A third member of a prestigious FDA panel has resigned over the approval of a controversial new Alzheimer's drug

• A third member of an FDA expert panel has resigned over the agency's accelerated approval of a new Alzheimer's drug.
• The committee voted against approving the treatment. The FDA isn't required to follow the panel's recommendation but usually does.
• Aduhelm failed one of its late-stage clinical trials and didn't produce conclusive results in another trial.

A third member of a Food and Drug Administration expert panel has resigned over the approval of a controversial new Alzheimer's drug.

In a resignation letter obtained by CNBC, Dr. Aaron Kesselheim, a professor of medicine at Harvard Medical School, said the agency's decision to approve Biogen's new Alzheimer's drug, Aduhelm, "was probably the worst drug approval decision in recent US history."

Kesselheim joins two other former members of the FDA's Peripheral and Central Nervous System Drugs Advisory Committee, who resigned from their positions earlier this week, as the backlash against the agency's accelerated approval process continues to mount.

Aduhelm, formerly known as aducanumab, was approved by the FDA on Monday, despite the prestigious advisory committee voting against the approval of the treatment in November. Though the FDA isn't required to follow the panel's recommendation, it typically does so.

The drug has been a point of debate in the scientific community for years, because it failed one of its late-stage clinical trials, and another trial failed to produce conclusive evidence that Aduhelm helped patients with memory and cognition issues.

But facing ongoing pressure from Alzheimer's patients' friends and family, the FDA decided to approve the drug under accelerated approval, a special mechanism that allows authorization on the condition that Biogen runs a follow-up trial to confirm the drug works. The method is usually used for cancer medications, according to CNBC.

In his resignation letter, Kesselheim said the FDA switched its review to the accelerated pathway "at the last minute" based on a "debatable premise" about the drug's effectiveness, CNBC reported. He also said it was clear to him that the agency is not "presently capable of adequately integrating the committee's scientific recommendations into its approval decisions."

"This will undermine the care of these patients, public trust in the FDA, the pursuit of useful therapeutic innovation, and the affordability of the health care system," Kesselheim wrote.

The FDA did not immediately respond to Insider's request for comment.

Dr. David Knopman, a neurologist at the Mayo Clinic whose resignation from the central nervous system panel was first reported by Insider's Allison DeAngelis, said he was baffled by the FDA's decision and felt the advisory committee had been "mistreated."

"The FDA, in using the accelerated approval mechanism, they could not endorse any evidence of demonstrable clinical benefit. That's what their press release said in so many words," he told Insider. "That seems illogical to me."

"I don't want to be a part of that in the future," Knopman added.

Neurologist Dr. Joel Perlmutter of Washington University in St. Louis also resigned from the panel on Monday.