Oral anticoagulation in the hospital: analysis of patients at risk.

Warfarin is one of the most commonly used medications associated with adverse events. Warfarin therapy is often initiated or continued in the hospital, yet hospitalization increases the risk of poor anticoagulation control with warfarin. To help understand this, we retrospectively reviewed the records of patients admitted to our hospital during a 6-month period who were given at least one dose of warfarin. To explore factors that may have contributed to poor anticoagulation control, we compared characteristics of patients with an international normalized ratio (INR) ≥ 5 at some point during hospitalization with those of a group of matched controls who also received warfarin and had INR <5. Among the 35 patients identified who had an INR ≥ 5, concomitant use of antibiotics was more common than among 105 matched controls; improper warfarin dosing also appeared to contribute to the high INRs. These findings indicate possible targets for intervention to improve patient safety.