Natalizumab and drug holiday in clinical practice: an observational study in very active relapsing remitting multiple sclerosis patients.

Background: In order to reduce the risk of progressive multifocal leucoencephalopathy when using natalizumab for more than 12 months, a 6-month drug holiday has been discussed. However, the consequences on short term disease activity have been poorly assessed.
Objective: The aim of this study was to assess clinical and radiological disease activity within 6 months after stopping natalizumab in very active relapsing remitting Multiple Sclerosis (RRMS) patients.
Methods: In 8 hospitals from Western France, we retrospectively collected clinical and MRI data from consecutive RRMS patients treated with natalizumab for at least 6 months, and who stopped the drug for various reasons except therapeutic failure. Patients didn't receive any other disease modifying treatment after discontinuing natalizumab.
Results: A total of 27 patients with very active RRMS before natalizumab start (mean annualized relapse rate of 2.3, MRI activity in 21 of 27 patients) were studied. Within 6 months after discontinuing natalizumab, 18 patients (67%) experienced clinical relapse and 3 additional patients had radiological activity, without clinical relapse. Four patients (15%) experienced a rebound activity, with severe relapse and 20 or more gadolinium enhancing lesions on MRI.
Conclusion: Such observational data didn't support the concept of drug holiday when using natalizumab in very active RRMS.
(Copyright © 2011. Published by Elsevier B.V.)