Over the weekend, specialty drugmaker Endo Pharmaceuticals (NASDAQ:ENDP) presented more clinical trial results for its already approved migraine treatment, Frova.

Frova was initially launched in 2002 to treat acute migraine headaches. Endo in-licensed the compound near the end of 2004 from drug developer Vernalis. So far the compound hasn't been much of a hit for Endo, with Frova sales growing in the single-digit percentage points to $41 million last year.

Frova was tested in two phase 3 label-expanding studies as a treatment for preventing menstrual migraines. The drug was originally up for FDA review on this label-expanding indication in May, but the FDA extended the PDUFA date another three months to Aug. 19. The data that Endo presented over the weekend was one of the phase 3 studies Endo is using to try and get this expanded label.

In this study, all doses of the drug produced highly statistically significant improvements in the number of headache-free perimenstrual periods for women who took Frova versus a placebo. The drug also reduced the incidence of severe headaches by nearly a third for one patient group taking Frova. These results, combined with the other Frova phase 3 study and the well-known drug profiles for the class of compounds that Frova is in, mean the drug stands a high chance of gaining regulatory approval in August to help prevent menstrual migraines.

It's clear that Endo will need new indications for which to market Frova if it wants to generate substantial new sales growth for the drug. One similar compound, Imitrex from GlaxoSmithKline (NYSE:GSK), had sales of more than $1 billion last year, primarily in the United States. This shows that there is plenty of room for Endo to expand Frova sales if it can market the drug more effectively by improving the product's label. Getting Frova approved to prevent menstrual migraines, rather than just treating acute migraines after they've occurred, would be a good start.

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Fool contributor Brian Lawler does not own shares of any company mentioned in this article. GlaxoSmithKline is an Income Investor recommendation. The Fool has a disclosure policy.