Heparin (unfractionated and low molecular weight forms) (UFH (unfractionated heparin), LMWH (low molecular weight heparin))

Heparin is a highly sulfated glycosaminoglycan used as an anticoagulant in clinical practice. Unfractionated heparin (UFH) is composed of polysaccharide chains of varying length and is primarily derived from animal tissues (porcine or bovine mucosa). Low molecular weight heparins (LMWHs) are produced by depolymerizing unfractionated heparin, resulting in shorter polysaccharide chains with differing pharmacokinetics and a more predictable anticoagulant response. Both UFH and LMWH act by binding to antithrombin, greatly accelerating its ability to inhibit certain serine proteases (primarily factor Xa and, for UFH, also thrombin) within the coagulation cascade. These agents are foundational for the prevention and treatment of venous thromboembolism, pulmonary embolism, and acute coronary syndromes, but are associated with significant risk of bleeding and rare but critical immune-mediated complications such as heparin-induced thrombocytopenia. UFH/LMWH are not biological molecules or receptors themselves but are pharmacological agents that modulate key regulators within the hemostatic system. Therefore, referring to "UFH/LMWH" as a target is conceptually incorrect. Note: "UFH/LMWH" are not molecular targets; they are complex drug classes. The actual target is antithrombin (sometimes antithrombin III), and their primary action is to enhance antithrombin's inhibition of factor Xa and, for UFH, also thrombin (factor IIa).

Other names

HeparinUnfractionated heparinLow molecular weight heparinStandard heparin (for UFH)Fractionated heparin (for LMWH)LMWHs (plural)

Both UFH and LMWH bind to antithrombin (AT), causing a conformational change that accelerates inhibition of key proteases in the coagulation cascade - UFH potentiates antithrombin-mediated inhibition of both thrombin (factor IIa) and factor Xa - LMWH preferentially increases inhibition of factor Xa, with less effect on thrombin due to smaller size/polysaccharide chain length Result: inhibition of fibrin formation and prevention of clot extension or formation