Urine assay for tenofovir to monitor adherence in real time to tenofovir disoproxil fumarate/emtricitabine as pre‐exposure prophylaxis

Objectives Tenofovir disoproxil fumarate/emtricitabine ( TDF / FTC ) is approved for pre‐exposure prophylaxis (Pr EP ) against HIV infection. Adherence is critical for the success of Pr EP , but current adherence measurements are inadequate for real‐time adherence monitoring. We developed and validated a urine assay to measure tenofovir ( TFV ) to objectively monitor adherence to Pr EP . Methods We developed a urine assay using high‐performance liquid chromatography coupled to tandem mass spectrometry with high sensitivity/specificity for TFV that allowed us to determine TFV concentrations in log 10 categories between 0 and 10 000 ng/ mL . We validated the assay in three cohorts: (1) HIV ‐positive subjects with undetectable viral loads on a TDF / FTC ‐based regimen, (2) healthy HIV ‐negative subjects who received a single dose of TDF / FTC , and (3) HIV ‐negative subjects receiving daily TDF / FTC as Pr EP for 24 weeks. Results The urine assay detected TFV with greater sensitivity than plasma‐based measures and with a window of measurements within 7 days of the last TDF / FTC dose. Based on the urine log‐linear clearance after the last dose and its concordance with all detectable plasma levels, a urine TFV concentration > 1000 ng/ mL was identified as highly predictive of the presence of TFV in plasma at > 10 ng/ mL . The urine assay was able to distinguish high and low adherence patterns within the last 48 h (> 1000 ng/ mL versus 10–1000 ng/ mL ), as well as nonadherence (< 10 ng/ mL ) extended over at least 1 week prior to measurement. Conclusions We provide proof of concept that a semiquantitative urine assay measuring levels of TFV could be further developed into a point‐of‐care test and be a useful tool to monitor adherence to Pr EP .