of verapamil. Compared with the control group, theCmax and AUC of verapamil increased approximately 2-fold in the rabbits pretreated with 15 mg/kg quercetin. There was no significant change in tmax and t1/2 of verapamil in the presence of quercetin. Consequently, absolute and relative bioavailability values of verapamil in the rabbits pretreated with quercetin were significantly higher (P<0.05) than those from the control group. In conclusion, pretreatment of quercetin significantly enhanced the oral exposure of verapamil [218].


### 5.1.3. Quercetin and Diltiazem

The effect of quercetin (2, 10, 20 mg/kg) pretreatment on the bioavailability of diltiazem (15 mg/kg) was studied in rabbits after oral administration. The plasma concentrations of diltiazem in the rabbits pretreated with quercetin were increased significantly (P<0.05, at 2 mg/kg; P<0.01, at 10 and 20 mg/kg) compared with the control, but the plasma concentrations of diltiazem coadministered with quercetin were not significant. The AUC and Cmax of the diltiazem in the rabbits pretreated with quercetin were significantly higher (P<0.05, at 2 mg/kg; P<0.01, at 10 and 20 mg/kg) than the control. The AB of diltiazem in the rabbits pretreated with quercetin was significantly (P<0.05 at 2 mg/kg, P<0.01 at 10 and 20 mg/kg) higher (9.10–12.81%) than the control (4.64%). The bioavailability of diltiazem in the rabbits pretreated with quercetin is increased significantly compared with the control, but not in the rabbits coadministered with quercetin [213].


### 5.1.4. Quercetin and Tamoxifen

The pharmacokinetic parameters of tamoxifen in plasma were determined after oral administration of tamoxifen (10 mg/kg) with or without quercetin (2.5, 7.5 and 15 mg/kg). The coadministration of quercetin (2.5 and 7.5 mg/kg) significantly (P<0.05) increased the Ka, Cmax, and AUC of tamoxifen. The AB of tamoxifen with 2.5 and 7.5 mg/kg quercetin ranged from 18.0 to 24.1%, which was significantly higher than the control group, 15.0% (P<0.05). The RB of tamoxifen coadministered with quercetin was 1.20–1.61 times higher than the control group. The coadministration of quercetin caused no significant changes in the terminal t1/2 and tmax of tamoxifen. The enhanced bioavailability of tamoxifen as a result of its coadministration with quercetin might be due to the effect of quercetin promoting the intestinal absorption and reducing the first-pass metabolism of tamoxifen [214].


### 5.1.5. Quercetin and Fexofenadine

Short-term effect of quercetin on the pharmacokinetics of fexofenadine was studied in 12 healthy volunteers. Subjects were treated daily for 7 days with 500 mg quercetin or placebo 3 times a day. On day 7, a single dose of 60 mg fexofenadine was administered orally. Effects on AUC,Cmax, t1/2, Kel, and ClR are shown in Table 30 after administration of fexofenadine and in combination with quercetin. The results showed that short-term use of quercetin elevated the plasma concentrations of fexofenadine in humans [219].Table 30
Pharmacokinetic parameters of fexofenadine (60 mg) and in combination quercetin (500) mg after a single-dose administration [50].
Parameters
Fexofenadine
Fexofenadine + quercetin
AUC0–∞ (ng·h/mL)
2,075.5 ± 461.7
3,227.1 ± 665.9
C
max (ng/mL)
295.3 ± 135.4
480.3 ± 163.7
t
max (h)
2.0 (0.5–5)
2 (1.5–3)
K
el
(/h)
0.16 ± 0.02
0.16 ± 0.05
t
1
/
2 (h)
4.5 ± 0.8
4.7 ± 1.5
Cl
R (L/h)
4.72 ± 1.13
4.29 ± 1.40
Data are expressed as mean ± SD except fortmax, which is expressed as median (range).


