AstraZeneca announced that its investigational treatment, gefurulimab, met the primary and all secondary endpoints in the Phase III PREVAIL trial for adults with generalized myasthenia gravis (gMG). At Week 26, patients taking gefurulimab showed a statistically significant improvement in daily activities, as measured by the Myasthenia Gravis Activities of Daily Living (MG-ADL) total score compared to placebo.
The trial was run by Alexion, AstraZeneca’s Rare Disease group, which is developing gefurulimab for people with AChR antibody-positive gMG, a group that makes up the majority of gMG cases.
gMG is a rare, chronic autoimmune neuromuscular disease that leads to muscle weakness and impaired communication between nerves and muscles. Symptoms often begin with drooping eyelids, blurred vision or slurred speech and can progress to more serious issues such as difficulty swallowing, fatigue and even respiratory failure.
gMG can affect anyone, but it most often appears in women before age 40 and in men after age 60. A challenging aspect of the disease is its unpredictability, which can greatly impact daily life and independence.
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Gefurulimab is an investigational, once-weekly injectable treatment that blocks a protein called C5, part of the immune system that becomes overactive in gMG. It’s a dual-binding nanobody that attaches to both C5 and a blood protein called albumin. This design extends its half-life and helps it remain active in the body longer.
Nanobodies are about one-tenth the size of traditional monoclonal antibodies, allowing for better tissue penetration and easier manufacturing.
The treatment is intended for subcutaneous self-administration and has received Orphan Drug designation in the US for myasthenia gravis.
While nanobody-based therapies are still up and coming in rare diseases, gMG treatment is currently led by biologics targeting the complement and neonatal Fc receptor (FcRn) pathways. These therapies offer more targeted, sustained control than conventional immunosuppressants.
PREVAIL was a global, Phase III, randomized, double-blind, placebo-controlled study that evaluated gefurulimab in adults with AChR antibody-positive gMG. It enrolled 260 patients across 20 countries. All participants had confirmed diagnoses of gMG for at least three months and met eligibility criteria based on clinical classification and antibody testing.
Participants were randomly assigned to receive either gefurulimab or a placebo over 26 weeks. Treatment began with a weight-based loading dose on Day 1, followed by weekly maintenance doses starting on Day 8. The primary endpoint was the change from baseline in the MG-ADL total score at Week 26 — a patient-reported measure that assesses how gMG symptoms affect daily tasks. Secondary endpoints assessed broader improvements in disease activity and functional outcomes.
Patients receiving gefurulimab had a statistically significant and clinically meaningful reduction in MG-ADL scores compared to those on placebo. All secondary endpoints were also achieved. The treatment was generally well tolerated, and no new safety issues were reported. The safety profile remained consistent with what has been observed in previous studies of C5 inhibitors for gMG.
Like gefurulimab, other therapies have also moved to self-administered options. In April 2025, the FDA had approved argenx’s prefilled syringe for Vyvgart Hytrulo, allowing patients with AChR-positive gMG to self-administer their treatment after proper training.
Related: New Vyvgart Hytrulo TV Ads Centered on Self-Treatment in gMG Launched by argenx
Another investigational treatment, Johnson & Johnson’s nipocalimab, which blocks FcRn, showed greater and sustained improvements in MG-ADL scores at multiple timepoints over 24 weeks, as presented at the 2025 European Academy of Neurology (EAN) Congress. These results came from population-adjusted indirect treatment comparisons with other approved FcRn therapies.
An open-label extension of the PREVAIL trial is ongoing, and AstraZeneca plans to share the full data at an upcoming medical meeting. The company also intends to submit the results to regulatory authorities for review, though no specific timelines have been announced.
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