The U.S. Food and Drug Administration (FDA) lists Zarontin in Pregnancy Category C. This indicates that caution is advised, but the benefits of the medication may outweigh the potential risks.

The babies of women taking antiepileptic drugs (AEDs) generally are more likely to have birth defects, although a large majority are normal. The risk of defects is higher for women who take more than one AED and for women with a family history of birth defects. The reasons for these differences are uncertain, since factors other than medication, such as genetics and seizures, also may play a role.

There is little solid evidence indicating whether particular AEDs are more teratogenic than others. We do know that ethosuximide crosses the placenta and plasma levels in neonates are similar to those of the mother.

Advise women who are capable of becoming pregnant to take 400 mcg (0.4 mg) of folic acid (folate) daily to help prevent neural tube defects. Women at high risk, such as those with a history of a neural tube defect in a previous pregnancy, should take 4000 mcg (4 mg) daily, beginning before they become pregnant.

About 20% to 35% of women have seizures more often during pregnancy because of changes in hormones or changes in how their medication is handled by the body. Check the blood levels of ethosuximide regularly during pregnancy so that the dosage can be adjusted as needed.

Ethosuximide appears in breast milk. Estimates are that a nursing infant might receive a dose of 13 to 38 mg per day. The effect of this dose on an infant is unknown. Discuss the options with women taking ethosuximide who are interested in breast-feeding, including staying with ethosuximide, switching to a different AED, or discontinuing their medication.

Reviewed February 2004 by Barry Gidal, PharmD, epilepsy.com Editorial Board.