Background: In the Phase 3 RAISE study (NCT04115293), zilucoplan significantly improved MG-specific outcomes in patients with acetylcholine receptor autoantibody-positive generalised MG. After the first 12 weeks of the open-label extension study, RAISE-XT (NCT04225871), corticosteroid dose could be changed per the investigator’s discretion. We evaluate changes in corticosteroid dose during treatment with zilucoplan in RAISE-XT. Methods: In RAISE-XT, adults who completed the Phase 2 or RAISE studies (N=200) self-administered daily subcutaneous zilucoplan 0.3mg/kg, either continuing with zilucoplan or switching from placebo. Primary outcome was incidence of treatment-emergent adverse events (TEAEs). We assessed ( post-hoc ) the proportion of patients who discontinued/reduced or increased corticosteroid dose relative to double-blind baseline up to Week 60. Results: At Week 60, 30% (n=18/60) and 22% (n=12/54) of patients receiving corticosteroids in the zilucoplan and placebo-switch groups, respectively, reduced/discontinued corticosteroids (mean dose reductions: 14mg and 16mg; mean [SD] CFB in MG-ADL scores: -5.00 [3.96] and -5.67 [6.89]. 12% (n=7/60) and 7% (n=4/54) of patients in the zilucoplan and placebo-switch groups, respectively, increased corticosteroid dose (~12mg mean increase in both groups). TEAEs occurred in 188 (94.0%) patients (data cut-off: 08 September 2022). Conclusions: While receiving zilucoplan, discontinuation or dose reduction in concomitant corticosteroids was possible with maintained efficacy.

P.055 Corticosteroid dose tapering in patients with generalised myasthenia gravis on zilucoplan: Interim analysis of RAISE-XT