Post-exposure prophylaxis (PEP) is a course of anti-HIV medication
that may prevent HIV infection after exposure. It can take HIV
between one and five days to become established in the CD4 T-cells
and lymph nodes after exposure. It is thought that a course of PEP
can act during this time to prevent the virus from taking hold, thus
preventing seroconversion in the person who was exposed.

Currently, the focal emphasis in the use of PEP is amongst health
workers who may be exposed to HIV infection due to needle pricks or other exposures to infected blood and blood products during patient management. There are however, renewed interest in preventing possible HIV infection through rape by the use of PeP. In South Africa, for example, where the incidence of rape is the highest in the world, it has been estimated that more than one million women are raped each year. Rape therefore constitutes a possible HIV infection risk route (when raped by someone who is HIV infected, not only is the semen loaded with HIV virus but the tears from forced penetration also further helps the entry of the virus into the body).

Evidence from studies show that very few cases of HIV transmission
have occurred after PEP, with only six reported transmissions
worldwide in healthcare workers since 1997. Studies of PEP after
sexual exposure have also been promising. For example, a Brazilian
study of gay men found that fewer men became infected after sexual exposure if they took a course of PEP than did a similar group who chose not to take it . A second Brazilian study found no
seroconversions in victims of sexual assault who took PEP within 72
hours of exposure. Similarly, only one of 500 sexual assault victims
in South Africa who were treated within 72 hours of the assault
subsequently developed HIV infection .

Despite this evidence, there are drawbacks to PeP. This include low
uptake due to a number of factors including lack of awareness, and
poor adherence, chiefly due to drug side-effects.