Plasma Tenofovir Levels to Support Adherence to TDF/FTC Preexposure Prophylaxis for HIV Prevention in MSM in Los Angeles, California

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Tenofovir disoproxil fumarate/emtricitabine preexposure prophylaxis (PrEP) is effective against HIV acquisition when taken as prescribed. Strategies that identify and intervene with those challenged by adherence to daily medication are needed.


PATH-PrEP was an open-label single-arm interventional cohort study conducted at 2 community-based clinical sites in Los Angeles, CA.


We enrolled self-identified men who have sex with men and transgender women ≥18 years of age at an elevated risk of HIV acquisition. Participants received a postexposure prophylaxis (PEP)–based or PrEP-based HIV prevention package for at least 48 weeks. Plasma tenofovir levels from each PrEP visit assessed as below the limit of quantitation (<10 ng/mL) triggered increased adherence support.


Three hundred one participants enrolled. Forty-eight–week retention in the PrEP cohort was 75.1%. Biomarker evidence of PrEP adherence consistent with ≥4 doses per week at weeks 4, 12, 24, 36, and 48 was found in 83.1%, 83.4%, 75.7%, 71.6%, and 65.5% of participants, respectively; younger and African American participants were less likely to have protective drug levels. Most of those with suboptimal adherence had adherence improvement after brief intervention. One seroconversion occurred in a participant who discontinued PrEP. Nearly half (46.4%) of participants were diagnosed with at least 1 incident sexually transmitted infection during 48 weeks of study follow-up.

Conclusions and Relevance:

PrEP was acceptable and well tolerated in a diverse population of men who have sex with men in Los Angeles. A brief intervention triggered from biomarkers of poor adherence was associated with improved adherence. Drug level monitoring has the potential to allow targeting of additional adherence support to those struggling with daily tablet adherence.

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