Correlations Among Subcutaneous Immunoglobulin Dosage, Immunoglobulin G Serum Pre-infusional Levels and Body Mass Index in Primary Antibody Deficiency Patients: A Pooled Analysis from the SHIFT/IBIS Studies

Background and Objective: In recent years, two Italian non-interventional studies evaluated subcutaneous immunoglobulin (SCIG) treatment in patients affected by primary antibody deficiency (PAD). The SHIFT study considered patients who were treated with intravenous immunoglobulin (IVIG) or SCIG 16% (Vivaglobin®) and then replaced this therapy with weekly treatments of SCIG 20% (Hizentra®). The IBIS study evaluated patients previously taking a weekly SCIG 20% regimen, who instead began therapy with biweekly SCIG 20% to assess the correlation between the dose of immunoglobulin G (IgG) administered and the body mass index (BMI) of patients, determine if there is a need for dosage adjustments on a BMI basis, and identify the predictors of serum IgG trough levels in our cohort. Methods: In this study, we analyzed the pooled data of 109 PAD patients enrolled in the SHIFT and IBIS studies. Only prospective phases were considered. Results: The total monthly SCIG dose showed comparable trends among weight categories, except for underweight patients. When we considered the monthly SCIG dosage per kilogram of body weight, a significant decreasing trend according to BMI was observed. Data on IgG trough levels were available for 88 patients, with a mean IgG serum level of 8.4 ± 1.6 g/L. A stepwise regression model revealed that the mean monthly dosage of SCIG 20% (p = 0.04248) and the mean monthly dosage of IgG per kilogram of body weight were the only two independent predictors associated with IgG trough levels. No association was found between BMI and IgG trough levels. Conclusions: These findings support the concept that the cumulative monthly dose of SCIG and the dose of SCIG per kilogram of body weight affect IgG trough levels in PAD patients, irrespective of BMI.