Some advocacy groups, like the Alzheimer’s Association, have criticized the registry requirement, calling it an unnecessary barrier to access. But medical experts say registry programs are common and easy to comply with. Their concern is that the registry won’t be comparing Leqembi patients with others, so it won’t be able to say if Leqembi slows cognitive decline.
The F.D.A.’s approval on Thursday was based on a large trial indicating that patients receiving Leqembi declined 27 percent more slowly over 18 months than patients receiving a placebo. The difference between those receiving drug and placebo was small — less than half a point, on an 18-point cognitive scale that assesses functions like memory and problem-solving. Some Alzheimer’s experts say that for slowing of decline to be clinically meaningful, or noticeable to patients and families, the difference between the groups must be at least one point.
Leqembi patients also declined more slowly on three secondary measures of cognition and daily function, and data on biological markers was generally stronger for Leqembi than for the placebo. All these measures moving in the same direction strengthens the idea that the drug can benefit patients, experts say.
Still, a report on the data, published in The New England Journal of Medicine and co-written by scientists from Eisai, concluded that “longer trials are warranted to determine the efficacy and safety.”
Concerns about safety have been stoked by reports of deaths of three clinical trial participants who experienced brain swelling and brain bleeding, two of whom were being treated with blood thinners. Eisai has said it is unclear if Leqembi contributed to their deaths because the patients had complex medical issues.
“You’ve got small benefits and a certain risk for serious adverse events, and that has to be balanced,” said Dr. Lon Schneider, director of the California Alzheimer’s Disease Center at the University of Southern California, who said he will prescribe Leqembi to carefully evaluated patients.
“If its efficacy were greater, we would not be talking about adverse events as much because we would see a clear benefit,” he said, adding, “I think many people will see this and say it’s not worth the effort, it’s not worth twice-a-month infusions.”