Special Contribution

Yonago Acta medica 2009;52:1–9

Interactions between Grapefruit Juice andCalcium Channel Antagonists
Masakazu Hayashibara
Division of Pharmacy, Tottori University Hospital, Yonago 683-8504 JapanThe extent of interaction between calcium channel antagonists and grapefruit juice varies
widely among drugs. Coadministration of calcium channel antagonists with grapefruit
juice can elevate the bioavailability of drugs and alter pharmacokinetic parameters of the
drug. A calcium channel antagonist with lower bioavailability is likely to be more affected by grapefruit juice. The area under the concentration-time curve and peak serum concentrations of azelnidipine, efonidipine, felodipine, manidipine, nicardipine, nifedipine,nisoldipine, nitrendipine and verapamil are influenced by grapefruit juice. Conversely,
pharmacokinetic parameters of amlodipine and diltiazem are not affected by grapefruit
juice. The action of grapefruit juice is rapid, and a single exposure to one glass of juice
can usually produce a significant interaction. Furanocoumarins primarily contribute tograpefruit juice-drug interactions in humans. Cytochrome P4503A4 and P-glycoprotein
may act in tandem as a barrier to oral delivery of drugs. The main mechanism for enhanced bioavailability of drugs by grapefruit juice is, presumably, the inhibition of cytochrome P4503A4 in the small intestine and only to a minor extent affected by P-glycoprotein function. There are dose-dependent and time-dependent effects of grapefruit juice
on cytochrome P4503A4. Since biosynthesis of new cytochrome P4503A4 is necessary, theduration of the interaction is consistent with the pharmacological mechanism of interaction; inhibition of enzyme activities by grapefruit juice persists for approximately 3 days.
Key words: calcium channel antagonist; cytochrome P450; grapefruit juice; interaction; pharmacokinetic parameter
Patients are frequently treated with multiple medicines concurrently in order to treat one or more
medical problems with drug therapy. Althoughconcomitant intake of 2 or more drugs can alter
their efficacy, available information regarding
drug activity pertains to each drug separately.
Hence, an interaction is said to take place whenthe effects of one drug are modified by the presence of another drug, food or environmental
chemical agent. For approximately 2 decades, amajor focal point in the area of food-drug interactions has been regarding interactions of grapefruit with several drugs, such as lipid-loweringdrugs and calcium channel antagonists (Bailey

and Dresser, 2004). In an initial report regarding grapefruit juice (GFJ) and drug interactions,investigators observed an interaction between
felodipine and GFJ in a study of felodipine andethanol in which GFJ was used to mask the tasteof ethanol (Bailey et al., 1989). Subsequent studies confirmed that GFJ significantly increased theoral bioavailability of felodipine (Bailey et al.,
1991; Edgar et al., 1992).
Drug concentration at the cellular site ofaction represents the net result of absorption,
distribution and elimination, which is often determined by mechanisms involving the metabolism
or transport of a drug (Bailey and Dresser, 2004).

Abbreviations: AUC, area under the concentration-time curve; Cmax, peak serum concentration; CYP, cytochrome
P450; GFJ, grapefruit juice1M. Hayashibara

Many endogenous compounds, in addition to
drugs, are metabolized in the body by cytochrome
P450 (CYP) enzyme systems through oxidative
biotransformation. The isozyme CYP3A4 is the
predominant form in the human small intestine(Kolars et al., 1992), while a very limited numberof other CYP isoforms are expressed in the small
intestine (Zhang et al., 1999). The location of
CYP3A4 in the small bowel and liver permits aneffect on both presystemic and systemic drug disposition (Dresser et al., 2000b). In most cases, theextent of drug interaction varies markedly amongindividuals; this is likely to be dependent on interindividual differences in CYP3A4 tissue content, pre-existing medical conditions and possiblyage (Dresser et al., 2000b). Clinically important
CYP3A4 inhibitors include itraconazole, ketokonazole, clarithromycin, erythromycin, nefazodone,
ritonavir and GFJ (Dresser et al., 2000b).
There are more than 10 oral calcium channel
antagonists available in Japan. Calcium channel
antagonists are used widely in clinical treatmentof hypertension and angina pectoris. Calcium
channel antagonists are well absorbed from theintestine, and the first-pass metabolism mediatedby CYP3A4 in the liver and intestine is a major
determinant of bioavailability. The coadministration of these drugs with GFJ can markedly elevatebioavailability of drugs and can alter pharmacokinetic parameters of the drug. Although the extent
of interaction between calcium channel antagonists
and GFJ varies widely among individuals, in the
short term this interaction is reproducible within
individuals. A drug with lower bioavailability islikely to be more impacted by GFJ (Fuhr, 1998;
Ohnishi et al., 2006). A calcium channel antagonist with lower bioavailability or higher plasma
protein binding ratio is likely to exhibit a morepotent interaction with GFJ (Ohnishi et al., 2006).
Ohnishi et al. (2006) considered that this information should be useful to avoid adverse drug interactions and to predict the extent of interaction ina clinical situation and during drug development.
Amlodipine and nifedipine have better inherent
oral bioavailability and hence are less affected by

