Real-World Experience With Proactive Therapeutic Drug Monitoring During Infliximab Reintroduction

Background: Interruptions in infliximab therapy are associated with the development of antibodies to infliximab (ATI), infusion reactions (IRs), and loss of response. Despite these challenges, recent observational studies suggest that reinitiating infliximab after a drug holiday can be safe and effective. We assessed the utility of our protocol for restarting infliximab using early serum infliximab and ATI measurements. Methods: A retrospective cohort study of patients restarted on infliximab after at least a 6-month drug holiday. The cohort was divided into 2 groups: a "therapeutic drug monitoring (TDM) group," those who had serum infliximab and ATI measured 1-3 weeks after first reinduction dose, and a "non-TDM group." Outcomes included results of TDM, occurrence of immediate IR (IIR) and delayed hypersensitivity reactions, and medication persistence at 14 weeks and 1 year. Results: About 76 patients were included: 49 in the TDM group and 27 in the non-TDM group. Of 76, 67 (88%) patients tolerated the first reinduction dose without IR. Formation of ATI was seen in 17 of 49 (35%) patients and was associated with longer drug holidays. Most did not experience IR during the entire therapy course-in 26 of 32 (81%) without ATI and 20 of 27 (74%) in the non-TDM group. Infliximab persistence at 14 weeks and 1 year was 76% and 57% for the cohort, respectively. Conclusion: Infliximab can be safely and effectively restarted after a drug holiday. We suggest performing TDM with a drug-tolerant assay 1-3 weeks after the first reinduction infusion as a means to identify patients at risk for severe IIR at the second dose. Lay Summary Interruption in infliximab therapy increases the risk for an infusion reaction once therapy is resumed. The presence of antibodies to infliximab after the first restart dose identifies patients who are at risk for a serious reaction with the subsequent dose.