Poor accuracy of self-reported adherence to PrEP versus drug detection in many settings

Study product adherence measurement in the iPrEx placebo-controlled trial: concordance with drug detection.

Amico KR, Marcus JL, McMahan V, Liu A, Koester KA, Goicochea P, Anderson PL, Glidden D, Guanira J, Grant R. J Acquir Immune Defic Syndr. 2014 May 21. [Epub ahead of print]

Objective: To evaluate the concordance between adherence estimated by self-report (in-person interview or computer-assisted self-interview [CASI]), in-clinic pill counts, and pharmacy dispensation records and drug detection among participants in a placebo-controlled, pre-exposure prophylaxis (PrEP) HIV prevention trial (iPrEx).

Design: Cross-sectional evaluation of 510 participants who had drug concentration data and matched adherence assessments from their week-24 study visit.

Methods: Self-reported adherence collected via (1) interview and (2) CASI surveys, (3) adherence estimated by pill count, and (4) medication possession ratio (MPR) were contrasted to having a detectable level of drug concentrations (either tenofovir diphosphate [TFV-DP] or emtricitabine triphosphate [FTC-TP]) as well as to having evidence of consistent dosing (TFV-DP>/=16 fmol/10 cells), focusing on positive predictive values (PPV), overall and by research site.

Results: Overall, self-report and pharmacy records suggested high rates of product use (over 90% adherence); however, large discrepancies between these measures and drug detection were noted, which varied considerably between sites (PPV from 34% to 62%). Measures of adherence performed generally well in the US sites, but had poor accuracy in other research locations. MPR outperformed other measures but still had relatively low discrimination.

Conclusions: The sizable discrepancy between adherence measures and drug detection in certain regions highlights the potential contribution of factors that may have incentivized efforts to appear adherent. Understanding the processes driving adherence reporting in some settings, but not others, is essential for finding effective ways to increase accuracy in measurement of product use and may generalize to promotion efforts for open-label PrEP.

Abstract access [1] 

Editor’s notes: This paper discusses the results of a sub-study conducted as part of the iPrEX randomised placebo-controlled trial. This trial tested the efficacy of once daily oral pre-exposure prophylaxis (PrEP) for HIV prevention for men who have sex with men (MSM) and transgender women, in several sites globally. The iPrEX study was the first PrEP efficacy study providing tenofovir-based PrEP which reported positive results. It found a 44% protection against HIV acquisition. After further analysis, researchers discovered that participants with higher adherence rates as measured by drug concentrations in the blood, achieved higher levels of protection. This finding, coupled with analyses of the other PrEP prevention trials, highlighted the need to understand why participants in the trials did not take the PrEP. The study also emphasised the need to develop optimal measures of adherence, support strategies for adherence, and strategies for delivering the programme to those who are motivated to take PrEP, for future research and implementation purposes. This sub-study specifically examined the optimal strategies for measuring adherence, and found that measures relying on self-reporting and pill counts did not reflect drug level concentrations in the blood. The discrepancies with drug levels varied across sites, with wider discrepancies found in the more resource poor settings. The findings indicate a need for qualitative research to confirm suspicions, and to further understand how best to measure adherence, and encourage it, in future HIV prevention research studies. 

Africa [7], Asia [8], Latin America [9], Northern America [10]
Brazil [11], Ecuador [12], Peru [13], South Africa [14], Thailand [15], United States of America [16]
  • [17]