Abstract
OBJECTIVES: Tenofovir disoproxil fumarate/emtricitabine (TDF/FTC) is approved for pre-exposure prophylaxis (PrEP) against HIV infection. Adherence is critical for the success of PrEP, 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 PrEP. 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 PrEP 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 PrEP.