FDA Leader Explains Rationale Leading to Controversial Alzheimer's Drug Approval

Deborah Brauser

June 23, 2021

The US Food and Drug Administration (FDA) has provided a detailed and documented account of how it arrived at its decision to approve the controversial Alzheimer's drug aducanumab (Aduhelm, Biogen/Eisai), including the release of several internal documents.

Dr Patrizia Cavazzoni

In a letter sent to members of the FDA's Center for Drug Evaluation Research (CDER), CDER Director Patrizia Cavazzoni, MD, noted that in view of the "fierce public debate" that erupted immediately following the drug's approval, she felt compelled to explain how the agency came to its decision.

Also publicly released today on the FDA's updated aducanumab landing page was "the first set of review memos," for the drug.

"We're releasing these documents with the intent of informing public discourse — providing interested parties with the opportunity to explore the data that helped shape our decision to grant accelerated approval," Cavazzoni wrote. "The rest of the approval package will be released over the next several days," she added.

Immediate Backlash

The FDA's June 7 approval of aducanumab was met with instant backlash. As reported by Medscape Medical News, in November, the agency's Peripheral and Central Nervous System Drugs Advisory Committee voted nearly unanimously to not vote in favor of approval because of a lack of evidence proving its efficacy.

Since the drug was approved, three of the advisory committee's members resigned in protest. In addition, the high-profile consumer advocacy group Public Citizen sent a letter to the secretary of the US Department of Health & Human Services demanding the removal of three FDA officials, including acting FDA Commissioner Janet Woodcock, MD.

In its letter, the group noted that the FDA's decision "showed a stunning disregard for science, eviscerated the agency's standards for approving new drugs, and ranks as one of the most irresponsible and egregious decisions in the history of the agency."

Even the Alzheimer's Association, which was a staunch supporter of the drug throughout its development process and applauded its approval, expressed outrage over its more than $56,000-a-year cost to patients and called the price "simply unacceptable" in a statement.

In today's letter, the CDER director noted, "this was one of the most complex applications in recent history" and admitted that deliberations were lengthy and difficult.

"It's also not surprising, in fact it was to be expected, that there would be different viewpoints about the data, including dissenting opinions about the approval decision," Cavazzoni wrote.

However, this "is what scientific debate is all about; and while difficult at times, it should be celebrated," she added. "Please know that every opinion was heard, and the approval is a direct reflection of this open and robust scientific and regulatory debate."

Accelerated Approval Pathway

Documents newly posted to the FDA's aducanumab landing page include CDER's Office of Neurology's Summary Review Memorandum, which includes details on the basis for the approval; the Concurrence Memorandum from the director of CDER's Office of New Drugs; and the Concurrence Memorandum from Cavazzoni.

"The remaining scientific review documents in the Aduhelm action package are not yet available, but will be made available to the public as soon as the internal process of review and redaction is complete," the FDA noted on its site.

In the document, FDA's Decision to Approve New Treatment for Alzheimer's Disease, Cavazzoni noted that the "highly complex" data included in the submission package for the drug "left residual uncertainties regarding clinical benefit."

However, after listening to the patient community and reviewing all the data, the FDA chose to use the Accelerated Approval pathway, deciding that the potential benefit to patients outweighed the drug's risks.

Of two phase 3 trials, only one met its primary endpoint. However, in all trials, including earlier studies, "Aduhelm consistently and very convincingly reduced the level of amyloid plaques in the brain in a dose- and time-dependent fashion," Cavazzoni wrote.

"It is expected that the reduction in amyloid plaque will result in a reduction in clinical decline," she added.

Cavazzoni noted that although the Advisory Committee did not agree that clinical benefit from one trial meeting its primary endpoint was enough for approval, "the option of Accelerated Approval was not discussed" at that time.

This type of approval "is based on a surrogate or intermediate clinical endpoint, in this case reduction of amyloid plaque in the brain" and requires post-approval studies to verify clinical benefit.

Cavazzoni added that the drug could still be removed from the market if its confirmatory trial does not verify this type of benefit.

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