Zithromax (Azithromycin): Side Effects, Uses, Dosage, Interactions, Warnings (2024)

Description for Zithromax

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-[(2,6-dideoxy-3-C-methyl-3-O-methyl-α-L-ribo-hexopyranosyl)oxy]-2-ethyl- 3,4,10-trihydroxy-3,5,6,8,10,12,14-heptamethyl-11-[[3,4,6- trideoxy-3-(dimethylamino)-β-D-xylo-hexopyranosyl]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 C₃₈H₇₂N₂O₁₂•2H₂O 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.

Uses for Zithromax

ZITHROMAX (azithromycin) for injection is a macrolide antibacterial drug indicated for the treatmentof patients with infections caused by susceptible strains of the designated microorganisms in theconditions listed below.

Community-Acquired Pneumonia

due to Chlamydophila pneumoniae, Haemophilus influenzae, Legionella pneumophila, Moraxellacatarrhalis, Mycoplasma pneumoniae, Staphylococcus aureus, or Streptococcus pneumoniae in patientswho require initial intravenous therapy.

Pelvic Inflammatory Disease

due to Chlamydia trachomatis, Neisseria gonorrhoeae, or Mycoplasma hominis in patients who requireinitial intravenous therapy. If anaerobic microorganisms are suspected of contributing to the infection,an antimicrobial agent with anaerobic activity should be administered in combination withZITHROMAX.

ZITHROMAX for injection should be followed by ZITHROMAX by the oral route as required. [see DOSAGE AND ADMINISTRATION]

Usage

To reduce the development of drug-resistant bacteria and maintain the effectiveness of ZITHROMAX(azithromycin) and other antibacterial drugs, ZITHROMAX (azithromycin) should be used only to treatinfections that are proven or strongly suspected to be caused by susceptible bacteria. When culture andsusceptibility information are available, they should be considered in selecting or modifyingantibacterial therapy. In the absence of such data, local epidemiology and susceptibility patterns maycontribute to the empiric selection of therapy.

Dosage for Zithromax

[see INDICATIONS and CLINICAL PHARMACOLOGY]

Community-Acquired Pneumonia

The recommended dose of ZITHROMAX for injection for the treatment of adult patients withcommunity-acquired pneumonia due to the indicated organisms is 500 mg as a single daily dose by theintravenous route for at least two days. Intravenous therapy should be followed by azithromycin by theoral 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.

Pelvic Inflammatory Disease

The recommended dose of ZITHROMAX for injection for the treatment of adult patients with pelvicinflammatory disease due to the indicated organisms is 500 mg as a single daily dose by the intravenousSections or subsections omitted from the full prescribing information are not listed.route for one or two days. Intravenous therapy should be followed by azithromycin by the oral route at asingle, daily dose of 250 mg to complete a 7-day course of therapy. The timing of the switch to oraltherapy should be done at the discretion of the physician and in accordance with clinical response.

Preparation Of The Solution For Intravenous Administration

The infusate concentration and rate of infusion for ZITHROMAX for injection should be either 1mg/mL over 3 hr or 2 mg/mL over 1 hr. ZITHROMAX for injection should not be given as a bolus or asn intramuscular injection.

Reconstitution

Prepare the initial solution of ZITHROMAX for injection by adding 4.8 mL of Sterile Water forInjection to the 500 mg vial, and shaking the vial until all of the drug is dissolved. Since ZITHROMAXfor injection is supplied under vacuum, it is recommended that a standard 5 mL (non-automated) syringebe used to ensure that the exact amount of 4.8 mL of Sterile Water is dispensed. Each mL ofreconstituted solution contains 100 mg azithromycin. Reconstituted solution is stable for 24 hr whenstored below 30°C (86°F).

Parenteral drug products should be inspected visually for particulate matter prior to administration. Ifparticulate matter is evident in reconstituted fluids, the drug solution should be discarded.

Dilute this solution further prior to administration as instructed below.

