Managing reactivation of multiple sclerosis during treatment with natalizumab

Background: Following natalizumab failure, it is unknown whether switching to alternative high-efficacy therapies offers superior effectiveness over continuing natalizumab. Objective: To compare different treatment strategies following natalizumab failure. Methods: Patients suffering a relapse during natalizumab treatment with adequate follow-up were identified from the MSBase registry. Following natalizumab failure, natalizumab continuation was compared to switching to anti-CD20 therapies/alemtuzumab/lower-efficacy therapies and treatment discontinuation. The primary outcome was the risk of further relapses. Secondary outcomes included risk of subsequent magnetic resonance imaging (MRI) activity, confirmed disability worsening and disease-activity-free survival. Multivariable proportional hazards models compared outcomes during time-varying therapy exposures. Four sensitivity analyses were conducted with varied inclusion criteria and treatment failure definitions. Results: Of 1553 patients experiencing a relapse during natalizumab treatment, 1037 met the inclusion criteria. Following natalizumab failure, switch to anti-CD20 therapy was associated with a lower relapse risk (heart rate (HR) = 0.48, 95% confidence interval (CI) = 0.27–0.84) compared to continuing natalizumab; no differences were observed in MRI or disability outcomes. Treatment de-escalation or cessation was associated with increased relapse risk (HR = 1.46, 95% CI = 1.15–1.85; HR = 2.08, 95% CI = 1.22–3.55, respectively). We did not find evidence of a difference for switching to alemtuzumab. Sensitivity analyses replicated primary findings. Conclusion: This exploratory study indicates that switching to anti-CD20 therapies following natalizumab failure is associated with a >50% reduction in relapse risk. No differences were seen in secondary outcomes, despite consistent trends. Clinicians may consider anti-CD20 therapies following natalizumab failure, noting further research is needed to confirm differences in MRI and disability outcomes.