Vitamin K
Like all 4-hydroxycoumarin drugs it is a competitive inhibitor of vitamin K epoxide reductase, an enzyme that recycles vitamin K, thus causing depletion of active vitamin K in blood. This prevents the formation of the active form of prothrombin and several other coagulant enzymes. These compounds are not antagonists of Vitamin K directly—as they are in pharmaceutical uses—but rather promote depletion of vitamin K in bodily tissues allowing vitamin K's mechanism of action as a potent medication for dicoumarol toxicity. The mechanism of action of Vitamin K along with the toxicity of dicoumarol are measured with the prothrombin time (PT) blood test.