Azithromycin (oral)

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# Overview
Azithromycin (oral) is a macrolide antibacterial that is FDA approved for the treatment of sexually transmitted diseases, mycobacterial infections, community-acquired pneumonia, and pelvic inflammatory disease.   Common adverse reactions include diarrhea, nausea, abdominal pain, and vomiting.

# Adult Indications and Dosage

## FDA-Labeled Indications and Dosage (Adult)
- Non-gonococcal urethritis and cervicitis due to Chlamydia trachomatis
- The recommended dose of ZITHROMAX for the treatment of non-gonococcal urethritis and cervicitis due to C. trachomatis is a single 1 gram (1000 mg) dose of ZITHROMAX. This dose can be administered as one single dose packet (1 g).
- Prevention of Disseminated MAC Infections
- The recommended dose of ZITHROMAX for the prevention of disseminated Mycobacterium avium complex (MAC) disease is: 1200 mg taken once weekly. This dose of ZITHROMAX may be combined with the approved dosage regimen of rifabutin.
- Treatment of Disseminated MAC Infections
- ZITHROMAX should be taken at a daily dose of 600 mg, in combination with ethambutol at the recommended daily dose of 15 mg/kg. Other antimycobacterial drugs that have shown in vitro activity against MAC may be added to the regimen of azithromycin plus ethambutol at the discretion of the physician or health care provider.
- The recommended dose of ZITHROMAX (azithromycin for injection) for the treatment of adult patients with community-acquired pneumonia due to the indicated organisms is: 500 mg as a single daily dose by the intravenous route for at least two days. Intravenous therapy should be followed by azithromycin by the oral route at a single, daily dose of 500 mg, administered as two 250-mg tablets to complete a 7- to 10-day course of therapy. The timing of the switch to oral therapy should be done at the discretion of the physician and in accordance with clinical response.
- The recommended dose of ZITHROMAX (azithromycin for injection) for the treatment of adult patients with pelvic inflammatory disease due to the indicated organisms is: 500 mg as a single daily dose by the intravenous route for one or two days. Intravenous therapy should be followed by azithromycin by the oral route at a single, daily dose of 250 mg to complete a 7-day course of therapy. The timing of the switch to oral therapy should be done at the discretion of the physician and in accordance with clinical response. If anaerobic microorganisms are suspected of contributing to the infection, an antimicrobial agent with anaerobic activity should be administered in combination with ZITHROMAX.

## Off-Label Use and Dosage (Adult)

### Guideline-Supported Use
- Developed by: AHA
- Class of Recommendation: Class IIa
- Strength of Evidence: Category C
- Dosing Information
- Azithromycin 500 mg orally.
- Developed by: CDC/NIH/IDSA
- Class of Recommendation: Class IIb
- Strength of Evidence: Category C
- Dosing Information
- Azithromycin 500 mg orally once daily for at least 3 months.
- Developed by: CDC
- Class of Recommendation: Class IIa
- Strength of Evidence: Category B
- Dosing Information
- Azithromycin 1 g orally in a single dose.

### NonGuideline-Supported Use
Azithromycin 500 mg initially, then 250 mg daily, orally for 7 days.
- Single dose of oral azithromycin 20 mg/kg up to a maximum dose of 1 g.
- 7 days of azithromycin (1 g on day 1 followed by 500 mg once daily for the next 6 days).
- Azithromycin 1000 mg as a single dose.
- Single oral dose of 1 g of azithromycin.
- Azithromycin dosed as 250 mg 3 days weekly in patients who weighed less than 40 kg and as 500 mg 3 days weekly in patients who weighed 40 kg or more.
- Oral, twice-daily, quadruple therapy for 2 weeks as follows: azithromycin 250 mg, omeprazole 20 mg, bismuth subcitrate 240 mg, and ofloxacin 200 mg.
- Azithromycin 10 mg/kg daily on day 1 (maximum dose 500 mg) and 5 mg/kg daily on days 2 to 5 (maximum dose 250 mg) for 7 days.

# Pediatric Indications and Dosage

## FDA-Labeled Indications and Dosage (Pediatric)
There is limited information regarding FDA-Labeled Use of Azithromycin (oral) in pediatric patients.

## Off-Label Use and Dosage (Pediatric)

### Guideline-Supported Use
- Developed by: AHA
- Class of Recommendation: Class IIa
- Strength of Evidence: Category C
- Dosing Information
- Azithromycin 15 mg/kg orally.

### NonGuideline-Supported Use
- Single-dose azithromycin (20 mg/kg).
- Oral azithromycin 20 mg/kg/day (maximum dose 1000 mg/day).

# Contraindications
- Hypersensitivity
- ZITHROMAX is contraindicated in patients with known hypersensitivity to azithromycin, erythromycin, any macrolide, or ketolide drug.
- Hepatic Dysfunction
- ZITHROMAX is contraindicated in patients with a history of cholestatic jaundice/hepatic dysfunction associated with prior use of azithromycin.

