Low-dose oral vitamin K to normalize the international normalized ratio prior to surgery in patients who require temporary interruption of warfarin.
BACKGROUND
In patients who require warfarin interruption before surgery and have an elevated international normalized ratio (INR) before surgery, low-dose vitamin K may normalize the INR in time for surgery.


METHODS
In a retrospective cohort study, we assessed the efficacy of 1 mg oral vitamin K to normalize the INR for surgery and whether resistance to re-anticoagulation occurs when warfarin is restarted after surgery. We studied a cohort of patients with an INR 1.4-1.9 on the day before surgery who received 1 mg oral vitamin K (vitamin K group), and a comparator group of patients with a normal INR (< or = 1.3) on the day before surgery who did not receive vitamin K (no vitamin K group). In both patient groups, we determined the proportion of patients with a normalized INR on the day of surgery and compared the mean INR after surgery when warfarin was resumed.


RESULTS
Of 43 patients in the vitamin K group, the INR was normalized (< or = 1.3) in 33 patients (76.6; 95% confidence interval [CI]: 64.1-89.4), and the INR was normal or near-normal (< or = 1.4) in 39 patients (90.7; 95% CI: 82.0-99.4) on the day of surgery. The mean (standard deviation) INR in the vitamin K and no vitamin K group 4-8 days after surgery was 1.75 (0.34) and 1.59 (0.36), respectively (P = 0.56).


CONCLUSIONS
In patients requiring interruption of warfarin for surgery, 1 mg oral vitamin K on the day before surgery can normalize the INR by the day of surgery and may not confer resistance to warfarin re-anticoagulation after surgery.
Woods
Karen
K
Department of Medicine, McMaster University and St. Joseph's Healthcare, Room F-544, 50 Charlton Ave. East, Hamilton, ON, Canada L8N 4A6.
Douketis
James D
JD
Kathirgamanathan
Kala
K
Yi
Qilong
Q
Crowther
Mark A
MA
D000284:Administration, Oral; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000925:Anticoagulants / Q000627:therapeutic use; D001777:Blood Coagulation / Q000187:drug effects; D000075202:Contraindications; D004341:Drug Evaluation; D005260:Female; D006801:Humans; D019934:International Normalized Ratio; D008297:Male; D008875:Middle Aged; D019990:Perioperative Care; D012189:Retrospective Studies; D014812:Vitamin K / Q000008:administration & dosage*; D014859:Warfarin
D000925:Anticoagulants; D014812:Vitamin K; D014859:Warfarin