Daily Truvada as pre-exposure prophylaxis (PrEP) against HIV takes five to seven days to reach top estimated effectiveness among men who have sex with men (MSM). High levels of protection are maintained for perhaps a week after the last dose. According to levels of drug detected in peripheral blood mononuclear cells (PBMCs), and comparisons of those results to drug levels estimated in previous research to correspond to varying degrees of protection against HIV, one day on PrEP led to a 75 to 91 risk reduction, three days meant a 95 to 97 percent risk reduction, and five and seven days translated to a 98 to 99 percent risk reduction. The presumed risk reduction stayed higher than 90 percent for seven days after the last dose. Although the study included female participants, it was not meant to estimate how well PrEP dosing protects them or other groups, just MSM. The iPrEx study used as the reference point for Truvada’s effectiveness at various concentrations in PBMCs was only conducted among MSM and trans women.
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