Model-informed Dose De-escalation of Infliximab in Patients With Inflammatory Bowel Diseases

Inclusion Criteria: * The subject or, when applicable, the subject's legally acceptable representative signs and dates a written informed consent form and any required privacy authorisation prior to the initiation of any study procedures. * The subject is aged 18 to 80 years inclusive. * The subject has a good understanding of the Dutch language. * The subject is diagnosed with moderately to severely active ulcerative colitis or Crohn's disease, confirmed by clinical, endoscopic, histological, and/or imaging criteria. * The subject was in maintenance therapy, later lost their response to treatment and subsequently gained steroid-free, clinical and biological remission following infliximab dose escalation (i.e., by increasing the dose and/or shortening the dosing interval) and had an infliximab trough concentration ≥5 mg/L. * Adequate contraception in female subjects of reproductive age (oral contraception, intra-uterine device, sterilisation or barrier method). Exclusion Criteria: * The subject is aged \<18 years or \>80 years. * The subject receives infliximab prophylactically (e.g. in the immediate postoperative setting). * The subject has an ostomy or an ileal anal pouch anastomosis. * If female subjects, when pregnant (based on a positive serum sample) or lactating or intending to become pregnant or nurse before, during or within 15 weeks after the last dose of study drug; or intending to donate ova during such time period. * The subject is participating in another interventional clinical trial.