A combination of two common antibiotics may help delay symptoms of Alzheimer's disease, research shows.
Alzheimer's is set to increase
A team from McMaster University in Canada treated patients either with doxycycline and rifampin, or dummy pills for three months.
Those given antibiotics showed significantly less mental decline.
Experts warn that a 101-patient study is too small to draw firm conclusions.
Canadian researchers say more work is needed to replicate their findings.
But they say their results indicate that antibiotic treatment produces results comparable with currently available treatments - which only work for around half of all patients.
Lead researcher Dr Mark Loeb said: "The antibiotic regimen might allow a person suffering from Alzheimer's disease to remain home and avoid having to go to a nursing home or other institution, at least for a period of
There is a theory that a common bacterium that causes pneumonia might play a role in causing Alzheimer's.
But the antibiotic treatment did not lead to as significant a reduction in bacteria levels as might have been expected.
Dr Leob suggested the antibiotics may work by interfering with the build-up of plaques around brain cells that are a hallmark of Alzheimer's.
He said it was also possible that the anti-inflammatory effects of the antibiotics are critical.
The trial found that mental scores of those in the placebo group declined by an average of 2.75 points more over six months than those who received the antibiotic, out of a 70-point scale.
At 12 months, there was still a difference between the groups, but it was not considered significant.
Dr David Wilkinson, of the UK Alzheimer's Research Trust, said more research was required before any firm conclusions could be drawn.
However, he told BBC News Online: "There is a clear understanding by doctors in this field that infections like flu can worsen Alzheimer's disease and cause confusion even in some elderly people without obvious signs of dementia.
"One theory is that the changes in the brain in Alzheimer's cause the immune response of the brain to be very sensitive to the chemicals the body produces when dealing with new infections, and to overreact causing even more damage to the brain.
"Damping down this response by the use of anti-inflammatory drugs or, as in this case, by the early or prophylactic treatment of infections could be one way of lessening the effects of the disease and slowing the decline."
However, Dr Wilkinson warned that overuse of antibiotics was a serious concern, as bacteria were increasingly developing resistance to current drugs.
He said that if the theory proved to be correct, then alternative ways to dampen down the immune response would be preferable.
Dr Susanne Sorensen, head of research for the UK Alzheimer's Society, agreed that it would not be desirable to increase the use of antibiotics.
She said: "We still don't really know what triggers Alzheimer's, or all the processes that progress the disease."
Details of the research were presented at a meeting of the Infectious Diseases Society of America.