Warfarin exerts its anticoagulant effect by inhibiting which enzyme?

• A Gamma-glutamyl carboxylase
• B Thromboxane A2 synthase
• C Factor Xa directly
• D Vitamin K epoxide reductase ✓

Explanation

Warfarin blocks VKORC1, the enzyme that regenerates reduced vitamin K from vitamin K epoxide. Reduced vitamin K is the cofactor for gamma-glutamyl carboxylase, so carboxylation of factors II, VII, IX and X and proteins C and S fails. The distractor A is tempting because gamma-glutamyl carboxylase is the downstream step, but it is not inhibited; it simply lacks its cofactor. This is why the anticoagulant effect is delayed until preformed factors decay.

Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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