Mezzion Pharmaceuticals Reaches Key Enrollment Milestone in World's Largest Fontan Clinical Trial

SEOUL, South Korea, July 31, 2025 /PRNewswire/ -- Mezzion Pharmaceuticals, Inc. (Mezzion) announced that its confirmatory Phase 3 FUEL-2 study evaluating JURVIGO® (udenafil)¹ in adolescents and young adults with Fontan circulation has surpassed a key enrollment milestone randomizing approximately 50% of the planned 400+ participants.

FUEL-2 is the largest randomized clinical trial ever conducted for the Fontan population, a group of patients born with single ventricle congenital heart disease who require a series of surgeries culminating in the Fontan procedure. This population remains at high risk for heart failure, organ dysfunction, and early mortality, with no FDA-approved pharmacologic therapies available today.

"The Fontan journey is long, complex, and often isolating," said Dr. Rahul Rathod, Global Principal Investigator for FUEL-2 and Director of the Single Ventricle Program at Boston Children's Hospital. "With FUEL-2, we're doing more than just advancing a treatment – we're building hope, community, and scientific clarity around a disease that has gone too long without answers."

Udenafil, a highly selective and long-acting PDE5 inhibitor, has demonstrated its clinical benefit in Fontan patients with reduced functional capacity (peak VO₂ < 80% of predicted). In the original FUEL trial, this subgroup experienced the most pronounced improvements, particularly in submaximal exercise measures such as ventilatory efficiency and anaerobic threshold – indicators closely tied to functional status in daily life. These findings, combined with FDA-aligned guidance and a growing body of published evidence, informed the focused enrollment criteria for FUEL-2, which is evaluating udenafil exclusively in this higher-risk population. 

Udenafil has been shown to be safe and well tolerated across more than five years of cumulative exposure, including long-term use in a diverse group of adolescents and young adults from the FUEL trial's open-label extension. In FUEL-2, the primary efficacy endpoint is the change in peak VO₂ (mL/kg/min) following 26 weeks of treatment. Peak VO₂ is a validated surrogate for major clinical outcomes, including hospitalization, transplant, and mortality, and a 10% decline is associated with nearly double the risk of death or transplant in Fontan patients.²

"We believe every child and young adult living with Fontan circulation deserves a future with better options," said Dong Hyun 'Dean' Park, Chairman and CEO of Mezzion. "FUEL-2 reflects our deep commitment not only to science but also to the families, clinicians, and advocates who have helped bring this vision to life."

To ensure the highest data quality, all cardiopulmonary exercise testing (CPET) in FUEL-2 is centrally reviewed by The Lundquist Institute, an internationally recognized leader in cardiopulmonary diagnostics. This centralized approach enhances consistency and precision in measuring both primary and secondary endpoints across all global sites.

FUEL-2 is being conducted at more than 30 of the world's leading children's hospitals across the United States and South Korea. The trial is supported by a global coalition of patient advocacy organizations, clinical investigators, and families dedicated to improving long-term outcomes for individuals with Fontan circulation.

Join the Movement

Patients and families interested in learning more or joining the study can visit www.FUEL2Study.com or speak with their care team at a participating center. Clinical sites and investigators are encouraged to continue building on this momentum as we enter the second half of enrollment. Your partnership is critical to delivering the first potential FDA-approved therapy for this vulnerable and resilient community.

About Mezzion

Mezzion Pharmaceuticals, Inc., a U.S.-based subsidiary of Mezzion Pharma Co., Ltd. (KOSDAQ: 140410), is a late-stage biopharmaceutical company focused on developing life-changing therapies for patients with rare and underserved diseases. Headquartered in New Jersey, Mezzion leads the global clinical development and commercialization of JURVIGO® (udenafil), an investigational therapy currently in Phase 3 trials for patients with single ventricle heart disease and Fontan physiology. The company has received Rare Pediatric Disease Designation from the U.S. FDA and anticipates submitting a New Drug Application (NDA) following completion of the FUEL-2 trial.

For more information, visit www.mezzion.com and www.FUEL2Study.com.

¹ JURVIGO® (udenafil) is an investigational drug and has not been approved for the treatment of Fontan patients by the U.S. FDA or any other regulatory authority. The safety and efficacy of JURVIGO® in this population have not been established.

² Cunningham JW, Nathan AS, Rhodes J, Shafer K, Landzberg MJ, Opotowsky AR. Decline in peak oxygen consumption over time predicts death or transplantation in adults with a Fontan circulation. Am Heart J. 2017;189:184–192. https://pubmed.ncbi.nlm.nih.gov/28625375

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SOURCE Mezzion Pharmaceuticals, Inc