# Warnings

### Precautions
- Hypersensitivity
- Serious allergic reactions, including angioedema, anaphylaxis, and dermatologic reactions including Stevens-Johnson Syndrome and toxic epidermal necrolysis, have been reported rarely in patients on azithromycin therapy.
- Fatalities have been reported. Despite initially successful symptomatic treatment of the allergic symptoms, when symptomatic therapy was discontinued, the allergic symptoms recurred soon thereafter in some patients without further azithromycin exposure. These patients required prolonged periods of observation and symptomatic treatment. The relationship of these episodes to the long tissue half-life of azithromycin and subsequent prolonged exposure to antigen is presently unknown.
- If an allergic reaction occurs, the drug should be discontinued and appropriate therapy should be instituted. Physicians should be aware that allergic symptoms may reappear when symptomatic therapy is discontinued.
- Hepatotoxicity
- Abnormal liver function, hepatitis, cholestatic jaundice, hepatic necrosis, and hepatic failure have been reported, some of which have resulted in death. Discontinue azithromycin immediately if signs and symptoms of hepatitis occur.
- QT Prolongation
- Prolonged cardiac repolarization and QT interval, imparting a risk of developing cardiac arrhythmia and torsades de pointes, have been seen with treatment with macrolides, including azithromycin. Cases of torsades de pointes have been spontaneously reported during postmarketing surveillance in patients receiving azithromycin. Providers should consider the risk of QT prolongation which can be fatal when weighing the risks and benefits of azithromycin for at-risk groups including:
patients with known prolongation of the QT interval, a history of torsades de pointes, congenital long QT syndrome, bradyarrhythmias or uncompensated heart failure
patients on drugs known to prolong the QT interval
patients with ongoing proarrhythmic conditions such as uncorrected hypokalemia or hypomagnesemia, clinically significant bradycardia, and in patients receiving Class IA (quinidine, procainamide) or Class III (dofetilide, amiodarone, sotalol) antiarrhythmic agents.
- patients with known prolongation of the QT interval, a history of torsades de pointes, congenital long QT syndrome, bradyarrhythmias or uncompensated heart failure
- patients on drugs known to prolong the QT interval
- patients with ongoing proarrhythmic conditions such as uncorrected hypokalemia or hypomagnesemia, clinically significant bradycardia, and in patients receiving Class IA (quinidine, procainamide) or Class III (dofetilide, amiodarone, sotalol) antiarrhythmic agents.
- Elderly patients may be more susceptible to drug-associated effects on the QT interval.
- Clostridium difficile-Associated Diarrhea (CDAD)
- CDAD has been reported with use of nearly all antibacterial agents, including ZITHROMAX, and may range in severity from mild diarrhea to fatal colitis. Treatment with antibacterial agents alters the normal flora of the colon, leading to overgrowth of C. difficile.
- C. difficile produces toxins A and B which contribute to the development of CDAD. Hypertoxin-producing strains of C. difficile cause increased morbidity and mortality, as these infections can be refractory to antibacterial therapy and may require colectomy. CDAD must be considered in all patients who present with diarrhea following antibiotic use. Careful medical history is necessary since CDAD has been reported to occur over two months after the administration of antibacterial agents.
- If CDAD is suspected or confirmed, ongoing antibiotic use not directed against C. difficile may need to be discontinued. Appropriate fluid and electrolyte management, protein supplementation, antibiotic treatment of C. difficile, and surgical evaluation should be instituted as clinically indicated.
- Exacerbation of Myasthenia Gravis
- Exacerbations of symptoms of myasthenia gravis and new onset of myasthenic syndrome have been reported in patients receiving azithromycin therapy.
- Use in Sexually Transmitted Infections
- ZITHROMAX, (single dose 1 g packet) at the recommended dose, should not be relied upon to treat gonorrhea or syphilis. Antibacterial agents used in high doses for short periods of time to treat non-gonococcal urethritis may mask or delay the symptoms of incubating gonorrhea or syphilis. All patients with sexually transmitted urethritis or cervicitis should have a serologic test for syphilis and appropriate cultures for gonorrhea performed at the time of diagnosis. Appropriate antibacterial therapy and follow-up tests for these diseases should be initiated if infection is confirmed.
- Development of Drug-Resistant Bacteria
- Prescribing ZITHROMAX in the absence of a proven or strongly suspected bacterial infection or a prophylactic indication is unlikely to provide benefit to the patient and increases the risk of the development of drug-resistant bacteria.

