SAT0206 Tocilizumab Serum Levels and Antidrug Antibodies and Its Relationship with Disease Activity in Rheumatic Diseases

BackgroundTocilizumab (TCZ) is a humanized anti-IL-6 receptor-blocking monoclonal antibody used for the treatment of rheumatoid arthritis (RA), idiopathic juvenile arthritis (IJA) and off-label in Adult Onset Still Disease (AOSD). The development of anti-TCZ antibodies could reduce treatment efficacy or induce treatment failure.ObjectivesTo analyse TCZ serum levels and antidrug antibodies (ADA) in a cohort of RA, IJA and AOSD patients treated with TCZ, and to evaluate its relationship with Disease Activity Score using a 28-joint count (DAS28), C-reactive protein (CRP) levels and the presence of combined treatment with glucocorticoids or DMARDs.MethodsCross-section study including all patients undergoing chronic treatment with TCZ in a tertiary academic hospital. Referral area: 850,000 inhabitants. Twenty-two patients were included. TCZ serum and ADA levels were measured by ELISA (Theradiag) at baseline (before infusion), 15 days and 30 days after infusion.ResultsTwenty-two patients were studied: 18 RA, 3 IJA and 1 AOSD, 81.8% female; mean age and mean disease duration: 54.2 (±13) and 15.5 (±12) years respectively; 73% of the RA patients were positive for anti-CCP and 70% for rheumatoid factor, mean DAS28-CRP at day 0 and 30: 2.9 and 2.6 respectively. Fifteen patients were treated with TCZ for more than 1 year (range 12-58 months), 19 were treated with TCZ at 8 mg/kg, 2 at 6mg/kg, and one at 5mg/kg every 4 weeks due to low disease activity. Thirteen patients received TCZ in monotherapy, 9 received DMARDs combined treatment, 10 with glucocorticoids (mean dose 4mg/day, range 2-10mg). TCZ serum levels were at baseline: 1.2- 61.7 μg/ml, 15 days: