SS-31 (Elamipretide)

SS-31, developed as elamipretide, is a mitochondria-targeted tetrapeptide that received FDA accelerated approval in September 2025 as Forzinity for Barth syndrome. It is approved for that indication only, and product sold as SS-31 outside that channel is unapproved. Vegalab does not make, sell or source it.

Molecule and mechanism

Elamipretide (D-Arg-dimethylTyr-Lys-Phe-NH2, about 640 Da as free base) is a cell-permeable, water-soluble tetrapeptide with alternating aromatic and cationic residues. It concentrates in the inner mitochondrial membrane, where it binds cardiolipin, a phospholipid required for cristae structure and electron transport chain function. The D-amino acid and amidated C-terminus make it resistant to many proteases. Binding to cardiolipin is proposed to stabilize cristae and reduce reactive oxygen species production. Its distribution to mitochondria does not depend on membrane potential, unlike many mitochondria-targeted cations.

Regulatory status

FDA granted accelerated approval to Forzinity (elamipretide hydrochloride) in 2025 for Barth syndrome, a rare X-linked disorder of cardiolipin remodeling, based on improvement in knee extensor muscle strength, with continued approval dependent on confirmatory evidence. Earlier trials in primary mitochondrial myopathy and heart failure did not meet primary endpoints. Outside the approved product, SS-31 remains an unapproved compound, and WADA S0 should be checked for any use not covered by an approval.

Delivery facts

Forzinity is given by daily subcutaneous injection. Injection-site reactions were the most common adverse event in trials. Its small size and protease resistance make it a better candidate for alternative routes than most peptides, although its positive charges limit passive oral absorption. The approved product's regimen and handling are set by its label, and research uses outside that label are not supported by the approval. Alternative formats, such as topical ophthalmic forms, have been studied by the developer in separate programs.

What this means for delivery research

Elamipretide is a precedent for a small, stabilized peptide reaching approval in a rare disease, and its injection-site burden is a delivery problem in its own right. It also shows the regulatory path for such peptides: rare disease focus, functional endpoints, and accelerated approval with confirmatory requirements. Delivery improvements for such products are typically registered as new formulations by the license holder, supported by bridging pharmacokinetic studies. That is standard practice for reformulated injectables.

Key facts

• FDA granted accelerated approval to Forzinity (elamipretide) for Barth syndrome in September 2025 (FDA label, Forzinity 2025)
• SS-31 selectively targets cardiolipin in the inner mitochondrial membrane (Szeto 2014, Br J Pharmacol 171:2029)
• Injection-site reactions were the most common adverse reaction with subcutaneous elamipretide (FDA label, Forzinity 2025)

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