ROCHESTER, Minn. — Aduhelm, the first treatment ever approved by the FDA to target Alzheimer's disease at the level of brain deterioration, will likely be available only for limited populations at Mayo Clinic.

That's according to a clinic neurologist who studied the drug and has expressed concerns about its effectiveness.

"I've publicly expressed my views that I thought the data that showed there were clinical benefits were very weak," Mayo Clinic neurologist Dr. David Knopman said of the treatment, whose generic name is aducanumab.

"We're going to restrict it to people like those who were in the trial," he said. "We're not going to treat patients (with the drug) who are too severe, and we are not going to treat patients who are asymptomatic."

An intravenous medication manufactured by Massachusetts-based drugmaker Biogen, the monoclonal antibody attacks amyloid plaque, dense proteins in the brain that are associated with the disease.

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The drug is proven to reduce the plaque, a so-called biomarker of the illness, but critics question whether doing so will reduce clinical features such as memory loss and cognitive decline.

"The decision today by the FDA was to approve the drug based on the fact that it lowered brain amyloid levels," Knopman said. "Even though there was no acknowledgment by the FDA that the drug had consistent clinical benefits for patients."

Under FDA rules, two positive studies are needed to approve a drug for sale. While two identical trials demonstrated aducanumab does cause a significant decrease in amyloid plaque, only one showed positive effects on cognitive features of the disease, and those were modest.

"In one of (the studies) there was no delay in progression," Knopman said. "In the other, there was a slight delay in progression of symptoms. Nobody got better. Nobody stayed the same."

"They just found that people didn't get worse as quickly in the one study that showed some benefit."

Dr. David Knopman. Photo: Mayo Clinic
Dr. David Knopman. Photo: Mayo Clinic

The FDA has retained the right to withdraw its approval of aducanumab if a follow-up trial does not show clinical benefits, but cited unmet need in giving the drug the green light under a lower regulatory threshold.

Regulators gave the drug their nod over objections of their own panel of experts.

Biogen announced on Monday, June 7, it plans to charge $56,000 for Aduhelm. Its stock reached a record high following the announcement.

Clinicians on Monday strove to reduce expectations for the treatment, access to which will likely prove galvanizing for the families of some 6 million Americans afflicted with Alzheimer's disease.

Mayo Clinic neurologist Dr. Ronald Peterson in the medical publication STAT cautioned that "this is not going to be penicillin for Alzheimer's disease."

Knopman, a site investigator in one of the two trials of the drug, was joined last fall by fellow Mayo neurologist Dr. David T. Jones and a colleague from Stanford in coauthoring a paper calling for more research on the drug.

The article cautioned that "approval would have a massive impact on health-care economics and the feasibility of conducting future clinical trials" of the medication.

Alzheimer's & Dementia, which published their paper, is the journal of the patient advocacy group the Alzheimer's Association. It is an enthusiastic supporter of the drug.

"The Alzheimer’s Association will do everything in its power to ensure access to the drug," the organization stated on its website Monday.

It called Aduhelm's approval "historic," and the start of "an exciting era in Alzheimer’s and dementia treatment and research."

"They know that I strongly disagree with their position," says Knopman, who has served as vice chair to the organization's Medical and Scientific Advisory Council and who is currently a senior advisor. "So we respectfully disagree with one another."

"There were two very large Phase III studies," Knopman said of the evidence for the new drug. "One of them showed some statistically significant evidence of benefits, very small, but statistically significant. The other was designed in an identical manner, was done identically, and found no benefit at all. "

"If you approach it as a lay person, you tried something once and it worked, but you tried the same thing again and it didn't work. Would you conclude you'd want to sail across the ocean in that ship? You'd want to test it a little more, wouldn't you?"