MajorClass III antiarrhythmics (Vaughan Williams)×Imidazole derivatives (antiprotozoal / antibacterial)
Updated · Methodology
Mechanism
Metronidazole prolongs the QT interval. Combined with amiodarone, torsades de pointes has been reported, especially with hypokalaemia.
Symptoms
QT prolongation on ECG. Dizziness, syncope, palpitations. Severe cases: polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia and hypomagnesaemia.
Management
Avoid the combination. Alternative antibiotics without QT effect: a cephalosporin, amoxicillin-clavulanate, or fosfomycin. For anaerobic infection requiring metronidazole: ECG before start and at day 2.
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
- FDA: Amiodarone hydrochloride tablet (Dr. Reddy's Labratories Inc.) – Prescribing Information (2018)– ; DailyMed setid 95cef33b-c0e6-b17c-7cbb-f5c066872705
- 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 Metronidazol Normon 250 mg comprimidos EFG (2026)– AEMPS, CIMA, nº registro 62223, revisión 01/2026, sección 4.5
- FDA: Flagyl (metronidazole) capsules – Prescribing Information (2026)– FDA, DailyMed SPL, Pfizer, Precautions (Drug Interactions)