Efficacy and safety of natalizumab extended interval dosing.

Objective: It is postulated that extending the dosing interval of natalizumab (NTZ) from 4 to 5-8 weeks might decrease the risk of progressive multifocal leukoencephalopathy (PML). The aim of this study was to assess the effect of extended interval dosing (EID) on the therapeutic efficacy of natalizumab.

Methods: We reviewed 85 patients treated at two MS centers in the Middle East with natalizumab for at least 6 months using EID. Patients were shifted after an initial treatment period at standard interval dosing (SID) to an EID ranging from 5-8 weeks.

Results: The mean treatment duration on SID and EID was 15.4 ± 11.9 and 11.8 ± 7.0 months, respectively. By the end of SID and EID treatment 95.3% and 93.9% of patients were free of relapses (P = 0.41) with an annualized relapse rate (ARR) of 0.0006 and 0.001 respectively (P = 0.42). The mean EDSS at the end of SID and EID periods was 2.56 ± 1.62 and 2.59 ± 1.61 respectively (P = 0.84). A total of 97.6% and 94.7% of patients had no enhancing lesions on MRI during the SID and EID periods respectively (P = 0.18). There were no cases of PML and the rate of infections was lower during the EID period.

Conclusion: In patients treated with natalizumab, shifting from SID to EID has no negative effect on efficacy as evidenced by relapse rate, disability progression and MRI activity.