End of dose interval (EDI) symptoms in patients undergoing treatment with natalizumab

Background and aims: Many patients treated with Natalizumab experience End of Dose Interval (EDI) symptoms towards the end of the administration cycle. During the pandemic, due to the unknown effects of SARS-CoV-2 infection on patients undergoing treatment with Natalizumab (NTZ), we decided to shift patients on NTZ from a Standard Interval Dosing (SID of 4 weeks) to an Extended Interval Dosing (EID of 5–6 weeks). Our main objective was to study the prevalence and incidence of EDI symptoms in our MS center, along with its efficacy and safety. Methods We reviewed 102 patients in our MS center treated with natalizumab for at least 12 months using EID. When tolerated/possible, patients were shifted from a SID of 4 weeks to an EID of 5–6 weeks. Patients were asked to report any worsening of their symptoms during the administration cycle, fatigue was assessed right before the administration of NTZ, with surveys and Fatigue Severity Scale (FSS). Results: Among the 102 patients, 41 (40.19%) reported end of dose interval (EDI) symptoms, and the most common one was fatigue. Among those 41 patients: 26 (63%) had a Relapsing Remitting (RR) course while 15 (37%) had a Secondary Progressive (SP) course. Of note, 15 (36.58%) patients reported a new onset of fatigue where none was present before the EID. Our data suggest that with EID efficacy is still preserved since only 6 patients showed new lesions on follow-up-MRI and with little clinical significance. Conclusions: Our study shows that when EID was adopted, fatigue was higher in the RR course group, with efficacy still preserved.