Bioanalytical methods
Concentrations (denoted as [drug or metabolite]) of TFV, FTC, and the pro-drug TAF, were measured in plasma and foreskin tissue. Concentrations of the active phosphorylated intracellular metabolites – tenofovir-diphosphate (TFV-DP) and emtricitabine-triphosphate (FTC-TP) were determined in PBMCs, foreskin tissue, and isolated foreskin CD4+ and CD4-cells. Analyte quantification was performed using a SCIEX 4500 or 5500 triple quadrupole mass spectrometer (AB Sciex UK Limited; Warrington, UK). Data acquisition and processing were performed using FDA CFR Part 11 compliant SCIEX Analyst and Multiquant software platforms. LC-MS assays were validated in accordance with FDA Bioanalytical Method Validation Guidelines.