# Adverse Reactions

## Clinical Trials Experience
- Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.
- In clinical trials, most of the reported adverse reactions were mild to moderate in severity and were reversible upon discontinuation of the drug. Approximately 0.7% of the patients from the multiple-dose clinical trials discontinued ZITHROMAX (azithromycin) therapy because of treatment-related adverse reactions. Serious adverse reactions included angioedema and cholestatic jaundice. Most of the adverse reactions leading to discontinuation were related to the gastrointestinal tract, e.g., nausea, vomiting,,diarrhea, or abdominal pain.
- Multiple-dose regimen
- Overall, the most common adverse reactions in adult patients receiving a multiple-dose regimen of ZITHROMAX were related to the gastrointestinal system with diarrhea/loose stools (5%), nausea (3%), and abdominal pain (3%) being the most frequently reported.
- No other adverse reactions occurred in patients on the multiple-dose regimen of ZITHROMAX with a frequency greater than 1%. Adverse reactions that occurred with a frequency of 1% or less included the following:
Palpitations and chest pain.
Dyspepsia, flatulence, vomiting, melena, and cholestatic jaundice.
Monilia, vaginitis, and nephritis.
Dizziness, headache, vertigo, and somnolence.
Fatigue.
Rash, photosensitivity, and angioedema.
- Chronic therapy with 1200 mg weekly regimen
- The nature of adverse reactions seen with the 1200 mg weekly dosing regimen for the prevention of Mycobacterium avium infection in severely immunocompromised HIV-infected patients were similar to those seen with short-term dosing regimens.
- Chronic therapy with 600 mg daily regimen combined with ethambutol
- The nature of adverse reactions seen with the 600 mg daily dosing regimen for the treatment of Mycobacterium avium complex infection in severely immunocompromised HIV-infected patients were similar to those seen with short term dosing regimens. Five percent of patients experienced reversible hearing impairment in the pivotal clinical trial for the treatment of disseminated MAC in patients with AIDS. Hearing impairment has been reported with macrolide antibiotics, especially at higher doses. Other treatment-related adverse reactions occurring in >5% of subjects and seen at any time during a median of 87.5 days of therapy include: abdominal pain (14%), nausea (14%), vomiting (13%), diarrhea (12%), flatulence (5%), headache (5%), and abnormal vision (5%). Discontinuations from treatment due to laboratory abnormalities or adverse reactions considered related to study drug occurred in 8 of 88 (9.1%) of subjects.
- Single 1 gram dose regimen
- Overall, the most common adverse reactions in patients receiving a single-dose regimen of 1 gram of ZITHROMAX were related to the gastrointestinal system and were more frequently reported than in patients receiving the multiple-dose regimen.
- Adverse reactions that occurred in patients on the single 1 gram dosing regimen of ZITHROMAX with a frequency of 1% or greater included diarrhea/loose stools (7%), nausea (5%), abdominal pain (5%), vomiting (2%), dyspepsia (1%), and vaginitis (1%).

## Postmarketing Experience
- The following adverse reactions have been identified during post approval use of azithromycin. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.
- Adverse reactions reported with azithromycin during the postmarketing period in adult and/or pediatric patients for which a causal relationship may not be established include:
Arthralgia, edema, urticaria, and angioedema.
Arrhythmias, including ventricular tachycardia, and hypotension. There have been reports of QT prolongation and torsades de pointes.
Anorexia, constipation, dyspepsia, flatulence, vomiting/diarrhea pseudomembranous colitis, pancreatitis, oral candidiasis, pyloric stenosis, and tongue discoloration.
Asthenia, paresthesia, fatigue, malaise, and anaphylaxis
Interstitial nephritis, acute renal failure, and vaginitis.
Thrombocytopenia.
Abnormal liver function, hepatitis, cholestatic jaundice, hepatic necrosis, and hepatic failure.
Convulsions, dizziness/vertigo, headache, somnolence, hyperactivity, nervousness, agitation, and syncope.
Aggressive reaction and anxiety.
Pruritus, and serious skin reactions including erythema multiforme, Stevens-Johnson Syndrome, and toxic epidermal necrolysis.
Hearing disturbances including hearing loss, deafness, and/or tinnitus, and reports of taste/smell perversion and/or loss.

# Drug Interactions
- Nelfinavir
- Co-administration of nelfinavir at steady-state with a single oral dose of azithromycin resulted in increased azithromycin serum concentrations. Although a dose adjustment of azithromycin is not recommended when administered in combination with nelfinavir, close monitoring for known adverse reactions of azithromycin, such as liver enzyme abnormalities and hearing impairment, is warranted.
- Warfarin
- Spontaneous post-marketing reports suggest that concomitant administration of azithromycin may potentiate the effects of oral anticoagulants such as warfarin, although the prothrombin time was not affected in the dedicated drug interaction study with azithromycin and warfarin. Prothrombin times should be carefully monitored while patients are receiving azithromycin and oral anticoagulants concomitantly.
- Potential Drug-Drug Interaction with Macrolides
- Interactions with the following drugs listed below have not been reported in clinical trials with azithromycin; however, no specific drug interaction studies have been performed to evaluate potential drug-drug interaction. However, drug interactions have been observed with other macrolide products. Until further data are developed regarding drug interactions when digoxin or phenytoin are used with azithromycin careful monitoring of patients is advised.

# Use in Specific Populations

### Pregnancy
Pregnancy Category (FDA):
- Pregnancy Category B
- Reproduction studies have been performed in rats and mice at doses up to moderately maternally toxic dose levels (i.e., 200 mg/kg/day). These daily doses in rats and mice, based on body surface area, are estimated to be 3.2 and 1.6 times, respectively, an adult daily dose of 600 mg. In the animal studies, no evidence of harm to the fetus due to azithromycin was found. There are, however, no adequate and well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, azithromycin should be used during pregnancy only if clearly needed.
Pregnancy Category (AUS):
- Australian Drug Evaluation Committee (ADEC) Pregnancy Category
There is no Australian Drug Evaluation Committee (ADEC) guidance on usage of Azithromycin (oral) in women who are pregnant.

