Therapy related coagulopathies
Warfarin (Coumadin™)

Author: Jeremy Parsons, M.D. (see Authors page)

Revised: 25 April 2016, last major update June 2012

Copyright: (c) 2002-2016,, Inc.

PubMed Search: Warfarin [title] AND Coumadin [title]

Cite this page: Warfarin (Coumadin). website. Accessed October 28th, 2016.
Definition / General
  • 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
Diagrams / Tables

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Biochemistry of coumarins

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: