The recently published NOR-DRUM B trial demonstrated that proactive therapeutic drug monitoring (TDM) during maintenance therapy with infliximab was more effective in sustaining disease control in immune- mediated inflammatory diseases than treatment without TDM. We believe these results must be interpreted with caution. Prior trials that evaluated proactive TDM in inflammatory bowel disease (IBD) during maintenance infliximab therapy did not prove the effectiveness of this approach. Moreover, unintentional bias may have affected the primary outcome results of the NOR-DRUM B trial because data about infliximab levels and antidrug antibodies were not available for the standard therapy group at any time during the trial. Current guidelines for IBD conditionally recommend use of TDM during maintenance therapy in response to suboptimal disease control. Therapeutic drug monitoring may therefore drive the tailoring of IBD therapy (eg, escalation of infliximab therapy, introduction of an immunomodulator or another biologic drug).Moreover, as stated in the Limitations section, in this open-label trial the subjective assessment of disease worsening (defined by consensus between patient and physician) was also prone to bias. Therefore, it is not surprising that clinicians treating patients randomized to the standard therapy group may increase the infliximab dose if TDM results are unavailable. In this study, the infliximab dose was increased in 51.0% of patients in the standard therapy vs 31.6% of patients in the TDM group. We believe that failure to use TDM may have adversely affected the treatment and primary outcome results of some individuals with IBD randomized to the standard therapy group, and this should be noted as a study limitation.
