Stealth BioTherapeutics Resubmits Rare Disease Drug to FDA, Seeking Accelerated Approval

Stealth BioTherapeutics has resubmitted its new drug application (NDA) for elamipretide, a potential treatment for the ultra-rare genetic disorder Barth syndrome, to the U.S. Food and Drug Administration (FDA). This marks the company's third attempt to gain approval for the drug, following a rejection in May 2025 that led to significant corporate restructuring.

Resubmission Details and FDA Response

The resubmission, announced on August 18, 2025, comes after Stealth claims to have addressed the FDA's previous concerns regarding safety and manufacturing. The company has also included a proposed post-approval trial to confirm the drug's benefits, as requested by the agency.

While the FDA has indicated a standard six-month evaluation period for this resubmission, Stealth has requested a "Class 1" review, which could potentially shorten the process to two months. The company is urging the FDA to "act with urgency" in line with its commitment to expedite review of therapies for rare diseases.

Clinical Data and Regulatory History

Elamipretide, a peptide targeting mitochondria, aims to boost muscle function in patients with Barth syndrome, a condition affecting approximately one in a million children. The drug's development has been marked by several regulatory challenges:

• An FDA advisory committee previously concluded that elamipretide demonstrated effectiveness, despite concerns from agency reviewers about statistical improvements in walking tests.
• The May 2025 rejection came after a lengthy initial review that included delays and missed deadlines.
• The FDA has now agreed to consider the drug's effects on muscle strength as an "intermediate clinical endpoint" that could support accelerated approval.

Stealth reports that knee extensor muscle strength improved by more than 45% in a phase 2 open-label study, correlating significantly with improvements in the six-minute walk test.

Corporate Implications and Industry Response

The regulatory journey of elamipretide has become a focal point in discussions about FDA efficiency and innovation in rare disease treatments. Following the May rejection, Stealth was forced to lay off 30% of its staff to conserve cash.

The company's CEO has publicly questioned the FDA's handling of the application, stating, "Without more immediate action from the FDA, we cannot ensure continued drug availability to this vulnerable community or our sustainability as a company."

As the pharmaceutical industry closely watches this case, it may have broader implications for the development and approval processes of treatments for ultra-rare diseases.