In a CMAJ editorial, Namrata Bains and Duncan Hunter used hospital separation and mortality data to estimate that 0.05% of in-hospital mortality is associated with coded adverse drug reactions. [1] They extrapolated their data to rank mortality associated with adverse drug reactions as the 19th leading cause of death in Canada. This contrasts with the findings of Lazarou and colleagues, [2] who ranked adverse drug reactions as between the 4th and 6th leading cause of death in the US (106 000 deaths per year).
The fundamental issue is whether coding adverse drug reactions in the medical record provides reliable and valid data on the true numbers of adverse drug reactions. Several studies have shown that self-reporting only identifies 5% of events. [3–5] Daily chart review and solicited reporting have detected 5 times as many adverse drug reactions as coding. [6]
Methodologically, the first stage involved in linking a drug to an incident is the screening and correlation of an adverse clinical event to a specific drug. Thus, an adverse drug event only indicates suspected incidents, not causation. [6] Detection is better using a combination of complementary methods. [4, 7] Next, the probability of a drug causing the event is determined, and then the incident is classified as an adverse drug reaction, [8] using systematic criteria such as the algorithm of Naranjo and colleagues. [9]
The annual number of deaths due to adverse drug reactions in Canada can be estimated using the 1:10 ratio of the population of Canada to that of the US. Bates and colleagues reported that 76 000 deaths are due to adverse drug reactions annually in the US. [6] This estimate would rank adverse drug reaction fatalities as the 7th leading cause of death in Canada, after cancer, heart disease, stroke, pulmonary disease and accidents, using 1995 Statistics Canada data.
Adverse drug reactions prolong hospital stay by an average of 4.6 days in Canada, costing Can$300 million annually. [10] If one-third of adverse drug reaction deaths are preventable, [2, 6] then we should ensure that research dollars are used to minimize this problem.
David Rosenbloom, PharmD
Christine Wynne, BSc Phm
McMaster University Medical Centre; Hamilton, Ont.