Impact of Beneficiary Characteristics, Drug Plan Formulary Policies, and Environmental Factors on Medication Adherence among Low Income Beneficiaries Covered by Medicare Part D

Abstract

Research suggests that low income individuals often fail to take medications as prescribed. Various individual characteristics have been studied in relation to adherence outcomes, however, little is known regarding how drug plan formulary policies and external environmental factors may affect individuals' medication adherence. This dissertation evaluated the independent effects of beneficiary characteristics, drug plan formulary policies, and external environmental factors on medication adherence for oral hypoglycemic agents (OHAs), statins, and renin angiotensin system (RAS) antagonists in a cohort of low-income subsidy (LIS) recipients enrolled in randomly assigned benchmark Part D plans. The data source included a random 5% sample of 2012 Medicare administrative claims and a customized dataset capturing beneficiaries' plan assignment history. Three hosts of beneficiary characteristics, including demographics, comorbidity burden, and health services utilization, were analyzed. The formulary policies of interest included non-coverage, prior authorization, and step therapy, while the environmental factors of interest were socioeconomic environment, availability of healthcare resources, health culture, evidence-based medicine practice, and quality of primary care. Results indicated that beneficiary characteristics, Part D plan, and external environmental factors all could significantly influence LIS recipients' medication adherence. Older age, male gender, use of multiple chronic medications were associated with higher medication adherence, whereas black race, Hispanic ethnicity, high comorbidity burden, and frequent hospitalizations and ER visits were inversely related to the adherence outcomes. Placing formulary restrictions on brand-name drugs could shift utilization toward generics and lower cost per prescription fill but had minimal impact on medication adherence among LIS recipients. Geographic variation in adherence rates was observed consistently across all three drug classes of interest. Those living in areas with low socioeconomic environment and poor quality of primary care were less likely to achieve acceptable levels of medication adherence than their counterparts. In conclusion, low income beneficiaries' medication adherence is influenced by multiple levels of factors. Policies aimed at improving low income population's adherence for chronic medications may consider plan- and environment-oriented programs in addition to interventions targeting at individuals' behaviors.