Elamipretide

SS-31

Grade A: Approved and proven

TL;DR: Elamipretide (Forzinity, SS-31) received FDA accelerated approval on September 19, 2025, to improve muscle strength in adult and pediatric patients (weighing at least 30 kg) with Barth syndrome, a rare X-linked mitochondrial cardiomyopathy. Accelerated approval was based on improvement in knee extensor muscle strength as an intermediate endpoint reasonably likely to predict clinical benefit, supported by efficacy and safety data from the TAZPOWER randomized crossover trial (n=12 in the blinded phase, with open-label extension). Continued approval is contingent on verification of clinical benefit in a confirmatory trial. For other indications where elamipretide has been studied, including primary mitochondrial myopathy (MMPOWER-3 trial, n=218) and heart failure with preserved ejection fraction, Phase 3 trials did not meet their primary endpoints; elamipretide is not approved for these conditions. The evidence base outside the Barth syndrome indication is insufficient to support a Grade A rating for those uses.

Key Takeaways

Grade A: Approved and proven
FDA approved: FDA accelerated approval (September 19, 2025) for Barth syndrome to improve muscle strength; not approved for primary mitochondrial myopathy, heart failure, or any other indication; confirmatory trial required.
Compounding: FDA-approved as Forzinity (subcutaneous injection) for Barth syndrome under accelerated approval as of September 2025. The approval is indication-specific (Barth syndrome, weight ≥30 kg); use for other mitochondrial conditions is not approved. Prior to FDA approval, elamipretide was available only in clinical trials; any compounded SS-31 remains unapproved and lacks FDA quality oversight.

Elamipretide chemical structure — Structure via PubChem CID 11764719

Mechanism

Elamipretide is a mitochondria-targeting tetrapeptide that binds cardiolipin in the inner mitochondrial membrane, stabilizing the electron transport chain and improving mitochondrial bioenergetics.

Evidence

Elamipretide (Forzinity, SS-31) received FDA accelerated approval on September 19, 2025, to improve muscle strength in adult and pediatric patients (weighing at least 30 kg) with Barth syndrome, a rare X-linked mitochondrial cardiomyopathy. Accelerated approval was based on improvement in knee extensor muscle strength as an intermediate endpoint reasonably likely to predict clinical benefit, supported by efficacy and safety data from the TAZPOWER randomized crossover trial (n=12 in the blinded phase, with open-label extension). Continued approval is contingent on verification of clinical benefit in a confirmatory trial. For other indications where elamipretide has been studied, including primary mitochondrial myopathy (MMPOWER-3 trial, n=218) and heart failure with preserved ejection fraction, Phase 3 trials did not meet their primary endpoints; elamipretide is not approved for these conditions. The evidence base outside the Barth syndrome indication is insufficient to support a Grade A rating for those uses.

Safety and risks

Injection site reactions are the most common adverse effect documented across clinical trials: they occur frequently, are typically mild to moderate, present as erythema, induration, bruising, pruritus, pain, or urticaria, and generally resolve the day of last administration; they can be managed with oral antihistamines or topical corticosteroids. Hypersensitivity reactions have been reported and patients should be monitored. Because Barth syndrome itself involves cardiomyopathy and skeletal myopathy, distinguishing drug effects from disease progression requires careful follow-up. Long-term safety data beyond the 168-week open-label TAZPOWER extension are limited given the very small patient population. The accelerated approval pathway means the full clinical benefit and risk profile have not been established with the level of evidence required for standard approval; confirmatory trial data are required.

Interactions

No specific drug-drug interactions are characterized in the available label information; given the drug's mitochondrial site of action and the cardiac comorbidities in Barth syndrome patients, concurrent cardiac medications should be managed by a specialist.

Federal compounding status

FDA-approved drug as of 2026-06-02.

An FDA-approved drug that should be obtained as the licensed product. It is not a 503A bulk-substance candidate; compounding from bulk is limited under federal rules and generally permitted only during a declared shortage.

Federal status only, from public FDA records. State pharmacy-board rules vary and are not covered here. This is regulatory reporting, not legal advice. All compounds.

Compounding legality

FDA-approved as Forzinity (subcutaneous injection) for Barth syndrome under accelerated approval as of September 2025. The approval is indication-specific (Barth syndrome, weight ≥30 kg); use for other mitochondrial conditions is not approved. Prior to FDA approval, elamipretide was available only in clinical trials; any compounded SS-31 remains unapproved and lacks FDA quality oversight.

Sources

Elamipretide is FDA approved. PeptideGrids presents evidence and regulatory status for informational purposes only. We do not sell, supply, source, or help anyone obtain this compound, and we provide no dosing or administration guidance. This is not medical advice; consult a licensed clinician. Full disclaimer.

Last reviewed June 1, 2026 by PeptideGrids editorial team (independently audited).