Clinical Utility of Measuring Infliximab and Human Anti-Chimeric Antibody Concentrations in Patients With Inflammatory Bowel Disease

OBJECTIVES: Human anti-chimeric antibodies (HACAs) and subtherapeutic infliximab concentrations are associated with decreased duration of response. We evaluated the clinical utility of measuring HACA and infliximab concentrations. METHODS: The medical records of patients with infl ammatory bowel disease (IBD) who had HACA and infliximab concentrations measured were reviewed to determine whether the result affected clinical management. RESULTS: One hundred fifty-five patients had HACA and infliximab concentrations measured. The main indications for testing were loss of response to infliximab (49%), partial response after initiation of infl iximab (22%), and possible autoimmune/delayed hypersensitivity reaction (10%). HACAs were identified in 35 patients (23%) and therapeutic infl iximab concentrations in 51 patients (33%). Of 177 tests assessed, the results impacted treatment decisions in 73%. In HACA-positive patients, change to another anti-tumor necrosis factor (TNF) agent was associated with a complete or partial response in 92% of patients, whereas dose escalation had a response of 17%. In patients with subtherapeutic infl iximab concentrations, dose escalation was associated with complete or partial clinical response in 86% of patients, whereas changing to another anti-TNF agent had a response of 33%. Patients with clinical symptoms and therapeutic infl iximab concentrations were continued at the same dose 76% of the time and had no evidence of active inflammation by endoscopic/radiographic assessment 62% of the time. CONCLUSIONS: Measurement of HACA and infl iximab concentration impacts management and is clinically useful. Increasing the infl iximab dose in patients who have HACAs is ineffective, whereas in patients with subtherapeutic infl iximab concentrations, this strategy may be a good alternative to changing to another anti-TNF agent.