by Marie Daghlian
Just 25 years ago, HIV-AIDS was a death sentence for anyone who contracted the disease. Although it can now be controlled by antiretroviral therapies, preventing infection has not been very effective as an estimated 2.7 million people contract the disease each year. Now, a major study has demonstrated that Gilead’s (NASDAQ:GILD) combination pill Truvada can protect high-risk men without the disease from becoming infected with HIV.
The study shows that individuals at high risk for HIV infection who took a single daily tablet containing two widely used HIV medications, emtricitabine and tenofovir, which are marketed by Gilead as Truveda, experienced an average of 44 percent fewer HIV infections than those who received a placebo pill. Results, reported in the New England Journal of Medicine, are the first evidence that this new prevention method—pre-exposure prophylaxis or PrEP—reduces HIV infection risk in people.
“We now have strong evidence that pre-exposure prophylaxis with an antiretroviral drug can reduce the risk of HIV acquisition among men who have sex with men, a segment of the population disproportionately affected by HIV/AIDS,” says Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases. “Additional research is needed, but certainly this is an important finding that provides the basis for further investigating, developing and employing this prevention strategy, which has the potential to make a significant impact in the fight against HIV/AIDS.”
Led by study chair Robert Grant of the Gladstone Institute of Virology and Immunology, and study co-chair Javier Lama of Investigaciones Medicas en Salud, a Peruvian-based research organization, the study enrolled a total of 2,499 men and transgender women who have sex with men, who were HIV-negative at the time of enrollment but were at high risk for HIV infection, at 11 sites in Brazil, Ecuador, Peru, South Africa, Thailand and the United States.
All study participants received a comprehensive package of prevention services designed to reduce their risk of HIV infection throughout the trial, including HIV testing, intensive safer sex counseling, condoms and treatment and care for sexually transmitted infections. Half of study participants also received the PrEP pill, while the other half received a placebo.
In all, 64 HIV infections were recorded among the 1,248 study participants who received a placebo pill, while 36 HIV infections were recorded among the 1,251 participants who received the study drug. The average reduction in HIV infection risk of 44 percent includes all study participants—even those who did not take the daily pill consistently.
The study found that PrEP was more protective among those who reported taking the pill more regularly. Among participants who used the tablet on 50 percent or more of days, as measured by pill counts, bottle counts and self-reports, risk of HIV infection fell by 50 percent; among those who used the pill on 90 percent or more of days, as determined by the same measures, the PrEP pill reduced infection risk by 73 percent.
Side effects from use of the PrEP pill were mild and infrequent in the study. Researchers will continue to collect and analyze data on low level side effects related to bone mineral density or kidney function, which have been associated with some HIV therapies. Two study participants who received the active drug developed resistance to the emtricitabine component. Use of the PrEP pill did not cause study participants to relax their use of safer sex practices. In fact, self-reported HIV risk behavior decreased among participants in both arms of the study, and condom use increased.
Other studies of PrEP are currently underway among heterosexual men and women, serodiscordant couples and injection drug users. Researchers are careful to point out that those trials should continue, as results from this study cannot be extrapolated to predict the impact of PrEP on other populations. Approximately 20,000 participants are currently or expected to be enrolled in PrEP trials worldwide. PrEP was previously demonstrated to be highly effective in animal studies.
“A variety of expert and community advisory groups at the federal, state and local levels are looking closely at the study data and will move forward in a deliberative and measured way over the coming months to determine whether and how these findings should be incorporated into ongoing HIV prevention programs,” says Howard Koh, assistant secretary for health at the U.S. Department of Health and Human Services.
Investigators will conduct a follow-on study in which all HIV-negative study participants will be offered the combination drug for 18 months. That study, which will begin in 2011, is designed to provide additional information about the drug’s long-term effectiveness and safety as well as participant risk behavior and pill-taking practices.
The National Institute of Health cautions that correct and consistent condom use and a reduced number of sexual partners remain the most effective ways for gay and bisexual men to protect against HIV infection.
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