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J Acquir Immune Defic Syndr. 2014 Dec 15;67(5):528-37. doi: 10.1097/QAI.0000000000000351.

Patterns and correlates of PrEP drug detection among MSM and transgender women in the Global iPrEx Study.

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*Bridge HIV, San Francisco Department of Public Health, San Francisco, CA; Departments of †Medicine; ‡Epidemiology and Biostatistics, University of California, San Francisco, San Francisco, CA; §Department of Pharmaceutical Sciences, University of Colorado, Aurora, CO; ‖Department of Health Behavior and Health Education, University of Michigan, Ann Arbor, Michigan; ¶Gladstone Institutes, San Francisco, CA; #Asociación Civil Impacta Salud y Educación, Lima, Peru; **Investigaciones Médicas en Salud, Lima, Peru; ††Asociación Civil Selva Amazónica, Iquitos, Peru; ‡‡Fundación Ecuatoriana Equidad, Guayaquil, Ecuador; §§Instituto de Pesquisa Clinica Evandro Chagas-IPEC/FIOCRUZ, Rio de Janeiro, Brazil; ‖‖Projeto Praça Onze, Hospital Escola São Francisco de Assis, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil; ¶¶Universidade de São Paulo, Sao Paulo, Brazil; ##Research Institute for Health Sciences, Chiang Mai University, Chiang Mai, Thailand; ***Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand; †††The Desmond Tutu HIV Centre, University of Cape Town, Cape Town, South Africa; ‡‡‡The Fenway Institute, Fenway Health, and Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA.



Adherence to pre-exposure prophylaxis (PrEP) is critical for efficacy. Antiretroviral concentrations are an objective measure of PrEP use and correlate with efficacy. Understanding patterns and correlates of drug detection can identify populations at risk for nonadherence and inform design of PrEP adherence interventions.


Blood antiretroviral concentrations were assessed among active arm participants in iPrEx, a randomized placebo-controlled trial of emtricitabine/tenofovir in men who have sex with men and transgender women in 6 countries. We evaluated rates and correlates of drug detection among a random sample of 470 participants at week 8 and a longitudinal cohort of 303 participants through 72 weeks of follow-up.


Overall, 55% of participants (95% confidence interval: 49 to 60) tested at week 8 had drug detected. Drug detection was associated with older age and varied by study site. In longitudinal analysis, 31% never had drug detected, 30% always had drug detected, and 39% had an inconsistent pattern. Overall detection rates declined over time. Drug detection at some or all visits was associated with older age, indices of sexual risk, including condomless receptive anal sex, and responding "don't know" to a question about belief of PrEP efficacy (0-10 scale).


Distinct patterns of study product use were identified, with a significant proportion demonstrating no drug detection at any visit. Research literacy may explain greater drug detection among populations having greater research experience, such as older men who have sex with men in the United States. Greater drug detection among those reporting highest risk sexual practices is expected to increase the impact and cost-effectiveness of PrEP.


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