Pharmacology · Class
Vitamin K antagonists !
Oral anticoagulants that stop the liver from making working clotting factors. Slow to start, slow to wear off, and checked with the INR.
Updated 2026-11-01
What they are
Oral anticoagulants that block the recycling of vitamin K, so the liver makes fewer functional clotting factors.
Mechanism of action
They inhibit vitamin K epoxide reductase (VKORC1), the enzyme that recycles vitamin K. With less active vitamin K, the liver makes fewer functional factors II, VII, IX and X, and also less of the natural anticoagulants protein C and protein S. The effect builds over days, as the factors already in the blood are used up.
Target: Vitamin K epoxide reductase (VKORC1)
Drugs in this class
Others in the class
- acenocoumarol
- phenprocoumon
- fluindione
Test yourself
Think of the answer, then tap the question to see it.
Which clotting proteins depend on vitamin K for their synthesis?
Factors II, VII, IX and X, and also the anticoagulant proteins C and S.
Why does a vitamin K antagonist take days to reach full effect?
It does not destroy factors already in the blood; it only limits the making of new functional ones. Peak effect comes once the old factors have been cleared.
Which anticoagulant class is used with a mechanical heart valve?
Vitamin K antagonists such as warfarin. Dabigatran is contraindicated with mechanical valves and rivaroxaban is not recommended with prosthetic valves.
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - WARFARIN SODIUM tablet (DailyMed (U.S. National Library of Medicine), 2026); Warfarin: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.