Impact of Medicare Part D on Medicare-Medicaid dual-eligible beneficiaries' prescription utilization and expenditures.

OBJECTIVE To examine the effect of Part D on 65-78-year-old noninstitutionalized dual eligibles' prescription utilization and expenditures. DATA SOURCE Random sample of unique pharmacy customers of a national retail pharmacy chain who filled at least one prescription during both 2005 and 2006. For each subject, we obtained claims data for every prescription filled between January 1, 2005, and April 31, 2007. STUDY DESIGN Generalized estimating equations were used to examine the experience of a "treatment" group (dual eligibles between 65 and 78 years on January 1, 2005) with that of a "control" group (near-elderly patients with Medicaid coverage between 60 and 63 years on January 1, 2005) during the first 18 months after Part D implementation. PRINCIPAL FINDINGS Expenditures for the treatment and control groups tracked each other closely in the pre-Part D period. Immediately following the implementation of Part D, expenditures for both groups decreased and then leveled off. There were no significant changes in trends in the dual eligibles' out-of-pocket expenditures, total monthly expenditures, pill-days, or total number of prescriptions due to Part D. CONCLUSIONS We find no evidence that Part D adversely affected pharmaceutical utilization or out-of-pocket expenditures of dual eligibles during the transition period, nor during the 16 months subsequent to Part D implementation.