STUDY OBJECTIVE:

To determine the effect of very low-dose subcutaneous vitamin K (SCVK) compared with withholding 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 microg 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 [CI] 1.86-2.33) after SCVK, compared with 2.73 (95% CI 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 INRs. Investigations in other populations and assessment of the effect of low-dose SCVK on postoperative bleeding are indicated.