Long-term effectiveness, safety, and cost-effectiveness of intravenous immunoglobulin for generalized myasthenia gravis in an era of molecular targeted drugs: Insights from Japanese post-marketing surveillance.

OBJECTIVES Intravenous immunoglobulin (IVIg) is widely used for generalized myasthenia gravis (gMG), but long-term, large-scale, real-world evidence remains limited. This study evaluated the 2-year effectiveness, safety, and cost-effectiveness of IVIg in Japanese patients with gMG.

METHODS This retrospective, observational, post-marketing surveillance study was conducted between 2011 and 2016 at 316 facilities across Japan. All patients with gMG who received the first IVIg dose were eligible for enrolment. Patients who did not receive corticosteroids or immunosuppressants before IVIg initiation were excluded. The primary outcome was the time to retreatment with IVIg, intravenous methylprednisolone, plasmapheresis, or thymectomy due to disease progression or relapse. The cost-effectiveness of IVIg and molecular targeted drugs was evaluated using cost per responder and cost per Myasthenia Gravis Activities of Daily Living (MG-ADL) improvement analyses.

RESULTS In total, 1041 patients were included in this study (mean age, 58.7 years; women, 674 [65%]; mean MG-ADL score, 9.45; mean follow-up period, 331.5 days). The median time to retreatment was 386 days (95% confidence interval [CI]: 302-545) in all patients and 175 days (95% CI: 147-214) in 410 patients who received the second IVIg dose (p < 0.0001, log-rank test). The MG-ADL responder rate (≥2-point improvement) was 65.7% on day 14 and 46.7% on day 180. The cost per MG-ADL improvement was estimated at 7000-17,000 Japanese yen, which was substantially lower than that for molecular targeted drugs.

DISCUSSION These findings support the long-term effectiveness and cost-effectiveness of IVIg for gMG, without new safety concerns.