Stealth scores FDA approval for first Barth syndrome treatment

After a tumultuous journey filled with delays and rejection, the FDA has approved Stealth BioTherapeutics’ treatment for the ultrarare disease Barth syndrome, marking the peptide as the first therapy for the condition.

The FDA gave the green light via its accelerated pathway, according to a Sept. 19 release.

Stealth’s injection, known as elamipretide, will be sold as Forzinity for the treatment of Barth syndrome, an X-linked genetic disorder that weakens the heart and other muscles. Death rates are highest in the first four years of life, and patients don’t typically live past their 40s.

The daily injection can be used for patients weighing at least 60 pounds, according to the approval.

The FDA believes that Forzinity will fill a gap in care for a serious disease and that existing evidence is “reasonably likely to predict patient benefit but does not directly assess the benefit to the patient.”

The regulatory nod was based on data showing that the drug improved strength of the muscle used to straighten the leg at the knee. The FDA said the improvement likely predicted better clinical outcomes, “such as an ability to stand more easily or walk farther.”

As a condition of the accelerated approval, the FDA is requiring the manufacturer of Forzinity to conduct a post-approval randomized, double-blind, placebo-controlled trial to confirm that the findings on knee muscle strength equate to patient benefit.

“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,” George Tidmarsh, M.D., Ph.D., director of the FDA’s Center for Drug Evaluation and Research, said in the release.

It’s been a long and arduous journey for Stealth’s peptide treatment.

After already rejecting the drug once, the FDA again denied approval this May after a protracted priority review period that took more than 16 months. The agency’s decision followed several delays and a split advisory committee vote that ultimately favored approval.

The rejection was based on Forzinity’s failure to meet a six-minute walk test endpoint in a clinical trial. 

After the agency rebuff, Stealth submitted another new drug application that sought accelerated approval based on improvements in knee extensor muscle strength, an intermediate clinical endpoint.

While the FDA gave Stealth a PDUFA date for Feb. 15, 2026, the agency said in August that it planned on providing a decision by Sept. 26.

The sense of urgency was likely fueled by a wide-ranging public outcry surrounding the agency’s several delays and refusal to approve the rare disease candidate.

In a June 30 letter, 14 members of Congress urged FDA Commissioner Marty Makary, M.D., to provide clarity about the approval process for Forzinity. Less than a month later, seven Congress members wrote to him again, voicing concern about the regulatory path for the experimental drug.

Weeks later, a coalition of physicians and scientists sent Makary another letter asking that he immediately reverse course.

“These delays have brought the drug’s sponsor to the brink of financial collapse, leading to forced withdrawal of our patients from elamipretide as early as September,” the group wrote.

Stealth had questioned its own viability after the rejection, laying off 30% of staffers in efforts to save cash right after receiving the complete response letter.