Management of heparin-induced thrombocytopenia: a critical comparison of lepirudin and argatroban
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Heparin-induced thrombocytopenia (HIT) is a transient hypercoagulability state initiated, paradoxically, by the anticoagulant, heparin. It is characterized by antibody-induced activation of platelets, leading to thrombin generation. Many patients with HIT develop thrombosis; even when heparin is stopped because of "isolated HIT" detected during routine platelet count monitoring, 25-50% of patients subsequently develop symptomatic thrombosis. Thus, an alternative anticoagulant should be substituted for heparin when HIT is strongly suspected. Two direct thrombin inhibitors (DTIs), lepirudin and argatroban, have been studied for prevention and treatment of thrombosis in HIT patients. Lepirudin is a polypeptide that binds irreversibly to the fibrin-binding and catalytic sites on thrombin (bivalent inhibitor). In contrast, argatroban is a synthetic, small-molecule DTI that binds reversibly to the catalytic site alone (univalent inhibitor). Results of historically controlled clinical trials suggest both agents are effective for preventing and treating thrombosis in HIT. However, these agents have not been compared directly, and important differences in study design limit conclusions from indirect comparison. For example, lepirudin was given for 12-14 days (mean) in treatment studies of thrombosis complicating HIT, whereas argatroban was given only for 6-7 days, a difference that could explain apparent lower thrombosis rates (and greater bleeding) with lepirudin. Recently, the transition from DTI therapy to oral anticoagulation in patients with deep venous thrombosis (DVT) complicating HIT has been identified as a risk period for coumarin-induced venous limb gangrene. Thus, the DTI should be given alone during acute HIT, with oral anticoagulants deferred until substantial resolution of the thrombocytopenia has occurred.
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