Prediction of Belimumab Pharmacokinetics in Chinese Pediatric Patients with Systemic Lupus Erythematosus

BACKGROUND AND OBJECTIVE: Intravenous (IV) belimumab is the first treatment approved for children ≥5 years of age with active autoantibody-positive systemic lupus erythematosus (SLE) in the USA, Europe, and Japan. Pharmacokinetic data for belimumab were collected from several clinical trials in Chinese and non-Chinese adults and non-Chinese pediatric patients with SLE. This study aimed to predict the belimumab dose-exposure relationship to Chinese pediatric patients with SLE, as part of the belimumab registration process for this population in China, using a population PK modeling approach. METHODS: An initial linear two-compartment population pharmacokinetic model was built using data from adults only, and considering and adjusting for the covariates age, body weight, body mass index, fat-free mass, race, baseline albumin and immunoglobulin G levels. The model was used to study possible ethnic differences between Chinese and non-Chinese adults and to predict pediatric pharmacokinetic data in a study of non-Chinese pediatric patients (PLUTO study; NCT01649765). The predicted data were compared with the observed data from PLUTO. The model was then updated with pediatric data from PLUTO to predict steady-state belimumab exposure in Chinese pediatric patients with SLE receiving belimumab 10 mg/kg IV every 4 weeks. RESULTS: The dataset comprised 9650 sampled concentration values from 1783 patients. The pharmacokinetics of belimumab were adequately described by the final model using all adult and pediatric data with the estimated typical clearance of 238 ml/day in adult and pediatric patients and steady-state volume of distribution of 4915 ml in adults. Between-patient variability was modest (coefficients of variation: 26.1% for clearance; 8.9% and 28.5%, respectively, for volumes of distribution of the central and peripheral compartments). Six covariates were identified that influenced pharmacokinetics: age, fat-free mass, an indicator of North East Asian race, baseline albumin, immunoglobulin G, and an early study indicator (two early phase I and phase II belimumab studies: LBSL01 and LBSL02). The analysis showed no apparent difference in steady-state exposure between Chinese and non-Chinese populations and between pediatric and adult populations receiving belimumab 10 mg/kg IV. CONCLUSIONS: In Chinese pediatric patients with SLE, belimumab 10 mg/kg IV every 4 weeks is expected to have exposure similar to that in Chinese adults and non-Chinese pediatric patients with SLE, supporting the use of this regimen in Chinese pediatric patients with SLE. CLINICAL TRIAL REGISTRATION NUMBERS: NCT01649765, NCT00657007, NCT00071487, NCT01345253, NCT01516450, NCT00410384, NCT00424476, NCT02880852, NCT01583530. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s40268-021-00363-2.