Outcomes of Emergency Department Patients Presenting With Adverse Drug Events

Study objective

Our objectives are to describe the outcomes of patients presenting to the emergency department (ED) because of an adverse drug event and to compare them with outcomes of patients presenting for other reasons.

Methods

This prospective observational study was conducted at Vancouver General Hospital, a 955-bed tertiary care hospital. We prospectively enrolled adults presenting to the ED between March and June 2006, using a systematic sampling algorithm. Pharmacists and physicians independently evaluated patients for adverse drug events. An independent committee reviewed and adjudicated cases in which assessments were discordant or uncertain. Data from the index visit were linked to vital statistics, administrative health services utilization, and cost of care data.

Results

Of 1,000 patients, 122 (12.2%; 95% confidence interval [CI] 10.3% to 14.4%) presented to the ED because of an adverse drug event. Of these, 48 presented because of an adverse drug reaction (one type of adverse drug event defined as an unintended response that occurred despite use of an appropriate drug dosage). We found no difference in mortality among patients presenting with and without adverse drug reactions (14.6% versus 5.9%; hazard ratio 1.57; 95% CI 0.70 to 3.52). After adjustment, patients with adverse drug events had a higher risk of spending additional days in the hospital per month (6.3% versus 3.4%; odds ratio 1.52; 95% CI 1.43 to 1.62) and higher rate of outpatient health care encounters (1.73 versus 1.22; rate ratio 1.20; 95% CI 1.03 to 1.40). The adjusted median monthly cost of care was 1.90 times higher (Can $325 versus $96; 95% CI 1.18 to 3.08).

Conclusion

ED patients presenting with an adverse drug event incurred greater health services utilization and costs during a 6-month follow-up period compared with patients presenting for other reasons.

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.