Accuracy of Self-Report and Pill-Count Measures of Adherence in the FEM-PrEP Clinical Trial: Implications for Future HIV-Prevention Trials

AIDS Behav. 2015 May;19(5):743-51. doi: 10.1007/s10461-014-0859-z.


Oral emtricitabine/tenofovir disoproxil fumarate (FTC/TDF) has been evaluated as pre-exposure prophylaxis (PrEP). We describe the accuracy of self-reported adherence to FTC/TDF and pill counts when compared to drug concentrations in the FEM-PrEP trial. Using drug concentrations of plasma tenofovir (TFV) and intracellular tenofovir diphosphate (TFVdp) among a random sub-sample of 150 participants assigned to FTC/TDF, we estimated the positive predictive value (PPV) of four adherence measures. We also assessed factors associated with misreporting of adherence using multiple drug-concentration thresholds and explored pill use and misreporting using semi-structured interviews (SSIs). Reporting use of ≥1 pill in the previous 7 days had the highest PPV, while pill-count data consistent with missing ≤1 day had the lowest PPV. However, all four measures demonstrated poor PPV. Reported use of oral contraceptives (OR 2.26; p = 0.014) and weeks of time in the study (OR 1.02; p < 0.001) were significantly associated with misreporting adherence. Although most SSI participants said they did not misreport adherence, participant-dependent adherence measures were clearly unreliable in the FEM-PrEP trial. Pharmacokinetic monitoring remains the measure of choice until more reliable participant-dependent measures are developed.

Publication types

  • Randomized Controlled Trial
  • Research Support, N.I.H., Intramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Adenine / blood
  • Adenine / therapeutic use*
  • Adult
  • Anti-HIV Agents / blood
  • Anti-HIV Agents / therapeutic use*
  • Drug Therapy, Combination
  • Female
  • HIV Infections / prevention & control*
  • Humans
  • Interviews as Topic
  • Kenya
  • Male
  • Medication Adherence / statistics & numerical data*
  • Middle Aged
  • Organophosphonates / therapeutic use*
  • Pre-Exposure Prophylaxis*
  • Predictive Value of Tests
  • Qualitative Research
  • Self Report
  • Tenofovir / blood*
  • Tenofovir / therapeutic use
  • Treatment Outcome


  • Anti-HIV Agents
  • Organophosphonates
  • Tenofovir
  • Adenine