Researchers in the U.S. say a drug which was at one time used to treat hay fever "significantly improves" symptoms in patients with mild to moderate Alzheimer's disease.
The drug Dimebon was once licensed in Russia as an antihistamine but was withdrawn from the market when more effective drugs became available.
The researchers found in a trial of 183 Russians, all with untreated mild to moderate dementia, that Dimebon improved memory, behaviour and the ability to conduct simple activities.
In the trial half of the participants were given 20 mg of Dimebon 20 three times a day while the others were given a look-a-like placebo.
After a six month period, all were given tests such as memorising a list of words and performing simple tasks and the research team found that those taking the drug scored four points lower on a scale designed to measure the severity of Alzheimer's disease, which indicated they were less badly affected.
Patients taking the drug performed better than they did at the start of the study while those on the placebo deteriorated over the six-month period.
Alzheimer's disease causes brain cells to be killed by a build up of toxic plaques and tangled proteins, leading to forgetfulness, mood swings, dementia and death and the researchers suspect the drug halts the brain-rotting plaques of the disease.
There are currently no approved therapies for mild to moderate Alzheimer's disease which have shown increasing improvement over 12 months and experts have expressed cautious optimism about these latest results.
Study leader Dr. Rachelle Doody, says in a smaller group of patients who continued with the trial for a further six months there was an even greater seven-point gap between those on Dimebon and those on the placebo.
Dr. Doody from Baylor College of Medicine in Houston, Texas, says while it is not clear exactly how the drug works, in animals it has been shown to have a protective effect on nerve cells in the brain.
Dr. Doody says the results are encouraging and the ongoing improvement seen in the study was particularly important.
Experts say in view of the many people suffering from dementia more research was needed to replicate the results.
The research is published in the current issue of The Lancet.