Higher Postinduction Infliximab Concentrations Are Associated With Improved Clinical Outcomes in Fistulizing Crohn's Disease: An ACCENT-II Post Hoc Analysis

INTRODUCTION: There are only limited data regarding the role of therapeutic drug monitoring in fistulizing Crohn's disease (CD). We investigated the association between both induction and maintenance serum infliximab concentrations and favorable therapeutic outcomes in patients with fistulizing CD. METHODS: This was a post hoc analysis of the ACCENT-II trial evaluating patients with fistulizing CD receiving induction (n = 282) and maintenance infliximab therapy (n = 139). Investigated therapeutic outcomes at both week 14 and week 54 included fistula response, complete fistula response, C-reactive protein (CRP) normalization (≤5 mg/L) in patients with an elevated baseline CRP, and a more stringent outcome of composite remission, defined as combined complete fistula response and CRP normalization. Associations between serum infliximab concentrations and outcomes were assessed by multivariable logistic regression models. RESULTS: Higher week 14 infliximab concentrations were independently associated with week 14 fistula response (odds ratio [OR]: 1.16; 95% confidence interval [CI]: 1.02–1.32; P = 0.019), and composite remission (OR: 2.32; 95% CI: 1.55–3.49; P < 0.001). Higher week 14 infliximab concentrations were also independently associated with week 54 composite remission (OR: 2.05; 95% CI: 1.10–3.82; P = 0.023). Based on receiver operating characteristic curve analysis, week 14 infliximab concentrations thresholds with combined maximal sensitivity and specificity of ≥20.2 μg/mL at week 2, ≥15 μg/mL at week 6, and ≥7.2 μg/mL at week 14 were associated with week 14 composite remission. DISCUSSION: Higher post-induction infliximab concentrations are associated with early and long-term favorable therapeutic outcomes in patients with fistulizing CD.