A Risk Stratification Tool for Relapse After Intravenous-To-Subcutaneous Switching of Infliximab in Patients With Inflammatory Bowel Diseases

INTRODUCTION: A subcutaneous formulation of infliximab was recently approved for maintenance therapy of inflammatory bowel disease (IBD). However, limited clinical experience, particularly with patients on escalated intravenous infliximab regimens, poses challenges for the transition to subcutaneous therapy. We investigated the pharmacokinetics and pharmacodynamics of subcutaneous infliximab to identify early predictors of relapse on switching. METHODS: We repurposed data from a prospective, multicenter trial involving patients with IBD switching from intravenous to subcutaneous infliximab. We estimated each patient's infliximab clearance using Bayesian forecasting from a preswitch sample and a population pharmacokinetics model. We performed pharmacodynamics modeling to evaluate preswitch predictors of postswitch relapse. Relapse was defined as clinical recurrence (partial Mayo score >2 or Harvey-Bradshaw Index >4 leading to therapeutic escalation) or an increase in fecal calprotectin ≥150 μg/g on switching. RESULTS: Using data from 98 patients with IBD, we identified infliximab clearance and fecal calprotectin as independent predictors of relapse. A 2-item risk score stratified patients into the low-risk (<19% probability of relapse; 75/98; 77%) and high-risk (≥19% probability of relapse; 23/98; 23%) groups (sensitivity 0.75 [95% CI 0.48−0.93], specificity 0.87 [95% CI 0.77−0.93] positive predictive value 52% [95% CI 31−73%], negative predictive value 95% [95% CI 87−99%]). Our pharmacokinetics-pharmacodynamics model classified patients with and without relapse ( P < 0.0001) with an area under the receiver operating characteristic curve of 0.83 (95% CI 0.71−0.93). DISCUSSION: Preswitch infliximab clearance and fecal calprotectin are accurate predictors of relapse after switching to subcutaneous infliximab. An interactive risk stratification tool facilitates confirmation of a stratified medicine approach to improve infliximab therapy in IBD.