Alzheimer's drugs which are currently being denied to some NHS patients may have a dramatic impact on the pathology of the brain according to researchers in the UK. Campaigners are fighting to get cholinesterase inhibitors, which have been rejected for use in mild cases of Alzheimer's, available on the NHS after post-mortems showed that they found a 70% fall of a protein linked to dementia in those who had taken them.

Post-mortem examinations were done on 12 patients who took part in UK trials of the drugs - donepezil, rivastigmine, tacrine and galantamine. Professor Clive Ballard, director of research at the Alzheimer's Society, and his colleagues measured the concentrations of two proteins associated with the build up of plaques found in the brains with people with dementia. These results were then compared with 12 patients studied before cholinesterase drugs were available.

Deposits of one of the proteins, beta amyloid, which is linked to dementia, in the plaques were 70% lower in the brains of people who received the drugs in the trial. Professor Ballard said: "We knew there may be some reduction in the levels of beta-amyloid among people prescribed cholinesterase drugs, but the sheer magnitude of the reduction was a real surprise. The study looked at dementia with Lewy bodies but beta-amyloid is also a hallmark in Alzheimer's disease. The results suggest that if we want to slow down the progression of these diseases the earlier we start prescribing these treatments the better."

Guidance from the National Institute for Health and Clinical Excellence (NICE) in 2001 recommended that donepezil, rivastigmine and galantamine should be used as standard in cases of dementia but in November 2006 the watchdog announced people with newly diagnosed, mild Alzheimer's would be exempt. The Alzheimer's Society is set to go to the High Court next month as part of a judicial review of the decision and this research forms the basis of its campaign to see the drugs made available on the NHS.

Neil Hunt, chief executive of the Alzheimer's Society, added: "People with Alzheimer's disease and their carers have known about the life-changing benefits of these drugs for some time now and this study provides the first hard evidence of the physical benefits of the same treatments."

The study was also backed by Rebecca Wood, chief executive of the Alzheimer's Research Trust, who said: "Although the scientists looked at Lewy Body disease rather than Alzheimer's, the two conditions have much in common and this study shows how a class of drugs, restricted by NICE for so-called performance reasons, do help to prevent the physical progression of dementia."

However, Dr Declan McCloughlin, senior lecturer in the Medical Research Council Centre for Neurodegeneration, said there could be other explanations for the findings. "This is a very interesting but preliminary finding which could have happened by chance because the sample groups are small. We know from clinical trials the drugs have modest benefits and so if they have an effect on the underlying molecular pathology it's not a very big effect. But is shows there may be some improvement in one of the key pathologies of the disease."