Background: Intravenous corticosteroids (IVCS) remain the mainstay of therapy in acute severe ulcerative colitis (ASUC) patients. Exclusive enteral nutrition (EEN) with a semielemental formula has been shown to enhance corticosteroid responsiveness in patients with ASUC. The effectiveness of polymeric EEN in ASUC has not been studied. Our aim was to assess the effectiveness and tolerability of polymeric EEN as an adjunctive therapy to current standard of care (SOC) in patients with ASUC. Methods: Between September 2021 and October 2022, 31 consecutive adults who were hospitalized with ASUC (meeting Truelove and Witts’ criteria) received 7 days of polymeric EEN (Ensure Plus ®) in addition to current SOC. Outcomes were compared to a matched historical cohort of 38 patients (admitted between 2016 – 2020) managed as per SOC. The primary outcome was corticosteroid failure defined as requiring medical rescue therapy or colectomy. The decision for initiation of rescue therapy was made at the treating physician’s discretion as per international guidelines. Results: A total of 69 patients were included (EEN n=31, SOC n=38). Baseline characteristics are presented in Table 1. In the EEN group, 22/31 (71%) failed to respond to IVCS and received medical rescue therapy, compared to 16/38 (42.1%) in the historical cohort, p = 0.028 (RR 1.69 [95%CI 1.09 – 2.60], crude OR 3.36 [95%CI 1.24 – 9.08], p = 0.015). Percentage of steroid failure and mode of rescue therapy are presented in Figure 1. On adjusting for sex, disease duration, disease extent, smoking status and current biologic use, the adjusted OR 2.5 [95%CI 0.32 – 19.57, p = 0.07] and the adjusted RR 1.57 [95%CI 0.63 – 3.91, p 0.697] were not statistically significant. Most patients completed 7 days of EEN (n=25, 78.1%). Reasons for early discontinuation of EEN included palatability (n = 4), diarrhoea (n = 1), and patient choice (n = 1). Stool frequency, CRP and albumin levels on days 3 and 7, and length of hospital stay, did not significantly differ between the EEN and SOC groups (Table 2.) Conclusion: More patients in the EEN group failed intravenous corticosteroids and required medical rescue therapy as compared to SOC group. Further controlled studies are required to determine the benefit of polymeric EEN as an adjunctive therapy to standard of care in ASUC.