How should we measure medication adherence in clinical trials and practice?

OBJECTIVE To determine if simple adherence measures, such as twenty-four hour recall and refill history, are accurate for routine use, compared to more time-consuming measures such as pill counts. DESIGN Randomized, double-blind, placebo-controlled trial. SETTING Walter Reed Army Medical Center, a tertiary medical center in Washington. PATIENTS Men and women >30 years old with known coronary heart disease and taking a statin medication. INTERVENTION Clinical pharmacists met with patients for adherence assessments. MAIN OUTCOME MEASURES Adherence was measured by pill counts, twenty-four hour recall by patient, and refill history per computer record. Temporal changes in these adherence measures were assessed using general linear models for repeated measures. RESULTS Adherence was consistently greater for the experimental agent than for the statin therapy (n = 148). Mean pill count adherence for statin drug was 78.7 +/- 25.2% compared to 93.5 +/- 11.6% (P < 0.001) for the study agent. Refill history and twenty-four hour recall inaccurately measured adherence when compared to pill counts. Adherence, as determined by pill count, for both experimental (P = 0.029) and statin therapy (P = 0.015) showed significant variability across time in general linear models. Neither refill history nor twenty-four hour recall was sensitive to temporal changes. CONCLUSIONS Twenty-four hour recall and refill history inaccurately measure medication adherence for both clinical trial and clinical practice pharmacotherapies. Further, these measures are insensitive to changes in adherence. For a single or multiple assessments across time, pill count more accurately measures medication adherence. Pill count should be the standard for monitoring medication adherence for both clinical trials and clinical practice.