LAUSR

Background The management of systemic inflammatory diseases, such as Rheumatoid arthritis (RA) and Ankylosing spondylitis (AS) has been revolutionized with the introduction of tumor necrosis factor alpha inhibitors (TNF-I). Significant reduction in disease activity and achievment of remission resulted in halting of joint damage and improved quality of life. Unfortunately, approximatly 15–30% of patients fail to reach desirable improvement or lose drug effectiveness with time. It may be explained by immunogenicity and production of human anti chimeric antibodies (HACA). Presence of HACA against TNF-I have been associated with low levels of the drug and lose of therapeutic response. The prevalence of HACA in RA is estimated between 20–40%, and in AS between 25–64%. The difference in the pathogenesis of RA and AS as well as diverce approach in using disease modifying anti-rheumatic drugs (DMARDs) may influence HACA production and TNF-I levels in these conditions. Objectives To compare the incidence of HACA and Infliximab, Etanercept, Adalimumab levels in patients with RA and AS with respect to concomitant DMARDs. Methods Patients' with RA and AS data treated with TNF-I for at least 3 months in whom tests for HACA and Infliximab, Etanercept, Adalimumab levels were available were extracted from patients' files. Data included: demographics, concomitant treatment, and disease activity scores (BASDAI for AS and DAS-28 for RA). Serum for assessment of drugs level (ELISA) and HACA (ADAb;Promonitor, Bridging, ELISA) was obtained before the next drug administration. Univariate comparison was done using Student t test for the continuous variables and Chi square test for the categorical variables (P <.05 was considered significant). Results Data on 53 patients with AS (mean age 47.9±11.9 years, 41.5. % female) and 29 patients with RA (mean age 54.8±8.1 years, 75, 9% female) were available: 22 RA patients were treated with Methotrexate and 7 with other DMARDs; no one AS patient was treated with concomitant DMARDs. High level of HACA was found in 22.6% AS patients and in 34.5% RA patients (p>0.05); 86.8% patients with AS reached theurapethic level of drug compared to 69% RA patients (p=0.027). Drugs levels were similar in AS and RA patients (Table). Low disease activity (DAS28-CRP<3.2) was registered in 62.1% RA patients and in 81.4% AS patients (BASDAI <4). Conclusions Despite significant difference in the use of concomitant DMARDs, patients with AS and RA had similar prevalence of HACA. Moreover, higher proportion of patients in AS group reached therapeutic level of TNF-I. The data supports the hypothesis, that immune responce to TNF-I may be different in AS and RA and, therefore, the addition of DMARDs to prevent development of HACA in patients with AS may be unnecessary. Disclosure of Interest None declared