Macaque study shows similar protection from rectal exposure using 2-hour pre- and 24-hour post exposure prophylaxis with tenofovir plus FTC compared to daily regimen
Simon Collins, HIV i-Base
Results in macaque studies showing protection from HIV infection using daily tenofovir, and similar protection with reduced risk of resistance from using tenofovir plus FTC, provided sufficient confidence for large scale studies in humans to proceed, even though most of these studies have run into practical difficulties.
Results from another important macaque study adds further supportive evidence for this concept, with perhaps additional implications for drug exposure.
J. Geraldo Garcia-Lerma and colleagues from the US DAIDS Centres for Disease Control (CDC) presented results from two different PrEP regimens. 
They first exposed six macaques by rectal administration on a once-weekly basis for 14 weeks. Dosing of TDF (22mg/kg) and FTC (20mg/kg) was given sub-cutaneously 2 hours prior and 24 hours after exposure, and results were compared to 21 control animals (9 real-time and 12 historical) and to previous study results using daily dosing. A second approach looked at using only 2-hour pre-dosing in another 6 animals.
20/21 untreated macaques became infected after a median of 2.5 exposures, with the majority infected during the first four challenges.
All animals receiving either daily dosing or the reduced pre- and post-only dosing were protected for the full 14 weeks. The 2-hour pre-exposure only dose for which only limited results were available reported infection in 1/6 animals.
- Garcia-Lerma JG, Otten R, Cong M et al. Intermittent antiretroviral prophylaxis with tenofovir and emtricitabine protects macaques against repeated rectal SHIV exposures. XVI International HIV Drug Resistance Workshop, 12-16 June 2007, Barbados. Abstract 85. Published as part of Antiviral Therapy (Volume 12 Issue 5). Antiviral Therapy. 2007;12:S65. Antiviral therapy 2007; 12:S96.