To Örebro University

Background: Natalizumab (NTZ) is a highly effective disease modulatory treatment for relapsing-remitting multiple sclerosis (RRMS). Post-marketing surveillance is important for evaluation of 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 NTZ launch in Sweden (Aug 2006).

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

Methods: In Sweden MS patients are registered in the nationwide Swedish Neuro Registry (NeuroReg). IMSE 1 includes patients starting NTZ treatment and data is collected from NeuroReg. Adverse events (AEs), JC-virus status (JCV) and clinical effec-tiveness measures are registered prospectively.

Results: A total of 3141 patients were included in the IMSE 1 study from August 2006 until April 2019 (72% female; men age 35 years; 79% RRMS; mean treatment duration 50 months) and 288 had been treated for at least 96 months. 71% of these 288 patients (71% female; men age 37 years; 82% RRMS; mean treatment duration 118 months) were treated with interferons and glatiramer acetate prior NTZ. At some point of time, 31% (90/288) discontin-ued NTZ treatment of which 41% discontinued due to JCV posi-tive (JCV+). In total, 30% (86/288) of these patients were JCV+with a mean JCV index of 1.2±1.0 (6% missing data). Relapses before treatment were reduced from 388/1000 patient years to 54 during treatment, 62% were relapse-free and 17% had 1 relapse during the entire treatment period (12% missing data). All clinical effectiveness measures (Extended Disability Status Scale (EDSS), Multiple Sclerosis Severity Scale (MSSS), Multiple Sclerosis Impact Scale (MSIS-29) and Symbol Digit Modalities Test (SDMT)) showed statistically significant improvement between baseline and 96 months. Over the entire observation time, 104 Serious AEs had been reported to the Swedish MPA and included 9 cases (2 fatal) of progressive multifocal leukoencephalopathy (PML) of which 8 between 2008 and 2012, and 1in 2018. 16 patients died during or within 6 months of last NTZ infusion. None were judged to be directly associated with NTZ.

Conclusions: NTZ is generally well tolerated with sustained effectiveness regarding cognitive, physical and psychological measures, as well as relapse-control. Introduction of JCV testing has led to fewer treated JCV+ patients, which likely explains a drastic drop in the incidence of PML.