Azithromycin Drug Interactions
Azithromycin has clinically significant interactions with warfarin (requiring INR monitoring), nelfinavir (which increases azithromycin levels), and QT-prolonging drugs (particularly hydroxychloroquine), while having minimal interactions with most other medications due to its lack of cytochrome P450 metabolism. 1
Critical High-Risk Interactions
QT Interval Prolongation
- Avoid combining azithromycin with other QT-prolonging agents (hydroxychloroquine, class IA/III antiarrhythmics) as both are listed as definite causes of torsade de pointes 2
- Withhold azithromycin if baseline QTc ≥500 ms or in patients with congenital long-QT syndrome 2
- Monitor ECG and discontinue if QTc exceeds 500 ms during therapy 2
- Risk factors include hypokalemia, hypomagnesemia, fever, and inflammatory states 2
Anticoagulants
- Monitor prothrombin time/INR closely when co-administering with warfarin despite no interaction in controlled studies, spontaneous post-marketing reports suggest azithromycin may potentiate anticoagulant effects 1
- Case reports document INR elevation to 15.16 in stabilized patients after azithromycin initiation 3
Antiretroviral Agents
- Nelfinavir significantly increases azithromycin exposure (Cmax increased 2.36-fold, AUC increased 2.12-fold) 1
- Monitor for azithromycin side effects (liver enzyme abnormalities, hearing impairment) when combined with nelfinavir 1
- No dose adjustment recommended, but heightened surveillance required 1
Moderate Interactions Requiring Awareness
Ergot Alkaloids
- Risk of acute ergot toxicity with severe peripheral vasospasm and dysesthesia 1
- Avoid concurrent use based on macrolide class effect
Digoxin
- May cause elevated digoxin concentrations 1
- Monitor digoxin levels if co-administered
Antacids
- Only interaction affecting azithromycin bioavailability 4
- Separate administration times
Minimal or No Interaction (No Dose Adjustment Needed)
The following drugs show modest or no clinically significant interactions with azithromycin 1:
- Atorvastatin, carbamazepine, cetirizine
- Didanosine, efavirenz, fluconazole, indinavir
- Midazolam, rifabutin, sildenafil
- Theophylline (both IV and oral)
- Triazolam, trimethoprim/sulfamethoxazole, zidovudine
Key Mechanistic Advantage
Unlike erythromycin and clarithromycin, azithromycin does not inhibit cytochrome P450 3A enzymes, explaining its superior interaction profile compared to other macrolides 5, 6. This makes it the safest macrolide choice when multiple drug therapy is required.
Common Pitfalls to Avoid
- Do not assume azithromycin is interaction-free - the QT prolongation and warfarin interactions are clinically significant
- Elderly women are at higher risk for QT prolongation and arrhythmias 2
- COVID-19 context: The combination of azithromycin + hydroxychloroquine showed 90% mortality in severe interaction cases during the pandemic 4
- Polypharmacy patients: 5.1% of azithromycin users receive it with potentially risky QT-prolonging drugs, most commonly loratadine (77.1%) 7