Pharmacokinetic and Pharmacodynamic Analysis of Subcutaneous Tocilizumab in Patients With Rheumatoid Arthritis From 2 Randomized, Controlled Trials: SUMMACTA and BREVACTA

Hisham Abdallah, Joy C. Hsu, Peng Lu, Scott Fettner, Xiaoping Zhang, Wendy Douglass, Min Bao, Lucy Rowell, Gerd R. Burmester, Alan Kivitz

Tocilizumab is a humanized anti-interleukin-6 receptor antibody for treating rheumatoid arthritis. Pharmacokinetic/pharmacodynamic analysis was performed on the 24-week, double-blind parts of 2 randomized controlled trials: SUMMACTA and BREVACTA. SUMMACTA compared subcutaneous tocilizumab 162 mg every week (QW) to intravenous tocilizumab 8 mg/kg every 4 weeks (Q4W), while BREVACTA evaluated 162 mg subcutaneous tocilizumab every 2 weeks (Q2W) versus placebo. In addition to noncompartmental analysis, a two-compartment population pharmacokinetic model, with first-order absorption (for SC) and linear and Michaelis-Menten elimination was used. Mean observed steady-state predose tocilizumab concentrations at week 24 were 40 μg/mL and 7.4 μg/mL for subcutaneous QW and Q2W dosing, respectively, and 18 μg/mL for IV. In the population PK model, body weight was an important covariate affecting clearance and volume of distribution. Mean (SD) population predicted predose concentration for patients ≥100 kg was 23.0 (13.5) μg/mL for subcutaneous tocilizumab QW and 1.0 (1.6) μg/mL for Q2W. Efficacy was lowest with SC Q2W dosing in patients >100 kg, reflecting lower exposure. The SC Q2W regimen is not recommended for these patients. Pharmacodynamic responses were comparable for the QW SC and Q4W IV regimens, and less pronounced with the Q2W SC regimen. No trend was observed for increased adverse events with increasing tocilizumab exposure. The results of this analysis are consistent with the non-inferiority of efficacy of the QW SC regimen to Q4W IV and the superiority of the Q2W SC to placebo. These results support the label recommendations for subcutaneous dosing of tocilizumab in rheumatoid arthritis patients. This article is protected by copyright. All rights reserved.