Kerry Weems, the head of the Centers for Medicare and Medicaid Services (CMS), said seniors and disabled beneficiaries "may see significant premium increases or changes" in their plans.
It is unclear how drastic the changes will be. Drug plans vary state to state and even county to county. Most of the hundreds of private drug plans nationwide won't release benefit and cost information until the middle of next month, according to CMS.
But Weems said beneficiaries may see "significant premium increases" in their plans, as well as reduced coverage in Part D's "gap." That's where Medicare stops paying drug benefits after spending reaches $2,510 and doesn't pick up again until most beneficiaries have spent $5,726 on their medications.
"We encourage individual beneficiaries to review how their plans are changing and what other options are available to them to determine which plan best meets their needs," Weems told reporters.
Officials said beneficiaries in every state would be able to purchase plans that cover drugs in the gap. The fast majority of those plans cover generic drugs, with only a handful covering a wide range of brand-name drugs.
Vicki Gottlich, a senior policy attorney at the Center for Medicare Advocacy, said "a huge number" of Medicare beneficiaries will end up having to change their plans or confront reduced coverage or higher costs in their existing plans.
But she said it was too early to know how many patients would need to change.
"Its difficult for folks to have to go through the process of having to go through the whole process every year," said Gottlich, whose group is a critic of Part D's private-based drug insurance.
Plans are required to notify beneficiaries of changes to their coverage by Oct. 31.
Medicare has two general types of Part D plans: standalone plans and plans that are part of Medicare Advantage managed care packages.
CMS said the average monthly premiums for standalone plans would be $28 in 2009, up $3 from this year. Drug plans folded into Medicare Advantage are set to rise from an average of $16 dollars this year to $17 in 2009.
Beneficiaries can sign up, change, or discontinue a Medicare drug plan from Nov. 15 to Dec. 31.