Association between body weight and tocilizumab effectiveness in rheumatoid arthritis: results from the BSRBR-RA.

Objectives: Tocilizumab is an IL-6 receptor humanized monoclonal antibody for the treatment of rheumatoid arthritis (RA) with intravenous (IV) and subcutaneous (SC) preparations available. Only IV tocilizumab is dosed adjusting for weight. Therefore, we aimed to study the association between body weight and the effectiveness of tocilizumab by the route of administration.

Methods: Patients with RA-administered tocilizumab in the BSRBR-RA were included in the analysis and stratified by route of administration. Outcomes included the 6-month change in DAS28, the proportion of patients achieving DAS28 remission, 6-month EULAR response and persistence of the first route of tocilizumab administration. The exposure was every increase in 10 kg of body weight. Adjusted regression models appropriate to outcome were used to study the associations between body weight and outcomes. Multiple imputations accounted for missing data.

Results: A total of 2612 patients were included. Body weight was associated with reduced response to SC tocilizumab measured by change in DAS28: adjusted regression coefficient (95% CI) all patients 0.01 (-0.04, 0.07); IV: -0.03, (-0.1, 0.5); SC: 0.1 (0.02, 0.2) but not odds in achieving DAS28 remission or EULAR response. There was no significant association between body weight and the persistence of IV or SC tocilizumab.

Conclusion: Body weight was associated with the initial response to SC tocilizumab, although the difference in response was small, but not drug persistence. Physicians should monitor the body weight of patients and consider interventions to promote maintenance of a healthy weight.