Week 14 Infliximab Level Provides Modest Benefit to Clinical Outcomes in Children with Crohn's Disease.

Purpose: Benefits of a proactive compared to a reactive therapeutic drug monitoring strategy when commencing infliximab (IFX) in children with Crohn's disease are unclear. We evaluated the 6- and 12-month outcomes in children commencing IFX with a week 14 level (W14) determined compared to without (NoW14). Methods: Single-centre, retrospective study of children with Crohn's disease aged 0-18 years with a primary response to IFX induction between 2018-2021. W14 group had a week 14 IFX drug level determined and NoW14 group did not. Baseline patient, medication and disease characteristics were compared across the two groups. Clinical and biochemical disease activity measures, and IFX dose, frequency and drug level were compared at week 0, 6- and 12-months post-induction. Failure was defined by biologic switch, corticosteroid use, hospitalisation or surgery. Results: We included 83 children diagnosed at median 13 years, with a median disease duration of 5 years. The W14 group (40/83, 48.2%) had a higher C-reactive protein (CRP) than NoW14 group. At 12-months, there was no difference in failure rates (33% vs. 33%, Conclusion: Knowledge of a week 14 level without strict thresholds on how and when to respond may be of minor benefit for children commencing infliximab for Crohn's disease.