Population pharmacokinetic analysis of tocilizumab in patients with rheumatoid arthritis

Tocilizumab is a humanized anti-interleukin-6 (IL-6) receptor monoclonal antibody that has demonstrated efficacy in the treatment of rheumatoid arthritis (RA). A population pharmacokinetic (PK) model was developed using nonlinear mixed effect modeling to describe the PK profile of tocilizumab and used to estimate interindividual variability and assess the influence of covariates on PK parameters. The model was constructed based on data collected from 1793 patients with moderate to severe RA who received tocilizumab (4 or 8 mg/kg), via intravenous infusion every 4 weeks, during 4 phase III clinical trials. Serum concentration-time profiles of tocilizumab were adequately described by a 2-compartment disposition model with parallel linear and nonlinear elimination kinetics. The 8-mg/kg dose of tocilizumab, compared with the 4-mg/kg dose, resulted in a more pronounced saturation of the nonlinear clearance pathway over the dosing interval, and this nonlinear clearance was representative of target-mediated elimination due to tocilizumab binding to the IL-6 receptor.