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.
Global public, philanthropic and commercial investment in PrEP increased to US$36 million in 2013, bringing the total investment over the past eight years to US$333 million. Investment increased by US$5 million in 2013 due in part to a number of new demonstration and implementation projects that began in late 2012 and early 2013 focused on the use of PrEP in different settings. Additionally, the initiation of several studies testing long-acting PrEP formulations in 2013 also resulted in an increase of investment in clinical trials.
In July 2012, based on evidence from several trials, the US Food and Drug Administration (FDA) approved daily oral tenofovir (TDF/FTC, marketed as Truvada) for use as PrEP for HIV prevention in HIV-negative women and men. Daily TDF/FTC has proven effective at reducing risk of HIV via sexual exposure in heterosexual men and women, gay men and other MSM and transgender women. The FDA decision led to preparation for and initiation of demonstration projects and follow-on trials to better assess and understand how to rollout PrEP for prevention. More than ten demonstration projects began in 2013 alone, with additional projects slated to begin in the coming years.
In June 2013, results from the Bangkok Tenofovir Study (BTS) were published, showing 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. The follow-up study to the BTS is ongoing, funded by the US CDC and the Thailand Ministry of Public Health.
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.