A drug normally used against epilepsy can prevent migraine headaches, according to two studies.

The research trials are the first to test the drug topiramate in hundreds of migraine patients. The combined results are likely to push topiramate closer to Food and Drug Administration approval for use against migraines, says neurologist Jan Lewis Brandes of Vanderbilt University School of Medicine in Nashville and the research clinic Nashville Neuroscience Group.

Marketed as Topamax by Ortho-McNeil Pharmaceutical in Raritan, N.J., topiramate is already prescribed by many doctors for migraines, even though the FDA has formally approved it only for preventing epileptic seizures, says neurologist Stephen D. Silberstein of Thomas Jefferson University in Philadelphia.

But some physicians hesitate to prescribe drugs not specifically approved for a condition, even though they're permitted to do so in the United States.

In the Feb. 25 Journal of the American Medical Association, Brandes and her colleagues report that 70 patients getting 200 milligrams a day of topiramate for 6 months saw their monthly migraine episodes drop from 5.1 to 3.0, on average. Another 63 volunteers taking 100 mg/day reduced their average number of episodes from 5.8 to 3.5 per month. Meanwhile, 122 people receiving a lower dose or the placebo experienced less of a decline.

In the other study, partial results of which have been presented at scientific meetings, Silberstein and his colleagues obtained almost identical findings. Their final results will be published later this year.

The biological mechanism by which topiramate reduces migraines isn't fully understood, the scientists acknowledge. As an antiepilepsy drug, topiramate limits overstimulation of brain cells. The same action may partly explain how topiramate helps migraine sufferers, says neuropharmacologist John Claude Krusz of Anodyne Headache and PainCare Center in Dallas. However, he says, topiramate has multiple effects on brain cells, and researchers are still investigating how its other properties might also thwart migraines.

In any case, the new studies will "defuse a lot of the fears" about prescribing the epilepsy drug for migraines, Krusz says.

The most common side effects among patients in both studies were tingling and numbness in fingers and toes and loss of appetite. The prospect of shedding pounds could be attractive to migraine sufferers, particularly because some other migraine medicines lead to weight gain, says Richard B. Lipton, a neurologist at the Albert Einstein College of Medicine in New York.

Also, research suggests that chronic migraines can cause structural damage in the brain. Topiramate might avert some of this destruction by lessening migraine attacks, Lipton says. The drug could also prevent overuse of other pain medications, such as opiates, that have long-term drawbacks, he says.

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