Dosing interval and diagnosis predict infliximab levels in patients with inflammatory bowel disease on maintenance treatment.

Objective: The aim of the study was to identify factors influencing infliximab (IFX) trough levels (TL) in patients with inflammatory bowel disease (IBD).

Methods: This was a multicentre cross-sectional study performed at 5 large IBD centres in Slovakia. The cohort consisted of IBD patients, treated either with original IFX or CT-P13 biosimilar, who were examined for the IFX TL and antidrug antibodies (ADA) in a central laboratory.

Results: The patient cohort consisted of 116 consecutive IBD patients, 68 with Crohn's disease (CD) and 48 with ulcerative colitis (UC). CD patients had significantly lower IFX TL compared to UC, 2.41 (0.998-5.56) mg/L vs. 4.49 (1.76-8.41) mg/L, p = 0.017. During maintenance treatment, significantly higher mean IFX TL were observed in patients with a 4 week dosing interval than in patients with a 6 or 8 (7.44±3.6 μg/mL vs. 4.19±4.2 vs. 3.30±3.1 μg/mL, p = 0.011 and p< 0.0001, respectively). There was no difference in median TL IFX between original IFX and biosimilar CT-P13 (3.25 (1.24-6.52) mg/L vs. 3.03 (1.30-7.10)). IFX TL correlated with ADA (p=0.005). Multiple regression analysis revealed two independent factors for IFX TL: dosing interval (p<0.0001) and diagnosis (p=0.02).

Conclusion: In the present study we observed that IBD patients assigned to an intensified dosing interval during maintenance therapy have significantly higher IFX TL than patients receiving conventional 8 week interval. Patients with UC had significantly higher IFX TL.