09/16/2013 11:48 EDT | Updated 11/16/2013 05:12 EST

Alzheimer's drugs may harm people with mild memory issues

Drugs to treat Alzheimer's disease don't help patients with mild cognitive impairment and are linked to greater risk of harm, a Canadian review concludes.

People with mild cognitive impairment show symptoms of memory problems that are not severe enough to be considered dementia or to interfere with day-to-day functioning. Each year, three to 17 per cent of people with mild cognitive impairment deteriorate to dementia, research suggests.

It was hoped that "cognitive enhancers" used to treat dementia might delay progression to dementia.

Dr. Sharon Straus of the department of geriatric medicine at the University of Toronto and her team reviewed clinical trials and reports on the effects of four cognitive enhancers.

"Cognitive enhancers did not improve cognition or function among patients with mild cognitive impairment and were associated with a greater risk of gastrointestinal harms," the reviewers concluded in Monday's issue of the Canadian Medical Association Journal.

"Our findings do not support the use of cognitive enhancers for mild cognitive impairment."

The medications act on different neurotransmitters in the brain, such as acetylcholine. The drugs are:

- Donepezil (Aricept).

- Rivastigmine (Exelon).

- Galantamine (Reminyl).

- Memantine (Ebixa).

Straus says patients and their families are increasingly requesting the medications and she suspects that some of the off-label prescriptions are for mild cognitive impairment, a use that Health Canada hasn't officially approved.

The trials were done between 1999 and 2007 in North America, Europe, New Zealand, Australia, South America, Israel and Turkey. All the studies compared cognitive enhancers with placebos. The average age of the patients ranged from 66 to 73.

Cognitive enhancers improved cognition on a tool called the Alzheimer's Disease Assessment Score after 12 to 84 weeks, but there was no difference after that, the reviewers found.

The meta-analysis showed patients taking the medications experienced more nausea, diarrhea, vomiting and headaches than those taking placebos. One study found a higher incidence of bradycardia, or slow heart rate, among patients taking galantamine.

"Patients and their families should consider this information when requesting these medications. Similarly, health care decision-makers may not wish to approve the use of these medications for mild cognitive impairment, because these drugs might not be effective and are likely associated with harm," the authors advised.

They also suggested longer-term trials to ensure accuracy of results beyond 84 weeks of followup.

The Canadian Consensus Conferences on the Diagnosis and Treatment of Dementia have also not been recommending acetylcholinesterase inhibitors for mild cognitive impairment.

The review was funded by the Drug Safety and Effectiveness Network /Canadian Institutes of Health Research.