In vitro, both intact IgG as well as its Fc fragments inhibit HIT antibody-induced platelet activation, an effect that depends somewhat on the method of immunoglo-bulin preparation (Greinacher et al., 1994a) (see Chapter 8). Case reports describe rapid increase in the platelet counts after high-dose ivIgG (Vender et al., 1986; Frame et al., 1989; Nurden et al., 1991; Grau et al., 1992; Prull et al., 1992; Warkentin and Kelton, 1994). The possibility that ivIgG treatment interrupts platelet activation by HIT antibodies provides a rationale for its use as an adjunct to anticoagulant therapy in certain life- or limb-threatening situations. The dose should be 1 g/kg body weight per day for two consecutive days.
Recommendation. ivIgG is a possible adjunctive treatment in selected patients requiring rapid blockade of the Fc receptor-dependent platelet-activating effects of HIT antibodies (e.g., management of patients with cerebral venous thrombosis, severe limb ischemia, or very severe thrombocytopenia) (grade 2C).
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