Dilution

To provide azithromycin over a concentration range of 1.0–2.0 mg/mL, transfer 5 mL of the 100 mg/mLazithromycin solution into the appropriate amount of any of the diluents listed below:

Normal Saline (0.9% sodium chloride)
1/2 Normal Saline (0.45% sodium chloride)
5% Dextrose in Water
Lactated Ringer's Solution
5% Dextrose in 1/2 Normal Saline (0.45% sodium chloride) with 20 mEq KCl
5% Dextrose in Lactated Ringer's Solution
5% Dextrose in 1/3 Normal Saline (0.3% sodium chloride)
5% Dextrose in 1/2 Normal Saline (0.45% sodium chloride)
Normosol^®-M in 5% Dextrose
Normosol^®-R in 5% Dextrose

When used with the Vial-Mate^® drug reconstitution device, please reference the Vial-Mateinstructions for assembly and reconstitution.

Other intravenous substances, additives, or medications should not be added to ZITHROMAX forinjection, or infused simultaneously through the same intravenous line.

Storage

When diluted according to the instructions (1.0 mg/mL to 2.0 mg/mL), ZITHROMAX for injection isstable for 24 hr at or below room temperature 30°C (86°F), or for 7 days if stored under refrigeration5°C (41°F).

HOW SUPPLIED

Dosage Forms And Strengths

ZITHROMAX for injection is supplied in lyophilized form in a 10 mL vial equivalent to 500 mg ofazithromycin for intravenous administration.

Storage And Handling

ZITHROMAX is supplied in lyophilized form under a vacuum in a 10 mL vial equivalent to 500 mg of azithromycin for intravenous administration. Each vial also contains sodium hydroxide and 413.6 mg citric acid.

These are packaged as follows:

10 vials of 500 mg NDC 0069-3150-83
10 vials of 500 mg with 1 Vial-Mate^® Adaptoreach NDC 0069-3150-14

Distributed by: Pfizer Labs Division opf Pfizer Inc New York, NY 10017. Revised: Aug 2018

Side Effects for Zithromax

Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observedin the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drugand may not reflect the rates observed in practice.

In clinical trials of intravenous azithromycin for community-acquired pneumonia, in which 2 to 5 IVdoses were given, the reported adverse reactions were mild to moderate in severity and werereversible upon discontinuation of the drug. The majority of patients in these trials had one or more comorbiddiseases and were receiving concomitant medications. Approximately 1.2% of the patientsdiscontinued intravenous ZITHROMAX therapy, and a total of 2.4% discontinued azithromycin therapyby either the intravenous or oral route because of clinical or laboratory side effects.

In clinical trials conducted in patients with pelvic inflammatory disease, in which 1 to 2 IV doses weregiven, 2% of women who received monotherapy with azithromycin and 4% who received azithromycinplus metronidazole discontinued therapy due to clinical side effects.

Clinical adverse reactions leading to discontinuations from these studies were gastrointestinal(abdominal pain, nausea, vomiting, diarrhea), and rashes; laboratory side effects leading todiscontinuation were increases in transaminase levels and/or alkaline phosphatase levels.

Overall, the most common adverse reactions associated with treatment in adult patients who receivedIV/Oral ZITHROMAX in studies of community-acquired pneumonia were related to the gastrointestinalsystem with diarrhea/loose stools (4.3%), nausea (3.9%), abdominal pain (2.7%), and vomiting (1.4%)being the most frequently reported.

Approximately 12% of patients experienced a side effect related to the intravenous infusion; mostcommon were pain at the injection site (6.5%) and local inflammation (3.1%).

The most common adverse reactions associated with treatment in adult women who received IV/OralZITHROMAX in trials of pelvic inflammatory disease were related to the gastrointestinal system.Diarrhea (8.5%) and nausea (6.6%) were most commonly reported, followed by vaginitis (2.8%),abdominal pain (1.9%), anorexia (1.9%), rash and pruritus (1.9%). When azithromycin was coadministeredwith metronidazole in these trials, a higher proportion of women experienced adversereactions of nausea (10.3%), abdominal pain (3.7%), vomiting (2.8%), infusion site reaction, stomatitis,dizziness, or dyspnea (all at 1.9%).

Adverse reactions that occurred with a frequency of 1% or less included the following:

Gastrointestinal: Dyspepsia, flatulence, mucositis, oral moniliasis, and gastritis.