### Labor and Delivery
There is no FDA guidance on use of Azithromycin (oral) during labor and delivery.

### Nursing Mothers
Azithromycin has been reported to be excreted in breast milk in small amounts. Caution should be exercised when azithromycin is administered to a nursing woman.

### Pediatric Use
- In controlled clinical studies, azithromycin has been administered to pediatric patients ranging in age from 6 months to 12 years.
- HIV-Infected Pediatric Patients: The safety and efficacy of azithromycin for the prevention or treatment of MAC in HIV-infected children have not been established. Safety data are available for 72 children 5 months to 18 years of age (mean 7 years) who received azithromycin for treatment of opportunistic infections. The mean duration of therapy was 242 days (range 32004 days) at doses of <;&lt1 to 52 mg/kg/day (mean 12 mg/kg/day). Adverse reactions were similar to those observed in the adult population, most of which involved the gastrointestinal tract. Treatment-related reversible hearing impairment in children was observed in 4 subjects (5.6%). Two (2.8%) children prematurely discontinued treatment due to adverse reactions: one due to back pain and one due to abdominal pain, hot and cold flushes, dizziness, headache, and numbness. A third child discontinued due to a laboratory abnormality (eosinophilia). The protocols upon which these data are based specified a daily dose of 1020 mg/kg/day (oral and/or IV) of azithromycin.

### Geriatic Use
- In multiple-dose clinical trials of oral azithromycin, 9% of patients were at least 65 years of age (458/4949) and 3% of patients (144/4949) were at least 75 years of age. No overall differences in safety or effectiveness were observed between these subjects and younger subjects, and other reported clinical experience has not identified differences in responses between the elderly and younger patients, but greater sensitivity of some older individuals cannot be ruled out.
- Elderly patients may be more susceptible to development of torsades de pointes arrhythmias than younger patients.
- ZITHROMAX 600 mg tablets contain 2.1 mg of sodium per tablet. ZITHROMAX for oral suspension 1 gram single-dose packets contain 37.0 mg of sodium per packet.
- Geriatric Patients with Opportunistic Infections, Including (MAC) Disease: Safety data are available for 30 patients (6594 years old) treated with azithromycin at doses >300 mg/day for a mean of 207 days. These patients were treated for a variety of opportunistic infections, including MAC. The adverse reaction were generally similar to that seen in younger patients, except for a higher incidence of adverse reactions relating to the gastrointestinal system and to reversible impairment of hearing.

### Gender
There is no FDA guidance on the use of Azithromycin (oral) with respect to specific gender populations.

### Race
There is no FDA guidance on the use of Azithromycin (oral) with respect to specific racial populations.

### Renal Impairment
There is no FDA guidance on the use of Azithromycin (oral) in patients with renal impairment.

### Hepatic Impairment
There is no FDA guidance on the use of Azithromycin (oral) in patients with hepatic impairment.

### Females of Reproductive Potential and Males
There is no FDA guidance on the use of Azithromycin (oral) in women of reproductive potentials and males.

### Immunocompromised Patients
There is no FDA guidance one the use of Azithromycin (oral) in patients who are immunocompromised.

# Administration and Monitoring

### Administration
- Oral
- Intravenous

### Monitoring
There is limited information regarding Monitoring of Azithromycin (oral) in the drug label.

# IV Compatibility
There is limited information regarding IV Compatibility of Azithromycin (oral) in the drug label.

# Overdosage

## Chronic Overdose
There is limited information regarding Chronic Overdose of Azithromycin (oral) in the drug label.

# Pharmacology

## Mechanism of Action
- Azithromycin acts by binding to the 50S ribosomal subunit of susceptible microorganisms and, thus, interfering with microbial protein synthesis. Nucleic acid synthesis is not affected.
- Azithromycin concentrates in phagocytes and fibroblasts as demonstrated by in vitro incubation techniques. Using such methodology, the ratio of intracellular to extra-cellular concentration was >30 after one hour incubation. In vivo studies suggest that concentration in phagocytes may contribute to drug distribution to inflamed tissues.

## Structure
- ZITHROMAX (azithromycin tablets and oral suspension) contains the active ingredient azithromycin, a macrolide antibacterial drug , for oral administration. Azithromycin has the chemical name (2R,3S,4R,5R,8R,10R,11R,12S,13S,14R)-13--2-ethyl- 3,4,10-trihydroxy-3,5,6,8,10,12,14-heptamethyl-11-oxy]-1-oxa-6-azacyclopentadecan-15-one. Azithromycin is derived from erythromycin; however, it differs chemically from erythromycin in that a methyl-substituted nitrogen atom is incorporated into the lactone ring. Its molecular formula is C38H72N2O12, and its molecular weight is 749.0. Azithromycin has the following structural formula:
- Azithromycin, as the dihydrate, is a white crystalline powder with a molecular formula of C38H72N2O122H2O and a molecular weight of 785.0.
- ZITHROMAX tablets contain azithromycin dihydrate equivalent to 600 mg azithromycin. They also contain the following inactive ingredients: dibasic calcium phosphate anhydrous, pregelatinized starch, sodium croscarmellose, magnesium stearate, sodium lauryl sulfate, and an aqueous film coat consisting of hypromellose, titanium dioxide, lactose, and triacetin.
- ZITHROMAX for oral suspension is supplied in a single-dose packet containing azithromycin dihydrate equivalent to 1 g azithromycin. It also contains the following inactive ingredients: colloidal silicon dioxide, sodium phosphate tribasic, anhydrous; spray dried artificial banana flavor, spray dried artificial cherry flavor, and sucrose.

