To Örebro University

Introduction: Natalizumab (NTZ) is a highly effective disease modulatory treatment for relapsing multiple sclerosis (RMS) originally launched as an intravenous (IV) therapy in Sweden in August 2006. A new subcutaneous (SC) administration method for NTZ was launched in April 2021.

Objectives/Aims: To investigate how the administration of NTZ has evolved in Sweden since the introduction of SC NTZ in 2021, and to explore potential differences in treatment discontinuation patterns between the SC or IV administration modalities.

Methods: Descriptive data will be presented from the “Immunomodulation and Multiple Sclerosis Epidemiology Study” (IMSE 1) study cohort. Data is collected from the nationwide Swedish Neuro Registry (NeuroReg). The drug survival is assessed using the Kaplan Meier one-year drug survival curve and Breslow Wilcoxon test of equality distribution.

Results: A total of 4247 NTZ participants were included in the IMSE 1 study from August 2006 until March 2024 (71% female; mean age 36 years; 82% RMS; mean treatment duration 50 months). Since July 2021 498 patients have initiated treatment of which 468 had available data on administration. In this cohort, 181 (39%) initiated IV NTZ, of which 21 (12%) later switched to SC. 287 (61%) initiated treatment with SC NTZ of which 1 later switched to IV. The distribution between administration methods altered over time, where IV was more common in Q3 2021 (65%) and then successively dropped to 24% in Q1 2024.

The mean age at treatment start was 38 years (37 for IV and 38 for SC) and 67% (69% IV, 66% SC) were female.

Out of 468 participants, 273 (58%) later discontinued treatment. Discontinuation was significantly more common in the IV group (70%) compared with the SC group (51%) even though the percentage of patients positive for the John Cunningham virus (JCV+) and mean treatment duration in each group was similar.

The most common reason for discontinuation in both groups was JCV+ followed by “Other reason: unspecified”. Seven patients discontinued due to neutralizing NTZ antibodies; 7 from SC and 3 from IV.

Conclusion: The SC administration has become the preferred administration method for NTZ since its launch in the spring of 2021, with 61% of NTZ treatment initiations being administered using SC method. Significant differences in discontinuation rates between the two administration methods were seen. Longer observation periods will be needed to assess possible differences in tolerability and treatment adherence between the two administration modalities.