Nervous system: Headache, somnolence.

Allergic: Bronchospasm.

Special senses: Taste perversion.

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 alwayspossible to reliably estimate their frequency or establish a causal relationship to drug exposure.

Adverse reactions reported with azithromycin during the post-marketing period in adult and/or pediatricpatients for which a causal relationship may not be established include:

Allergic: Arthralgia, edema, urticaria and angioedema.

Cardiovascular: Arrhythmias including ventricular tachycardia and hypotension. There have beenreports of QT prolongation and torsades de pointes.

Gastrointestinal: Anorexia, constipation, dyspepsia, flatulence, vomiting/diarrhea, pseudomembranouscolitis, pancreatitis, oral candidiasis, pyloric stenosis, and reports of tongue discoloration.

General: Asthenia, paresthesia, fatigue, malaise and anaphylaxis (including fatalities).

Genitourinary: Interstitial nephritis and acute renal failure and vaginitis.

Hematopoietic: Thrombocytopenia.

Liver/biliary: Abnormal liver function, hepatitis, cholestatic jaundice, hepatic necrosis, and hepaticfailure. [see WARNINGS AND PRECAUTIONS]

Nervous system: Convulsions, dizziness/vertigo, headache, somnolence, hyperactivity, nervousness, agitation and syncope.

Psychiatric: Aggressive reaction and anxiety.

Skin/appendages: Pruritus, serious skin reactions including, erythema multiforme, AGEP, Stevens- Johnson syndrome, toxic epidermal necrolysis, and DRESS.

Special senses: Hearing disturbances including hearing loss, deafness and/or tinnitus and reports of taste/smell perversion and/or loss.

Laboratory Abnormalities

Significant abnormalities (irrespective of drug relationship) occurring during the clinical trials were reported as follows:

• elevated ALT (SGPT), AST (SGOT), creatinine (4 to 6%)
• elevated LDH, bilirubin (1 to 3%)
• leukopenia, neutropenia, decreased platelet count, and elevated serum alkaline phosphatase (less than 1%)

When follow-up was provided, changes in laboratory tests appeared to be reversible.

In multiple-dose clinical trials involving more than 750 patients treated with ZITHROMAX (IV/Oral),less than 2% of patients discontinued azithromycin therapy because of treatment-related liver enzymeabnormalities.

Drug Interactions for Zithromax

Nelfinavir

Co-administration of nelfinavir at steady-state with a single oral dose of azithromycin resulted inincreased azithromycin serum concentrations. Although a dose adjustment of azithromycin is notrecommended when administered in combination with nelfinavir, close monitoring for known adversereactions of azithromycin, such as liver enzyme abnormalities and hearing impairment, is warranted. [see ADVERSE REACTIONS]

Warfarin

Spontaneous post-marketing reports suggest that concomitant administration of azithromycin maypotentiate the effects of oral anticoagulants such as warfarin, although the prothrombin time was notaffected in the dedicated drug interaction study with azithromycin and warfarin. Prothrombin timesshould be carefully monitored while patients are receiving azithromycin and oral anticoagulantsconcomitantly.

Potential Drug-Drug Interaction With Macrolides

Interactions with the following drugs listed below have not been reported in clinical trials withazithromycin; however, no specific drug interaction studies have been performed to evaluate potentialdrug-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 withazithromycin careful monitoring of patients is advised.

Warnings for Zithromax

Included as part of the "PRECAUTIONS" Section

Precautions for Zithromax

Hypersensitivity

Serious allergic reactions, including angioedema, anaphylaxis, and dermatologic reactions includingAcute Generalized Exanthematous Pustulosis (AGEP), Stevens-Johnson Syndrome, and toxic epidermalnecrolysis have been reported in patients on azithromycin therapy. [see CONTRAINDICATIONS]

Fatalities have been reported. Cases of Drug Reaction with Eosinophilia and Systemic Symptoms(DRESS) have also been reported. Despite initially successful symptomatic treatment of the allergicsymptoms, when symptomatic therapy was discontinued, the allergic symptoms recurred soon thereafterin some patients without further azithromycin exposure. These patients required prolonged periods ofobservation and symptomatic treatment. The relationship of these episodes to the long tissue half-life ofazithromycin and subsequent prolonged exposure to antigen is unknown at present.

