Anti-infliximab antibodies and low infliximab levels correlate with drug discontinuation in pediatric inflammatory bowel disease

Background: Infliximab (IFX) use is limited by loss of response often due to the development of anti-IFX antibodies and low drug levels. Methods: We performed a single center prospective observational cohort study of pediatric and young adult subjects with inflammatory bowel disease (IBD) on IFX with over 3 years of follow-up. Infliximab levels (IFXL) and antibodies to infliximab (ATI) were measured throughout the study. Subjects were followed until IFX was discontinued. Results: We enrolled 219 subjects with IBD (184: Crohn's disease; 33: Ulcerative colitis; and 2 Indeterminant colitis; 84 female, median age 14.4 years, 37% on concomitant immunomodulator). Nine hundred and nineteen serum samples (mean 4.2 +/- 2.1 per patient) were tested for IFXL and ATI. During the study, 31 (14%) subjects discontinued IFX. Sixty patients had ATI. Twenty-two of those 60 patients with ATI discontinued IFX; 14 of 31 patients who discontinued IFX had detectable ATI at study onset. The combination of ATI and IFXL < 5 g/mL at study entry was associated with the highest risk of drug discontinuation (hazard ratios [HR] ATI 4.27 [p < 0.001] and IFXL < 5 mu g/mL [HR]: 3.2 p = 0.001). Patients with IFXL 5-10 mu g/mL had the lowest rate of discontinuation (6%). IFX dose escalation eliminated ATI in 21 of 60 subjects. Conclusions: ATI is a strong predictor of needing to stop IFX use and inversely correlates with IFXL. Detection of ATI during therapeutic drug monitoring postinduction but also periodically during maintenance therapy identifies individuals who may benefit from IFX dose escalation and/or the addition of an immunomodulator, as these interventions may reduce or eliminate ATI.