How does drug treatment for diabetes compare between medicare advantage prescription drug plans (MAPDs) and stand-alone prescription drug plans (PDPs)?

Abstract

Objective To compare the use of guideline-recommended prescription medications for diabetes among Medicare beneficiaries enrolled in stand-alone prescription drug plans (PDPs) with Medicare Advantage prescription drug plans (MAPDs) in the presence of potential selection bias. Data Sources/Study Setting Centers for Medicare and Medicaid Services' Chronic Condition Data Warehouse (2006, 2007). Study Design Retrospective cross-sectional comparison of drug use and proportion of days covered (PDC) for oral-antidiabetics, ACE-inhibitors/ARBs, and antihyperlipidemics among PDP and MAPD enrollees with diabetes. We estimated "naïve" regression models assuming exogenous plan choice and two-stage residual inclusion (2SRI) models to study endogeneity in choice of Part D plan type. Data Collection/Extraction Methods We identified 111,290 diabetics based on ICD-9 codes in Medicare claims from a random 5 percent sample of Medicare beneficiaries in 2005 excluding dual eligibles. Principal Findings The naïve regression models indicated lower probability of drug use for oral-antidiabetics (-4 percent; p