Association between Higher Generic Drug Use and Medicare Part D Star Ratings: An Observational Analysis

Increasing generic drug use, due to potential for cost savings and drug access, is a viable consideration for Medicare prescription drug plans to achieve high star ratings and improve quality of plan offerings for Medicare beneficiaries.

To examine the association between contract-level proportion of generic drugs dispensed (pGDD) and Medicare Part D star ratings.

This was a retrospective study of linked 2011 Medicare Part D star rating data with contract-level pGDD data. A total of 477 individual Medicare prescription contracts were included, representing 75% of total Prescription Drug Plans and more than 65% of total Medicare Advantage Prescription Drug Plans available by the end of 2010. Primary outcomes were Medicare Part D summary and domain star ratings (1-5 indicating lowest to highest performance), incorporating a range of quality measures for access, cost, beneficiary satisfaction, and health services outcomes and processes. Ordinal logistic regression models were used to examine associations between pGDD and Medicare Part D summary and domain star ratings, controlling for contract type and number of beneficiary enrollment.

Higher pGDD was associated with higher summary star ratings (adjusted odds ratio 1.08 with 95% confidence interval 1.04-1.12) and higher "member experience with drug plan" domain ratings (adjusted odds ratio 1.07 with 95% confidence interval 1.03-1.11).

Prescription formulary benefit design targeting increasing generic drug use appears to be associated with improved member experience and higher plan star ratings. Consideration may be given to incorporating pGDD into Medicare Part D star rating measures to improve quality of prescription plans.