Use of Tocilizumab Drug Levels to Optimize Treatment in RA

Tocilizumab concentrations above 1 mg/L are likely to be sufficient for normalizing C-reactive protein (CRP) production in patients with rheumatoid arthritis (RA). In practice, however, a large variability in the concentrations of tocilizumab is found, and a large proportion of patients treated with tocilizumab subcutaneously (sc) have concentrations far above 1 mg/L. These patients can probably lower their doses without losing clinical response. A 52 weeks non-inferiority, multicenter, randomized controlled study will be performed to investigate whether patients with RA with serum trough concentrations of tocilizumab higher than 15 mg/L can increase their dosing interval to every two weeks without losing clinical response. Patients with relatively high trough concentrations will be randomly assigned to continuation of the standard dose or to increase dosing interval to every two weeks. The main objective is to investigate the difference in mean time weighted Disease Activity Score in 28 joints, including erythrocyte sedimentation rate (DAS28-ESR) between the two groups after 28 weeks. It is expected that patients with relatively high trough concentrations can safely increase their dosing interval without losing response.