Major
carvedilol × diltiazem
Alpha and beta blocker (non-selective β + α1)×Calcium channel blocker, non-DHP (benzothiazepine derivative)
Mechanism
Non-dihydropyridine calcium channel blocker (diltiazem) + beta-blocker (carvedilol) – additive AV node blockade and negative inotropic effect. Carvedilol's α1-blockade amplifies hypotension.
Symptoms
Bradycardia (heart rate below 50/min), dizziness, syncope. ECG: first- to second-degree AV block. Older patients: fall risk.
Management
Avoid the combination. Alternative for combined heart failure and angina: carvedilol + amlodipine (dihydropyridine, no AV effect) or diltiazem with carvedilol withdrawn.