## Pharmacodynamics
- Based on animal models of infection, the antibacterial activity of azithromycin appears to correlate with the ratio of area under the concentration-time curve to minimum inhibitory concentration (AUC/MIC) for certain pathogens (S. pneumoniae and S. aureus).
- The principal pharmacokinetic/pharmacodynamic parameter best associated with clinical and microbiological cure has not been elucidated in clinical trials with azithromycin.
- Cardiac Electrophysiology
- QTc interval prolongation was studied in a randomized, placebo-controlled parallel trial in 116 healthy subjects who received either chloroquine (1000 mg) alone or in combination with oral azithromycin (500 mg, 1000 mg, and 1500 mg once daily). Co- administration of azithromycin increased the QTc interval in a dose- and concentration- dependent manner. In comparison to chloroquine alone, the maximum mean (95% upper confidence bound) increases in QTcF were 5 (10) ms, 7 (12) ms and 9 (14) ms with the co-administration of 500 mg, 1000 mg and 1500 mg azithromycin, respectively.

## Pharmacokinetics
- The pharmacokinetic parameters of azithromycin in plasma after dosing as per labeled recommendations in healthy young adults and asymptomatic HIV-positive adults (age 1840 years old) are portrayed in the following chart:
- With a regimen of 500 mg on Day 1 and 250 mg/day on Days 25, Cmin and Cmax remained essentially unchanged from Day 2 through Day 5 of therapy. However, without a loading dose, azithromycin Cmin levels required 5 to 7 days to reach steady state.
- In asymptomatic HIV-positive adult subjects receiving 600 mg ZITHROMAX tablets once daily for 22 days, steady state azithromycin serum levels were achieved by Day 15 of dosing.
- The high values in adults for apparent steady-state volume of distribution (31.1 L/kg) and plasma clearance (630 mL/min) suggest that the prolonged half-life is due to extensive uptake and subsequent release of drug from tissues.
- Absorption
- The 1 gram single-dose packet is bioequivalent to four 250 mg azithromycin capsule
- When the oral suspension of azithromycin was administered with food, the Cmax increased by 46% and the AUC by 14%.
- The absolute bioavailability of two 600 mg tablets was 34% (CV=56%). Administration of two 600 mg tablets with food increased Cmax by 31% (CV=43%) while the extent of absorption (AUC) was unchanged (mean ratio of AUCs=1.00; CV=55%).
- Distribution
- The serum protein binding of azithromycin is variable in the concentration range approximating human exposure, decreasing from 51% at 0.02 g/mL to 7% at 2 g/mL.
- The antibacterial activity of azithromycin is pH related and appears to be reduced with decreasing pH. However, the extensive distribution of drug to tissues may be relevant to clinical activity.
- Azithromycin has been shown to penetrate into tissues in humans, including skin, lung, tonsil, and cervix.. Extensive tissue distribution was confirmed by examination of additional tissues and fluids (bone, ejaculum, prostate, ovary, uterus, salpinx, stomach, liver, and gallbladder). As there are no data from adequate and well-controlled studies of azithromycin treatment of infections in these additional body sites, the clinical importance of these tissue concentration data is unknown.
- Following oral administration of a single 1200 mg dose (two 600 mg tablets), the mean maximum concentration in peripheral leukocytes was 140g/mL. Concentration remained above 32 g/mL, for approximately 60 hours. The mean half-lives for 6 males and 6 females were 34 hours and 57 hours, respectively. Leukocyte-to-plasma Cmax ratios for males and females were 258 (77%) and 175 (60%), respectively, and the AUC ratios were 804 (31%) and 541 (28%) respectively. The clinical relevance of these findings is unknown.
- Following oral administration of multiple daily doses of 600 mg (1 tablet/day) to asymptomatic HIV-positive adults, mean maximum concentration in peripheral leukocytes was 252 g/mL (49%). Trough concentrations in peripheral leukocytes at steady-state averaged 146 g/mL (33%). The mean leukocyte-to-serum Cmax ratio was 456 (38%) and the mean leukocyte to serum AUC ratio was 816 (31%). The clinical relevance of these findings is unknown..
- Metabolism
- In vitro and in vivo studies to assess the metabolism of azithromycin have not been performed.
- Elimination
- Plasma concentrations of azithromycin following single 500 mg oral and IV doses declined in a polyphasic pattern resulting in an average terminal half-life of 68 hours. Biliary excretion of azithromycin, predominantly as unchanged drug, is a major route of elimination. Over the course of a week, approximately 6% of the administered dose appears as unchanged drug in urine.
- Specific Populations
- Renal Insufficiency
- Azithromycin pharmacokinetics was investigated in 42 adults (21 to 85 years of age) with varying degrees of renal impairment. Following the oral administration of a single 1.0 g dose of azithromycin (4  250 mg capsules), the mean Cmax and AUC0120 increased by 5.1% and 4.2%, respectively, in subjects with GFR 10 to 80 mL/min compared to subjects with normal renal function (GFR >80 mL/min). The mean Cmax and AUC0120 increased 61% and 35%, respectively, in subjects with end-stage renal disease (GFR 80 mL/min).
- Hepatic Insufficiency
- The pharmacokinetics of azithromycin in subjects with hepatic impairment has not been established.
- Gender
- There are no significant differences in the disposition of azithromycin between male and female subjects. No dosage adjustment is recommended on the basis of gender.
- Geriatric Patients
- Pharmacokinetic parameters in older volunteers (65 to 85 years old) were similar to those in younger volunteers (18 to 40 years old) for the 5-day therapeutic regimen. Dosage adjustment does not appear to be necessary for older patients with normal renal and hepatic function receiving treatment with this dosage regimen.
- Pediatric Patients
- For information regarding the pharmacokinetics of ZITHROMAX (azithromycin for oral suspension) in pediatric patients, see the prescribing information for ZITHROMAX (azithromycin for oral suspension) 100 mg/5 mL and 200 mg/5 mL bottles.
- Drug-drug Interactions
- Drug interaction studies were performed with azithromycin and other drugs likely to be co-administered. The effects of co-administration of azithromycin on the pharmacokinetics of other drugs are shown in Table 1 and the effects of other drugs on the pharmacokinetics of azithromycin are shown in Table 2.
- Co-administration of azithromycin at therapeutic doses had a modest effect on the pharmacokinetics of the drugs listed in Table 1. No dosage adjustment of drugs listed in Table 1 is recommended when co-administered with azithromycin.
- Co-administration of azithromycin with efavirenz or fluconazole had a modest effect on the pharmacokinetics of azithromycin. Nelfinavir significantly increased the Cmax and AUC of azithromycin. No dosage adjustment of azithromycin is recommended when administered with drugs listed in Table 2.

