Warfarin VKORC1 Inhibition — FRCA Primary MCQ
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Correct answer: A — Inhibiting vitamin K epoxide reductase blocking the carboxylation of vitamin K-dependent clotting factors
Warfarin inhibits vitamin K epoxide reductase (VKORC1) preventing regeneration of the active (reduced) form of vitamin K. This blocks gamma-carboxylation of factors II VII IX and X and proteins C and S. Onset is delayed (2-7 days) because existing carboxylated factors must be cleared first. Factor VII has the shortest half-life (~6 hours) so PT/INR rises first.
Reference: Peck Hill Williams 2014 Pharmacology for Anaesthesia and Intensive Care