Comparison of low molecular weight heparins and unfractionated heparin after successive subcutaneous administration. A randomized controlled study in healthy volunteers.

The biological response to 4 different heparins after successive subcutaneous administration once daily for 5 days at a dose used for primary prophylaxis of deep vein thrombosis was investigated in a randomized cross-over study in 12 volunteers. Three different preparations of low molecular weight heparins (LMWH) were administered, 10,000 U unfractionated heparin (UFH) was used as a control. The anticoagulant properties in terms of anti-Xa activities, as measured by a chromogenic substrate assay or Heptest, showed high interindividual variations with peak levels 2 to 4 h following injections. There was a significantly higher increase of anti-Xa activities 3 h after administration at day 5, when compared with day 1, for two LMWH's, suggesting an accumulation of the anticoagulatory effect. The anticoagulant activity, especially when measured by Heptest, was significantly influenced by the body weight. This could be observed for all LMWH's. For the assessment of anticoagulant activity in LMWH-treated individuals, the chromogenic substrate assay and Heptest revealed maximal correlation (r = 0.51), while in UFH-treated individuals, peak correlation (r = 0.75) was observed between the partial thromboplastin time and thrombin clotting time. The chromogenic substrate method was the most sensitive anti-Xa assay, showing also the smallest interindividual variation. No significant influence of heparins neither on platelet count and function nor on fibrinolysis were recognized. Enhanced lipolytic activities were not observed. There was an increase of alanine aminotransferases induced by UFH as well as LMWH's, which, however, was most pronounced after UFH.