Overview of unfractionated heparin

Unfractionated heparin (UFH) is a parenteral anticoagulant that indirectly (via antithrombin III) inactivates thrombin (factor IIa), factor Xa and to a lesser extent factors XIIa, XIa and IXa. UFH activity is dependent on the presence of adequate antithrombin III. When full-dose therapeutic anticoagulation is required, UFH is usually given by continuous intravenous infusion (rather than subcutaneously) because it has a short half-life.

UFH is rarely the anticoagulant of first choice, except for patients with severe kidney impairment, or perioperatively when the short half-life of UFH and its complete reversibility with protamine allow tight control of anticoagulation. UFH can be used safely during pregnancy and breastfeeding.

Heparin-induced thrombocytopenia (HIT) is an uncommon but dangerous complication of UFH therapy, with an incidence of 2.6% in surgical patientsMartel, 2005. Do not give UFH to patients with a history of HIT; for alternative anticoagulant therapy, see Treatment of heparin-induced thrombocytopenia.