Improving Treatment of Inflammatory Bowel Diseases Through Better Understanding Infliximab Drug and Antibody Levels

Inclusion Criteria: * a diagnosis of CD or UC by usual criteria, * moderate to severely active CD defined by a CDAI ≥ 220, with confirmed endoscopic activity (CDEIS ≥ 6) or moderate to severely active UC, defined by a Mayo Score ≥ 6, with a Mayo endoscopic subscore ≥ 2, * a need for treatment with IFX for induction of remission as clinically indicated * patients previously exposed to adalimumab and/or certolizumab who are naïve to infliximab will be allowed to participate. Exclusion Criteria: * perianal CD exclusively * disease limited to the rectum in patients with UC (i.e., disease must extend ≥ 15 cm from the anal verge) * patients with known antibodies to IFX (ADAs) at baseline * a contraindication to infliximab therapy * a contraindication to endoscopy * an ostomy * planned surgery * evidence of severe or unstable hepatic, gastrointestinal, cardiovascular, respiratory, neurological, psychiatric, hematological or renal disease at the discretion of the investigator, * Pregnancy or breastfeeding, * treatment with any investigational drug in the past 30 days, or 5 half lives (whichever is longer).