Using Tenofovir Diphosphate Levels to Evaluate Factors Associated With PrEP Non‐Adherence and Performance of Indirect Adherence Measures in Latin America: A Prospective, Single‐Arm, Open‐Label, Multicentre Implementation Study (ImPrEP)

INTRODUCTION: Tenofovir-based oral pre-exposure prophylaxis (PrEP) is pivotal for HIV prevention in Latin America. Monitoring PrEP adherence is crucial for maximizing its impact and identifying individuals who may benefit from additional support. We evaluated the performance of indirect adherence measures and factors associated with PrEP non-adherence in Brazil, Mexico and Peru. METHODS: ImPrEP was a prospective, multicentre, PrEP implementation study which enrolled 9509 persons from 6 February 2018 to 30 June 2021. For this analysis, we included men who have sex with men (MSM) aged 18-24 years and transgender women aged 18+ years with at least one dried blood spot (DBS) sample collected. Adherence was assessed objectively (tenofovir diphosphate [TFV-DP] levels in DBS) and indirectly (medication possession rate [MPR] and self-report). We estimated area under the curve (AUC) to evaluate the performance of each indirect adherence measure, and the optimal cut-off points for discriminating protective TFV-DP levels based on the Youden index. We used generalized estimating equations to identify factors associated with PrEP non-adherence (TFV-DP