Background Depending on individual therapeutic response, infliximab (IFX) dosage and infusion interval may be adjusted. Despite this therapeutic optimisation, loss of efficacy can be observed, such as a decrease in trough IFX levels. Few paediatric studies have been performed to determine a threshold value that correlates with better clinical status.

Purpose To correlate trough IFX concentrations with clinical remission in paediatric patients with inflammatory bowel disease (IBD) and to determine an IFX threshold associated with clinical remission.

Material and methods The study was performed with 2.5 years of retrospective records of IBD patients <18 years of age (Crohn’s disease (CD), ulcerative colitis (UC), indeterminate colitis (IC)) treated with more than three IFX perfusions (maintenance phase). Two scores were calculated to determine the clinical activity of the disease: Harvey Bradshow Index for CD and the Paediatric Ulcerative Colitis Activity Index for UC and IC. ANOVA test for repeated measures and logistic regression were used for analysis and equations.

Results 67 patients were included in the study. There were 553 active/non-active disease observations for 55 CD patients and 169 for 12 UC and IC patients. Analysing the concentration every 6 weeks (best predictive target) between responders and non-responders, the rates were, respectively, 5.5 and 3.1 mg/L for CD and 5.2 and 3.7 mg/L for UC/IC (p<10^-4). From two equations, the probability of clinical remission was nearly 100% when the threshold was 5.5 µg/mL. The study showed that a pharmacokinetic target can be reached. Moreover, a flowchart of therapeutic decisions based on IFX rate was established. The level was a little higher than in other studies. Indeed, a 2014 paediatric study conducted at week 14 (different from our study design) in responders and non-responders showed, respectively, a concentration for median trough IFX levels of 4.7 µg/mL and 2.6 µg/mL (p=0.03).

Conclusion IFX threshold was correlated with clinical remission in IBD children. The trough concentration was 5.5 mg/L at 6 weeks post-infusion and was found to be a ‘maker’ related to disease activity. This rate is particularly useful for paediatric gastroenterology departments that perform these assays. A prospective study should be performed to confirm our research.

No conflict of interest