Objectives: To evaluate whether subcutaneous vedolizumab therapeutic drug monitoring (TDM)-guided de-escalation will be cost-effective, compared to normal dosing regimen in patients with inflammatory bowel disease in remission. The secondary objective is to investigate the efficacy of TDM-guided de-escalation subcutaneous vedolizumab dosing compared to standard dosing. Study design: This is a single-centre, randomized controlled, open-label pilot study. Study population: 40 patients with inflammatory bowel disease (Crohn's disease or ulcerative colitis) in steroid-free clinical and biochemical remission with subcutaneous vedolizumab maintenance therapy of 108 mg every other week for at least 6 months. Intervention: Patients will be randomized (1:1) to the 'TDM-guided subcutaneous vedolizumab de-escalation' strategy versus 'standard care' (e.g. continuing standard subcutaneous vedolizumab dosing regimen of 108 mg every other week). Main study parameters/endpoints: Primary endpoint: cost-effectiveness of the TDM-guided de-escalation group compared to the standard dosing group over 48 weeks. Secondary endpoints include: proportion of patients with sustained clinical remission (based on Harvey-Bradshaw Index or Simple Clinical Colitis Activity Index), proportion of patients with (sustained) biochemical remission (based on c-reactive protein and fecal calprotectin), pharmacokinetic differences (vedolizumab levels and immunogenicity), safety and quality of life (measured by SIBDQ and EQ-5D-5L).