Exposure–response analysis for selection of optimal dosage regimen of anifrolumab in patients with systemic lupus erythematosus

OBJECTIVES: The randomized, double-blind, phase 2 b MUSE study evaluated the efficacy and safety of the type I IFN receptor antibody anifrolumab (300 mg or 1000 mg every 4 weeks) compared with placebo for 52 weeks in patients with chronic, moderate to severe SLE. Characterizing the exposure-response relationship of anifrolumab in MUSE will enable selection of its optimal dosage regimen in two phase 3 studies in patients with SLE. METHODS: The exposure-response relationship, pharmacokinetics (PK) and SLE Responder Index (SRI(4)) efficacy data were analysed using a population approach. A dropout hazard function was also incorporated into the SRI(4) model to describe the voluntary patient withdrawals during the 1-year treatment period. RESULTS: The population PK model found that type I IFNGS-high patients, and patients with a higher body weight, had significantly greater clearance of anifrolumab. Stochastic clinical simulations demonstrated that doses <300 mg would lead to a greater-than-proportional reduction in drug exposure owing to type I IFN alpha receptor-mediated drug clearance (antigen-sink effect, more rapid drug clearance at lower concentrations) and suboptimal SRI(4) responses with wider confidence intervals. CONCLUSIONS: Based on PK, efficacy and safety considerations, anifrolumab 300 mg every 4 weeks was recommended as the optimal dosage for pivotal phase 3 studies in patients with SLE.