Subcutaneous (SC) infliximab (IFX) has recently been approved for the treatment of chronic inflammatory rheumatic diseases (CIR), largely based on the results of large randomized trials in rheumatoid arthritis. However, real-world evidence remains limited and is mainly retrospective. The aim of this study was to evaluate the safety and effectiveness of SC IFX following a non-medical switch from intravenous (IV) IFX in patients with CIR.

We conducted a prospective, single-center, observational study. Adult patients with controlled CIR who had received stable IV IFX at standard doses (3–5 mg/kg every 6–8 weeks) for at least three infusions were eligible. The switch was first proposed to the treating physician and, upon agreement, to the patient. Clinical, biological, and patient-reported outcomes were collected at 3, 6, and 12 months. IFX serum concentrations and anti-IFX antibodies were measured at baseline, 6 months, and 12 months. Additional patients who switched to SC IFX during the same period as part of routine care were also evaluated to estimate treatment retention.

Among 173 patients treated with IV IFX as of January1, 2023, 73 were eligible for inclusion. The main reason for non-eligibility was non-standard dosing ( n = 65). After physician and patient discussion, 22/73 patients (30%) were enrolled (16 axial spondyloarthritis, 5 psoriatic arthritis, 1 unclassified CIR). One-third were receiving IFX as first-line biologic therapy, with a mean treatment duration of 8.9 ± 5 years, corresponding to 63 ± 39 IV infusions. Thirteen additional patients switched to SC IFX in routine care. At 6 and 12 months, 19/22 patients (86%) remained on SC IFX. Six patients reported mild adverse events (pruritus n = 1; injection pain n = 2; injection-site reactions n = 4), which resolved in all but one patient by study end. Mean serum IFX levels increased from 11 ± 7μg/mL before the scheduled IV infusion to 30 ± 17.6 μg/mL at 6 months and 25.6 ± 13.1 μg/mL at 12 months after switching to SC administration. No anti-drug antibodies were detected. Patient satisfaction was high, with a mean score of 9.7 ± 0.37 out of 10. Among patients switched in routine care, 8/13 remained on SC IFX at one year. The annual mean treatment cost per patient was significantly lower with SC IFX (€ 4,627 ± 23) than with IV IFX (€ 7,456 ± 1,331; P < 0.001).

These findings support the effectiveness of SC IFX in maintaining disease control in CIR, with a favorable safety profile and significant economic benefits. The pharmacokinetic results suggest that SC IFX may have broader clinical applicability.