A label expansion for Vyvgart (efgartigimod alfa-fcab) and Vyvgart Hytrulo (efgartigimod alfa and hyaluronidase-qvfc) makes the two formulations the first approved treatments covering all antibody serotypes in adult generalized myasthenia gravis, argenx SE (Euronext/Nasdaq: ARGX) announced. The Netherlands-based company said the US FDA approved a supplemental Biologics License Application extending the indication to include anti-MuSK-Ab positive, anti-LRP4-Ab positive, and triple seronegative patients, in addition to the previously covered anti-AChR-Ab positive population.
The approved label expansion removes the antibody-status restriction that had previously limited prescribing, allowing clinicians to initiate efgartigimod treatment based on a clinical diagnosis of generalized myasthenia gravis (gMG) without requiring confirmed AChR antibody positivity. Vyvgart is administered as an intravenous infusion; Vyvgart Hytrulo delivers the same active molecule subcutaneously, including via a prefilled syringe for self-injection.
The approval is based on data from the Phase III ADAPT SERON study, a randomized, double-blind, placebo-controlled, multicenter trial enrolling 119 adults with anti-AChR antibody negative gMG across North America, Europe, China, and the Middle East — described by argenx as the largest study to date in this patient subgroup. The primary endpoint was change from baseline in the MG-ADL total score at week 4. Patients treated with efgartigimod achieved a statistically significant improvement over placebo (p=0.0068), with a mean 3.35-point improvement in MG-ADL score in the overall study population. The safety profile was consistent with that observed in anti-AChR-Ab positive patients in prior studies.
Roughly 20% of gMG patients lack detectable AChR antibodies, a subgroup that has historically been underrepresented in clinical trials and, according to investigators cited by argenx, carries a higher disease burden as a result. Triple seronegative patients — those without detectable antibodies against AChR, MuSK, or LRP4 — account for approximately 10% of all gMG cases and had been largely excluded from registrational studies prior to ADAPT SERON. The expanded label positions efgartigimod as the only approved therapy with data across all four major serological categories in adult gMG, adding to a competitive landscape that includes zilucoplan (UCB’s Zilbrysq) and rozanolixizumab (also UCB, Rystiggo), both approved for anti-AChR-Ab positive gMG.
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