A DOUBLE-BLIND, PLACEBO-CONTROLLED INTERACTION STUDY BETWEEN OXCARBAZEPINE AND CARBAMAZEPINE, SODIUM VALPROATE AND PHENYTOIN IN EPILEPTIC PATIENTS

1 The effect of carbamazepine (CBZ), sodium valproate (VPA) and phenyt oin (PHT) on the pharmacokinetics of oxcarbazepine (OXC) was explored in three groups of 12 epileptic patients taking one of these drug as m onotherapy. 2 Each patient took a single 600 mg dose of OXC followed 7 days later by 3 weeks' treatment with OXC 300 mg thrice daily and mat ched placebo in random order. 3 Seven untreated patients, acting as co ntrols, were prescribed the single OXC dose and 3 weeks' active treatm ent only. 4 In those patients completing the study, the area under the concentration-time curve (AUC) at steady-state for hydroxycarbazepine (OHCZ), the active metabolite of OXC, was significantly lower in the CBZ-treated group than in controls (P < 0.05). 5 No other differences in AUCs or elimination half-lives for OHCZ were found between treated and untreated patients following single or multiple OXC dosing.6 Media n AUCs of CBZ, VPA and PHT during a dosage interval did not differ sig nificantly after treatment with OXC and placebo. 7 Ten patients comple ting the study complained of side-effects during treatment with OXC co mpared with one taking placebo (P < 0.01). 8 There were no important c hanges in cognitive function testing during administration of OXC comp ared with placebo. 9 Standard doses of OXC can be given as add-on ther apy in epileptic patients receiving CBZ, VPA or PHT without producing a clinically relevant pharmacokinetic interaction.