Warfarin (Coumadin)

Topic Completed: 1 June 2012

Revised: 4 January 2019, last major update June 2012

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

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

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Cite this page: Parsons J. Warfarin (Coumadin). website. Accessed July 13th, 2020.
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:
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