Geographic variation in medication adherence in commercial and Medicare part D populations.

BACKGROUND: Previous literature has emphasized the importance of cost sharing, health literacy, socioeconomic status, cognitive function, disease burden, and polypharmacy as some of the determinants of medication adherence. Little research has been published examining disparities in adherence rates when comparing different regions of the United States.
OBJECTIVE: To examine the impact of geography, socioeconomic status, and other demographic variables on medication adherence rates in a large national sample of Medicare Part D and commercially insured beneficiaries.
METHODS: This study focused on users of oral antidiabetic, antihypertensive, and/or antilipidemic medications. Beneficiaries who had at least 2 antidiabetic, antihypertensive, or antilipidemic prescription fills in 2010, 2011, or 2012 and who were enrolled in a large commercial or Medicare Part D prescription drug plan for at least 80% of one of these years (9.6 months) were included in this study. Results were stratified by year and by benefit type. Logistic regression was used to test for the adherence differences among the 9 U.S. regions as defined by the U.S. Census Bureau. Additional variables included in the model to control for population differences were age, gender, socioeconomic status, and yearly out-of-pocket medication expenses.
RESULTS: After meeting all inclusion and exclusion criteria, 379,533 beneficiaries were in the 2012 Medicare cohort, and 659,553 beneficiaries were in the 2012 commercial cohort. New England was statistically the most adherent geographic region in both cohorts (Medicare odds ratio [OR] = 1.512, CI = 1.399-1.635); commercial OR = 1.193, CI = 1.109-1.284). Younger age beneficiaries, lower income beneficiaries, and females were less adherent in both groups.
CONCLUSIONS: In the commercial and Medicare populations, geography, socioeconomic status, age, and gender all impact the likelihood of a beneficiary being adherent to chronic medications for hypertension, diabetes, and hyperlipidemia. While this study does not elucidate the specific factors (i.e., health literacy, disease severity) driving geographic and other differences in medication adherence observed between groups, it does highlight the limitations of quality metrics and wellness initiatives that assume relative homogeneity in beneficiary characteristics across the United States.