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Pre-Exposure Prophylaxis (PrEP)

What is PrEP?

PrEP is short for Pre-Exposure Prophylaxis. It is a new HIV prevention method in which people who do not have HIV take a daily pill to reduce their risk of becoming infected. When used consistently, PrEP has been shown to reduce the risk of HIV infection among adult men and women at very high risk for HIV infection through sex or injecting drug use.

Based on studies to date, in July 2012 the U.S. Food and Drug Administration approved the combination medication tenofovir disoproxil fumarate plus emtricitabine (TDF/FTC) for use as PrEP among sexually active adults at risk for HIV infection.

For some individuals at high risk for HIV infection, PrEP may represent a much-needed additional prevention method, but it will not be right for everyone and is not intended to be used in isolation, but rather in combination with other methods to reduce the risk of getting HIV infection. If it is delivered effectively and targeted to those at highest risk, PrEP may play a role in helping to reduce the significant continuing toll of new HIV infections in the United States. CDC is currently working with partners to ensure safe and effective PrEP use and begin to address key questions about acceptability, access, adherence, behavioral risks, and patient outcomes in community settings.

CDC PrEP Guidance

CDC is leading national efforts to develop comprehensive Public Health Service guidelines for PrEP. Until those more detailed guidelines are available, CDC has developed interim guidance for physicians electing to provide PrEP for HIV prevention among MSM, heterosexually active women and men and people who inject drugs.

PrEP Research

In November 2010, the National Institutes of Health (NIH) announced the results of the iPrEx clinical trial, a large, multi-country research study examining PrEP among MSM. The study found that daily oral use of TDF/FTC provided an average of 44% additional protection to MSM who also received a comprehensive package of prevention services that included monthly HIV testing, condom provision, and management of other sexually transmitted infections. The level of protection varied widely depending on how consistently participants used PrEP, with significantly greater levels of protection among those who adhered well to the daily regimen. Among MSM with detectable levels of the medication in their blood, the risk of HIV acquisition was reduced by more than 90 percent.

In July 2011, a CDC study called TDF2, along with a separate trial by the University of Washington (Partners PrEP), provided evidence that a daily oral dose of antiretroviral drugs used to treat HIV infection can reduce HIV acquisition among uninfected adults exposed to the virus through heterosexual sex.

TDF2, conducted in partnership with the Botswana Ministry of Health, found that once-daily TDF/FTC reduced the risk of acquiring HIV infection by 62 percent overall in the study population of uninfected heterosexually-active men and women. Blood level data showed that participants who became infected had far less drug in their blood, compared with matched participants who remained uninfected suggesting that medication adherence is associated with the efficacy of PrEP in preventing HIV infection.

Partners PrEP found that two separate antiretroviral regimens – TDF/FTC in combination and tenofovir alone – when provided to uninfected persons whose partners have HIV infection (sero-discordant couples) significantly reduced HIV acquisition (by 75 percent and 67 percent, respectively). Participants in the TDF/FTC group with detectable levels of the medication experienced a 90 percent reduction in risk for HIV infection; in the tenofovir- only group, the presence of medication in the blood was associated with an 86 percent reduction in risk. CDC co-managed two of the nine sites for this study.

Two other research studies among women, FEM-PrEP and VOICE, found that participants provided PrEP did not experience any protection against HIV. Analyses of blood level data showed that very few women assigned to use the study drugs in either study were actually taking the pills as directed, indicating that lack of adherence was likely the major factor contributing to the lack of effectiveness in these studies.

In June 2013, the Bangkok Tenofovir Study, conducted by CDC, the Bangkok Metropolitan Administration and the Thailand Ministry of Public Health, reported that a once-daily tablet containing tenofovir reduced the risk of acquiring HIV by approximately 49 percent among men and women who inject drugs.

Consistent with prior research, participants who took the medication consistently had higher levels of protection. In an analysis of participants known to be adherent because they were observed taking their medication and had tenofovir detected in their blood, the risk of HIV acquisition was reduced by approximately 74 percent.

No studies conducted to date have identified any significant safety concerns associated with use of daily oral PrEP.

Additional CDC Publications

CDC Interim Guidance on PrEP Use among MSM

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