Formulary
Azithromycin: Uses, Dosing, Side Effects and Indian Brand Names
Azithromycin is an azalide macrolide with an exceptionally long tissue half-life enabling 3-5 day treatment courses, first-line for atypical pneumonia and single-dose therapy for genital chlamydia.
MedNext Academy | 4 min read
Clinically reviewed by Awaiting clinical review
Azithromycin: Uses, Dosing, Side Effects and Indian Brand Names
Azithromycin is an azalide macrolide with an exceptionally long tissue half-life enabling 3-5 day treatment courses, first-line for atypical pneumonia and single-dose therapy for genital chlamydia.
NEET PG High-Yield: 50S ribosomal subunit inhibition (same as chloramphenicol, clindamycin, linezolid -- mnemonic: '50 CCL-Az'). Longest tissue half-life of any common antibiotic (68-72h). NOT a CYP3A4 inhibitor (unlike erythromycin, clarithromycin). Drug of choice for Chlamydia (single dose). Covers Mycoplasma, Chlamydophila, Legionella (atypical pathogens). QT prolongation risk. Trojan horse effect (concentrates in phagocytes).
Clinical overview
Azithromycin is the most prescribed macrolide antibiotic in India, valued for its broad spectrum, excellent tissue penetration, and uniquely long half-life (68-72 hours) that allows short-course therapy -- 3 to 5 days of treatment achieves tissue concentrations above the MIC for 7-10 days after the last dose. The drug concentrates extensively in tissues, reaching intracellular levels 10-100 times higher than plasma, with particular accumulation in phagocytes that then deliver the drug to sites of infection (Trojan horse effect). This high tissue-to-plasma ratio means that measuring serum levels is misleading. Azithromycin covers typical and atypical respiratory pathogens (S. pneumoniae, H. influenzae, Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella), making it a first-line option for community-acquired pneumonia in penicillin-allergic patients and the empiric agent of choice for atypical pneumonia. It is also the drug of choice for genital Chlamydia trachomatis (single 1 g dose), chancroid (H. ducreyi), and traveller's diarrhoea. The cardiac risk of azithromycin (QT prolongation and risk of torsades de pointes) became prominent after the 2012 Ray et al. study, and caution is warranted in patients with pre-existing QT prolongation or electrolyte abnormalities. Unlike erythromycin and clarithromycin, azithromycin is NOT a significant CYP3A4 inhibitor, giving it a much cleaner drug interaction profile.
Pharmacological class
Azithromycin belongs to the Macrolide Antibiotics (Azalide) class. Binds to the 50S ribosomal subunit (specifically the 23S rRNA of the peptidyl transferase centre), blocking translocation of the growing peptide chain and inhibiting bacterial protein synthesis. Bacteriostatic at usual concentrations, but may be bactericidal at high concentrations against certain organisms (e.g., Streptococcus pneumoniae, H. influenzae). Classified as an azalide -- a subclass of macrolides with a 15-membered ring (compared to 14 for erythromycin and clarithromycin).
Indian brand names and formulations
Available as: Azithral (Alembic), Azee (Cipla), Zithromax (Pfizer), Azicip (Cipla).
Tablets: 250 mg, 500 mg. Capsules: 250 mg. Suspension: 100 mg/5 mL, 200 mg/5 mL. Sachets: 1 g (single-dose). IV infusion: 500 mg vial (limited use in India). Eye drops: 1% (for trachoma).
Regulatory status
Azithromycin is classified under Schedule H in India under the Drugs and Cosmetics Act, 1940. Prescription-only. One of the most overused antibiotics in India, particularly for viral URTIs. Subject to antimicrobial stewardship concerns.
Indications
- Community-acquired pneumonia (atypical pathogens: Mycoplasma, Chlamydophila, Legionella)
- Acute bacterial exacerbation of COPD
- Genital Chlamydia trachomatis infection (single 1 g dose)
- Chancroid (Haemophilus ducreyi)
- Traveller's diarrhoea (single dose or 3-day course)
- Pharyngitis/tonsillitis (penicillin-allergic patients)
- Non-gonococcal urethritis
- MAC prophylaxis in HIV (1200 mg weekly)
Dosing
CAP and respiratory infections: 500 mg on day 1, then 250 mg on days 2-5 (total 1.5 g over 5 days). Alternatively: 500 mg daily for 3 days. Chlamydia: 1 g single dose. MAC prophylaxis: 1200 mg once weekly. Traveller's diarrhoea: 1000 mg single dose or 500 mg daily for 3 days. Children: 10 mg/kg on day 1, then 5 mg/kg on days 2-5.
