(Adds background on rival drugs, analyst comment, shares)
June 14 (Reuters) - GlaxoSmithKline's two-drug treatment for HIV, the virus that causes AIDS, met its main goal in late stage studies, scoring key points in its rivalry with Gilead in the medical field.
The combination of dolutegravir and lamivudine was shown to be as effective as a dolutegravir-based combination of three drugs, GSK's majority-owned ViiV Healthcare said on Thursday.
It said its push for two-drug regimens addressed long-term toxicity concerns of people living with HIV by reducing the number of medicines.
Rival Gilead Sciences in February won U.S. Food and Drug Administration approval for Biktarvy, a triple-combination HIV treatment, paving the way for the biotech company to capture more of the multibillion-dollar HIV drug market.
Thursday's results should help GSK defend its dolutegravir-based business against competition from Biktarvy, said Jefferies analyst Ian Hilliker, who forecast peak year sales of $1.5 billion for the dolutegravir/ lamivudine combination.
The shares were up 2 percent at 1200 GMT, also bolstered by further delays in Mylan's quest to bring a generic version of GSK's blockbuster inhaled lung drug Advair to market.
Jefferies's Hilliker said that GSK's dolutegravir/ lamivudine cocktail would likely have an edge over another two-drug combination by GSK known as Juluca, which won approval in Europe and the United States over the last six months.
"Key opinion leaders we have spoken to see the dolutegravir/ lamivudine combination as a more attractive initial therapy or switch strategy as lamivudine has a very good toxicity profile and generic versions are available, which should reduce cost," the analyst said.
In a recent setback, however, U.S. and European regulators started assessing evidence that dolutegravir might be linked to birth defects.
ViiV, in which Pfizer and Shionogi have small stakes, said it plans regulatory submissions for the two-drug combination later this year and that full results from the studies would be presented at a conference. (Reporting by Ludwig Burger in Frankfurt and Arathy S Nair in Bengaluru; editing by Alexander Smith, Jason Neely and Alexandra Hudson)