Differential impact of contraceptive methods on seizures varies by antiepileptic drug category: Findings of the Epilepsy Birth Control Registry.

PURPOSE: The aim of this study was to determine whether categories of contraception differ in their impact on seizures in women with epilepsy and whether the impact varies by antiepileptic drug category.

METHODS: Retrospective survey data came from 2712 contraceptive experiences reported by 1144 women with epilepsy. We compared risk ratios for reports of increase and decrease in seizure frequency on hormonal versus nonhormonal contraception, stratified by antiepileptic drug categories.

RESULTS: More women with epilepsy reported a change in seizures on hormonal (28.2%) than on nonhormonal contraception (9.7%) (p<0.0001). The risk ratio for seizure increase on hormonal (18.7%) versus nonhormonal contraception (4.2%) was 4.47 (p<0.0001). The risk ratio for seizure decrease on hormonal (9.5%) versus nonhormonal contraception (5.5%) was 1.71, p<0.0001. On hormonal contraception, the risk ratio for seizure increase was greater than for decrease (1.98, p<0.0001). In comparison to combined pills, both hormonal patch and progestin-only pills had greater risk ratios for seizure increase. Depomedroxyprogesterone was the only hormonal method with a greater risk ratio for seizure decrease than combined pills. Seizure increase was greater for hormonal than nonhormonal contraception for each antiepileptic drug category (p<0.001). On hormonal contraception, relative to the non-enzyme-inducing antiepileptic drug category which had the lowest rate, each of the other categories had significantly greater risks for seizure increase, especially the enzyme-inhibiting (valproate) category (risk ratio=2.53, p=0.0002).

CONCLUSION: The findings provide community-based, epidemiological survey evidence that contraceptive methods may differ in their impact on seizures and that this impact may vary by antiepileptic drug category.