4CPS-046 Therapeutic drug monitoring of infliximab in paediatric severe very early-onset inflammatory bowel disease

<h3>Background and Importance</h3> Very early-onset inflammatory bowel disease (VEOIBD), patients whose age of onset is younger than 6 years, is a heterogeneous condition that tends to be refractory to conventional treatment. Infliximab (IFX) therapeutic drug monitoring (TDM) can guide high-dose therapy and improve response rates. <h3>Aim and Objectives</h3> To assess the effectiveness and safety of IFX through a multidisciplinary TDM programme combined with Bayesian forecasting in severe VEOIBD (S-VEOIBD) patients compared to other children with inflammatory bowel disease (O-IBD). <h3>Material and Methods</h3> Retrospective study including patients treated with IFX between September 2015 and September 2023 in a tertiary hospital. We analysed biological and clinical remission, treatment failure (TF), hospitalisations, emergency visits and adverse reactions (ARs). S-VEOIBD patients were considered those requiring intensified doses and frequencies during maintenance treatment to achieve IFX trough concentrations (Cmin) &gt;10 µg/ml. <h3>Results</h3> Four (10.5%) patients were classified as S-VEOIBD and compared with 34 O-IBD patients. Median age at diagnosis was 1.96 (interquartile range (IQR) 1.01–2.99) and 12.06 (9.78–14.53) years, and median (IQR) duration of follow-up was 1.03 (0.84–1.45) and 1.84 (1.08–2.54) years for S-VEOIBD and O-IBD groups, respectively. Mean [standard deviation, (SD)] dose was 10.27 (2.37) and 7.80 (1.87) mg/kg, the frequency in maintenance [mean (SD)] was 3.29 (1.38) and 6.50 (1.62) weeks and mean (SD) IFX Cmin in maintenance, 18.26 (12.77) and 8.55 (5.01) µg/mL for S-VEOIBD and O-IBD, respectively. Although there was no TF IFX in S-VEOIBD during induction (0.0% vs. 5.9%; p=0.50), any patient achieved remission at week 14 (0.0% vs. 73.5%; p &lt;0.01). At week 54, S-VEOIBD had more TF (25.0% vs 6.5%; p=0.25) and less children in remission (50.00% vs. 64.51%; p=0.58). Kaplan-Meier analysis did not demonstrate higher cumulative probability of TF in S-VEOIBD compared with O-IBD (log-rank P=0.62). Hospitalisations (50.0% vs. 14.7%) and emergency visits (25.0% vs. 8.8%) were higher in S-VEOIBD. ARs were more common in S-VEOIBD (75.0% vs. 26.5%); 88.9% were infections and 11.1% infusion-related reactions. <h3>Conclusion and Relevance</h3> Compared with O-IBD, S-VEOIBD patients did not have higher cumulative probability of TF. Accelerated induction and maintenance drug monitoring with high Cmin can prevent TF in S-VEOIBD. High-dose regimens may be associated with a higher rate of ARs, mainly infectious. <h3>References and/or Acknowledgements</h3> <h3>Conflict of Interest</h3> No conflict of interest