P337 Usefulness of drug-level monitoring in therapeutic guidance in patients with ulcerative colitis on anti-TNF-α maintenance therapy

Abstract Background While treatment optimisation using therapeutic drug monitoring (TDM) of anti-TNF-α agents has become more common in clinical practices, studies comparing its correlation with clinical remission (CR), biochemical remission (BR) and mucosal healing (MH) in patients with ulcerative colitis (UC) are still lacking Methods Trough levels of infliximab/adalimumab (TLIs/TLAs) and levels of antibody to infliximab/adalimumab (ATI/ATA levels) were measured using serum samples collected between August 2017 and September 2019 from patients with UC on anti-TNF-α maintenance therapy. CR, BR and MH were defined as partial Mayo score of 0–1, within normal range of both ESR and serum C-reactive protein (CRP) level, and Mayo endoscopic subscore of 0–1, respectively. Results This study included 115 patients (72.8%, 91 [76.5%] on infliximab and 24 [61.5%] on adalimumab) in CR and 43 patients (27.2%) in non-CR. ATI/ATA were positive in 31 (26.1%) and 2 (5.1%) patients on infliximab/adalimumab therapy, respectively. TLI showed significant differences according to stats of CR (2.146 [0.273–4.296] vs. 0.405 [0.001–2.962], p = 0.019), BR (2.843 [0.282–4.835] vs. 0.987 [0.022–2.914], p = 0.007) and MH (2.411 [0.282–4.439] vs. 0.240 [0.001–1.674], p = 0.001), however, TLA didn’t (p = 0.783, 0.893 and 0.853, respectively) (Table 1 and Figure 1). In receiver operating characteristics (ROC) curve analysis, TLI of 2.314 μg/ml was identified as cut-off value discriminating MH (area under ROC 0.705, p = 0.001, sensitivity 0.527, specificity 0.885, negative predictive value [NPV] 0.343, positive predictive value [PPV] 0.942). After excluding 36 patients with MH even though their TLI < 1ug/ml, AUROC increased to 0.931 (p < 0.001, sensitivity 0.860, specificity 0.885, NPV 0.742, PPV 0.942) while cut-off TLI remained same. In incremental graph by ranges of TLI, MH rates showed plateau over 4 μg/ml of TLI. In multivariate logistic regression analysis, extensive colitis (hazard ratio [HR] 0.289, 95% confidence interval [CI] 0.079–1.060, p = 0.061) and TLI (HR 1.282, 95% CI 0.974–1.687, p = 0.076) were marginally associated with MH (Table 2). Conclusion In this study, TLIs correlated with CR, BR and MH, while TLAs did not. TLI should be targeted to be above 2.3 μg/ml.