The heterogeneity of the anticoagulant response to heparin.

Difficulties in evaluating the anticoagulant effect of heparin led to studies of the rate of disappearance of its effect on the whole body partial thromboplastin time, and of its simultaneously bioassayed plasma concentration. The slope of the anticoagulant's dose-effect curve varied with each subject's baseline coagulation status, which probably accounts for the wide range of clinically observed responses to the drug. The mean rate of disappearance of bioassayed heparin was less than the mean rate of disappearance of the drug's effect on the clotting time, probably because of heparin's extensive binding to the plasma proteins which comprise its site of action. That these two kinds of rate of disappearance were found not to be correlated may also reflect the protein-binding capacity of heparin.