Incentivizing adherence to pre-exposure prophylaxis for HIV prevention: a randomized pilot trial among male sex workers in Mexico

Abstract

Low adherence to preventative medications against life-long health conditions is a major contributor to global morbidity and mortality. We implemented a pilot randomized controlled trial in Mexico to measure the extent to which conditional economic incentives help male sex workers increase their adherence to pre-exposure prophylaxis (PrEP) for HIV prevention. We followed n = 110 male sex workers over 6 months. At each quarterly visit (at months 0, 3, and 6), all workers received a $10 transport reimbursement, a free 3-month PrEP supply, and completed socio-behavioral surveys. The primary outcome was an objective biomarker of medication adherence based on tenofovir (TFV) drug concentration levels in hair collected at each visit. Individuals randomized to the intervention received incentives based on a grading system as a function of PrEP adherence: those with high (> 0.043 ng/mg TFV concentration), medium (0.011 to 0.042 ng/mg), or low (< 0.011 ng/mg) adherence received $20, $10, or $0, respectively. Six-month pooled effects of incentives on PrEP adherence were analyzed using population-averaged gamma generalized estimating equation models. We estimated heterogeneous treatment effects by sex worker characteristics. The incentive intervention led to a 28.7% increase in hair antiretroviral concentration levels over 6 months consistent with increased PrEP adherence (p = 0.05). The effect of incentives on PrEP adherence was greater for male sex workers who were street-based (vs. internet) workers (p < 0.10). These pilot findings suggest that modest conditional economic incentives could be effective, at scale, for improving PrEP adherence among male sex workers, and should be tested in larger implementation trials. ClinicalTrials.gov Identifier: NCT03674983.

Keywords: Adherence; Conditional economic incentives; HIV prevention; Male sex workers; Pre-exposure prophylaxis (PrEP).

Fig. 1

Hair sample result adherence grades, by randomized intervention assignment and time. Notes The x-axis shows the visits (1 to 3) by treatment allocation; and the y-axis shows percent of total participants. Adherence grades were assigned from measured antiretroviral [tenofovir (TDF) and emtricitabine (FTC)] concentration in scalp hair (ng/mg) at study visits 1 (baseline), 2 (at three months), and 3 (at six months), left to right; and by randomized intervention assignment (Control and Conditional Economic Incentive), respectively. A grade of 0 = no antiretroviral detected [red]; C = antiretroviral concentration consistent with taking PrEP two days per week or less (FTC/TDF concentration of > 0 to < 0.011 ng/mg) [orange]; B = antiretroviral concentration consistent with taking PrEP three or four times per week (FTC/TDF concentration of 0.011 to 0.042 ng/mg) [light yellow]; A = antiretroviral concentration consistent with taking PrEP five to seven days per week (FTC/TDF concentration of > 0.043 ng/mg) [green]. In terms of sample size, at time 1, n = 43 and n = 62 were in the incentive and control arms, respectively. At time 2, n = 40 and n = 63 were in the incentive and control arms, respectively. At time 3, n = 43 and n = 56 were in the incentive and control arms, respectively