Carbamazepine-induced changes in plasma levels of neuroleptics.

We compared the effect of carbamazepine and oxcarbazepine treatment on the plasma levels of clozapine and thioridazine in 12 patients. There was a 47% decrease in the plasma levels of clozapine (p < 0.005, Students two-tailed t-test) during carbamazepine treatment, while the effects on the thioridazine levels were less marked (n.s.). Since carbamazepine is also used in patients receiving concurrent clozapine therapy, it is important to take this marked interaction between these two drugs into account.