GFJ (Bailey et al., 1991; Josefsson et al., 1996).
Although metabolized in vivo by CYP3A4, thenondihydropyridine calcium channel antagonists
diltiazem and verapamil were not affected by GFJ
in small clinical studies (Zaidenstein et al., 1998).
Amounts of GFJ in the range normally consumed(up to 3 glasses per day) seem to have intestinal
activity only (Garvan and James, 2000).
This short review reveals the effect of GFJ
on pharmacokinetic parameters, such as the peakplasma (or serum) concentration (Cmax) and thearea under the concentration-time curve (AUC),
as well as pharmacodynamic parameters, suchas blood pressure and heart rate, of oral calcium
channel antagonists in humans.

Mechanism of interaction
A food-drug interaction may be defined mainly
as the alteration of absorption and/or metabolism
of a drug by a food component. The underlying
mechanisms can be classified into 2 broad categories. The first is pharmacokinetics, including
alterations in absorption, distribution, metabolism
and excretion; the second is pharmacodynamics,
describing alterations in the drug concentrationeffect relationship (Dresser et al., 2000b). The action of GFJ is rapid and a single exposure to one
glass of juice can usually produce a significant
interaction (Lundahl et al., 1998). There are dosedependent (Lilja et al., 2000) and time-dependent(Lundahl et al., 1995) effects of GFJ on CYP3A4.
Uesawa and Mohri (2008) reported that lipophilicity is an important factor in the strength ofpharmacokinetics of dihydropyridines with GFJ
intake based on the result that logP values indicate significant positive correlations with interaction strength.
CYP enzymes are predominantly expressedin the liver, although they are also present in theextra-hepatic tissues such as the intestinal mucosa.
CYP3A comprises on average 30% of all CYP in
the liver and as much as 70% in small intestineepithelial cells (Kane and Lipsky, 2000). CY2

GFJ-calcium channel antagonist interaction

P3A4 is the most abundantly expressed isoform
and is highly expressed in the intestinal mucosa.
Although the liver was assumed to be the majorsite of grapefruit-drug interactions initially, it isindicated that the interaction may take place during the gastrointestinal absorption phase, basedon the result that the interaction only occurs whendrugs are administered orally, not intravenously(Lundahl et al., 1997). GFJ can inhibit the activity of intestinal CYP3A4, leading to an interaction with drugs during their first passage from theintestinal lumen into systemic circulation (Lown
et al., 1997). Dahan and Altman (2004) reported
that only intestinal CYP3A4 is inhibited by GFJ,
while liver resident CYP3A4 enzymes are not affected. This result is supported by the finding thatinteraction with GFJ markedly elevated the AUC,
while no significant change has been observed inelimination half-life or systemic clearance (Bailey
et al., 1991). The effect of GFJ on felodipine has
been shown to exist at approximately 30% of its
maximum even when the drug was administered
24 h following juice intake (Lundahl et al., 1995).
Since biosynthesis of a new CYP3A4 is necessary,the duration of the interaction is consistent withthe pharmacological mechanism of interaction.
P-glycoprotein, one of the multiple drug
resistance transporters, reduces the fraction of
drug absorbed by carrying the drug from the enterocyte back to the intestinal lumen (Gottesman
et al., 1996). GFJ modifies P-glycoprotein transporter activity. Although there was little data suggesting activation of P-glycoprotein efflux by GFJ(Phang et al., 1993; Soldner et al., 1999), most investigators observed inhibition of transporter activity (Takanaga et al., 1998; Eagling et al., 1999;
Wang et al., 2001; Tian et al., 2002). Inhibitionof P-glycoprotein is a possible mechanism that
increases oral drug bioavailability by reducing intestinal and/or hepatic efflux transport (Bailey andDresser, 2004). Kane and Lipsky (2000) reported
CYP3A4 and P-glycoprotein may act in tandem
as a barrier to the oral delivery of many drugs.
Goosen et al. (2004) reported that bergamottin enhanced the oral bioavailability of felodipine