Contraindications
- Known hypersensitivity to macrolide or ketolide antibiotics
- History of cholestatic jaundice/hepatic dysfunction associated with prior azithromycin use
- Concomitant use with ergotamine or dihydroergotamine (risk of ergot toxicity)
Adverse effects
- Diarrhoea and abdominal pain (most common)
- Nausea and vomiting (less than erythromycin due to weaker motilin agonism)
- QT prolongation and risk of torsades de pointes (caution in patients with pre-existing long QT, hypokalaemia, hypomagnesaemia)
- Hepatotoxicity (rare but can be severe -- cholestatic jaundice)
- Hearing loss (usually reversible, with high doses or prolonged use)
Drug interactions
- QT-prolonging drugs (amiodarone, sotalol, haloperidol, fluoroquinolones): additive risk of torsades de pointes
- Warfarin: may increase INR; monitor closely (mechanism: gut flora disruption and possibly mild CYP inhibition)
- Antacids (aluminium/magnesium): reduce azithromycin absorption; separate by 2 hours
- Note: Unlike erythromycin and clarithromycin, azithromycin has MINIMAL CYP3A4 inhibition -- it does NOT significantly interact with theophylline, carbamazepine, or statins
Pregnancy and lactation
Category B. Generally considered safe. Used as single-dose treatment for chlamydia in pregnancy (preferred over doxycycline which is contraindicated). Also used for MAC prophylaxis in HIV-positive pregnant women.
Exam-style clinical scenario
A 30-year-old man presents with dry cough for 2 weeks, low-grade fever, and bilateral diffuse interstitial infiltrates on CXR. Gram stain of sputum is negative. What is the most likely organism and drug of choice? Mycoplasma pneumoniae (atypical pneumonia) -- azithromycin 500 mg on day 1 followed by 250 mg for 4 days.
Cost in India
Rs 50-120 for a strip of 3 tablets (500 mg). Single-dose 1 g sachets: Rs 60-100. Suspension: Rs 60-100 for 15 mL.
Clinical governance
Author: MedNext Editorial Team. Clinical reviewer: Awaiting clinical review. Jurisdiction: India (Drugs and Cosmetics Act, 1940). Sources: CIMS India, Indian Pharmacopoeia. Publication state: Awaiting clinical review. Correction: Report errors at support@mednext.academy.
Frequently Asked Questions
Why is azithromycin preferred over erythromycin in practice?
Azithromycin has major advantages: much longer half-life (68h vs 1.5h) allowing shorter courses, better GI tolerance (less motilin receptor agonism so less nausea), fewer drug interactions (minimal CYP3A4 inhibition), and oral bioavailability unaffected by food (unlike erythromycin base). The main disadvantage is the QT prolongation risk, which erythromycin also shares.
Why does azithromycin work with a 3-day course?
Azithromycin concentrates in tissues at 10-100x plasma levels, especially in phagocytes. Its tissue half-life is 68-72 hours. After a 3-day course, tissue concentrations remain above the MIC of susceptible organisms for 7-10 additional days. Plasma levels fall quickly (misleadingly low), but the drug is slowly released from tissue depots, maintaining antibacterial activity.
Is azithromycin effective against tuberculosis?
Azithromycin has activity against Mycobacterium avium complex (MAC) and is used for MAC prophylaxis and treatment in immunocompromised patients. However, it has NO role in treating Mycobacterium tuberculosis -- the standard RIPE regimen (rifampicin, isoniazid, pyrazinamide, ethambutol) is required. Do not confuse MAC coverage with TB coverage.
Inside MedNext for this topic
- 411 MedNext-authored chapters
- 80,000+ MCQ bank
- 15 study modes
- Growing visual cheat sheets
Study modes
- Notes
- MCQ
- Audio
- Video
- Visual
- 3D Anatomy
- Trace
- Flashcards
- Mnemonics
- Image Bank
- Clinical
- Microscopy
- Audio QBank
- Cadaver
- Book Match
Continue reading
Subject HubPharmacology Hub
All pharmacology resources in one place.
Drug SchedulesIndian Drug Schedules
Schedule H, H1, X and G classifications.
Test yourself on Azithromycin
Challenge yourself with targeted pharmacology MCQs on this drug class. Every explanation links back to the chapter that teaches the concept.
Start drug challengeExplore the full formulary

