THU0208 Efficacy of Switching Tumor Necrosis Factor α Inhibitor to a Second Tumor Necrosis Factor α Inhibitor and the Influence of Drug Levels and Anti-Drug Antibodies in Patients with Ankylosing Spondylitis and Psoriatic Arthritis

BackgroundSwitching from the first Tumor Necrosis Factor α inhibitor (TNFi) to a second in rheumatoid arthritis is an effective strategy to decrease disease activity. Especially, when antidrug antibodies (ADA) against the first TNFi were detected [1,2]. In addition, patients with detectable ADA against the first TNFi had an increased risk to develop ADA against a second TNFi. In ankylosing spondylitis (AS) and psoriatic arthritis (PsA), switching from the first TNFi to the second is effective, although switchers have a poorer clinical outcome compared with patients who continued their first TNFi [3,4].ObjectivesTo investigate clinical response in AS and PsA patients who switched to a second TNFi versus biological naïve starters. Secondly, to study the association between reason for switching and efficacy of the second TNFi. Finally, investigate predictive value of drug level and ADA of the first TNFi and efficacy to the second.MethodsIn this retrospective study 2 years data were collected from observational cohorts of patients with AS and PsA, in whom TNFi was started. Disease activity and response in AS was assessed by the use of AS Disease Activity Score (ASDAS) and Patient Global Disease Activity (PGDA). For PsA, the Disease activity Scale using 28 joint count (DAS28) and PGDA were used for this purpose. Switchers response to 2nd TNFi use was compared with response during 1st TNFi use of the control group (further mentioned as: switcher vs control). Drug- and ADA levels were measured by an Enzyme-linked immunosorbent assay and an antibody binding test, respectively.ResultsA total of consecutive 486 patients were included of which 65 (AS, n=35; PsA n=30) were switchers. Generalized estimating equation (GEE) demonstrated a significant difference between ASDAS response, switchers vs control; Odds ratio (OR): 0.32 (95% CI 0.14-0.75) p=0.008; and a significant difference between PGDA, switchers vs control, regression coefficient (RC): 1.09 (95% CI 0.30-1.89) p=0.007. In PsA, a significant difference between DAS28 response, switchers vs control; OR 0.28 (95% CI 0.12-0.67) p=0.004; and a significant difference between PGDA of switchers vs control; RC: 15.0 (95% CI 8.8-21.2) p