and may cause a clinically relevant drug interaction in susceptible individuals. Furthermore,
GFJ-drug interactions likely also involve otherfuranocoumarins, possibly acting in combination
by additive or synergistic mechanisms. Kakar
et al. (2004) reported that 6',7'-dihydrobergamottin is an important contributor to the GFJ effect.
Paine et al. (2006) reported that furanocoumarins(bergamottin, 6',7'-dihydrobergamottin and furanocoumarin dimers) are the active ingredients in
GFJ responsible for enhancing systemic exposureof felodipine.
Presumably, the main mechanism for enhanced bioavailability of drugs by GFJ is the inhibition of CYP3A4 in the small intestine (Edwards
et al., 1996; Lown et al., 1997), resulting in a significant reduction of presystemic metabolism, andonly to a minor extent influenced by P-glycoproteinfunction (Dahan and Altman, 2004).

Drug interactions ineach calcium channel antagonist (Table 1)
Dihydropyridines
Amlodipine
Amlodipine has a different pharmacokinetic
profile from other dihydropyridines (Abernethy,
1989; Meredith and Elliott, 1992). Specifically,
amlodipine has a lower hepatic extraction ratio,
hence its higher oral bioavailability, and a latertime to peak plasma concentration in addition to alonger plasma elimination half-life compared withother dihydropyridines. When amlodipine (5 mg)
was coadministered with a glass of GFJ (250 mL),
Cmax was 115% and AUC (0–72 h) was 116%
compared with water administration in healthy
volunteers. There were no significant differencesin blood pressure and heart rate between the 2treatments (Josefsson et al., 1996). The AUC ratioof GFJ (250 mL once daily for 9 days) to water
for amlodipine (10 mg) was 107.8% and the Cmax
ratio was 107.1%. There were no statistically significant treatment effects on blood pressure during3

M. Hayashibara

Table 1. Pharmacokinetic interactions between calcium channel antagonists and GFJ
Calcium
Dose GFJ
channel(mg) (mL)antagonist			

AUC
Cmax
Bio(value relative (value relative availability
to control)
to control)(%)

Dihydropyridine
Amlodipine

Reference

5
250
1.14
1.15
64
10
240
1.08
1.07		
Azelnidipine
8
250
3.28
2.49
NA
Efonidipine
40
250
1.67
1.55
NA
Felodipine
5200, 250
2.51–2.88
2.23–4.00
15
10200, 240
1.72–2.16
2.38–3.25		
						
						
						
Manidipine
40250			
NA(S)-manidipine		
2.37
2.40
(R)-manidipine		
3.03
3.39
Nicardipine
40300			
15–45(+)-nicardipine		
1.43—		
(–)-nicardipine		
1.84—
Nifedipine
10200
1.47–1.58
1.04–1.16
43
20200, 250
1.09–2.02
1.27–2.00		
						
						
Nisoldipine
10
250
4.55
3.06
3.7–8.420250
1.76
3.50 								
Nitrendipine
20150			
5–30(S)-nitrendipine		
2.22
2.01		
(R)-nitrendipine		
2.36
2.15 		

Josefsson et al., 1996
Vincent et al., 2000
Hirashima et al., 2006
Yajima et al., 2003
Bailey et al., 1991
Edgar et al., 1992
Lown et al., 1997
Lundahl et al., 1997, 1998
Dresser et al., 2000a
Uno et al., 2006

