Ethnic Disparities in Adherence to Antihypertensive Medications of Medicare Part D Beneficiaries

OBJECTIVES: To determine the level of adherence to medications and characteristics of Part D beneficiaries associated with higher levels of antihypertensive medication adherence. DESIGN: Retrospective cohort study. SETTING: Medicare claims and Part D event files. PARTICIPANTS: Medicare Part D enrollees with prevalent uncomplicated hypertension who filled at least one antihypertensive prescription in 2006 and two prescriptions in 2007. MEASUREMENTS: Medication adherence was defined as an average medication possession ratio of 80% or greater. Potential factors associated with adherence evaluated were age, sex, race or ethnicity, socioeconomic factors, comorbidity, medication use, copayments, being in the coverage gap, and number of unique prescribers. RESULTS: Overall adherence was 79.5% of 168,522 Medicare Part D enrollees with prevalent uncomplicated hypertension receiving antihypertensive medicines in 2007. In univariate analysis, adherence varied significantly according to most patient factors. In multivariable analysis, lower odds of adherence persisted for blacks (odds ratio (OR) = 0.53, 95% confidence interval (CI) = 0.51-0.55), Hispanics (OR = 0.58, 95% CI = 0.55-0.61), and other non-white races (OR = 0.80 95% CI = 0.75-0.85) than for whites. Greater comorbidity and concurrent medication use were also associated with poorer adherence. Adherence was significantly different across several geographic regions. CONCLUSION: A number of associations were identified between patient factors and adherence to antihypertensive drugs, with significant differences in adherence according to ethnicity. Improving adherence could have significant public health implications and could improve outcomes specific to hypertension, as well as improving cost and healthcare utilization.