FDA approves elamipretide HCI as first treatment for Barth syndrome

FDA approves elamipretide HCI as first treatment for Barth syndrome | Image Credit: Contemporary Pediatrics

On September 19, 2025, the FDA granted accelerated approval to elamipretide HCl (Forzinity; Stealth BioTherapeutics) for the treatment of Barth syndrome in adult and pediatric patients weighing at least 30 kg, according to the agency. The decision marks the first approved therapy for the ultra-rare mitochondrial disease, which primarily affects males and can lead to severe cardiac and skeletal muscle complications as well as premature death.^1,2

Barth syndrome is characterized by mitochondrial dysfunction that often presents in infancy with severe heart failure and contributes to fatigue, poor stamina, and exercise intolerance throughout life. Approximately 150 individuals in the United States are affected by this condition.²

“The FDA remains committed to facilitating the development of effective and safe therapies for rare diseases and will continue to work diligently to help ensure patients with rare diseases have access to innovative treatments,” said George Tidmarsh, MD, PhD, director of the FDA’s Center for Drug Evaluation and Research, in a statement.¹

Clinical evidence for elamipretide HCl

Elamipretide HCl is designed to bind to the inner mitochondrial membrane to improve structure and function. Its accelerated approval was based on improved strength of the muscle used to straighten the leg at the knee, which the FDA considered reasonably likely to predict meaningful patient benefits such as improved ability to stand or walk farther. Elamipretide HCl is administered once daily by subcutaneous injection.

The approval was supported by efficacy and safety results from the TAZPOWER clinical trial. During the open-label portion of the trial, participants showed improvements in knee muscle strength. The most common adverse events were injection site reactions, generally mild to moderate and manageable with oral antihistamines or topical corticosteroids (Stealth BioTherapeutics).²

“I am thrilled to have an FDA-approved treatment to offer to patients with Barth syndrome, who often face serious manifestations including severe muscle weakness,” said Hilary Vernon, MD, PhD, professor of Genetic Medicine at Johns Hopkins University School of Medicine and Founder and Director of the Barth Syndrome Clinic at the Kennedy Krieger Institute. “As the director of one of only two interdisciplinary Barth syndrome clinics worldwide, I have the privilege of interacting with a large percentage of the Barth community in the US and around the world, and I am grateful to have a new therapeutic option available for patients living with Barth syndrome."

The FDA is requiring Stealth Bio Therapeutics to conduct a randomized, double-blind, placebo-controlled post-approval trial to confirm clinical benefit. Continued approval may depend on verification of these outcomes.¹

“The approval of FORZINITY, the first treatment option for Barth syndrome and the first approved mitochondria-targeted therapeutic, is a pivotal victory for the Barth syndrome community and offers hope for expedited regulatory attention to other ultra-rare diseases,” said Reenie McCarthy, Stealth’s Chief Executive Officer (Stealth BioTherapeutics).²

The company highlighted ongoing plans to provide access to children under 30 kg who are not yet covered by FDA-approved treatments. “We plan to continue providing expanded access to children weighing less than 30 kilograms who are currently receiving treatment or require emergency access, while we work with the FDA to generate data needed to expand the indication to include these children,” McCarthy added.

Regulatory designations and next steps

Elamipretide HCl received multiple designations, including Orphan Drug, Fast Track, Priority Review, and Rare Pediatric Disease from the FDA, along with Orphan Drug Designation from the European Medicines Agency.

In connection with the approval, the FDA also awarded Stealth a Rare Pediatric Disease Priority Review Voucher. The company expects Forzinity to be available for prescription in the United States by year-end through a specialty pharmacy.¹

References:

1. FDA grants accelerated approval to first treatment for Barth syndrome. FDA. Press release. September 19, 2025. Accessed September 22, 2025.
2. Stealth BioTherapeutics announces FDA accelerated approval of Forzinity (elamipretide HCI), the first therapy for progressive and life-limiting ultra-rare genetic disease Barth syndrome. Stealth BioTherapeutics. Press release. September 19, 2025. Accessed September 22, 2025. https://stealthbt.com/stealth-biotherapeutics-announces-fda-accelerated-approval-of-forzinity-elamipretide-hcl-the-first-therapy-for-progressive-and-life-limiting-ultra-rare-genetic-disease-barth-syndrome/