Early literature on Inflammatory Bowel Disease (IBD) regarding the switch from intravenous (IV) to subcutaneous (SC) infliximab has reported reassuring mid-term efficacy and treatment persistence rates. However, real-world data remain limited.

We conducted a retrospective, multicenter, observational study across four french centers: one tertiary and three secondary care institutions. Eligible patients were adults (≥18 years) with IBD in clinical remission for at least 6 months under IV infliximab who subsequently switched to SC infliximab. Exclusion criteria included clinical remission <6 months, combination with another advanced biological therapy, corticosteroid use within the past 4 months, pregnancy, or breastfeeding.The primary endpoint was the treatment persistence rate of SC infliximab at week 48 (W48). Secondary endpoints included: differences in persistence according to prior IV optimization status and combination therapy; changes in clinical scores (Harvey–Bradshaw Index, partial Mayo score) and inflammatory biomarkers between IV and SC treatment; reasons for SC treatment discontinuation; disease relapse rate under SC infliximab; correlation between clinical symptoms and objective evidence of relapse; and the incidence of adverse events (AEs) and serious adverse events (SAEs).

Eighty-seven patients treated with SC infliximab (IFX-SC) were included. IV-to-SC transitions occurred between July 2022 and July 2024.The median age was 40 years, and most patients had Crohn’s disease (86.2%). The mean duration of IV therapy before switching was 5.4 years, predominantly at a non-optimized standard dose (77%). At the time of switching, 17.2% were on combination therapy with an immunosuppressive agent , and 33.3% had previously received at least one other biological therapy. Regarding the primary endpoint, persistence of SC infliximab at W48 was 74.4% (65/87). There was no statistically significant difference among subgroups: combination therapy with immunosuppressive agent(66.6%, p=0.53), previously optimized IV treatment (70%, p=0.78), or standard IV dosage(76.6%, p=0.57). Clinically and biologically, no significant differences were observed between IV and SC periods in clinical scores, mean leukocyte count, CRP, or albumin levels. Fecal calprotectin showed no significant change (IV: 107 µg/g vs SC: 281 µg/g, p=0.16). Among the 22 discontinuations, most were due to clinical relapse (n=16, 72.7%). Objective evidence of disease activity (elevated fecal calprotectin, imaging, or endoscopy) was confirmed in only 6 of these 16 patients (37.5%). Other causes of discontinuation included injection fatigue and poorly tolerated local injection reactions. SC infliximab optimization was required in 22/87 cases (25.3%), with a treatment persistence rate of 77.3% at W48 in this subgroup. Only 5 optimized patients were among the 22 who discontinued IFX-SC.Overall SC infliximab tolerance was good, with few AEs (5.7%), including only one SAE. The 74.4% persistence rate at W48 was lower than previously reported in the literature (e.g., GETAID PEREM study, with 95.3% persistence at W48).

In real-world conditions, switching from IV to SC infliximab proved safe, effective, and well tolerated, with a 74.4% persistence rate at week 48. The main reason for discontinuation was clinical relapse (16/22), which was not consistently supported by objective evidence, in a population largely not optimized under SC therapy. These findings highlight the importance of individualized dose optimization, to objective evidence of relapse in patients who may be anxious about switching to the SC and close follow-up to enhance long-term treatment persistence with SC infliximab.