<prompt> What is the mode of action of warfarin?Factor Xa inhibitorVitamin K antagonistActivates antithrombin IIIActivates factor IX  <response>: Ref: KD Tripathi, 7th ed. pg. 620, 621 Warfarin and its congeners act as anticoagulants only in vivo body, NOT in vitro lab. It acts by inhibiting Vitamin K. Due to overdose, hematuria is the first manifestation noted. Dose monitoring is done by INR Antidote of warfarin overdose: Vitamin K 