Effect of warfarin on blood clotting proteins

The activity of various clotting proteins (logarithmic scale) is shown here as a function of time after ingestion of warfarin (10 mg/day PO for four consecutive days) by a normal subject. Factor VII activity, to which the prothrombin time is most sensitive, is the first to decrease. Full anticoagulation, however, does not occur until factors IX, X, and prothrombin are sufficiently reduced. Protein C activity falls quickly, and, in some patients, a transient hypercoagulable state may ensue (eg, coumarin necrosis).