POSSIBLE INTERACTION BETWEEN PHENOBARBITAL, CARBAMAZEPINE AND ITRACONAZOLE

We report a case of a possible interaction between itraconazole, pheno barbital and carbamazepine. The first plasma itraconazole concentratio n, measured when the patient had been taking phenobarbital for 2 month s, was very low. The second measurement, 2 months after withdrawing ph enobarbital, was higher but below the therapeutic range. However, carb amazepine, a well known enzyme inducer, had been initiated 15 days bef ore. 20 days after carbamazepine was withdrawn, the itraconazole conce ntration 4 hours after administration was near the lower end of the th erapeutic range. The mechanism of this possible interaction is probabl y the same for phenobarbital and carbamazepine, involving hepatic micr osomal enzyme system induction.