Delayed-onset heparin-induced thrombocytopenia type-2 during fondiparinux (Arixtra) therapy

Heparin is the most commonly used anticoagulant drug for prevention and treatment of thromboembolic diseases. Heparin-induced thrombocytopenia (HIT) is a well-known and potentially fatal side-effect of heparin therapy. HIT type 1 (HIT-1) is transient and relatively common; it usually develops within 1-7 days of initial heparin exposure. Type 2 HIT (HIT-2) is more severe and is associated with thrombocytopenia and thrombosis. HIT-2 usually develops 5 or more days after initial heparin exposure. It is an immune-mediated disorder that is presumably caused by development of platelet activating antibody against platelet factor 4 (PF4)/heparin complex. Fondaparinux (Arixtra) is a fast-acting selective inhibitor of factor Xa believed to be non-reactive to HIT sera and therefore may be used as prophylaxis for thrombosis in patients with a history of HIT-1 or HIT-2. Development of HIT-2 in patients currently taking fondaparinux prophylaxis is rare. Here we present a fatal case of delayed-onset HIT-2 (1 year after heparin exposure) manifesting while on fondaparinux prophylaxis.