Toxicology/original researchOutcomes of Emergency Department Patients Presenting With Adverse Drug Events
Introduction
Adverse drug events are untoward and unintended events arising from the use or misuse of medications.1 They represent the most common cause of preventable nonsurgical adverse events in medicine.2, 3, 4, 5 Adverse drug events limit the therapeutic benefit of medications, are associated with additional health resource utilization, and are the fourth to sixth leading cause of death in the United States.4, 6, 7, 8, 9, 10, 11, 12 It has been estimated that between 3% and 24% of hospital admissions are due to adverse drug events and that 30% of inpatients experience an adverse drug event as an unexpected complication of therapy.4, 13, 14 Studies quantifying health resource utilization and cost attributable to inhospital adverse drug events have estimated an excess length of hospital stay of 1.9 to 2.2 days. Their attributable cost, converted to 2008 Canadian dollars for ease of comparison, was estimated at $3,034 to $4,352 (Can $1=US $1) per event.7, 8, 15 Extrapolating these numbers, the national burden associated with inhospital adverse drug events has been estimated at more than 1.5 million hospital days, leading to hospital costs in 2008 dollars of $2.2 to $5.6 billion annually.7, 8
Daunting as these estimates are, they do not take into account the public health burden arising from medication use among nonhospitalized patients. The associated burden is expected to be large, and to increase farther, as outpatient medication use increases because of an aging population, a trend toward outpatient health care delivery, increasing chemoprevention, and improved access to medications through over-the-counter availability and legislation improving drug coverage.16, 17 Quality improvement efforts and technological advancements aimed at preventing outpatient adverse drug events will require large investments in infrastructure and technology. Therefore, documentation of their effect must be provided to guide administrators, policymakers, and the public in priority setting.
We are aware of only 2 studies that have assessed the effect of outpatient adverse drug events on health services utilization and cost, both of which found increased adjusted health care costs associated with adverse drug events.18, 19 However, health outcomes and cost of care of patients presenting to the emergency department (ED) with an outpatient adverse drug event have never been studied, despite that outpatient adverse drug events are among the most common reasons for adult ED visits.20, 21, 22
The objectives of this study were to document the mortality, health services utilization, and cost of care for patients presenting to the ED with an adverse drug event within 6 months of the index visit and to compare these with outcomes of patients who present to the ED for other reasons.
Section snippets
Study Design and Setting
This was an a priori planned substudy of a large prospective observational study examining the incidence of drug-related ED visits.21 This study was conducted at Vancouver General Hospital, a 955-bed adult tertiary care referral and teaching hospital with an annual ED census of 75,000 patients in British Columbia, Canada. The University of British Columbia Clinical Research Ethics Board approved the study protocol.
Selection of Participants
Patients presenting to the ED between March 13 and June 4, 2006, were eligible
Results
Of 1,000 patients meeting inclusion criteria, 122 (12.2%; 95% confidence interval [CI] 10.3% to 14.4%) received a diagnosis of an adverse drug event–related ED visit (Figure 2). Of these events, 48 (39.3%) were due to an adverse drug reaction and 34 (27.9%) were due to nonadherence. Details of all adverse drug events have been published and are included in Table E1, Table E2 (available online at http://www.annemergmed.com).21, 36 The majority of events, 103 of 122 (84.4%; 95% CI 76.9% to 89.8%)
Limitations
Several limitations should be considered when our results are interpreted. Even though we enrolled 1,000 patients, 122 patients received a diagnosis of an adverse drug event and 48 patients of an adverse drug reaction. Because of this, the SEMs on regression coefficients are large, leading to wide CIs. In addition, this study was conducted at 1 tertiary care center, limiting its generalizability to similar centers.
An element of subjective judgment is inherent in the diagnosis of adverse drug
Discussion
ED visits related to adverse drug events arising from outpatient medications were associated with high subsequent health services utilization and cost. Patients presenting with an adverse drug event spent 2.4 to 7.8 additional days in the hospital during the 6-month follow-up period compared with patients presenting to the ED for other reasons. The adjusted odds of spending additional days in the hospital were 51% greater for patients presenting with adverse drug events. When we stratified our
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Funding and support: By Annals policy, all authors are required to disclose any and all commercial, financial, and other relationships in any way related to the subject of this article as per ICMJE conflict of interest guidelines (see www.icmje.org). Dr. Hohl was supported by a Mentored Clinician Scientist Award, and Dr. Brubacher by an Established Clinician Scientist Award from the Vancouver Coastal Health Research Institute. The Michael Smith Foundation for Health Research provided infrastructure funding for this study, and the Department of Surgery at the University of British Columbia provided operating funds.
Please see page 271 for the Editor's Capsule Summary of this article.
Supervising editor: Richard C. Dart, MD, PhD
Publication date: Available online February 26, 2011.
Author contributions: CMH and PJZ acquired the data. CMH, BN, LK, and BS were responsible for analysis and interpretation of data. CMH drafted the article. BN, LK, and BS were responsible for statistical analysis. CMH, PJZ, JRB, RBA-L, and SBS obtained funding. CMH, LK, PJZ, and BS were responsible for administrative, technical, and material support. CMH supervised the study. All authors were responsible for study concept and design and critical revision of the article for important intellectual content, had full access to all the data in the study, and take responsibility for the integrity of the data and the accuracy of the data analysis. CMH takes responsibility for the paper as a whole.
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