If an allergic reaction occurs, the drug should be discontinued and appropriate therapy should beinstituted. Physicians should be aware that the allergic symptoms may reappear after symptomatictherapy has been discontinued.

Hepatotoxicity

Abnormal liver function, hepatitis, cholestatic jaundice, hepatic necrosis, and hepatic failure have beenreported, some of which have resulted in death. Discontinue azithromycin immediately if signs andsymptoms of hepatitis occur.

Infantile Hypertrophic Pyloric Stenosis (IHPS)

Following the use of azithromycin in neonates (treatment up to 42 days of life), IHPS has been reported.Direct parents and caregivers to contact their physician if vomiting or irritability with feeding occurs.

QT Prolongation

Prolonged cardiac repolarization and QT interval, imparting a risk of developing cardiac arrhythmia andtorsades de pointes, have been seen with treatment with macrolides, including azithromycin. Cases oftorsades de pointes have been spontaneously reported during postmarketing surveillance in patientsreceiving azithromycin. Providers should consider the risk of QT prolongation, which can be fatalwhen 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.

Elderly patients may be more susceptible to drug-associated effects on the QT interval.

Clostridium Difficile-Associated Diarrhea

Clostridium difficile associated diarrhea (CDAD) has been reported with use of nearly all antibacterialagents, including ZITHROMAX (azithromycin for injection), and may range in severity from milddiarrhea to fatal colitis. Treatment with antibacterial agents alters the normal flora of the colon leadingto overgrowth of C. difficile.

C. difficile produces toxins A and B which contribute to the development of CDAD. Hypertoxinproducing strains of C. difficile cause increased morbidity and mortality, as these infections can berefractory to antibacterial therapy and may require colectomy. CDAD must be considered in all patientswho present with diarrhea following antibacterial use. Careful medical history is necessary sinceCDAD has been reported to occur over two months after the administration of antibacterial agents.

If CDAD is suspected or confirmed, ongoing antibacterial use not directed against C. difficile may needto be discontinued. Appropriate fluid and electrolyte management, protein supplementation, antibacterialtreatment 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 beenreported in patients receiving azitrhromycin therapy.

Infusion Site Reactions

ZITHROMAX for injection should be reconstituted and diluted as directed and administered as anintravenous infusion over not less than 60 minutes. [see DOSAGE AND ADMINISTRATION]

Local IV site reactions have been reported with the intravenous administration of azithromycin. Theincidence and severity of these reactions were the same when 500 mg azithromycin was given over 1hour (2 mg/mL as 250 mL infusion) or over 3 hr (1 mg/mL as 500 mL infusion) [see ADVERSE REACTIONS]. All volunteers who received infusate concentrations above 2.0 mg/mL experienced local IV sitereactions and, therefore, higher concentrations should be avoided.

Development Of Drug-Resistant Bacteria

Prescribing ZITHROMAX in the absence of a proven or strongly suspected bacterial infection isunlikely to provide benefit to the patient and increases the risk of the development of drug-resistantbacteria.

Nonclinical Toxicology

Carcinogenesis, Mutagenesis, Impairment Of Fertility

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 500 mg based on body surface area).

Use In Specific Populations

Pregnancy

Teratogenic Effects

Pregnancy Category B:

Reproductive and development studies have not beenconducted using IV administration of azithromycin to animals. Reproduction studies have beenperformed in rats and mice using oral administration at doses up to moderately maternally toxic doseconcentrations (i.e., 200 mg/kg/day). These daily doses in rats and mice based on body surface area, areestimated to be 4 and 2 times, respectively, an adult daily dose of 500 mg. In the animal studies, noevidence of harm to the fetus due to azithromycin was found. There are, however, no adequate andwell-controlled studies in pregnant women. Because animal reproduction studies are not alwayspredictive of human response, azithromycin should be used during pregnancy only if clearly needed.

Nursing Mothers

Azithromycin has been reported to be excreted in human breast milk in small amounts. Caution should beexercised when azithromycin is administered to a nursing woman.

