* Trelegy Ellipta approved in U.S. for chronic lung disease
* First once-daily single inhaler triple therapy for COPD
* CEO sees it as one of three "critical" new drug launches (Adds detail on competition, analyst reaction, shares)
LONDON, Sept 18 (Reuters) - U.S. regulators have approved GlaxoSmithKline's three-in-one inhaler for chronic lung disease, a key new product for the group as it strives to keep its lead in respiratory medicine despite falling sales of the older drug Advair.
Trelegy Ellipta is the first once-daily triple medicine for chronic obstructive pulmonary disease (COPD), putting Britain's biggest drugmaker ahead of rivals such as AstraZeneca and Novartis.
Last week, the inhaler, which GSK developed with Innoviva , also won a recommendation for approval from the European Medicines Agency.
Chief Executive Emma Walmsley sees the triple lung drug as one of three "critical" launches as GSK seeks to fill a revenue gap left by falling sales of Advair, which is expected to face U.S. generic competition sometime next year.
Its two other key new products are Shingrix, a shingles vaccine that was unanimously recommended for approval by a U.S. Food and Drug Administration (FDA) advisory panel last week, and a novel dual-drug regimen for HIV.
GSK estimates about a quarter of COPD patients are already using three drugs to control their lung disease, suggesting plentiful demand for more intensive treatment.
Such patients will now get all three medicines in one easy-to-use inhaler, although how exactly that will translate into overall sales is less easy to calculate.
The new product is likely to be attractive in some markets, since it will reduce co-payments for patients by offering a single prescription, but GSK will inevitably cannibalize sales of some of its other drugs.
At the same time, prices for inhaled respiratory medicines are continuing to decline due to increased competition.
Still, by launching Trelegy Ellipta before generic Advair hits the U.S. market, GSK will have more breathing space to switch patients to the newer product, Berenberg analysts said in a note.
GSK, whose shares were little changed in early trade on Tuesday following overnight news of the FDA approval, said it would make Trelegy Ellipta available in the United States "shortly."
The GSK inhaler combines the drugs fluticasone furoate, umeclidinium and vilanterol, offering three different mechanisms to help open airways of patients with severe COPD. The drug is not indicated for asthma.
GSK has been the respiratory market world leader since launching its Ventolin inhaler in 1969 and Walmsley, who took over as CEO in April, has made lung disease a continuing priority for the years ahead.
In July, she announced plans to narrow the focus of the group's drug research and allocate 80 percent of its R&D budget to respiratory and HIV/infectious diseases, along with two other potential areas of oncology and immuno-inflammation. (Additional reporting by Rama Venkat Raman in Bengaluru; Editing by Leslie Adler and Louise Heavens)