Population Pharmacokinetic and Pharmacodynamic Analysis of Belimumab Administered Subcutaneously in Healthy Volunteers and Patients with Systemic Lupus Erythematosus

Intravenous belimumab 10 mg/kg every 4 weeks is indicated in patients with active, autoantibody-positive systemic lupus erythematosus receiving standard systemic lupus erythematosus care. Subcutaneous 200-mg weekly administration, which may prove more convenient for patients and improve adherence, is currently under investigation.

The objective of this study was to characterize the population pharmacokinetics and exposure-efficacy response of subcutaneous belimumab in a pooled analysis of pharmacokinetic data [phase I: BEL114448 (NCT01583530) and BEL116119 (NCT01516450) in healthy subjects (n = 134); phase III: BEL112341 (NCT01484496) in adults with systemic lupus erythematosus (n = 554)] and pharmacodynamic data [BEL112341 in adults with systemic lupus erythematosus (n = 833)].

Non-linear mixed-effects modeling (NONMEM®) was used to develop a population pharmacokinetic model and perform a covariate analysis. Subsequently, exploratory exposure-response analysis and logistic regression modeling was performed based on the individual parameter estimates of the population pharmacokinetic model.

Population-pharmacokinetic parameters for subcutaneous belimumab were consistent with those for intravenous belimumab and other immunoglobulin G1 monoclonal antibodies. Pharmacokinetic parameters and subcutaneous belimumab exposure were consistent between healthy subjects and patients with systemic lupus erythematosus, and no evidence for target-mediated disposition of belimumab was found. Subcutaneous belimumab steady-state exposure was achieved after ~11 weeks; subcutaneous belimumab steady-state minimum concentration exceeded that of intravenous belimumab after <4 weeks, and average steady-state concentration was similar to that achieved following intravenous administration. In patients with moderate-to-severe systemic lupus erythematosus, subcutaneous belimumab 200 mg once weekly plus standard of care significantly improved the systemic lupus erythematosus responder index. However, at this dose, the systemic lupus erythematosus responder index response was not significantly associated with belimumab exposure concentrations.

The analysis demonstrates that a 200-mg once-weekly dose of belimumab is appropriate for subcutaneous administration in patients with systemic lupus erythematosus and that no dose adjustments are required for adult patients to maintain efficacy and safety.