Pre-Exposure Prophylaxis and the Promise of Combination Prevention Approaches, Susan P. Buchbinder and Albert Liu, AIDS BEHAV (2011)

This article examines issues raised by Pre-Exposure Prophylaxis (PrEP) – the use of oral and topical drugs to help prevent HIV infection. Unlike Post-Exposure Prophylaxis (PEP), which is administered after HIV exposure, PrEP is administered daily as a pill or applied topically as an ointment before sex to reduce the risk of HIV transmission.

To date, PrEP trials, while limited in scope and duration, show promise when adherence is consistent. For example, women who participated in the CAPRISA 004 study and used tenofovir vaginal gel at least 80 percent of the time before potential sexual exposures experienced 54 percent greater protection against seroconversion than women who did not use the gel. Women who participated in the study but did not adhere to tenofovir gel use consistently did not experience a statistically significant increase in HIV transmission prevention.

There are many aspects of PrEP that still need to be explored before reliance on it as a mode of HIV prevention can be broadly recommended. One fear the authors reference is the risk that those using PrEP will be more likely to rely on it exclusively to prevent HIV infection, and consequently engage in risk behaviors because of assumed protection. Studies are currently investigating the impact of PrEP on incidence of risk behaviors. Current data suggest that PrEP utilizing tenofovir or Truvada is not detrimental to the health of HIV-negative individuals. Studies of African women after up to 12 months of oral tenofovir use and American MSM after up to 24 months of oral tenofovir use have confirmed its safety. One of the reasons many PrEP studies use tenofovir is because it is generally well tolerated, and has a strong clinical safety record and resistance profile. The impact of sustained PrEP on bone mineral density is under investigation. The long-term impact of PrEP, as well as its safety for use among pregnant or lactating women, youths, or individuals with underlying medical conditions, is not yet known.

The authors suggest that while PrEP may aid in controlling the HIV epidemic, it will have to be used in combination with other prevention techniques to effectively eliminate HIV. PrEP as a mechanism for blocking sexually transmitted HIV is still being tested in numerous clinical trials throughout the globe. Methods of PrEP data analysis and study design must be reviewed continuously to assess its efficacy in preventing HIV transmission, social acceptability, cost-effectiveness, and long-term safety.