Therapeutic drug monitoring of biologics in inflammatory bowel disease

Biologics have revolutionized the management of patients with inflammatory bowel disease (IBD), in both ulcerative colitis (UC) and Crohn’s disease (CD). There are several classes of biologics used to treat IBD, including monoclonal antibodies directed against TNF, integrin, IL12/23, and IL-23 monoclonal antibodies. Despite the effectiveness of anti-TNF medications, approximately 30% of patients are primary non-responders (PNR), and another 50% lose response over time (secondary loss of response [SLR]). Therapeutic drug monitoring (TDM) provides a tool for biologic dose optimization by measuring drug trough concentrations and anti-drug antibodies (ADA). Drug concentrations are positively correlated to therapeutic benefits, but questions remain on how, when and for whom to perform TDM. Successful implementation is challenged by several factors such as variations in optimal drug targets, different types of drug detection assays, individual pharmacokinetics, and disease severity. Over recent years, various expert groups have provided guidelines on reactive TDM of anti-TNF therapies; however, a knowledge gap still exists on the role of proactive TDM, as well as reactive TDM for non-anti-TNF biologics. The most recent and comprehensive expert consensus statement published in the American Journal of Gastroenterology (AJG), attempted to fill this gap by advocating for the use of reactive TDM for anti-TNF medications, as well as for proactive TDM in certain scenarios.