Pediatric Use

Safety and effectiveness of azithromycin for injection in children or adolescents under 16 years havenot been established. In controlled clinical studies, azithromycin has been administered to pediatricpatients (age 6 months to 16 years) by the oral route. For information regarding the use ofZITHROMAX (azithromycin for oral suspension) in the treatment of pediatric patients, [see INDICATIONS, and DOSAGE AND ADMINISTRATION ] of the prescribing information for ZITHROMAX(azithromycin for oral suspension) 100 mg/5 mL and 200 mg/5 mL bottles.

Geriatric Use

Pharmaco*kinetic studies with intravenous azithromycin have not been performed in older volunteers.Pharmaco*kinetics of azithromycin following oral administration in older volunteers (65–85 years old)were similar to those in younger volunteers (18–40 years old) for the 5-day therapeutic regimen.

In multiple-dose clinical trials of intravenous azithromycin in the treatment of community-acquiredpneumonia, 45% of patients (188/414) were at least 65 years of age and 22% of patients (91/414) wereat least 75 years of age. No overall differences in safety were observed between these subjects andyounger subjects in terms of adverse reactions, laboratory abnormalities, and discontinuations. Similardecreases in clinical response were noted in azithromycin- and comparator-treated patients withincreasing age.

ZITHROMAX (azithromycin for injection) contains 114 mg (4.96 mEq) of sodium per vial. At the usualrecommended doses, patients would receive 114 mg (4.96 mEq) of sodium. The geriatric populationmay respond with a blunted natriuresis to salt loading. The total sodium content from dietary and nondietarysources may be clinically important with regard to such diseases as congestive heart failure.

Elderly patients may be more susceptible to development of torsades de pointes arrhythmias thanyounger patients. [see WARNINGS AND PRECAUTIONS]

Overdose Information for Zithromax

Adverse reactions experienced in higher than recommended doses were similar to those seen at normaldoses particularly nausea, diarrhea, and vomiting. In the event of overdosage, general symptomatic andsupportive measures are indicated as required.

Contraindications for Zithromax

Hypersensitivity

ZITHROMAX is contraindicated in patients with known hypersensitivity to azithromycin, erythromycin,any macrolide or ketolide drugs.

Hepatic Dysfunction

ZITHROMAX is contraindicated in patients with a history of cholestatic jaundice/hepatic dysfunctionassociated with prior use of azithromycin.

Clinical Pharmacology for Zithromax

Mechanism Of Action

Azithromycin is a macrolide antibacterial drug [see Microbiology]

Pharmacodynamics

Based on animal models of infection, the antibacterial activity of azithromycin appears to correlate withthe ratio of area under the concentration-time curve to minimum inhibitory concentration (AUC/MIC) forcertain pathogens (S. pneumoniae and S. aureus). The principal pharmaco*kinetic/pharmacodynamicparameter best associated with clinical and microbiological cure has not been elucidated in clinicaltrials with azithromycin.

Cardiac Electrophysiology

QTc interval prolongation was studied in a randomized, placebo-controlled parallel trial in 116 healthysubjects 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 QTcinterval in a dose- and concentration- dependent manner. In comparison to chloroquine alone, themaximum 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.

Since the mean Cmax of azithromycin following a 500 mg IV dose given over 1 hr is higher than themean Cmax of azithromycin following the administration of a 1500 mg oral dose, it is possible that QTcmay be prolonged to a greater extent with IV azithromycin at close proximity to a one hour infusion of500 mg.

Pharmaco*kinetics

In patients hospitalized with community-acquired pneumonia receiving single daily one-hourintravenous infusions for 2 to 5 days of 500 mg azithromycin at a concentration of 2 mg/mL, the meanCmax ± S.D. achieved was 3.63 ± 1.60 mcg/mL, while the 24-hour trough level was 0.20 ± 0.15mcg/mL, and the AUC24 was 9.60 ± 4.80 mcg·hr/mL.

The mean Cmax, 24-hour trough and AUC24 values were 1.14 ± 0.14 mcg/mL, 0.18 ± 0.02 mcg/mL, and8.03 ± 0.86 mcg·hr/mL, respectively, in normal volunteers receiving a 3-hour intravenous infusion of500 mg azithromycin at a concentration of 1 mg/mL. Similar pharmaco*kinetic values were obtained inpatients hospitalized with community-acquired pneumonia who received the same 3-hour dosageregimen for 2–5 days.