### 5.1.6. Quercetin and Etoposide

The effect of quercetin on the pharmacokinetics of etoposide was studied in rats. Etoposide was administered to rats orally (9 mg/kg) or intravenous (3 mg/kg) without or with quercetin (1, 5, or 15 mg/kg). The plasma concentration of etoposide was determined by HPLC with fluorescence detector. In the presence of quercetin, the pharmacokinetic parameters of etoposide were significantly altered in the oral group, but not in the intravenous group. The presence of quercetin significantly (5 mg/kg,P<0.05; 15 mg/kg, P<0.01) increased the AUC of orally administered etoposide from 43.0–53.2%. The presence of 5 or 15 mg/kg of quercetin significantly (P<0.05) decreased the CLB of oral etoposide. Consequently, compared to the control group (8.87%), the presence of quercetin significantly (5 mg/kg, P<0.05; 15 mg/kg, P<0.01) increased the AB of etoposide to 12.7 or 13.6%. The results from Table 31 indicated that oral bioavailability of etoposide was enhanced by quercetin [220].Table 31
Pharmacokinetic parameters of etoposide (9 mg/kg) and in combination with quercetin after oral administration in rats [220].
Parameters
Etoposide control
Quercetin + etoposide
1 mg/kg
5 mg/kg
15 mg/kg
AUC (ng·h/mL)
1226 ± 154
1419 ± 222
1753 ± 315*
1878 ± 364**
C
max (ng/mL)
484 ± 74.7
455 ± 80.5
586 ± 89.5*
673 ± 93.3*
Cl
B (mL/kg/h)
8265 ± 1566
7178 ± 1391
5980 ± 1292*
5481 ± 1167*
t
max (h)
0.500 ± 0.158
0.667 ± 0.129
0.693 ± 0.154
0.708 ± 0.188
K
el (/h)
0.255 ± 0.031
0.230 ± 0.027
0.225 ± 0.025
0.221 ± 0.018
t
1
/
2 (h)
2.75 ± 0.32
3.05 ± 0.37
3.11 ± 0.39
3.16 ± 0.41
AB (%)
8.87 ± 1.33
10.3 ± 1.55
12.7 ± 1.96*
13.6 ± 2.24**
RB (%)
100
116
143
153
n = 6, mean ± SD; *P < 0.05, **P < 0.01 compared to control.


### 5.1.7. Quercetin and Epigallocatechin Gallate

Epigallocatechin gallate (EGCG) is a main anticancer component in green tea. The pharmacokinetic parameters after oral administration of green tea extract (GTE) and GTE + quercetin (Q). In rat, supplementations of GTE and GTE + Q raised the plasmaCmax were 55.29±1.70 and 94.44±1.59 ng/mL, respectively. The corresponding t1/2 elimination was 2.04±0.2 h and 2.28±0.049 h. The AUC0-24h was 510.16±9.88 ng·h/mL and 794.08±15.27 ng·h/mL (P≤0.05), respectively. The results showed that quercetin increased bioavailability of EGCG in rats [221].


