Carbamazepine neurotoxic reaction after administration of diltiazem

A patient with epilepsy controlled by carbamazepine developed a carbamazepine neurotoxic reaction after being given an increased dosage of diltiazem hydrochloride as adjunctive therapy. Abrupt withdrawal of diltiazem reduced the circulating carbamazepine concentration and resulted in an epileptic attack. Awareness of the interaction between diltiazem and carbamazepine and careful monitoring of carbamazepine blood levels is recommended to prevent the dangerous neurotoxic effect associated with this combination.