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The AIDS Pill
by Sarah Post
Could Preventing AIDS Really Be This Easy?
What if a pill could prevent AIDS?
Such a discovery would be a watershed moment. Optimistic visions immediately spring to mind: with the tremendous publicity and advocacy such a discovery would generate, the drug would move quickly from the lab to the field where it is desperately needed. It could turn the epidemic into a dark historical lesson rather than a gruesome everyday reality for millions.
As it turns out, such a drug may already exist. It's called tenofovir disoproxil fumarate (marketed as Viread), a potent antiretroviral drug that has been used since 2001 to treat active HIV infections. Early evidence shows that, when taken daily, Viread could prevent HIV in uninfected individuals.
Yet the first clinical trials designed to assess this potential breakthrough have aroused a firestorm of criticism. Concerns about the trials stem from the conflicting priorities of research ethics. If misconceptions about these trials are not clarified, attempts to reach the real holy grail of AIDS prevention-a safe and effective vaccine-may be lost.
However, an even greater concern exists. The "breakthrough" of Viread may hinder the development of a completely functional vaccine. Paradoxically, the introduction of this seemingly miraculous intervention may, in the end, undermine the fight against AIDS.
Background
Using antiretrovirals to prevent HIV transmission is not a new idea; AIDS drugs are often prescribed to HIV-infected pregnant women around the time of delivery to prevent mother-to-child transmission. Such drugs are also commonly prescribed after potential exposure to the virus through needle sticks or unprotected sex. The practice is known as post-exposure prophylaxis (PEP): a course of antiretrovirals, if started soon enough, can stop the virus from multiplying to prevent permanent infection. Its use, now common among health-care workers, is increasing thanks to publicity efforts aimed at high-risk groups such as men who have sex with men (MSM) and intravenous drug users. The same mechanisms that make post-exposure prophylaxis effective could probably be extended to prevent infection before any exposure occurs. Such pre-exposure prophylaxis (PrEP) could be applied through daily drug therapy.
The antiretroviral drug Viread was developed by Gilead Sciences and approved by the FDA in October 2001. After its release, it quickly became the most frequently-prescribed antiretroviral drug in the United States, with sales climbing to more than $550 million in 2003. In 1995, a study published in Science demonstrated that Viread worked as pre-exposure prophylaxis in macaques. Viread may be an ideal PrEP candidate because, compared to many other similar drugs, it causes few significant side-effects, has few drug interactions, and needs to be taken only once a day. Also, resistance to Viread develops much more slowly than for other drugs, making it more practical for long-term use.
Trials and Tribulations
The hope that Viread will serve as an effective pre-exposure prophylactic has lead to trials designed to test its safety. While the drug has already undergone testing as a treatment for HIV infection, whether it's safe for uninfected individuals, and whether it would indeed protect them, remains uncertain.
Several trials are currently being organized: Family Health International, supported by the Bill and Melinda Gates Foundation, is running trials on 1200 women in Cameroon, Ghana, and Nigeria and on 400 heterosexual men in Malawi. The University of California, San Francisco received also received an NIH grant to test the drug on 960 Cambodian sex workers, in collaboration with Australia's University of New South Wales, also supported by the Gates Foundation. Finally, the Centers for Disease Control and Prevention (CDC) is currently recruiting 400 MSM for a trial in Atlanta and San Francisco.
These trials have been controversial. All clinical trials face the challenge of preserving the careful balance between ethics and effectiveness. Indeed, each trial involves some potential hazard to their participants; a drug may cause side effects, for instance, or a placebo may be inferior to an active treatment. Naturally, if those conducting where fully aware of the exact harms and benefits of a potential drug, there would be no need for the trial; the potential harm is considered ethically acceptable. Theoretically, the knowledge gained through the results ultimately benefits society more than the dangers of the trial itself.
Continued
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