FIGURE 1.

The coagulation cascade requires vitamin K in the reduced form (vitamin K [H₂]) as a cofactor for γ-glutamyl-carboxylase to convert inactive factors II, VII, IX, and X to the active forms that are required for coagulation. Vitamin K (H₂) is oxidized during this process to vitamin K epoxide. To conserve vitamin K (H₂), the enzyme vitamin K epoxide reductase (VKOR) converts vitamin K epoxide back into vitamin K (H₂). Warfarin inhibits VKOR, decreasing vitamin K (H₂) availability, diminishing activatable factors II, VII, IX, and X and thus inhibiting coagulation. CO₂ = carbon dioxide; O₂ = oxygen.