Extending the natalizumab interval after the 24th administration could reduce the risk of progressive multifocal leukoencephalopathy (PML) without efficacy reduction.
To evaluate the non-inferiority of the efficacy of an extended interval dosing (EID) regimen compared with the standard interval dosing (SID) of natalizumab regarding the multiple sclerosis (MS) MRI activity.
It is an observational, multicenter (14 Italian centers), retrospective cohort study, starting from the 24th natalizumab infusion to the loss of follow-up or 2 years after baseline. Patients were grouped in 2 categories according to the mean number of weeks between doses: < 5 weeks, SID; ≥ 5 weeks, EID. Three hundred and eight patients were enrolled. Median dose interval (MDI) following 24th infusion was 5 weeks, with a bimodal distribution (modes at 4 and 6 weeks).
Two hundred and sixteen patients were in the SID group (MDI = 4.4 weeks) and 144 in the EID group (MDI 6 weeks). The risk to develop active lesions on MRI is similar in SID and EID groups during the 6 and 12 months after the 24th natalizumab infusion, respectively 2.98% (95% CI: 0.56-5.40) vs 3.32% (95% CI: 0.00-6.65%) [p=0.88] and 6.65% (95% CI: 3.02-10.29) vs 5.67% (95% CI: 1.76-9.58%) [p=0.73]. The EID regimen does not increase the occurrence of MRI activity after 6 and 12 months.
There is no evidence of a reduced efficacy of natalizumab in an EID setting regarding the MRI activity. This observation confirms previous clinical results and together with the increasing evidence of a reduced risk of PML associated to an EID regimen, supports the need of a bigger randomized study to assess the need to change the standard of the natalizumab dosing schedule, in order to better manage JCV-positive patients after 24 doses of natalizumab.