Azithromycin
Brand names: Zithromax, Azitrocin, Sumamed
Macrolide antibiotic
Azithromycin is a macrolide antibiotic with a long tissue half-life, allowing short 3–5 day courses. It is widely used for respiratory infections, atypical pneumonia, and sexually transmitted infections, and is an important alternative for penicillin-allergic patients.
Drug Class
Macrolide antibiotic
Category
Antibiotics
Forms Available
Tablets (250 mg, 500 mg), Oral suspension
How It Works
Azithromycin binds to the 50S ribosomal subunit of bacteria, inhibiting protein synthesis. It is bacteriostatic (stops bacterial growth) rather than bactericidal at usual doses. Its long tissue half-life allows sustained concentrations at infection sites long after the last dose.
What It's Used For
- Community-acquired pneumonia (especially atypical — Mycoplasma, Chlamydophila, Legionella)
- Acute exacerbations of chronic bronchitis
- Sinusitis and pharyngitis (penicillin-allergic patients)
- Chlamydia trachomatis infection (single 1 g dose)
- Traveller's diarrhoea (Campylobacter)
- Prevention of MAC (mycobacterium avium complex) in HIV patients
Available Forms
Side Effects
Common Side Effects
- Nausea, vomiting, diarrhoea — the most common GI effects
- Abdominal pain
- Headache
Serious Side Effects
- QT interval prolongation — risk of cardiac arrhythmia, particularly with other QT-prolonging drugs
- Hepatotoxicity (rare but reported)
- Hypersensitivity reactions including Stevens-Johnson syndrome (very rare)
Drug Interactions
- Antacids — reduce absorption; take azithromycin 1 hour before or 2 hours after antacids
- QT-prolonging drugs (amiodarone, haloperidol, clarithromycin) — additive arrhythmia risk
- Warfarin — may increase anticoagulant effect
- Ergot derivatives — risk of ergotism
When to Avoid
- Macrolide antibiotic allergy
- Known QT prolongation or concurrent QT-prolonging medications (with caution)
- Severe hepatic impairment
Patient Tips
- Azithromycin packs often come as a 3-day or 5-day course — complete all doses
- Tissue levels remain therapeutic for days after the last dose — the antibiotic continues working
- May be taken with or without food
- Tell your doctor about all other medications due to QT prolongation risk
The 'Z-pack' and antibiotic stewardship
Azithromycin became one of the world's most prescribed antibiotics partly due to its convenience (short course, once daily). However, overuse — particularly for viral respiratory infections — has driven significant macrolide resistance among Streptococcus pneumoniae and Mycoplasma pneumoniae globally.
Azithromycin should not be used for sore throats or ear infections unless penicillin cannot be used. Your doctor's prescription should match the likely pathogen and local resistance data.
Related Medicines
Medical disclaimer
This page is for educational reference only. Always follow the dosage and instructions given by your prescriber or pharmacist. Do not start, stop, or change medicines without medical advice.
Reviewed 2026-06-01 · Looms Medical Team