A female client is started on warfarin (Coumadin) 5 mg po bid.

(A) Thrombolytic agents (e.g., streptokinase) directly activate plasminogen, dissolving fibrin deposits, which in turn dissolves clots that have already formed. (B) Heparin prevents the formation of clots by potentiating the effects of antithrombin III and the conversion of prothrombin to thrombin. (C) Warfarin prevents the formation of clots by interfering with the hepatic synthesis of the vitamin K-dependent clotting factors. (D) Platelets initiate the coagulation of blood by adhering to each other and the site of injury to form platelet plugs.