What is "pre-exposure prophylaxis"

n. A preventative medical regiment of HIV medicines used to protect against HIV seroconversion after an exposure.

PrEP, an acronym from Pre-Exposure Prophylaxis, is the use of prescription drugs as a strategy for the prevention of HIV/AIDS by people who do not have HIV/AIDS. It is an optional treatment which may be taken by people who are HIV negative, but who have substantial, higher-than-average risk of contracting an HIV infection.

Currently, the only drug which any health organization recommends for PrEP is Truvada, which is the brand name of the Gilead Sciences drug combination of tenofovir/emtricitabine. The Centers for Disease Control says that "PrEP is a powerful HIV prevention tool and can be combined with condoms and other prevention methods to provide even greater protection than when used alone. But people who use PrEP must commit to taking the drug every day and seeing their health care provider for follow-up every 3 months."

One of PrEP's active ingredients, tenofovir disoproxil (TDF), is a nucleotide analog reverse transcriptase inhibitor. TDF effectively blocks HIV from incorporating its genetic material into the host's genome, and thus prevents HIV infection.

PrEP is intended for use with condoms, so that each method can compensate for essential or casual efficacy deficits of the other. There are social groups which both support and oppose the use of PrEP.