Brief Report: Quantifiable Plasma Tenofovir Among South African Women Using Daily Oral Pre-exposure Prophylaxis During the ECHO Trial

HIV endpoint–driven clinical trials provide oral pre-exposure prophylaxis (PrEP) as HIV prevention standard of care. We evaluated quantifiable plasma tenofovir among South African women who used oral PrEP during the Evidence for Contraceptive Options and HIV Outcomes (ECHO) Trial. METHODS: ECHO, a randomized trial conducted in 4 African countries between 2015 and 2018, assessed HIV incidence among HIV-uninfected women, aged 16–35 years, randomized to 1 of 3 contraceptives. Oral PrEP was offered onsite as part of the HIV prevention package at the South African trial sites. We measured tenofovir in plasma samples collected at the final trial visit among women reporting ongoing PrEP use. We used bivariate and multivariate logistical regression to assess demographic and sexual risk factors associated with plasma tenofovir quantification. RESULTS: Of 260 women included, 52% were ≤24 years and 22% had Chlamydia trachomatis at enrollment. At PrEP initiation, 68% reported inconsistent/nonuse of condoms. The median duration of PrEP use was 90 days (IQR: 83–104). Tenofovir was quantified in 36% (n = 94) of samples. Women >24 years had twice the odds of having tenofovir quantified vs younger women (OR = 2.12; 95% confidence interval = 1.27 to 3.56). Women who reported inconsistent/nonuse of condoms had lower odds of tenofovir quantification (age-adjusted OR = 0.47; 95% confidence interval = 0.26 to 0.83). CONCLUSIONS: Over a third of women initiating PrEP and reporting ongoing use at the final trial visit had evidence of recent drug exposure. Clinical trials may serve as an entry point for PrEP initiation among women at substantial risk for HIV infection with referral to local facilities for ongoing access at trial end. CLINICAL TRIAL NUMBER: NCT02550067.