## Nonclinical Toxicology
- Long-term studies in animals have not been performed to evaluate carcinogenic potential. Azithromycin has shown no mutagenic potential in standard laboratory tests: mouse lymphoma assay, human lymphocyte clastogenic assay, and mouse bone marrow clastogenic assay. No evidence of impaired fertility due to azithromycin was found in rats given daily doses up to 10 mg/kg (approximately 0.2 times an adult daily dose of 600 mg based on body surface area).
- Phospholipidosis (intracellular phospholipid accumulation) has been observed in some tissues of mice, rats, and dogs given multiple doses of azithromycin. It has been demonstrated in numerous organ systems (e.g., eye, dorsal root ganglia, liver, gallbladder, kidney, spleen, and/or pancreas) in dogs and rats treated with azithromycin at doses which, expressed on the basis of body surface area, are similar to or less than the highest recommended adult human dose. This effect has been shown to be reversible after cessation of azithromycin treatment. Based on the pharmacokinetic data, phospholipidosis has been seen in the rat (50 mg/kg/day dose) at the observed maximal plasma concentration of 1.3 g/mL (1.6 times the observed Cmax of 0.821 g/mL at the adult dose of 2 g.) Similarly, it has been shown in the dog (10 mg/kg/day dose) at the observed maximal serum concentration of 1 g/mL (1.2 times the observed Cmax of 0.821 g/mL at the adult dose of 2 g).
- Phospholipidosis was also observed in neonatal rats dosed for 18 days at 30 mg/kg/day, which is less than the pediatric dose of 60 mg/kg based on the surface area. It was not observed in neonatal rats treated for 10 days at 40 mg/kg/day with mean maximal serum concentrations of 1.86 g/ml, approximately 1.5 times the Cmax of 1.27 g/ml at the pediatric dose. Phospholipidosis has been observed in neonatal dogs (10 mg/kg/day) at maximum mean whole blood concentrations of 3.54 g/ml, approximately 3 times the pediatric dose Cmax.
- The significance of the finding for animals and for humans is unknown.

