SAT0558 Association Between Etanercept Concentrations and Disease Activity in Psoriatic Arthritis During 52 Weeks of Follow-Up
Authors: E. Vogelzang, C.L. Krieckaert, M.T. Nurmohamed, E.L. Kneepkens, T. Rispens, A.W. Van Kuijk, G. Wolbink
Journal: Annals of the Rheumatic Diseases (2015)

<h3>Background</h3> In registration trials, etanercept has shown to improve clinical outcome for patients with psoriatic arthritis (PsA).[1] However a proportion of patients does not respond or lose response to the drug. In patients with rheumatoid arthritis (RA) it was observed that etanercept trough concentrations were significantly lower in EULAR moderate and non responders compared to good responders.[2] Thus far, etanercept concentrations, have not yet been investigated in PsA. <h3>Objectives</h3> To investigate the relationship between etanercept concentrations and clinical response in a prospective cohort of PsA patients starting etanercept treatment. <h3>Methods</h3> This prospective cohort study comprised 154 consecutive PsA patients with mainly peripheral joint involvement and treated with etanercept once 50 mg or twice 25 mg every week. At baseline and during follow up at 4, 16, 28, 40 and 52 weeks trough serum samples were collected and disease activity was assessed using the disease activity score using 28 joint count (DAS28), C-reactive protein (CRP) and Psoriasis Area Severity Index (PASI). Low disease activity was defined as DAS28&lt;2.6. Etanercept trough concentrations were measured using an enzyme-linked immunosorbent assay (ELISA). Patients were categorised into tertiles based on etanercept trough concentrations at week 52 as followed: low, intermediate and high. Generalized estimating equation (GEE) and χ2 were used for statistical analysis. <h3>Results</h3> Etanercept concentration tertiles were: high concentrations &gt;2.12 mg/L with median 2.80 mg/L (IQR 2.43-3.12), intermediate concentrations 1.35-2.12 mg/L with median 1.76 mg/L (IQR 1.58-1.92) and low concentrations &lt;1.34 mg/L with median 0.99 mg/L (IQR 0.72-1.19). A significant difference was shown in the percentage of patients that achieved low disease activity between low and high etanercept levels; 30% vs. 38%, respectively, p=0.023 (figure 1). No significant difference in low disease activity percentages were found for intermediate vs. low and intermediate vs. high etanercept concentrations. Furthermore, using GEE, patients with higher disease activity during 52 weeks of follow-up, had significantly lower etanercept concentrations (β -0.114, 95%CI -0.204 - -0.024, p=0.013). However, no significant difference was found for CRP (β -0.365, 95%CI -0.911 - 0.181, p=0.190) or PASI (β 0.281, 95%CI -0.283 - 0.845, p=0.328). <h3>Conclusions</h3> Patients with high etanercept trough concentrations did achieve low disease activity more often compared to patients with low etanercept concentrations. For CRP and PASI no association was found. <h3>References</h3> Mease PJ, Goffe BS, Metz J, et al. Etanercept in the treatment of psoriatic arthritis and psoriasis: a randomised trial. Lancet 2000; 356:385-90. Jamnitski A, Krieckaert CL, Nurmohamed MT, et al. Patients non-responding to etanercept obtain lower etanercept concentrations compared with responding patients. Ann Rheum Dis 2012;71:88–91. <h3>Disclosure of Interest</h3> E. Vogelzang: None declared, C. Krieckaert Speakers bureau: Pfizer and Abbvie, M. Nurmohamed Consultant for: Abbott, Roche, Pfizer, MSD, UCB, SOBI and BMS, Speakers bureau: Abott, Roche and Pfizer, E. Kneepkens Speakers bureau: Pfizer, T. Rispens Speakers bureau: Pfizer and Abbvie, A. Van Kuijk: None declared, G. Wolbink Grant/research support from: Pfizer (paid to the institution), Speakers bureau: Pfizer and Amgen