Bergsmark C [1], Kristensen VA [1,2], Sjåmo MB [1], Høivik ML [1,2], Anisdahl KA [1,2]

Affiliates

Department of Gastroenterology, Oslo University Hospital [1], Institute of Clinical Medicine, University of Oslo [2]

Abstract

Background: The subcutaneous (SC) formulation of infliximab (IFX) was approved for inflammatory bowel disease (IBD) in Norway in December 2023. Randomized trials and real-world studies have shown that SC IFX is as effective and safe as intravenous (IV) administration. However, there is limited data on switching high-dose IV IFX patients and which patient groups that require intensified dosing of SC IFX. Moreover, guidelines for the target serum concentration in SC administration are lacking. The aim of the project was to confirm the feasibility and safety of switching to SC IFX in patients on IV IFX maintenance therapy, as well as to examine IFX serum concentrations during SC treatment.
Methods: We conducted a quality assurance study at the Department of Gastroenterology at Oslo University Hospital (OUH). Data were collected from the OUH-IBD registry. All patients that had received IV IFX for ≥12 weeks were consecutively considered for switching to SC IFX. Exclusion criteria were physician-assessed non-remission, planned treatment change, planned surgery within the next 3 months, pregnancy, and reduced compliance. High dose IV IFX was defined as patients receiving ≥1.5 mg/kg/week. These patients were switched to intensified SC regimen (240 mg/14 days). All other patients were switched to standard SC regimen (120 mg/14 days). The first SC dose was administered halfway through the established IV infusion interval. Fecal calprotectin (FC), IFX serum concentration, CRP, and Harvey Bradshaw Index (HBI) or partial Mayo score (PMS) were recorded at last infusion and at follow-up 3 months after the first SC dose. Clinical remission was defined as HBI≤4 or PMS≤2. Biochemical remission was defined as FC≤250 and CRP<5. IV serum concentrations were assessed as trough levels. SC serum concentrations were assessed without relation to time of drug administrations.
Results: The project is ongoing. As of October 29, 2024, a total of 217 patients had been assessed as eligible for switching, and 77% (n = 167) had been switched to SC IFX. Of these, 89% received standard SC regimen and 11% received intensified SC regimen. At present, 63 patients have completed the 3-month follow-up. At the last infusion, 97% were in clinical remission based on HBI or PMS scores, and 86% were in biochemical remission. At the 3-month follow up, 97% were in clinical remission (p = 1.00) and 82% were in biochemical remission (p=0.77). No severe adverse events were recorded. Two patients reported mild injection reactions, and one patient developed a mild rash. Two patients discontinued SC IFX before the 3-month follow-up. For patients on standard SC regimen, the median serum concentration before switch was 8.4 mg/L (IQR: 6.3-10.2 mg/L) and 23.5 mg/L (IQR: 17.5-29.0 mg/L) at the 3-month follow-up. For patients on intensified SC regimen, the respective median serum concentrations were 8.3 mg/L (IQR: 5.8-15.9 mg/L) and 33.5 mg/L (IQR: 29.7-37.1 mg/L).
Conclusion: Switching from IV IFX maintenance therapy to SC IFX is safe, feasible, and well accepted in IBD patients in remission irrespective of IV dosing regimens and IV serum concentrations. SC serum concentration at 3-months were slightly higher than previous reports. Patients on intensified SC regimen tended to have higher serum concentration than patients on standard SC regimen.

Poster_P5_Camilla Bergsmark