Effects of Medicare Part D on drug affordability and use: Are seniors with prior high out-of-pocket drug spending affected more?

Background: Medicare Part D was expected to have differential impacts on patient drug expenditures and use based on beneficiaries' levels of pre-Part D patient drug spending, but it is unknown whether these projections have borne out.
Objectives: We sought to evaluate whether and how the policy effect of Medicare Part D on drug expenditures and use was modified by levels of pre-Part D drug spending.
Methods: A quasi-experimental, pretest-posttest, nonequivalent control group design was used. Data were obtained from a regional supermarket chain for all prescriptions dispensed between January 1, 2005, and December 31, 2007 (n=1,230,612) to patients aged 60 years and older as of January 1, 2005 (n=51,305) to construct 12-month pre-Part D and post-Part D periods. Annual medication use was measured as the total number of pill days acquired. Annual drug expenditures were measured as total expenditures, patient out-of-pocket expenditures, and the proportion of total expenditures paid out of pocket by the patient.
Results: Part D resulted in significant reductions in out-of-pocket spending (17.6%) and significant increases in drug use (4.0%) for individuals in the highest pre-Part D drug-spending group relative to controls. The reduction in out-of-pocket spending for the highest pre-part D spending group was significantly greater compared with the moderate and lowest pre-Part D spending groups.
Conclusions: Our findings suggest that, as expected, Part D facilitated access to medications for patients who previously experienced the greatest costs without adversely increasing use and costs among those with the lowest prior cost.
(Copyright 2010 Elsevier Inc. All rights reserved.)