• Alyssa A Toorop, Zoé L E van Kempen, Maurice Steenhuis, Jessica Nielsen, L G F Sinnige, Gert van Dijk, Christiaan M Roosendaal, ArnoldusEdo P JEPJDepartment of Neurology, Elisabeth-TweeSteden Hospital, Tilburg, The Netherlands., Elske Hoitsma, Birgit I Lissenberg-Witte, Brigit A de Jong, OostenBob W vanBWVDepartment of Neurology, MS Center Amsterdam, Amsterdam UMC Location VUMC, Amsterdam, The Netherlands., Eva M M Strijbis, UitdehaagBernard M JBMJDepartment of Neurology, MS Center Amsterdam, Amsterdam UMC Location VUMC, Amsterdam, The Netherlands., Theo Rispens, Joep Killestein, and NEXT-MS study group.
• Department of Neurology, MS Center Amsterdam, Amsterdam UMC Location VUMC, Amsterdam, The Netherlands a.toorop@amsterdamumc.nl.
• J. Neurol. Neurosurg. Psychiatr. 2023 Jun 1; 94 (6): 482486482-486.

BackgroundNatalizumab is effective in the treatment of multiple sclerosis (MS). In 2021, the European Medicines Agency approved the subcutaneous (SC) variant of natalizumab which can be used instead of intravenous administration. However, the course of drug levels varies between administration routes, and the Food and Drug Administration rejected the request for approval of natalizumab SC for reasons that were not disclosed. Our objective was to evaluate the course of natalizumab trough drug levels in patients who switched from natalizumab intravenous to SC on various treatment intervals.MethodsThe NEXT-MS trial (N=382) investigates personalised treatment of natalizumab, in which infusion intervals are prolonged based on individual natalizumab trough drug levels. In 2021, an amendment was approved allowing participants to switch from intravenous to SC administration with frequent measurements of natalizumab drug levels and antidrug antibodies (ADAs). Results were compared with linear mixed model analyses.ResultsUntil December 2022, 15 participants switched to SC natalizumab. Natalizumab drug levels with SC administration were on average 55% lower compared with intravenous administration (Exp (estimate) 0.45, 95% CI 0.39 to 0.53, p<0.001), leading to very low trough drug levels in three patients on extended treatment intervals. No natalizumab ADAs were detected during intravenous or SC treatment. None of the participants on natalizumab SC showed evidence of MS disease activity.ConclusionsNatalizumab trough drug levels can decrease after switching from natalizumab intravenous to SC administration. We advise to monitor trough drug levels in patients with low natalizumab drug levels during intravenous treatment, patients with higher body mass index or patients on extended treatment intervals who switch to SC administration of natalizumab.© Author(s) (or their employer(s)) 2023. No commercial re-use. See rights and permissions. Published by BMJ.

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