P487 Early vedolizumab trough levels are not associated with a short-term response in patients with inflammatory bowel disease

Background : Data on usefulness of therapeutic drug monitoring in vedolizumab therapy are sparse and conflicting. Our aim was to assess association between early vedolizumab trough levels (VTL) and response to induction therapy in patients with inflammatory bowel diseases (IBD). Methods : Study population comprised consecutive IBD patients from a prospective cohort of vedolizumab treated patients at our centre who had VTL and anti-vedolizumab antibodies (AVA) measured during induction phase of therapy. Included patients obtained vedolizumab 300mg at weeks 0, 2, 6 with extra dose at week 10 in case of inadequate response after 3 rd infusion. Clinical response evaluated by physician global assessment was assessed one month after last induction dose (week 10 or 14). Measurement of VTL and AVA was performed by ELISA assays. Results : Eighty-seven patients, 31 with Crohn´s disease and 56 with ulcerative colitis were included. Only 15 % of patients were naive to anti-TNF-α therapy; 61 % used concomitant systemic steroids and 26 % thiopurines. Additional dose at week 10 was given to 39 % of individuals. Clinical response to induction was reported in 77 % of IBD patients. Median VTLs at week 6 were 30.6 µg/mL (range: 1.1-80.0). Comparing patients with and without clinical response to vedolizumab no significant difference in median VTL at week 6 was found (29.4 vs. 34.4 µg/mL; p=0.71). Likewise, VTL did not differ significantly in individuals with additional dose at week 10 compared to those with standard induction (40.0 vs. 28.5; p=0.69. Seven percent of patients developed positive AVA until week 10-14. No impact of diagnosis type, concomitant immunosuppressantsor previous biologic therapy on VTL was observed. Conclusion : No association between early VTL and clinical response to induction therapy was found in our study. Further studies will have to address the clinical relevance of therapeutic drug monitoring in long-term vedolizumab treatment.