P704 Association between trough levels of vedolizumab and therapy outcome in a cohort of patients with inflammatory bowel disease

Vedolizumab(VDZ) is an α4β7 integrin antagonist for the treatment of IBD. The role of VDZ therapeutic drug monitoring has not been clearly defined. We aimed to investigate the association between VDZ trough levels and therapy outcome in a cohort of patients with inflammatory bowel disease (IBD) and the association between VDZ trough levels and clinical and biochemical variables. IBD patients receiving VDZ were identified in a cross-sectional study where serum samples were not collected at a pre-specified time point. Ulcerative colitis(UC) and Crohn’s disease(CD) clinical activity was quantified using Mayo clinical subscore (MCS, remission MCS ≤ 1) and Harvey–Bradshaw Index (HBI, remission HBI < 5). VDZ and antibody-to-vedolizumab (AVA) concentrations determined by Prometheus® Anser® laboratories using non-radio-labelled liquid-phase mobility shift assays. p-values < 0.05 were considered significant. N = 35 IBD patients included (57% UC, 54% male, median age(range) 44.3 years(17.7–76.2), 9% receiving immunomodulators, 83% prior anti-TNF. 34/35 patients had trough VDZ level performed during maintenance therapy. Median(range) trough VDZ concentration 9.5 µg / ml(0 – 25). 0/35 subjects had detectable AVAs. No association between MCS or HBI defined remission and trough VDZ concentrations was observed p = 0.38 and p = 0.83, respectively. No difference in trough VDZ concentrations observed comparing by IBD phenotype(p = 0.50); prior biologic exposure(n = 0.37); or concomitant immunomodulator use(p = 0.68). CRP and albumin levels were not correlated with trough VDZ concentrations, correlation coefficient −2.2(p = 0.36) and 0.21(p = 0.36) respectively. In a real-world study of IBD patients receiving VDZ no clear association between VDZ trough levels and therapy outcome was observed. Significant immunogenicity was not observed supporting the use of VDZ monotherapy in uncomplicated patients. Further study is required to determine the utility of therapeutic drug monitoring in VDZ-treated patients.