### 5.1.8. Quercetin and Doxorubicin

The pharmacokinetic parameters of doxorubicin were determined in rats after oral (50 mg/kg) or intravenous (10 mg/kg) administration in the presence and absence of quercetin (0.6, 3 or 15 mg/kg). Compared to control, quercetin significantly increased the AUC andCmax of oral doxorubicin, while there was no significant change in tmax and t1/2 of doxorubicin. Consequently, the AB of doxorubicin was increased by quercetin compared to control, and the RB of oral doxorubicin was increased by 1.32–2.36-fold (Table 32). In contrast, the pharmacokinetics of intravenous doxorubicin was not affected by quercetin [215].Table 32
Pharmacokinetic parameters of doxorubicin (50 mg/kg) and in the presence or absence (control) of quercetin (0.6, 3, and 15 mg/kg) after oral administration [215].
Parameters
Doxorubicin (control)
Doxorubicin + quercetin
0.6 mg/kg
3 mg/kg
15 mg/kg
AUC0–∞ (ng·h/mL)
186 ± 44.6
244 ± 63.2*
344 ± 98.6**
439 ± 107.3**
C
max (ng/mL)
20.2 ± 5.13
27.3 ± 6.42*
38.0 ± 9.28*
45.6 ± 11.16**
t
max (h)
0.25
0.25
0.25
0.25
V
ss (L/min)
6.54 ± 1.45
5.06 ± 1.13
2.88 ± 0.64*
2.23 ± 0.52*
t
1
/
2 (h)
13.5 ± 3.32
13.7 ± 3.41
13.8 ± 3.51
13.9 ± 3.82
AB (%)
3.04 ± 0.74
4.01 ± 0.94*
5.58 ± 1.32**
7.12 ± 1.71**
RB (%)
100
132
185
236
n = 7, mean ± SD; *P < 0.05, **P < 0.01 significant difference compared to control.Park et al. [223] reported that quercetin did not affect the in vivo pharmacokinetics of intravenously administered doxorubicin.


## 5.1.1. Quercetin and Paclitaxel

The effect of quercetin on the bioavailability of paclitaxel was studied after oral administration in rats. Paclitaxel (40 mg/kg) and prodrug (280 mg/kg, 40 mg/kg as the paclitaxel) were administered orally to rats pretreated with quercetin (2, 10, 20 mg/kg). The pharmacokinetic parameters shown in Table29 indicated that quercetin increases bioavailability of paclitaxel in rats [217].Table 29
Pharmacokinetic parameters of paclitaxel (40 mg/kg) and in combination with pretreated quercetin rats after oral administration [218].
Parameters
Paclitaxel control
Quercetin pretreatment
2 mg/kg
10 mg/kg
20 mg/kg
3 days, 10 mg/kg
3 days, 20 mg/kg
AUC (ng·h/mL)
1605 ± 409
2835 ± 721*
4205 ± 1103**
4978 ± 1211**
5123 ± 1263**
5301 ± 1328**
C
max (ng/mL)
104 ± 27
161 ± 31*
248 ± 63**
279 ± 71**
288 ± 74**
299 ± 76**
t
max (h)
2.0 ± 0.6
1.6 ± 0.5
1.5 ± 0.4
1.5 ± 0.5
1.5 ± 0.4
1.5 ± 0.4
t
1
/
2 (h)
9.9 ± 2.5
13.9 ± 3.5
16.6 ± 4.4*
17.5 ± 4.5*
17.6 ± 4.6*
17.9 ± 4.7*
MRT (h)
15 ± 3.8
22 ± 5.6
25 ± 6.4*
26 ± 6.5*
26 ± 6.4*
26 ± 6.5*
AB (%)
2.0
3.5*
5.3**
6.2**
6.4**
6.6**
RB (%)
100
176
261
309
318
329
n = 8, mean ± SD; *P < 0.05; **P < 0.01, significant difference compared to control.


## 5.1.2. Quercetin and Verapamil

Pharmacokinetic parameters of verapamil and norverapamil were determined after the oral administration of verapamil (10 mg/kg) to rabbits in the presence and absence of quercetin (5.0 and 15 mg/kg). While coadministration of quercetin concurrently was not effective to enhance the oral exposure of verapamil, pretreatment of quercetin 30 min before verapamil administration significantly altered the pharmacokinetics of verapamil. Compared with the control group, theCmax and AUC of verapamil increased approximately 2-fold in the rabbits pretreated with 15 mg/kg quercetin. There was no significant change in tmax and t1/2 of verapamil in the presence of quercetin. Consequently, absolute and relative bioavailability values of verapamil in the rabbits pretreated with quercetin were significantly higher (P<0.05) than those from the control group. In conclusion, pretreatment of quercetin significantly enhanced the oral exposure of verapamil [218].


