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BOSTON (Reuters) - A trial designed to test whether a drug made by Gilead Sciences Inc(GILD.O) could prevent HIV infection in women at high risk of exposure to the virus was halted early after investigators determined it would probably not be effective.
Gilead shares closed 3.3 percent lower, compared with a drop of 1.5 percent for the NYSEArca biotech index.
The trial, known as FEM-PrEP, was conducted by the nonprofit organization Family Health International (FHI) and tested women in Kenya, South Africa and Tanzania who were not already infected with HIV, the virus that causes AIDS.
Women in the trial were given Truvada, a drug made by Gilead that combines two antiretroviral drugs in a single pill that is taken once a day. The drug has been proven safe and effective as a treatment for people who already have HIV.
As of Feb. 18, 2011, the study had screened 3,752 women and enrolled 1,951, according to a statement from FHI. Preliminary data showed the approximate rate of new HIV infections among trial participants was 5 percent a year. A total of 56 new HIV infections had occurred, with an equal number found in those taking Truvada as in those taking a dummy pill.
FHI said it will initiate an orderly closure of the trial, which was funded by the United States Agency for International Development, with early funding from the Bill & Melinda Gates Foundation.
"While this development is a disappointing one, Gilead believes that antiretroviral therapies remain a promising potential HIV prevention strategy," Gilead said in a statement. "We continue to support ongoing studies evaluating the company's antiretroviral therapies as potential preventatives."
Gilead Chief Executive John Martin said in January the company planned to file in the first half of this year for U.S. regulatory approval of Truvada for the prevention of HIV in men who have sex with men.
He acknowledged the company did not expect a significant commercial opportunity.
"The prevention study really has no major financial impact to the company," BMO Capital Markets analyst Jason Zhang said on Monday.
FHI said the outcome of the trial is "surprising and disappointing, given a number of earlier studies suggesting the promise of pre-exposure prophylaxis using antiretrovirals."
The organization said possible reasons for the study findings included low adherence to the study regimen, a true lack of effect of the product among women, or other factors still to be determined. FHI said it will be conducting further analyses and share additional findings in the coming months.
Gilead shares fell $1.38 to close at $40.32 on Nasdaq.
(Reporting by Toni Clarke, additional reporting by Deena Beasley; editing by Gary Hill editing by Andre Grenon)