The earliest effective approach to thromboembolic disease made use of heparin and the coumarin drugs. Ideally, these agents should dissolve an existing thrombus, but their only therapeutic action lies in preventing an extension or embolization of the thrombus.1 Their role in the actual prevention of recurrent thrombosis is subject to question in many series because of the lack of control clinical material. Much evidence is based on subjective findings, rather than objective data. None of the anticoagulant drugs satisfy the process of complete clot dissolution in vivo.2-4 After several weeks the body may partially overcome the tissue damage, and recanalization may occur after injury.
With the realization that fibrin is the primary constituent of intravascular thrombi, and with the discovery of an intrinsic fibrinolytic system in plasma5 (which in the dog is more active than in the human), investigation surged forward to find the ideal agent.