Comparison of the plasma pharmaco*kinetic parameters following the 1st and 5th daily doses of 500 mgintravenous azithromycin showed only an 8% increase in Cmax but a 61% increase in AUC24 reflectinga threefold rise in C₂₄ trough levels.

Following single-oral doses of 500 mg azithromycin (two 250 mg capsules) to 12 healthy volunteers,Cmax, trough level, and AUC24 were reported to be 0.41 mcg/mL, 0.05 mcg/mL, and 2.6 mcg·hr/mL, respectively. These oral values are approximately 38%, 83%, and 52% of the values observedfollowing a single 500-mg I.V. 3-hour infusion (Cmax : 1.08 mcg/mL, trough: 0.06 mcg/mL, and AUC24 :5.0 mcg·hr/mL). Thus, plasma concentrations are higher following the intravenous regimen throughoutthe 24-hour interval.

Distribution

The serum protein binding of azithromycin is variable in the concentration range approximating human exposure, decreasing from 51% at 0.02 mcg/mL to 7% at 2 mcg/mL.

Tissue concentrations have not been obtained following intravenous infusions of azithromycin, but following oral administration in humans azithromycin has been shown to penetrate into tissues, including skin, lung, tonsil, and cervix.

Tissue levels were determined following a single oral dose of 500 mg azithromycin in 7 gynecological patients. Approximately 17 hr after dosing, azithromycin concentrations were 2.7 mcg/g in ovarian tissue, 3.5 mcg/g in uterine tissue, and 3.3 mcg/g in salpinx. Following a regimen of 500 mg on the first day followed by 250 mg daily for 4 days, concentrations in the cerebrospinal fluid were less than 0.01 mcg/mL in the presence of non-inflamed meninges.

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 with a mean apparent plasma clearance of 630 mL/min and terminal elimination halflife of 68 hr. The prolonged terminal half-life is thought to be due to extensive uptake and subsequent release of drug from tissues.

In a multiple-dose study in 12 normal volunteers utilizing a 500 mg (1 mg/mL) one-hour intravenousmax dosage regimen for five days, the amount of administered azithromycin dose excreted in urine in 24 hr was about 11% after the 1st dose and 14% after the 5th dose. These values are greater than the reported 6% excreted unchanged in urine after oral administration of azithromycin. Biliary excretion is a major route of elimination for unchanged drug, following oral administration.

Specific Populations

Renal Insufficiency

Azithromycin pharmaco*kinetics were investigated in 42 adults (21 to 85 years of age) with varying degrees of renal impairment. Following the oral administration of a single 1,000 mg dose of azithromycin, mean Cmax and AUC0-120 increased by 5.1% and 4.2%, respectively in subjects with mild to moderate renal impairment (GFR 10 to 80 mL/min) compared to subjects with normal renal function (GFR >80 mL/min). The mean Cmax and AUC0-120 increased 61% and 35%, respectively in subjects with severe renal impairment (GFR <10 mL/min) compared to subjects with normal renal function (GFR >80 mL/min).

Hepatic Insufficiency

The pharmaco*kinetics 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 based on gender.

Geriatric Patients

Pharmaco*kinetic studies with intravenous azithromycin have not been performed in older volunteers. Pharmaco*kinetics of azithromycin following oral administration in older volunteers (65–85 years old) were similar to those in younger volunteers (18–40 years old) for the 5-day therapeutic regimen. [seeGeriatric Use].

Pediatric Patients

Pharmaco*kinetic studies with intravenous azithromycin have not been performed in children.

Drug-Drug Interactions

Drug interaction studies were performed with oral azithromycin and other drugs likely to be coadministered. The effects of co-administration of azithromycin on the pharmaco*kinetics of other drugs are shown in Table 1 and the effects of other drugs on the pharmaco*kinetics of azithromycin are shown in Table 2.

