Oxcarbazepine disposition: preliminary observations in patients

We describe a preliminary retrospective study based on the concentration of two hydroxylated metabolites of oxcarbazepine (OCZ), a new anticonvulsant substance, measured in the plasma of 15 patients with epilepsy. Their ages ranged from 8 to 68 years, 6 of them also received phenobarbital and/or phenytoin as co-medication. The concentration of 10-hydroxy-10,11-dihydrocarbamazepine (HCBZ) or of trans-10,11-dihydroxy-10,11-dihydrocarbamazepine (DHCBZ), the metabolites measured, are significantly correlated with the dose of OCZ (p less than 0.05 and p less than 0.01, respectively). DHCBZ concentrations, standardized to a constant OCZ dose or to a constant HCBZ concentration, are significantly higher during co-medication (p less than 0.01 and p less than 0.05, respectively); HCBZ levels are unaffected. These results confirm that enzyme-inducing drugs, although accelerating the oxidation HCBZ, do not induce its formation. Since HCBZ is the active metabolite, such drug interaction seems unlikely to alter OCZ pharmacological activity.