SS-31 (elamipretide)

Also: Elamipretide, MTP-131, Bendavia, Forzinity

Summary

SS-31, known as elamipretide in clinical development, is a synthetic four-amino-acid peptide that concentrates in mitochondria and binds cardiolipin, a lipid of the inner mitochondrial membrane. It was developed by Stealth BioTherapeutics. In September 2025 the US FDA granted it accelerated approval, under the brand name Forzinity, for Barth syndrome, a rare genetic mitochondrial disease. That is the only approved use; its other studied uses remain investigational.

What it targets

Elamipretide is described in the literature as stabilising mitochondrial membrane structure, reducing oxidative stress and supporting ATP production. In a phase 3 trial of 218 adults with primary mitochondrial myopathy it did not improve walking distance or fatigue over placebo at 24 weeks, though it was well tolerated. In Barth syndrome, a 168-week open-label extension in ten patients reported sustained improvements in walking distance and cardiac measures, and a single newborn case report described improved heart function under expanded access. A 2025 review collects the preclinical models (heart failure, neurodegeneration, ischaemia) and the clinical programme.

Barth syndrome (open-label extension, n=10; case report)primary mitochondrial myopathy (phase 3, n=218, primary endpoints not met)mitochondrial function (preclinical models, review)

Clinical Research

Efficacy and Safety of Elamipretide in Individuals With Primary Mitochondrial Myopathy: The MMPOWER-3 Randomized Clinical Trial
Karaa A, Bertini E, Carelli V, et al. (MMPOWER-3 Trial Investigators) (2023). Neurology. human adults with genetically confirmed primary mitochondrial myopathy, phase 3, n=218
Long-term efficacy and safety of elamipretide in patients with Barth syndrome: 168-week open-label extension results of TAZPOWER
Thompson WR, Manuel R, Abbruscato A, et al. (2024). Genetics in Medicine. human people with Barth syndrome, open-label extension, n=10 (8 reached week 168)
Expanded-access use of elamipretide in a newborn with Barth syndrome: a case report
Ortmann L, Velasco D, Cole J (2025). European Heart Journal - Case Reports. human single newborn with Barth syndrome, case report
Elamipretide: A Review of Its Structure, Mechanism of Action, and Therapeutic Potential
Tung C, Varzideh F, Farroni E, et al. (2025). International Journal of Molecular Sciences. review n/a (review)

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