Waller et al., 1984
Rashid et al., 1993, 1995
Sigusch et al., 1994
Azuma et al., 1998
Friedel and Sorkin, 1988
Bailey et al., 1993
Azuma et al., 1998
Krol et al., 1987
Mikus et al., 1987
Soons et al., 1989, 1991

Non-dihydropyridine
Diltiazem
120
200, 250
1.10–1.18
1.02–1.14
40–50						
						
Verapamil
120
250			
20(S)-verapamil		
1.36–1.47
1.58–1.70		
(R)-verapamil		
1.28–1.41
1.40–1.54		

Buckley et al., 1990
Sigusch et al., 1994
Christensen et al., 2002
McTavish and Sorkin, 1989
Ho et al., 2000
Fuhr et al., 2002

Guengerich et al., 1991
Uno et al., 2000

AUC, area under the concentration-time curve; Cmax, peak plasma (or serum) concentration; GFJ, grapefruit juice;NA, not available.

amlodipine administration. Vincent et al. (2000)
concluded that once daily GFJ administration
with usual oral doses of amlodipine is unlikely toalter the profile of response in clinical practice.

cause sinus bradycardia in patients and ii) longerlasting pharmacological effects even with a once
daily dose of 8 to 16 mg (Kuramoto et al., 2003).
Concomitant administration of azelnidipine with
GFJ increased the Cmax of azelnidipine by 2.5fold and the AUC by 3.3-fold compared withwater. No serious adverse events were observed
except one subject described mild symptoms ofdrug-related headache and flushing accompaniedwith orthostatic hypotension at 4 h after administration of GFJ (Hirashima et al., 2006).

Azelnidipine
Azelnidipine is an L-type calcium channel antagonist, which is categorized as third generation
type-B (Toyo-oka, 2006). The remarkable characteristics of azelnidipine that differentiate it fromother analogues are i) the lower possibility to4

GFJ-calcium channel antagonist interaction

immediately before felodipine administration resulted in more pronounced hemodynamic effectsof the drug in diastolic blood pressure and heart
rate (Lundahl et al., 1997). Twelve elderly subjects received oral felodipine (5 mg) with 250 mL
of GFJ or water; AUC and Cmax of felodipine
were 2.9- and 4.0-fold greater, respectively, with
GFJ. Systolic and diastolic blood pressures werelower with GFJ in the single-dose study (Dresser
et al., 2000a).

Efonidipine
Efonidipine has longer-lasting pharmacologicaleffects. Cmax and AUC of efonidipine (40 mg) in
20 male volunteers coadministered with GFJ were155% and 167% of those taking efonidipine without GFJ, respectively. There were no significant
differences in the incidence of adverse events between administrations with or without GFJ. The
transitional patterns of blood pressure and heart
rate were very similar between those with GFJand those without (Yajima et al., 2003).

Manidipine
Manidipine has potent and long-lasting activities(Cheer and McClelln, 2001). The pharmacological effects of manidipine enantiomers are known
to be different and the pharmacological potencyof (S)-type has been found to be greater than thatof (R)-type (Kajino et al., 1989). GFJ significantly
increased Cmax and AUC of (S)-manidipine by
2.4- and 2.3-fold, respectively; and Cmax and
AUC of (R)-manidipine increased by 3.4- and
3.0-fold, respectively. There were significant differences in GFJ-mediated percentage increases inCmax and AUC of (S)-manidipine compared withthose of (R)-manidipine. There were no significant differences in pharmacodynamic variables,
arterial blood pressure and heart rate, between the
2 enantiomers (Uno et al., 2006).

