The purpose of this observational study is to assess the safety and effectiveness of biosimilar Infliximab in patients with inflammatory bowel disease (IBD) in Saudi Arabia where no visits or intervention(s) additional to the daily practice will be performed.

A multicenter, observational, prospective, cohort study to assess the safety and effectiveness of biosimilar Infliximab (Remsima®) in newly diagnosed and in switched IBD patients diagnosed with active Crohn's disease (CD), fistulizing CD, or Ulcerative Colitis (UC). Each patient is expected to be treated for a total of 38 weeks if naive or 40 weeks if switched. The study duration will be between 46 and 48 weeks (up to 12 months). Follow-up is expected to end 8 weeks after the last treatment visit.

Inclusion Criteria:

• - Adult patients with moderate to severe active CD who have not responded despite a full and adequate course of therapy with corticosteroids and/or immunosuppressive agents, or who are intolerant to or have medical contraindications to such therapies.
• Adult patients with fistulizing active CD who have not responded despite a full and adequate course of therapy with conventional treatment (including antibiotics, drainage and immunosuppressive therapy).
• Adult patients with moderate to severe active UC who have had an inadequate response to conventional therapy including corticosteroids and 6-mercaptopurine (6-MP) or azathioprine (AZA), or who are intolerant or have medical contraindications to such therapies.
• Switched patients who received at least one dose of Infliximab reference medicinal product (RMP) before the first infusion of Remsima®.
• Patients who agree to join the study and give a written informed consent

Exclusion Criteria:

• - Patients with a known history of hypersensitivity to infliximab, to other murine proteins, or to any of the excipients (Sucrose, Polysorbate 80, Monobasic sodium phosphate and/or Dibasic sodium phosphate).
• Patients who have shown intolerance or inefficacy to biologics for IBD treatment.
• Female patients who are known to be pregnant or breastfeeding.
• Patients with a past or present history of chronic infection with Hepatitis B, Hepatitis C, or human immunodeficiency virus (HIV), or those with positive test at screening.
• Patients who are diagnosed with tuberculosis (TB) or previously diagnosed with TB with no evidence of complete resolution
• Patients with severe or chronic infections (e.g. sepsis, abscesses, opportunistic infections, invasive fungal infections), or severe or chronic infection, without sufficient documentation of complete resolution following treatment
• Patients with recent exposure to persons with active TB, or a positive test result for latent TB at Screening. A patient who has received at least the first 30 days or recommended period of country-specific TB prophylactic therapy and intends to complete the entire course of therapy may be enrolled. Recommended methods to screening latent TB are interferon-γ release assay [IGRA] test, with a chest X-ray, however, other methods could be used according to local guideline.
• Patients with moderate or severe heart failure (New York Heart Association NYHA class III/IV).
• Patients for whom the treatment with Tumor necrosis factor-alpha (TNF-α) blockers is concerning due to a history of malignancy within the previous five years prior to enrollment or a history of herpes zoster within one month prior to enrollment, may be excluded at the investigator's discretion.
• Patients who meet any of the contraindications to the administration of infliximab

Patients will be recruited from approximately 6 sites in Saudi Arabia