hepariny

Heparins are a class of anticoagulant medicines derived from animal tissues. They exert their effect by enhancing antithrombin III, which inhibits thrombin (factor IIa) and factor Xa, thereby slowing clot formation. They are used to prevent and treat venous thromboembolism, to maintain patency during procedures, and to bridge anticoagulation around surgical interventions.

Clinical forms include unfractionated heparin (UFH) and low-molecular-weight heparins (LMWHs) such as enoxaparin, dalteparin, and tinzaparin. UFH is given intravenously or subcutaneously and requires laboratory monitoring; LMWHs are usually given subcutaneously with more predictable effects and less routine monitoring. A synthetic pentasaccharide, fondaparinux, is related in mechanism but not classified as a heparin.

UFH inhibits both thrombin and factor Xa; LMWHs predominantly inhibit Xa with less anti-thrombin IIa activity. UFH has a short, variable half-life; LMWHs have longer, more predictable half-lives.

Reversal is possible with protamine sulfate for UFH and, to a lesser extent, LMWH. Monitoring for UFH uses the aPTT; LMWHs require little routine monitoring, though anti-Xa testing may be used in special populations. Common adverse effects include bleeding and, less frequently, heparin-induced thrombocytopenia.

Safety and use: Heparins do not cross the placenta, making them preferred during pregnancy when anticoagulation is needed. Cautions include active bleeding, recent neurosurgery or spinal procedures, and renal impairment, particularly with LMWHs.

History: Heparin was discovered in 1916 by Jay M. McLean and William Henry Howell in liver-derived tissue; the name derives from hepar, the Greek word for liver. Modern sources include porcine intestinal mucosa and bovine tissues.