How Does Drug Treatment for Diabetes Compare between Medicare Advantage Prescription Drug Plans ( MAPD s) and Stand‐Alone Prescription Drug Plans ( PDP s)?

Objective To compare the use of guideline‐recommended prescription medications for diabetes among M edicare beneficiaries enrolled in stand‐alone prescription drug plans ( PDP s) with M edicare A dvantage prescription drug plans ( MAPD s) in the presence of potential selection bias. Data Sources/Study Setting Centers for M edicare and M edicaid S ervices' C hronic C ondition D ata W arehouse (2006, 2007). Study Design Retrospective cross‐sectional comparison of drug use and proportion of days covered ( PDC ) for oral‐antidiabetics, ACE ‐inhibitors/ ARB s, and antihyperlipidemics among PDP and MAPD enrollees with diabetes. We estimated “naïve” regression models assuming exogenous plan choice and two‐stage residual inclusion (2 SRI ) 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 M edicare claims from a random 5 percent sample of M edicare beneficiaries in 2005 excluding dual eligibles. Principal Findings The naïve regression models indicated lower probability of drug use for oral‐antidiabetics (−4 percent; p  < .001) and ACE ‐inhibitors/ ARBS (−2 percent; p  = .004) among PDP enrollees, but their PDC was higher (3–5 percent) for all drug classes ( p  < .001). 2 SRI models produced no significant differences in any‐use equations, but significantly higher PDC values for PDP enrollees for oral‐antidiabetics and ACE ‐inhibitors/ ARB s. Conclusions We found similar overall use of recommended drugs in diabetes treatment and no consistent evidence of favorable or adverse selection into PDP s and MAPD s.