Pozen (Nasdaq: POZN) got a pleasant surprise on Wednesday when the FDA actually approved its migraine drug Treximet on its PDUFA date. And I'm sure CV Therapeutics (Nasdaq: CVTX) and Cardiome (Nasdaq: CRME) were jealous.

The FDA headache that has been plaguing Pozen and marketing partner GlaxoSmithKline (NYSE: GSK) for so long seems to finally be cured. It started with an FDA approvable letter back in 2006. After the duo cleared up the FDA's cardiovascular issue, the agency came up with a new hurdle for them to jump over -- one of the preclinical tests suggested that the drug combination might be causing DNA damage, which could lead to cancer. One short clinical trial and a lot of data crunching later, Pozen concluded that the preclinical data was an anomaly, which led to this week's approval.

The drug is set to be launched by Glaxo in the middle of next month. Pozen will reportedly get tiered royalties starting in the low single digits and going to the high teens, depending on sales through 2009, and then royalties jump into the high teens after that.

Pozen no longer has to worry about whether the FDA will approve the drug, but it still has to worry whether anyone will buy the stuff. You see, Treximet is a combination of naproxen, which is available as a generic, and Glaxo's Imitrex, which goes off patent in November. Late this year, doctors may be inclined to write two prescriptions to make their own generic combination rather than prescribe the more costly Treximet for their patients. Even if doctors are willing to write the scripts for Treximet, it's not clear if insurers will cover the high-priced brand name if patients can just build their own generic cocktail.

It's not an insurmountable feat, but if Flamel Technologies' (Nasdaq: FLML) experience with Glaxo's ability to switch patients from one drug about to go off patent (Coreg IR) to a new drug (Coreg CR) is an example of what Pozen can expect, the company might have another headache coming its way. At least now it has an FDA-approved drug to relieve it.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. Glaxo is a selection of the Income Investor newsletter. Flamel is a former Motley Fool Hidden Gems pick. The Fool's disclosure policy has yet to convert from using Betamax.