Felodipine
Bioavailability of felodipine is low (15%) at a doseof 5 mg per person (Edgar et al., 1992). There aremany reports about interaction between felodipine
and GFJ. Six men with borderline hypertension
received felodipine (5 mg) with 250 mL of water or with 250 mL of GFJ. GFJ increased AUC
and bioavailability by 284% (range 164–469) and
134% (range 108–169), respectively. Diastolicblood pressure was reduced more (–20 versus –11)
and heart rate increased more (22 versus 9) with
GFJ than with water (Bailey et al., 1991). When
felodipine (5 mg) was administered with either
200 mL of water or GFJ in 9 healthy male volunteers, GFJ increased Cmax of felodipine from 6 to
16 nmol/L, and AUC from 23 to 65 nmol/L compared to water. Blood pressure measured in themorning 3 h after dosing with GFJ was 9% lower
compared to control (Edgar et al., 1992). In arandomized cross-over study in 9 volunteers, GFJ
administered 1, 4, 10 or 24 h before and simultaneously with drug administration resulted in a 32–
99% increase in Cmax of felodipine (10 mg), relative to concomitant water and felodipine intake.
The effect on AUC was also significant when GFJ
was ingested up to 10 h before administration of
the drug. Interaction decreased with an increasein time between GFJ and drug intake (Lundahl etal., 1995). Twelve healthy volunteers received 150
mL water or 150 mL of GFJ 15 min prior to oral
felodipine (10 mg) administration. GFJ increased
AUC, Cmax and the absolute bioavailability by
72%, 173% and 112%, respectively. GFJ intake

Nicardipine
Containing a chiral center like other dihydropyridines, nicardipine possesses potent activities(Freedman and Waters, 1987). Bioavailabilityof nicardipine is low (15–45%) at a dose of 10 to
40 mg per person, due to extensive presystemic
elimination (Guengerich et al., 1991). When nicardipine (40 mg) was administered 30 min afteringestion of 300 mL of water or concentrated
GFJ in 6 normal healthy male volunteers, GFJ
increased the mean oral bioavailability of (+)- and(–)-nicardipine, 48.6% and 105.6% respectively,
compared with water intake. AUC was 143%
and 191% compared with water for (+) and (–)
enantiomers, respectively. Compared against water, GFJ did not alter the mean pharmacodynamic
variables assessed in the study except for heart5M. Hayashibara

rates at 1 h and 2 h, following the oral dosing of
racemic nicardipine (Uno et al., 2000). However all of the mean kinetic parameters of bothenantiomers following intravenous dosing of racemic nicardipine did not differ between the GFJ
and water intake. Uno et al. (2000) concluded
that the gut is the major presystemic disposal siteof racemic nicardipine in humans.

tween 90 min to 6 h compared with water. Nisoldipine Cmax was 406% (range 107–836), and
AUC was 198% (range 81–682) compared withwater. Minor effects on supine blood pressureand heart rate were observed, probably because
subjects were normotensive (Bailey et al., 1993).
Eight healthy volunteers received oral nisoldipine(10 mg), and significant increases in Cmax and
AUC were observed when the drug was administered with GFJ and 1 h after subjects ingested GFJcompared with drug administration with water
only. Nisoldipine was also well tolerated in 4 dosing schedules (Azuma et al., 1998). In a clinicalstudy investigating the effect of various schedulesof GFJ intake on nisoldipine pharmacokinetics
and pharmacodynamics with 8 healthy volunteers,
the effect of GFJ decreased time dependently andlasted for at least 3 days after ingestion (Takanaga
et al., 2000). They suggested that it is necessary
to withhold GFJ for at least 3 days before administration of the nisoldipine to prevent GFJ-druginteraction.

Nifedipine
Nifedipine is a lipid-soluble drug which is absorbed completely from the gut but has a low
bioavailability due to extensive presystemic metabolism (Foster et al., 1983; Waller et al., 1984).
Bioavailability of nifedipine was reported as 43%(Waller et al., 1984). Eight healthy volunteers received nifedipine (10 mg) with 200 mL of wateror double strength GFJ; the AUC for nifedipine
with GFJ (320 ng•h/mL) increased significantly
compared with the AUC when nifedipine wasgiven alone (218 ng•h /mL). The Cmax was unchanged by administration of GFJ (Rashid et al.,1993). In another study, 8 healthy volunteers received nifedipine (10 mg) with 200 mL of wateror double strength GFJ both 2 h before and at thetime of dosing; the administration of GFJ resulted
in a significantly increased AUC (191 versus 301
ng•h/mL) and bioavailability (0.63 versus 0.86).
The elimination half-life was unchanged by administration of GFJ (Rashid et al., 1995). Ten
healthy volunteers received 20 mg nifedipine(control-released tablet) with 200 mL of GFJ orwater; the AUC and Cmax of GFJ phase were on
average 103% (range 48–265) and 94% (range–23 to 259) higher than those in the control phase(Sigusch et al., 1994). Eight healthy volunteers received oral nifedipine (20 mg), and no particulardifferences were shown in the plasma concentrations of nifedipine with GFJ (250 mL) or water
ingestion. Nifedipine was also well tolerated in 4
dosing schedules (Azuma et al., 1998).

