Estimated Pill Intake With On-Demand Prep With Oral Tdf/Ftc Using Tfv-Dp Concentration In Dried Blood Spots In The Anrs Ipergay Trial

Background: Tenofovir diphosphate (TFV-DP) concentration in dried blood spots (DBSs) is a reliable pharmacokinetics biomarker of adherence to tenofovir disoproxil fumarate (TDF). We aimed to use DBSs to estimate pill intake among participants using on-demand pre-exposure prophylaxis (PrEP) and to identify predictive factors associated with higher TFV-DP concentrations.Methods: DBSs were collected at the last study visit of the open-label phase of the ANRS IPERGAY study, assessing on-demand oral TDF/emtricitabine for PrEP among MSM and transgender female participants. We quantified TFV-DP in DBSs centrally. We assessed correlation between pill count and TFV-DP concentration by Spearman correlation and explored associations between participant demographics, sexual behaviour and PrEP use during sexual intercourse (SI) with TFV-DP concentrations by univariate and multivariate logistic regression models.Results: The median age of the 245 participants included in this study was 40years, with a median body weight of 73kg. Median (IQR) TFV-DP concentration reached 517 (128-868)fmol/punch, corresponding to an estimated intake of 8-12tablets per month (2-3doses per week). Only 39% of participants had a TFV-DP concentration above 700fmol/punch. TFV-DP concentrations were moderately correlated with pill count (r: 0.59; P<0.001). In multivariate analysis, only systematic use of PrEP during SI and more frequent episodes of SI in the past 4weeks were significantly associated with higher TFV-DP levels [OR (95% CI): 11.30 (3.62-35.33) and 1.46 (1.19-1.79), respectively; P<0.001].Conclusions: Among participants using on-demand PrEP, estimated pill intake reached 8-12 tablets per month and was correlated with frequency and systematic use of PrEP for SI.