Pre-exposure prophylaxis (PrEP) is the use of antiretrovirals prior
to exposure to HIV to prevent infection. PrEP is intended for use by
people who may be at frequent risk for HIV. This includes people who engage in high-risk behaviour groups such as sex workers, injecting drug users, and people who have unsafe sex with a multiple partners (or whose partners have multiple partners). Currently, no
antiretroviral is yet approved or in use as PrEP. Serodiscordant
couples (sexual stable relationships where a partner is infected
with HIV and the other is not) could also benefit from PreP use.

Much of the data on PrEP result from research conducted in monkeys.
In general though not clearly so, these studies have demonstrated
that PrEP can decrease the risk of infection to varying degree.
these studies have also used different models for testing, making
comparisons of results across studies difficult.

The only human data to date, from a Family Health International
study of tenofovir PrEP in which recruitment was abandoned at two
sites due to a controversy over post-trial care, show no serious
safety concerns during an average of nine months’ follow-up.

Four PrEP studies are ongoing and three others are planned for
rollout as of february 2008. The ongoing studies are:
• An efficacy study tenofovir among injection drug users in
Thailand, sponsored by the United States Centers for Disease Control and Prevention (CDC) – expected to report efficacy results in 2009.

• A safety study of tenofovir among men who have sex with men in the United States, also sponsored by the CDC – expected to report safety results 2009.

•An efficacy study of Truvada among heterosexuals in Botswana, also sponsored by the CDC – expected to report efficacy data in 2010.

• An efficacy study of Truvada among men who sex with men in Peru
and Ecuador sponsored by the NIH – expected results in 2010.
The risk of HIV transmission is influenced by a number of biological
and environmental factors, including stage of disease, number of
exposures, viral load in blood and semen, as well as the presence of
other sexually transmitted infections. In addition, studies have
shown that most transmission occurs during the acute stage of
infection or at the late stage of disease, when viral loads are
high. According to studies from serodiscordant couples conducted in
Africa, HIV-positive individuals in the acute stage of infection
were responsible for 43% of all HIV transmissions. Knowing this. HIV
control strategy must be multiprong with a wide range of use options
for all persons affected by epidemic.