SS-31 (Elamipretide)
A mitochondria-targeting aromatic-cationic tetrapeptide studied for cardiolipin binding, inner-membrane organisation and cellular bioenergetics.
This selector presents total vial contents in the PHONYX research portfolio. Vial content must not be confused with doses used in clinical trials or in an authorised medicinal product.
Interested in this compound?
Contact the PHONYX team for availability and catalogue information.
What is SS-31?
SS-31 is the research name of elamipretide, also known during development as MTP-131 and Bendavia. It is a synthetic four-amino-acid peptide designed to cross cell membranes and concentrate at the inner mitochondrial membrane, where it associates with cardiolipin.
Cardiolipin helps organise mitochondrial cristae and respiratory-chain protein complexes. Research on elamipretide therefore focuses on mitochondrial membrane structure, electron transport, oxidative stress and ATP-related bioenergetics. Since September 2025, an authorised elamipretide medicine has existed in the United States for a narrowly defined Barth-syndrome indication. That authorisation does not apply to unrelated research vials or establish equivalence with the PHONYX catalogue material.
Cardiolipin binding and mitochondrial membrane biology
Cardiolipin association
Elamipretide is studied for reversible interaction with cardiolipin, a phospholipid concentrated in the inner mitochondrial membrane and closely linked with cristae organisation.
Respiratory-chain organisation
By influencing the cardiolipin environment, SS-31 may help preserve the spatial organisation of respiratory complexes and reduce inefficient electron transfer under cellular stress.
Bioenergetic adaptation
Preclinical studies examine changes in reactive oxygen species, membrane potential, ATP production and tissue performance. The relevance of each effect depends on the disease model and study design.
How SS-31 differs from MOTS-c
| Feature | SS-31 / Elamipretide | MOTS-c |
|---|---|---|
| Origin | Synthetic tetrapeptide | Mitochondrially encoded peptide |
| Primary research focus | Cardiolipin and inner-membrane structure | Metabolic and stress signalling |
| Clinical development | Extensive trials; one specific US approval | Predominantly preclinical and observational human evidence |
From mitochondrial-myopathy trials to Barth-syndrome approval
Phase 1/2 MMPOWER intravenous dose-escalation study
Adults with genetically confirmed primary mitochondrial myopathy received five days of two-hour intravenous infusions at 0.01, 0.10 or 0.25 mg/kg/hour, or placebo. The study assessed safety, exercise performance and early dose-response signals.
Phase 2 MMPOWER-2 and Barth syndrome studies
MMPOWER-2 evaluated 40 mg elamipretide subcutaneously once daily for four weeks in a crossover design. The SPIBA-201 Barth-syndrome programme evaluated 40 mg subcutaneously once daily for 12 weeks, followed by crossover and later open-label extension.
Phase 3 MMPOWER-3 primary mitochondrial myopathy
MMPOWER-3 randomised 218 participants to 40 mg elamipretide or placebo subcutaneously once daily for 24 weeks. The trial did not meet its two primary efficacy endpoints, although tolerability was generally characterised as acceptable apart from frequent injection-site reactions.
Regulatory FORZINITY approval in the United States
In September 2025, the FDA granted accelerated approval to the elamipretide medicine FORZINITY to improve muscle strength in adults and children with Barth syndrome weighing at least 30 kg. The authorised product is a regulated 80 mg/mL injection and is distinct from PHONYX research-format material.
Documented protocols and study regimens
| Programme | Documented dose | Route / frequency | Study period |
|---|---|---|---|
| MMPOWER dose escalation | 0.01, 0.10 or 0.25 mg/kg/hour | 2-hour IV infusion once daily | 5 days |
| MMPOWER-2 | 40 mg | Subcutaneous once daily | 4 weeks, crossover protocol |
| MMPOWER-3 | 40 mg (0.5 mL investigational solution) | Subcutaneous once daily | 24 weeks; extension planned |
| SPIBA-201 Barth syndrome | 40 mg | Subcutaneous once daily | 12-week periods, 4-week washout, then extension |
| Friedreich ataxia investigator study | 20–30 mg low-dose arm; 40–60 mg high-dose arm | Subcutaneous once daily | 52 weeks |
| Authorised US medicine | 40 mg for patients weighing ≥30 kg | Subcutaneous once daily | Per official prescribing information |
Example of the SPIBA-201 crossover structure
The 10 mg and 50 mg PHONYX formats state total labelled vial content. They do not define a clinical dose, concentration, administration volume or treatment duration.
