Associations Between Anti-TNF Pharmacokinetics, Immunogenicity, and Therapeutic Response in Iraqi Patients with Inflammatory Bowel Disease: A Real-World Therapeutic Drug Monitoring Study.

Background: Therapeutic drug monitoring (TDM) has emerged as an important strategy for optimizing anti-tumor necrosis factor (anti-TNF) therapy in patients with inflammatory bowel disease (IBD). However, data regarding anti-TNF pharmacokinetics and immunogenicity from Middle Eastern populations remain limited. This study evaluated the associations between serum anti-TNF trough concentrations, anti-drug antibody (ADAb) levels, and therapeutic response among Iraqi patients with IBD receiving infliximab or adalimumab therapy. Methods: This cross-sectional observational study included 80 patients with Crohn's disease or ulcerative colitis receiving maintenance infliximab or adalimumab therapy at a tertiary Gastroenterology Center in Iraq. Patients were categorized as responders or non-responders according to clinical disease activity indices and biochemical assessment. Serum trough levels of infliximab and adalimumab, as well as ADAb concentrations, were measured using an enzyme-linked immunosorbent assay (ELISA). Results: Responders had significantly higher serum trough concentrations than non-responders for both infliximab [3.75 µg/mL (IQR: 3.40-4.15) vs. 1.05 µg/mL (IQR: 0.92-1.12), p < 0.001] and adalimumab [6.32 µg/mL (IQR: 5.67-7.15) vs. 3.30 µg/mL (IQR: 2.70-4.26), p < 0.001]. Adalimumab-treated non-responders had significantly higher ADAb levels compared with responders (p = 0.047). Conclusions: Favorable therapeutic outcomes in Iraqi IBD patients treated with anti-TNF agents were associated with adequate serum trough levels and low ADAb levels. Reactive therapeutic drug monitoring may provide clinically valuable pharmacokinetic information capable of guiding individualized treatment optimization and identifying mechanisms of treatment failure in patients receiving infliximab or adalimumab therapy.