The overall goal of this proposal is to investigate effects of obesity on pharmacokinetics of immunoglobulin G (IgG) and to develop strategies for optimization of dosing of IgG in obese patients. There is an ongoing debate regarding the most appropriate dosing of IgG formulations in obese patients. Obesity poses significant health risks; and evidence supporting dosing strategies of IgG in obese patients is inadequate. Some of the adverse reactions have been attributed to a relative overdosing in these patients, due to a limited distribution of IgG into fat tissue.

The estimated prevalence of overweight and obese individuals >20 years in the US is 154.7 million (nearly double since the early 1960s), and over 1.6 billion people are considered overweight or obese worldwide. Compounding the health risks associated with obesity is the insufficient data supporting dosing strategies for a variety of medication used to treat conditions encountered in obese patients. No consensus on the best dosing strategy for IgG in obese patients has been established. Total (TBW), ideal (IBW), and adjusted (AdjBW) body weight-based dosing are being utilized by different institutions. Thus, there is an urgent need to identify evidence supporting optimal dosing strategies for IgG.

It has been proposed that using TBW to dose IgG in obese patients may increase the risk of thrombosis owing to increased blood viscosity, activation of platelets, or vasospasm; and the increase in blood viscosity has been reported as IgG dose dependent. The use of using IBW or AdjBW has been advocated to reduce the side effect and drug expenditures. It is currently unknown what the clinical impact is of using measures of body weight other than TBW to calculate IgG doses, and the effect of obesity on IgG pharmacokinetics has not been experimentally evaluated.

Inclusion Criteria:

• aged 18 to 75 years
• currently treated with IVIG

Exclusion Criteria:

• liver impairment (elevations in liver enzymes of greater than 3 times the upper limit of normal)
• reduced renal function (CrCl < 50 mL/min)
• Patients with a pacemaker or an automatic implantable cardioverter-defibrillator

Male and female patients receiving the institutional standard intravenous immune globulin therapy. Differences in IgG concentrations will be analyzed between normal weight subjects (BMI 18.5 - 25 kg/m2) and overweight or obese subjects (BMI > 25 kg/m2).