Natalizumab is a high-efficacy therapy for recurrent multiple sclerosis (RMS) with a four-week administration interval. Controlled trials have shown that extending this interval to six weeks led to better safety without increasing the risk of relapse. We aimed to analyze the safety of extending the natalizumab interdose interval from 4 to 6 weeks in a real-life setting.
This monocentric retrospective self-controlled study included adult patients with RMS treated with natalizumab with a four-week interval between infusions for a minimum of six months, before switching to a six-week interval. The main outcomes were the incidence of MS relapse, new MRI lesions, and MRI activity signs during the two periods, with patients being their own controls.
Fifty-seven patients were included in the analysis. The mean (95%CI) annualized relapse rate (AAR) before natalizumab introduction was 1.03 (0.52; 1.55). During the four-week interval dosing period, no patient presented with an MS relapse, and seven (13.5%) patients had new MRI lesions. During the six-week interval dosing period, no relapse was observed and two (3.6%) patients had new MRI lesions.
We did not observe more relapses or signs of MRI activity when extending the interval between natalizumab infusions from four to six weeks.

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