Effective reversal of warfarin-induced excessive anticoagulation with low dose vitamin K1.

Reversal of the anticoagulant effect of warfarin in patients with no active haemorrhage can be achieved by administration of intravenous vitamin K1. Currently recommended doses of intravenous vitamin K1, for this purpose often result in subsequent difficulties in anticoagulation. We observed the response to low dose intravenous vitamin K1 in patients requiring reversal of anticoagulant therapy. Ten consecutive patients received 1 mg and 21 further patients received 0.5 mg of intravenous vitamin K1. In 50% of the patients who received 1 mg of vitamin K1 the INR (International Normalised Ratio) fell below 2 at 24 h whereas in patients who received 0.5 mg the INR fell below 5.5 in all subjects after 24 h and in none did it fall below 2.0. No patient had any thrombotic or haemorrhagic complications and no difficulty was encountered in re-establishing anticoagulant control after 24 h. We recommend 0.5 mg of vitamin K1 as an effective and convenient method of predictable and fine control of oral anticoagulant therapy.