Imagine if there was a pill that everyone could take and it would magically prevent transmission of the AIDS virus.
Well, there is, at least in theory. But just how useful, appropriate and affordable it is in the real world is a point of much contention.
Earlier this month, the U.S. Food and Drug Administration approved Truvada to be used for prevention of AIDS in people who are not infected with the human immunodeficiency virus.
The approach, called pre-exposure prophylaxis or PrEP, has created a lot of buzz at the the 19th International AIDS Conference, being held this week in Washington.
"This is a powerful tool that can be used for vulnerable HIV-negative individuals. We've waited a long time for this," Nelly Mugo, head of research at Kenyatta National Hospital in Nairobi, Kenya, told delegates.
The target market for PrEP is people in "discordant" couples – meaning men or women who have a partner who is HIV-positive, of which there are some five million worldwide. The approach could, theoretically, also help slow the infection rate in high-risk groups like sex workers and intravenous drug users, who are estimated to number some three million who are HIV positive. (According to the World Health Organization, approximately 34-million people worldwide are HIV-positive).
Newly-published research shows that taking Truvada (which is a combination of two antiretrovirals, emtricitabine and tenofovir) daily reduced the risk of infection by 73 per cent in discordant heterosexual couples in Africa; couples where the uninfected partner took tenofovir alone, saw their risk drop 62 per cent. Smaller studies show similar risk reductions in discordant homosexual couples in the U.S.
But another study, also conducted in Africa, found that taking the "prevention pill" did not benefit high-risk women at all; in fact, it may have increased their risk. That confirmed fears that the "anti-AIDS" pill could lead people to neglect other simple, proven prevention methods like use of condoms, microbicides and circumcision.
"Pre-exposure prophylaxis…is not a panacea for HIV infection," said Robert Steinbrook of the department of internal medicine at Yale School of Medicine in New Haven, Conn. "It is not an effective morning-before pill or morning-after pill…it is not a replacement for condoms or other safe sex practices." The drug has to be taken daily to be effective and that level of compliance seems unrealistic, given experience with birth control pills. A study of IV drug users in Bangkok found only half were able to take their pills daily for three months.
"To pretend that PrEP is going to be a solution is just not realistic," said Julio Montaner, director of the B.C. Centre for Excellence in HIV/AIDS.
He worries that interest in PrEP will distract from the "treatment as prevention" strategy that has become the gold standard.
The TAP approach, pioneered by Dr. Montaner and his colleagues, consists of treatment for everyone infected with HIV with antiretroviral (ARV) cocktails to suppress the virus, which dramatically reduces their ability to infect others and keeps them healthier.
Worldwide, there are more than seven million HIV-positive people taking ARVs, and the plan is to scale that up to 15 million by 2015.
"When you do treatment as prevention, the prevention benefit to the HIV-negative comes at no extra cost," Dr. Montaner said. "You don't need a whole new infrastructure." Cost is, of course, a big issue.
Truvada costs $13,900 a year in the U.S.; in the developing world, it costs about $150 to $250 annually. In both cases, that is more than standard drug cocktails used to treat those who are infected.
The drug can also have significant side effects so giving it to people who are not infected poses tough ethical questions.
When the initial enthusiasm passes and the barriers to extensive pre-exposure prophylaxis – financial, ethical and practical – sink in, the most likely outcome is that it will become a niche prevention strategy.
Dr. Mugo said it could be used, for example, by discordant couples who are trying to conceive.
Dr. Montaner said that, in his practice, PrEP might be useful for partners of HIV-infected patients who cannot tolerate drug cocktails, or by sex workers who are forced into unprotected sex.
"I'm not opposed to PrEP in individual circumstances," he said. "I just don't want us to lose our focus. We need to use the tools we have that work like treatment as prevention."