28 Nov 2008

Pills to prevent HIV?

Anti-HIV medicines have rescued tens of thousands or perhaps even millions of people from what was once certain death from AIDS.

Now researchers are testing whether the pills available since the middle of the 1990s to slow down the progress of the HIV virus that causes AIDS might also deliver another miracle - prevention of the disease in high risk populations.

Clinical trials are underway to see whether the pills could preventively block the virus and protect people who are not infected yet by the virus.

Depending on the results, they could offer another arrow in the quivers of those on the forefront of fighting the disease that has claimed 25 million lives and left another 32 million people infected with HIV since the 1980s.

Cautious optimism
The top US AIDS warrior, Anthony S Fauci, says he is "cautiously optimistic" and even "somewhat enthusiastic" about the new approach.

In fact, world scientists have been frustrated by the extremely tricky and deceptive virus which has eluded more than a decade of efforts to find a vaccine. Thus any new ideas to prevent the spread of HIV gain quick traction.

Fauci, director of the US National Institute of Allergy and Infectious Diseases (NIAID) at the National Institutes of Health (NIH) in Bethesda, Maryland, spoke with Deutsche Presse-Agentur dpa this week.

No concrete results
So far, there are no concrete results, but animal testing, including with non-human primates, has offered some hope for the antiretroviral (ARV) medications to be used for prevention. Fauci hopes for interim results sometime next year at the earliest.

Two pills are being tested. One contains the substance Tenofovir, the other one includes Emtricitabine. The medications, which when taken together are known as highly active antiretroviral therapy (HAART), have been effective in preventing the HIV virus from spreading through the body by lowering the HIV count in the blood, semen and vaginal mucous.

Researchers have concluded that patients on HAART therapy are less infectious, and believe the same pills might protect someone who is not yet infected.

Fauci's institute, NIAID, is participating in a study (HPTN 052) to test whether adults could benefit from the same phenomenon that protects babies from HIV infections who are given medicine before and after delivery, and are protected even though their mothers are HIV positive.

Rape victims have also been shown to benefit from the potent combination of anti-HIV drugs shortly after their exposure.

ARVs prior to exposure
The new tests are focused on delivering ARVs prior to exposure to HIV, an an idea known as pre-exposure prophylaxis (PrEP). The tests involve 1 750 couples in the US, Brazil, Thailand, India and South Africa. In each couple, one partner is HIV positive and the other is healthy.

In separate tests, scientists are looking at how such medicines can protect high risk groups such as homosexuals, drug addicts and prostitutes.

"The best case scenario would be that PrEP works in people who adhere to it in a way that really does prevent infection, and that does not give them the impetus to be even more risky in their behaviour," Fauci said.

The research holds out hope especially for women, and particularly in Africa, where having sex with an infected partner who is often unwilling to use condoms is a daily game of roulette.

Worst case scenario
And the downside of such a new approach to prevention? "The worst case scenario is that people do not regularly take their medication and would feel that because they take it some of the time they are protected and then increase their risky behaviour," Fauci said.

Often, people who feel protected "subconsciously or consciously take more risks than otherwise," Fauci said.

Fauci says the PrEP possibilities do not represent a "breakthrough" as such - but rather would only offer another weapon to complement the battery of methods now being used to fight the disease: condom use, abstinence, behaviour modification, circumcision, topical microbicides, needle exchange and treatment for the ill.

He points out that the HAART drugs are quite expensive. There are 2.7 million new infections every year worldwide, and only 30 per cent of infected people in lower income countries receive treatment.

PrEP could however help bridge through the period until an effective vaccine is developed.

"For every person we put on therapy, two to three people become newly infected," Fauci noted. "The big Holy Grail of scientific work is getting a successful vaccine. – (Sapa-dpa)