EFFECTS OF CARBAMAZEPINE COADMINISTRATION ON PLASMA-CONCENTRATIONS OFTRAZODONE AND ITS ACTIVE METABOLITE, M-CHLOROPHENYLPIPERAZINE

Effects of carbamazepine coadministration on plasma concentrations of trazodone and its active metabolite, m-chlorophenylpiperazine (m-CPP) were studied in six depressed patients treated with trazodone. The dai ly dose of trazodone was 150 mg in three cases and 300 mg in three cas es. Carbamazepine, 400 mg/day, was coadministered for 4 weeks, and blo od samples were taken before carbamazepine addition and at weekly inte rvals after the addition. Carbamazepine significantly (p < 0.01) decre ased plasma concentrations of not only trazodone but also m-CPP at eac h week. On the average, plasma concentrations of trazodone and m-CPP a t 4 weeks were 24 and 40% of the corresponding precarbamazepine values . This study thus suggests that carbamazepine coadministration decreas es plasma concentrations of trazodone and m-CPP by inducing the metabo lism of these compounds.