February 26, 2009
In an oral presentation at CROI 2009 in Montreal, Canada, data from a recent study shows that intermittent use of Truvada (tenofovir + emtricitabine) prevents rectal infection of simian HIV (sHIV) in macaque monkeys. This study compared the intermittent use of Truvada to its daily use.
PrEP, or Pre-Exposure Prevention, is using HIV therapy before an HIV exposure in hopes of preventing (but not treating) HIV infection. Intermittent PrEP, or iPrEP, refers to taking Truvada just before a planned sexual event rather than taking it daily to prevent HIV infection. This animal study also explored the effectiveness of using Truvada shortly after an exposure to prevent infection, called PEP or Post-Exposure Prevention. PrEP studies using Truvada are ongoing in humans, but they use daily not intermittent PrEP.
The HIV drugs in Truvada have two highly desirable qualities when used in PrEP settings. First, they have long half-lives (over ten hours), which means it takes about ten hours for half of the drug to clear from the blood. This means the drug is in the blood, exerting its anti-HIV affects for a long time after it's taken.
Second, the Truvada drugs show high concentrations within cells and in genital fluids, which is important when used in sexual exposures to HIV. Since HIV is most vulnerable to the anti-HIV effects of treatment during early infection, these two qualities make Truvada an excellent choice for preventing HIV infection from sexual exposures.
This study compared 2-dose iPrEP regimens in 4 groups of 6 male monkeys to 27 untreated monkeys (6 real time and 21 historical controls).
All groups were rectally exposed to simian HIV, or sHIV, weekly for 14 weeks.
After 14 rectal exposures to sHIV, the results showed that of the 27 untreated animals, 26 of them became infected on average within 2 exposures to sHIV. Of the treated animals, in group 1, 3 of the 6 did not become infected. In groups 2 and 3, 5 of the 6 monkeys remained uninfected. And in group 4, 3 of 6 remained uninfected with sHIV.
This small proof-of-concept study provides fodder for further research of iPrEP in humans. If PrEP proves effective, using HIV drugs intermittently would decrease the number of pills a person would need to take, decrease overall exposure to the drug and possibly reduce long-term side effects.