TNF and inflammatory bowel disease: Reactive TDM is superior to standardized dose optimization regimens at treatment failure and is recommended by the AGA to guide treatment changes in patients with active IBD receiving TNF inhibitors.94,97 The American College of Gastroenterology (ACG) guidelines also suggest reactive TDM at treatment failure,53,58 and ECCO–European Society of Gastrointestinal and Abdominal Radiology (ESGAR) guidelines state that reactive TDM may be beneficial in patients with IBD who are non-responsive to TNF inhibitors.98