MajorClass III antiarrhythmics (Vaughan Williams)×Selective β1-adrenoceptor blockers
Updated · Methodology
Mechanism
Dual mechanism. Amiodarone non-competitively blocks β-adrenoceptors and depresses atrioventricular (AV) conduction; metoprolol is a competitive β-blocker. Effects add up: lowered heart rate and AV conduction. Amiodarone also inhibits CYP2D6 and metoprolol plasma levels rise.
Symptoms
Bradycardia (heart rate below 50/min), dizziness, syncope. ECG: first- to second-degree AV block, prolonged PR. In heart failure: worsening dyspnoea and oedema.
Management
The combination is appropriate in cardiology (atrial fibrillation, post-infarction care). Halve the metoprolol dose when starting amiodarone. Check pulse and ECG at 1 and 4 weeks. If pulse drops below 50 or second-degree AV block appears, adjust metoprolol further.
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
- Lexicomp: Lexicomp Drug Interactions (2024)– Wolters Kluwer Clinical Drug Information, Inc. Lexi-Interact Online, 2024
- ESC: 2024 ESC Guidelines for the management of atrial fibrillation developed in collaboration with the EACTS (2024)– Eur Heart J 2024;45(36):3314–3414
- AEMPS: Ficha técnica: Metoprolol 100 mg (Aurovitas) (nº registro 82000), sección 4.5 (2026)– AEMPS, CIMA, nº registro 82000, revisión 04/2026, sección 4.5