## 5.1.3. Quercetin and Diltiazem

The effect of quercetin (2, 10, 20 mg/kg) pretreatment on the bioavailability of diltiazem (15 mg/kg) was studied in rabbits after oral administration. The plasma concentrations of diltiazem in the rabbits pretreated with quercetin were increased significantly (P<0.05, at 2 mg/kg; P<0.01, at 10 and 20 mg/kg) compared with the control, but the plasma concentrations of diltiazem coadministered with quercetin were not significant. The AUC and Cmax of the diltiazem in the rabbits pretreated with quercetin were significantly higher (P<0.05, at 2 mg/kg; P<0.01, at 10 and 20 mg/kg) than the control. The AB of diltiazem in the rabbits pretreated with quercetin was significantly (P<0.05 at 2 mg/kg, P<0.01 at 10 and 20 mg/kg) higher (9.10–12.81%) than the control (4.64%). The bioavailability of diltiazem in the rabbits pretreated with quercetin is increased significantly compared with the control, but not in the rabbits coadministered with quercetin [213].


## 5.1.4. Quercetin and Tamoxifen

The pharmacokinetic parameters of tamoxifen in plasma were determined after oral administration of tamoxifen (10 mg/kg) with or without quercetin (2.5, 7.5 and 15 mg/kg). The coadministration of quercetin (2.5 and 7.5 mg/kg) significantly (P<0.05) increased the Ka, Cmax, and AUC of tamoxifen. The AB of tamoxifen with 2.5 and 7.5 mg/kg quercetin ranged from 18.0 to 24.1%, which was significantly higher than the control group, 15.0% (P<0.05). The RB of tamoxifen coadministered with quercetin was 1.20–1.61 times higher than the control group. The coadministration of quercetin caused no significant changes in the terminal t1/2 and tmax of tamoxifen. The enhanced bioavailability of tamoxifen as a result of its coadministration with quercetin might be due to the effect of quercetin promoting the intestinal absorption and reducing the first-pass metabolism of tamoxifen [214].


## 5.1.5. Quercetin and Fexofenadine

Short-term effect of quercetin on the pharmacokinetics of fexofenadine was studied in 12 healthy volunteers. Subjects were treated daily for 7 days with 500 mg quercetin or placebo 3 times a day. On day 7, a single dose of 60 mg fexofenadine was administered orally. Effects on AUC,Cmax, t1/2, Kel, and ClR are shown in Table 30 after administration of fexofenadine and in combination with quercetin. The results showed that short-term use of quercetin elevated the plasma concentrations of fexofenadine in humans [219].Table 30
Pharmacokinetic parameters of fexofenadine (60 mg) and in combination quercetin (500) mg after a single-dose administration [50].
Parameters
Fexofenadine
Fexofenadine + quercetin
AUC0–∞ (ng·h/mL)
2,075.5 ± 461.7
3,227.1 ± 665.9
C
max (ng/mL)
295.3 ± 135.4
480.3 ± 163.7
t
max (h)
2.0 (0.5–5)
2 (1.5–3)
K
el
(/h)
0.16 ± 0.02
0.16 ± 0.05
t
1
/
2 (h)
4.5 ± 0.8
4.7 ± 1.5
Cl
R (L/h)
4.72 ± 1.13
4.29 ± 1.40
Data are expressed as mean ± SD except fortmax, which is expressed as median (range).


