The U.S. Food and Drug Administration (FDA) lists Zarontin (ethosuximide) 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 who take seizure medicines generally are more likely to have birth defects, although a large majority are normal. The risk is higher if the woman takes more than one medicine or has a family history of birth defects. Doctors are not sure how much of the added risk is caused by the medicines and how much is the result of factors such as genetics or seizures themselves.
Also, there is little specific information about whether particular seizure medicines are more likely to cause birth defects than others. We know that ethosuximide crosses freely from the mother into the baby during pregnancy, but we don't know much about its effects.
Women who are capable of becoming pregnant should take at least 400 mcg (0.4 mg) of folic acid (folate) daily to help prevent a type of birth defect called a neural tube defect. (The best-known of these is spina bifida, in which the spinal cord is not completely enclosed.) Women at high risk, such as those who have had a baby with this kind of 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. The doctor may recommend checking the level of medication in the blood regularly during pregnancy so that the dosage can be adjusted as needed.
Ethosuximide (Zarontin) 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. Women taking ethosuximide who are interested in breast-feeding should discuss their options with their doctor.
Reviewed February 2004 by Barry Gidal, PharmD, epilepsy.com Editorial Board.
