Switching natalizumab to fingolimod within 6 weeks reduces recurrence of disease activity in MS patients

BACKGROUND: Natalizumab is an effective treatment in relapsing-remitting multiple sclerosis (MS). Mainly because of the risk of progressive multifocal leukoencephalopathy (PML), a substantial proportion of John Cunningham (JC) virus–positive patients switch to fingolimod. Previous reports show a clear benefit when the duration of a washout (WO) period of natalizumab is 0–3 months in comparison to longer WO periods. However, there is no consensus regarding the optimal duration of a WO period under 3 months. OBJECTIVE: We compared MS disease activity after different WO periods. In addition, we investigated several factors that possibly influence recurrence of disease activity, including serum natalizumab concentration and lymphocyte counts. METHODS: From a prospective observational cohort study of natalizumab-treated patients, we selected 52 patients who switched to fingolimod. We divided the patients in three groups (<6 weeks, 6–8 weeks, >8 weeks WO). Serum natalizumab concentration and lymphocyte count were assessed during and after natalizumab treatment. RESULTS: Patients with a WO period of >8 weeks had a significant higher recurrence of disease activity (odds ratio, 6.8; 95% confidence interval, 1.4–32.8) compared to patients with a WO period of <6 weeks. Serum natalizumab concentration and lymphocyte count did not predict recurrence of disease activity. INTERPRETATION: A short WO period decreases the risk of recurrence of disease activity. The possible impact of a short WO period on the risk of carry-over PML in JC virus–positive patients remains uncertain.