# Clinical Studies
- Prevention of Disseminated MAC Disease
- Two randomized, double-blind clinical trials were performed in patients with CD4 counts <100 cells/L. The first trial (Study 155) compared azithromycin (1200 mg once weekly) to placebo and enrolled 182 patients with a mean CD4 count of 35 cells/mcgL. The second trial (Study 174) randomized 723 patients to either azithromycin (1200 mg once weekly), rifabutin (300 mg daily), or the combination of both. The mean CD4 count was 51 cells/mcgL. The primary endpoint in these trials was disseminated MAC disease. Other endpoints included the incidence of clinically significant MAC disease and discontinuations from therapy for drug-related side effects.
- MAC bacteremia
- In Study 155, 85 patients randomized to receive azithromycin and 89 patients randomized to receive placebo met the entrance criteria. Cumulative incidences at 6, 12, and 18 months of the possible outcomes are in the following table:
- The difference in the one-year cumulative incidence rates of disseminated MAC disease (placebo  azithromycin) is 10.9%. This difference is statistically significant (p=0.037) with a 95% confidence interval for this difference of 0.8%, 20.9%. The comparable number of patients experiencing adverse events and the fewer number of patients lost to follow-up on azithromycin should be taken into account when interpreting the significance of this difference.
- In Study 174, 223 patients randomized to receive rifabutin, 223 patients randomized to receive azithromycin, and 218 patients randomized to receive both rifabutin and azithromycin met the entrance criteria. Cumulative incidences at 6, 12, and 18 months of the possible outcomes are recorded in the following table:
- Comparing the cumulative one-year incidence rates, azithromycin monotherapy is at least as effective as rifabutin monotherapy. The difference (rifabutin  azithromycin) in the one-year rates (7.6%) is statistically significant (p=0.022) with an adjusted 95% confidence interval (0.9%, 14.3%). Additionally, azithromycin/rifabutin combination therapy is more effective than rifabutin alone. The difference (rifabutin  azithromycin/rifabutin) in the cumulative one-year incidence rates (12.5%) is statistically significant (p<0.001) with an adjusted 95% confidence interval of 6.6%, 18.4%. The comparable number of patients experiencing adverse events and the fewer number of patients lost to follow-up on rifabutin should be taken into account when interpreting the significance of this difference.
- In Study 174, sensitivity testing5 was performed on all available MAC isolates from subjects randomized to either azithromycin, rifabutin, or the combination. The distribution of MIC values for azithromycin from susceptibility testing of the breakthrough isolates was similar between trial arms. As the efficacy of azithromycin in the treatment of disseminated MAC has not been established, the clinical relevance of these in vitro MICs as an indicator of susceptibility or resistance is not known.
- Clinically Significant Disseminated MAC Disease
- In association with the decreased incidence of bacteremia, patients in the groups randomized to either azithromycin alone or azithromycin in combination with rifabutin showed reductions in the signs and symptoms of disseminated MAC disease, including fever or night sweats, weight loss, and anemia.
- Discontinuations from Therapy for Drug-Related Side Effects
- In Study 155, discontinuations for drug-related toxicity occurred in 8.2% of subjects treated with azithromycin and 2.3% of those given placebo (p=0.121). In Study 174, more subjects discontinued from the combination of azithromycin and rifabutin (22.7%) than from azithromycin alone (13.5%; p=0.026) or rifabutin alone (15.9%; p=0.209).
- Safety
- As these patients with advanced HIV disease were taking multiple concomitant medications and experienced a variety of intercurrent illnesses, it was often difficult to attribute adverse reactions to study medication. Overall, the nature of adverse reactions seen on the weekly dosage regimen of azithromycin over a period of approximately one year in patients with advanced HIV disease were similar to that previously reported for shorter course therapies.
- Adverse reactions related to the gastrointestinal tract were seen more frequently in patients receiving azithromycin than in those receiving placebo or rifabutin. In Study 174, 86% of diarrheal episodes were mild to moderate in nature with discontinuation of therapy for this reason occurring in only 9/233 (3.8%) of patients.
- Changes in Laboratory Values
- In these immunocompromised patients with advanced HIV infection, it was necessary to assess laboratory abnormalities developing on trial with additional criteria if baseline values were outside the relevant normal range.
- One randomized, double-blind clinical trial (Study 189) was performed in patients with disseminated MAC. In this trial, 246 HIV-infected patients with disseminated MAC received either azithromycin 250 mg daily (N=65), azithromycin 600 mg daily (N=91), or clarithromycin 500 mg twice a day (N=90), each administered with ethambutol 15 mg/kg daily, for 24 weeks. Blood cultures and clinical assessments were performed every 3 weeks through week 12 and monthly thereafter through week 24. After week 24, patients were switched to any open-label therapy at the discretion of the investigator and followed every 3 months through the last follow-up visit of the trial. Patients were followed from the baseline visit for a period of up to 3.7 years (median: 9 months). MAC isolates recovered during treatment or post-treatment were obtained whenever possible.
- The primary endpoint was sterilization by week 24. Sterilization was based on data from the central laboratory, and was defined as two consecutive observed negative blood cultures for MAC, independent of missing culture data between the two negative observations. Analyses were performed on all randomized patients who had a positive baseline culture for MAC.
- The azithromycin 250 mg arm was discontinued after an interim analysis at 12 weeks showed a significantly lower clearance of bacteremia compared to clarithromycin 500 mg twice a day . Efficacy results for the azithromycin 600 mg daily and clarithromycin 500 mg twice a day treatment regimens are described in the following table:
- The primary endpoint, rate of sterilization of blood cultures (two consecutive negative cultures) at 24 weeks, was lower in the azithromycin 600 mg daily group than in the clarithromycin 500 mg twice a day group.
- Sterilization by Baseline Colony Count
- Within both treatment groups, the sterilization rates at week 24 decreased as the range of MAC cfu/mL increased.
- Susceptibility Pattern of MAC Isolates
- Susceptibility testing was performed on MAC isolates recovered at baseline, at the time of breakthrough on therapy or during post-therapy follow-up. The T100 radiometric broth method was employed to determine azithromycin and clarithromycin MIC values. Azithromycin MIC values ranged from 256 g/mL and clarithromycin MICs ranged from 32 g/mL. The individual MAC susceptibility results demonstrated that azithromycin MIC values could be 4 to 32-fold higher than clarithromycin MIC values.
- During treatment and post-treatment follow-up for up to 3.7 years (median: 9 months) in Study 189, a total of 6/68 (9%) and 6/57 (11%) of the patients randomized to azithromycin 600 mg daily and clarithromycin 500 mg twice a day respectively, developed MAC blood culture isolates that had a sharp increase in MIC values. All twelve MAC isolates had azithromycin MICs 256 g/mL and clarithromycin MICs >32 g/mL. These high MIC values suggest development of drug resistance. However, at this time, specific breakpoints for separating susceptible and resistant MAC isolates have not been established for either macrolide.
- In a controlled study of community-acquired pneumonia performed in the U.S., azithromycin (500 mg as a single daily dose by the intravenous route for 25 days, followed by 500 mg/day by the oral route to complete 710 days therapy) was compared to cefuroxime (2250 mg/day in three divided doses by the intravenous route for 25 days followed by 1000 mg/day in two divided doses by the oral route to complete 710 days therapy), with or without erythromycin. For the 291 patients who were evaluable for clinical efficacy, the clinical outcome rates, i.e., cure, improved, and success (cure + improved) among the 277 patients seen at 1014 days post-therapy were as follows:
- In a separate, uncontrolled clinical and microbiological trial performed in the U.S., 94 patients with community-acquired pneumonia who received azithromycin in the same regimen were evaluable for clinical efficacy. The clinical outcome rates, i.e., cure, improved, and success (cure + improved) among the 84 patients seen at 1014 days post-therapy were as follows:
- Microbiological determinations in both trials were made at the pre-treatment visit and, where applicable, were reassessed at later visits. Serological testing was done on baseline and final visit specimens. The following combined presumptive bacteriological eradication rates were obtained from the evaluable groups:
- Combined Bacteriological Eradication Rates for Azithromycin:
- The presumed bacteriological outcomes at 1014 days post-therapy for patients treated with azithromycin with evidence (serology and/or culture) of atypical pathogens for both trials were as follows:

# How Supplied
- ZITHROMAX 600 mg tablets (engraved on front with "PFIZER" and on back with "308") are supplied as white, modified oval-shaped, film-coated tablets containing azithromycin dihydrate equivalent to 600 mg azithromycin. These are packaged in bottles of 30 tablets. ZITHROMAX tablets are supplied as follows:
- Bottles of 30     NDC 0069-3080-30
- Tablets should be stored at or below 30C (86F).
- ZITHROMAX for oral suspension is supplied in single-dose packets containing azithromycin dihydrate equivalent to 1 gram of azithromycin as follows:
- Boxes of 10 single-dose packets (1 g)     NDC 0069-3051-07
- Boxes of 3 single-dose packets (1 g)     NDC 0069-3051-75
- Store single-dose packets between 5 and 30C (41 and 86F).

## Storage
There is limited information regarding Azithromycin (oral) Storage in the drug label.

# Images

## Drug Images

## Package and Label Display Panel

# Patient Counseling Information
- ZITHROMAX tablets may be taken with or without food. However, increased tolerability has been observed when tablets are taken with food.
- ZITHROMAX for oral suspension in single 1 g packets can be taken with or without food after constitution.
- Patients should also be cautioned not to take aluminum- and magnesium-containing antacids and azithromycin simultaneously.
- The patient should be directed to discontinue azithromycin immediately and contact a physician if any signs of an allergic reaction occur.
- Patients should be counseled that antibacterial drugs, including ZITHROMAX, should only be used to treat bacterial infections. They do not treat viral infections (e.g., the common cold). When ZITHROMAX is prescribed to treat bacterial infection, patients should be told that although it is common to feel better early in the course of therapy, the medication should be taken exactly as directed. Skipping doses or not completing the full course of therapy may (1) decrease the effectiveness of the immediate treatment and (2) increase the likelihood that bacteria will develop resistance and will not be treatable by ZITHROMAX or other antibacterial drugs in the future.
- Diarrhea is a common problem caused by antibacterial which usually ends when the antibiotic is discontinued. Sometimes after starting treatment with antibacterials, patients can develop watery and bloody stools (with or without stomach cramps and fever) even as late as two or more months after having taken the last dose of the antibacterial. If this occurs, patients should contact their physician as soon as possible.

# Precautions with Alcohol
- Alcohol-Azithromycin (oral) interaction has not been established. Talk to your doctor about the effects of taking alcohol with this medication.

# Brand Names
- ZITHROMAX

# Look-Alike Drug Names
There is limited information regarding Azithromycin (oral) Look-Alike Drug Names in the drug label.

# Drug Shortage Status

# Price