Good News for Tenofovir PReP

Over the summer tenofovir was approved by several regulatory agencies as the first pre-exposure prophylaxis (PReP) for HIV/AIDS. At the time, many people expressed concern that the use of one of the first line ARVs as a prophylactic measure would lead to an increase in cases of drug-resistant HIV. An October study in the Journal of virology suggest that these fears may be exaggerated.

The study, which was conducted out of the Center for AIDS research University of North Carolina, found examined the effect of tenofovir resistant HIV on transmission rates. The goal was to discover is people on PReP who get infected might spread a dangerous drug-resistant strain of HIV. Surprisingly, the study found that the HIV mutation which leads to drug resistance to tenofovir is significantly less likely to be transmitted through vaginal intercourse than normal HIV variants.

A secondary goal of the study was to look at what happened to the drug resistant variants after infection. The study also found that when tenofovir resistant HIV is transmitted, after transmission it would to wild type, non-drug resistant, HIV approximately 66% of the time.

These findings are not directly relevant to people who are on tenofovir or as PReP, instead they the addresses the likelihood that people who are on tenofovir or PReP well, if infected, spread a tenofovir resistant version of HIV. Because tenofovir resistant HIV is less likely to transmit through vaginal intercourse, a person who is infected with HIV while on tenofovir or prep will, even if they do develop tenofovir resistant HIV strains, be unlikely to spread the infection to other people. This means that the risk about a tenofovir resistant strain of HIV becoming endemic and interfering with normal treatment plans is less than initially feared. Further, because the tenofovir resistant strain reverts to a wild type strain most of the time when it is transmitted, people who are infected with HIV by someone who has a tenofovir resistant strain of HIV, should still be able to use tenofovir or as first-line treatment by the time the infection advances to the point of needing HAART.

This study used animal models, so it isn’t conclusive. It is likely that there will be some difference in how HIV reacts to PReP in the real world. It is likely, however, that the model will closely reflect the reality.

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