Co-administration of azithromycin at therapeutic doses had a modest effect on the pharmaco*kinetics of the drugs listed in Table 1. No dosage adjustment of drugs listed in Table 1 is recommended when coadministered with azithromycin.

Co-administration of azithromycin with efavirenz or fluconazole had a modest effect on the pharmaco*kinetics 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 [see DRUG INTERACTIONS].

Table 1. Drug Interactions: Pharmaco*kinetic Parameters for Co-administered Drugs in thePresence of Azithromycin

Table 2. Drug Interactions : Pharmaco*kinetic Parameters for Azithromycin in the Presenceof Co-administered Drugs [see DRUG INTERACTIONS].

Microbiology

Mechanism Of Action

Azithromycin acts by binding to the 23S rRNA of the 50S ribosomal subunit of susceptible microorganisms inhibiting bacterial protein synthesis and impeding the assembly of the 50S ribosomal subunit.

Resistance

Azithromycin demonstrates cross-resistance with erythromycin. The most frequently encountered mechanism of resistance to azithromycin is modification of the 23S rRNA target, most often by methylation. Ribosomal modifications can determine cross resistance to other macrolides, lincosamides and streptogramin B (MLS_B phenotype).

Antimicrobial Activity

Azithromycin has been shown to be active against the following microorganisms, both in vitro and in clinical infections. [see INDICATIONS]

Gram-positive Bacteria

Staphylococcus aureus
Streptococcus pneumoniae

Gram-negative Bacteria

Haemophilus influenzae
Moraxella catarrhalis
Neisseria gonorrhoeae
Legionella pneumophila

Other Bacteria

Chlamydophila pneumoniae
Chlamydia trachomatis
Mycoplasma hominis
Mycoplasma pneumoniae

The following in vitro data are available, but their clinical significance is unknown. At least 90 percent of the following bacteria exhibit an in vitro minimum inhibitory concentration (MIC) less than or equal to the susceptible breakpoint for azithromycin against isolates of similar genus or organism group. However, the efficacy of azithromycin in treating clinical infections caused by these bacteria has not been established in adequate and well-controlled clinical trials.

Aerobic Gram-Positive Bacteria

Streptococci (Groups C, F, G)
Viridans group streptococci

Gram-Negative Bacteria

Bordetella pertussis

Anaerobic Bacteria

Peptostreptococcus species
Prevotella bivia

Other Bacteria

Ureaplasma urealyticum

Susceptibility Testing

For specific information regarding susceptibility test interpretive criteria and associated test methods and quality control standards recognized by FDA for this drug, please see: https://www.fda.gov/STIC.

Animal Toxicology And/Or Pharmacology

Phospholipidosis (intracellular phospholipid accumulation) has been observed in some tissues of mice, rats, and dogs given multiple oral 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 pharmaco*kinetic data, phospholipidosis has been seen in the rat (50 mg/kg/day dose) at the observed maximal plasma concentration of 1.3 mcg/mL (1.6 times the observed Cmax of 0.821 mcg /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 mcg /mL (1.2 times the observed Cmax of 0.821 mcg /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 body 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 mcg /ml, approximately 1.5 times the Cmax of 1.27 mcg/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 mcg /ml, approximately 3 times the pediatric dose Cmax. The significance of the findings for animals and for humans is unknown.

Clinical Studies

Community-Acquired Pneumonia

In a controlled trial of community-acquired pneumonia performed in the U.S., azithromycin (500 mg as a single daily dose by the intravenous route for 2 to 5 days, followed by 500 mg/day by the oral route to complete 7 to 10 days therapy) was compared to cefuroxime (2250 mg/day in three divided doses by the intravenous route for 2 to 5 days followed by 1000 mg/day in two divided doses by the oral route to complete 7 to 10 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 10 to 14 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 10 to 14 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 10 to 14 days post-therapy for patients treated with azithromycin with evidence (serology and/or culture) of atypical pathogens for both trials were as follows:

Patient Information for Zithromax

Patients should be informed of the following serious and potentially serious adverse reactions that havebeen associated with ZITHROMAX^®

Diarrhea

Inform patients that diarrhe is a common problem caused by antibacterial drugs which usually ends when the antibacterial 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 notify their physician as soon as possible.