Alzheimer's drug shows promise

Experts hailed full data showing a new drug can slow cognitive decline in Alzheimer's patients, but warned improvements were comparatively small and the treatment can have serious side effects.

Preliminary data from a trial of lecanemab - an experimental drug developed by firms Biogen and Eisai - was released in September and found it slowed cognitive decline by 27 percent across an 18-month period.

The complete trial data fleshes out those findings but also raises concern about "adverse effects" - including brain bleeds and swelling.

The results showed 17.3 percent of patients experienced brain bleeds, compared with nine percent of those receiving a placebo. And 12.6 percent experienced brain swelling, compared with 1.7 percent of those in the placebo group.

Deaths were reported at approximately the same rate in both arms of the trials.

In Alzheimer's disease, two key proteins - tau and amyloid beta - build into plaques, which cause brain cells to die. Lecanemab works by targeting those proteins.

The phase 3 trial involved nearly 1,800 people, divided between those given the drug and given a placebo, and ran over 18 months.

They were assessed on a clinical scale for Alzheimer's patients that measures cognition and function, as well as for changes in amyloid levels and other indicators.

But expert Tara Spires-Jones noted that "there is not a clear definition of clinically meaningful effects." Many researchers stressed the need to observe the long-term effects of lecanemab.

The drug also only targets those in the early stages of the disease. An overhaul in early diagnosis would be needed to ensure more people could benefit from the treatment.

Biogen and Eisai previously brought the Alzheimer's drug Aduhelm to market, but there was controversy over the evidence that it worked and its approval led to three high-level resignations in the US Food and Drug Administration.