Version July 2025
CRP: C-reactive protein; IBD: inflammatory bowel disease; IL: interleukin; JAK: Janus kinase; TNF: tumor necrosis factor.
* Higher infliximab and adalimumab levels have been associated with healing of perianal fistula related to Crohn disease, and some clinicians use a level of ≥10 mcg/mL for patients with fistulizing Crohn disease. Some clinicians also use an infliximab or adalimumab level of ≥10 mcg/mL for patients with ulcerative colitis.
¶ Examples of other drug classes for IBD include anti-IL 12/23 antibody therapy, anti-IL 23 antibody therapy, anti-integrin therapy, and JAK inhibitor therapy.
Δ Reporting of anti-drug antibodies varies among laboratories and has not been standardized. In general, low antibody levels occur with detectable drug levels, whereas high antibody levels usually occur when drug levels are undetectable. Anti-drug antibody levels <25 mcg/mL are generally regarded as low, whereas levels >85 mcg/mL are regarded as high. For patients with intermediate antibody levels (ie, between 25 mcg/mL and 85 mcg/mL), management is individualized.
◊ Immunomodulators that are typically used in combination with anti-TNF agents include azathioprine, 6-mercaptopurine, or methotrexate. For patients with anti-drug antibodies who start a different anti-TNF agent, we typically also initiate an immunomodulator (ie, combination therapy). For such patients who do not start an immunomodulator, we perform proactive therapeutic drug monitoring.
§ Options for escalating anti-TNF therapy include shortening dosing interval and/or increasing drug dose.
