Therapeutic drug monitoring (TDM) of infliximab (IFX) trough levels and anti-drug antibodies in conjunction with symptoms, disease history, and investigations can aid decision-making. This study evaluated 1-year outcomes of patients with decisions that were altered on the basis of TDM results, in order to investigate whether outcomes from TDM-based decisions to adjust or stop IFX treatment are durable.
We retrospectively collected clinical outcomes 12 months post treatment decisions based on proactive TDM. Patients whose initial treatment decisions were altered on the basis of TDM results were compared with those where the decision remained unchanged. Events of interest were inpatient admissions with active inflammatory bowel disease (IBD), further changes to biologic therapy, and IBD-related health-care costs.
Of 189 patients, 54 (28%) had initial treatment decisions altered in the light of TDM results. The 135 patients whose initial decision was not altered in light of TDM results served as the comparator. There were no differences in hospitalization rates or subsequent biologic switches between the altered decision groups and the comparator group. IBD-related health-care costs were higher in those whose initial decision was altered (median GBP 7,912 vs. GBP 6,521; 
Our study demonstrates good outcomes from changes to IFX treatment based on TDM. Patients with a decision to stop, switch, or continue with an adjusted IFX dose experienced comparable clinical outcomes but had higher drug-related expenditure than those whose treatment decision was not altered in light of TDM.