THU0204 Correlation Between Serum Level of Infliximab or Adalimumab and Clinical Response in Spondyloarthritis Seems too Strong to Give the Opportunity of an Interest on Dosage for Therapeutic Adaptation

Background Anti-TNF are the only biologics available in spondyloarthritis. Although in rheumatoid arthritis, there are several studies on anti-TNF serum level and efficacy, few data concern spondyloarthritis Objectives To analyse the clinical relevance of serum levels of infliximab (INF) and adalimumab (ADA) of patients with spondyloarthritis on therapeutic adaptation. Methods 69 patients were included in a retrospective study on a cohort of SA followed in an university hospital who got at least on dosage of serum level of INF or ADA (ELISA done in Tours, laboratory CNRS, UMR 6239). The results were expressed as weak, target or increased concentration compared to expected modeled concentration. Two groups of patients were defined: patients in remission and patients with treatment failure. Impact of level of IFN or ADA on therapeutic adaptation and continued therapy at 1 year has been analyzed in each patient. Results 109 dosages have been done in 69 patients. 55.1% of the dosages have been used finally by the clinician for therapeutic adaptation. In remission group, 25 dosages have been analyzed. Treatment reduction was done more frequently when the dosage results was unknown (60% versus 40% p=0.3). 78.6% of patients in who treatment dose has been decreased had targeted or increased level of IFN or ADA. Whatever the level of dosage and even if weak, 100% of patients have maintained the decreased dose of treatment at 1 year. There was no influence of dosage of serum level INF or ADA and continued of low dose anti-TNF at 1 year in SA. In the group with treatment failure, 71 dosages have been analyzed. There was no difference between our decision on therapy (increased dose or switch) whatever clinician knew the level of dosage (increased dose 52.9% versus 56.2% and switching 47.1% versus 43.8%).72% of patients with treatment failure had weak level of IFN or ADA. So there is a significant correlation between serum level and clinical response (p=0.012). But only 22.2% of the patients have maintained the therapeutic adaptation at one year with no influence of serum level of IFX or ADA. Conclusions Our study show a significant correlation between serum level of IFX or ADA and clinical response in SA and this correlation seems too strong to give the opportunity of an interest on dosage for therapeutic adaptation. Disclosure of Interest None declared