IUD advocated for women using antiepileptics.(Gynecology)

NEW ORLEANS -- The best contraceptive choices for women on antiepileptic medications are probably a progesterone-eluting intrauterine device or intramuscular medroxyprogesterone, with the higher doses of oral contraceptives running in second place, Anne Davis, M.D., said at the annual meeting of the American Epilepsy Society.

Some antiepileptic drugs--carbamazepine, oxcarbazepine, phenytoin, barbiturates (phenobarbital, mephobarbital and primidone), and topiramate--enhance the P450 cytochrome enzyme system. "This decline potentially decreases the effectiveness of hormonal methods of contraception," said Dr. Davis of Columbia University, New York.

The intrauterine device (IUD) and the depot medroxyprogesterone acetate (DMPA) (Depo-Provera) injection are not as prone to these drug interactions. The progesterone-eluting IUD thickens cervical mucus, impairs sperm movement, suppresses endometrial development, and has a slight anovulatory effect. DMPA suppresses ovulation and its progesterone content protects its effect from alterations in the enzyme system, Dr. Davis said.

In addition, the high progesterone content might have antiseizure properties. "This is a little bit of a teaser, something that's out there in the literature. Progesterone decreased seizure frequency in animal models, and DMPA decreased seizure frequency in women with intractable epilepsy. It's a tantalizing thing, but there's too little information out there to make any conclusions."

The second choice for women on the CYP450-en-hancing drugs would be higher dose oral contraceptives. "It's a little misleading to actually call some oral contraceptives 'high dose,' because everything these days is really low dose," she said. "What we're really talking about is differentiating between ...