Defibrotide is antithrombotic and thrombolytic against rabbit venous thrombosis

Defibrotide (D) is a polydeoxyribonucleotide of mammalian origin that has no anticoagulant activity or hemodynamic effects but has considerable profibrinolytic and antithrombotic activities under several experimental conditions. In this paper the dynamics of D's antithrombotic effects after oral administration and D's thrombolystic activity after intravemous infusion on venous collagen-induced thrombosis in the rabbit are reported. D administered orally (12.5, 25 or 50 mg kg-1), from 0 to 360 min before thrombus induction, was able to impede thrombus formation in the first 2 h of growth. There is a linear correlation between the dose of D and peak activity and a correlation, described by a power function, between the dose and the area under the experimental inhibition curve. D infused intravenously (20, 31.7 or 50 mg kg-1 h-1 X 6 h) into rabbits with 24-hour-old thrombi, had significant and impressive dose-related thrombolytic activity. There is a direct relationship between the thrombolytic effect and plasma levels. In this experimental model, urokinase infused intravenously (750, 1,500 or 3,000 IU kg-1 h-1) had the same thrombolytic activity as D; heparin (76 IU kg-1 h-1) was completely ineffective and PGI2 showed a modest activity at 60 nmol kg-1 h-1. The antithrombotic and thrombolytic activities of D may be partly due to its ability to promote release of plasminogen activator factor and of prostacyclin from vascular tissue.