The Centers for Medicare & Medicaid Services recently disclosed that 234 drug manufacturers that sell drugs covered by Medicare Part D have signed a pledge to provide a 50% discount to seniors who fall into the coverage gap, or doughnut hole.

The drug manufacturers on the list represent 99.9% of all drugs covered by Medicare Part D in 2009, according to CMS. One manufacturer declined to sign the agreement, taking three drugs out of the Part D formulary. These drugs had limited use in 2009, and will be replaced in 2011, according to a Bureau of National Affairs report. CMS is expected to post a list specifying products covered by the agreement on or around Oct. 1.

In related news, a study from Avalere Health finds that the number of prescription drug plans that will cover brand-name drugs in the Part D coverage gap will climb to 106 in 2011, up from just 35 this year. The plans are expected to cost slightly more, and will cover only a select amount of drugs in the coverage gap—typically drugs for chronic illnesses, according to The Associated Press.