Pharmacology of fibrinolysis

Fibrinolytic therapy has an expanding role in the treatment of many thromboembolic disorders. Four fibrinolytic drugs are currently marketed: streptokinase, anisoylated plasminogen-streptokinase activator complex, urokinase, and recombinant human tissue-type plasminogen activator. All 4 of these drugs activate the fibrinolytic system by converting plasminogen to the active enzyme, plasmin. Plasmin present in the confines of a thrombus degrades fibrin and dissolves the thrombus. Plasmin free in the circulation degrades fibrinogen and other coagulation factors. All 4 of the currently available fibrinolytic agents are capable of initiating thrombus dissolution and, at doses currently recommended, cause degradation of fibrinogen and predispose to bleeding complications. Differences in the mechanisms of plasminogen activation among the available agents provide a theoretical basis for postulating the superiority of one agent over another in clinical practice. However, the relative roles of these agents in treatment of thromboembolic disorders depend on the outcome of properly designed and executed clinical trials.