Intervention: Methotrexate
Trial phase: Phase 3
ATC code: L01BA01 | L04AX03
SMILES: CN(Cc1cnc2nc(N)nc(N)c2n1)c1ccc(C(=O)N[C@@H](CCC(=O)O)C(=O)O)cc1
Sex: All
Age groups: Child | Adult
Healthy volunteers: No
Participants at risk: 156
Group description: Methotrexate (10, 12.5, or 15 mg), once weekly. Weight-based dosing. Ondansetron (4 mg), twice weekly, 1 hour prior to methotrexate dose and the morning after methotrexate dose.

Folic Acid (1 mg) daily

Methotrexate: 1) Oral methotrexate (MTX): The weekly dose will be 15 mg for children ≥ 40kg, 12.5 mg for children 30 to <40 kg, and 10 mg for children 20 to <30 kg. 2) A twice per week, 4mg dose of ondansetron will be provided as pre-treatment to prevent nausea (study provider may opt-out of this component based on clinical judgement). 3) A 1 mg dose of folic acid per day will be provided. This will help to reduce the risk of side effects in the MTX group.

Drug kits will contain a 3 month supply of each medication. Refills will be provided every 3 months until week 156 unless there is a failure to induce and maintain remission, development of unacceptable toxicity, pregnancy in a female participant, or failure of the participant to attend scheduled study visits.
Eligibility criteria:
Inclusion Criteria:

Pediatric Crohn's Disease (PCD) patients, < 21 years of age, ≥20 kg, initiating anti-TNF therapy with infliximab or adalimumab (including biosimilars).
Diagnosis of Crohn's Disease (CD) established confirmed by the treating clinician, and established by standard clinical criteria (radiography, endoscopy, histology).
Ability to provide parental permission and child assent (where applicable), or adult consent for patients ages 18-20.

Exclusion Criteria:

Prior use of anti-TNF or other biological therapy for CD
Lack of stable home address that study medications can be mailed to
Anticipated short length of follow up at study center (plans for family to move, transition to adult GI (gastrointestinal) provider, etc.). Patients expected to leave practice < 12 months from enrollment should not be enrolled.
Concurrent pelvic or abdominal abscess. A recent history of abdominal or pelvic abscess, which is controlled, does not exclude the subject.
Prior intra-abdominal surgery without a clinically significant relapse (i.e. patients starting on anti-TNF for post-op prophylaxis or for endoscopic recurrence only should not be included)
Receipt of a live virus vaccine within the last 30 days
Pregnancy, planning to become pregnant, or high risk of pregnancy as determined by the local investigator
Breastfeeding
Refusal to stay abstinent or utilize 2 forms of birth control while on study medication (for female patients)
BMI > 98% for gender and age
Known previous or concurrent malignancy (other than that considered surgically cured, with no evidence for recurrence for 5 years). A recent history of basal cell or squamous cell carcinoma, which is considered surgically cured, does not exclude the subject.Those with a recent history of colonic adenoma or dysplastic lesions should be excluded.
Known high alcohol consumption (more than seven drinks per week)
Patients with serum albumin < 2.5 g/dl
Patients with white blood cell count (WBC) < 3.0 x109th/L
Patients with platelet count < 100 x109th/L
Patients with initial elevation of liver enzymes (AST or ALT) > 1.5 times above normal limit
Patients with known active infection with Clostridium difficile (C. difficile) (untreated infection based on clinician assessment does not apply to colonization or infection controlled with current or prior treatment.)
Patients with pre-existing hepatic disease
Patients with pre-existing renal dysfunction (creatinine > 0.8 for children age<10, creatinine > 1.2 mg/dl for children age 10-18, and creatinine > 1.5 mg/dl for adults age 18 years and older).
Patients with a pre-existing chronic lung disease other than well controlled asthma
Current treatment with one of the following drugs: Probenecid (Probalan), Acitretin (Soriatane), Streptozocin (Zanosar), Azathioprine (Imuran, Azasan), 6-mercaptopurine (Purinethol, Purixan)
Other concerns about the patient/family's ability to participate in the study