The drug is said to be the first treatment to attack the disease's progression, providing new hope for patients, CBS2's Dr. Max Gomez reported.
The new drug is called aducanumab, a monoclonal antibody that will be marketed by Biogen under the brand name Aduhelm.
It targets sticky plaque, called amyloid beta, found in the brains of Alzheimer's patients.
Aduhelm was studied in patients with early Alzheimer's who had amyloid plaques on brain scans. A number of other drugs have been able to clear brain amyloid, but then failed in clinical trials.
"None of the agents that have been tested so far have had the effect size on amyloid that this agent has," said Dr. Mary Sano from Icahn School of Medicine at Mount Sinai. "There are many studies that were completed with agents that supposedly removed amyloid, but we did not see this size of an effect."
Aduhelm was very effective at clearing amyloid from brains - the hope being that early removal will slow disease progression.
But studies did not show a significant effect on Alzheimer's symptoms, which led the FDA's independent advisory committee to overwhelmingly recommend against approval.
Dr. Sano, who studies Alzheimer's and is a consultant to Biogen, explained the disconnect.
"It remains unclear as to how tightly associated amyloid is to the clinical signs and symptoms of the disease. That's still true and unknown," Dr. Sano said. "In fact, most of us believe that amyloid actually occurs before any signs or symptoms of the disease."
Many Alzheimer's support groups lauded the approval, even though there were instances of potentially serious brain swelling.
The FDA said Biogen must conduct a post-approval clinical trial to verify the drug's clinical benefit. If the drug doesn't work as intended, the agency can remove it from the market.
The drug is given monthly by IV and is expected to cost $10,000-$50,000 per year.
Biogen said it's now in talks with private insurers, Medicare and the Department of Veterans Affairs, since Alzheimer's primarily affects older adults.
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