More women on hormonal contraceptives also reported having a decrease in seizures after starting contraception, compared with those starting on a nonhormonal method (9.5% vs. 5.2%, respectively), which calculated to a 85% relative rate increase for decreased seizures. Depot medroxyprogesterone acetate was the only specific hormonal contraceptive that linked with a higher rate of seizure decreases, compared with combined oral pills, a 95% higher rate.
A second analysis of the results by Dr. Herzog and his associates examined the frequencies of seizure outcomes on hormonal and nonhormonal contraceptives stratifying by type of antiepileptic drug women used when starting a particular contraceptive method. This analysis broke down antiepileptic drugs into four types: enzyme inducing (29%), glucuronidated (such as lamotrigine; 27%), nonenzyme inducing (such as levetiracetam; 22%), enzyme inhibiting (valproate; 8%), and a fifth category that included women who were not on any antiepileptic drug (14%).
This analysis showed that the frequency of seizure increases was significantly greater with hormonal contraceptive use, compared with nonhormonal methods, across all five subgroups of antiepileptic drug type. In addition, the frequency of seizure increases with hormonal contraceptives differed significantly, depending on which antiepileptic drug type women used, but these significant differences among the antiepileptic drug types also occurred among women using nonhormonal contraception.
Women receiving a nonenzyme-inducing drug when starting a hormonal contraceptive reported the lowest frequency of seizure increases, a 12% rate. In contrast, women on an enzyme-inhibiting drug, valproate, had the highest rate of increased seizures when starting a hormonal contraceptive, 29%. This calculated out to about a 2.5-fold relative risk increase for having more seizures when starting hormonal contraception while on valproate, compared with women on a nonenzyme-inducing drug, Dr. Herzog reported.
Physicians “need to be on the lookout for the possibility that seizures could increase when women start a hormonal contraceptive,” he concluded.
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