To assess short term relapse and disability risk after switching from natalizumab (NTZ) to ocrelizumab (OCR) or cladribine (CLAD) in patients with relapsing-remitting multiple sclerosis (RRMS)

The relapse risk after stopping NTZ varies between 9 and 80% and seems to be lower after switching to second line drugs as fingolimod. Information on disease activity after switching to newer drugs as OCR/CLAD is scarce.

Patients were recruited from several academic centers (AC) throughout Germany and two national registries (Denmark (DMSR)/Germany (GMSR)). We included 223 adults with RRMS who stopped NTZ (treated ≥3 months) and switched to OCR/CLAD  6 months after the last infusion with at least 6 months follow up on OCR/CLAD (exposure).

The frequency of relapses was assessed in different phases after FTY was discontinued.

196 patients (DMSR: N=61, GMSR: N=79, AC: N=56) switched from NTZ to OCR, 27 patients (DMSR: N=17, GMSR: N=8, AC: N=2) from NTZ to CLAD.

In the treatment free switching interval regardless of following switch treatment 11/4.93% patients had ≥1 relapse in 42.23 patient years (py) (DMSR: N=1/1.28% in 12.85 py, GMSR: N=5/5.75% in 17.47 py, AC: N=5/8.62% in 12.01 py).

 During the first six months after OCR/CLAD start 20/8.97% had ≥1 relapse regardless of following switch treatment.

Stratified by drug type 16/8.16% of the OCR switchers had ≥1 relapse (DMSR: N=2/3.28%, GMSR: N=6/7.59%, AC: N=8/14.29%) and 4/14.81% of the CLAD switchers (DMSR: N=1/5.88%, GMSR: N=2/25%, AC: N=1/50%).

The overall relapse risk during the treatment free switching interval was low in our cohort but varied by data source.