Holtz TH, Chitwarakorn A, Hughes JP, Curlin ME, Varangrat A, Li M, Amico KR, Mock PA, Grant RM, Thai HAST. HPTN 067/ADAPT: Correlates of Sex-Related Pre-exposure Prophylaxis Adherence, Thai Men Who Have Sex With Men, and Transgender Women, 2012-2013. JAIDS. 2019, 82: e18-e26. PMC6742570
BACKGROUND: We identified correlates of sex-related pre-exposure prophylaxis (PrEP) adherence in HPTN067/ADAPT, a phase 2, open-label feasibility study of daily and nondaily regimens of emtricitabine/tenofovir disoproxil fumarate (FTC/TDF)-based PrEP, among Thai men who have sex with men (MSM), and transgender women (TGW), Bangkok. METHODS: Participants were randomly assigned to one of three self-administered dosing regimens for 24 weeks: daily, time-driven, or event-driven. Demographic and behavioral information was obtained at screening. Pill-container opening was recorded with electronic dose monitoring, and self-reported information on PrEP use, sex events, and substance use was obtained during weekly interviews to confirm dose data. Sex-related PrEP adherence was calculated as the proportion of sex events covered by PrEP use (at least one tablet taken within 4 days before sex and at least one tablet taken within 24 hours after sex) to total sex events. We used multivariate modeling with sex event as the unit of analysis to evaluate correlates associated with sex-related PrEP adherence. RESULTS: Among 178 MSM and TGW, sex-related PrEP adherence was similar in the daily and time-driven arms (P = 0.79), both significantly greater than the event-driven arm (P = 0.02 compared to daily). Sex-related PrEP adherence by those reporting stimulant use (74.2%) was similar to those reporting other nonalcohol drug use (76.3%, P = 0.80), but lower than those reporting no substance use (84.6%, P = 0.04). In a multivariable model, randomization to the event-driven arm, a higher prestudy number of reported sex events, and use of stimulant drugs were associated with significantly lower sex-related PrEP adherence. CONCLUSION: Adherence was influenced by treatment schedule and adversely affected by nonalcoholic substance use. Regardless of these factors, Thai MSM and TGW maintained high adherence levels to oral PrEP dosing regimens and coverage of sexual exposures.