Abstract Background While standard infliximab (IFX) rescue dosing is effective for most acute severe ulcerative colitis (ASUC) patients, those with higher inflammatory burden and drug clearance may benefit from dose-intensified and accelerated regimens1. There is limited data guiding point-of-care (POC)-IFX drug level driven ASUC treatment strategies, although recent findings from PREDICT-UC suggest day-3 IFX levels predict non-response and 3-month colectomy rates2. We assessed the real-world application of 48-hour POC-IFX testing in ASUC clinical decision-making. Methods Prospective, single-centre cohort study using convenience sampling of adult ASUC patients at a tertiary Australian IBD unit who underwent POC-IFX testing between August 2023 - February 2025. No formal protocol was followed, however, 48-hour adjusted POC-IFX levels were reviewed by our IBD MDT to determine the following decisions: discharge, further IFX rescue, salvage therapy (JAK-inhibitor) or colectomy. Kruskal-Wallis test and Dunn’s test were performed for statistical significance. Results 31 patients had 35 POC tests. 74% were male. Median age of 34. 45% was an index presentation. 97% had E2/E3 disease extent. 13% were biologic experienced. Median UCEIS score was 7. 19% had CRP ≥50 mg/L and 32% albumin 25 g/L. Table 1: those responding to IFX and discharged had high median IFX levels. Those inadequately responding and received sequential JAKi salvage therapy or colectomy had high median IFX levels. Those inadequately responding and received further IFX had low median IFX levels. Poor response with high IFX levels demonstrated pharmacodynamic failure and poor response to IFX with low levels demonstrated pharmacokinetic failure. Figure 1A shows the distribution of levels differed statistically significantly between outcomes. Figure 1B shows statistically significant difference in IFX levels between discharge and Further IFX outcomes. This study was limited by the small sample size, no formal research protocol, and the clearance calculator used to obtain the 48-hour IFX levels was developed for moderate-severe UC, not ASUC. Conclusion IFX-POC tests are rapid, affordable and helpful in delineating between pharmacokinetic and pharmacodynamic failure in patients who have not adequately responded to initial IFX treatment. This differentiation helps to personalise the approach to ASUC treatment through the early identification of those who would benefit from further IFX and who would benefit from earlier switch to salvage therapy or a colectomy. Although PREDICT-UC has given day-3 level targets, further research is required to confirm 48-hour target levels. There is also the potential role for IFX-POC testing to be integrated into predictive calculators of IFX response. References: 1. Choy MC, Li Wai Suen CFD, Con D, et al. Intensified versus standard dose infliximab induction therapy for steroid-refractory acute severe ulcerative colitis (PREDICT-UC): an open-label, multicentre, randomised controlled trial. Lancet Gastroenterology and Hepatology. 2024;9(11):981-996 2. Li Wai Suen CFD, Choy MC, Con D, et al. Early Infliximab Levels and Clearance Predict Outcomes After Infliximab Rescue in Acute Severe Ulcerative Colitis: Results From PREDICT-UC. Gastroenterology. Published online July 21, 2025. Conflict of interest: Dr. Malloy, Reuben: No conflict of interest Goetz, Naeman: No conflicts of interest. Etchegary, Amirah: No conflict of interest kumar, rina: No conflict of interest Phillips, Jennifer: No conflict of interest Tambakis, George: No conflict of interest brown, allison: No conflict of interest Croft, Anthony: No conflict of interest Radford-Smith, Graham Lindsay: No conflict of interest Walker, Gareth: No conflict of interest
Malloy et al. (2026) studied this question.