What's the News: A daily dose of anti-HIV drugs can significantly reduce the likelihood that straight men and women will contract HIV from an infected partner, according to two new clinical studies. These studies add strong evidence to earlier findings that taking HIV drugs can prevent healthy people from contracting the disease, and are the first to show that the drugs reliably lower transmission risk in heterosexuals. How the Heck:
One study enrolled 4,758 straight couples in Kenya and Uganda, in which one partner---either male or female---had HIV and the other didn't.
The uninfected partners were split into three even groups. Each group was given a different type of pill, which they were instructed to take daily: a pill containing the antiretroviral drug tenofovir; a pill with both tenofovir and another HIV drug, emtricitabine; or a placebo.
Over course of the three-year study, 47 participants taking the placebo contracted HIV, compared with 18 taking tenofovir and 13 taking the combination pill---meaning that the drug regimens reduced HIV transmission by 62% and 73%, respectively.
The other study enrolled over 1200 heterosexual men and women. Half the participants were given the tenofovir and emtricitabine pill to take daily, and the other half were given a placebo.
Overall, the risk of contracting HIV for people taking the drug was 63% lower than those for people taking the placebo pill. The researchers also looked just at participants consistently taking the drug---leaving out participants who had left the study or stopped taking the drug for at least a month---and compared them to the placebo group. Risk for this group, the team found, was reduced by 78% compared to the placebo group.
The results of both trials were so promising they were halted early; the drug was working so well the researchers could no longer in good conscience keep giving people the placebo instead.
What's the Context:
A study last year of gay men in San Francisco showed the same effect: Taking tenofovir reduced a healthy participant's risk of contracting HIV by 44% compared to men taking a placebo. For those who adhered most faithfully to the drug regimen, taking the pill almost every day, their risk dropped by 73%.
This April, however, a study testing this approach in African women was stopped early because the drug didn't seem to be effectively protecting the women. Some researchers wondered if some women in the study were giving some pills to their infected partners---since these same pills are used to keep HIV infections in check---rather than taking them all themselves.
Worldwide, heterosexuals in Africa are hit hardest by HIV, says Kevin Fenton, director of AIDS prevention at the CDC, "and these studies offer the first compelling evidence that PReP can work to reduce HIV infection among them," Time's Healthland blog reports.
Preventative drugs alone won't halt the spread of HIV, but experts are hopeful that they can make a big difference. "We're beginning to understand that these antiretroviral drugs are powerful tools for prevention tool kits," Fenton told the Wall Street Journal. Talking to the Los Angeles Times, Mitchell Warren, head of the AIDS Vaccine Advocacy Coalition, called the studies "two more nails in the coffin of HIV."
These drugs are relatively cheap, an important factor in considering their use for widespread prevention. Gilead, the company that makes the drugs, sells them for as little as 21¢ per day in parts of the developing world.
The Future Holds:
The CDC has announced it will immediately start working with public health groups to formulate guidelines for using the drugs preventatively for heterosexuals in the US (interim guidelines already exist for gay men).
