Azithromycin

Macrolide (azalide) antibiotic · 50S ribosomal subunit inhibitor · Brands: Zithromax, Zmax, Azee

FDA Approved · 1991 Oral & IV formulations Multiple Indications QT prolongation warning

Overview & Mechanism

Drug identity

Generic nameAzithromycin Drug classMacrolide antibiotic Pharmacological classAzalide macrolide; 50S ribosomal subunit inhibitor Therapeutic areaInfectious disease ATC classificationJ01FA10 Common brand namesZithromax, Zmax, Azee Dosage formsTablets, capsules, oral suspension, extended-release oral suspension, intravenous formulation Common strengths250 mg, 500 mg, 600 mg tablets; oral suspensions vary by formulation ManufacturerPfizer

Overview

Azithromycin is a macrolide antibiotic used to treat a range of bacterial infections involving the respiratory tract, skin and skin structures, and certain sexually transmitted infections. It is also used to prevent and treat disseminated Mycobacterium avium complex (MAC) disease in some patients with advanced HIV infection.

It works by interfering with bacterial protein production. Its long tissue half-life allows many infections to be treated with once-daily dosing and relatively short courses. It is available in oral and intravenous forms, with paediatric oral formulations for selected infections.

Use responsiblyUse only for bacterial infections that are proven or strongly suspected to be susceptible. Unnecessary antibiotic use drives antimicrobial resistance.

Mechanism of action

Azithromycin binds to the 23S rRNA of the 50S bacterial ribosomal subunit and inhibits protein synthesis. This blocks the ribosome's movement along messenger RNA, so susceptible bacteria cannot make the proteins they need to grow and replicate.

It is generally bacteriostatic, although bactericidal activity may occur against certain organisms at high enough concentrations.

Pharmacokinetics

AbsorptionPeak plasma levels about 2–3 hours after an oral dose.

DistributionExtensive; tissue levels far exceed plasma levels.

MetabolismLimited hepatic metabolism; low CYP3A4 interaction potential.

EliminationMostly biliary/faecal; a smaller share in urine. Terminal half-life about 68 hours.

Antimicrobial activity

Active against selected Gram-positive and Gram-negative bacteria, atypical respiratory pathogens and some sexually transmitted pathogens. Usefulness is limited by organism-specific susceptibility and rising resistance.

Clinical Use & Dosing

FDA-approved uses

Approved in the United States for selected mild-to-moderate bacterial infections caused by susceptible organisms. Indications vary by formulation.

Respiratory infectionsAcute bacterial exacerbations of chronic bronchitis (adults) · Acute bacterial sinusitis (adults) · Community-acquired pneumonia (adults and children 6 months+) · Pharyngitis/tonsillitis (2 years+, alternative to first-line) · Acute otitis media (6 months+)

Skin & skin structureUncomplicated skin and skin-structure infections caused by susceptible organisms.

Sexually transmitted infectionsNon-gonococcal urethritis and cervicitis caused by Chlamydia trachomatis; others in specific US labels.

Mycobacterial infectionsPrevention of disseminated MAC in advanced HIV; treatment of disseminated MAC with ethambutol.

Important limitationNot for use as the sole oral treatment in pneumonia that is moderate-to-severe, or where oral therapy is otherwise inappropriate.

Evidence-supported or guideline-dependent uses may apply according to local guidelines and specialist judgment. These are not FDA-approved indications.

Dosage & administration · Adults

Dosing depends on indication, formulation, age and weight. These are commonly used US labeled regimens; always check the specific product's prescribing information.

Community-acquired pneumonia500 mg Day 1, then 250 mg once daily on Days 2–5 Acute bacterial sinusitis500 mg once daily for 3 days Acute exacerbation of chronic bronchitis500 mg once daily × 3 days, or 500 mg Day 1 then 250 mg Days 2–5 Skin & skin-structure infections500 mg Day 1, then 250 mg once daily on Days 2–5 Chlamydial urethritis/cervicitis1,000 mg as a single oral dose Disseminated MAC prevention1,200 mg once weekly, alone or with rifabutin Disseminated MAC treatment600 mg once daily with ethambutol

Paediatric patients

Dosed by age, weight, infection and formulation, usually in mg/kg per product labeling. Safety and effectiveness below 6 months of age are not established in current US labeling.

Administration

Tablets may generally be taken with or without food; some formulations have specific food instructions.
Shake oral suspension well and use a proper measuring device.
Complete the prescribed course unless advised otherwise.

Renal impairmentNo routine adjustment for mild-to-moderate impairment; take care in severe dysfunction.

Hepatic impairmentUse cautiously; stop if signs of hepatitis develop.

