Gilead Sciences has thrown down a challenge to GlaxoSmithKline with good clinical trial results for an experimental HIV drug that works in the same way as the British group's successful dolutegravir.

Gilead's bictegravir, another so-called integrase inhibitor drug, delivered 97 percent virus suppression, making it just as effective as GSK's product, data presented at a medical meeting in Seattle late on Monday showed.

Importantly, there were no cases of resistance emerging to the new medicine in the 98-patient Phase II study and no patients discontinued treatment due to kidney problems, which can be an issue with HIV treatments.

Potential drug resistance is a key consideration for the new drug because dolutegravir is valued by doctors for its excellent resistance profile.

Berenberg analyst Laura Sutcliffe said the results were good news for Gilead but the data was not yet conclusive, since findings from larger Phase III tests are due later in the year.

Gilead is pinning its hopes on bictegravir to stay competitive with GSK and the U.S. company has been testing the new medicine alongside two older drugs.

GSK, meanwhile, is working on a dolutegravir-based two-drug treatment regimen for controlling the virus behind AIDS, a development that marks a departure from conventional triple drug cocktails.

Detailed findings from two Phase III trials testing the new two-drug combination were presented at the Conference on Retroviruses and Opportunistic Infections in Seattle. GSK already said in December that these studies were successful.

GSK sells its HIV drugs through its majority-owned ViiV Healthcare unit, in which Pfizer and Japan's Shionogi hold minority stakes.

GSK shares were 0.6 percent lower by 0830 GMT.