Development and Evaluation of a Self-Report Tool to Predict Low Pharmacy Refill Adherence in Elderly Patients with Uncontrolled Hypertension

Abstract

To develop and evaluate a short self-report tool to predict low pharmacy refill adherence in older patients with uncontrolled hypertension. Cross-sectional analysis of survey and administrative data from the Cohort Study of Medication Adherence Among Older Adults (CoSMO). A total of 394 adults with uncontrolled blood pressure; mean ± SD age was 76.6 ± 5.6 years, 33.0% were black, 66.0% were women, and 23.4% had a low medication possession ratio (MPR). We considered 164 self-reported candidate items for development of a prediction rule for low (less than 0.8) versus high (0.8 or more) MPR from pharmacy refill data. Risk prediction models were evaluated by using best subsets analyses, and the final model was chosen based on clinical relevance and model parsimony. Bootstrap simulations assessed internal validity. The performance of the final four-item model was compared to the eight-item Morisky Medication Adherence Scale (MMAS-8) and the nine-item Hill-Bone Compliance Scale. The four-item self-report tool for predicting pharmacy refill adherence showed moderate discrimination (C statistic 0.704, 95% confidence interval [CI], 0.683-0.714) and good model fit (Hosmer-Lemeshow χ² = 1.238, p=0.743). Sensitivity and specificity were 67.4% and 67.8%, respectively. The concordance (C) statistics for MMAS-8 and the Hill-Bone Compliance Scale were lower at 0.665 (95% CI 0.632-0.683) and 0.660 (95% CI 0.622-0.674), respectively. A four-item self-report tool moderately discriminated low from high pharmacy refill adherers, and its test performance was comparable with existing eight- and nine-item adherence scales. Parsimonious self-report tools predicting low pharmacy refill in patients with uncontrolled blood pressure could facilitate hypertension management in the elderly.