Cite this page: Parsons JC. Warfarin (Coumadin). PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/coagulationcoumadin.html. Accessed January 18th, 2021.
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
Images hosted on other servers:
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:
- Vitamin K, fresh frozen plasma; also prothrombin complex concentrates (J Clin Pathol 2004;57:1132, J Thromb Haemost 2006;4:1853)
