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 4011 NTZ participants were included in the IMSE 1 study from August 2006 until March 2023 (72% female; mean age 36 years; 80% RRMS; mean treatment duration 49 months), including 295 since July 2021, of which 264 had available data on method of administration. In this cohort, 109 (41%) initiated IV NTZ, of which 16 (15%) later switched to SC administration, and 155 (59%) initiated treatment with SC NTZ. The distribution between administration methods altered over time, where IV was more common in Q3 2021 (70%) and then successively dropped to 31% in Q1 2023.The mean age at treatment start was 36 years (35 for IV and 37 for SC) and 69% (70% IV, 68% SC) were female.Out of 264 participants, 73 (28%) later discontinued treatment. Discontinuation was numerically more common in the IV group compared with the SC group, but differences in the one-year drug survival rate did not reach statistical significance.The most common reason for discontinuation in the IV group was “other reason; unspecified” followed by positive JC-virus serology (JCV+). In the SC group JCV+ was the most common reason for discontinuation. Four patients discontinued due to neutralizing NTZ antibodies; 2 in each group.

Conclusion: The SC administration has become the preferred administration method for NTZ since its launch in the spring of 2021, with 59% of NTZ treatment initiations being administered using SC method. We did not find significant differences in discontinuation rates between the two administration methods. Longer observation periods will be needed to assess possible differences in tolerability and treatment adherence between the two administration modalities.