The country's ethics board has approved the first trial of an HIV-prevention drug,

likely clearing the way for the study to begin before the end of the year.

Julian Elliott, an advisor at the National Center for HIV/AIDS, Dermatology and STIs

(NCHADS), said the trial would test the effectiveness of tenofovir, an anti-retroviral

drug (ARV), to prevent HIV infections among up to 800 sex workers recruited for the

study.

He said participants would receive a daily dose of either the drug or a placebo and

a "standard prevention package" including counseling, condoms and STD screening.

Anyone who contracts the virus during the trial will also receive long-term ARV treatment.

"There is an ethical responsibility to see that people infected during the study

have access to adequate care and treatment," he said.

The study, conducted in partnership with University of California San Francisco in

the US and the University of New South Wales in Australia, is developing informed

consent procedures and recruiting volunteers. It will take at least two years before

any results are published.

The largely unsuccessful global effort to prevent HIV infection has to date employed

mainly vaccines, microbicides and medications. But tenofovir, part of a new class

of drugs, is among the most promising possibilities.

The drug, manufactured by pharmaceutical firm Gilead, is afforable and widely available

in combination drug therapy.

This study, along with three others set to start in Ghana, Nigeria and Cameroon,

will be the first to evaluate the drug for HIV prevention. Studies found it to be

highly effective in animals, but have not confirmed that result in humans.

Cambodia has one of the highest HIV infection rates in Asia with 157,000 infected

people. Although prevalence rates have dropped from a high of 3.3 percent in 1998

to 2.6 percent, the disease has spread to a wider cross-section of society.

"The epidemic has evolved," said Kim Green, an AIDS specialist with CARE

Cambodia. "Now the men who have been more sexually active are transmitting it

to their wives and, through them, more children."

For most, the health care response has been inadequate. Fewer than 1,000 of an estimated

10,000 AIDS patients here receive ARV treatment, said Jennifer Hines, medical director

at the Center of Hope hospital.

"The problem is quite huge compared to what we're doing now," she said.

If tenofovir is proven effective, it could be a major boon to the country, said Dr

Ly Penh Sun, an NCHADS official and one of the principal investigators of the study.

"Condoms were proven long ago to be effective," he said. "But this

will fill in the gap [in prevention] and provide more options to people, especially

women."