Subcutaneous Infliximab Achieves Higher Colonic Tissue Drug Levels Than Intravenous Therapy: UEG Journal | March 2026

• Infliximab exerts its therapeutic effect within intestinal tissue, yet most therapeutic drug monitoring currently relies on serum concentrations.
• This study is the first to directly compare serum and colonic tissue infliximab concentrations between subcutaneous (SC) and intravenous (IV) infliximab in patients with IBD.
• Patients receiving subcutaneous infliximab achieved significantly higher serum drug concentrations compared with those receiving intravenous therapy.
• More importantly, colonic tissue infliximab concentrations were also significantly higher with subcutaneous administration, suggesting enhanced delivery to the therapeutic target organ.
• Serum and tissue drug concentrations were positively correlated in both treatment groups, confirming that systemic exposure reflects, at least partially, mucosal drug availability.
• Patients with higher colonic tissue infliximab concentrations experienced better clinical outcomes and were more likely to maintain sustained remission.
• Colonic tissue drug levels demonstrated stronger predictive value for long-term remission than serum trough levels.
• Tissue concentrations appeared highest in areas with mild-to-moderate inflammation, supporting the concept that active inflammatory tissue may facilitate local drug accumulation.
• The findings provide a biological explanation for the favorable pharmacokinetic profile observed with subcutaneous infliximab in previous clinical studies.
• The study raises an important concept: the true therapeutic target is the intestinal mucosa, not the bloodstream.
• Current therapeutic drug monitoring strategies may therefore underestimate clinically relevant drug exposure when relying solely on serum concentrations.
• Although tissue-based monitoring is not yet practical for routine clinical care, these data support future development of mucosal pharmacokinetic biomarkers.
• The study also reinforces growing evidence that subcutaneous infliximab is not merely non-inferior to intravenous therapy but may offer pharmacologic advantages.
• Larger prospective studies will be required to determine whether targeting tissue drug concentrations can further optimize treatment outcomes.

Bottom line: Subcutaneous infliximab produces significantly higher serum and colonic tissue drug concentrations than intravenous infliximab. Colonic tissue drug levels correlate strongly with clinical remission and may represent the next frontier in therapeutic drug monitoring for IBD.