Reinitiating warfarin: relationships between dose and selected patient, clinical and hospital measures.

BACKGROUND: Warfarin is an oral anticoagulant used in the long-term treatment/prevention of venothromboembolic disease. Patients undergoing elective surgical and non-surgical procedures may require temporary warfarin discontinuation followed by reinitiation after their procedure. Because little information is available regarding best methods for warfarin reinitiation, we investigated current practices to inform management decisions.
METHODS: Subjects were required to have a known and stable warfarin dose prior to discontinuation, which was operationalized by requiring, within 7-days prior to discontinuation, that they have at least one INR in therapeutic range (2.0-3.5), no INR(s) out of range, and no more than a 15% change in warfarin dose. Stable dose prior to discontinuation was defined as the average daily dose received in the 7 days immediately prior to discontinuation. Reinitiation dose was defined as the average daily dose received in the first 3 days after warfarin was restarted. Subjects were divided into three groups based on whether they received approximately the same, a higher, or a lower dose at reinitiation and were also grouped by calendar time into three distinct periods that reflected differing levels of availability of electronic and patient care data that may impact reinitiation dose decisions. These groupings facilitated analyses and descriptions of trends in reinitiation dosing and supported other analyses, including tests for association between dose group and selected subject demographic, clinical, medication and hospitalization measures. All study data were abstracted from Marshfield Clinic electronic patient care and administrative databases and electronic patient care databases from Ministry St. Joseph's Hospital (Marshfield, WI).
RESULTS: We identified 205 subjects with warfarin temporarily discontinued between 1994 and 2012: 99 subjects in same dose group, 32 subjects in the low group, and 74 subjects in the high group. Because relatively wide differences were observed in the proportion of same dose subjects during more recent years (2007-2012) compared to earlier years (54% vs 35%), we focused our analyses on this recent period, which included 140 subjects. Review of physician notes and other documents yielded virtually no information about reasons for reinitiation dose decisions. In addition, tests for association between reinitiation dose group and subject demographic, clinical, medication and hospital measures were uniformly uninformative.
CONCLUSIONS: We observed varied dosing strategies for reinitiating patients on warfarin and, in more recent years, an apparent trend toward reinitiating patients on the same dose. However we could not associate dosing strategy with specific patient demographic, clinical, medication or hospital factors. Many factors influence whether a physician reinitiates a patient at a different dose than his/her prior stable warfarin dose. However, in the absence of clinical indications for modification, we believe patients with a previously established effective dose should be reinitiated at that same dose following temporary warfarin discontinuation.