Fifty-four different companies entered the stand-alone prescription drug insurance market under Medicare Part D Jan. 1. But, even before the program began, it was clear that not all 54 would be competing on an equal footing in the race for enrollment in 2006. A handful of companies dominated the initial enrollment in Part D, because they bid most aggressively to serve former Medicaid recipients who were randomly assigned to plans. (See "Medicare Market Share: Drug Plan Starts With Big Four," IN VIVO, October, 2005 Also see "Medicare Market Share: Drug Plan Starts With Big Four" - In Vivo, 1 October, 2005..)
Three months into the program, the market is even more concentrated. The top 10 plan sponsors represent about 90% of the enrollment in Part D, and the top five companies...
