Medicare recipients who have arthritis, cancer or other complex conditions may find they have to pay thousands of dollars a year for their medications, even if their insurance plan covers most prescriptions.

For 2016 the out-of-pocket costs can reach as high as $11,538 for a single drug — far more than the maximum catastrophic threshold of $4,850 for Medicare beneficiaries, according to an analysis of Medicare Part D drug coverage released Tuesday by the Kaiser Family Foundation and Georgetown University's Health Policy Institute.

That threshold is supposed to be the upper limit for the out-of-pocket expenses a beneficiary has to pay during a single year. But Tricia Neuman, director of the program on Medicare policy at Kaiser, called that limit "leaky," because Medicare still requires seniors to pay 5 percent of a drug's cost after they reach the limit.

And that out-of-pocket amount can increase quickly, especially for someone taking multiple expensive medications for cancer, hepatitis C, multiple sclerosis or certain other illnesses or chronic conditions.

"We were struck by the thousands and thousands of dollars that some people can pay for specialty drugs, in some cases, even after they reach the catastrophic level," Neuman says.

The analysis showed, for example, that seniors taking Revlimid for cancer could end up paying $11,538 of their own money in 2016, even when that medicine is covered under their Medicare prescription drug plan.

Some people may not realize they can be on the hook for such expenses, Neuman says. "They could find themselves with an unpleasant surprise when they exceed the limit and still have to pay hundreds, if not thousands, of dollars," she says.

Neuman urges people to shop around for a Medicare plan that covers the particular prescriptions they need. "It really does pay to shop," she says. "We found that plans vary widely in terms of the drugs they cover and what they charge." Open enrollment for Medicare plans, including Part D prescription drug plans, ends on Dec. 7.

If Medicare customers take a medication that has been excluded from their plan, the costs can be exceptionally high, the report showed. The out-of-pocket cost for Enbrel, a rheumatoid arthritis medicine, for example, could reach almost $50,000 a year, if it's not covered. Other specialty drugs for conditions such as multiple sclerosis or hepatitis C can climb even higher.

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