Newer thrombolytic drugs for acute myocardial infarction.

Arterial thrombosis is the underlying cause of a wide variety of cardiovascular diseases such as myocardial infarction, stroke and pulmonary thromboembolism. All the currently used thrombolytic agents are plasminogen activators, which are very efficient in restoring the blood flow. The fibrinolytic system comprises an inactive proenzyme plasminogen, that is converted by plasminogen activators to the enzyme plasmin, that degrades fibrin. Despite the widespread use of established thrombolytic agents such as streptokinase, tissue-plasminogen activator and urokinase, all these agents suffer from a number of inadequacies including resistance to reperfusion, occurrence of acute coronary reocclusion and bleeding complications. The quest continues for thrombolytic agents with a higher potency, specific thrombolytic activity and fibrin selectivity. Several lines of research towards improvement of thrombolytic agents are being explored including the construction of mutants and variants of plasminogen activators, chimeric plasminogen activators and conjugates of plasminogen activators with monoclonal antibodies. Newer molecules such as pro-urokinase, saruplase, alteplase, K1K2Pu and staphylokinase have shown promise in animal models of arterial and venous thrombosis and also in pilot scale clinical studies in patients with myocardial infarction. However, more clinical trials are needed to determine whether these novel recombinant thrombolytic agents shows improved efficacy and fibrin specificity with minimal bleeding tendencies.