HIV Antiretroviral Postexposure Prophylaxis: A Cautionary Note

Antiretroviral therapy can be used in 3 ways to prevent the sexual transmission of HIV infection: (1) to reduce an infected persons viral burden below a critical threshold; (2) as preexposure prophylaxis for people with persistent high-risk behavior(s); and (3) as postexposure prophylaxis (PEP) to be used after occupational needlesticks or sexual or other nonoccupational risks. The first 2 approaches are currently being tested in clinical trials to evaluate their efficacy. However PEP has already found its way into widespread clinical practice. Antiretroviral PEP initiated after occupational needlesticks has been used in an attempt to protect health care workers after exposure to HIV. On the basis of historical data Cardo et al. used a casecontrol design and reported that zidovudine appeared to reduce the risk of HIV infection by 81% from ~1 in 200 to 1 in 10000. But it has been impossible to design case-control or prospective studies to determine the efficacy of the nonoccupational use of PEP against sexual transmission when a partners HIV infection status is unknown and given the poor efficiency of the transmission of HIV infection. Data generated in studies of macaques suggest that therapy for HIV infection initiated within 72 h after genital tract exposure and continued for 28 days can prevent sexual acquisition of HIV infection in the majority of animals. (excerpt)