Therapeutic Drug Monitoring of Biologics for Inflammatory Bowel Disease: An Answer to Optimized Treatment?

Therapeutic drug monitoring (TDM), or the measurement of drug concentrations in blood and antidrug antibodies, for biologic therapies used to treat inflammatory bowel disease (IBD) is an area of growing interest within the IBD community. When there is a definable relationship between drug concentration and clinical effect, blood concentration of biologics (and antidrug antibodies assessment) could be used to predict patient response and to titrate the biologics to maximize therapeutic benefit. This dose individualization has been proven to be more efficacious and cost-effective than empiric dose adjustment and can better guide therapeutic decisions regarding therapy withdrawal or switch. Appropriate implementation and interpretation of drug concentration measurement in TDM are essential to ensure full clinical benefit. Factors that need to be considered include sources of variability, timing of blood sampling, dosing history, analytical performance, immunogenicity, comedications, and clinical status of the patients. Desired target concentrations for biologics used in IBD have not been clearly determined yet. Published concentration thresholds differed widely for a given biologic, indicating a lack of consistent information. Factors other than drug concentration that may contribute to the dose-response variation are largely missing in the current TDM setting. A target range is likely preferable to a single value for TDM of biologics in IBD, and additional prospective research needs to be conducted in order to establish these ranges. Moving forward, TDM may be combined with pharmacodynamic end points and modeling and simulation tools for improved therapeutic benefit in IBD.