HIT/HITT and alternative anticoagulation: Current concepts

It is important to have a high index of clinical suspicion in a patient with a falling platelet count who is receiving heparin. It is imperative to discontinue all sources of heparin even before the laboratory confirmation of HIT. Platelet transfusion is contraindicated as this can exacerbate the serious thrombotic complications. Circulating antibodies bind to the transfused platelets and release platelet microparticles, leading to a thrombotic state. Treatment is intended to reduce the thromboembolic complications. There are several pharmaceutical agents available for the treatment of HIT. Before starting any of these agents, the clinician should decide which of them is safe and effective for the individual patient. Lepirudin is an irreversible, direct thrombin inhibitor that has shown effectiveness in treating patients with HIT type II. It does not cross-react with heparin and can be readily monitored with the aPTT and ECT. Disadvantages include a prolonged half-life, prolongation of the prothrombin time, possible antibody formation, and the requirement for dose adjustments in patients with renal impairment. Argatroban is the newest agent used for HIT type II. It binds reversibly to thrombin and is monitored with the aPTT. Patients who require anticoagulation and have renal impairment may benefit from the use of argatroban because of its hepatic metabolism. A disadvantage of this agent is prolongation of the prothrombin time (necessitating additional monitoring in patients who are also receiving warfarin), and dose adjustment in patients with hepatic impairment. Danaparoid, prostacyclin analogues and desirudin, although previously used in HIT, are not licensed for the treatment of HIT or HITT.