The world is “on the cusp of a first generation of treatments for Alzheimer's disease”, trials have indicated, as the company behind a new drug revealed early results.

Donanemab, made by Eli Lilly and Company, slowed cognitive and functional decline by 35 per cent to 36 per cent in a late-stage phase three clinical trial, the company said.

Dr Susan Kohlhaas, executive director of research and partnerships at Alzheimer's Research UK, said: “This is incredibly encouraging, and another hugely significant moment for dementia research.”

“We're now on the cusp of a first generation of treatments for Alzheimer's disease, something that many thought impossible only a decade ago.

“The treatment effect is modest, as is the case for many first-generation drugs, and there are risks of serious side effects that need to be fully scrutinised before donanemab can be marketed and used.”

In January, the US Food and Drug Administration approved the Alzheimer's drug lecanemab developed by Eisai and Biogen for patients in the earliest stages of the disease.

Donanemab appeared to slow progression of Alzheimer's compared to placebo in 1,182 people with early-stage disease based on those with intermediate levels of a protein known as tau, Lilly said.

The drug also resulted in 40 per cent less decline in the ability to perform activities of daily living, according to the firm.

“This is the first phase three trial of any investigational medicine for Alzheimer's disease to deliver 35 per cent slowing of clinical and functional decline,” said Daniel Skovronsky, Eli Lilly's chief scientific and medical officer.

In the trials, 47 per cent of those on donanemab had no clinical progression of disease at one year compared with 29 per cent on placebo.

Participants on donanemab experienced a 39 per cent lower risk of progressing to the next stage of disease compared to placebo, according to Eli Lilly.

“After 20 years with no new Alzheimer's drugs, we now have two potential new drugs in just 12 months — and for the first time, drugs that seem to slow the progression of disease,” said Dr Richard Oakley, associate director of research at the Alzheimer's Society.

“This could be the beginning of the end of Alzheimer's disease.

“Based on today's early results, donanemab appears to slow the progression of Alzheimer's symptoms by 36 per cent.

“Promisingly, the trial also demonstrated a 40 per cent slowing in decline of everyday activities such as driving, doing hobbies and managing finances.”

In those patients who received donanemab, brain swelling — a known side effect of drugs of this type — occurred in 24 per cent of participants, with 6.1 per cent experiencing symptoms.

Brain bleeding occurred in 31.4 per cent of the donanemab group and 13.6 per cent of the placebo group.

Lilly said the incidence of serious brain swelling in the donanemab study was 1.6 per cent, including two participants whose deaths were attributed to the condition and a third who died after an incident of serious brain swelling.

It said most cases of swelling or bleeds were “mild to moderate” and responded to treatment.

Dr Charles Marshall, consultant neurologist at Queen Mary University of London, said: “This is hugely exciting news as it provides further evidence that it is possible to slow down Alzheimer's disease.

“When the full results are published as a paper we will be able to start carefully balancing the risks and benefits, and this will inform decisions about whether donanemab should be routinely given to patients with Alzheimer's disease.”

John Hardy, professor of neuroscience and group leader at the UK Dementia Research Institute, University College London, said: “It is great news to have success with a second anti-amyloid Alzheimer's drug.

“This should dispel any lingering doubts about this approach.”