Status report on Medicare Part D enrollment in 2006: analysis of plan-specific market share and coverage.

The centerpiece of the Medicare Prescription Drug, Improvement, and Modernization Act of 2003 was the Part D drug benefit, provided through new stand-alone prescription drug plans (PDPs) and Medicare Advantage prescription drug (MA-PD) plans. We examine 2006 Part D enrollment data to analyze organization- and plan-level market share and enrollment by plan type, benefit design, and gap coverage. Ten organizations captured 72 percent of Part D enrollment, primarily in low-premium plans and those with name recognition. More than twelve million Part D enrollees without low-income subsidies enrolled in plans with limited or no gap coverage in 2006, but the number with actual spending in the gap remains to be seen.