Pre-exposure prophylaxis (PrEP) is any medical or public health procedure used before exposure to the disease causing agent, its purpose is to prevent, rather than treat or cure a disease. An example would be if a doctor gave a medication used to treat a disease to a healthy person who is not thought to have that disease, but is at risk for contracting it. More specifically, this practice is common with people who are about to travel from an area without malaria to an area where malaria is a risk, and also it is being researched as a tool to prevent persons from contracting HIV.
Pre-exposure prophylaxis can also refer to the aggressive use of vaccination, for example in an attempt to prevent rabies in people such as laboratory workers who are high risk for being bitten by rabid animals.
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The CDC publishes recommendations for travels advising about the risk of contracting malaria in various countries.[1]
Some of the factors in deciding whether to use chemotherapy as malaria PreP include the specific itinerary, length of trip, cost of drug, previous adverse reactions to antimalarials, drug allergies, and current medical history.[1]
Most commonly, the term "pre-exposure prophylaxis" refers to an experimental HIV-prevention strategy that would use antiretrovirals to protect HIV-negative people from HIV infection. PrEP is not proven to work; in the strategy that is currently being tested, HIV-negative people would take a single drug, or a combination of drugs, with the hopes that it would lower the risk of infection if exposed to HIV. Along with AIDS vaccines and microbicides, PrEP is one of the experimental HIV prevention strategies being tested in clinical trials today.
Studies of PrEP strategies in non-human primates have shown a reduced risk of infection among animals that receive ARVs prior to exposure to a simian form of HIV. A 2007 study at UT-Southwestern (Dallas) and the University of Minnesota showed PrEP to be effective in "humanized" laboratory mice.[2] Another rationale of PrEP comes from strategies to prevent mother-to-child transmission, which use ARVs given to the mother and the infant to help reduce the risk of transmission.
Today the two PrEP strategies under study are (1) a single drug called tenofovir disoproxil fumarate (TDF) and (2) a combination drug called Truvada , which combines TDF with the drug emtricitabine [3]. Currently there are eight human trials of daily oral PrEP, with almost 20,000 participants currently or soon to be enrolled.[4]
The CDC (Centers for Disease Control) is conducting an extended safety trial in the U.S.,[5] and expects the final data analysis to take place in early 2010 (see timeline).[6]
There are several current and future PrEP challenges, from biomedical concerns (such as safety and effectiveness) to concerns of behavioral repercussions.
One criticism of PrEP for HIV is that it may encourage risky behavior including unprotected sex, possibly increasing, rather than decreasing, the risk of HIV infection in sero-discordant partners.
iPrEx is the name of a specific clinical trial completed in 2010 which demonstrated that PreP has some efficacy in reducing some people's risk of contracting HIV. It is notable for being the first PreP research project to announce this result.
With an estimated 39.5 million people living with HIV worldwide and 4.3 million new infections per year, many people are at risk for HIV infection through sexual transmission, and therefore preemptive measures must be taken to prevent further dissemination.[7] Pre-exposure prophylaxis (PrEP) supplies a promising prevention strategy for further sexual transmission. Although many trials in the past have failed to demonstrate the effectiveness of PrEP in HIV prevention, there are two promising treatments. One recent study indicated that the pill Truvada, made up of tenofovir and emtricitabine, reduced HIV transmission by 44% among sexually active men.[8] Moreover, tenofovir in the form of a vaginal microbicide gel has been shown to slow HIV sexual transmission by 39%.[9]