To Örebro University

Introduction: Natalizumab (NTZ) is a highly effective disease modulatory treatment for relapsing multiple sclerosis (RMS). Post-marketing surveillance is important to evaluate the long-term safety and effectiveness in a real-world setting. To this end the “Immunomodulation and Multiple Sclerosis Epidemiology Study” (IMSE 1) was initiated upon launch of NTZ in Sweden (Aug 2006).

Objectives/Aims: To follow-up the long-term effectiveness and safety of NTZ in a real-world setting.

Methods: Adverse events (AEs), Serious AEs (SAEs), John Cunningham virus status (JCV) and clinical effectiveness measures; Extended Disability Status Scale (EDSS), Multiple Sclerosis Severity Scale (MSSS), Symbol Digit Modalities Test (SDMT) and Multiple Sclerosis Impact Scale (MSIS-29) data were collected from the nationwide Swedish Neuro Registry (NeuroReg). Effectiveness measures were assessed using the Wilcoxon Signed Rank Test.

Results: A total of 4011 NTZ patients were included in the IMSE 1 study from August 2006 until March 2023 (72% female; mean age 36 years; 80% RRMS; mean treatment duration 52 months) and 249 had been treated for at least 132 months. Of the 132-month cohort, 75% were female, the mean age was 36 years, 88% had RRMS, and the mean treatment duration was 160 months. The majority were treated with interferons and glatiramer acetate prior to NTZ (68%), where 30% (74/249) discontinued NTZ treatment; 43% (32/74) due to being JCV positive (JCV+), with a mean JCV index of 1.1±0.9 (n=66). Annualized relapse rates dropped from 0.40 in the year before treatment start to 0.04 during treatment, where 68% were entirely free of relapses and 21% had only 1 relapse during the entire treatment period (17% missing data). All clinical effectiveness measures, except EDSS showed statistically significant improvement between baseline and 132 months (p<0.05).From the entire IMSE1 cohort (N=4011), 132 SAEs have been reported to the Swedish MPA, including 9 cases (2 fatal) of progressive multifocal leukoencephalopathy (PML) of which 8 occurred between 2008 and 2012, and one in 2018.

Conclusion: NTZ is generally well tolerated and displays sustained effectiveness regarding cognitive, physical and psychological measures, as well as relapse-control. Introduction of JCV testing has led to fewer treated JCV+ patients, likely explaining a drastically reduced incidence of PML.