What is PrEP for HIV Prevention?
PrEP refers to an experimental HIV prevention strategy that proposes using antiretrovirals (ARVs) to reduce the risk of HIV infection in healthy uninfected people at risk for acquiring the virus. With PrEP, individuals would take a single drug or a combination of drugs orally, or through intramuscular injection, with the hope that it would lower the risk of infection if exposed to HIV. There are for ARVs currently being tested in PrEP human safety and efficacy trials: maraviroc, tenofovir (TDF), rilpivirine (TMC278) and a combination of tenofovir and emtricitabine (FTC). Scientists have focused on these drugs because they can be conveniently taken orally once a day, may have relatively low rates of minor side effects compared to benefit when used as prevention, and because there is significant data on their long-term safety and resistance profiles in HIV positive people. And, in the case of rilpivirine, because it can be taken in long acting formulation by injection.
PrEP clinical trials are currently planned or underway in countries in Africa, Asia, Latin America and North America. Taken together, these trials are designed to answer questions about how PrEP works in different parts of the world, and in individuals who are exposed to HIV through anal, vaginal and intravenous routes. These trials have enrolled people with different types of behaviors that might put them at risk for HIV, including injection drug use and unprotected anal or vaginal sex. It’s important to learn how PrEP works in the context of different routes of exposure (for example via injection, anal or vaginal sex.)
Global public, philanthropic and commercial investment in PrEP was US$31 million in 2012, bringing the total investment in this technology over the past seven years to US$297 million. However, funding for PrEP fell by US$20.7 million between 2011 and 2012, a significant decline. In July 2012, based on evidence from several trials, the US FDA approved daily oral TDF/FTC for use as PrEP for HIV prevention in HIV-negative women and men. Daily TDF/FTC has now been proven effective at reducing risk of HIV via sexual exposure in heterosexual men and women, gay men and other MSM and transgender women. This marked the first time the FDA approved a drug to reduce HIV risk via sexual exposure. The FDA decision led to preparation for, and initiation of, demonstration projects and follow-on trials to better assess and understand how to roll out PrEP for prevention. 2012 was a year of planning, with nearly 15 PrEP demonstration projects slated to begin in 2013 and the years beyond.
In June 2013, results from the Bangkok Tenofovir Study were published, finding that a daily dose of oral tenofovir reduced the risk of HIV infection in a population of IDUs by 49 percent overall. The study began in 2005 and enrolled more than 2,400 men and women. Ongoing studies are exploring different dosing strategies, including intermittent, time-driven and exposure-based use of PrEP. New PrEP strategies are also in development, including testing of long-acting TMC278 and, in another trial, maraviroc as an HIV prevention agent together with TDF and FTC.