Emergency department visits for outpatient adverse drug events: Demonstration for a national surveillance system

Study objective: This project demonstrates the operational feasibility and epidemiologic usefulness of modifying a national injury surveillance system for active surveillance of outpatient adverse drug events treated in hospital emergency departments (EDs). Methods: Coders were trained to identify and report physician-documented adverse drug event's in 9 of 64 National Electronic Injury Surveillance System-All Injury Program hospital EDs (occurring July 17, 2002, to September 30, 2002). Feasibility was measured by timeliness and completeness of adverse drug event reporting. Outcomes (ED discharge disposition and injury type) and associated variables (age, sex, drug category, and adverse drug event mechanism) were measured. Results: There were 598 patients with physician-documented adverse drug events (7 per 1,000 visits). Nearly 70% of adverse drug event cases were reported within 7 days of the ED visit; key data elements (drug name, disposition from ED, and event description) were completed for more than 98% of cases. Nine percent of patients with adverse drug events were hospitalized, and unintentional overdoses was the most common mechanism of adverse drug events (39%). Patients with unintentional overdoses were more likely to be hospitalized than those with adverse drug reactions (adjusted odds ratio [OR] 5.9, 95% confidence interval [Cl] 2.2 to 16; adverse-effects referent; allergic reactions, adjusted OR 0.7, 95% Cl 0.2 to 2.4). Warfarin and insulins were associated with 16% of adverse drug events overall and 33% of-adverse drug events in patients aged 50 years or older. Conclusion: Active surveillance for outpatient adverse drug events using the National Electronic Injury Surveillance System-All Injury Program is feasible. Ongoing, population-based ED surveillance can help characterize the burden of outpatient adverse drug events, prioritize areas for further research and intervention, and monitor progress on adverse drug event prevention.