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October 10, 2006 (Reuters Health)—Tenofovir disoproxil fumarate (TDF), the oral prodrug of tenofovir, provides some protection to macaques repeatedly challenged with simian human immunodeficiency virus (SHIV), researchers report. The findings hint that pre-exposure prophylaxis against HIV might be possible.
As senior researcher Dr. Thomas Folks told Reuters Health, "the recent work showing a delay in mucosal SHIV infection in adult monkeys gives a first glimpse of partially successful pre-exposure prophylaxis (PrEP) with an oral drug and provides some guidance for PrEP studies in future human clinical trials."
As reported in the October 1st issue of the Journal of Infectious Diseases, Dr. Folks of the Centers for Disease Control and Prevention, Atlanta, and colleagues inoculated 12 male Chinese rhesus macaques intrarectally with SHIV.
These doses, which were about 5 times higher than HIV levels in human semen noted during acute infection, were repeated weekly for up to 14 weeks or until the animals became infected.
Four animals received daily oral TDF starting some hours after the SHIV injection, another four did so once weekly and the remaining 4 animals acted as controls.
Control animals became infected after a median of 1.5 inoculations. Those given the daily dose of TDF became infected at a median of 6 weeks, although one animal remained uninfected at 14 weeks. The corresponding interval in those given the weekly dose was 7 weeks.
These differences were not significant. However, the researchers point out the study was limited by the small numbers of animals involved and the variable blood levels of TDF resulting from oral dosing.
In an accompanying editorial, Drs. Mark A. Wainberg of McGill University, Montreal and Robert M. Grant of the University of California, San Francisco, note that clinical trials of TDF PrEP have already achieved "substantial enrollment." These trials will help evaluate whether TDF alone is sufficient in humans, although, they say "this approach was only partially effective for animals."
