Comparison of adherence measurement tools used in a pre-exposure prophylaxis demonstration study among female sex workers in Benin

Abstract

Background: Measuring adherence to PrEP (pre-exposure prophylaxis) remains challenging. Biological adherence measurements are reported to be more accurate than self-reports and pill counts but can be expensive and not suitable on a daily basis in resource-limited countries. Using data from a demonstration project on PrEP among female sex workers in Benin, we aimed to measure adherence to PrEP and compare self-report and pill count adherence to tenofovir (TFV) disoproxil fumarate (TDF) concentration in plasma to determine if these 2 measures are reliable and correlate well with biological adherence measurements. Methods: Plasma TFV concentrations were analyzed in samples collected at day 14 follow-up visit and months 6, 12, 18, and 24 (or at last visit when follow-up was shorter). Self-reported adherence was captured at day 14 follow-up visit and then quarterly by asking participants to report the number of missed pills within the last week. For pill count, medications were refilled monthly and participants were asked to bring in their medication bottles at each follow-up visit. Using generalized estimating equations adherence measured by self-report and pill count was compared to plasma drug concentrations. Results: Of 255 participants, 47.1% completed follow-up. Weighted optimal adherence combining data from all visits was 26.8% for TFV concentration, 56.0% by self-report and 18.9% by pill count. Adherence measured by both TFV concentrations and self-report decreased over time (P = .009 and P = .019, respectively), while the decreasing trend in adherence by pill count was not significant (P = .087). The decrease in adherence was greater using TFV concentrations than the other 2 adherence measures. Conclusion: With high levels of misreporting of adherence using self-report and pill count, the objective biomedical assessment of adherence via laboratory testing is optimal and more accurately reflects PrEP uptake and persistence. Alternative inexpensive and accurate approaches to monitor PrEP adherence should be investigated.

Determinants of HIV Preexposure Prophylaxis Adherence Among Female Sex Workers in a Demonstration Study in Cotonou, Benin: A Study of Behavioral and Demographic Factors

“…Adherence assessment was described elsewhere. 18 Briefly, TFV measurements were taken 14 days after recruitment (D-14) and at months 6, 12, 18, and 24 (or early final visit) follow-up visits. The concentrations of TFV in plasma were analyzed in batch using a previously described liquid chromatographic–mass spectrometric assay.…”

Mathematical Model Impact Analysis of a Real-Life Pre-exposure Prophylaxis and Treatment-As-Prevention Study Among Female Sex Workers in Cotonou, Benin

“…Third, there was better adherence and thus higher preventative efficacy for TasP than PrEP (averaging 81% pFSW on ART virally suppressed vs. 37% of visits with perfect PrEP adherence). 25 , 28 Finally, TasP reduces mortality, 69 and thus gaining life-years among HIV+ pFSW.…”

“…Second, the PrEP/TasP study data provided estimates for key parameters including uptake, retention, and individual biological measures of adherence every 6 months: blood plasma tenofovir concentration for PrEP and viral load for TasP. 25 , 28 Accounting for outreach, adherence counseling, migration, leaving sex work, and other legal and structural barriers to PrEP/TasP use among pFSW, our analysis is significantly more realistic compared with previous studies that did not reflect such data. 13 , 72 , 74 – 77 …”

“…21 , 23 , 34 , 65 , 66 PrEP was unavailable in Cotonou before the PrEP/TasP study. The study provided biologically measured estimates of drug adherence (PrEP: up to 5 repeat tenofovir blood plasma concentration measures per individual; TasP: viral load), 28 dropout rates (derived from visit attendance over the 2 years), and TasP and PrEP initiation and coverage. 25 PrEP efficacies by the adherence level (Table 1 E) were derived from Donnell et al 9 …”

“… 25 Final visit viral suppression among TasP participants was 87% (N = 62), and tenofovir was detectable in blood plasma in 53% of 569 visits by PrEP participants; 2 seroconversions associated with poor adherence were observed in the PrEP arm. 25 , 28 …”