The number of drugs on Medicare Part D plan formularies will increase as much as 13%, according to an analysis by the Centers for Medicare & Medicaid Services.

CMS compared 2006 formularies to 2007 formularies. It found that for stand-alone prescription drug plans, the number of items should rise by 13% next year; for Medicare Advantage plans, the drugs on formularies could expand by 10%, on average. In its report, “Information Partners Can Use on Medicare Part D 2007 Formulary Changes,” CMS also noted a decrease next year in the number of drugs with quantity-limit restrictions and a small increase in the number of drugs requiring step therapy.

CMS also examined the top 100 drugs used by the elderly. In 2007, the number of these top drugs on the formularies of stand-alone plans will increase about 8%; they will rise about 6% on Medicare Advantage formularies.