Article

Annually, about 701 000 individuals treated in hospital emergency departments (EDs) in the United States suffer adverse drug events (ADEs), accounting for 6.7 % of all ED visits that result in hospitalization.1 Anticoagulants are among the most common drugs associated with preventable ADEs; they accounted for more than 36 000 ADEs treated in an ED in 2004-2005, ranking third behind insulins and opioid analgesics.1 Budnitz et al1,2 report that patients aged 65 years or older are at significantly greater risk of an ADE when compared with younger patients (relative risk [RR] = 2.4; 95 % confidence interval [CI] = 1.8-3.0) and account for approximately 177 000 ED visits annually; slightly more than 17 % of these ADEs are attributable to warfarin. Warfarin, a vitamin K antagonist widely used for the prevention and treatment of venous thrombosis, pulmo-nary embolism, and thromboembolic complications asso-ciated with atrial fibrillation and mechanical cardiac valve replacement, has been referred to as the “cornerstone of anticoagulation.”3 Despite accounting for nearly 31 mil-lion outpatient prescriptions annually, warfarin has a nar-row therapeutic range, is difficult to manage, and i