Current dosing practices for immunoglobulin G (IgG) may be inadequate in extreme body weight. The current study will evaluate the influence of body composition on intravenous and subcutaneous administration of immunoglobulin G in patients.

Current dosing practices for immunoglobulin G (IgG) may be inadequate in extreme body weight. Total (TBW), ideal (IBW), and adjusted (AdjBW) body weight-based dosing strategies are suggested, but these recommendations are based on expert opinion rather than high quality evidence. The adoption of a specific strategy is highly variable depending on the clinician and/or institutional setting. Recently, payors have also adopted strategies to reduce IgG therapy costs of by capping doses. These recommendations are often based on the presumption that IgG distribution is limited to the vascular space. While this assertion is logical, it does not account for changes adipose tissue may confer on target sites, nor does it account for the potential for adipose tissue to function serve as a metabolic sink or a source of inflammatory mediators. The later would be especially important in patients receiving SCIG. Several observational studies have evaluated IgG dosing in obese patients and have been the source of support for dosing strategies. Many of these studies were not representative of specific populations, contained a wide variety of patients with different IgG indications, and had inadequate serum sampling. More recently, the phase III randomized controlled PATH trial did not find a correlation with serum IgG concentrations and clinical endpoints. However, it is important to note that the study was not designed to evaluate pharmacokinetic and pharmacodynamic endpoints. There is also considerable interpatient variation in response; therefore, identification of patient characteristics that predict response or IgG change from baseline will be a useful tool to improve patient responses. Our study will evaluate the influence of body composition and other patient characteristics may have on IgG exposure when given intravenously or subcutaneously.

Inclusion Criteria:

• Patients aged >18 years with a current diagnosis of CIDP (based on European Federation of Neurological sciences / Peripheral Nerve Society CIDP diagnostic criteria).
• 1:1 conversion of IVIG to SCIG (weekly dose conversion) must fall within 0.2-to-0.4 mg/kg dose for SCIG.

Exclusion Criteria:

• Patients receiving IVIG for indications other than CIDP will be excluded.
• Patients with liver impairment (elevations in liver enzymes of greater than 3 times the upper limit of normal) or reduced renal function (CrCl < 50 mL/min) will be excluded
• Active malignancies
• Diabetes
• Myasthenia gravis
• Immunodeficiency
• Autoimmune disease