Subcutaneous infliximab cut-off points in patients with inflammatory bowel disease. Data from the ENEIDA registry.

Background and aims: Switching from the intravenous to the subcutaneous biosimilar infliximab (SC-IFX) has been shown to safely maintain clinical remission and increase drug levels in patients with Crohn's disease (CD) and ulcerative colitis (UC). The aim of this study was to evaluate long-term outcomes after switching from intravenous IFX (IV-IFX) to SC-IFX, the drug concentration thresholds for maintaining remission and other predictors for loss of response after the switch.

Methods: Multicenter observational study involving CD and UC patients who were in clinical remission for at least 24 weeks and scheduled to switch from IV-IFX to SC-IFX.

Results: Two hundred and twenty patients were included [74 UC (34%) and 146 (66%) CD]. IV-IFX was administered for 52.5 months [range 25-89]. Pre-switch, 106 (49%) patients were receiving intensified IV-IFX. While SC-IFX levels significantly increased following the switch from IV to SC-IFX, clinical parameters, C-reactive protein and faecal calprotectin remained unchanged during follow-up. SC-IFX levels were significantly higher between patients receiving the standard IV-IFX dose than those with the intensified dose. Immunomodulator therapy at baseline and perianal disease had no effect on IFX trough levels, whereas higher body mass index was associated with increased levels. The suggested optimal SC-IFX cut-off concentration for clinical and biochemical remission based on ROC analysis was 12.2 μg/mL (AUC: 0.62) at week 12 and 13.2 μg/mL (AUC: 0.57) at week 52. Drug persistence was 92% at week 52, with a good safety profile.

Conclusion: Switching from IV-IFX to SC-IFX safely maintains long-term remission in patients with CD and UC. In maintenance, the optimal cut-off point associated with remission was 12-13 μg/mL.