Inflammatory bowel disease (IBD), encompassing Crohn’s disease and ulcerative colitis, is a chronic inflammatory disorder of the gastrointestinal tract characterized by alternating periods of flares and remission. Its etiopathogenesis remains unclear, however genetic, immunologic, and environmental factors are implicated, and recent research increasingly highlights a role for oxidative stress. In a meta-analysis and two clinical studies, we evaluated associations between oxidative stress-related biomarkers, disease activity, and health-related quality of life in patients with IBD. In patients with ulcerative colitis, we examined relationships between ustekinumab concentrations, quality of life, and treatment outcomes, and subsequently developed a population pharmacokinetic–pharmacodynamic (PK–PD) model for ustekinumab. We demonstrated accumulation of biomarkers of oxidative damage to biomacromolecules alongside reductions in antioxidant levels, with larger effect sizes in active disease than in remission. Patients in remission still exhibited significantly elevated oxidative stress compared with healthy controls, further supporting its involvement in IBD pathogenesis. We identified key biomarkers for distinguishing active Crohn’s disease and active ulcerative colitis from their respective remission states. Blood-based oxidative stress-related biomarkers effectively capture inflammation reflected in the systemic circulation but do not adequately detect localized intestinal mucosal inflammation. Patients who fail to achieve C-reactive protein–based remission show heightened oxidative stress already at therapy initiation. Oxidative-stress biomarkers were not associated with quality of life in IBD, while higher ustekinumab exposure in UC was associated with better quality of life. Higher ustekinumab exposure during induction was also linked to improved clinical, biochemical, and endoscopic outcomes. Finally, we developed a two-compartment, target-mediated drug disposition model that integrates ustekinumab concentrations, patient characteristics (fat-free mass, serum albumin, and CRP), and the time course of fecal calprotectin concentrations. This model supports individualized, model-informed ustekinumab dosing and treatment optimization.
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