These findings are important because several commonly prescribed anti-epileptic drugs (AEDs) may reduce the effectiveness of oral contraceptives, a potentially serious drug interaction for some women with epilepsy.
The study examined the effect of clinically relevant Zonegran maintenance doses on the pharmacokinetics (serum concentrations, distribution, and elimination) of ethinyl estradiol (EE) and norethindrone (NOR), the two components of Ortho-McNeil’s commonly prescribed oral contraceptive, Ortho-Novum 1/35.
The researchers compared the concentrations of EE and NOR during oral contraceptive dosing alone to those following the administration of Zonegran. Mean serum EE and NOR concentrations were similar before and after Zonegran dosing, indicating that steady-state dosing of Zonegran had no clinically relevant effect on the pharmacokinetics of EE or NOR.
Because this study was conducted in healthy individuals, the titration schedule was more aggressive than the schedule recommended for people with epilepsy. Despite rapid titration, Zonegran was reasonably well-tolerated in 26 subjects at the target dose of 400mg/d when taken with a combination oral contraceptive containing EE and NOR, although the incidence of adverse events was higher than when dose escalation is slower.