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

Abstract

Background: 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.

Methods: 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.

Results: 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).

Conclusions: 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.

Trial registration: ClinicalTrials.gov NCT00458393.

Conflict of interest statement

Conflicts of Interest:

For the remaining authors, no conflicts of interest were declared.

Figures

Figure 1

a. Proportion of participants with drug detection over time, by visit week b: Longitudinal drug detection in plasma in the iPrEx cohort, by individual participant and visit week Lines in orange and green represent participants who had drug detected and not detected respectively at the earliest follow-up visit with drug level testing. Plasma was tested every 12 weeks. By design, participants in iPrEx had a variable duration of follow-up, based on date of study entry. Overall declining Ns reflect fewer individuals with longer duration of follow-up due to enrolling on a later date, as well as loss to follow-up (approximately 24% of participants had an early termination visit).