The Food and Drug Administration’s decision on approving a closely watched Alzheimer’s disease drug developed by Eli Lilly and Co. has been delayed as the agency asks an advisory panel to weigh in, the drugmaker said Friday.

Lilly said the FDA informed it that it wants to further understand the safety and efficacy of donanemab and will convene a meeting of its Peripheral and Central Nervous System Drugs Advisory Committee.

The FDA was widely expected to authorize the drug this month. Lilly called the delay “unexpected” and noted it is unusual for an advisory committee to be called upon after the anticipated FDA action date.

It’s not yet known when the meeting will take place. Lilly said the FDA’s decision will be delayed at least into the second quarter of 2024. 

The FDA told Spectrum News it cannot comment on possible or pending product applications or approvals.

"We are confident in donanemab's potential to offer very meaningful benefits to people with early symptomatic Alzheimer's disease,” Anne White, executive vice president of Eli Lilly and Co., said in a statement. “It was unexpected to learn the FDA will convene an advisory committee at this stage in the review process, but we look forward to the opportunity to further present the … results and put donanemab's strong efficacy in the context of safety.”

Lilly’s clinical trial of more than 1,700 people found the donanemab slowed cognitive and functional decline in patients with early symptomatic Alzheimer’s by 35% at 76 weeks compared to those who took a placebo, and all groups of trial participants saw improvement.

Given as a monthly intravenous infusion, the drug targets amyloid plaque that builds up between nerve cells in the brain.

About 6 million Americans are living with Alzheimer’s disease, the most common type of dementia, according to the Centers for Disease Control and Prevention.

More than three-quarters of all participants in the study achieved amyloid clearance at 76 weeks, compared to 0.3% in the placebo group.

There, however, were side effects with donanemab, including brain swelling in 24% among those who took the drug. There was brain bleeding in 31.4% of participants in the donanemab group and 13.6% in the placebo group.

While Lilly said the majority of the side effects were mild to moderate and resolved or stabilized with appropriate management, three participants died from brain swelling.

If authorized by the FDA, donanemab would become the third Alzheimer’s drug in its class to hit the market in the United States. Regulators granted accelerated approval to Leqembi, developed by Eisai and Biogen, in January 2023. 

In 2021, the FDA approved Aduhelm, made by the same two companies. That authorization was controversial because there was weak evidence showing it would benefit patients. Biogen announced in January it was abandoning its ownership rights to the drug.

Note: This article was updated to include the FDA's response.