Background: Since its inception, Medicare Part D requires beneficiaries to choose from a myriad of insurance plans in order to receive prescription drug coverage. Moreover, each year beneficiaries are confronted with plan cancellations, new plan offerings, changes in existing plan formularies and cost-sharing structure. Objective: This study prospectively examined the relationship between stand-alone prescription drug plan (PDP) costs, subsidy status, and the number of plans offered in California from 2009-2012. Methods: Forty-one community outreach events were held throughout Central/Northern California during the Medicare Part D annual election periods from 2008-2011. In total, 1,578 beneficiaries were assisted, 983 (62.2%) of whom had a PDP. During each intervention, beneficiary subsidy status, cost data for the beneficiary's current plan and lowest cost plan for the upcoming year were recorded from the Medicare website. The percent of beneficiaries that did not need to switch plans to reduce their out-of-pocket (OOP) drug costs was compared to the number of available plans in the subsequent year.Results: On average, 14.3-23.7% of beneficiaries would have been enrolled in the lowest cost plan in the upcoming year had they remained in their current plan. Subsidy recipients were significantly more likely to be in the lowest cost plan each year. The chance of being in the lowest cost plan was significantly negatively correlated to the number of drug plans offered in the subsequent year.

Conclusion: Annual Part D plan reexamination is essential to ensure that beneficiaries optimize their prescription medication coverage and minimize their OOP costs.