Major
Carbamazepine × diltiazem
Antiepileptics. Carboxamide derivatives×Calcium channel blocker, non-DHP (benzothiazepine derivative)
Mechanism
Diltiazem blocks CYP3A4 – the main carbamazepine metabolic route. Carbamazepine plasma levels rise 1.5-fold. Neurotoxicity risk emerges (ataxia, diplopia, sedation).
Symptoms
Ataxia, diplopia, nausea, drowsiness, tremor. Severe cases: cardiac conduction abnormalities and AV block.
Management
Avoid the combination. Alternative calcium channel blocker without CYP3A4 inhibition: amlodipine (with caution). If unavoidable, check carbamazepine level at 1 and 4 weeks.
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.