Essence of this Article

Two types of heparins are commonly used as anticoagulants – unfractionated heparin (UFH) and low molecular weight heparins (LMWHs). UFH has been used for the prevention and treatment of thrombosis for several decades. UFH has variable anticoagulant effects and pharmacological properties and also has limited bioavailability and highly variable anticoagulant response. LMWHs are derived from UFH by depolymerization. Each LMWH product has a specific molecular weight distribution that determines its anticoagulant activity and duration of action. LMWHs are associated with a predictable dose–response and have fewer non-haemorrhagic side-effects. Because of these clinical advantages, LMWHs have gradually replaced UFH for most indications.

Unfractionated and low molecular weight heparins

Unfractionated heparin:

  • Used for the prevention and treatment of thrombosis for several decades
  • Heparin is mainly obtained from porcine intestine101
  • A mixture of sulphated glycosaminoglycans of variable lengths and molecular weights
  • Anticoagulant effects and pharmacological properties vary with the size of the molecules
  • Administered parenterally
  • Binding to plasma proteins, platelet (platelet factor 4), macrophages, and endothelial cells limit its bioavailability and account for the highly variable anticoagulant response103
  • Inactivates several coagulation enzymes, including Factors IIa (thrombin), Xa, IXa, XIa, and XIIa, by binding to the cofactor AT103

Low molecular weight heparins:

  • Derived from UFH by depolymerization101
  • Each LMWH product has a specific molecular weight distribution that determines its anticoagulant activity and duration of action, so one product cannot always be substituted for another
  • LMWHs in current use globally include enoxaparin, dalteparin, nadroparin, tinzaparin, certoparin, reviparin, ardeparin, parnaparin and bemiparin104
  • Administered subcutaneously for VTE prevention
  • Like UFH, LMWHs inactivate several coagulation enzymes by binding to AT50 but have a lower affinity for binding to proteins other than AT and are, therefore, associated with a predictable dose–response and have fewer non-haemorrhagic side-effects105

Because of several clinical advantages, LMWHs have gradually replaced UFH for most indications. Danaparoid, available in several countries, is classified as a heparinoid. It is composed of sulphated glycosaminoglycans and can be used as an alternative to heparin in patients suffering from an antibody-mediated form of heparin-induced thrombocytopenia103