Heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia is the most common immune-mediated adverse drug reaction, occurring in 1% to 3% of postoperative patients receiving unfractionated heparin prophylaxis for 7 to 14 days. Approximately 1 in 100 patients receiving a therapeutic dose of unfractionated heparin for a week or more will experience thrombosis related to heparin-induced thrombocytopenia. Heparin-induced thrombocytopenia is characterized by activation of coagulation and platelets. Diagnosis of the condition should take into account the timing of the thrombocytopenia (which typically occurs on day 5 to 10 after initiation of heparin), the degree of the thrombocytopenia, and the presence of new thrombosis. Use of warfarin alone to treat acute heparin-induced thrombocytopenia complicated by deep venous thrombosis sometimes results in loss of a limb because of venous limb gangrene, probably because warfarin can cause severe reduction in protein C without a simultaneous reduction in the generation of thrombin in these patients. New treatments now available in Canada to reduce thrombin generation in heparin-induced thrombocytopenia (such as danaparoid and lepirudin) are useful in managing the thrombotic consequences of heparin- induced thrombocytopenia.