In London trading, shares of GlaxoSmithKline Plc. tumbled after the US health regulators issued a warning against the long-term use of the pharmaceutical company's popular and commonly used offering, the Advair asthma treatment. Also, the Food and Drug Administration called for further study of potential health risks.

While warning that the FDA's findings might end up hurting the sales of the product throughout US, and hamper the development of a new compound for lung disease that Glaxo is working on with Theravance Inc., Mark Purcell and Brian Bourdot of Barclays Capital said, "The FDA language may be ambiguous, but the intent seems clear. The FDA would like to see LABA use come down".

Advair, in addition to some other renowned medicines, combines treatments from a class known as long-acting beta agonists with inhaled corticosteroids. FDA has now advised against the long-term use of drugs which contain long- acting beta agonists alone.

On the news, Glaxo slipped by 13 pence, or 1.1%, to 1,230.5 pence at about 9:20 AM.