Adverse reactions to the prescription drugs taken by seniors cost the health-care system more than $13.6 million in Ontario a year, a new study suggests.

In Wednesday's issue of the journal Drug Safety, researchers estimated the cost of emergency department visits and hospitalizations related to adverse drug reactions — harmful responses to drugs given at normal doses for prevention, diagnosis or treatment.

Dr. Walter Wodchis, a senior scientist at Toronto’s Institute for Clinical Evaluative Sciences, and his colleagues analyzed five linked health-care databases for people 66 and older from April 2003 to March 2008.

For 2007, the costs of adverse drug reactions were estimated in 2008 dollars at:

  • $333 per emergency department visit.
  • $7,528 per hospitalization.
  • $13.6 million in Ontario, or an estimated $35.7 million in Canada.

"Adverse drug reactions are an important public health issue that threaten the safety of drug therapy and results in significant economic burden to the health-care system," the study's authors concluded.


Computerized monitoring programs for patients taking multiple medications could help reduce adverse drug reactions. (Keith Srakocic/Associated Press)

For severe reactions, the emergency costs were almost three times higher than with mild reactions.

The average age for adverse reactions was 77, and age was a risk factor for severe adverse drug reactions (ADRs).

Taking a dozen medications

"Most of these people are on 10, 12 even more drugs," said Wodchis.

"Having three or more pharmacies involved in your care was a particularly important risk factor for having these adverse drug reactions. So not only do people have different physicians prescribing the drugs but they're filling them from different pharmacies. No one knows all of the medications that someone's on."

He added that computerized monitoring programs and programs to reconcile medications may help patients taking multiple drugs — not only those prescribed at a hospital but drugs in the medicine cabinet at home as well.

More than half of the patients, nearly 61 per cent, took 11 distinct drugs in the year before they went to emergency, the researchers found.

In 2009, about 63 per cent of Canadians aged 65 and older took five or more prescription drugs from different drug classes, with 23 per cent taking 10 or more, according to the Canadian Institute for Health Information.

CIHI said that in the same year, about one in 10 Canadian seniors was taking a drug from the Beers list — an internationally recognized list of prescription drugs considered potentially inappropriate for use by seniors. Use of those drugs declined over the past decade.

Over the study period, the incidence of emergency visits for adverse drug reactions was stable at about 0.75 per cent.

The incidence is lower than studies based on single hospitals, which Wodchis's team suggests could be because adverse drug reactions are underestimated using administrative databases.

The study looked back at emergency visits and hospitalizations, and data could be missing or inaccurate, the authors said.

They were unable to tell which specific drug might have caused the hospital visit.

The researchers said the findings are likely representative across Canada.

With files from CBC's Kim Brunhuber