* GSK approach challenges Gilead's triple-drug strategy
* Dolutegravir and rilpivirine work well in Phase III tests (Adds further reaction, more detail on competition)
By Ben Hirschler
LONDON, Dec 20 (Reuters) - GlaxoSmithKline's alreadyfast-growing HIV drug business has received an important boostafter two major clinical studies successfully tested a newtwo-drug treatment regimen to control the virus that causesAIDS.
The approach is a departure from conventional triple drugcocktails that can cause troublesome side effects, especiallyamong older patients who make up a growing proportion of thosetreated for the disease.
Antiretroviral therapy has turned HIV from a death sentenceinto a manageable condition but patients need to stay ontreatment for life, so there is a growing focus on makingmedication as well-tolerated as possible.
GSK has developed the new two-drug cocktail through itsmajority-owned ViiV Healthcare, in which Pfizer andShionogi also hold stakes. The aim is to offer thetwo-drug regimen as a single tablet.
Easing back from triple therapy is the opposite approach tothat being pursued by HIV market leader Gilead Sciences, which is banking on improving triple regimens.
"The key debate remains whether Gilead will gain the upperhand again or whether a disruptive two-drug regimen becomesstandard of care, favouring GSK," said UBS analyst MichaelLeuchten.
In addition to developing its new two-in-one HIV tablet, GSKis also working on long-acting drug injections for both treatingand preventing HIV.
Results of the two Phase III tablet studies, announced lateon Monday, showed that the combination of GSK's dolutegravir andJohnson & Johnson's rilpivirine worked as well as three-or four-drug regimens.
Dominique Limet, chief executive of ViiV, said the resultswere "an important milestone in our understanding of how HIV canbe treated", since they represent the first late-stage trialevidence for the two-drug approach.
ViiV will release detailed findings from the studies at amedical meeting next year and plans to seek regulatory approvalfor the new treatment approach in 2017.
Deutsche Bank analyst Richard Parkes said doctors mayrequire reassurance from longer-term studies over the risk ofresistance developing before dual therapy is widely accepted.
HIV dual therapy is one of a number of pipeline projectsthat GSK is banking on to revive its core prescription drugbusiness as new chief executive Emma Walmsley prepares to takeover from the end of March.
In all, the company expects important clinical results forbetween 20 and 30 experimental medicines by the end of 2018.
GSK also announced on Monday it was bolstering scientificexpertise on its board by establishing a new science committee,charged with overseeing research. (Editing by Louise Heavens and Susan Fenton)