Higher Serum Infliximab Concentrations Following Subcutaneous Dosing are Associated with Deep Remission in Patients with Inflammatory Bowel Disease

Background: The relationship between subcutaneous infliximab [SC-IFX] concentrations and favourable therapeutic outcomes in patients with Crohn's disease [CD] and ulcerative colitis [UC] remains elusive.Patients and Methods: This cross-sectional study included consecutive adult patients with inflammatory bowel disease [IBD] treated with SC-IFX at a maintenance dose of 120 mg/2 weeks. Investigated therapeutic outcomes included sustained clinical remission; composite clinical and biomarker remission [clinical remission and C-reactive protein <5 mg/L]; biochemical remission [faecal calprotectin <250 mu g/g]; and deep remission [clinical, biological, and biochemical remission].Results: Of 91 patients identified, 71 qualified for inclusion in the study [70% with CD; 27% with concomitant immunomodulators]. At the time of drug concentration measurement [median 13.5 months after switch], 55 [77%] patients had sustained clinical remission; n = 44 [62%] composite clinical and biomarker remission; n = 40 [56%] biochemical remission; and n = 31 [43%] deep remission. The mean SC-IFX concentrations were significantly higher in patients with sustained clinical remission [p = 0.014]; composite clinical and biomarker remission [p = 0.003]; biochemical remission [p < 0.001]; and deep remission [p < 0.001] compared to patients without having these outcomes. In multivariate analysis, SC-IFX concentration was the only factor independently associated with sustained clinical remission (odds ratio [OR]: 4.7, 95% confidence interval [CI]: 3.1-12.2, p = 0.005); clinical and biomarker remission [OR: 9.21, 95% CI: 6.09-18.7, p = 0.006]; biochemical remission [OR: 37, 95% CI: 14-39.3, p < 0.001]; and deep remission [OR: 29, 95% CI: 15.7-37.4, p < 0.001]. The optimal SC-IFX concentration cut-off associated with deep remission based on ROC analysis was 20 mu g/mL [sensitivity: 0.91, specificity: 0.80, accuracy: 0.85]. Combination with an immunomodulator failed to improve SC-IFX pharmacokinetics.Conclusion: Higher SC-IFX concentrations are associated with higher rates of favourable therapeutic outcomes in IBD patients. Serum SC-IFX concentrations >20 mu g/mL were significantly associated with deep remission.