Lilia Malkin, BSc

Adverse drug reactions (ADRs) account for a significant proportion of morbidity and mortality in the geriatric population. According to the 1993 Canadian Medical Association (CMA) Policy Summary, over 20 percent of acute care hospital admissions of Canadian seniors may result directly from ADRs. Other studies have reported the incidence of ADR-related admissions ranging from 8 to 35 percent.

The World Health Organization (WHO) defines an adverse drug reaction as "a noxious, unintended effect of a drug that occurs in doses normally used in humans for the diagnosis, prophylaxis, or treatment of disease." ADRs can be divided into two categories: predictable (Type A) and unpredictable (Type B). Predictable reactions make up the vast majority of ADRs at 80 percent. Type A reactions are frequently dose-dependent and related to the augmented pharmacologic action of the medication: toxicity, side effects, indirect effects, and drug interactions. Unpredictable ADRs are less common, and include intolerance, allergy or hypersensitivity, idiosyncrasy, and psycho-genic reactions. Recognition of the pertinent risk factors for both predictable and unpredictable ADRs has direct application to ADR prediction, prevention, and management in the geriatric population.

ADR Prediction: Risk Factors

Older Canadians have a four- to seven-fold higher risk of suffering an ADR compared to younger individuals. According to Dr.