A widely used anti-epilepsy drug called topiramate raises the risk of birth defects as much as 14-fold when taken by pregnant women, especially in combination with another drug called valproate, British researchers reported today.
Experts were quick to caution, however, that the study involved only 203 women, and thus significant statistical uncertainty remained about the research.
"You can't make any definitive statements from the data," said Dr. Kimford J. Meador of the University of Florida in Gainesville, who was not involved in the study.
But the results are not surprising, experts added, because topiramate -- sold by Johnson & Johnson under the brand name Topamax -- has been shown to cause similar defects in animals.
Other epilepsy drugs that have been studied have also been found to increase the risk of such defects, suggesting that the entire class of drugs may interfere with the reproductive process.
Despite the enormous risks, doctors say that epileptic women cannot stop taking the drugs during pregnancy because seizures can also damage the unborn infant, perhaps even more severely.
But women who are taking the drug to prevent migraines should halt its use if they become pregnant or are planning to do so, said Dr. John Craig of the Royal Group of Hospitals in Belfast, Northern Ireland, who led the research published in the journal Neurology.
Epilepsy, which affects an estimated 2.7 million Americans, is a disorder characterized by powerful seizures. Topamax accounts for about 1 in 5 prescriptions for treatment.
Valproate, which is one of the most common drugs used in treating the disorder, has previously been associated with birth defects or fetal death in about 20% of women who take it.
Craig and his colleagues studied 203 women who became pregnant while taking topiramate on its own or in combination with other epilepsy drugs.
Of the 203 pregnancies, 18 ended in spontaneous abortions, two in stillbirths and five in induced abortions.
Of the 178 babies born, 16 had major birth defects. In three of those cases, the mothers had taken only topiramate, and in the other 13, the mothers had taken it in combination with other drugs.
Four of the babies had cleft palates or lips, a rate 11 times the normal rate of 1 in 500 expected among women not taking epilepsy drugs. Four male babies had genital birth defects, which is 14 times the normal rate of 1 in 300.
The women in the study were part of the U.K. Epilepsy and Pregnancy Register, which was set up to determine the relative safety of such drugs.
Five other registries have also been established, including one in the United States. Results from two of the larger registries may be released later this year.