All three insulin makers in the United States said that they would participate in the program, but representatives for companies that operate Medicare plans, such as CVS and Express Scripts, did not comment.

Sanofi said Wednesday that it would take part. “We believe their plan, based on shared contributions from both manufacturers and Part D plans to directly lower out-of-pocket costs for Medicare beneficiaries, is the right approach,” Ashleigh Koss, a Sanofi spokeswoman, said in a statement, referring to the Part D drug coverage plans operated by private insurers.

Another insulin maker, Novo Nordisk, said, “We look forward to collaborating in this public-private approach to do even more to help seniors with diabetes afford the insulin they need.”

Eli Lilly said on Wednesday that it, too, would participate in the program. “This is a great example of collaboration between the government and private companies to address a problem faced by many seniors taking insulin,” said David A. Ricks, the company’s chief executive.

Elizabeth Pfiester, the founder and executive director of the group T1International, a patient group that has advocated for people who can’t afford insulin, said while the proposal showed the issue was a priority, it doesn’t include everyone who needs relief.

“It still leaves huge numbers of people with diabetes who rely on insulin in the same place they were before — rationing and suffering,” she said in a statement. “Many of the deaths we are seeing from rationing are young people without insurance, so we need federal action that provides immediate relief and long-term solutions for everyone.”

People who are covered by Medicare’s drug benefit program are particularly exposed to the rising list price of drugs because they enter several different phases of coverage, including an initial deductible phase in which they must pay close to the list price of a drug. Later in the year — after they and their plan have spent $4,020 on drugs — they enter a coverage gap (called the “doughnut hole”) in which they pay 25 percent of the drug’s price.