Possible interaction between oxcarbazepine and an oral contraceptive

The effect of oxcarbazepine (OCBZ) on the kinetics of an oral contraceptive containing ethinyloestradiol (EE) and levonorgestrel (LNG) was investigated in 13 healthy female volunteers who had previously received the contraceptive for at least 3 months. After 15 days of the first study cycle, each subject received, in addition to the oral contraceptive, 300 mg OCBZ on day 16, 300 mg twice daily on day 17, and 300 mg three times daily from day 18 of the first cycle to day 18 of the next menstrual cycle. The area under the curve values for both EE and LNG decreased when OCBZ was given with the oral contraceptive (p = 0.006, analysis of variance). The results indicate that OCBZ, like most antiepileptic drugs (AEDs), decreases the bioavailability of EE and LNG, perhaps by affecting metabolism or protein binding.