Low molecular weight heparins – Pharmacological principles and indications in clinical practice

Summary

 The pharmacological effects of low molecular weight heparins are characterized by an increased inhibition of factor Xa and decreased inhibition of thrombin of the coagulation cascade in comparison to unfractionated heparins. After administration into the circulation blood, levels are sustained twice as long as for unfractionated heparin on factor Xa inhibition leading to a biological half-life of 2 h after intravenous administration and of 4 h after subcutaneous administration. The clearance of LMW heparins is decreased and the area under the activity time curve is increased more than 2-fold compared to unfraction-ated heparin. The effects on bleeding time and hemorrhage are decreased in animal models.

In postoperative medicine LMW heparins once daily (o.d.) have a higher efficacy as low dose unfractionated heparin three times daily (t.e.d.). In medical bedridden hospitalized patients LMW heparin o.d. is as effective and probably safer than unfractionated heparin t.e.d. Heparin-induced thrombocytopenia type II occurs less frequently. Treatment of recent deep venous thrombosis is performed more effectively and safely using low molecular weight heparins. So far, there is no sufficient evidence for different efficacies of LMW heparins in these indications. The efficacy and safety of low molecular weight heparins is currently proven in patients with cerebral ischaemia and unstable angina.