Therapeutic defibrination and heparin therapy in the prevention and resolution of experimental venous thrombosis.

The application of phenol to the femoral veins of anesthetized dogs resulted in an occluding thrombus in 24 of 25 veins at 1 week. Serial venography and eventual histology showed that these veins remained occluded over a 5-week observation period, the thrombi undergoing organization. Therapeutic defibrination was achieved with administration of an enzyme from venom of the pit viper (Arvin). Arvin, administered for 1 week immediately following phenol application and before thrombus formation had occurred, prevented thrombosis in all 10 such veins, and serial venography for a further 4 weeks showed that the veins remained patent. Administration of Arvin was begun 24 hours postoperatively, when venography had demonstrated an occluding thrombus and failed to clear any of 11 veins after 3 weeks of treatment. Intravenous administration of heparin, 10,000 units, at 6, 6, and 12-hour intervals in a 24-hour period, was begun immediately after phenol application and continued for 1 week; 10 of 12 veins were blocked at 1 week. Following the same dose of heparin every 6 hours four of eight veins were blocked at 1 week. The results indicate that when the vascular endothelium is damaged, therapeutic defibrination is more effective than heparin therapy in preventing venous thrombosis. Arvin therapy has no significant thrombolytic effect even if the thrombus is less than 24 hours old.