Valproate and lamotrigine level variation with menstrual cycle phase and oral contraceptive use

Objective: To determine whether 1) combined oral contraceptive (COC) use affects serum levels of valproate (VPA) as well as lamotrigine (LTG) and 2) the naturally occurring high (mid-luteal) and low (early-mid follicular) reproductive steroid level phases of the menstrual cycle might affect antiepileptic drug levels as well. Methods: This investigation compared serum antiepileptic drug levels at two timepoints during a single menstrual cycle in four groups of women with epilepsy: 12 on VPA, 12 on VPA plus COC (VPA-COC), 12 on LTG, and 12 on LTG plus COC (LTG-COC). Results: Both VPA and LTG levels were lower ( p p = NS). Conclusions: The findings suggest that valproate (VPA), like lamotrigine (LTG), has substantially and significantly lower serum levels while women take active combined oral contraceptives as compared to inactive pills. Larger sample sizes will be required to determine whether LTG levels may drop significantly also during the luteal (high steroid) phase of natural menstrual cycles and whether VPA levels may show greater stability in levels across the phases of the menstrual cycle. AED = antiepileptic drug; BMI = basal metabolic index; COC = combined oral contraceptive; EIAED = enzyme-inducing antiepileptic drug; IGE = idiopathic generalized epilepsy; LRE = localization-related epilepsy; LTG = lamotrigine; VPA = valproate.