PrEP Studies Show Possible Effectiveness; Scientists Say Further Tests Must Be Completed for Confirmation

Results from a clinical trial that investigated the potential use of tenofovir and Gilead's combination pill Truvada as pre-exposure prophylaxis to prevent HIV transmission show possible effectiveness, but scientists say that the low number of people involved in the study means that the effectiveness cannot be guaranteed, the AP/Forbes reports (Marchione, AP/Forbes, 8/12). PrEP is an experimental approach to HIV prevention, in which HIV-negative people receive antiretroviral drugs to prevent HIV transmission (Kaiser Daily HIV/AIDS Report, 8/11). The study -- run by Family Health International, funded in part by the Bill & Melinda Gates Foundation, and released Saturday ahead of the XVI International AIDS Conference in Toronto -- involved 400 HIV-negative women in Ghana, half of whom took Gilead's Viread, which is known generically as tenofovir, for one year (AP/Forbes, 8/12). Half of the women took a placebo. Two study participants taking Viread tested HIV-positive at the end of the trial, compared with six women taking the placebo pill, according to the study. The results are not statistically significant, Ward Cates, president of research at FHI who was involved in the study, said. In addition, the study finds Viread to be safe despite previous concerns about potential drug toxicity to the kidney, liver or bones. Some study participants reported stomach pains and headaches, along with malaria, an unrelated illness, according to the researchers (Chase, Wall Street Journal, 8/12). Cates also said that the women in the study did not have an increased amount of sex and continued to use condoms.

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Although the trial in Ghana produced positive results, scientists say there need to be further studies to confirm the pill's effectiveness, Reuters reports. Cates said, "The encouraging news was in regard to safety, acceptability and risk" (Fox, Reuters, 8/12). But "[b]ecause the numbers were low, we could have observed this (infection rate) by chance," he said, adding that it would be "irresponsible to draw conclusions" on the effectiveness of the drug "at this time." He also said that the study "underscore[s] the importance of moving forward very quickly ... on the other studies on the drawing board" (AP/Forbes, 8/12). Researchers are conducting studies in Botswana, Peru and Thailand (Kaiser Daily HIV/AIDS Report, 8/11). These studies are expected to involve a total of about 4,600 people, which could solve the question of whether tenofovir and Truvada are effective as PrEP, according to Cates (Wall Street Journal, 8/12). If further studies prove their effectiveness, the drugs "would be an incredibly important new prevention tool that we should make available as soon as possible," Helene Gayle, president of CARE and co-chair of the conference, said, adding that the results of the study, regardless of their statistical significance, are "incredibly encouraging" (AP/Forbes, 8/12). The International AIDS Society held a session titled "What if PrEP works?" at the conference to discuss the most safe and ethical ways to distribute a prevention pill to groups at an increased risk of contracting HIV (Wall Street Journal, 8/12).

Kaisernetwork.org is serving as the official webcaster of the conference. View the guide to coverage and all webcasts, interviews and a daily video round up of conference highlights at www.kaisernetwork.org/aids2006.

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