Serum trough IgG level and annual intravenous immunoglobulin dose are not related to body size in patients on regular replacement therapy.

Therapeutic regimens of intravenous immunoglobulin are currently based on actual body weight. The relationship between immunoglobulin dose and serum IgG level in relation to body size was retrospectively explored in patients on replacement therapy. Data were collected as part of a national audit on immunoglobulin therapy in patients with common variable immunodeficiency. 107 patients received immunoglobulin titrated to optimum effect. Correlations were sought between body mass index, trough IgG levels, infusion frequency and total annual dose. The mean (±SD) trough IgG level was 8.4±1.6 g/L and annual immunoglobulin dose received was 456.8±129.4 g. There was no relationship between annual dose and trough IgG level, regardless of infusion frequency, or adjustment for weight or body mass index. These results support the clinical practice of immunoglobulin prescription by clinical outcome rather than fixed dose by body weight. Future studies exploring immunoglobulin efficacy should include treatment arms with dosages based on both ideal and actual body weight, as ideal body weight-based prescribing would save significant amounts of product.