## 5.1.6. Quercetin and Etoposide

The effect of quercetin on the pharmacokinetics of etoposide was studied in rats. Etoposide was administered to rats orally (9 mg/kg) or intravenous (3 mg/kg) without or with quercetin (1, 5, or 15 mg/kg). The plasma concentration of etoposide was determined by HPLC with fluorescence detector. In the presence of quercetin, the pharmacokinetic parameters of etoposide were significantly altered in the oral group, but not in the intravenous group. The presence of quercetin significantly (5 mg/kg,P<0.05; 15 mg/kg, P<0.01) increased the AUC of orally administered etoposide from 43.0–53.2%. The presence of 5 or 15 mg/kg of quercetin significantly (P<0.05) decreased the CLB of oral etoposide. Consequently, compared to the control group (8.87%), the presence of quercetin significantly (5 mg/kg, P<0.05; 15 mg/kg, P<0.01) increased the AB of etoposide to 12.7 or 13.6%. The results from Table 31 indicated that oral bioavailability of etoposide was enhanced by quercetin [220].Table 31
Pharmacokinetic parameters of etoposide (9 mg/kg) and in combination with quercetin after oral administration in rats [220].
Parameters
Etoposide control
Quercetin + etoposide
1 mg/kg
5 mg/kg
15 mg/kg
AUC (ng·h/mL)
1226 ± 154
1419 ± 222
1753 ± 315*
1878 ± 364**
C
max (ng/mL)
484 ± 74.7
455 ± 80.5
586 ± 89.5*
673 ± 93.3*
Cl
B (mL/kg/h)
8265 ± 1566
7178 ± 1391
5980 ± 1292*
5481 ± 1167*
t
max (h)
0.500 ± 0.158
0.667 ± 0.129
0.693 ± 0.154
0.708 ± 0.188
K
el (/h)
0.255 ± 0.031
0.230 ± 0.027
0.225 ± 0.025
0.221 ± 0.018
t
1
/
2 (h)
2.75 ± 0.32
3.05 ± 0.37
3.11 ± 0.39
3.16 ± 0.41
AB (%)
8.87 ± 1.33
10.3 ± 1.55
12.7 ± 1.96*
13.6 ± 2.24**
RB (%)
100
116
143
153
n = 6, mean ± SD; *P < 0.05, **P < 0.01 compared to control.


## 5.1.7. Quercetin and Epigallocatechin Gallate

Epigallocatechin gallate (EGCG) is a main anticancer component in green tea. The pharmacokinetic parameters after oral administration of green tea extract (GTE) and GTE + quercetin (Q). In rat, supplementations of GTE and GTE + Q raised the plasmaCmax were 55.29±1.70 and 94.44±1.59 ng/mL, respectively. The corresponding t1/2 elimination was 2.04±0.2 h and 2.28±0.049 h. The AUC0-24h was 510.16±9.88 ng·h/mL and 794.08±15.27 ng·h/mL (P≤0.05), respectively. The results showed that quercetin increased bioavailability of EGCG in rats [221].


## 5.1.8. Quercetin and Doxorubicin

The pharmacokinetic parameters of doxorubicin were determined in rats after oral (50 mg/kg) or intravenous (10 mg/kg) administration in the presence and absence of quercetin (0.6, 3 or 15 mg/kg). Compared to control, quercetin significantly increased the AUC andCmax of oral doxorubicin, while there was no significant change in tmax and t1/2 of doxorubicin. Consequently, the AB of doxorubicin was increased by quercetin compared to control, and the RB of oral doxorubicin was increased by 1.32–2.36-fold (Table 32). In contrast, the pharmacokinetics of intravenous doxorubicin was not affected by quercetin [215].Table 32
Pharmacokinetic parameters of doxorubicin (50 mg/kg) and in the presence or absence (control) of quercetin (0.6, 3, and 15 mg/kg) after oral administration [215].
Parameters
Doxorubicin (control)
Doxorubicin + quercetin
0.6 mg/kg
3 mg/kg
15 mg/kg
AUC0–∞ (ng·h/mL)
186 ± 44.6
244 ± 63.2*
344 ± 98.6**
439 ± 107.3**
C
max (ng/mL)
20.2 ± 5.13
27.3 ± 6.42*
38.0 ± 9.28*
45.6 ± 11.16**
t
max (h)
0.25
0.25
0.25
0.25
V
ss (L/min)
6.54 ± 1.45
5.06 ± 1.13
2.88 ± 0.64*
2.23 ± 0.52*
t
1
/
2 (h)
13.5 ± 3.32
13.7 ± 3.41
13.8 ± 3.51
13.9 ± 3.82
AB (%)
3.04 ± 0.74
4.01 ± 0.94*
5.58 ± 1.32**
7.12 ± 1.71**
RB (%)
100
132
185
236
n = 7, mean ± SD; *P < 0.05, **P < 0.01 significant difference compared to control.Park et al. [223] reported that quercetin did not affect the in vivo pharmacokinetics of intravenously administered doxorubicin.


