Medicare Part D's effect on the under- and overuse of medications: a systematic review.

OBJECTIVES: To evaluate the literature regarding the effect of Medicare Part D on the under- and overuse of specific medications and corresponding health outcomes.
DESIGN: Systematic review.
SETTING: Medline search of the peer-reviewed literature from January 1, 2006, to October 8, 2010. PARTICIPANTS: Medicare beneficiaries who obtained drug insurance from the Part D program. MEASUREMENTS: The review evaluated changes in the use of specific drugs or drug classes after implementation of Part D, as described in original, peer-reviewed articles.
RESULTS: Nineteen articles met inclusion criteria. Part D's implementation was associated with greater use of essential medications such as clopidogrel and statins, especially in beneficiaries who had been previously uninsured, but increases in inappropriate antibiotic use for the treatment of acute respiratory tract infections and increases in claims for the often overused proton pump inhibitor drug class were also observed. In the Part D transition period, dually eligible beneficiaries' drug use remained largely unchanged. When beneficiary cost sharing increased in the coverage gap, use of essential and overused medications declined.
CONCLUSION: Increasing drug coverage led to greater use of underused essential medications and inappropriate, or overused, medications under Medicare Part D. Despite efforts to have it do so, the Part D benefit did not sufficiently discriminate between essential and nonessential medication use.