Pre-exposure Prophylaxis Adherence Measured by Plasma Drug Level in MTN-001: Comparison Between Vaginal Gel and Oral Tablets in Two Geographic Regions.

Despite strong evidence that daily oral pre-exposure prophylaxis (PrEP) reduces HIV risk, effectiveness across studies has varied. Inconsistent adherence constitutes one explanation. Efforts to examine adherence are limited when they rely on self-reported measures. We examined recent adherence as measured by plasma tenofovir (TFV) concentration in participants of MTN-001, a phase 2 cross-over trial comparing oral tablet and vaginal gel formulations of TFV among 144 HIV-uninfected women at sites in the United States (U.S.) and sub-Saharan Africa (SSA). Adherence to daily product use was higher in the U.S. than in the SSA sites. Within region, however, adherence was similar between products. In the U.S., gel adherence was higher among married women, and lower among women using male condoms and injectable contraceptives. At the SSA sites, gel adherence was lower for younger women. Inconsistent adherence points to challenges in use of daily PrEP, even during a trial of short duration.