Potential drug-drug interactions in the outpatient setting.

Background: Although medication safety research has tended to focus on inpatients, the safety of drug use among outpatients is also a concern.

Objective: We estimate the frequency of potentially interacting concomitant medication dispensing among outpatients.

Research Design: We report the number and percent of patients annually dispensed an object drug of interest (ie, warfarin, digoxin, cyclosporine, or lovastatin/simvastatin) with a potentially interacting drug among a random sample of insured adults receiving care from 10 integrated delivery systems.