# Higher induction and maintenance infliximab trough levels are associated with radiological perianal fistula healing in pediatric patients with Crohn's disease

## TL;DR

Higher levels of infliximab in the blood during treatment are linked to better healing of perianal fistulas in children with Crohn's disease.

## Contribution

This study identifies specific infliximab trough level thresholds associated with radiological healing of perianal fistulas in pediatric Crohn's disease patients.

## Key findings

- 57 out of 82 pediatric patients achieved radiological fistula healing after one year of infliximab treatment.
- Higher infliximab trough levels at weeks 6 and 54 were significantly associated with radiological healing.
- Optimal cut-off levels of 9.7 μg/ml at week 6 and 5.1 μg/ml at week 54 predicted healing with high accuracy.

## Abstract

Literature on the association between high infliximab (IFX) trough levels and perianal fistula response in pediatric patients with perianal fistulizing Crohn's disease (PFCD) is limited. This study aimed to evaluate the association between IFX trough levels and radiological perianal fistula healing in pediatric patients with PFCD undergoing long-term IFX treatment.

The study included pediatric patients (aged <18 years) diagnosed with PFCD who received IFX treatment and underwent follow-up magnetic resonance imaging (MRI) at 1 year. The primary outcome was radiological fistula healing on MRI one year after IFX treatment.

A total of 82 patients were included and 57 (69.5%) achieved radiological fistula healing at the 1-year follow-up. Patients with radiological fistula healing had lower rates of reoperation (p = 0.021), and higher median IFX trough levels at week 2 (median, 17.6 vs. 14.1 μg/ml), week 6 (11.79 vs. 7.11 μg/ml), week 30 (3.9 vs. 1.1 μg/ml), and week 54 (7.6 vs. 3.7 μg/ml) (p = 0.043, 0.003, 0.007 and <0.001, respectively) compared to those who had no fistula healing. In the multivariate analysis, higher median IFX trough levels at week 6 and week 54 remained significant factors associated with radiological fistula healing (p = 0.039 and 0.018, respectively). Optimal cut-off IFX trough levels for radiological fistula healing showing the highest area under curve (AUC) score was 9.7 μg/ml [AUC: 0.792, 95% confidence interval (CI): 0.630–0.955; p = 0.005] for week 6, and 5.1 μg/ml (AUC, 0.848; 95% CI: 0.750–0.947; p < 0.001) for week 54.

There was a significant association between higher serum IFX trough levels (during induction and maintenance) and radiological perianal fistula healing after 1 year of IFX treatment in pediatric patients with PFCD.