Mixed findings across indications
MMPOWER-2 difference
The four-week crossover study reported a numerical 6-minute-walk difference favouring elamipretide, but the confidence interval crossed zero and the primary comparison was not statistically significant.
MMPOWER-3 primary success
The 218-participant phase 3 trial did not improve the 6-minute walk test or the primary fatigue score versus placebo at 24 weeks.
Barth programme dose
The controlled crossover and long-term extension used the same once-daily subcutaneous dose.
FDA pathway
The 2025 US approval was based on improvement in knee-extensor muscle strength, with confirmatory evidence still required.
These results show why evidence must be interpreted by indication. A negative trial in broad primary mitochondrial myopathy does not erase findings in Barth syndrome, but neither do open-label extension signals prove effectiveness across unrelated mitochondrial, cardiovascular, renal, ophthalmic or healthy-aging settings.
Injection-site reactions dominate the clinical safety profile
Across subcutaneous studies, local administration reactions were common. In the small controlled Barth-syndrome dataset used by the FDA, injection-site erythema occurred in all elamipretide-treated participants, while pain, induration and pruritus were also frequently recorded. Most events in broader trials were described as mild or moderate, but small study populations limit precision.
Clinical safety information applies to characterised investigational or authorised formulations manufactured under pharmaceutical controls. It cannot be transferred automatically to an unapproved research vial, where identity, concentration, sterility, endotoxin, particulate matter and stability require separate analytical verification.
A short peptide designed for mitochondrial localisation
Elamipretide is an aromatic-cationic tetrapeptide that penetrates cellular membranes and transiently localises to the inner mitochondrial membrane. Clinical programmes have used both intravenous infusion and once-daily subcutaneous administration. Exposure, clearance and renal-dose considerations depend on the pharmaceutical formulation and patient characteristics.
PHONYX portfolio formats
Evidence behind the key claims
Frequently asked questions
Are SS-31 and elamipretide the same compound?
SS-31 is the research name commonly used for elamipretide. MTP-131 and Bendavia also appeared during development.
What is cardiolipin?
Cardiolipin is a specialised phospholipid enriched in the inner mitochondrial membrane and involved in cristae structure and respiratory-chain organisation.
What doses were used in major subcutaneous trials?
Several major mitochondrial-myopathy and Barth-syndrome studies evaluated 40 mg once daily subcutaneously. Other protocols investigated different dose ranges or intravenous exposure.
Does the 10 mg or 50 mg vial represent a clinical dose?
No. These numbers state total labelled vial content in the PHONYX research catalogue. They do not specify a clinical regimen, concentration or administration volume.
Is elamipretide approved?
An elamipretide medicine was granted accelerated US approval in 2025 for improving muscle strength in Barth-syndrome patients weighing at least 30 kg. That approval is product- and indication-specific.
Did elamipretide succeed in primary mitochondrial myopathy?
The large MMPOWER-3 phase 3 trial did not meet its primary walking-distance or fatigue endpoints at 24 weeks.
What was observed in Barth syndrome?
The controlled crossover phase did not meet its original primary endpoints, while the longer open-label extension reported improvements in selected functional measures. The FDA later relied on muscle-strength evidence for accelerated approval.
What are the most prominent reported adverse reactions?
Injection-site reactions—including redness, pain, induration and itching—were prominent in subcutaneous studies.
How does SS-31 differ from MOTS-c?
SS-31 is a synthetic cardiolipin-interacting tetrapeptide. MOTS-c is a mitochondrially encoded signalling peptide studied mainly in metabolic adaptation and stress-response pathways.
Why are clinical-trial doses shown?
They document the design of published research and regulatory programmes. They are not self-administration instructions or medical advice.
Research Disclaimer
This PHONYX product is presented exclusively for laboratory and scientific research. It is not the authorised FORZINITY medicinal product and is not intended for human consumption, self-administration, diagnosis, treatment, cure or prevention of disease. Clinical-trial and prescribing-information doses are reproduced solely for documentary and educational context and must not be interpreted as instructions for reconstitution, administration or medical treatment.