ViiV Healthcare, which is majority-owned by GlaxoSmithKline and has Pfizer Inc. and Shionogi as shareholders, reported on Thursday positive early results from two late-stage trials testing its two-drug regimen in patients new to HIV treatment relative to a three-drug regimen. GlaxoSmithKline shares rose 2.4% in premarket trade on Thursday after the news. The two late-stage studies, Gemini-1 and Gemini-2, met their primary endpoint at week 48, the company said. It plans to file for regulatory approvals of the two-drug regimen, composed of the drugs dolutegravir and lamivudine, later this year, and also has plans to present full results at an upcoming scientific meeting. Until then, questions remain about the drug’s resistance profile, said EvercoreISI analyst Umer Raffat, who noted that there were no numbers in the company’s press release. Gilead Sciences Inc. , which makes three-drug HIV regimens, had shares rise 0.3% premarket. “Though [ViiV Healthcare] did not see any treatment-emergent resistance in these studies, which had been a key question about this regimen, we believe concerns over resistance risks in the real-world setting will make GILD’s triple cocktails the drugs of choice,” said RBC Capital Markets analyst Brian Abrahams. ViiV Healthcare had another two-drug HIV regimen, intended for individuals with HIV-1 who have been stable on a regimen for at least half a year, approved by the FDA in November. GlaxoSmithKline shares have surged nearly 11% over the last three months, compared with a nearly 1% rise in the S&P 500 and a 1.8% rise in the Dow Jones Industrial Average .