Stealth BioTherapeutics Reports Strong Early Uptake for FORZINITY in Barth Syndrome Treatment
Key Insights
Stealth BioTherapeutics (search) reports 33 patients have initiated therapy with FORZINITY (search) for Barth syndrome (search), achieving 85% full coverage and less than 30 days average time to therapy initiation.
The company has aligned with FDA on a pathway for potential label expansion to children weighing less than 30 kg through a pharmacokinetic study planned for 2026.
Pipeline advancement includes ongoing Phase 3 ReNEW trial for dry AMD and completed Phase 1 enrollment for bevemipretide eye drops with Phase 2 initiation planned for late 2026.
Stealth BioTherapeutics (search) has reported encouraging early commercial performance for FORZINITY (search) (elamipretide) injection, the first FDA-approved treatment for Barth syndrome (search), with 33 patients initiating therapy and demonstrating rapid patient access within 30 days of prescription.
Strong Commercial Launch Metrics
The commercial launch data reveals significant early adoption across treatment centers, with 85% of patients achieving full coverage and broad reimbursement access across the payer universe. The average time from start form submission to prescription fulfillment is less than 30 days, highlighting effective coordination across access channels.
"We are encouraged that the strong early momentum of the FORZINITY (search) launch is facilitating prompt access for patients living with Barth syndrome (search)," said Reenie McCarthy, Chief Executive Officer of Stealth BioTherapeutics (search).
The company's Mito Assist patient support program has achieved 100% enrollment among eligible patients with FORZINITY (search) prescriptions, providing comprehensive support throughout the treatment journey. The medical and commercial organization buildout is nearing completion, with the field medical team deployed in early April and sales team launch scheduled for early May.
FDA Alignment on Label Expansion
Stealth has achieved regulatory alignment with the FDA on a pathway toward potential label expansion for Barth syndrome (search) patients who do not currently meet the approved weight threshold of 30 kg. The pathway involves a 1-month pharmacokinetic study to inform dosing for children weighing less than 30 kilograms, which the company plans to initiate this year to support a potential 2027 supplemental New Drug Application submission for children as young as age 5.
For infants and younger children, the FDA has encouraged continued provision of access through the company's expanded access program, with plans to initiate a registry to standardize data collection for FDA review. The company has initiated the first site in its Phase 4 trial in Bristol, UK, meeting all FDA-required post-marketing commitments.
Pipeline Development Progress
POLG-Related Myopathy
The company engaged constructively with the FDA in mid-April 2026 to discuss the regulatory pathway for elamipretide in mitochondrial myopathy due to polymerase gamma (POLG) mutations. At the FDA's request, Stealth will submit a synopsis for its proposed new pivotal trial for further discussion during the second half of the year.
Dry Age-Related Macular Degeneration
The Phase 3 ReNEW clinical trial of elamipretide for dry age-related macular degeneration (search) remains on track, with recent FDA guidance supporting the potential for a single trial to serve as the basis for approval. The company has completed enrollment in its Phase 1 trial of bevemipretide eye drops, with preliminary data expected at the 2026 ARVO Annual Meeting and Phase 2 initiation planned for late 2026.
Broader Pipeline Activities
Stealth continues advancing its investigational mitochondria-targeted therapies, including participation in the XPRIZE Healthspan competition evaluating elamipretide in age-related functional decline and newly funded preclinical work on SBT-589 in Leigh syndrome (search) through a collaboration supported by the UK Medical Research Council.
About Barth Syndrome and FORZINITY
Barth syndrome (search) is an ultra-rare genetic condition characterized by mitochondrial abnormalities leading to muscle weakness, exercise intolerance, debilitating fatigue, heart failure, recurrent infections, and delayed growth. The disease is associated with reduced life expectancy, with 85% of early deaths occurring by age 5. BTHS occurs primarily in males and is estimated to affect one in 1,000,000 male births.
FORZINITY (search) is a mitochondrial cardiolipin (search) binder indicated to improve muscle strength in adult and pediatric patients with Barth syndrome (search) weighing at least 30 kg. The indication was approved under accelerated approval based on improvement in knee extensor muscle strength, an intermediate clinical endpoint. The drug received FDA accelerated approval in September 2025, marking Stealth's transition to a commercial-stage biotechnology company.
The most common adverse reactions occurring more frequently on FORZINITY (search) than placebo included injection site reactions such as erythema, pain, induration, pruritus, bruising, and urticaria. The drug is contraindicated in patients with serious hypersensitivity to elamipretide and contains benzyl alcohol, making it unsuitable for neonates.