Coumarin necrosis occurs due to:

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 1/2 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 necrosis/Coumarin 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.