[Subcutaneous Injection of Efgartigimod, a New Therapeutic Agent for Generalized Myasthenia Gravis]

Patients with generalized myasthenia gravis (gMG) suffer from significant physical and social burdens. Although immunotherapies have been widely used for the treatment of gMG, some patients do not achieve or maintain remission. Recently, several molecular-targeting therapies of gMG, including the intravenous infusion of efgartigimod alfa (efgartigimod IV), a neonatal Fc receptor inhibitor, have been developed and are clinically used in Japan. In 2024, combination subcutaneous injection of efgartigimod alfa and vorhyaluronidase alfa (efgartigimod SC) was approved for the treatment of patients with gMG (only when treatment with steroids or non-steroidal immunotherapies does not lead to sufficient response). Efgartigimod SC contains vorhyaluronidase alfa, which temporarily and locally facilitates diffusion of efgartigimod alfa, resulting in its absorption enhancement. An international phase III, ADAPT-SC study in patients with gMG, including Japanese demonstrates the non-inferiority of efgartigimod SC to efgartigimod IV in reduction of total IgG by 4 weeks treatment. An extension ADAPT-SC+ study demonstrates the long-term safety and tolerability as well as repeatable clinical benefit across multiple efgartigimod SC treatment cycles. As a self-injectable drug, efgartigimod SC may not only contribute to satisfy unmet medical needs in gMG therapy, but also improve convenience for patients and healthcare providers. (Received July 11, 2024; Accepted September 13, 2024; Published January 1, 2025).