Los Angeles-based AIDS Healthcare Foundation (AHF) has petitioned the Food and Drug Administration on the grounds that studies have shown that the pill, Truvada, made by Gilead Sciences, is only partially effective in preventing transmission. The drug is already approved to treat people infected with the human immunodeficiency virus that causes AIDS.

Because Truvada must be taken every day, protection from the virus will falter if, as is likely in everyday life, a dose is missed, the AHF said.

"Any approach that relies on adherence for people who don't have a disease is going to fail," AHF President Michael Weinstein said at a press conference on Thursday.

The Fenway Institute, which advocates for lesbian, gay, bisexual and transgender people, and several other HIV organizations are in favor of using antiretroviral medication, along with risk reduction counseling and condoms, to prevent HIV transmission.

A coalition of 25 health organization in January contacted the FDA expressing their support for the Truvada application.

Officials at Gilead declined to comment.

A decision by the FDA, which granted an expedited review of the company's application, is expected by June 15 and a panel of experts will review the issue in May.

AHF estimates the cost of Truvada for preventing transmission of HIV at $14,000 a year.

Gilead is seeking permission for Truvada -- a combination of its HIV drugs Emtriva, also known as emtricitabine, and Viread, or tenofovir -- to be used as a form of "pre-exposure prophylaxis," often shortened to PrEP.

Results from a PrEP trial involving 4,758 heterosexual Kenyan and Ugandan couples presented this week at the Conference on Retroviruses and Opportunistic Infections found that 82 HIV infections occurred, 17 in patients treated with tenofovir, 13 in patients given Truvada, and 52 among those treated with a placebo.

"People who take PrEP even haphazardly will consider themselves protected" and could well let up on safe-sex measures, such as condoms, said AHF General Counsel Tom Myers.

The AHF said Truvada is associated with kidney problems and that use of the drug by healthy people could cause them to become resistant to it, complicating treatment if they contract HIV.

"Expanding the use of antiretrovirals to include pre-exposure prophylaxis will increase the risk of resistance, which is already a serious problem," British medical journal Lancet said in an editorial last year. "HIV is a rapidly evolving virus and development of resistance creates the need for ever-changing regimens of drugs in various classes."

Scientists are exploring a variety of tactics for using AIDS drug formulations to prevent HIV infection, including long-acting injections, gels and vaginal rings.

"There are very good scientific arguments in favor of treatment as prevention," said Daria Hazuda, vice president for infectious disease discovery at Merck & Co. "It's an issue of timing, cost and do you have the right intervention."

An estimated 1.2 million Americans have HIV, according to the Centers for Disease Control and Prevention.

In preliminary guidelines issued last year, the CDC said only high-risk gay and bisexual men should use a daily AIDS pill to protect themselves from the virus.

(Reporting By Deena Beasley; Editing by Tim Dobbyn)

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