The aim of this study is to evaluate the IFX exposure (AUC), effectiveness, presence of ADAbs and treatment burden before and after switching from IV to SC IFX maintenance treatment in a real-world cohort of IBD patients with quiescent disease on IFX monotherapy and combination therapy of IFX and an immunomodulator.

Methods: this is a prospective, single centre, open-label cohort study, conducted in Zuyderland Medical Centre in which 36 adult IBD patients in remission on stable IV IFX therapy are switched to SC CT-P13 of which 18 patients use an immunomodulator in addition to IFX (cohort 2). After the switch to SC CT-P13, patients are followed for 24 weeks.

The study is subdivided into two phases: the IV IFX treatment phase before switching and the SC CT-P13 treatment phase after the switch. After enrolment, the subject receives a final dose of IV IFX according to their own maintenance schedule. Primary endpoints are the Area under the concentration-time curve (AUC) at steady state (1) before and after the switch to SC CT-P13 and (2) with or without concomitant immunomodulator during SC therapy. AUCs will be estimated using pharmacokinetic modelling in MwPharm. Besides IFX trough level, treatment related time expenditure, quality-of-life and patient satisfaction will be assessed before and after the switch.

On demand.

Inclusion Criteria:

• Adult patients (18-75 years) with an confirmed diagnosis of IBD according to usual criteria, including previous endoscopic examination.
• Patients on IV IFX maintenance therapy at a stable dose and dosing interval for at least 16 weeks of 5-10 mg/kg every 6-8 weeks without side effects of IFX.
• IBD in clinical remission for at least 16 weeks without treatment with systemic corticosteroids in the previous 16 weeks. Clinical remission in adult patients is defined as a Harvey-Bradshaw index (HBI) < 4 for CD [18] or a partial Mayo Index (PMI) <2 for UC [19], with faecal calprotectin levels <250 μg/g faeces and CRP <10 mg/L.
• Concomitant immunomodulators are allowed, i.e. in stable doses were received for at least 12 weeks prior to study enrolment. These doses will be continued throughout the study, including azathioprine (AZA), 6-mercaptopurine (6-MP), tioguanine (TG) and MTX.
• Written informed consent

Exclusion Criteria:

• Patient <18 years of age.
• Allergy or hypersensitivity to any of the excipients of SC CT-P13.
• Patient with active perianal fistula.
• Patient with another autoimmune disease in addition to IBD.
• Patient treated concomitantly with another Mab in addition to IFX.
• Patients who, after starting IV IFX, have developed new contraindications to IFX according to European Public Assessment Report (EPAR).[3]
• Female patient who is currently pregnant or breastfeeding, or is planning to become pregnant or breastfeed within 6 months of the last dose of IFX.
• Patient has a serious acute or chronic medical or psychiatric condition that might increase the risk associated with study participation or investigational product administration or that might interfere with the interpretation of study results.
• Patients who, in the opinion of their general practitioner or investigator, should not participate in the study (e.g. non-adherence, mental health problems, illiteracy).