Subcutaneous Belimumab Demonstrates Consistent Steady-State Pharmacokinetics and is Well Tolerated in Paediatric Patients with SLE in China: An Open-Label Study.

INTRODUCTION: This study assessed pharmacokinetics and safety of subcutaneous (SC) belimumab in Chinese paediatric patients with systemic lupus erythematosus (cSLE) who previously received intravenous (IV) belimumab; only the IV form is approved for cSLE in China. METHODS: This single-arm, open-label, 12-week bridging study (GSK Study 217091) characterised belimumab 200 mg SC exposure in Chinese paediatric patients (5-17 years) with cSLE who completed the 48-week IV belimumab Phase 4 trial (GSK Study 213560). Safety and tolerability of SC belimumab on-treatment and in a 16-week follow-up period were also assessed. Patients were categorised based on weight; data were summarised using descriptive statistics. RESULTS: Overall, 16 patients were enrolled (≥ 15- < 30 kg, n = 1; ≥ 30- < 50 kg, n = 5; ≥ 50 kg, n = 10) with a mean age of 12.9 years. The geometric mean approximate Cmax (3 days post-administration) after the first and last dose were 92.44, 63.41 and 68.87 μg/mL, and 28.01, 85.11 and 88.61 μg/mL for the three weight groups, respectively. The geometric mean Ctrough at steady state were, 20.44, 71.57 and 85.55 μg/mL for the ≥ 15- < 30 kg, ≥ 30- < 50 kg and ≥ 50 kg weight groups, respectively. Thirteen patients (81%) reported ≥ 1 AE. No SAEs, severe AEs, AESIs, AEs resulting in belimumab discontinuation, deaths, or local injection site reactions were reported. CONCLUSION: SC belimumab demonstrated expected steady-state exposure and tolerability in Chinese paediatric patients with SLE, supporting its use in this patient population. TRIAL REGISTRATION: GSK Study 217091; NCT05917288.