Safety & Interactions

Key safety concerns

QT prolongation & cardiac arrhythmiasCan prolong the QT interval; associated with torsades de pointes and potentially fatal arrhythmias. Higher risk with known QT prolongation, prior torsades, significant bradycardia, low potassium or magnesium, certain cardiac diseases, or other QT-prolonging medicines. FDA strengthened this warning in 2013.

HepatotoxicityHepatitis, cholestatic jaundice and, rarely, severe or fatal hepatic failure. Stop if signs of hepatitis develop.

HypersensitivityAnaphylaxis, angioedema and severe skin reactions including SJS and TEN have been reported.

C. difficile-associated diarrhoeaCan occur during or after treatment.

Infantile hypertrophic pyloric stenosisReported after exposure in neonates, especially in the first weeks of life.

Myasthenia gravisMay worsen muscle weakness.

Antimicrobial resistanceUse only when a susceptible bacterial infection is suspected or confirmed.

Common adverse effects

DiarrhoeaNauseaAbdominal painVomitingHeadache

Drug interactions

WarfarinMay increase anticoagulant effect; monitor coagulation when appropriate. DigoxinMay increase digoxin exposure; watch for toxicity. QT-prolonging medicinesHigher risk of serious cardiac arrhythmias. Antacids (Al/Mg)May be taken together; follow product-specific instructions. NelfinavirMay increase azithromycin exposure; monitor liver enzymes and hearing effects. CyclosporineExposure may change; consider monitoring levels. Other interacting drugsReview medicines linked to QT prolongation, arrhythmias or hepatic effects.

Special Populations & Practical Use

Special populations

PregnancyHuman data have not shown a consistent link with major congenital malformations. Weigh maternal infection, alternatives, benefits and risks.

BreastfeedingPresent in breast milk. No consistent pattern of serious infant effects; watch for GI or unusual symptoms.

Paediatric patientsApproved for otitis media and CAP from 6 months, pharyngitis/tonsillitis from 2 years. Extra caution in neonates (pyloric stenosis).

Older adultsMay be more susceptible to QT-related arrhythmias, especially with other risk factors.

Hepatic impairmentUse cautiously; stop if significant hepatitis develops.

Renal impairmentNo routine adjustment for mild-to-moderate; monitor in severe dysfunction.

Practical information

Taking azithromycin

Take exactly as prescribed and complete the course.
Do not use leftover antibiotics or share them.
Shake suspensions well and use the supplied measuring device.

Missed dose

Take it when remembered unless the next dose is near. Do not double up unless told to.

Seek medical attention forSevere or persistent diarrhoea · yellow skin or eyes · dark urine · severe rash or blistering · difficulty breathing or facial swelling · fainting or palpitations · new or worsening muscle weakness.

OverdoseMay cause GI and hearing-related effects. Treatment is supportive; no specific antidote.

MonitoringNot routine for short courses. Consider with liver disease, cardiac risk, QT drugs, warfarin, long courses or MAC.

StorageFollow product labeling. Reconstituted suspension has a limited shelf life.

Regulatory & Clinical Evidence

Regulatory history

1 Nov 1991 Initial approval Respiratory, skin and skin-structure, and sexually transmitted infections.
1990s–2000s New formulations and uses Paediatric suspension, 600 mg tablets and IV injection (30 Jan 1997). MAC prevention and treatment in advanced HIV added.
Mar 2013 QT prolongation warning Safety Risk of abnormal heart rhythm, including potentially fatal torsades de pointes.
2017 Paediatric labeling Safety Warning on infantile hypertrophic pyloric stenosis after neonatal exposure.
2021 Cardiovascular risk labeling Safety Possible rise in short-term cardiovascular death, mainly in the first five days.

Clinical evidence

Respiratory infectionsTrials supporting approval showed efficacy in CAP, bronchitis exacerbations and other susceptible respiratory infections.

Community-acquired pneumoniaEffective against S. pneumoniae, H. influenzae, M. pneumoniae and C. pneumoniae in patients suited to oral therapy.

Sexually transmitted infectionsEvidence supports activity against C. trachomatis; follow current guidelines as resistance evolves.

Disseminated MACRandomised studies in advanced HIV support prevention (with rifabutin) and treatment (with ethambutol).

The evidence base spans respiratory, sexually transmitted and mycobacterial infections, with extensive post-marketing experience. Current prescribing must account for resistance and key risks, especially QT prolongation and hepatotoxicity.

References & sources

Fact-Checked Reviewed by Pharmacally Editorial Team · Last reviewed 1 Nov 2026

This profile summarises regulator labeling and published evidence for education. It is not a substitute for the full prescribing information or professional medical advice. How we source drug data

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