Precision Dosing of Intravenous Tocilizumab: Development of Pharmacokinetic Model-Derived Tapering Strategies for Patients With Rheumatoid Arthritis.

Background: Tocilizumab targets the interleukin-6 receptor, and dosing is complex owing to its nonlinear clearance related to target binding. Therefore, tapering tocilizumab requires a different approach than that of tumor necrosis factor inhibitors (TNFi). This study aimed to identify these differences and enable personalized treatment of rheumatoid arthritis (RA) beyond TNFi therapy.

Methods: A population pharmacokinetic model of intravenous tocilizumab was developed using data from a randomized controlled trial of dose tapering in patients with RA. Subsequent population-level Monte Carlo and individual Bayesian simulations were performed to create tapering strategies involving dose reduction and interval extension. The target trough concentration of tocilizumab was 5 mg/L. Finally, the drug savings were compared between the 2 methods.

Results: The pharmacokinetic of tocilizumab was described with a 2-compartment model with parallel linear (CL 0.20 L/d) and nonlinear (VM 5.2 mg/d, KM 0.19 mg/L) elimination. The linear clearance rate and central volume of distribution increased with lean body mass, and men exhibited higher clearance rates than women. The simulated concentration-time profiles demonstrated that, owing to nonlinear clearance, drug concentrations decreased more than dose-proportionally with lower doses. Tapering based on an individual Bayesian approach emerged as the most promising strategy, yielding a 39% reduction in drug use across virtual populations.

Conclusions: Tapering strategies were developed for intravenous tocilizumab, offering potential application in patients with RA who have reached low disease activity or remission, pending clinical validation. The developed strategies demonstrate that the tapering of tocilizumab should be approached more carefully and in smaller steps than that of TNFi.