Comparative Effectiveness of Rituximab and Cladribine in Relapsing-Remitting Multiple Sclerosis: A Target Trial Emulation

Background Head-to-head comparisons of high-efficacy therapies for relapsing-remitting multiple sclerosis (RRMS) are lacking. We emulated a target trial to compare the long-term effectiveness of rituximab and cladribine. Methods We estimated the effect of initiating treatment with rituximab or cladribine by emulating a target trial using data from the Norwegian MS Registry and Biobank at two university hospitals with different treatment strategies. Cumulative incidence and risk differences after 4 years were estimated using a weighted Kaplan-Meier estimator, adjusted for baseline covariates. The primary outcome was MRI disease activity, with the secondary outcomes including relapses and safety. Results The study included 285 patients, 159 receiving rituximab and 126 receiving cladribine, with a median follow-up of 4.5 years (IQR 4.0 to 5.0). Rituximab-treated patients had a lower risk of new MRI disease activity compared to cladribine-treated patients ( p < 0.0001). The 4-year risk was 18% (95% CI 11 to 23) for the rituximab-treated patients and 57% (95% CI 48 to 65) for cladribine-treated patients, yielding a risk difference (RD) of 38 percentage-points (95% CI 29 to 51). The 4-year RD for relapse was 11.2 percentage-points (95% CI 3 to 18) and the RD for discontinuation or a third dose of cladribine was 13.7 percentage-points (95% CI 9 to 25). The incidence of hospitalizations related to potential adverse events was 6.0 per 100 person-years for rituximab and 4.1 per 100 person-years for cladribine. Conclusions These findings suggest that rituximab has superior effectiveness compared to cladribine during a median follow-up of 4.5 years.