Background/Purpose Debate is still ongoing regarding rituximab (RTX) as a first or second line biologic therapy. The objective of present study is to assess correlations between patient’s characteristics, including previous treatments  with drug level, clinical response and further evolution.

Methods A group of 62 consecutive rheumatoid arthritis (RA) patients treated with RTX according to National Guideline (2 iv infusions of 1 g separated by 2 weeks, every 6 months) were followed for 2 years. All patients were previously diagnosed according to ACR 1987 or ACR/EULAR 2010 criteria. Demographic data, clinical (number of tender and swollen joints) and laboratory (ESR-erythrocyte sedimentation rate, CRP- C reactive protein, RF -rheumatoid factor, ACPA – anti cyclic citrullinated peptide) variables were collected at baseline and at each reevaluation. RA activity was evaluated in all patients by using DAS28 4v, Simplified Disease Activity Index (SDAI). All clinical evaluation was performed by two independent  assessors. RTX drug level and anti drug antibodies were measured just before a new infusion using Progenika kits (Promonitor®-RTX, Promonitor®-anti-RTX). Patients were excluded if between baseline and next reevaluation had a change in their treatment regimen. The study was approved by local Ethics Committee and all patients gave written informed consent before inclusion. Statistical analysis was performed using SPSS statistical software, version 20.0.

Results Mean rituximab treatment duration in the cohort was 41,79±27,76 months. All patients had Methotrexate associated. No antidrug atibodies were found. During evaluation period 25 patients (40.32%) had signs of inadequate response to treatment. At baseline, 9 (36%) of this patients had undetectable drug level. At that moment there was no difference between patients with detectable and undetectable drug level regarding DAS28 (3,65±1,12 vs 3,45±1,19, P=0.678) and SDAI (20±15,7 vs 21,7±29,6, P=0.845), nor in their treatment duration (48.8±53.4 vs 27.7±13.7, P=0.294). At follow-up, 6 months from dosing RTX, patients with detectable drug level had significantly lower DAS28 (mean DAS28 2,93±1,2 vs 3,27±1,47, P=0.01) and SDAI (mean 12,33±14,13 vs 14,83±20,51, P=0.033). Significantly higher number of patients with detectable rituximab level had anti citrulinated antibodies (P=0.021) and were rheumatoid factor positive (P=0.049). Number of previous anti TNF agents correlated to rituximab level (r=0.514, P=0.009). 62% of patients with detectable rituximab level were were non-responders to two or more anti TNF agents. All patients with undetectable drug level had only one anti TNF agent as previous biologic treatment.

Conclusion Significant differences were found in clinical response in patients depending on the rituximab level and number of previous anti TNF agents used. RTX detectable drug level and 2 or more anti TNFs correlated with better clinical response at follow-up. This result support the actual guidelines for RA treatment regarding rituximab as a second line biologic agent.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/relation-between-number-of-previous-anti-tnf-agents-and-clinical-response-in-rheumatoid-arthritis-patients-treated-with-rituximab/