Concentration-Guided Tocilizumab Dose Reduction Versus Standard Dosing in Rheumatoid Arthritis: A Randomized, International, Multicenter, Non-Inferiority Trial

The primary objective of this study is to evaluate the difference in the mean time-weighted **Disease Activity Score in 28 joints**, including erythrocyte sedimentation rate (DAS28-ESR), in patients with **rheumatoid arthritis** (RA) who have serum trough concentrations of **tocilizumab** higher than 15 mg/L. Participants are randomly assigned to either continue with the standard dosing regimen or to extend the dosing interval to every two weeks. This investigation is clinically relevant as it aims to optimize the dosing strategy of tocilizumab, potentially improving patient outcomes by reducing medication exposure while maintaining disease control.

The clinical trial involves participants diagnosed with **rheumatoid arthritis**. The study population includes both male and female subjects, with an age range spanning from 18 to 64 years. Participants are generally in stable health, as indicated by the absence of recent changes in glucocorticoid and DMARD treatments, such as methotrexate, in the past three months. The trial does not include a vulnerable population. The selection criteria require current use of subcutaneous tocilizumab 162 mg weekly for at least the last six months, and the treating rheumatologist must be convinced of the benefit of continuing tocilizumab. Written informed consent is also a prerequisite. The sponsor has not provided information regarding the total number of participants. Lifestyle factors such as diet and physical activity are not specified as part of the trial's considerations.

The clinical trial is designed to evaluate the efficacy of **tocilizumab** dose optimization in patients with **rheumatoid arthritis**. This study is a randomized, international, multicenter, non-inferiority trial. Participants will be randomly assigned to either continue with the standard dosing regimen or to a concentration-guided dose reduction, where the dosing interval is increased to every two weeks. The trial will span a total duration of 52 weeks, with primary and secondary endpoints assessed at 28 and 52 weeks, respectively. The primary endpoint is the difference in mean time-weighted Disease Activity Score in 28 joints (DAS28) after 28 weeks between the two treatment groups. Secondary endpoints include differences in DAS28 after 52 weeks, as well as other clinical measures such as CDAI, SDAI, and HAQ scores, and the number and severity of adverse events.

Participants will undergo a series of study visits, beginning with an inclusion (screening) visit to confirm eligibility based on criteria such as a diagnosis of rheumatoid arthritis according to ACR criteria, current use of subcutaneous tocilizumab 162 mg weekly for at least six months, and no recent changes in glucocorticoid or DMARD therapy. Written informed consent is required. Follow-up visits will occur at regular intervals to monitor disease activity, drug levels, and any adverse events. The end-of-study visit will occur at the conclusion of the 52-week period, where final assessments will be conducted.

The expected length of participant involvement is approximately 52 weeks. Conditions that may lead to early termination from the study include withdrawal of consent, significant protocol deviations, or adverse events that compromise participant safety. The trial aims to provide insights into the therapeutic range of tocilizumab and develop a pharmacokinetic model to optimize dosing strategies for improved patient outcomes.

The clinical trial involves the administration of **tocilizumab**, an experimental medication used in the treatment of rheumatoid arthritis. Tocilizumab is a monoclonal antibody classified under the ATC code L04AC07. It is administered in the form of a subcutaneous injection, with a pharmaceutical form designated as PHF00231MIG. The maximum daily and total dose of tocilizumab is 162 mg, and the treatment period is limited to one time unit, as specified in the trial protocol. The active substance, tocilizumab, is a protein of non-human origin, and it is also known by synonyms such as RO4877533, BIIB800, and atlizumab. The trial aims to compare concentration-guided dose reduction with standard dosing in patients with rheumatoid arthritis.

In addition to the experimental treatment, the study may include non-experimental treatments such as standard-of-care therapy or placebo, depending on the specific trial design. The trial is structured as a randomized, international, multicenter, non-inferiority study, focusing on the difference in mean time-weighted Disease Activity Score in 28 joints, including erythrocyte sedimentation rate (DAS28-ESR), in patients with rheumatoid arthritis. Participants are monitored for compliance with the dosing schedule, and the trial's main objective is to assess the efficacy of adjusting the dosing interval based on serum trough concentrations exceeding 15 mg/L.

Efficacy in this clinical trial will be assessed primarily through the evaluation of the mean time-weighted **Disease Activity Score in 28 joints**, including erythrocyte sedimentation rate (DAS28-ESR), in patients with rheumatoid arthritis (RA). The primary endpoint is to compare the mean time-weighted DAS28 after 28 weeks between two groups: those receiving concentration-guided dose reduction and those on standard dosing. This analysis will be conducted under the non-inferiority principle, anticipating no worse outcomes for patients with adjusted dosing intervals compared to those continuing the regular tocilizumab dose.

Secondary endpoints include the assessment of the mean time-weighted DAS28 after 52 weeks, differences in Clinical Disease Activity Index (CDAI), Simplified Disease Activity Index (SDAI), and Health Assessment Questionnaire (HAQ) scores at 28 and 52 weeks between the treatment groups. Additional parameters include the evaluation of direct medical costs of therapeutic drug monitoring (TDM) versus standard treatment, the number and severity of flares and adverse events, changes in drug levels from baseline to 52 weeks, and the relationship between dose, drug concentration, and clinical disease activity. The trial will also explore the therapeutic range of tocilizumab, develop a pharmacokinetic model, and gather patient perspectives on dose optimization through TDM.