Home   Chapter Home   Jobs   Conferences   Fellowships   Books



Therapy related coagulopathies

Warfarin (Coumadin™)

Reviewer: Jeremy Parsons, M.D. (see Reviewers page)
Revised: 12 June 2012, last major update June 2012
Copyright: (c) 2002-2012, PathologyOutlines.com, Inc.


● Therapeutic anticoagulant to prevent thromboembolism by impairing regeneration of active vitamin K (warfarin is a synthetic derivation based on coumarin)
● The name incorporates the acronym for the organization which funded the key research (WARF, for Wisconsin Alumni Research Foundation) and the ending -arin, indicating its link with coumarin


● Vitamin K is a cofactor in reactions that carboxylate glutamic acid residues in factors II, VII, IX, X, protein C, protein S
● These “GLA” domains enable the coagulation factors to bind to phospholipid membranes in the presence of calcium
● Therapeutic warfarin or Vitamin K deficiency cause decreased activity of these proteins, making the enzymes less able to participate in the clotting cascade, which prolongs the PT

Clinical features

● Takes 4-5 days for complete therapeutic effect due to long half-life of factors II and X
● Must be supplemented with another anticoagulant such as heparin (“bridged”) until INR is in therapeutic range for 2 consecutive days to prevent Warfarin Skin Necrosis in those with low Protein C
● Therapeutic effect is measured by INR - goal is often INR between 2 and 3
● INR may be elevated by lupus anticoagulants or use of hirudin with warfarin
● Warfarin should not be used alone for acute heparin-induced thrombocytopenia because it causes paradoxical thrombosis - must add a rapid acting anticoagulant (hirudin, danaparoid, argatroban) until INR is therapeutic
● Note: PTT may be normal if low warfarin levels

Treatment of bleeding/overdose:
● Vitamin K, fresh frozen plasma; also prothrombin complex concentrates (J Clin Pathol 2004;57:1132, J Thromb Haemost 2006;4:1853)


Biochemistry of coumarins

End of Coagulation > Therapy related coagulopathies > Warfarin (Coumadin™)

This information is intended for physicians and related personnel, who understand that medical information is often imperfect, and must be interpreted in the context of a patient's clinical data using reasonable medical judgment. This website should not be used as a substitute for the advice of a licensed physician.

All information on this website is protected by copyright of PathologyOutlines.com, Inc. Information from third parties may also be protected by copyright. Please contact us at copyrightPathOut@gmail.com with any questions (click here for other contact information).