## 5.2. Naringin

Naringin is the major flavonoid glycoside found in grapefruit, apples, onions, and tea [224]. Naringin exerts a variety of pharmacological effects such as antioxidant activity, antiulcer activity, antiallergic activity and anticancer activity [211], and blood lipid lowering. Naringin has been reported as a CYP3A4 inhibitor [225, 226] as well as a P-glycoprotein modulator [226, 227]. Park et al. [223] reported that naringin did not affect the in vivo pharmacokinetics of intravenously administered doxorubicin.


### 5.2.1. Naringin and Diltiazem

Pharmacokinetic parameters of diltiazem were determined in rats following an oral administration of diltiazem (15 mg/kg) to rats in the presence and absence of naringin (5 and 15 mg/kg). Compared to the control given diltiazem alone, theCmax and AUC of diltiazem increased by 2-fold in rats pretreated with naringin, while there was no significant change in tmax and terminal t1/2 of diltiazem. Consequently, AB and RB values of diltiazem in the presence of naringin were significantly higher (P<0.05) than those from the control group. Metabolite-parent AUC ratio in the presence of naringin decreased by 30% compared to the control group, implying that naringin could be effective to inhibit the metabolism of diltiazem. In conclusion, the concomitant use of naringin significantly enhanced the oral exposure of diltiazem in rats [228].


### 5.2.2. Naringin and Paclitaxel

The effect of oral naringin on the pharmacokinetics of intravenous paclitaxel was studied in rats. Oral naringin (3.3 and 10 mg/kg) was pretreated 30 min before intravenous (3 mg/kg) administration of paclitaxel. After intravenous administration of paclitaxel, the AUC was significantly greater (40.8% and 49.1% for naringin doses of 3.3 and 10 mg/kg, resp.), andClB was significantly slower (29.0% and 33.0% decrease, resp.) than controls. The significantly greater AUC could be due mainly to an inhibition of metabolism of paclitaxel via CYP3A1/2 by oral naringin. The inhibition of hepatic P-glycoprotein by oral naringin could also contribute to the significantly greater AUC of intravenous paclitaxel by oral naringin [229].


### 5.2.3. Naringin and Verapamil

The effect of naringin on the pharmacokinetics of verapamil was studied in rabbits. The pharmacokinetic parameters of verapamil were determined after administering verapamil (9 mg/kg) orally to rabbits in the pretreated with naringin (1.5, 7.5, and 15 mg/kg). Naringin pretreatment significantly altered the pharmacokinetic parameters of verapamil. Compared with the control group (given verapamil alone), theKa, Cmax, and AUC of verapamil were significantly increased in the pretreatment of naringin. However, there were no significant change in tmax and t1/2 of verapamil. Consequently, pretreatment of naringin significantly increased the AB of verapamil significantly in a dose-dependent manner and elevated the RB of verapamil by 1.26–1.69-fold (Table 33). In conclusion, pretreatment of naringin enhanced the oral bioavailability of verapamil [222].Table 33
Pharmacokinetic parameters of verapamil (9 mg/kg) and in combination with naringin pretreated rabbits after oral administration [222].
Parameters
Verapamil control
Naringin pretreatment
1.5 mg/kg
7.5 mg/kg
15 mg/kg
AUC (ng·h/mL)
291 ± 75.7
370 ± 96.1*
445 ± 1025**
494 ± 142**
C
max (ng/mL)
55.3 ± 14.4
66.5 ± 17.3
86.9 ± 53.3**
92.6 ± 54.5**
t
max (h)
0.25 ± 0.07
0.25 ± 0.08
0.25 ± 0.06
0.25 ± 0.08
K
a(/h)
3.8 ± 0.99
5.1 ± 1.30
6.1 ± 1.59*
6.8 ± 1.72*
t
1
/
2 (h)
12.0 ± 3.12
13.4 ± 3.46
13.6 ± 3.51
13.9 ± 3.61
AB (%)
8.8 ± 2.3
11.2 ± 2.8*
13.5 ± 3.2**
15.0 ± 3.4**
RB (%)
100
126
153
169
n = 6, mean ± SD; *P < 0.05, **P < 0.01, significant difference compared to control.


