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The oral coumarin anticoagulants, warfarin and phenindione, interfere with Vitamin K metabolism in hepatic cells and their effects can be reversed by vitamin K. If anticoagulation with warfarin is to be continued but rapid reversal of over- anticoagulation is needed a small oral dose of 0.5 to 1mg of vitamin K is generally sufficient. Larger doses lead to prolonged resistance to warfarin.
Intravenous injections of vitamin K should be given with caution as anaphylaxis may occur.