Combining drugs into a single pill or shot can be a good way to boost sales of an already-approved drug. GlaxoSmithKline (NYSE: GSK) has been the king of combo treatments over the last few days -- which seems only appropriate, given its name -- with a combination of good and bad results.

On Friday, the drugmaker announced that the Food and Drug Administration issued a complete response letter for MenHibrix, its combination vaccine against both meningococcal and Haemophilus influenzae type b (Hib) diseases. In typical pharma fashion, the company didn't give investors much clue about what the FDA needs for approval. The real losers here are kids who might otherwise get more immunity with fewer shots.

Yesterday, the combo-drug karma turned in Glaxo's favor, when the FDA approved Jalyn. This combination of Glaxo's Avodart and Flomax is sold by Astellas and Boehringer Ingelheim, but it's recently seen its patents expire. Both drugs treat benign prostatic hyperplasia (BPH).

Combining patented drugs with generics is a fairly common strategy for drugmakers. Merck (NYSE: MRK) and Glaxo have combined metformin with their diabetes drugs Januvia and Avandia, respectively. Merck also plans to combine its cholesterol drug Zetia with Pfizer's (NYSE: PFE) Lipitor once it goes off-patent. Some patients will just switch to taking two pills instead of one, but that can also increase sales, since the combo product may work better than competitors' single-agent pills.

In Jalyn's case, that's especially important, given the crowded BPH space. In addition to branded drugs such as sanofi-aventis's (NYSE: SNY) Uroxatral and Watson Pharmaceuticals' (NYSE: WPI) Rapaflo, the space is also filled with lots of cheap generics of drugs like Pfizer's Cardura, Merck's Proscar, and Abbott Labs' (NYSE: ABT) Hytrin.

Jalyn probably won't be a blockbuster in its own right, but every incremental increase in sales still helps.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool owns shares of GlaxoSmithKine. The Fool's disclosure policy is a combination of disclosures in a policy form.