<prompt> Coumarin necrosis occurs due to:HeparinLow molecular weight heparinWarfarinClopidogrel  <response>: Ref: Goodman Gillman 13th ed. P 593-94 Warfarin one of coumarin derivative is an oral antagonist acts by antagonizing vitamin K dependent factors. Vitamin K dependent clotting factor: II, VII, IX, X Vitamin K dependent anticlotting factors: Protein C and Protein S Warfarin is administered as a racemic mixture of S- and R-warfarin. S-Warfarin is 3- to 5-fold more potent than R-warfarin and is mainly metabolized by CYP2C9. Because of the long t 12 of coagulation factors, the antithrombotic action of warfarin is achieved in 4-5 daysSIDE EFFECTS Bleeding: Most common side effect risk high if INR 4 Birth defect and abortion if administered during pregnancy fetal warfarin syndrome Skin necrosisCoumarin necrosis: Can occur 3-10 days after initiation of warfarin. Usually due to protein C and S deficiency Purple toe syndrome-blue tinged discoloration of plantar surface and side of toes, that blanches with pressure. Can occur 3-8 weeks after initiation of therapy. 