Phenindione inhibits vitamin K reductase, resulting in depletion of the reduced form of vitamin K (vitamin KH2). As vitamin K is a cofactor for the carboxylation of glutamate residues on the N-terminal regions of vitamin K-dependent proteins, this limits the gamma-carboxylation and subsequent activation of the vitamin K-dependent coagulant proteins. The synthesis of vitamin K-dependent coagulation factors II, VII, IX, and X and anticoagulant proteins C and S is inhibited. Depression of three of the four vitamin K-dependent coagulation factors (factors II, VII, and X) results in decreased prothrombin levels and a decrease in the amount of thrombin generated and bound to fibrin. This reduces the thrombogenicity of clots.
Phenindione thins the blood by antagonizing vitamin K which is required for the production of clotting factors in the liver. Anticoagulants such as Phenindione have no direct effect on an established thrombus, nor do they reverse ischemic tissue damage (damage caused by an inadequate blood supply to an organ or part of the body). However, once a thrombus has occurred, the goal of anticoagulant treatment is to prevent further extension of the formed clot and prevent secondary thromboembolic complications which may result in serious and possibly fatal sequelae. Phenindione has actions similar to warfarin, but it is now rarely employed because of its higer incidence of severe adverse effects.
Oral, mouse: LD50 = 175 mg/kg; Oral, rat: LD50 = 163 mg/kg.