SHERIDAN, WYOMING – July 25, 2025 – AstraZeneca has reported positive topline results from its Phase III PREVAIL trial evaluating gefurulimab, a complement C5-inhibiting nanobody, for the treatment of generalized myasthenia gravis (gMG). The investigational therapy met all primary and secondary endpoints, signaling a potential new contender in the highly competitive $20 billion gMG market.
Phase III Results Suggest Clinical Significance
According to AstraZeneca’s announcement, gefurulimab demonstrated “a statistically significant and clinically meaningful improvement from baseline” based on the Myasthenia Gravis Activities of Daily Living (MG-ADL) scale. Although specific trial data have not yet been published, the company confirmed that the results apply to patients with anti-acetylcholine receptor (AChR) antibody-positive gMG—representing approximately 85% of all gMG cases.
The PREVAIL trial focused on self-administered weekly treatment in adults with AChR Ab+ gMG. While detailed efficacy data are pending release at a future medical meeting, analysts at William Blair noted, “the minimal clinically important difference on the MG-ADL scale is considered to be ≥2 points from baseline.” For comparison, they referenced a 4.39-point reduction seen in UCB’s Zilbrysq during its own Phase III trial.
Strategic Positioning in a Crowded Therapeutic Market
Gefurulimab enters a competitive field that includes Zilbrysq, currently the only FDA-approved subcutaneous treatment for gMG, and argenx’s Vyvgart, which remains the market leader following its FDA approval in June 2023.
Despite the growing number of available treatments, gefurulimab may offer several strategic advantages:
- Nanobody format enables precise targeting of the complement C5 protein.
- Weekly self-administration offers greater convenience compared to infusion-based alternatives.
- Addresses the largest gMG patient subgroup (AChR Ab+), enhancing population coverage.
While analysts acknowledged the drug’s potential to challenge Zilbrysq, they cautioned that “argenx’s Vyvgart still leads in the $20 billion myasthenia gravis market, given its two-year head-start.”
Further Data Expected at Upcoming Scientific Conference
AstraZeneca indicated that full results from PREVAIL would be presented at an upcoming medical conference. Industry speculation points to the Myasthenia Gravis Foundation of America’s sessions at the American Association of Neuromuscular & Electrodiagnostic Medicine (AANEM) Annual Meeting on October 29.
Continued Momentum in Rare Disease and Manufacturing Initiatives
The PREVAIL news follows a flurry of corporate developments for AstraZeneca. Last week, its antibody anselamimab failed to meet endpoints in an amyloidosis trial. However, the company rebounded earlier this week with a strategic announcement of a $50 billion investment in U.S. manufacturing, including a new facility in Virginia dedicated to producing metabolic drugs for cardiovascular and obesity-related conditions.
Both AstraZeneca and argenx saw stock price increases of approximately 1.2% in morning trading following the gefurulimab news, reflecting investor confidence in the therapeutic potential and commercial viability of the treatment.
Learn more at www.astrazeneca.com