(CNN) -- An experimental Alzheimer's medication slowed declines in patients' ability to think clearly and perform daily tasks by more than a third in a large clinical trial, drugmaker Eli Lilly said Wednesday.
Based on the results, in people with early symptomatic Alzheimer's disease, Lilly said it plans to file for approval from the US Food and Drug Administration by the end of June.
The medicine, donanemab, works by removing plaque buildups in the brain known as amyloid that are a hallmark of Alzheimer's disease.
However, there were some side effects reported; there were three deaths in the trial among people taking the drug, two of which were attributed to adverse events such as brain swelling or microhemorrhages, known as amyloid-related imaging abnormalities or ARIA. The trial was run on more than 1,700 patients for 18 months.
"For every medicine, for every disease, there are potential risks and potential benefits," said Lilly's chief scientific and medical officer, Dr. Daniel Skovronsky. But he noted that almost half of the participants taking the drug, 47%, showed no decline in a key measure of cognition over the course of a year, compared with 29% of people taking a placebo.
That's "the kind of efficacy that's never been seen before in Alzheimer's disease," Skovronsky said.
Alzheimer's affects more than 6 million Americans, with an estimated 1.7 million to 2 million people over 65 in the early stages of the disease, according to Lilly.
Drug development for Alzheimer's has been riddled with failures, but Lilly's drug is among a new group showing promise.
The first, Eisai and Biogen's Leqembi, received accelerated FDA approval in January.
Skovronsky, who noted he's been working in the field of Alzheimer's for 25 years, said the new class of medicines is different because of "the amount of amyloid they can clear and how quickly they can clear it."
The medicine is given by infusion once a month.
Donanemab clears amyloid so effectively, the company says, that a majority of patients in the trial -- 52% -- were able to stop taking the medicine by one year, and 72% were able to do so by a year and a half. Researchers will continue to monitor these patients' progress.
In the trial, researchers looked at the participants in two groups, separated by levels of a brain protein known as tau. A 35% slowing in cognitive and functional decline was seen in the group with intermediate levels of tau, whose disease hadn't progressed as far. When this intermediate group was combined with the group with higher levels of tau, the figure was 22%. The results have not been peer-reviewed or published in a journal.
Lilly filed for accelerated approval with the FDA for donanemab based on earlier results but was rejected in January as the agency sought more data. With these results, the company will file for full approval, which is expected to lead to broader insurance reimbursement for the medicine. Leqembi was approved on an accelerated basis in January, and Medicare is not expected to cover the drug broadly until it receives full approval as well, most likely by early July.
Leqembi is priced at $26,500 a year. Skovronsky declined to discuss potential pricing for donanemab before the drug is approved.
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