Geosocial factors associated with adherence to statin medications
Background: Individual patient characteristics, social determinants, and geographic access may be associated with patients engaging in appropriate health behaviors. Objective: To assess the relationship between statin adherence, geographic accessibility to pharmacies, and neighborhood sociodemographic characteristics in Michigan. Methods: The proportion of days covered (PDC) was calculated from pharmacy claims of a large insurer of adults who had prescriptions for statins between July 2009 and June 2010. A PDC ≥0.80 was defined as adherent. The predictor of interest was a ZIP code tabulation area (ZCTA)-level measure of geographic accessibility to pharmacies, measured using a method that integrates availability and access into a single index. We fit unadjusted models as well as adjusted models controlling for age, sex, and ZCTA-level measures of socioeconomic status (SES), racial isolation (RI) of non-Hispanic blacks, and urbanicity. Results: More than 174 000 patients' claims data were analyzed. In adjusted models, pharmacy access was not associated with adherence (0.99; 95% CI: 0.96, 1.03). Greater RI (0.87; 95% CI: 0.85, 0.88) and urban status (0.93; 95% CI: 0.89, 0.96) were associated with lower odds of adherence. Individuals in ZCTAs with higher SES had higher odds of adherence, as were men and older age groups. Conclusion and Relevance: Adherence to statin prescriptions was lower for patients living in areas characterized as being racially segregated or lower income. Initiating interventions to enhance adherence, informed by understanding the social and systematic barriers patients face when refilling medication, is an important public health initiative that pharmacists practicing in these areas may undertake.