March 8 - The U.S. Food and Drug Administration has delayed a decision on whether to approve Eli Lilly's experimental treatment for patients with early Alzheimer's disease and will hold a meeting of outside experts to discuss its safety and efficacy, the company said on Friday.

This is the second regulatory delay for the drug, donanemab, after the company released clinical trial data last year that it says showed the treatment to be safe and effective.

Lilly said no date has been set yet for the advisory committee meeting to discuss the medicine, but it could be several months before it is held.

The Indianapolis-based drugmaker had first expected a decision by the end of last year, but in November said the FDA pushed that back until the first quarter of 2024 because the agency needed more time to review the approval application.

Lilly said there was no change to its 2024 financial forecast.

Donanemab, given by infusion every two weeks, is designed to clear from the brain a sticky protein called amyloid tied to the fatal, memory-robbing disease.

"This was definitely unexpected for us," Anne White, president of Lilly Neuroscience, said in an interview. She noted that the news came very late in the review process and said the company had been ready to launch the drug.

White said the FDA wants the expert panel to discuss some of the unique aspects of the clinical trial used in its request for a traditional FDA approval, including issues around efficacy and safety.

In the trial, participants could stop treatment as soon as brain imaging showed that the drug had cleared the amyloid.

The drug is associated with swelling and bleeding in the brain and three people on the treatment in the company's trial died.

The FDA also wants to review the implications of assessing patients based on levels of another Alzheimer's-related protein called tau, which is closely linked with disease progression, White said.

"We don't have a lot of details," she said, noting that the agency has indicated a desire to move quickly. White said the agency will publish the meeting date in the Federal Register. They typically take place about two months after that publication.

"We certainly hope that after the advisory committee, they will make a decision quickly, and then we can make this medicine available to patients as we believe it should be," White said.

The surprise delay follows the FDA's decision a year ago not to grant the company an accelerated approval for the drug.

Donanemab would compete with a rival treatment, Leqembi, from Eisai and Biogen, which the FDA last year granted standard authorization and works in a similar manner.

More than 6 million Americans have Alzheimer's, according to the Alzheimer's Association.

Lilly said last year that donanemab was shown in a large clinical trial to slow progression of memory and thinking problems by 22% to 29% overall, depending on the rating scale used, which was roughly comparable to the 27% slowing seen with Leqembi.

In patients with low-to-medium levels of tau, the drug slowed disease progression by 35.1% compared with placebo, which was the main goal of the study.

Lilly's late-stage study showed that brain swelling occurred in 24% of the donanemab treatment group. Brain bleeding occurred in 31% of the donanemab group and about 14% of the placebo group.

Analysts on average expect donanemab sales of $189.6 million in 2024, rising to $837 million next year, according to LSEG data. In February, Lilly forecast 2024 revenue of $40.4 billion to $41.6 billion, driven largely by its weight-loss and diabetes drugs. (Reporting by Julie Steenhuysen in Chicago and Patrick Wingrove in New York; editing by Caroline Humer, Bill Berkrot and Alexander Smith)