EVALUATION OF THROMBOLYTIC AGENTS

The mechanism of action of currently available thrombolytic agents, su ch as streptokinase, urokinase, alteplase (recombinant tissue-type pla sminogen activator; rt-PA) and anistreplase (anisoylated plasminogen s treptokinase activator complex; APSAC), involves conversion of inactiv e plasminogen to plasmin, a potent fibrinolytic. However, the relative ly weak substrate specificity of first generation agents (streptokinas e and urokinase) can result in a state of systemic fibrinolysis and as sociated bleeding complications. The second generation drugs such as a lteplase were developed in an attempt to enhance fibrin specificity, s o that only enzymatic conversion of fibrin-complexed plasminogen would take place, thus avoiding systemic fibrinolysis. Results from large c linical trials have failed to consistently show any significant differ ences between first and second generation thrombolytic agents in the i ncidence of bleeding. In the clinical setting, thrombolytic agents hav e been evaluated primarily in patients with acute myocardial infarctio n and have been shown to significantly reduce morbidity and mortality compared with conservative treatment. The focus of current and future research is to investigate these agents in patients with other vaso-oc clusive or ischaemic conditions (e.g. stroke), and also to evaluate di fferent drug administration regimens and the use of adjunctive therapi es such as aspirin (acetylsalicylic acid) and heparin.