Differences in Cumulative Exposure and Adherence to Tenofovir in the VOICE, iPrEx OLE, and PrEP Demo Studies as Determined via Hair Concentrations

Pre-exposure prophylaxis (PrEP) with oral tenofovir disoproxil fumarate (TDF)/emtricitabine (FTC) prevented HIV acquisition among men and women in several trials and is broadly recommended. In the VOICE and FEM-PrEP trials, however, TDF/FTC-based PrEP did not prevent HIV acquisition among women in eastern and southern Africa. Tenofovir was detected in plasma, reflecting exposure and adherence in recent days, in fewer than one-third of participants. Drug concentrations in hair, which represent cumulative exposure and adherence over weeks to months, have never previously been examined among women on PrEP. We compared tenofovir hair concentrations among women assigned to oral TDF/FTC in the VOICE trial to those among men and transgender women enrolled in 2 open-label PrEP studies, the iPrEx open-label extension (OLE) study and the U.S. PrEP Demonstration Project (PrEP Demo). Tenofovir hair concentrations were detectable in 55% of person-visits in VOICE, 75% of person-visits in iPrEx OLE (p = .006), and 98% of person-visits in PrEP Demo (p < .001). Median tenofovir hair concentrations corresponded to an estimated 0.2, 2.9, and 6.0 TDF/FTC doses taken per week in the three studies, respectively. In VOICE, combining tenofovir concentration data from plasma and hair suggested inconsistent, low-level product use. Incorporation of both short- and long-term adherence measures may allow for an improved understanding of patterns of drug-taking among women during global PrEP roll-out.