Background:  With more than 2.5 million new HIV infections annually, the use of HAART to decrease HIV transmission and acquisition has gained increased attention. HAART decreases genital tract HIV, and several studies have found that patients on ART may be likely to transmit HIV to their partners. However, for HAART to be optimally effective for prevention, patients will need to be adherent, have stable medical care, and modify risk taking behaviors, since some residual genital secretion HIV may be detected in some patients whose plasma viremia is suppressed on HAART, particularly in the setting of inter-current sexually transmitted diseases. ART may also be used to protect uninfected persons from HIV acquisition, either administered prior to, or post, a high-risk exposure (PrEP or PEP). Animal studies, a retrospective case-control, and observational data have helped to demonstrate the utility of PEP. Animal data suggest that either topical or systemic antiretroviral chemoprophylaxis may be effective, and studies are currently underway in multiple countries, evaluating the efficacy of oral or topical PrEP in diverse, high risk populations.  Although tenofovir plus/minus emtricitabine has been the most studied chemoprophylaxis medications, newer studies are evaluating drugs with other mechanisms of actions, including entry inhibitors and non-nucleoside reverse transcriptase inhibitors, as well as long-acting formulations delivered via intravaginal rings or injections.

Conclusions:  If the current chemoprophylaxis studies demonstrate efficacy, longer term monitoring will be needed to evaluate potential long term toxicities, risk compensation, and virologic resistance, in order to fully understand the risks and benefits of chemoprophylaxis.