One in 200 Canadian seniors had to be admitted to hospital because of adverse reaction to a drug, according to a new report.

Tuesday's report by the Canadian Institute of Health Information (CIHI) suggested more than 26,000 people aged 65 and older experienced an adverse effect of a drug that was given at the correct dose in 2010-2011.

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The number of drugs a senior takes is one of the risk factors for adverse reactions. (Stew Milne/Associated Press)

Since 2006, the rate of hospital stays related to adverse events remained relatively stable as a proportion of all hospital stays for seniors, the report's authors said.

Blood thinners, often used to prevent heart attack and stroke, were the class of drugs most commonly associated with reactions like bleeding, at 12.6 per cent. Most of the bleeds were among people taking warfarin, a drug that needs to be closely monitored with blood tests to adjust the dose immediately if too high or too low.

Next were chemotherapy drugs, 12.1 per cent, and opioid painkillers at 7.4 per cent. Low white blood cell count from  chemotherapy drugs and constipation from opioids were the most likely reasons for hospital stays based on drug classes.

"In some cases, other drugs can be given or diet changes can be recommended to avoid or reduce the risk of constipation, for example," said Jordan Hunt, CIHI's manager of pharmaceuticals in Ottawa. "But it's really starting at that low dose and working your way up to find the balance between pain relief and side-effects."

Michael Gaucher, the institute's director of pharmaceuticals and health workforce information services, said while it's often appropriate for people to be using these medications, seniors, their caregivers and health professionals should manage the risks.

To minimize the risk, seniors should regularly review medications, including those taken without a prescription, with their doctor and pharmacist and let them know about any changes, geriatricians recommend.

The report's authors suggest the electronic drug information systems rolling out in provinces could also help provide more complete information on patients' medications.

Costs $35.7M a year

In the study, it was common to change the dose of blood thinners and opioids after a hospital stay related to adverse drug reactions (ADRs).

Last year, researchers at the Institute for Clinical Evaluative Sciences estimated that emergency department visits and hospital admissions due to adverse drug reactions among seniors in Canada cost an estimated $35.7 million. More than 80 per cent of those costs were related to hospital care.

A patient's age and sex, other illnesses, number of drugs, number of pharmacies visited, number of prescribers and hospitalizations are known to increase the risk of adverse drug reactions.

Over the same study period, one in 1,000 Canadian non-seniors had an ADR-related hospitalization. 

The report's authors said the hospital data they looked back on likely underestimated the prevalence since data could be missing or inaccurately recorded. The drug-claims data used in the analysis came from a national database on prescription drug use based on linkable data from Alberta, Manitoba and P.E.I.

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

Top 10 drug classes associated with seniors' ADR-related hospitalizations 2006-2011

Drug class                      

Common use    Most common diagnosis related to hospitalization Percentage of ADRs
AnticoagulantsHeart attack and stroke preventionHemorrhagic disorder (bleeding) due to circulating anticoagulants12.6%
Antineoplastic drugsCancerNeutropenia (low white blood cell count)12.1%
Opioids and related analgesicsPain managementConstipation7.4%
Glucocorticoids and synthetic analoguesAsthmaChronic obstructive pulmonary disease with acute lower respiratory infection6.9%
NSAIDs (non-steroidal anti-inflammatory drugs including salicylates)Arthritis, pain management, inflammationGastric ulcer, chronic or unspecified with hemorrhage (bleeding)4.9%
Beta-adrenoreceptor antagonists, not elsewhere classifiedHeart failure, high blood pressure, angina (chest pain)Bradycardia (low heart rate), unspecified4.6%
Other (non-thiazide, low-ceiling) diureticsHeart failure, high blood pressureHypo-osmolality and hyponatremia (low blood sodium)3.6%
Benzothiadiazine derivatives (thiazide diuretics)High blood pressureHypo-osmolality and hyponatremia (low blood sodium)3.2%
Cardiac-stimulant glycosides and drugs of similar action (e.g. digoxin)Heart failure, arrhythmia (irregular heartbeat)Bradycardia (low heart rate), unspecified3.1%
AntipsychoticsSymptoms of dementia, schizophrenia, bipolar disorderDisorientation, unspecified2.7%
Source: CIHI
With files from The Canadian Press