Reviewed by MedNext Clinical Team
Azithromycin's convenient dosing schedule — typically a 3-day or 5-day course — and broad-spectrum activity have made it one of the most prescribed antibiotics worldwide. However, concerns about cardiac safety and antibiotic stewardship mean it should be used judiciously [1].
Mechanism and Spectrum of Activity
Azithromycin is a macrolide antibiotic that inhibits bacterial protein synthesis by binding the 50S ribosomal subunit. It has excellent activity against atypical respiratory pathogens including Mycoplasma pneumoniae, Chlamydophila pneumoniae, and Legionella species, as well as Chlamydia trachomatis. Its long tissue half-life (exceeding 68 hours) accounts for its short-course efficacy.
Community-Acquired Pneumonia
Azithromycin is a recommended option for community-acquired pneumonia (CAP) in non-severe cases, particularly for atypical coverage when the pathogen is uncertain. For hospitalised patients with moderate-to-severe CAP, combination therapy with a beta-lactam is preferred to ensure adequate coverage of Streptococcus pneumoniae. Sole azithromycin therapy is insufficient for severe or bacteraemic pneumococcal pneumonia.
QT Prolongation and Cardiac Risk
Azithromycin prolongs cardiac repolarisation (QT interval) and has been associated with an increased risk of fatal cardiac arrhythmias, including torsades de pointes [1]. A landmark pharmacoepidemiological study found an elevated risk of cardiovascular death with azithromycin compared to amoxicillin, particularly among patients with pre-existing cardiovascular disease. Risk factors for QT prolongation (concurrent QT-prolonging drugs, hypokalaemia, hypomagnesaemia, bradycardia, female sex) should be assessed before prescribing.
Antibiotic Stewardship
Widespread azithromycin prescribing for upper respiratory tract infections — most of which are viral — contributes significantly to macrolide resistance, particularly in Streptococcus pneumoniae and Mycoplasma pneumoniae. Clinicians should resist patient pressure to prescribe antibiotics for self-limiting viral illnesses and reserve azithromycin for situations where a bacterial aetiology is likely and the patient cannot take the preferred first-line agent.
Interactions to Note
- Avoid combining with other QT-prolonging drugs (antipsychotics, antiarrhythmics, fluoroquinolones)
- Azithromycin is a mild CYP3A4 inhibitor — may increase exposure to some co-administered drugs
- Correct electrolyte abnormalities before prescribing in high-risk patients
References
- Ray WA, et al. Azithromycin and the risk of cardiovascular death. NEJM. 2012;366:1881-1890.