In patients with rheumatoid arthritis (RA), tocilizumab (TCZ) concentrations are associated with clinical improvement during the first 24 weeks of subcutaneous TCZ treatment, according to study results published in the Journal of Rheumatology.

The study included data from the Israeli branch of the multinational TOZURA study, which evaluated a weekly subcutaneous TCZ treatment regimen in a real-life clinical setting (n=100). The researchers used generalized estimating equations (GEE) to evaluate associations between TCZ levels and study outcomes. They used linear models and GEE to determine associations between participant characteristics and TCZ levels.

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At 12 weeks, the mean TCZ trough levels were 34±19 mg/ml, which increased to 41±23 mg/ml at 24 weeks.

The results indicated that there was a significant association between TCZ concentration and change in Clinical Disease Activity Index (CDAI) score (P =.024).

The researchers calculated that every increase of 10 mg/ml in the concentration of TCZ was associated with a 1.41 odds ratio (OR) of being in a state of CDAI remission or low disease activity compared with a moderate/high disease activity state (P =.001). Every 10 mg/ml increase was also associated with a 1.52 OR of being in Health Assessment Questionnaire without Disability Index (HAQ-DI) remission (P =.029).

The researchers found an inverse association between body mass index (BMI) and improvement in CDAI score. BMI was also inversely associated with TCZ concentrations, with patients who weighed >100 kg having lower TCZ concentrations compared with patients who weighed ≤100 kg.

“These results raise the possibility that in patients with an inadequate response to TCZ treatment, especially in obese patients, the clinical outcomes might be improved by monitoring and adjusting TCZ drug levels,” the researchers wrote.

Reference

Arad U, Elkayam O. Association of serum tocilizumab trough concentrations with clinical disease activity index scores in adult rheumatoid arthritis patients. [published online June 1, 2019]. J Rheumatol. doi:10.3899/jrheum.181431