Pozen (NASDAQ:POZN) is awaiting an FDA decision on its New Drug Application for Trexima as a treatment for migraine headaches. In June 2006, the company received an approvable letter from the FDA requesting more data, specifically on the interaction between Trexima's component drugs, naproxen and sumitriptan. The FDA is set to rule on this resubmission by Aug. 1.

The two drugs treat migraines in different ways. Sumatriptan stimulates serotonin receptors, constricting blood vessels to provide migraine relief, while naproxen is a non-steroidal anti-inflammatory drug. In addition to their varying approaches to attacking migraines, the two drugs may be absorbed by the body at different rates when jointly administered. This sort of combination therapy is common in treating cancer, and it's a good idea.

A recent paper in the Journal of the American Medical Association (JAMA) presented results from two phase 3 studies of Trexima, which Pozen is developing in partnership with GlaxoSmithKline (NYSE:GSK). In the studies cited in JAMA, patients who received a single Trexima tablet had better pain relief results than patients receiving either sumatriptan or naproxen alone. Other effects of migraines, including nausea and sensitivity to light and sound, were similarly reduced. The authors of the JAMA article also point out that the levels of the two drugs used in Trexima's current formulation may or may not be the most effective combination -- only further study will tell.

For me, this study leaves a pretty big unanswered question: What is the benefit of a single pill combining two existing drugs, compared to just taking each drug separately?

I did some more digging and discovered a paper published in 2005, which found that the combination of the two drugs was superior to either given alone.

With clear benefits to Trexima, it will be interesting to see whether Pozen can get the FDA's thumbs-up. The company has a dubious track record at getting such combination drugs approved; it recently settled a shareholder lawsuit arising from previous failures to do so.

Both of these drugs are well-known, so approval is likely, though not assured. But I'm also wondering whether insurance companies will foot the bill for Trexima. At the end of the day, sales are all that matter. With naproxen already available as a cheap generic, and sumatriptan soon to follow, convincing patients to pay more for a single pill may be tough.

If Trexima's not approved, Pozen's stock will clearly tank. Any benefits stemming from the drug's successful approval are harder to gauge. The stock price could get a bump up, or it could slump as investors betting on approval sell to lock in gains. In the long term, Trexima's sales will drive Pozen's share price. I don't think the prognosis looks good for either one.

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Fool contributor Andrew R. Vaino holds no financial position in any stock mentioned above. GlaxoSmithKline is an Income Investor recommendation. The Fool has a disclosure policy.