Therapeutic Drug Monitoring of Biologics for Patients with Inflammatory Bowel Diseases: How, When, and for Whom?

During the past decade, we have entered an era of biologics for the treatment of Crohn's disease and ulcerative colitis. The therapeutic goal of inflammatory bowel disease (IBD) management has evolved from symptom control and clinical remission to mucosal healing or even deep remission. Histological remission for ulcerative colitis and transmural healing of Crohn's disease are potential future goals. With the adoption of the treat-to-target concept, and given the need for tight control of IBD activity, therapeutic drug monitoring (TDM) is an important element of precision medicine. TDM involves the measurement of serum biologics and anti-drug antibodies levels, to confirm whether the right drug with the right dosage was prescribed to reach the right serum levels. TDM may help clinicians adjust biologics based on objective biomarkers instead of using empirical dosage escalation or making symptom-based therapeutic adjustments. Well-established reactive TDM algorithms have been proposed, and emerging evidence supports the clinical application of a proactive TDM strategy to enhance the duration of effective biologics and improve clinical outcomes. Recently, the proactive TDM strategy was shown to avoid the secondary loss of response to biologics, and improve long-term clinical outcomes in IBD patients. This review summarizes data from trials, and practice guidelines, on the clinical application of proactive and reactive TDM strategies for the daily care of biologic-treated IBD patients.