Comparison of a natural heparinoid with sodium and calcium heparin for their effect on the inhibitor of activated factor X.

The reaction between activated factor X (Xa) and its natural inhibitor (XaI) was accelerated in vitro by both sodium heparin and an heparinoid, which was about 3 times less potent than heparin. The s. c. administration in humans of 5,000 units of sodium and calcium heparin was followed by the detection of a plasma activity potentiating XaI. In the majority of subjects, the heparinoid was not effective. These observations indicate that the use of heparinoids should not be considered as an alternative to heparin in the prevention of thromboembolism.