TDM-based Infliximab Treatment for Active Perianal Fistulizing Crohn's Disease

Inclusion criteria

• Age: 19-80 years
• Subjects diagnosed with perianal fistulizing Crohn's disease based on clinical, endoscopic, histological, and radiologic findings, etc.
• Subjects naive to both biological drugs (anti-TNFs, anti-integrin, anti-IL12/23, etc.) and investigational new drugs
• Subjects with at least one draining perianal fistula
• Subjects not responding to two or more conventional treatments (antibiotics, drainage, immunosuppressants, etc.)
• Women with a childbearing potential: Those who agree to follow contraception during study drug administration and for at least 6 months from the last dosing of the study medication

Exclusion criteria

• In cases where written informed consents cannot be provided by the study subjects or the subjects' legally acceptable representative
• Subject with a probability of receiving bowel surgery within 12 weeks after baseline, decided by investigators
• Subjects with temporary or permanent stoma
• Subjects with short bowel syndrome
• Subjects not eligible due to significant bowel strictures or intra-abdominal abscesses
• Subjects who received bowel surgery within 6 months of baseline or subjects who were admitted due to complications associated with bowel strictures or intra-abdominal abscesses within 3 months of baseline
• Subjects with enterovaginal fistula, enterocutaneous fistula, or enteroenteric fistula
• Subjects previously exposed to biologics (anti-TNFs, anti-integrin, anti-IL12/23, etc.) or investigational new drugs
• Subjects with a history of hypersensitivity to monoclonal antibody
• Subjects requiring corticosteroid therapy. However, if oral corticosteroid dose lower or equivalent to prednisolone 20 mg/day before baseline is given and tapering of oral corticoseroid from baseline is planned, that subjects can be included in the study. Oral corticoseroid is tapered at a schedule of prednisolone 5 mg/7 days (example: if the subject was on oral prednisolone 20 mg/day before baseline, oral prednisolone is tapered as follows: 15 mg/day x 7 days -\> 10 mg/day x 7 days -\> 5 mg/day x 7 days -\> stopping of prednisolone)
• Subjects with active tuberculosis. However, if the subject has a history of tuberculosis, which was cured with standard anti-tuberculosis therapy according to the standard anti-tuberculosis treatment guidelines, that subject can be included
• Subjects with latent tuberculosis: Subjects determined to be positive for latent tuberculosis by the pulmonology specialist after history taking, physical examination, chest X-ray, and interferon gamma release assay during the screening period. However, even if positive for latent tuberculosis, if 4 week-treatment for latent tuberculosis is completed and if further treatment for latent tuberculosis is planned to be completed, that subject can be included
• Subjects positive for HBsAg. In cases of HBsAg (-), but with IgG Anti-HBc (+), real time quantitative PCR for HBV DNA is required. If HBV DNA is 10 IU/mL or over, that subject should be excluded
• Subjects positive for anti-HCV antibody
• Subjects with a history of infection with HIV or subject positive for HIV Ag
• Subjects positive for Clostridioides difficile toxin assay or Clostridioides difficile culture assay
• Subjects with a heart disease of NYHA Class III/IV
• Subjects with current or previous demyelinating disease
• Subject with a history of malignancy (excluding skin basal cell carcinoma, skin squamous cell carcinoma, and uterine cervix cancer) within 5 years or with a history of dysplasia of colon or small bowel within 5 years.
• Subjects with symptoms or signs of active infection or with a history of treatment for infection within 8 weeks
• Subjects with a history of organ transplantation
• Pregnant or lactating women
• Non-Korean ethnicity according to a family tree
• Subjects decided to be not eligible for the study by investigators