UPDATE 1-Gilead seen gaining share in AIDS drug market

(Adds company, analyst's comment, Glaxo share price, byline)

By Deena Beasley

LOS ANGELES, Feb 28 (Reuters) - A safety board has recommended that certain AIDS patients taking part in a study of GlaxoSmithKline Plc's (GSK.L: Quote, Profile, Research, Stock Buzz) Epzicom consider switching to Gilead Sciences Inc's (GILD.O: Quote, Profile, Research, Stock Buzz) Truvada, sending Gilead's shares up about 4 percent on Thursday.

The National Institute of Allergy and Infectious Disease's AIDS Clinical Trials Group, a unit of the National Institutes of Health, is comparing the two drugs in a head-to-head trial involving 1,858 patients.

The unit said on Thursday that an independent Data and Safety Monitoring Board recently found that for patients with high levels of HIV virus, treatment regimens containing Epzicom were less effective at controlling the virus than regimens containing Truvada.

The board also found that patients with high levels of HIV virus treated with Epzicom developed side effects such as body aches and high cholesterol more quickly.

Glaxo said in a statement that the NIH study did not routinely exclude patients at risk for a known reaction with Epzicom, which might have accounted for some adverse events.

The trial recommendation applies to about half the patients being treated with the Glaxo drug and, if translated to real world usage, could mean a 20 percent market share gain for Gilead's Truvada and Atripla, Morgan Stanley analyst Sapna Srivastava said in a research note on Thursday.

Truvada is a pill combining Gilead's Viread and Emtriva, also known as tenofovir and emtricitabine. Atripla is a three-drug pill that also includes Bristol-Myers Squibb Co's (BMY.N: Quote, Profile, Research, Stock Buzz) Sustiva.