## 5.2.1. Naringin and Diltiazem

Pharmacokinetic parameters of diltiazem were determined in rats following an oral administration of diltiazem (15 mg/kg) to rats in the presence and absence of naringin (5 and 15 mg/kg). Compared to the control given diltiazem alone, theCmax and AUC of diltiazem increased by 2-fold in rats pretreated with naringin, while there was no significant change in tmax and terminal t1/2 of diltiazem. Consequently, AB and RB values of diltiazem in the presence of naringin were significantly higher (P<0.05) than those from the control group. Metabolite-parent AUC ratio in the presence of naringin decreased by 30% compared to the control group, implying that naringin could be effective to inhibit the metabolism of diltiazem. In conclusion, the concomitant use of naringin significantly enhanced the oral exposure of diltiazem in rats [228].


## 5.2.2. Naringin and Paclitaxel

The effect of oral naringin on the pharmacokinetics of intravenous paclitaxel was studied in rats. Oral naringin (3.3 and 10 mg/kg) was pretreated 30 min before intravenous (3 mg/kg) administration of paclitaxel. After intravenous administration of paclitaxel, the AUC was significantly greater (40.8% and 49.1% for naringin doses of 3.3 and 10 mg/kg, resp.), andClB was significantly slower (29.0% and 33.0% decrease, resp.) than controls. The significantly greater AUC could be due mainly to an inhibition of metabolism of paclitaxel via CYP3A1/2 by oral naringin. The inhibition of hepatic P-glycoprotein by oral naringin could also contribute to the significantly greater AUC of intravenous paclitaxel by oral naringin [229].


## 5.2.3. Naringin and Verapamil

The effect of naringin on the pharmacokinetics of verapamil was studied in rabbits. The pharmacokinetic parameters of verapamil were determined after administering verapamil (9 mg/kg) orally to rabbits in the pretreated with naringin (1.5, 7.5, and 15 mg/kg). Naringin pretreatment significantly altered the pharmacokinetic parameters of verapamil. Compared with the control group (given verapamil alone), theKa, Cmax, and AUC of verapamil were significantly increased in the pretreatment of naringin. However, there were no significant change in tmax and t1/2 of verapamil. Consequently, pretreatment of naringin significantly increased the AB of verapamil significantly in a dose-dependent manner and elevated the RB of verapamil by 1.26–1.69-fold (Table 33). In conclusion, pretreatment of naringin enhanced the oral bioavailability of verapamil [222].Table 33
Pharmacokinetic parameters of verapamil (9 mg/kg) and in combination with naringin pretreated rabbits after oral administration [222].
Parameters
Verapamil control
Naringin pretreatment
1.5 mg/kg
7.5 mg/kg
15 mg/kg
AUC (ng·h/mL)
291 ± 75.7
370 ± 96.1*
445 ± 1025**
494 ± 142**
C
max (ng/mL)
55.3 ± 14.4
66.5 ± 17.3
86.9 ± 53.3**
92.6 ± 54.5**
t
max (h)
0.25 ± 0.07
0.25 ± 0.08
0.25 ± 0.06
0.25 ± 0.08
K
a(/h)
3.8 ± 0.99
5.1 ± 1.30
6.1 ± 1.59*
6.8 ± 1.72*
t
1
/
2 (h)
12.0 ± 3.12
13.4 ± 3.46
13.6 ± 3.51
13.9 ± 3.61
AB (%)
8.8 ± 2.3
11.2 ± 2.8*
13.5 ± 3.2**
15.0 ± 3.4**
RB (%)
100
126
153
169
n = 6, mean ± SD; *P < 0.05, **P < 0.01, significant difference compared to control.


