The epilepsy drug oxcarbazepine (Trileptal) does not appear to prevent migraine headaches as previously thought, a new research shows.

More than 28 million Americans are affected by migraines on regular basis and certain epilepsy drugs have been shown to be effective in preventing them. Women are more likely to experience migraine headaches than men, 18 percent of women versus six percent of men. That is why many assumed that oxcarbazepine would also work against migraines.

Dr. Stephen Silberstein of the Jefferson Headache Center in Philadelphia and associates randomly assigned 170 men and women with a history of migraine to a daily dose of oxcarbazepine or inactive placebo. All participants had three to nine migraine attacks within a month. The researchers found no difference between people taking oxcarbazepine or placebo in the number of migraines they suffered during the study.

“The results of this trial do not support preliminary data which had suggested oxcarbazepine was effective in preventing migraine. While several epilepsy drugs have been used for decades to prevent migraine, oxcarbazepine did not prevent migraine in this study despite it being shown to be safe and well-tolerated,” Silberstein noted in a written statement, according to Reuters.

Silberstein also says that the three epilepsy drugs that have been shown to prevent migraines, topiramate, divalproex and gabapentin have several mechanisms by which they treat migraine, including the ability to regulate a neurotransmitter known as GABA. Oxcarbazepine appears not to affect GABA activity. Silberstein notes that epilepsy drugs need to regulate GABA to prevent migraine.

The study was welcomed by Dr. Ellen Drexler, director of the Headache Center at Maimonides Medical Center in New York City.

“This is a study done by a group of experts in the field following all the usual standards of clinical research, so the findings can be accepted as valid. The results are not that surprising, as drugs with related mechanism of action such as carbamazepine and phenytoin have never been found to be efficacious for migraine prophylaxis,” Dr. Drexler said quoted by Forbes.

The study comes just one week after the U.S. Food and Drug Administration warned that 11 epilepsy drugs, including oxcarbazepine, might boost the risk of suicide among users.

The study, paid by Novartis Pharmaceuticals Corp., maker of oxcarbazepine, was published in the February 12, 2008 issue of Neurology, the medical journal of the American Academy of Neurology.