Developing a model of the determinants of medication nonadherence in older community-dwelling patients

Medication nonadherence is associated with adverse health outcomes in older populations. The aim of this study was to develop a model that describes the relationship between the determinants of nonadherence, per the World Health Organization (WHO) model of nonadherence and the necessity-concerns framework (NCF) and nonadherence in a cohort of older community-dwelling patients. A retrospective cohort study of 855 community-dwelling patients aged ≥70 years from 15 practices. Medication nonadherence was assessed by (i) medication possession ratio (MPR < 80%) and (ii) the median MPR across all drugs dispensed. Patient questionnaires, interviews, and medical records measured the determinants of nonadherence per the WHO and NCF frameworks. Confirmatory factor analysis (CFA) was undertaken to generate the model of best fit. Two structural equation models (SEM) were developed to evaluate the relationship between the WHO factors, the NCF, and nonadherence (Model 1: MPR < 80%, Model 2: median MPR). The CFA produced a reasonable fit (χ2(113) = 203, p < .001; root mean square error of approximation = 0.03; comparative fit index = 0.98, and weighted root mean square residual = 0.97) and adequate internal consistency (r = .26-.40). SEM analysis (Model 1) showed a significant direct relationship between patient-related (β = 0.45, p < .01), socioeconomic (β = 0.20, p < .01), and therapy-related factors (β = -0.27, p < .01) and nonadherence (MPR < 80%). Similar results were found for Model 2 (median MPR). There was a significant direct relationship between medication concerns (β = -0.13, p < .01) and nonadherence. Therapy-related (β = -0.04, p < .05) and patient-related factors (β = -0.06, p < .05) also had a significant mediating effect on nonadherence through medication concerns. Health care professionals need to address medication concerns and management of adverse effects in older populations to improve adherence and clinical outcomes.