In recent years, there has been a lot of attention placed on the use of Viread® (tenofovir) for pre-exposure prophylaxis (PREP) against HIV infection. While clinical trial data involving humans are not expected until 2007, recent primate studies suggest that Viread's efficacy may be limited, especially at the oral dose currently used to treat chronic HIV disease. In turn, investigators at the U.S. Centers for Disease Control have evaluated a PREP regimen consisting of injectable versions of Viread and Emtriva® (emtricitabine) in macaques, in an effort to improve PREP efficacy. Their data were reported at the 13th Conference on Retroviruses and Opportunistic Infections in Denver.
The study evaluated 12 macaques rectally exposed to simian immunodeficiency virus (SIV) once a week. Six macaques received subcutaneous injections of tenofovir (22 mg/kg) and emtricitabine (20 mg/kg), starting nine days prior to viral exposure. Six untreated macaques were also rectally challenged with SIV.
Among the macaques not receiving the drugs, five of the six were infected with SIV after 14 weeks of SIV exposure. Among the six macaques that received PREP, none were infected with SIV after 14 weeks of virus exposure.
These data are optimistic and will likely pave the way for dual-drug PREP studies involving human volunteers. In the meantime, the investigators warned against the assumption that Truvada, the oral drug containing both Viread and Emtriva, will afford the same protection in humans. While the injectable emtricitabine dose used in this study yielded Emtriva plasma concentrations similar to those seen in humans, the injected dose of tenofovir resulted in blood concentrations that were significantly higher than those seen in humans receiving oral Viread.
Source: Garcia-Lerma J, Otten R, Qari S, et al. Prevention of rectal SHIV transmission in macaques by tenofovir/FTC combination [Abstract 32LB]. 13th Conference on Retroviruses and Opportunistic Infections, Denver, 2006.
