Higher Infliximab Levels Are Not Associated With an Increase in Adverse Events in Inflammatory Bowel Disease

Background: Patients requiring optimization of therapy for suboptimal response and/or targeting more robust outcomes may eventually reach high serum levels. Data evaluating the relationship between infliximab concentration and toxicity are limited. The aim of this study was to evaluate the frequency of adverse events (AEs) in inflammatory bowel disease (IBD) patients with infliximab higher-range (HR) and lower-range (LR) trough levels. Methods: We performed a retrospective analysis of 180 patients with at least 1 measurement of serum infliximab from 2012 to 2016. The cohort was divided according to an infliximab level cutoff of 15 mu g/mL (HR and LR). The primary outcome was frequency of AEs, including infections, dermatological manifestations, and infusion reactions, between the 2 groups. The secondary outcomes included frequencies of all AEs (dermatological manifestations, infusion reactions, autoimmune reactions, and opportunistic and serious infections) in both groups. AEs were also compared against observed infliximab level quartiles using logistic regression analysis. Results: A total of 53 AEs in 47 patients were reported in the overall cohort. In the LR group, there were 36 AEs recorded in 30 patients, whereas in the HR group, 17 AEs were experienced by 17 patients. Patients with HR levels did not have a higher prevalence of infections in comparison with patients with LR levels (12.2% vs 18.8%; P = 0.3). Stratification of infliximab levels by quartiles showed a comparable frequency of infection. Conclusions: Our findings indicate that higher infliximab serum concentrations are not associated with a higher frequency of infections.