A CBC News investigation reveals that Canadian seniors account for 44 per cent of adverse drug reactions causing death that are reported to Health Canada, even though they make up just 13 per cent of the population.

• INDEPTH: Prescribed to Death - Seniors and drugs

CBC's analysis of Canada's adverse drug reaction database, obtained from Health Canada under Access to Information laws, suggests up to 16,500 elderly patients have died due to suspected drug reactions in the last five years.

"The way it's been calculated by CBC I think is quite cautious and is realistic," said Dr. Jim Wright, a clinical pharmacologist who studies the adverse effects of drugs. He's also the managing director of the Therapeutics Initiative at the University of British Columbia.

Older people are more vulnerable to drug reactions partly because they use more drugs than the general population. Seniors are also more vulnerable because they metabolize and excrete drugs more slowly.

But when drugs are being developed, they're rarely tested in seniors, so their effects can be a surprise, says Dr. Robyn Tamblyn, an epidemiologist and researcher at McGill University.

o Dr. Chris MacKnight, one of only 200 Canadian geriatricians.

"When a drug is approved to come into the market, you're almost in an experimental situation when you're trying it out on people for which it was never tested," said Tamblyn.

Tamblyn says that in a given year, nearly one in 10 seniors who take drugs will have a reaction serious enough to put them in hospital.

In most cases she says it's a result of inappropriate prescribing: the wrong drug, the wrong dose, the wrong combination of drugs, or even unreadable handwriting on prescriptions that leads to mistakes.

Canadian Medical Association president Albert Schumacher

But people are also living longer, in general, according to Dr. Chris MacKnight, one of only 200 Canadian geriatricians, doctors who specialize in treating the elderly.

That means it's more common to live with several chronic conditions, each of which might require its own medication.

MacKnight sees problems created by these multiple prescriptions in the people he treats at the Camp Hill Veterans Memorial Hospital in Halifax.

"The patients we see in the emergency room, probably 75 to 80 per cent of them, have a medication involved in their problem. They've almost always been started on something recently that they've [reacted badly] to," said MacKnight, who's also the president of the Canadian Geriatrics Society.

Drugs to avoid

One tool to help physicians avoid such problems is a study known as the Beers list, which outlines drugs seniors should generally avoid because they are either ineffective in the elderly or put seniors at an unnecessarily high risk when safer alternatives are available.

Last updated in 2003, lead author Donna Fick calls the peer-reviewed list the most user-friendly way for doctors to identify inappropriate drugs for seniors.

Although general practitioners write about 80 per cent of prescriptions, most, including Canadian Medical Association president Albert Schumacher, don't know about or use the Beers list.

Schumacher says he's not alarmed by the number of deaths attributed to Beers list drugs. He says doctors try to balance risk and benefit when they prescribe.

"No it doesn't necessarily raise alarms because, remember, with seniors we're dealing with many life-threatening illnesses," he said.

CBC found that in 2004, 1.5 million Canadian seniors – more than one-third – were given drugs that are either ineffective in the elderly or put seniors at an unnecessarily high risk when safer alternatives are available. This figure was arrived at using data provided by Brogan Inc., a health-care data and research company based in Ottawa.

MacKnight says family doctors are in a tough position when it comes to prescribing for seniors, and they need tools and training to help them do it more safely.

Health researchers like Donna Fick believe a good start would be for doctors to familiarize themselves with the Beers list.