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Tenofovir PrEP Adherence/Protection-After Drug Cessation
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Here are 2 studies relevant to the question about tenofovir PrEP regarding adherence, how many pills one can miss & perhaps still be covered, remember this is research not absolutely established, but apparently meaningful.
Adherence/how many Tenofovir PrEP pills worked in study - Uptake of pre-exposure prophylaxis, sexual practices, and HIV incidence in men and transgender women who have sex with men: a cohort study.....iPrEx open-label extension - (09/29/14)
"Drug concentrations in dried blood spots were strongly associated with HIV incidence among those receiving PrEP (figure 2). There were no infections at visits where tenofovir diphosphate concentration was 700 fmol per punch or greater, suggesting the use of four to seven tablets per week (table 2). Such protective drug concentrations were evident during 33% of visits among those receiving PrEP. The hazard ratio for infection was 0·00 (95% CI 0·00-0·17) compared with the previous placebo group and 0·00 (0·00-0·14; adjusted for baseline differences in HIV risk factors) compared with concurrent off-PrEP group. The dried blood spot concentration associated with 90% reduced risk of HIV acquisition relative to the off-PrEP group was 611 fmol per punch (95% CI 216-1006), consistent with use of two or three tablets per week."
Prediction of Intracellular (IC) Tenofovir Diphosphate (TFV-DP) and Emtricitabine Triphosphate (FTC-TP) Concentrations Following Drug Intake Cessation - (06/01/15)
"Twenty-four, 36, 48 and 72h after stopping drug, 6%, 0%, 1% and 4% of predicted TFV-DP and 56%, 78%, 83% and 83% of FTC-TP were <16fmol/106 cells and 3.7pmol/106 cells, respectively (iPrEx HIV prevention targets)."
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