The open-enrollment period for the 57 million Americans eligible for Medicare runs through Wednesday, Dec. 7, and an Atlanta-area internist is trying to help them save money on prescriptions.

Steven Cohen, a WellStar physician, noted that a 2012 study published by Health Affairs magazine found that only 5 percent of Medicare participants choose the least expensive Medicare D insurance plan and that the least expensive plan would save patients an average of $368 a year.

But choosing the wrong plan can be much more expensive. Cohen’s mother, Dot, died of lung cancer in 2009 and paid $1,500 a month out of pocket for the drug Tarceva. Discussing the drug with an oncologist in 2013, Cohen found that the annual cost in the Atlanta area that year ranged from $6,000 to $79,000, depending on which of the dozens of locally available Medicare plans was chosen.

Since 2006 the federal government has helped pay for outpatient medicines for people on Medicare by subsidizing the costs for Medicare D and Advantage insurance plans. To help pick a plan, the government provides the free Medicare Plan Finder at www.medicare.gov.

But the Kaiser Family Foundation estimates that 13 percent of Medicare participants have no prescription coverage, even though some zero-premium plans are available.

With the Medicare Plan Finder, you enter your ZIP code and medicines and receive an estimate of your annual costs for the available Medicare plans. You can then pick the least expensive plan. Georgia Cares at 866-552-4464 (Option 4) can provide one-on-one help with the selection, and you can ask general questions at 800-MEDICARE.

Cohen’s free www.medicaredrugsavings.org offers a series of instructional videos to explain how to use the Medicare Plan Finder. He said he started the site after one of his patients lost her home to foreclosure because she decided to pay for medicine instead of her mortgage.

The Jewish Federation of Greater Atlanta is working with Cohen to spread the word about the Medicare Plan Finder through the Naturally Occurring Retirement Community program and other organizations working with the Jewish population.

Anyone on Medicare A and B may sign up for a Medicare D or Advantage plan (for which Atlanta-area residents have more than 40 options, Cohen said).