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Information

Clinical Uses. Heparin is used extensively for multiple purposes and when administered IV has an immediate onset of action, whereas subcutaneous administration results in variable bioavailability with an onset of action in 1 to 2 hours.

  1. Heparin-Induced Thrombocytopenia

    1. Thrombocytopenia due to UFH is common and can begin within hours in patients exposed to heparin.

    2. A more severe and even life-threatening syndrome develops in 0.5% to 6.0% of patients, manifesting as severe thrombocytopenia (50% drop in platelet count or <100,000 cells/mm3), that can be associated with thrombotic events (heparin-induced thrombocytopenia with thrombosis). This severe response typically develops after 4 to 5 days of heparin therapy and is caused by heparin-dependent antibodies to platelet factor IV that trigger platelet aggregation and result in thrombocytopenia.

  2. Allergic Reactions. Heparin can cause allergic reactions, but these are rare and present in a manner typical of other hypersensitivity reactions.

  3. Anticoagulation with Protamine

    1. Positively charged alkaline protamine combines with the negatively charged acidic heparin to form a stable complex that is devoid of anticoagulant activity. These heparin-protamine complexes are removed by the reticuloendothelial system. Clearance of protamine by the reticuloendothelial system (within 20 minutes) is more rapid than heparin clearance and that may explain, in part, the phenomenon of heparin rebound.

    2. The dose of protamine required to antagonize heparin is typically 1 mg for every 100 units of circulating heparin activity.