Real World Effectiveness of Natalizumab Extended Interval Dosing in a French Cohort

Natalizumab (NTZ) use in Multiple Sclerosis (MS) in highly active patients has been largely established during the last Rationale 10 years in both clinical trials and real-world practice. Along with its efficacy, NTZ use has been limited by potential risk of progressive multifocal leukoencephalopathy (PML). Thus, several studies have tried to assess how to minimize this risk. One suggested approach is to move from the standard interval dose (SID) of 4 weeks to an extended interval dose (EID) of 5 weeks or longer. Extending the dosing interval of NTZ has been practiced by some physicians with the intention of improving the benefit/risk of the treatment by reducing the exposure-dependent risk of progressive multifocal leukoencephalopathy (PML) while maintaining efficacy. We propose to retrospectively analyze data from clinical records coming from RRMS patients treated in France at 5 different centers; Caen, Nice, Bobigny and Toulouse hospitals as well as Percy Military Hospital, to evaluate the effectiveness of natalizumab EID in subjects who have previously been treated with natalizumab SID for 12 months, in relation to continued SID treatment. In the clinical practice of these centers, patients are shifted after minimum 12 months under SID to an EID of 6 weeks regardless antibody JC serum status. Clinical, magnetic resonance imaging (MRI) and serum anti-JCV antibody status data are collected when available. The objective of this study is to assess the efficacy in term of ARR and safety.