Investors holding their breath for the approval of GlaxoSmithKline (NYSE: GSK) and Theravance's (Nasdaq: THRX) "son of Advair" won't have to wait too much longer. The companies said the clinical program testing the drug, which goes by the name Relovair, is complete. Glaxo plans to ask for approval to treat patients with chronic obstructive pulmonary disease in the U.S. and EU in the middle of this year. A submission for asthma in the EU will come about the same time as the U.S. asthma submission coming after further talks with the FDA.

The final two trials in COPD, pitting Relovair directly against Advair, weren't required to get Relovair on the market, but they will help sell the product. In one trial, Relovair was superior to Advair. In another the data was trending that way, but the improvement wasn't statistically significant. If the trials were required for approval, I'd be worried about the miss on the second trial, but since they're just to support marketing, the data seem solid enough.

On the asthma side, a trial comparing one of the active ingredients in Relovair, fluticasone furoate, to the similar compound in Advair, fluticasone propionate, showed they were both better than placebo in treating asthma patients. Glaxo didn't release the full data, but based on the P values, we can guess that the Relovair component was slightly better than the Advair component.

Converting patients from Advair, an $8.1 billion drug, to Relovair is important because of the possibility that Advair might face generic competition at some point. Relovair only has to be taken once a day, which is more convenient than the twice-daily Advair formulation. And the trial showing that Relovair is superior to Advair will help, although two statistically significant trials would obviously be better.

But Glaxo's best weapon for converting patients from Advair to Relovair might be that it owns Advair. Increasing the price of Advair will push insurers to encourage their members to switch to the lower-cost treatment. Glaxo just needs to be careful not to push patients off Advair and onto the competition: Merck's (NYSE: MRK) Foradil, AstraZeneca's (NYSE: AZN) Symbicort, and Spiriva HandiHaler, marketed by Boehringer Ingelheim and Pfizer (NYSE: PFE).

The son of Advair has been a long time coming -- the deal between Glaxo and Theravance dates back to 2002 -- but it looks like investors can breathe easy until next year, when competition heats up in the COPD market.

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