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

Abstract Background Therapeutic drug monitoring is useful in anti-TNFa treatment of inflammatory bowel disease (IBD). However, data on vedolizumab therapy are sparse. Our aim was to assess association between early vedolizumab trough levels (VTL) and response to induction therapy in patients with IBD. Methods Study population comprised consecutive IBD patients from a prospective cohort of vedolizumab treated patients at our centre who had vedolizumab trough levels (VTL) and anti-vedolizumab antibodies (AVA) measured during induction phase of therapy. Included patients obtained vedolizumab 300 mg at weeks 0, 2, 6 with additional dose at Week 10 in case of inadequate response after third infusion. Clinical response evaluated by physician global assessment (PGA) was assessed 1 month after last induction dose (Week 10 or 14). Measurement of VTL and AVA was performed by ELISA assays (ImmunoGuide®, Tani Medical) with a detection limit for VTL of 1.9 μg/ml and measurement range of 0 to 600 μg/ml, and with AVA cut-off value 3 AU/ml. Results We included 87 patients, 31 with Crohn’s disease and 56 with ulcerative colitis. At baseline, only 15% of patients were naïve to anti-TNFa therapy; 61% used systemic steroids and 26% thiopurines. Additional dose at Week 10 was needed in 39% of individuals. Clinical response to induction phase assessed by PGA was reported in 77% of IBD patients. Median VTL at Week 6 and Week 10–14 were 30.6 μg/ml (1.1–80.0) and 19.1 (0–80.0) μg/ml, respectively. Seven per cent of patients developed positive AVA until Week 10–14. Comparing patients with and without clinical response to vedolizumab no significant difference in median VTL was found, both at Week 6 (33.5 vs. 28.2 μg/ml; p = 0.71) and Week 10–14 (16.2 vs. 22.5 μg/ml; p = 0.27). Patients with previous anti-TNFa therapy had significantly lower trough levels at Week 10–14 compared with naïve ones (median 16.1 vs. 29.1 μg/ml, p = 0.02). Otherwise, no impact of diagnosis type or concomitant immunosuppressants on VTL was observed. Conclusions No association between early VTL and response to induction therapy was found in our study. Further studies have to address clinical utility of therapeutic drug monitoring in long-term vedolizumab treatment. The study was supported by the IBD-Comfort Foundation.