Pre-Exposure Use of HIV Medications Reduces Risk Of HIV Infection

In a finding with the potential to offer a new strategy to slow the global HIV epidemic, a new study called iPrEx shows that individuals at high risk for HIV infection who took a single daily tablet containing two widely used HIV medications, emtricitabine and tenofovir (FTC/TDF), experienced an average of 43.8 percent fewer HIV infections than those who were assigned to take a placebo pill.

The study, reported in the New England Journal of Medicine, is the first evidence that this new HIV prevention method, called pre-exposure prophylaxis or PrEP, reduces HIV infection in people at increased risk of infection.
The Fenway Institute at Fenway Health in Boston was one of two United States sites that enrolled study participants. The other U.S. site was at the San Francisco Department of Public Health and there were nine international sites in Brazil, Ecuador, Peru, South Africa and Thailand.

Dr. Kenneth Mayer, Medical Research Director and Co-Chair of The Fenway Institute, is one of the Principal Investigators on the study and an author on the New England Journal of Medicine article.

“We had reached a plateau in preventing the transmission of HIV,” said Dr. Mayer.  “For more than 15 years, the rate of new infections in the U.S, has been stuck at about 56 thousand per year; globally, there are more than 2.5 million new HIV infections per year. There has been no downward movement in this number; which has meant that we desperately needed a new approach.  Today’s announcement marks a tremendous step forward - it’s now possible that within the next few years, we can significantly reduce the number of new infections.”

A total of 2,499 gay and bisexual men, other men who have sex with men (MSM) and transgender women at high risk of HIV infection participated in the six-country, four continent iPrEx study. 

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 the study participants also received the PrEP pill, while the other half received a placebo.  

iPrEx studied the impact of PrEP on one of the populations hardest hit by the global HIV epidemic. 

Globally, even in regions with generalized HIV epidemics such as Africa and Asia, gay, bisexual and other MSM and transgender people often have much higher rates of HIV infection than the population at large. 

In the United States, the Centers for Disease Control and Prevention estimate that close to one in five gay and bisexual men in 21 major American cities are infected with HIV, and half of them do not know it. 

HIV prevention tools that reduce infection in gay, bisexual and other MSM not only have the potential to save thousands or millions of lives directly, but could also greatly reduce the impact of HIV on all communities at risk by reducing overall prevalence of the disease and thus the global risk of HIV infection. 

iPrEx is one of the largest HIV prevention clinical trials to focus on gay, bisexual and other men who have sex with men, the first HIV prevention study to focus on MSM to be conducted in either Africa or Asia, and the first demonstration of a biomedical intervention to prevent HIV infection in gay, bisexual and other MSM. 

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 43.8 percent includes all study participants – even those who did not take the daily pill consistently.  

The iPrEx 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 50.2 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 72.8 percent. 

“iPrEx proves that PrEP provides important additional protection against HIV when offered with other prevention methods such as HIV testing, counseling, condom use and management of sexually transmitted infections,” said iPrEx Protocol Chair Robert Grant, MD, MPH of the Gladstone Institutes and the University of California at San Francisco. “As with other prevention methods, the greatest protection comes with consistent use.  I hope this finding inspires a renewed commitment from communities, industry, and government to stop the spread of HIV.” 

The iPrEx study (Iniciativa Profilaxis Preexposicion or Prexposure Prophylaxis Initiative) (, is a double-blind, placebo controlled Phase III clinical trial that began in 2007 following three years of community consultation. 

iPrEx is the first human efficacy study of PrEP to report data.  The iPrEx study was sponsored by the U.S. National Institutes of Health through a grant to the Gladstone Institutes, a non-profit independent research organization affiliated with the University of California at San Francisco.  Additional support for iPrEx was provided by the Bill & Melinda Gates Foundation.  

Other PrEP studies are underway in Africa and Asia studying the use of oral medication to prevent HIV transmission in high risk women, heterosexual couples, and injecting drug users. Other studies are evaluating the use of a topical gel containing one of the drugs used in the iPrEx study (tenofovir) for HIV prevention, building on the success of the CAPRISA 004 study, published in Science this past August. 

Additional information about the iPrEx study and PrEP:
•     Manuscript URL:
•    iPrEx Study fact sheets:
•    iPrEx study materials from the National Institutes of Health (NIH):
•    Release:
•     Q&A:
•    Background information on pre-exposure prophylaxis for HIV from Global Advocacy for AIDS Prevention:,458
•    Information on the iPrEx study drug, FTC/TDF:

For nearly forty years, Fenway Health has been working to make life healthier for the people in our neighborhood, the LGBT community, people living with HIV/AIDS and the broader population.  The Fenway Institute at Fenway Health is an interdisciplinary center for research, training, education and policy development focusing on national and international health issues.  Fenway’s Sidney Borum Jr. Health Center is dedicated to providing the best quality health care for youth and young adults ages 12 to 29 who may not feel comfortable going anywhere else.  More about all of our programs and services can be found at

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