LONDON, Sept 10 (Reuters) - The threat of generic copies ofGlaxoSmithKline's best-selling lung drug Advair finallymaking it to market in the United States hit confidence in thedrugmaker on Tuesday, sending the stock down more than 3percent.
Fears of cheaper versions of the $8 billion-a-year sellerbeing launched in the world's biggest market were fuelled by adraft guidance document from the Food and Drug Administrationsetting out the requirements for generic versions of the inhaleddrug.
Bernstein analyst Tim Anderson said the requirements looked"fairly benign" for generic firms seeking to make copies thatcould be automatically substituted for Advair when patients havetheir prescriptions filled.
Citigroup said its worst-case scenario for an acceleratedU.S. Advair sales decline, following the FDA document, couldslice up to 5 percent off GSK's valuation.
Advair, which is marketed as Seretide outside the UnitedStates, is used to treat both asthma and chronic lung diseasecaused by smoking.
Although patents on the active ingredients used in themedicine have expired, it remains protected by U.S. patents onthe Diskus inhaler device that run until 2016, after whichcopies may reach the market.
Up until now, many investors had assumed that fullysubstitutable generic versions of Advair were unlikely in theUnited States and instead generics would have to compete asseparate brands. The FDA pathway to permitting "true" genericstherefore represents a heightened threat.
Shares in GSK were down 3.3 percent at 15.85 pounds by 0805GMT.
The uncertainty over Advair comes on the same day that aU.S. advisory panel is due to consider a new lung drug calledAnoro from GSK and Theravance. (Reporting by Ben Hirschler; Editing by Louise Heavens)
Glaxosmithkline (GSK)