Drug 'may prevent HIV infection'

Twenty-five years after the first AIDS cases jolted the world, US scientists think they soon may have a pill that could prevent HIV, the virus that causes the disease.

“This is the first thing I’ve seen at this point that I think really could have a prevention impact,” said Thomas Folks, head of the HIV research lab at the US Centre for Disease Control and Prevention.

“If it works, it could be distributed quickly and could blunt the epidemic,” he added.

Two drugs already used to treat HIV infection have shown such promise at preventing it in monkeys that officials last week said they would expand early human tests around the world.

The drugs are tenofovir (Viread) and emtricitabine, or FTC (Emtriva), sold in combination as Truvada by Gilead Sciences Inc, a California company best known for inventing Tamiflu, a drug showing promise against bird flu.

If larger tests show the drugs to be as effective on humans, they could be given to people at highest risk of HIV.

Condoms and counselling alone have not been enough – HIV spreads to 10 people every minute, 5 million every year. A vaccine remains the best hope but none is in sight.

Matthew Bell, a 32-year-old hotel manager in San Francisco who has volunteered for a safety study on one of the drugs, said he would welcome taking a drug as an added precaution to practising safe sex.

“As much as I want to make the right choices all of the time, that’s not the reality of it,” he said.

“If I thought there was a fallback parachute, a preventative, I would definitely want to add that.”

Some fear that this could make things worse.

“I’ve had people make comments to me, ‘Aren’t you just making the world safer for unsafe sex?”’ said Dr Lynn Paxton, team leader for the project at the Centre for Disease Control and Prevention.

But some uninfected gay men already are getting the drugs from friends with AIDS or doctors willing to prescribe them to patients who admit not using condoms. This kind of use could lead to drug resistance in infected and uninfected alike, and is one reason officials are rushing to expand studies.

“We need information about whether this approach is safe and effective” before recommending it, said Dr Susan Buchbinder, who leads one study in San Francisco.

Unlike vaccines, which work to boost the immune system – the very thing HIV destroys – AIDS drugs simply keep the virus from reproducing. They already are used to prevent infection in health care workers accidentally exposed to HIV, and in babies whose pregnant mothers receive them.

Taking them daily or weekly before exposure to the virus – the time frame is not known yet – may keep it from taking hold, just as taking malaria drugs in advance can prevent that disease when someone is bitten by an infected mosquito, scientists believe.

Tests on monkeys suggest they are right.

Specifically, six macaques were given the drugs and then challenged with a deadly combination of monkey and human AIDS viruses, administered in rectal doses to imitate how the germ spreads in gay men.

Despite 14 weekly blasts of the virus, none of the monkeys became infected. All but one of another group of monkeys that didn’t get the drugs did, typically after two exposures.

“Seeing complete protection is very promising,” and something never before achieved in HIV prevention experiments, said Walid Heneine, a CDC scientist working on the study.

What happened next, when scientists quit giving the drugs, was equally exciting.

“We wanted to see, was the drug holding the virus down so we didn’t detect it,” or was it truly preventing infection, said Folks. It turned out to be the latter.

“We’re now four months following the animals with no drug, no virus. They’re uninfected and healthy.”

Previous monkey studies using tenofovir alone had shown partial protection. The scientists thought to add the second drug, FTC, when Gilead’s combination pill, Truvada, came on the market last year.

The results, announced at a scientific meeting last month in Denver, so excited scientists that private and government funders alike have been looking at ways to expand human testing.

The US National Institute of Health is starting a tenofovir study in 1,400 gay men in Peru. Private and government funders are considering others. Tenofovir also is being tested in microbicide gels that women could use vaginally to try to prevent catching HIV.

“If you’re in an area where there’s a really high HIV incidence, something that’s even 40% effective could have a huge impact,” Dr Paxton said.