The role of therapeutic drug monitoring in the management of inflammatory bowel disease

Therapeutic drug monitoring (TDM) is performed when a drug has a narrow therapeutic range (e.g., thiopurines) or there is no linear drug response relationship (biologic agents). TDM is the measurement of drug and/or antibody concentration and individualizing the dose to maintain the drug concentration in the target range. Maintaining serum drug concentration in a therapeutic range is associated with a higher rate of favorable outcomes. Reactive drug monitoring is performed when the disease is active, and proactive drug monitoring is performed when the disease is in remission. Thiopurines still form an important therapeutic armamentarium in the treatment of inflammatory bowel disease (IBD) but have a narrow therapeutic range. Preemptive thiopurine methyl transferase and nucleoside diphosphate-linked moiety X-type motif (NUDT) genotype measurement can reduce the toxicity with appropriate dose initiation and thiopurine metabolite measurement can optimize the dose and reduce the toxicity. Antitumor necrosis factor agents brought about a paradigm shift in the management of moderate-to-severe IBD at the turn of the past century. Despite their efficacy, up to half the patients discontinue the biologic agents at the end of 1 year due to primary nonresponse or secondary loss of response. TDM can optimize the drug level and improve clinical response, reduce antibody formation, reduce cost, and can improve corticosteroid- free clinical remission. Despite postulated benefits and guidelines, the evidence for objective benefits from meta-analysis is mixed. This article reviews the current concepts regarding TDM.