Evaluation of Very Low‐Dose Subcutaneous Vitamin K During Postoperative Warfarin Therapy

Study Objective. To determine the effect of very low-dose subcutaneous vitamin K (SCVK) compared with witholding warfarin for above-target international normalized ratio (INR) values after joint surgery. Design. Historical controlled study. Setting. University hospital. Subjects. One hundred thirty-nine patients beginning warfarin after total joint surgery. Intervention. For a high INR, warfarin was either withheld or SCVK 100, 300, or 400 tag was administered, depending on INR value. Measurements and Main Results. The primary outcome was change in INR from the day of intervention (day 1) to the next day (day 2) Adjusting for day 1 INR, the mean day 2 INR was 2.10 (95% confidence interval [Cl] 1.86-2.33) after SCVK, compared with 2.73 (95% Cl 2.50-2.96) in controls. This corresponded to declines of -0.72 and -0.08, respectively (p=0.001). Conclusion. In orthopedic patients starting warfarin therapy, very low-dose SCVK was more effective than withholding warfarin in reducing high 1NRs. Investigations in other populations and assessment of the effect of low-dose SCVK on postoperative bleeding are indicated.