Abstract
BACKGROUND: Intestinal tissue levels of infliximab (IFX) in patients with inflammatory bowel disease (IBD) treated with subcutaneous (SC) therapy have not been previously assessed.
OBJECTIVE: To compare serum and colonic tissue IFX concentrations in IBD patients receiving SC versus intravenous (IV) IFX.
METHODS: This observational cross-sectional study included IBD patients on stable SC or IV IFX maintenance therapy undergoing routine follow-up colonoscopy. Clinical activity required elevated CDAI or Mayo score plus ≥ 1 biomarker (fecal calprotectin > 250 μg/g or CRP > 5 mg/L). Blood samples and two colonic biopsies were collected for serum and tissue IFX measurements.
RESULTS: Thirty-five patients were included. Serum and tissue IFX concentrations were significantly higher in the SC versus IV group (22 μg/mL vs. 9 μg/mL, p < 0.001; 25 μg/g vs. 10 μg/g, p = 0.002). Serum and colonic tissue IFX levels were positively correlated in both cohorts (IV: r = 0.42; p = 0.014; SC: r = 0.43; p = 0.001). Colonic tissue IFX concentrations were higher in patients with mild-moderate endoscopic activity than in those without active disease (p < 0.001). Serum and colonic tissue IFX levels both predicted sustained clinical remission, with optimal thresholds of 14.5 μg/mL (p = 0.015) and 17 μg/g (p < 0.005), respectively. Colonic tissue IFX showed higher predictive accuracy (AUROC 0.82, p = 0.01) than serum (AUROC 0.76, p = 0.045).
CONCLUSIONS: SC IFX achieved significantly higher serum and colonic tissue concentrations than IV IFX. Colonic tissue IFX levels demonstrated superior clinical relevance and may support future tissue-based therapeutic drug monitoring strategies in IBD.