Eli Lilly’s experimental drug donanemab slowed the progression of Alzheimer’s by 60 per cent for patients in the earliest stages of the brain-wasting disease, according to trial data presented at a medical meeting on Monday.

For those patients, the drug slowed cognitive decline by nearly twice the rate Lilly reported in May for the trial’s overall treatment group. The full analysis showed results were less robust for older, later-stage patients as well as those with higher levels of a protein called tau that has been linked to Alzheimer’s disease progression.

The findings underscore that “earlier detection and diagnosis can really change the trajectory of this disease,” said Anne White, president of neuroscience at Lilly.

The study showed that brain swelling, a side effect of donanemab, occurred in more than 40 per cent of patients with a genetic predisposition to develop Alzheimer’s.

The company had previously reported that 24per cent of the overall donanemab treatment group had brain swelling. Brain bleeding occurred in 31per cent of the donanemab group and about 14per cent of the placebo group. The deaths of three trial patients were linked to the treatment, researchers reported.

“These side effects should not be taken lightly,” but most cases were manageable by monitoring with magnetic resonance imaging (MRI) or stopping the drug, said study investigator Dr Liana Apostolova, professor in Alzheimer’s Disease research at Indiana University School of Medicine.

Doctors are likely to use “very stringent MRI safety screening while we treat these patients”, she said.

Donanemab, like Eisai and Biogen’s recently approved Leqembi, is an intravenous antibody designed to remove deposits of a protein called beta amyloid from the brains of Alzheimer’s patients.

Lilly said donanemab’s treatment effect continued to increase relative to placebo over the course of the 18-month trial, even for participants who had been taken off the drug after their levels of amyloid deposits fell significantly. “At the end of the trial, the average patient had been without the drug for seven months and yet they continued to benefit,” White said.