Subproject for Institution # SP0048602 Off-campus

Project: Research project


Young men who have sex with men (YMSM) are at high risk for HIV–particularly YMSM of color. Pre-exposure prophylaxis (PrEP) is extremely effective at reducing HIV transmission. Uptake has been lower than anticipated, but is increasing rapidly–though less so among Black YMSM. PrEP effectiveness hinges upon adherence. However, levels of adherence vary and tend to be lower among Black individuals and youth. Adherence to daily PrEP does not need to be perfect to obtain benefit–in iPrEx open-label extension, taking 2-3 doses/week was 84% efficacious (4+ was 100% efficacious). Non-daily dosing strategies are also under investigation (event- and time-driven dosing). Beyond adherence, patterns of use are critically important. Oral PrEP is unlikely to be a life-long strategy for most, and evidence suggests that many YMSM discontinue PrEP–particularly Black and Latino YMSM–but most discontinuers report continued HIV risk behaviors. Further, studies are beginning to examine episodic PrEP use during discrete periods of highest HIV risk. Finally, risk compensation (i.e., decreases in condom use after initiating PrEP) is a critical component of PrEP effectiveness as it may have maintain, or even increase, HIV transmission if adherence is not optimal. The goal of the current proposal is to characterize PrEP adherence across dosing strategies, describe patterns of use (continuous, episodic, discontinuation), and examine racial differences in adherence and patterns of use. We will embed novel mixed-methods research into RADAR, a diverse cohort of YMSM (N=1,062; age 16-29) assessed every 6 months (U01DA036939). We propose to add: a) a daily diary study of PrEP users to characterize adherence and patterns of use; and b) in-depth interviews with PrEP users to understand contextual influences on these issues. Aim 1: Describe PrEP adherence, dosing strategies, and usage patterns among YMSM. We will conduct a 3-month daily diary study with 120 YMSM PrEP users from RADAR to: a) characterize patterns of PrEP dosing strategies (daily, time-driven, event-driven), adherence, and usage patterns (continuous, episodic, discontinuation); b) Examine whether PrEP adherence or dosing strategies are associated with self-reported sexual risk behavior and STI infection; and c) describe racial differences in PrEP adherence, dosing strategies, and risk compensation. Aim 2: Assess correspondence between patterns of adherence and long- and short-term concentrations of PrEP in red blood cells. We will collect dried blood spot samples once per month during the diary study (3 samples) to assess concentrations of tenofovir-diphosphate (TDF-DP) and embtricitabine-triphosphate (FTC-TP). Aim 3: Characterize YMSM perspectives on adherence, patterns of use, and risk compensation. We will conduct in-depth interviews with 60 YMSM diary study participants to understand individual, interpersonal, and structural influences on PrEP adherence and patterns of use, with an emphasis on understanding racial differences. Data from this study will inform the development of messaging and behaviors interventions to improve PrEP effectiveness among diverse YMSM.
Effective start/end date9/1/183/31/22


  • National Institute on Minority Health and Health Disparities (1R01MD013609-01)


Pre-Exposure Prophylaxis
Sexually Transmitted Diseases
Hispanic Americans
Sexual Behavior
triphosphoric acid
tenofovir diphosphate