A. Chelating Ca.
B. Inhibiting antithrombin III.
C. Inhibiting Vitamin K dependent carboxylation.
D. Inhibiting thrombin.
Ans:C. Inhibiting Vitamin K dependent carboxylation..
Warfarin inhibits vitamin K dependent carboxylation of clotting factors by inhibiting the enzyme Vitamin K epoxide reductase.
- They act indirectly by interfering with the synthesis of vit K dependent clotting factors in liver.
- They interfere with regeneration of the active hydroquinone form of vit K, which is required for the final step gamma carboxylating glutamate residues of prothrombin (factor II) and factor VII, IX and X.
- This carboxylation is essential for the ability of the clotting factors to bind Ca+2 and to get bound to phospholipid surface, necessary for coagulation sequence to proceed.
Mechanism of action
- During y – carboxylation of the coagulant factor II, VII, LX and X in the liver, active vitamin K (Vit K hydroquinone) is oxidized to an epoxide (vit K epoxide).
- Vit K epoxide must be reduced to vit K hydroquinone to become active once again (vit K cycle).
- Vit K epoxide is reduced to vit K hydroquinone by vit K reductase.
- This vit K reductase is inhibited by oral anticoagulants.