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.
