A combination pill used to treat HIV could also help healthy gay men from becoming infected with the AIDS virus, an international study suggests. 

The study of nearly 2,500 people, all of whom were offered condoms and received counselling, found that men who took the pill daily cut their risk of infection by 44 per cent compared with those on placebo, researchers reported in Tuesday's online issue of the New England Journal of Medicine. 

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Daily doses of Truvada, already used to treat HIV infections, helped prevent healthy gay men and transgendered women from acquiring the disease through sex with an infected partner, according to an international study. ((Paul Sakuma/Associated Press))

In the trial, researchers randomly assigned 2,499 HIV-negative men — including some transgendered women — who had sex with men to take either the oral medication Truvada or a placebo once daily. Truvada combines the antiretroviral drugs tenofovir and emtricitabine,

The study involved 11 sites in Brazil, Ecuador, Peru, South Africa, Thailand and the United States.

Of the 100 HIV infections in the study, 64 occurred in the placebo group and 36 in the drug combination group.

Condom use, however, remains a cruicial in preventing the spread of HIV, experts said.

"It's not time for gay and bisexual men to throw out their condoms," said Dr. Kevin Fenton, AIDS prevention chief at the U.S. Centers for Disease Control and Prevention. The pill "should never be seen as a first line of defence against HIV."

Condoms also prevent other sexually transmitted diseases, said the study's lead author, Dr. Robert M. Grant of the Gladstone Institutes, a private foundation affiliated with the University of California, San Francisco.

'Exciting moment'

The drug combo works because HIV comes into contact with body tissues, it doesn't take effect because the medications are there to block it, said Dr. Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, which sponsored the study.

"It actually blocks the ability of the virus to initially infect you in the first place," Fauci said from Bethesda, Md., noting it would likely also have a preventive effect in heterosexual men and women, though this needs to be tested.

In the last 15 months, researchers have gained evidence that three different technologies — this drug combination, a microbicide undergoing clinical trials and a vaccine in trials — are working, said Canadian doctor Alan Bernstein, executive director of the Global HIV Vaccine Enterprise in New York, who called the developments "an exciting moment."

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Consistent and correct use of condoms remains key to preventing spread of HIV, doctors stressed. ((Daniel Munoz/Reuters))

"The level of per cent prevention of infection in this trial, the microbicide trial and in the vaccine trial are not high enough yet to consider these useful public health interventions," Bernstein cautioned in an interview with CBC News.

There are also questions about whether such a regimen would be taken without the intense reinforcement of counselling that was provided in the clinical trial, said Dr. Nelson Michael of the Walter Reed Army Institute of Research in Rockville, Md., who wrote a journal editorial accompanying the Truvada study. 

Only about half of the study participants took the medication consistently. Among those who did, the drug reduced their risk more, by 73 per cent.

Fatigue from taking a daily medication for years could also set in, and the potential long-term safety issues for healthy people, as well as those with other illnesses such as diabetes and hypertension, need to be addressed, Michael added.

Ethical dilemma

Elsewhere on Tuesday, the United Nations' HIV/AIDS program, UNAIDS, reported that only about a third of people who have AIDS and need antiretroviral drugs have access to the medications.

For that reason, the HIV prevention strategy of giving drugs to healthy people, known as pre-exposure prophylaxis, or PrEP, also raises an ethical dilemma, as cost is cited as a factor for not giving pills to people dying of AIDS in the developing world, Bernstein said.

The CDC is developing guidelines for doctors, as well as gay men. In the meantime, the agency cautioned:

  • There is no information about whether the Truvada drug combination helps heterosexuals or injection drug users.
  • Truvada is not currently indicated for HIV prevention and should not be used by those confirmed to be HIV-negative.
  • Consistent and correct use of condoms remains key.
  • Testing and treatment for other sexually transmitted infections such as syphilis and gonorrhea are needed.
  • Advice to reduce the number of sexual partners, risky sexual behaviour and drug use stands.

Dr. Bill Cameron, a professor of medicine at the University of Ottawa and president of the Canadian Association for HIV Research, called the findings an advance, but worried people taking the drug might take more risks.

About 30 per cent of Canadians living with HIV are unaware of their status, and frequent testing would be needed to monitor whether those taking Truvada or other drugs as part of a prophylaxis regime become infected, the AIDS Committee of Toronto said in welcoming the results.

As with most medications, side-effects could affect physical and mental health and reduce adherence to the drug, which minimizes its effectiveness, the group added.

Truvada is listed in Health Canada's database of approved medications to treat HIV, but not to prevent it.

With files from The Associated Press