FDA Expands Efgartigimod Indications to All Adult gMG Serotypes

On May 8, the United States Food and Drug Administration (FDA) has approved a label expansion for argenx’s efgartigimod alfa (Vyvgart) and efgartigimod alfa and hyaluronidase-qvfc (Vyvgart Hytrulo) to cover all adult patients with generalized myasthenia gravis (gMG) regardless of serotype — including anti-MuSK antibody–positive, anti-LRP4 antibody–positive, and triple seronegative patients.

The decision gives efgartigimod the broadest gMG label currently available and marks the first time any approved therapy has been explicitly indicated for the full spectrum of gMG serotypes. Previously, both formulations carried indications limited to anti-acetylcholine receptor antibody (anti-AChR-Ab)–positive gMG, leaving roughly 20% of the gMG population — those without detectable AChR antibodies — without a specifically approved targeted treatment option.¹

That 20% represents a clinically heterogeneous and historically underserved group. Anti-MuSK antibodies are detectable in approximately 1% to 10% of all gMG patients, anti-LRP4 antibodies in approximately 1% to 5%, and triple seronegative patients — those lacking detectable antibodies against AChR, MuSK, or LRP4 — account for roughly 10% of all gMG cases. This last subgroup has historically been excluded from randomized clinical trials and carries a disproportionate disease burden as a result.¹

The approval is based on the phase 3 ADAPT SERON study (NCT06298552), a randomized, double-blind, placebo-controlled, multicenter trial enrolling 119 adults with anti-AChR-Ab–negative gMG across North America, Europe, China, and the Middle East — the largest dedicated study in this population to date. Part A randomized participants 1:1 to four once-weekly infusions of efgartigimod IV or placebo, followed by a 5-week observation period. Eligible patients had a confirmed gMG diagnosis by independent expert panel review and a baseline MG-ADL total score of at least 5, and were required to be on a stable background gMG regimen including acetylcholinesterase inhibitors, corticosteroids, or nonsteroidal immunosuppressants.¹

The primary endpoint — MG-ADL total score change from baseline to day 29 — was met with statistical significance (P = .0068). In the overall population across all three seronegative serotypes, patients receiving efgartigimod IV achieved a mean 3.35-point improvement in MG-ADL total score at week 4. Clinically meaningful improvements in MG-ADL and Quantitative Myasthenia Gravis (QMG) scores were observed across subsequent treatment cycles and across all individual serotypes studied.¹ Per-serotype numerical breakdowns and QMG change data were not disclosed in the press release.

Part B of ADAPT SERON is an ongoing open-label extension in which participants receive fixed and then clinically guided repeat cycles of efgartigimod. Safety in ADAPT SERON was consistent with efgartigimod's established profile from the original ADAPT trial in AChR-Ab–positive gMG; no new safety signals were identified. The most common adverse events associated with efgartigimod include respiratory tract infection, headache, and urinary tract infection. Vyvgart Hytrulo additionally carries injection site reactions as a common adverse event.¹

The clinical rationale for FcRn blockade in seronegative gMG — while most studied in AChR-Ab–positive disease — rests on the shared IgG-mediated mechanism across subtypes. Efgartigimod binds the neonatal Fc receptor (FcRn), accelerating IgG catabolism and reducing circulating pathogenic autoantibodies. A December 2025 narrative review in Biomedicines synthesizing clinical trial and real-world data noted that efgartigimod's most pronounced clinical benefits consistently appeared within 3 to 5 weeks of treatment initiation across gMG populations, correlated with reductions in total IgG levels, and were sustained across repeat treatment cycles — a pharmacodynamic rationale that extends logically to non-AChR antibody–mediated disease.²

Efgartigimod is available in 2 formulations: an intravenous infusion (Vyvgart) and a subcutaneous combination product with recombinant human hyaluronidase PH20 (Vyvgart Hytrulo), which is also available as a self-administered prefilled syringe. Both are now indicated for all adult gMG serotypes. Efgartigimod also holds an existing approval for chronic inflammatory demyelinating polyneuropathy in its subcutaneous formulation.¹

argenx also recently reported positive topline results from the ADAPT OCULUS study of Vyvgart Hytrulo in ocular MG and is enrolling pediatric gMG patients in the ADAPT Jr study.¹

References

1. argenx. argenx announces U.S. FDA approval expanding Vyvgart and Vyvgart Hytrulo for use in all adult patients living with gMG. Press release. May 8, 2026. https://argenx.com/news/2026/press-release-3291372

2. Nteve G, Dalagiorgou G, Alexopoulos H, Dalakas MC. Efgartigimod for generalized myasthenia gravis and beyond: a narrative review of its pharmacological profile, clinical utility, and expanding applications. Biomedicines. 2025;13(12):2975. doi:10.3390/biomedicines13122975