Clinical efficacy of infliximab level and anti-infliximab antibody measurement in patients with inflammatory bowel disease: An audit

Background and Aims Infliximab (IFX) monitoring has been proposed for effective therapeutic management of inflammatory bowel disease (IBD). There is no data on infliximab levels and its antibody measurement in Indian patients. We assessed the clinical efficacy of IFX level and antibodies to infliximab (ATI) monitoring in IBD patients. Methods Infliximab trough level and antibody testing was done in 50 and 30 IBD patients, respectively using commercially available enzyme-linked immunosorbent assay (ELISA) kits. The levels were correlated with the disease status, albumin, and C-reactive protein (CRP) levels. The clinical efficacy of level-based change in patient management was evaluated. Results Of 50 patients, IFX levels were therapeutic in 8, sub-therapeutic in 40, and supra-therapeutic in 2. High ATI titer was present in 8/30 patients. The IFX level did not correlate with the dose of 5 or 10 mg/kg. Based on IFX level and ATI estimation, management was changed in 35 patients: increase in dose in 7, decrease in dosing interval in 17, increase in interval in 2, surgery in 2, change in biologic in 5, and cessation of IFX in 2 patients. Therapy modification based on IFX level improved the clinical response in 25 patients, of whom 5 are in remission at a median duration of 2 years. Conclusion Most (80%) of the IBD patients had subtherapeutic IFX levels while high ATI titers were found in 27% of the patients. There was no correlation between infliximab dose and drug levels. Therapy modification based on drug level benefitted the majority. Our results suggest that measurement of IFX level assists in attaining therapeutic levels and improves clinical response.