Higher infliximab trough levels are associated with perianal fistula healing in patients with Crohn's disease

Background: Infliximab has been found to be efficacious in the treatment of fistulas in the setting of Crohn's disease, even though some patients do not benefit from therapy. Aim: To assess the correlation between perianal fistula healing and trough levels of infliximab. Methods: In this cross-sectional study, we identified patients with Crohn's disease who had perianal fistulas and were treated with infliximab for at least 24 weeks. We excluded patients who underwent a faecal diversion procedure or proctectomy. Predictive variables included demographics, disease phenotype, disease activity, infliximab levels, anti-infliximab antibodies. The primary outcome was fistula healing defined as the absence of drainage. The secondary outcome was complete fistula closure and mucosal healing. Results: 117 patients were included. Patients with fistula healing had significantly higher median serum infliximab levels when compared to those with active fistulas [15.8 vs. 4.4 μg/mL, respectively (P < 0.0001)]. There was an incremental gain in fistula healing with higher infliximab levels. The AUC for the association between fistula healing and infliximab levels was 0.82 (P < 0.0001), while the AUC for the association of infliximab levels and fistula closure was 0.69 (P = 0.014). Patients with anti-infliximab antibodies had a lower chance of achieving fistula healing (OR: 0.04 [95%CI: 0.005–0.3], P < 0.001). Conclusions: There is a significant association between serum infliximab levels and rates of fistula healing. Achieving infliximab levels ≥10.1 mcg/mL in patients with Crohn's disease and perianal fistulas may improve outcomes as part of a treat-to-target strategy.