TORONTO - A drug in a potential new class of Alzheimer's medications showed promise in people with mild dementia, a new British and Canadian study suggests.

If further studies, which are well underway, confirm those findings, the drug - tarenflurbil or Flurizan - could be among the first that actually slows or even halts progression of the mind-robbing disease, experts predict. Currently available Alzheimer's drugs only mitigate the symptoms of the disease, and are only effective in some people.

"What this study showed was that in a preliminary trial - the numbers are small - nevertheless there were some pretty impressive differences," said Dr. Sandra Black, one of the authors and a neurologist at Toronto's Sunnybrook Health Sciences Centre.

This study was what is called a Phase 2 trial, one designed to get early answers about whether a drug seems to work and at what dose. Drugs that are effective at this stage are then tested in the larger Phase 3 trials that are needed to persuade regulatory agencies to license the medication.

The Phase 3 trial for tarenflurbil is expected to be published either this summer or in the autumn.

Black, who specializes in the interaction between stroke and Alzheimer's, said she is guardedly optimistic it and another larger study also underway will confirm that the drug is useful if given in the early stages of the disease.

"I'm hopeful but cautiously hopeful. Because until it's been tried out in a bigger sample, you just can't know," she said in an interview.

"I think the concept is if you get to people earlier with . . . less destruction of the brain, then you have more of a chance to stabilize and maybe even begin to reverse things."

Others in the field shared her cautious optimism about tarenflurbil after studying the results of the trial, published Wednesday in the journal Lancet Neurology.

"The fact that they got any benefit is, in a sense, impressive and intriguing and certainly tantalizing. And I think cautiously optimistic is an appropriate way to interpret this," said Dr. Howard Chertkow, director of the Bloomfield Centre for Research in Aging at Montreal's Jewish General Hospital.

Because of the way the drug works, it wouldn't have been surprising if the study failed to show an effect in the people being tested, Chertkow said. That's because trial participants already had mild or moderate Alzheimer's disease when they started on the medication.

The drug blocks formation of amyloid beta-42, a protein that creates the so-called amyloid plaques in the brain that are a hallmark of Alzheimer's disease. The plaques are known to be toxic to brain tissue and it's thought that the accumulation of these plaques - along with other brain changes - are what causes Alzheimer's.

While it is the leading theory of what causes the disease, it is still only a theory.

"If that is the cause of Alzheimer's disease and if this medication can block or prevent that to a significant degree without causing intolerable side-effects ... then in theory that could prevent or stop or perhaps even reverse the disease," Chertkow said.

"But that's a sentence with a lot of ifs."

The creation of amyloid plaques in the brain is a process that starts years before people who go on to develop Alzheimer's show symptoms. Starting treatment once a person is already symptomatic may be like closing the barn door after the horse bolts, experts say.

The results of the trial support the notion that the drug must be administered early, said Dr. Paul Verhoeff, a clinician-scientist at the Kunin-Lunenfeld Applied Research Unit at Baycrest, a University of Toronto teaching hospital that specializes in studies of aging.

The Phase 2 trial found people with mild Alzheimer's who were on a high dose of the drug scored significantly better on tests gauging their functional abilities when compared to people on placebo. People on a lower dose of the drug or people with moderate Alzheimer's did not show the same benefit.

"There seems to be a magic window, again pointing out that you probably have to be there fairly early in the disease to get the maximum bang for your buck," Verhoeff said.

Neither Verhoeff nor Chertkow were involved in the study, which was paid for by tarenflurbil's manufacturer, Myriad Pharmaceuticals.

Even those who did show benefit didn't score higher on cognitive tests - tests in which they might have been asked to remember words or list as many animals as they could think of, for example. The gains seen related to their ability to function, a critical part of prolonging independent life.

"It means that people were continuing to be able to do the things that they started off being able to do, and they didn't lose their abilities as quickly as the patients on the lower dose or on placebo," Black said.

"So that would translate into somebody who might still be able to look after finances. Or somebody might still be able to drive. Or somebody might still be able to take part in hobbies. Or even do part time work - that sort of thing."