Anticonvulsant Drugs: Relative Risks

Like all therapeutic drugs, anticonvulsants have unwanted side effects that affect some people more than others. Although the vast majority of women who take these medications during pregnancy have healthy children, it has long been recognized that they are, on average, about twice as likely as other women to have a baby with a major birth defect (4 – 6 percent vs 2 – 3 percent ). Major birth defects associated with anticonvulsants affect the heart, skeletal system, cleft lip, cleft palate, urogenital system and the neural tube, the last named giving rise to the condition known as spina bifida.

Until recently, little has been known about relative risks to women among the most widely prescribed anticonvulsants. Is drug A a safer bet than drug B? How about drug C, one of the newer drugs? Aside from reports on a specific drug’s known side effect profile and effectiveness in controlling seizures or other central nervous system disorders, physicians have had little to go on when prescribing for women of childbearing age. Earlier studies that sought more information on effects of anticonvulsants during pregnancy involved fairly small groups of women and were not designed to allow effective comparisons among drugs. Until recently, women were not enrolled in trials of new drugs. Indeed, the Food and Drug Administration (FDA)-approved prescribing information for all anticonvulsants is silent on the issue except for the phrase: “Safety in pregnancy has not been established.” Translation: “We can’t promise that this medication will not affect your pregnancy or your baby.” Adding to the importance of new information on relative risk is the fact that some anticonvulsants reduce the effectiveness of hormonal birth control, increasing the risk of unplanned pregnancy.