Heparin-Induced Thrombocytopenia Associated with Fondaparinux

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Abstract
Heparin-induced thrombocytopenia is a transient disorder in which thrombocytopenia appears about 1 week after exposure to heparin.1 Often there is also arterial or venous thrombosis, including adrenal necrosis due to adrenal-vein thrombosis. Heparin-induced thrombocytopenia is caused by platelet-activating antibodies against platelet factor 4 (PF4)–heparin complexes. Its frequency is reduced by a factor of about 10 with low-molecular-weight heparin as compared with unfractionated heparin. The risk of heparin-induced thrombocytopenia is believed to be even lower — perhaps negligible — with fondaparinux (Arixtra),2 a factor Xa inhibitor modeled after a critical heparin pentasaccharide sequence. To our knowledge, a causal association between fondaparinux therapy and the occurrence of heparin-induced thrombocytopenia has not been established.