4CPS-064 Pharmacokinetic monitoring of subcutaneous infliximab in patients with inflammatory bowel disease

<h3>Background and Importance</h3> Subcutaneous infliximab(SC-IFX) shows stable drug concentrations over time in patients with inflammatory bowel disease(IBD). Establishing an optimal cut-off would help ensure treatment effectiveness and safety. <h3>Aim and Objectives</h3> To analyse the variability of trough concentration(Cmin) of SC-IFX and establishing a cut-off to achieve clinical response(CR), biochemical remission(RemBq) and clinical remission(RemC) during the maintenance phase in IBD patients. <h3>Material and Methods</h3> Ambispective, observational study involving IBD patients with IFX Cmin starting SC-IFLX treatment between January 2020-June 2024. Clinical data were extracted from the Abucasis/MDIS programme. Variables analysed were sex, age, weight, diagnosis(Crohn disease(CD)/Ulcerative colitis(UC), pharmacotherapeutic data(Cmin, previous biological therapy), biochemical parameters(albumin, faecal calprotectin(FCP), C-reactive protein(CRP)) and clinical score(UC:Partial-Mayo Score(MS)/CD:Harvey-Bradshaw index(HB)) at each time point. Study objectives were defined as: Clinical Response(CR: maintaining a clinical score equal to/lower than the baseline); Biochemical Remission(RemBq: FCP&lt;250μg/g and CRP&lt;5mg/L); and Clinical Remission(RemC: HB&lt;5 and MS&lt;2). As a limitation due to the ambispective design, the available patient’s drug levels were variable at 3rd, 6th and 12th months(n=52,n=41,n=40). SC-IFLX Cmin was determined using a chemiluminescence assay(Theradiag). The results were expressed as percentage, and median[interquartile range(IQR)]. The Friedman test assessed differences between Cmin, and ROC curve analysis determined the optimal cut-off to maximise sensitivity(S) and specificity(E), using R v.4.3.3 for data analysis. <h3>Results</h3> Samples from 52 patients(n=42;CD) were analysed: 27 were male(51.9%). The median age and weight were 45.0 years[34.0–56.0] and 70.0 kg[62.0–83.0], respectively. A total of 8 patients had prior treatment with a biological therapy other than infliximab. Cmin at 3, 6, and 12 months were 15.1μg/mL[IQR:10.4–19.4], 13.7μg/mL[IQR:10.0–16.7], and 14.3μg/mL[IQR:10.2–17.4],p=0.226, respectively. Analytic parameters in the three visits were: albumin (4.4[IQR:4.2–4.6]; 4.4[IQR:4.2–4.5]; 4.4[IQR:4.3–4.7]g/dL), CRP(1.3[IQR:1.0–3.3]; 1.5[IQR:1.0–3.1]; 1.4[IQR:1.0–3.0]mg/L) and FCP(58.0[IQR:30.5–199.4]; 105.2[IQR:37.4 −265.1]; 75.6[IQR:32.3–316.2]μg/g, respectively. SC-IFX cut-off for CR at the 3rd and 12th months was 13.5μg/mL (AUC=0.90 [95% CI:0.82–0.98],p=0.024,S=0.83,E=0.87) and 13.7μg/mL (AUC=0.77 [95% CI:0.61–0.93],p=0.02,S=0.68,E=0.88), respectively. For RemBq, the cut-off at the 3rd month was 16.8μg/mL(AUC=0.76 [95% CI:0.63–0.90],p=0.07,S=0.53,E=0.92). No statistically significant differences were found for other study objectives. <h3>Conclusion and Relevance</h3> Based on the results, SC-IFLX Cmin remained stable over the follow-up period. A cut-off for CR was identified at 13.5μg/mL and 13.7μg/mL, and a cut-off of 16.8μg/mL for RemBq. However, further studies are required to confirm these findings and establish an optimal cut-off that ensures favourable clinical outcomes. <h3>References and/or Acknowledgements</h3> <h3>Conflict of Interest</h3> No conflict of interest