Incidence and risk of potential adverse drug interactions in the emergency room

To determine the incidence and risk factors of potential adverse drug interactions occurring in patients in the emergency department.

Survey of a random sample of medical records of elderly persons and other adults seeking care at an emergency department. The interactions were determined by a computer programme, reviewed using explicit criteria, and excluded if of uncertain or trivial clinical significance.

University Hospital Medical Emergency Department.

A total of 423 randomly selected adults seeking care at a university hospital emergency department. Attendances made by 195 persons over age 60 and 228 younger adults were evaluated. All subjects were treated on an outpatient basis.

Seventy percent of attendances led to the prescription of an added medication. In 5.4% of the attendances in which at least one medication was added, the new medication introduced a potential adverse interaction. The number of medications used at attendance was the best predictor of whether a potential interaction would occur. Additional medications prescribed in the emergency department that accounted for most of the added interactions were theophylline, macrolid antibiotics, digitalis glycosides, nonsteroidal anti-inflammatory agents, angiotensin converting-enzyme inhibitors and calcium antagonists.

Potential adverse drug interactions were more common in elderly patients because of the higher number of concurrent medications rather than age-based factors. Safeguards need to be introduced to prevent patients from receiving medications in the emergency departments that have the potential to cause adverse interactions.