Major
Carbamazepine × Verapamil
Antiepileptics. Carboxamide derivatives×Non-dihydropyridine calcium channel blocker
Mechanism
Verapamil blocks CYP3A4 – the main carbamazepine metabolic route. Carbamazepine plasma levels rise, with neurotoxicity risk.
Symptoms
Ataxia, diplopia, nausea, drowsiness, tremor. Severe cases include cardiac conduction abnormalities and AV block. Symptoms appear within 1–2 weeks.
Management
Avoid the combination. Alternative calcium channel blockers without CYP3A4 inhibition: amlodipine or diltiazem (use diltiazem with caution; it has a moderate CYP3A4 effect). If unavoidable, measure carbamazepine plasma levels at 1 and 4 weeks.