UPDATE 2-U.S. FDA approves Gilead triple HIV drug, rival files lawsuit

(Adds details on Glaxo lawsuit, updates share price)

Feb 7 (Reuters) - The U.S. Food and Drug Administration on Wednesday approved Biktarvy, Gilead Sciences Inc's once-daily triple-combination tablet for treatment of HIV infection, paving the way for the biotech company to capture more of the multibillion-dollar HIV drug market.

Rival ViiV Healthcare, a joint venture majority-owned by GlaxoSmithKline Plc with Pfizer Inc and Shionogi Ltd, quickly filed a lawsuit alleging that Gilead is infringing patents on ViiV's dolutegravir, a component of the venture's triple-drug HIV treatment Triumeq.

Officials at Gilead did not immediately respond to a request for comment on the lawsuit.

Biktarvy combines new integrase inhibitor bictegravir with Descovy, an older medication that combines nucleoside reverse transcriptase inhibitors emtricitabine and tenofovir alafenamide.

The approval helps "set the stage for long-term growth and sustainability of Gilead's core HIV franchise," RBC Capital Markets analyst Brian Abrahams said in a research note.

The Gilead drug's wholesale price, about $36,000 a year, is in line with current therapies, according to Guggenheim Securities.

The new drug's label includes a boxed warning that use could worsen hepatitis B infection in certain patients.

Wall Street analysts, on average, forecast Biktarvy sales of around $1 billion this year, rising to a peak of nearly $5 billion annually by 2024, according to Thomson Reuters I/B/E/S.

ViiV said it will seek to prove that Biktarvy infringes ViiV's U.S. and Canadian patents covering dolutegravir and many other compounds that include dolutegravirs unique chemical scaffold. The U.S. case was filed in the U.S. District Court for the District of Delaware and the Canadian case is filed in the Canadian Federal Court in Toronto.

Shares of Gilead, which rose 3 percent to close at $82.76 in regular trading, were down 0.6 percent at $82.30 after hours.

(Reporting by Deena Beasley in Los Angeles Editing by Lisa Shumaker and Matthew Lewis)