Human pharmacological studies of a defined low molecular weight heparin fraction (Fragmin) evidence for a simultaneous inhibition of factor Xa and IIa (thrombin).

The effect of a low molecular weight heparin (Fragmin) (20-80 U/kg) was studied in 10 healthy male volunteers after intravenous administration. Clotting abnormalities are extensive shortly after injection, lasting for 1-2 hours depending on heparin dosage. Dilute thrombin time, showing a close correlation to anti-F-Xa activity, is as sensitive as anti-F-Xa. The parallel time course of dilute thrombin time and anti-F-Xa activity clearly demonstrates that LMWH has an effect on F-IIa lasting as long as that of F-Xa. After subcutaneous administration clotting abnormalities are only slight with 40-60 U/kg, in contrast to the intravenous study. The platelet system remains unchanged.