COMPARISON OF THE ANTITHROMBOTIC, ANTICLOTTING AND ANTIPLATELET AGGREGATORY ACTIVITIES OFLOW MOLECULAR WEIGHT RD HEPARIN WITH HEPARIN

An initial comparison of in vitro plasma anti-factor Xa (anti Xa) and activated partial thromboplastin time (APTT) values of RD heparin with heparin based upon USP units shows increased anti Xa and decreased APTT activity of RD heparin. An ex vivo experiment in rabbits in which 100 USP units/kg of RD heparinand 200 USP units/kg of heparin, when given by the subcutaneous route, reflects the significantly increased anti Xa activity generated by RD heparin as wellas its longer duration of action. No significant difference in APTT activity was observed for the two heparins, but an increased anti Xa/APTT ratio (greaterthan two) was observed for the RD heparin. Heparin (10 yg/ml), but not RD heparin, potentiated adenosinediphosphate (ADP) induced platelet aggregation in human platelet rich plasma. Subcutaneous administration of RD heparin or heparin to rabbits over the dosage range of 0.75 to 1.75 mg/kg gives similar mean dose response lines for these heparins in the thrombosis-stasis model as measured by the extent of jugular vein clotting. Administration of these heparins to rabbits on a USP unitage basis shows a significantly greater antithrombotic effect for RD heparin at 120 and 160 USP units/kg. Moreover, this experiment indicates that if the optimum dosage of 120 USP units/kgfor RD heparin is exceeded then we begin to see an indication of loss of antithrombotic activity.