The Alzheimer's Society last night hailed an apparent breakthrough in the treatment of dementia by scientists at Aberdeen University. A team led by Professor Claude Wischik published results of early trials of a new drug, suggesting it could be at least twice as effective as current medicines in slowing progression of the disease.

The drug, called rember, slowed cognitive decline by 81%, Wischik said in a paper presented to the international conference on Alzheimer's disease in Chicago.

Rember is the first drug to act on a protein called tau that helps brain cells keep their structure and communicate with each other. In people with dementia this protein becomes tangled and causes brain cell death. Wischik's research suggested rember could reduce the tau tangles and slow the deterioration of the brain.

People taking it for 50 weeks had a slower decline in blood flow to the parts of the brain that are important for memory than those taking a dummy pill.

Wischik is co-founder of TauRx Therapeutics, which is developing the treatment. He said: "This is an unprecedented result in the treatment of Alzheimer's disease. We have demonstrated for the first time that it may be possible to arrest progression of the disease by targeting the tangles which are highly correlated with the disease."

The Alzheimer's Society, which is not connected to the company, said: "This is the first realistic evidence that a new drug can slow cognition decline in people with Alzheimer's, by targeting the protein tangles that cause brain cell death."

Prof Clive Ballard, the society's head of research, added: "This first modestly sized trial in humans is potentially exciting. It suggests the drug could be over twice as effective as any treatment that is currently available. However, we are not there yet.

"Larger-scale trials are now needed to confirm the safety of this drug and establish how far it could benefit the thousands of people living with this devastating disease."

Wischik's results were based on a "phase 2" study of 321 people with mild and moderate Alzheimer's disease in the UK and Singapore. They were divided into four groups, three taking different doses of rember and a fourth group taking a placebo.

After 50 weeks those with both mild and moderate Alzheimer's who were taking rember experienced an 81% reduction in mental decline compared with those on the placebo. Those on rember did not experience a significant decline in their mental function over 19 months, while those on a placebo got worse.

Images of the brain showed that the drug had its biggest effect in the parts of the brain linked to memory, where the density of tau tangles is greatest. The drug works by dissolving the tau fibres and prevents a build-up of the tangles.

The team at Aberdeen hopes to carry out the final "phase 3" trial next year, involving a larger group of people with the disease. If that trial proves successful, the drug could be available by 2012.

The society said: "Larger trials of the best dose are still needed to establish the benefit and safety of this compound, so this is still at least five years away from being a treatment that is available for people with Alzheimer's disease."

It added: "About 700,000 people in the UK have a form of dementia and more than half have Alzheimer's disease. In less than 20 years nearly 1 million people will be living with dementia, rising to 1.7m by 2051."

Case history

Sandra Sutherland had been struggling to focus on her job in accounts for many years when she was diagnosed with Alzheimer's. The 61-year-old, who lives with her husband, Ian, and two sons in the west end of Aberdeen, was diagnosed with the disease in 2005.

"I was absolutely gobsmacked," said Sutherland, now retired. She started on a trial of rember two years ago and believes the medication has helped her. "I feel more confident, more positive. I think my concentration has levelled off and not got any worse."

Her husband added: "Sandra still has days when she is not great, but ... it would appear that the medication is working."