Experimental investigations on the thrombosis-preventing effect of low-molecular-weight heparins

6 different preparations of low-molecular-weight heparin (LMWH) derivatives and 1 unfractionated heparin (UFH) were tested for their thromboprophylactic effects in an experimental model which closely simulates clinical conditions. Each preparation was tested in 5 rabbits 2 h and in 5 rabbits 12 h after subcutaneous application of 20-200 U/kg body weight (according to the suggestions of the manufacturers). The animals were anesthetized with intravenous pentobarbital sodium about 90 min or 11.5 h after the application of the heparin preparation. The right external jugular vein was dissected free and a thrombogenesis was provoked. There was no significant protection against occluding thrombosis 2 h after LMWH or UFH injection, when plasma levels of heparin-like activities were found to be high in another experimental series. Surprisingly, there were definite thromboprophylactic effects 12 h (when heparin-like plasma activities had disappeared) after application of 4 (out of 6) LMWH preparations. No protection against thrombosis was seen 12 h after application of UFH.