Extended interval dosing of natalizumab in MS; a New Zealand experience (P6.351)

Objective: Waiakto DHB is a tertiary hospital in New Zealand. It is standard practise for Natalizumab to be administered at 6 weekly intervals at Waikato DHB. We will report Waikato DHB’s prospectively collected data and show that there is no increased risk of clinical or radiological relapse compared with the standard dosing. Background: Natalizumab is a humanized monoclonal antibody directed against the α4β1 integrin. Natalizumab is highly efficacious in the treatment of relapsing-remitting multiple sclerosis (RRMS). However, natalizumab use is with strict surveillance due to its association with progressive multifocal leukoencephalopathy (PML) due to reactivation of the John Cunningham virus. To reduce the risk of PML, extended interval dosing (EID) has been evaluated. The dose of 300mg and dosing interval of 4 weeks is based upon a pharmacokinetic study by Sheremata in 1999. Natalizumab had been shown to be detectable upto 8 weeks post dose. The limited evidence shows that EID upto 8 weeks does not lead to an increased risk of clinical relapses and MRI detectable lesions. Design/Methods: All patients treated with natalizumab were recruited from 2012 to December 2016. They were prospectively followed up for clinical relapses, MRI changes, JC virus titre, optical coherence topography and neuropsychology changes. Results: 27 patients were treated with six weekly natalizumab infusions with an average treatment period of 2 years. The average EDSS was 2.97 with a range of 1.5–4. There was one reported clinical relapse (3.8%) treated with IV methylprednisone, however this was not diagnosed by a neurologist. There were no new lesions detected on MRI within the patient group. There was not a case of PML. Conclusions: Waikato DHB’s experience with 6 weekly natalizumab is comparable with previously published retrospective reviews. Our experience indicates there is not an increase in clinical or radiological relapse with six weekly natalizumab dosing in RRMS. Disclosure: Dr. Chan has nothing to disclose. Dr. Siu has nothing to disclose. Dr. Mellsop has nothing to disclose. Dr. Schepel has nothing to disclose.