Pharmacokinetic interaction between carbamazepine and neuroleptics after combined prolonged treatment in rats.

This study investigates how neuroleptics of phenothiazine or thioxanthene structure influence the pharmacokinetics of carbamazepine. Experiments were carried out on male Wistar rats. Carbamazepine and the neuroleptics were administered i.p., separately or together, for 2 weeks in the following daily doses (mg/kg): carbamazepine 15 during the 1st week of treatment and 20 during the 2nd week of treatment, promazine 10, chlorpromazine 2, perazine 10, chlorprothixene 2, flupenthixol 0.5. One hour after the last injection of carbamazepine and/or the neuroleptic, samples of blood plasma and brain were taken to determine the concentrations of carbamazepine and two of its metabolites: 10,11-epoxide and trans-10,11-diol. The neuroleptics increased the concentration of carbamazepine in plasma and in brain, but tended to decrease (with the exception of chlorpromazine) the concentration of the epoxide and increased the concentration of trans-10,11-diol. Metabolic in vitro studies did not show any significant differences between rats treated with carbamazepine alone and those treated with carbamazepine plus neuroleptic in the rates of the carbamazepine epoxidation, of 10,11-epoxide hydrolysis or of 1-naphthol glucuronidation.