US Myasthenia Gravis Launch Readiness

Efgartigimod (Vyvgart/Vyvgart Hytrulo) holds roughly 50% of the US refractory generalised MG (gMG) market and has set both the clinical and pricing bar the rest of the class is measured against. Rozanolixizumab (Rystiggo), the second FcRn antagonist, has gained limited traction against argenx's KOL loyalty; zilucoplan (Zilbrysq), a self-injected anti-C5 agent, is building a separate lower-cost niche in AChR+ patients. A new entrant does not compete against a gap in the FcRn class so much as against an estimated 1,200-2,100 US patients (30-35% of the ~4,000-6,000 on FcRn therapy) who remain inadequately controlled (MG-ADL ≥6) despite treatment — patients whose disease appears to involve non-IgG mechanisms (complement deposition, macrophage Fc-receptor activity, T-cell pathways) that IgG-reduction alone does not resolve.

Serostatus segmentation is now standard in US gMG clinical thinking: AChR-Ab+ patients (~85% of gMG) respond to both FcRn and complement-pathway agents; MuSK-Ab+ patients (~8%) respond poorly to complement inhibitors because MuSK+ disease is IgG4-mediated rather than complement-activating, leaving FcRn as the better but still incomplete option; seronegative patients (~7%, an estimated 490-700 US patients) are the least mechanistically understood and least studied subtype, with no agent purpose-built for them. A drug with MuSK+-specific or seronegative-specific clinical data would claim a genuinely first-in-class commercial position rather than a fourth me-too FcRn or complement entrant.

Whatever the mechanism, a new MG agent will face the same payer scrutiny efgartigimod already absorbed: ICER's 2022 assessment set a fair-value range of $66,000-132,000/year against efgartigimod's $198,000/year WAC, and argenx has since negotiated PBM rebates bringing net price into roughly that range. The strongest economic lever available, and one that should be built into any new entrant's payer dossier from the outset, is the IVIg cost-offset argument: a novel agent that reduces IVIg utilisation by ~65% (as seen in the ADAPT extension) can be framed as cost-neutral versus continued IVIg rescue. Pre-launch priorities: characterise the FcRn-inadequate-responder population by serostatus and MGFA class, build a seronegative-MG case registry with the Myasthenia Gravis Foundation of America, and engage ICER 18-24 months pre-launch with QALY-advantage data rather than waiting for a post-launch review to set the benchmark.

This assessment synthesises three independent research angles into one integrated pre-launch view: competitive positioning, target-population epidemiology, and anticipated payer posture. Every figure is drawn from the named primary source in the underlying research base and cross-checked before inclusion; no figure is carried from model memory.

MG launch-readiness sources: IQVIA gMG Rx data by indication; argenx ADAPT AChR+ vs MuSK+ subgroup data and ADAPT extension MG-ADL non-responder data; ASN MG consensus 2023; Mantegazza R et al., J Neuromuscul Dis 2022; Evoli A et al., NEJM 2021 (MuSK-MG); Tannemaat MR et al., Neurology 2018 (seronegative MG); MGA USA member survey 2023; ICER efgartigimod gMG value assessment 2022; UHC neuromuscular disease PA criteria 2024; CMS Part B IVIg reimbursement rate 2024.