MajorClass III antiarrhythmics (Vaughan Williams)×Macrolides
Updated · Methodology
Mechanism
Additive QT prolongation. Azithromycin received a 2013 FDA warning for fatal ventricular arrhythmia risk, particularly in patients with risk factors. Amiodarone is a potent QT-prolonging drug.
Symptoms
QT prolongation on ECG. Clinically: dizziness, syncope, palpitations. Severe cases progress to polymorphic ventricular tachycardia (torsades de pointes) with risk of ventricular fibrillation and sudden cardiac death. Risk is higher with hypokalaemia, hypomagnesaemia, bradycardia, and ischaemic heart disease.
Management
Avoid the combination. Alternative antibiotics: doxycycline or a cephalosporin. If azithromycin is needed, ECG before start and potassium and magnesium in range.
Check the full regimen, not just this pair
Opens the checker with these two drugs prefilled. Add the rest of the regimen and recompute additive risks.
Summary of a multi-drug list →
Medicine list: everything you take in one place →
Sources
- AHA: Drugs that Prolong QT and TdP – AHA Scientific Statement (2020)
- FDA: Pacerone (amiodarone hydrochloride) tablets – Prescribing Information (2025)– FDA, DailyMed SPL, Upsher-Smith Laboratories, раздел 7
- AEMPS: Ficha técnica Trangorex 200 mg comprimidos (amiodarona) (2022)– AEMPS, CIMA, nº registro 48048, revisión 01/2022, sección 4.5
- AEMPS: Ficha técnica Zitromax 250 mg cápsulas duras (azitromicina) (2026)– AEMPS, CIMA, nº registro 59616, revisión 07/2026, secciones 4.4 y 4.5
- FDA: Zithromax (azithromycin) tablets and oral suspension – Prescribing Information (2026)– FDA, DailyMed SPL, Pfizer, раздел 5.4