Background: Warfarin-associated coagulopathy is a frequent clinical complication. We aimed to assess whether treatment with vitamin K is safe and more effective than placebo in rapidly lowering the international normalised ratio (INR) into the therapeutic range in over anticoagulated patients receiving warfarin.
Methods: We did a multicentre, double-blind, placebo-controlled, randomised trial in five tertiary care hospitals. In this study, patients receiving warfarin who had an INR value between 4.5 and 10.0, and who did not have an indication for the immediate normalisation of their INR, had their warfarin withheld, and were randomly allocated to receive either 1 mg of vitamin K or placebo orally. The primary outcome measure was the INR value on the day after treatment. Secondary outcome measures included INR values on subsequent days, and the risk of haemorrhage and recurrent thrombosis over a 3 month follow-up period.
Findings: Patients given vitamin K had a more rapid decrease in the INR than those given placebo (25 of 45 (56%] vs nine of 44 [20%] patients with INR values of 1.8-3.2 on the day after treatment, respectively, p=0.001; odds ratio [OR] 0.21, 95% CI 0.07-0.57). Fewer patients given vitamin K had bleeding episodes during the follow-up period than those given placebo (two [4%] vs eight [17%] patients, respectively, p=0.050; OR 0.87, 95% CI 0.019-0.999).
Interpretation: Low dose oral vitamin K is more effective than placebo for the rapid lowering of raised INR values in patients taking warfarin.