Reinitiating Warfarin: Relationships Between Dose and Selected Patient, Clinical and Hospital Measures

Warfarin is approved for long-term anticoagulation management for treatment and prevention of thromboembolic events.1,2 Patients may require temporary discontinuation of warfarin before undergoing surgical and non-surgical procedures to allow their international normalization ratio (INR) to return to baseline to decrease the risk of bleeding.3–5 Following the medical procedure or period of increased bleeding risk, patients requiring long-term therapy may be restarted on a standard institutional dose, their previous dose, or a higher or lower dose, based on clinical judgment. During the past 15 years, many institutions, including Marshfield Clinic, have developed a separate outpatient department whose sole purpose is to manage patients’ anticoagulation. At the Marshfield Clinic, this department is called the Anticoagulation Service (ACS), also known as the “Coumadin Clinic.” Patients can go to the ACS Monday through Saturday to have their blood drawn, INR measured, and warfarin dose adjusted if needed. However when a patient is hospitalized his or her anticoagulation management becomes temporarily the responsibility of a physician, most typically a general internist, specialist, or hospitalist. Despite vast literature on warfarin initiation and management, to our knowledge, optimal strategies for reinitiation after temporary discontinuation of warfarin has not been developed or standardized across medical institutions.3,5 Only one case series with 36 patients attempted to answer this question, using time to therapeutic INR as the primary outcome.6 Strategies for warfarin reinitiation are not discussed in the American College of Physician guideline for warfarin managment.8 Given the limited study results available, we undertook this retrospective, observational study to investigate dosing patterns during warfarin reinitiation and their impacts on clinical measures normally assessed in warfarin management. Because our study subjects had been previously stabilized on a warfarin dose, we were especially interested in examining and characterizing relationships between reinitiation dose and prior stable dose, examining trends in reinitiation dose decisions that might result from advances in electronic health records and physician support tools, and through review of physician notes and other data, exploring if there were common patient characteristics and/or conditions that were systematically associated with reinitiation dose.