The goal of this prospective, multicenter, open-label, randomized controlled, non-inferiority trial is to test efficacy and safety of formulation switching between subcutaneous (SC) infliximab and intravenous (IV) infliximab in patients with moderately to severely active Crohn's disease (CD). The primary endpoint of this study is deep remission at week 54. The main questions this study aims to answer are:

Question-1) Is maintenance therapy with SC infliximab (120mg every 2 weeks) non-inferior to IV infliximab (5mg/kg every 8 weeks) in terms of deep remission at week 54? Question-2) Is maintenance therapy with SC infliximab (120mg every 2 weeks) non-inferior to IV infliximab (10mg/kg every 8 weeks) in terms of deep remission at week 54?

Remsima (CT-P13) is the first biosimilar of infliximab and its intravenous (IV) formulation has been used for patients with active Crohn's disease (CD).

Recently, subcutaneous (SC) formulation of Remsima (Remsima SC) was developed and approved by the Korean FDA (Food and Drug Administration). However, until now, besides a registration trial, real-life experiences of Remsima SC is still limited and the efficacy and safety of switching from SC to IV Remsima is still unknown.

In this study, patients with moderately to severely active CD who achieve clinical response to SC Remsima at week 30 (IV Remsima 5mg/kg at week 0 and 2, followed by SC Remsima 120mg every 2 weeks from week 6) will be randomly (1:1) assigned to IV Remsima group (Arm 2) or to continued SC Remsima group (Arm 3). Non-responders at week 30 will be allocated to Arm 1 (IV Remsima 10 mg/kg). The primary endpoint is the non-inferiority of Arm 3 compared with Arm 2 in terms of deep remission rate at week 54. The secondary endpoint is the non-inferiority of Arm 3 compared with Arm 1 in terms of deep remission rate at week 54. The non-inferiority margin is set as -20% and a total of 100 patients will be enrolled.

Through this study, the investigators aim to provide the clinical evidence for selecting the most optimal formulation of infliximab according to therapeutic response among Korean patients with CD.

Inclusion Criteria:

1. 18 years or older
2. Moderate to severe Crohn's disease (Crohn's disease activity index 220 to 450)
3. Ileocolonic Crohn's disease (CD) with Simple Endoscopic Score for Crohn Disease ≥6 or ileal or colonic CD with with Simple Endoscopic Score for Crohn Disease ≥4 and ulcer score ≥1 in at least one segment
4. Fecal calprotectin ≥250 µg/g or C-reactive protein≥0.5 mg/dL
5. Patients who have never been to exposed to any biologic agent
6. Patients who are non-responsive or intolerance to conventional therapy (corticosteroids, immunomodulators, or antibiotics, etc.) or contraindicated to conventional therapy
7. Patients who gave a voluntary informed consent

Exclusion Criteria:

1. Patients who have a history of hypersensitivity to humanized proteins

2. Patients ever treated with corticosteroids within 8 weeks of screening date

3. a) Symptomatic intestinal stricture, b) Symptomatic anal stricture, c) Untreated intra-abdominal abscess, d) Untreated perianal abscess, e) Abdominal surgery within 6 months, f) Patients who are expected to require intestinal surgeries during study period

   - However, the following patients can be included: from baseline, 4 weeks or more after proper drainage of perianal abscess and from baseline, 8 weeks or more after proper drainage of intra-abdominal abscess

4. Active tuberculosis. However, the following patients can be included: Patients who were diagnosed with tuberculosis, but were properly treated with anti-tuberculosis therapy according to the standard guidelines and who were confirmed to be cured.

5. Latent tuberculosis infection (LTBI): Patients confirmed as having latent tuberculosis through medical history, physical examination, chest X-ray, PPD (Purified Protein Derivative) skin test or interferon gamma release assay (IGRA) by a pulmonology specialist. However, patients with LTBI who finished proper treatment for LTBI for 4 weks and who are going to complete LTBI treatment.

6. HBsAg (Hepatitis B virus surface antigen)-positivity. Patients with negative HBsAg, but positive IgG anti-HBc (Immunoglobulin G anti-Hepatitis B core antibody) should be tested for HBV (hepatitis B virus) DNA real time quantitative PCR (polymerase chain reaction). If HBV DNA real time quantitative PCR ≥10 IU/mL should be excluded.

7. Anti-HCV (hepatitis C virus) antibody-positivity

8. History of HIV (human immunodeficiency virus) infection of positivity for anti-HIV

9. Heart disease of NYHA (New York Heart Association) Class III/IV

10. Active infection

11. Malignancy (excluding skin basal cell carcinoma, skin squamous cell carcinoma, and uterine cervix cancer) or history of colonic or small bowel dysplasia within 5 years

12. Pregnancy or lactating woman

13. Patients who are not applying proper contraceptive measures and patients who do not have a plan for proper contraceptive measures for at least 6 months after the last dose of infliximab (oral, parenteral, or implantable hormonal contraceptives, diaphragm, condom, intra-uterine device, or abstinence are accepted as proper contraceptive methods.

14. Patients who are decided to be not proper to be enrolled into the study by investigators.