WASHINGTON (AP) — Sen. Bernie Sanders is asking the White House to cut back a big Medicare premium hike set to take effect in weeks and tied to a pricey Alzheimer's drug whose benefits have been widely questioned.

In a letter Friday to President Joe Biden, the Vermont Independent called on the president to act immediately to prevent the portion of an "outrageous increase" in Medicare premiums that's attributable to Aduhelm, a newly approved Alzheimer's medicine from drugmaker Biogen priced at $56,000 a year.

If Biden agreed and found a way to do it, a planned January increase of $21.60 a month to Medicare's "Part B" premium for outpatient care would be slashed closer to $10. The monthly premium for 2022 would drop from $170.10 to about $159.

Democrats run the risk that seniors smarting from one of the biggest increases ever in Medicare premiums will turn against them in the 2022 midterm elections. The premium increase will claw back a big chunk of next year's Social Security cost-of-living allowance, a boost that works out to $92 a month for the average retired worker, to help cover rising prices for gas and food.

"Biogen's $56,000 price of Aduhelm is the poster child for how dysfunctional our prescription drug pricing system has become," Sanders wrote to Biden. "The notion that one pharmaceutical company can raise the price of one drug so much that it could negatively impact 57 million senior citizens and the future of Medicare is beyond absurd. With Democrats in control of the White House, the House and the Senate we cannot let that happen." A copy of the letter was provided to The Associated Press.

There was no immediate comment from the White House.

Sanders' letter comes as Democrats have had to step back from their dream of delivering dental and vision coverage to Medicare recipients as part of Biden's sweeping social agenda legislation. They've also had to narrow the scope of price negotiations with drug companies, although coverage for hearing aids stayed in the bill. Even if the legislation passes, its benefits will phase in over time and would not be available right away. But the premium hike would hit after the New Year.

Sanders wrote that "it could not come at a worse time for older Americans all over this country who are struggling economically."

The jump of $21.60 in monthly Medicare premiums is the biggest increase ever in dollar terms, although not percentage-wise. As recently as August, the Medicare Trustees' report had projected a smaller increase of $10 from the current $148.50. Medicare said it had to boost the rate higher to set aside a contingency fund in case the program formally approves coverage for Aduhelm.

Alzheimer's is a progressive neurological disease with no known cure, affecting about 6 million Americans, the vast majority old enough to qualify for Medicare.

Aduhelm is the first Alzheimer's medication in nearly 20 years, although it doesn't cure the disease. The Food and Drug Administration approved the drug this summer, determining that Aduhelm's ability to reduce clumps of plaque in the brain is likely to slow dementia. That decision was highly controversial, since the FDA overrode its own outside advisers. Many experts say Aduhelm's benefit has not been clearly demonstrated. The Department of Veterans Affairs declined to list the medicine on its roster of approved drugs.

Medicare has begun a formal assessment to determine whether it should cover the drug, and a final decision isn't likely until at least the spring. For now, Medicare is deciding on a case-by-case basis whether to pay for Aduhelm.

Sanders asked Biden to order Medicare to hold off on approving coverage of Aduhelm until there is scientific consensus about its benefits.

Biogen has defended its pricing, saying it looked carefully at costs of advanced medications to treat cancer and other conditions. A nonprofit think tank focused on drug pricing pegged Adulhelm's actual value at between $3,000 and $8,400 per year — not $56,000 — based on its unproven benefits.