April 3 (Bloomberg) -- GlaxoSmithKline Plc's experimental pill Trexima, combining the Imitrex tablet and the painkiller naproxen sodium, relieved migraine headaches more effectively than either drug alone, according to two studies.

The combination tablet stopped moderate or severe migraine headaches in as many as 65 percent of the 2,956 U.S. adults in the company-funded trials. Imitrex relieved headaches in up to 55 percent while naproxen sodium helped in as many as 44 percent, according to the studies, being published tomorrow in the Journal of the American Medical Association.

``We've used combination therapy for a long time based on the belief that it worked, but these two studies provide really solid evidence that the combination treatment is rational and provides better outcomes,'' Richard Lipton, a neurologist and director of the Montefiore Headache Unit in New York, said in a telephone interview. He wasn't an investigator in the studies.

The findings may boost London-based Glaxo's Trexima when generic-drug competitors begin selling copies of Imitrex in 2008. The company sought U.S. Food and Drug Administration approval to sell Trexima, a new formulation of 85 milligrams of Imitrex with 500 milligrams of naproxen, for treatment of migraines in 2005. The regulatory agency may rule on the application by Aug. 1.

Glaxo is developing the drug with Pozen Inc. of Chapel Hill, North Carolina.

More than 28 million people in the U.S. suffer migraines, Glaxo estimates. The headaches are recurrent, cause moderate to severe pain that can be throbbing or confined to one side of the head, and may be accompanied by nausea, vomiting or sensitivity to light and sound.

Light, Sound

Trexima also reduced sensitivity to light and sound after two hours more than either ingredient alone or a placebo, the studies showed. The absence of nausea after two hours was higher in the patients taking the combination treatment than in the groups on Imitrex, naproxen or placebo in one study and about the same in the second study.

The combined effect of Trexima may be greater than Imitrex or naproxen alone because it targets multiple mechanisms believed to play a role in migraines, the researchers who conducted the studies wrote. Imitrex, which belongs to a class of compounds known as triptans, may affect peripheral nervous system mechanisms, and naproxen, a non-steroidal anti- inflammatory drug, works on the central nervous system, they said.

Imitrex and a low-dose, over-the-counter formula known as Imigran brought in 711 million pounds ($1.4 billion) last year for Glaxo, the world's second-largest drugmaker after Pfizer Inc. The injectable form of Imitrex was approved in the U.S. in 1992 and faces generic competition next year. The tablet version was approved in 1995 and faces generic rivals in early 2009. Naproxen sodium is an over-the-counter painkiller used to treat arthritis.

To contact the reporter on this story: Andrea Gerlin in London agerlin@bloomberg.net

Last Updated: April 3, 2007 16:49 EDT