Abstract Background Infliximab (IFX) was the first TNF alpha inhibitor approved for treatment of inflammatory bowel disease (IBD). Since 2013 biosimilars of IFX and since 2023 sc formulation of IFX have been available. Remswitch study laid down the ground rules and additional studies provided data for designing algorithm for switching from iv to sc IFX. Start of sc IFX would best be foreseen earlier than 8 weeks after the last iv dose, but exact timeline is not fixed. Methods We performed a prospective, observational, single center, cohort study in IBD patients treated with maintenance IFX (mIFX). Objective was to switch patients from mIFX iv to sc at fixed time interval of 4 weeks between last iv and first sc injection independent of IFX type (originator or biosimilar) and of iv dosing regime (switch to 120 mg or 240 mg sc). Interim analysis was done at week 24. Maintenance of clinical remission at week 24 (partial Mayo score 2 in UC and Harvey Bradshaw Index 5 in CD) was observed primary outcome, achiving target serum IFX trough levels (TL) (≥7 mg/L in perianal CD and ≥5 mg/L in non-perianal CD and UC) before switching to sc formulation and patients’ satisfaction (TSQM-9 questionnaire) and quality of life (QoL) using short IBDQ were secondary outcomes. Serum IFX TL were measured with fluorescence immunoassay; ez-Trecker, Theradiag, France. Descriptive statistics was used to interpret results. Results Altogether 40 IBD patients treated with mIFX were included, 28 patients with CD and 12 patients with UC. Demographic data, disease characteristics and prior treatment data are presented in table 1. Primary outcome results: At week 24 92.6% of CD patients maintaned clinical remission and 7.4% had mild disease clinical activity (HBI 5-7 points), 100% of UC patients were in clinical remission according to pMayo score (2 points). Secondary outcomes: At baseline 35.7% of perianal CD patients and 71.4% non-perianal CD and UC patients were at target IFX TL on iv mIFX therapy. At week 4, before switching to sc formulation, significantly (p 0.001) higher percentage of patients reached target IFX TL, 92.9% of perianal CD patients and 96.4% of non-perianal and UC patients (graph 1). QoL and patients’ satisfaction on sc was comparable to iv administration during observed period until week 24. Conclusion The 4-week interval between last iv and first sc administration proved to be appropriate, as the vast majority of patients achieved target serum IFX TL before switching to sc. In both CD and UC patients treatment persistence after switch to sc IFX remained high at week 24 which in our opinion was a result of reaching target IFX TL at week 4. QoL and patients’ satisfaction on sc was not inferior to iv administration at week 24. References: 1. Buisson A, Nachury M, Reymond M, Yzet C, Wils P, Payen L, et al. Effectiveness of Switching From Intravenous to Subcutaneous Infliximab in Patients With Inflammatory Bowel Diseases: the REMSWITCH Study. Clin Gastroenterol Hepatol. 2023 Aug;21(9):2338-46.e3. 2. Fierens L, Liefferinckx C, Hoefkens E, Lobatòn T, Dreesen E, Sabino J, Ferrante M; IBD Research and Development (BIRD) group. Introduction of Subcutaneous Infliximab CT-P13 and Vedolizumab in Clinical Practice: A Multi-Stakeholder Position Statement Highlighting the Need for Post-Marketing Studies. J Crohns Colitis. 2022 Aug 4;16(7):1059-69. 3. Smith PJ, Critchley L, Storey D, Gregg B, Stenson J, Kneebone A, et al. Efficacy and Safety of Elective Switching from Intravenous to Subcutaneous Infliximab CT-P13: A Multicentre Cohort Study. J Crohns Colitis. 2022 Sep 8;16(9):1436-46. Conflict of interest: Dr. Ocepek, Andreja: No conflict of interest Bukovnik, Nejc: No conflict of interest Pernek, Robert: No conflict of interest Velkovski, Cvetanka: No conflict of interest Homšak, Evgenija: No conflict of interest Putniković, Dunja: No conflict of interest Nikolic, Sara: No conflict of interest
Ocepek et al. (Thu,) studied this question.