Macrolides · Anti-infectives
Azithromycin
Zithromax®(brand names vary by market)
A three-day course that keeps working for a week.
Also: oral liquid, infusion
Mechanism
Binds the 50S ribosomal subunit and blocks translocation. It concentrates inside cells and tissues far above plasma levels, which is what gives it atypical coverage and a very long tissue half-life.
Indications
- Community-acquired pneumonia, atypical coverage
- Chlamydia
- Pertussis
- Traveller's diarrhoea
- Exacerbation prophylaxis in bronchiectasis and COPD
Formulations
Dosing concepts
Short courses
Tissue concentrations persist for days after the last dose, which is why a three- or five-day course treats a longer illness.
Prophylaxis
Long-term thrice-weekly use in bronchiectasis and COPD works partly through anti-inflammatory rather than antibacterial effects, and requires attention to QT and to macrolide resistance.
Concepts, not prescribing instructions. Practice numbers live in current references and local protocols.
Pharmacokinetics
- Bioavailability
- ~37%
- Half-life
- ~68 h, tissue half-life longer still
- Elimination
- hepatic: Mainly biliary; minimal CYP3A4 inhibition, unlike clarithromycin
- Protein binding
- Low and concentration-dependent
Adverse effects
- Gastrointestinal upsetcommon
- QT prolongationserious
- Hearing loss with prolonged high-dose useserious
- Hepatotoxicityserious
Contraindications & precautions
Contraindications
- Prior macrolide-associated cholestatic jaundice
- Known QT prolongation with other risk factors
Precautions
- Concurrent QT-prolonging drugs
- Electrolyte disturbance
- Myasthenia gravis
Interactions
Monitoring
QT where other risk factors exist
Class effect
Clinical response
Macrolide resistance in pneumococcus is high in many regions
Hearing on long-term prophylaxis
Cumulative ototoxicity
Counselling points
- Complete the short course even though you may feel better quickly.
- It keeps working for several days after the last tablet.
- Tell us about palpitations or fainting.
Clinical pearls
- Its minimal CYP3A4 inhibition is the main practical reason to choose it over clarithromycin, particularly in a patient on a statin, a calcium channel blocker or warfarin.
- Pneumococcal macrolide resistance is high enough in many places that it is no longer trusted as monotherapy for pneumonia; it is added for atypical cover.
References & review
- Azithromycin product monograph (consult the current version for your market) (monograph)
- Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed. (reference-work)
Last reviewed 2026-08-16 · jurisdiction: global · drug information changes; verify against current references before practice use.