Nitrendipine
Nitrendipine is a chiral 1,4-dihydropyridine calcium channel antagonist. The systemic bioavailability of racemic nitrendipine is low and variable(5–30%) despite its almost complete gastrointestinal absorption (Krol et al., 1987; Mikus et al.,
1987; Soons et al., 1989). In 9 subjects, the AUCof oral racemic nitrendipine (20 mg) was increased by 150 mL of GFJ (mean increase 106%;interval 64–158%). Comparable results were obtained for the Cmax and both parameters of (S)and (R)-nitrendipine. There were highly significant differences in the AUC and Cmax between
enantiomers. There were no consistent effects on
blood pressure with GFJ, and GFJ did not affecthemodynamic parameters (Soons et al., 1991).
Nondihydropyridines
Diltiazem
Diltiazem is a benzothiazepine calcium channel
antagonist. The oral bioavailability of diltiazem
is approximately 40 to 50% due to extensive

Nisoldipine
Twelve healthy men received nisoldipine (20 mg)
with either 250 mL water or 250 mL GFJ; GFJ
increased plasma nisoldipine concentrations be6

GFJ-calcium channel antagonist interaction

presystemic metabolism (Buckley et al., 1990).
Consumption of a single dose of diltiazem (120mg) with GFJ (200 mL) followed by repeated
GFJ administration (at 0, 2, 4, 8 and 12 h) did notalter the AUC or Cmax of diltiazem. No statistically significant differences were found between
the GFJ treatment and the control values of themean arterial pressure, heart rate, and PR-interval(Sigusch et al., 1994). In another report, GFJ intake resulted in a statistically significant average
individual increase in AUC of 20% comparedwith water. The average individual increase inCmax of diltiazem after GFJ administration was
22%. However, there were no statistically significant differences in blood pressure and heart rate
between the 2 treatments in healthy volunteers(Christensen et al., 2002).

drugs to prevent GFJ-drug interaction. Although
the AUC and Cmax of azelnidipine, efonidipine,
felodipine, manidipine, nicardipine, nifedipine, nisoldipine, nitrendipine and verapamil are elevatedby GFJ intake, both pharmacokinetic parametersof amlodipine and diltiazem are not affected by
GFJ. It is advisable to avoid combination, especially with the more affected agents, azelnidipine,
felodipine, manidipine, nisoldipine and nitrendipine. Among dihydropyridines, amlodipine
could be an alternative drug with diltiazem as thealternative in the non dihydropyridine class. It is
important that awareness of food-drug interactions increases, and actions must be taken to avoid
undesired and harmful clinical events.

Verapamil
Verapamil is used therapeutically as a racemate. The systemic bioavailability of verapamilis only about 20% because of its extensive firstpass extraction (McTavish and Sorkin, 1989). In
9 healthy volunteers, GFJ significantly increased
AUC of S-verapamil by 36% during 12 h dose interval, and increased that of R-verapamil by 28%
in steady state. There were no significant differences in the pharmacodynamic parameters, bloodpressure, heart rate and PR-interval (Ho et al.,2000). GFJ significantly increased the AUC of(R, S)-verapamil at steady state by a mean of 45%
and Cmax at steady state by 63% in 24 volunteers.
Prolongation of PR intervals by GFJ coadministration was borderline significant; an increase
above 350 msec occurred in 2 individuals during
the GFJ period (Fuhr et al., 2002). Fuhr et al.
(2002) concluded that patients on verapamil treatment should abstain from GFJ.

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calcium channel antagonists and GFJ varies widely among drugs. It is necessary to withhold GFJ
for at least 3 days prior to administration of the7

M. Hayashibara

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Received January 30, 2009; accepted February 2, 2009
Corresponding author: Masakazu Hayashibara, PhD

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