Subcutaneous immunoglobulin loading regimens for previously untreated patients with primary antibody deficiency

Mechanisms of Obesity-Induced Changes in Pharmacokinetics of IgG in Rats

PURPOSE

To evaluate how obesity affects the pharmacokinetics of human IgG following subcutaneous (SC) and intravenous (IV) administration to rats and the homeostasis of endogenous rat IgG.

METHODS

Differences in body weight and size, body composition, and serum concentration of endogenous rat IgG in male Zucker obese (ZUC-FA/FA) and control (ZUC-LEAN) rats were measured from the age of 5 weeks up to 30 weeks. At the age of 23-24 weeks animals received a single IV or SC dose of human IgG (1 g/kg of total body weight), and serum pharmacokinetics was followed for 7 weeks. A mechanistic model linking obesity-related changes in pharmacokinetics with animal growth and changes in body composition was developed.

RESULTS

Significant differences were observed in both endogenous and exogenous IgG pharmacokinetics between obese and control groups. The AUC for human IgG was lower in obese groups (57.6% of control after IV and 48.1% after SC dosing), and clearance was 1.75-fold higher in obese animals. The mechanistic population model successfully captured the data and included several major components: endogenous rat IgG homeostasis with age-dependent synthesis rate; competition of human IgG and endogenous rat IgG for FcRn binding and its effect on endogenous rat IgG concentrations following injection of a high dose of human IgG; and the effect of body size and composition (changing over time and dependent on the obesity status) on pharmacokinetic parameters.

CONCLUSIONS

We identified important obesity-induced changes in the pharmacokinetics of IgG. Results can potentially facilitate optimization of the dosing of IgG-based therapeutics in the obese population.

Pharmacokinetic modeling and simulation of subcutaneous and intravenous IgG dosing in patients with primary immunodeficiency diseases

A population pharmacokinetic (PK) model for comparing the PK of subcutaneously administered immunoglobulin G (IgG) replacement therapy (SCIG) with Gamunex-C 10% or SCIG 20% formulations in patients with primary immunodeficiency diseases was developed using data from 3 clinical trials (N = 95, 69.5% adults, 30.5% <18 years) of intravenous IG (IVIG) 10% and SCIG 10% or SCIG 20%. Serum IgG exposure following switches from IVIG 10% every 3 or 4 weeks to biweekly SCIG 20% (dose adjustment factor 1.0 or 1.37) and from weekly SCIG 20% to biweekly SCIG 20% or SCIG 20% 2-7 times/week was simulated. The PK of IVIG 10% and SCIG 20% were adequately described by a 2-compartment model with first-order absorption rate constant of exogenous IgG from an SC depot compartment into the central compartment and first-order elimination from the central compartment. Switching from IVIG 10% every 4 weeks to biweekly SCIG 20% produced similar serum IgG exposure, with lower peak and higher trough serum IgG concentrations. Switching from IVIG 10% every 3 or 4 weeks to weekly and biweekly SCIG 20% yielded comparable IgG exposure and clinically effective trough IgG concentrations.

II Brazilian Consensus on the use of human immunoglobulin in patients with primary immunodeficiencies

In the last few years, new primary immunodeficiencies and genetic defects have been described. Recently, immunoglobulin products with improved compositions and for subcutaneous use have become available in Brazil. In order to guide physicians on the use of human immunoglobulin to treat primary immunodeficiencies, based on a narrative literature review and their professional experience, the members of the Primary Immunodeficiency Group of the Brazilian Society of Allergy and Immunology prepared an updated document of the 1^st Brazilian Consensus, published in 2010. The document presents new knowledge about the indications and efficacy of immunoglobulin therapy in primary immunodeficiencies, relevant production-related aspects, mode of use (routes of administration, pharmacokinetics, doses and intervals), adverse events (major, prevention, treatment and reporting), patient monitoring, presentations available and how to have access to this therapeutic resource in Brazil.

Effect of Kidney Function on Drug Kinetics and Dosing in Neonates, Infants, and Children

Neonates, infants, and children differ from adults in many aspects, not just in age, weight, and body composition. Growth, maturation and environmental factors affect drug kinetics, response and dosing in pediatric patients. Almost 80% of drugs have not been studied in children, and dosing of these drugs is derived from adult doses by adjusting for body weight/size. As developmental and maturational changes are complex processes, such simplified methods may result in subtherapeutic effects or adverse events. Kidney function is impaired during the first 2 years of life as a result of normal growth and development. Reduced kidney function during childhood has an impact not only on renal clearance but also on absorption, distribution, metabolism and nonrenal clearance of drugs. 'Omics'-based technologies, such as proteomics and metabolomics, can be leveraged to uncover novel markers for kidney function during normal development, acute kidney injury, and chronic diseases. Pharmacometric modeling and simulation can be applied to simplify the design of pediatric investigations, characterize the effects of kidney function on drug exposure and response, and fine-tune dosing in pediatric patients, especially in those with impaired kidney function. One case study of amikacin dosing in neonates with reduced kidney function is presented. Collaborative efforts between clinicians and scientists in academia, industry, and regulatory agencies are required to evaluate new renal biomarkers, collect and share prospective pharmacokinetic, genetic and clinical data, build integrated pharmacometric models for key drugs, optimize and standardize dosing strategies, develop bedside decision tools, and enhance labels of drugs utilized in neonates, infants, and children.