Extrapolation of the Efficacy and Pharmacokinetics of Belimumab to Support its Use in Children with Lupus Nephritis.

Background And Objective: Lupus nephritis (LN), a severe manifestation of systemic lupus erythematosus, has greater severity in children versus adults. Belimumab is approved for systemic lupus erythematosus treatment in patients aged ≥ 5 years, and for active LN in adults in the European Union, China, Japan and Latin America, and patients aged ≥ 5 years in the USA. Low prevalence of paediatric active LN makes conducting a clinical study within a reasonable period unfeasible. We describe a model-based extrapolation of belimumab efficacy and pharmacokinetics from adults to children with LN to support US Food and Drug Administration approval of intravenous belimumab 10 mg/kg (administered every 4 weeks after the loading dose) in children (aged 5-17 years) with active LN.

Methods: This concept assumed that disease progression, response to belimumab, exposure-response, and the target belimumab exposure for efficacy are similar across adult and paediatric systemic lupus erythematosus and LN, evaluated against the published literature for paediatric LN and belimumab systemic lupus erythematosus and LN clinical trial data in adults and children. A two-compartmental population pharmacokinetic model, previously developed for adults with LN, was used to extrapolate belimumab pharmacokinetics to children with LN.

Results: The model captured the dependence of time-varying proteinuria on belimumab clearance, and therefore exposure. Sufficient target exposures for efficacy were achieved in children with active LN. A small proportion of children aged 5-11 years are predicted to have exposures below adult levels but no impact to efficacy is expected.

Conclusions: Our model demonstrated that intravenous belimumab 10 mg/kg every 4 weeks is appropriate for children aged 5-17 years with active LN.