Environmental and Individual Predictors of Medication Adherence Among Elderly Patients with Hypertension and Chronic Kidney Disease: A Geospatial Approach

Background: Few studies have examined how adherence to antihypertensive medications varies across different regions or how neighborhood-level factors were related to individuals' medication-taking behaviors in patients.

Objective: To explore local variation in medication adherence and examine environmental and individual influences on adherence to angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin-receptor blockers (ARBs) among elderly hypertensive patients with chronic kidney disease (CKD) in the United States.

Methods: The Medicare 5% sample claim data (2006-2013), American Community Survey 5-Year Data (2005-2009) and the Health Resources and Services Administration Primary Care Service Area data (2007). The primary outcome was medication adherence, measured by Proportion of Days Covered (PDC). Geographically weighted regression (GWR) and linear mixed-effects models were used to investigate the relationship between environmental factors, individual risk factors and medication adherence.

Results: A total of 70,201 hypertensive CKD patients residing in 2,981 counties of the US were selected. Significant spatial autocorrelation was observed in ACEIs/ARBs PDC. The West North Central and New England regions demonstrated higher adherence compared to the East South Central and West South Central regions. Residing in Medically Underserved Areas, counties with high deprivation scores, and not receiving Part D Low-income Subsidy were associated with poor medication adherence.

Conclusions: Medication adherence is geographically differentiated across the US. Environmental and individual factors identified may be helpful in the design of local interventions focused on improving patient outcomes from a population perspective.