Three novel mechanisms reached US gMG in 24 months, and the AChR-antibody line decides which patients the C5 class can even reach.

Generalised myasthenia gravis is now a multi-mechanism market. The FcRn antagonists lower pathogenic IgG and carry broad labels with no complement-restricting serology requirement: efgartigimod (Vyvgart/Vyvgart Hytrulo, argenx) and rozanolixizumab (Rystiggo, UCB), both approved in 2023. The complement class splits by route: the IV C5 inhibitors eculizumab (Soliris) and ravulizumab (Ultomiris) from AstraZeneca/Alexion, and UCB's subcutaneous zilucoplan (Zilbrysq). Efgartigimod anchored the FcRn entry with a 68% MG-ADL responder rate versus 30% on placebo in the ADAPT trial.

The competitive story turns on two forces. Roughly 85% of gMG patients are AChR-antibody positive, and the C5 inhibitors are approved only in that subgroup, so MuSK-positive and seronegative patients, about 15% of the market, are reachable only by the FcRn class. UCB holds both an FcRn antagonist and a C5 inhibitor, so it participates on whichever side of the FcRn-versus-complement sequence a payer imposes, a dual-asset position no other manufacturer shares.

Antibody serology, not brand loyalty, decides which mechanism a patient can even access.

Five questions this report answers:

Q1 - How do the FcRn antagonists and C5 inhibitors differentiate on mechanism, route and serology eligibility?

Q2 - What does UCB's dual-asset position in both FcRn and C5 mean for its competitive strategy?

Q3 - How is AChR-positive versus MuSK-positive and seronegative segmentation reshaping targeting and share in gMG?

Q4 - Why can the roughly 15% of MuSK-positive and seronegative patients only be reached by the FcRn class?

Q5 - What did the ADAPT trial show for efgartigimod's MG-ADL responder rate against placebo?

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Mike || Global Pharma Commercial Marketing Head

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