Population pharmacokinetics of siltuximab: impact of disease state

To characterize the effects of disease type and clinical characteristics on the pharmacokinetics of siltuximab, an IL-6 inhibiting monoclonal antibody. Siltuximab pharmacokinetic data were combined from seven phase I/II clinical trials. A population pharmacokinetic model was developed to characterize changes in siltuximab disposition with disease type, albumin, liver and renal function, and patient demographics. A total of 7761 concentrations from 460 participants were used in the study. The data were well described by a two-compartment model. Castleman’s disease, healthy volunteer status, albumin, and ALT were independent predictors of clearance. Monte Carlo simulations of the final model for an 11 mg/kg dose resulted in a longer median half-life for healthy volunteers (24.5 days) as compared to Castleman’s disease (19.1 days) and other tumor types (22.2 days). Clearance varied 1.8-fold over the range of albumin values seen in the study (1.5–5.2 g/dL), while ALT resulted in minimal changes in clearance. Albumin and disease state are important factors for siltuximab disposition and will likely need to be considered for dosing in future therapeutic applications.