BACKGROUND Eculizumab is a terminal complement inhibitor used to treat myasthenia gravis in patients refractory (because of insufficient efficacy or intolerance) to other therapies, including intravenous immunoglobulin. However, information is lacking on how to transition patients from intravenous immunoglobulin to eculizumab, while avoiding a crossover effect of intravenous immunoglobulin and minimizing the risk of a transient worsening of symptoms if treatment that may be at least partially effective is interrupted. The aim of this study was to determine whether eculizumab can be safely initiated before complete intravenous immunoglobulin washout, using a standardized protocol. CASE REPORT A series of 13 patients with generalized treatment-refractory myasthenia gravis were transitioned to eculizumab 10-14 days after their last intravenous immunoglobulin infusion. Patients' clinical status was assessed before and 6 weeks after transition using the Myasthenia Gravis Composite Score. Most patients (8/13; 62%) had received ≥3 immunosuppressants as well as intravenous immunoglobulin. The median (range) Myasthenia Gravis Composite Score before and 6 weeks after transition was 21 (11-29) and 12 (6-18), respectively. Clinically significant improvements (score decrease ≥3) were observed in all patients. Two patients experienced mild myalgia during transition. CONCLUSIONS In this case series, patients with treatment-refractory myasthenia gravis were successfully transitioned to eculizumab 10-14 days after their last intravenous immunoglobulin infusion without any significant safety concerns.