Association of Infliximab Levels with Mucosal Healing is Time-Dependent in Crohn's Disease: Higher Drug Exposure is Required Postinduction Than During Maintenance Treatment

Background: Intliximab levels have been reported to be associated with mucosal healing (MH) in Crohn's disease (CD). However, whether the association differs between postinduction (week 14) and maintenance (week 30) has seldom been investigated. We aimed to analyze the association between scrum infliximab trough levels and MH at the 2 different time points. Methods: A retrospective study of CD patients treated with infliximab in a tertiary referral center between January 2012 and May 2018 was conducted. MH was defined as absence of ulceration by endoscopy. Correlations between infliximab level and MH were investigated at 2 specific time points, weeks 14 and 30. Results: Median infliximab levels were higher in patients with MH than those without at weeks 14 (7.5 vs 1.5 mu g/mL; P < 0.001) and 30 (5.9 vs 0.5 mu g/mL; P < 0.001). The median levels in patients with MH at week 14 were higher than at week 30 (7.5 vs 5.9 mu g/mL; P < 0.05). Multivariate analysis showed that infliximab level was independently associated with MR (both P < 0.001 at weeks 14 and 30). Infliximab level above 4.85 1.4/ mL and 2.85 mu g/mL identified patients with MH at week 14 (area under the curve [AUC], 0.796; P < 0.001) and week 30 (AUC, 0.780; P < 0.001) with 80% specificity. The rates of MH reached a plateau (>85%) when infliximab levels were above 10 and 6 mu g/mL at weeks 14 and 30, respectively. Conclusions: Infliximab levels correlated with MH at weeks 14 and 30 in CD patients. Higher levels might be required to achieve MH at postinduction than during maintenance treatment.