## 5.3. Capmul

Capmul is a glyceryl caprate produced from edible fats and oils. It is commonly used in lip products. Cho et al. [230] reported that capmul MCM C10 enhanced the bioavailability of ceftriaxone by 55–79% in rats.


## 5.4. Cow Urine Distillate

Cow urine distillate is more effective as bioenhancer than cow urine, to increase the effectiveness of antimicrobial, antifungal, and anticancer drugs [231].Cow urine has antitoxic activity against the cadmium chloride toxicity and it can be used as a bioenhancer of zinc. Mature male mice exposed to cadmium chloride only showed 0% fertility rate. However, the animals exposed to cadmium chloride + cow urine distillate + zinc sulfate showed 90% fertility rate with 100% viability and lactation indices. Fertility index was also found to be 88% in group treated with cadmium chloride + cow urine distillate. Thus, these results indicate that cow urine distillate works as an antitoxic against the cadmium chloride toxicity and it can be used as a bioenhancer of zinc [232].Cow urine distillate increased the activity of rifampicin by about 5–7 times againstEscherichia coli and 3–11 times against Gram-positive bacteria. It probably acts by enhancing the transport of antibiotics across the membrane of gastrointestinal tract. The enhancement in transport is approximately 2–7 times [109].Cow urine distillate enhanced the gonadotropin releasing hormone conjugate on the reproductive hormones and estrous cycle of female mice [233]. Cow urine distillate significantly enhanced the effect of gonadotropin releasing hormone on the gonadosomatic indices, sperm motility, sperm count, and sperm morphology, especially in 90- and 120-day-treated groups (P<0.05) in male mice.Cow urine distillate enhanced these effects because of its immunomodulatory properties [234].


## 6. Conclusions

The effective formulation strategy for the optimization of the pharmacokinetic characteristics of dietary components is crucial to improve theirin vivo performance and ultimately maximize their effectiveness as a bioavailability enhancer [235]. The available scientific research on bioenhancers has shown to produce significant enhancing effect on bioavailability when coadministered or pretreated with many drugs and nutraceuticals. These natural compounds include piperine, Zingiber officinale, niaziridin, glycyrrhizin, Cuminum cyminum,Carum carvi, allicin, lysergol, Aloe vera, Stevia rebaudiana, curcumin, sinomenine, genistein, Ammannia multiflora, capsaicin, quercetin, naringin, capmul and cow urine distillate. They reduce the dose, shorten treatment, and thus reduce drug-resistance and drug toxicity or adverse reactions. Due to dose economy, treatment is cost-effective. Bioenhancers are also found to decrease or having no effect or little effect on the bioavailability of some drugs [73, 128, 129].The current paper discussed the enhancing effects of bioenhancers of drugs in animals and humans but these compounds have not been completely explored in experimental animals till date. However, these studies lack information on their exact mechanism of action, toxicity evaluation of extracts, and suitable combinations. Therefore, we have to focus on this area for further research on their active principles, mechanisms of actions, toxicity evaluation, and suitable combinations with other drugs. So we can explore novel principles with high bioenhancing ability and less toxic effects.



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*Source: 637953-2012-09-17.xml*