Repeat Exposures to Culprit Drugs Contribute to Adverse Drug Events in Emergency Departments

Corinne Hohl, Johanna Trimble

Corinne Hohl, Johanna Trimble


Adverse drug events (ADEs), unintended and harmful events associated with medications, cause or contribute to 2 million annual emergency department (ED) visits in Canada. Australian data indicate that 27% of ADEs requiring admission may be events caused by re-exposure to drugs that previously caused harm. Our main objective was to estimate the frequency of repeat ADEs.


We reviewed the charts of ADE patients who had been enrolled in 1 of 3 prospective studies conducted in 2 tertiary care and 1 urban community ED. In the parent studies, researchers enrolled patients by applying a systematic selection algorithm to minimize selection bias, and physicians and pharmacists evaluated patients prospectively to evaluate the causal associations between the drug regimens and patient presentations. After completion of the parent studies, a research pharmacist and a physician independently reviewed the charts of ADE patients, abstracting data using electronic forms, and searched that hospital’s records for previously recorded ADEs. The main outcome was a repeat ADE, defined as a same or same-class drug re-exposure, or repeat inappropriate drug withdrawal, causing a same or similar presentation as a prior ADE. Sample size was based on enrolment into the parent studies.


We reviewed the charts of 614 ED patients diagnosed with 655 ADEs. Of these, 20% (133/665, 95%CI 17.0-23.0%) were repeat events. Most repeat ADEs were moderate (61%) or severe (32%) in nature, and 33% (95%CI 25.1-41.1%) required hospital admission. The most commonly implicated drugs were warfarin (10%), hydrochlorothiazide (4%) and insulin (4%), and the most commonly implicated drug classes were antithrombotics (17%), psychotropics (12%) and analgesics (9%). Repeat ADEs commonly required clinical monitoring (59%), additional medications to treat the ADE (50%) and follow-up lab testing (35%). Re-exposures were deemed potentially or definitely inappropriate in 61% of repeat events (95%CI 51.3-70.7%).


Repeat ADEs due to inappropriate re-exposures to medications that previously caused harm constitute a large proportion of ADEs, and may represent an ideal target for prevention. Our study was limited by our inability to search for repeat ADEs in the records of other hospitals that our patients may have visited, and therefore, it is likely we underestimated the true frequency of repeat ADEs.