Warfarin
Warfarin
- Last updated September 8, 2025
Objectives
By the end of these revision notes, you should be able to:
What is warfarin?
Warfarin is an oral anticoagulant that prevents blood from clotting. It is very commonly used for prevention and treatment of blood clots, including in conditions such as atrial fibrillation and deep vein thrombosis.
It is a vitamin K antagonist – it inhibits the clotting cascade by targeting the role of vitamin K in the production of clotting factors.
Mechanism of Action
Warfarin inhibits the enzyme vitamin K epoxide reductase. This is necessary in regenerating active vitamin K in the liver. Without the active vitamin K, the liver cannot produce the vitamin K-dependent clotting factors:
- Factor II (prothrombin)
- Factor VII
- Factor IX
- Factor X
- Protein C and Protein S
This will lead to impaired clot formation and a prolonged prothrombin time (PT). Warfarin usually takes 48 to 72 hours to fully show its effect.
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