Irish biotech group Elan has said initial trials for an experimental Alzheimer's drug have reduced a key protein associated with the disease.

The Lancet reports that Elan's bapineuzmab reduced the amount of beta amyloid in the brain by 25 percent.

The 18-month PET-PIB study also showed that it was possible to use advanced imaging technology to monitor the effects of potential treatments for Alzheimer’s disease.

Until now, such effects could only be determined at autopsy.

Elan says the trial was too small to provide solid evidence of efficacy and safety but that the treatment was generally well tolerated.

The scientists behind bapineuzumab hope it will be the first drug to treat the underlying cause of Alzheimer's.