Post-induction serum vedolizumab levels are not associated with better maintenance outcomes in patients with Crohn’s disease

Results on exposure-efficacy relationships for vedolizumab in patients with Crohn's disease are contentious. Our study aimed at exploring the relationship between vedolizumab serum concentrations measured during induction and maintenance and treatment outcomes in Crohn's disease patients in a real-world setting.Crohn's disease patients treated with vedolizumab between January 2014 and July 2022 at our tertiary care centre were included. Serum vedolizumab concentrations were measured on at least one of the following time points: week 2, 6, 12, 26, and/or 52. Treatment efficacy was evaluated at weeks 12, 26 and 52 as clinical remission based on patients reported outcomes, faecal calprotectin and C-reactive protein remission.In total, 58 patients (55.2% females) were included. At baseline, active disease, defined either by increased faecal calprotectin, C-reactive protein or patients reported outcomes, was observed in 53 patients (91.4%). Week 12 vedolizumab serum levels were higher in clinical remitters versus non-remitters at weeks 12 and 52 (p