Intravenous immune globulin (IVIg) is a purified preparation of gamma globulin, comprised of 4 subclasses of antibodies (ie, IgG, IgM, IgA, and IgE), approximating the distribution in human serum. IVIg is derived from large pools of human plasma (ie, greater than 1000 donors per lot) and purified to remove infective agents, vasoactive substances, and aggregated proteins.
IVIg is at least 90% intact IgG, the half-life of which is generally from 18 to 32 days in healthy adults, although it varies depending upon patient factors and which specific product is used. IgG is comprised of 4 subclasses of which IgG1 is the major component in normal serum and in IVIg. IgG1 is involved in tissue protection, complement activation, and virus inactivation. Peak serum levels of IgG are attained immediately after IVIg administration, but drop about half during the first week postinfusion, even though the reported half-life of IgG is somewhat longer. IVIg in immune deficient states simply replaces missing antibodies, whereas immunomodulatory doses of IVIg for autoimmune conditions are considerably larger. Various mechanisms have been proposed for immunomodulatatory actions of IVIg, including promoting blockade of Fc receptors in macrophages (thereby preventing phagocytosis of circulating opsonized platelets or cells tagged with autoantibodies), providing anti-idiotypic antibodies to neutralize pathogenic auto-antibodies, absorbing complement, down regulating immunoglobulin production, neutralizing viruses, enhancing suppression cells, inhibiting lymphocyte proliferation, and reducing interleukin (IL-1) production or activity.
IndicationsIVIg therapy is used either for immunomodulation of autoimmune conditions or for antibody replacement. Neurologic indications are genrally associated with an immunomodulatory role, and include Guillain-Barre syndrome and chronic inflammatory demyelinating neuropathy. Other nonneurologic indications associated with an immunomodulatory role include idiopathic thrombocytopenic purpura, Kawasaki syndrome, and acquired hemophilia. Indications suitable for treatment by IgG replacement include general or specific immunodeficiency states, hepatitis A or rubella prophylaxis, chronic lymphocytic leukemia with hypogammaglobulinemia, multiple myeloma with specific antibody deficiency, low birth weight babies at risk for infection, and infants or children with HIV.