SS-31 (elamipretide, also known as Bendavia and MTP-131) is a synthetic tetrapeptide with the sequence D-Arg-2',6'-dimethylTyr-Lys-Phe-NH2. It belongs to the Szeto-Schiller (SS) peptide family, co-discovered by Dr. Peter Schiller (IRCM, Montreal) and Dr. Hazel Szeto (Weill Cornell Medical College) around 2000. SS-31 was engineered to eliminate opioid receptor activity while retaining mitochondrial targeting, making it suitable for chronic therapeutic use.
SS-31 selectively targets the inner mitochondrial membrane (IMM), where it binds cardiolipin, a phospholipid found exclusively at this location. Cardiolipin organizes respiratory chain supercomplexes for efficient oxidative phosphorylation, maintains cristae architecture, and regulates apoptosis through cytochrome c interactions. When cardiolipin is damaged or abnormal, mitochondrial function degrades.
On September 19, 2025, the FDA granted accelerated approval to elamipretide (brand name Forzinity) to improve muscle strength in adult and pediatric patients with Barth syndrome, an ultra-rare X-linked genetic disorder caused by TAFAZZIN gene mutations leading to cardiolipin abnormalities. This makes elamipretide the first FDA-approved mitochondria-targeted therapeutic, a historical landmark validating the direct targeting of mitochondrial membrane biology.
Beyond Barth syndrome, elamipretide is under investigation in Phase 3 trials for primary mitochondrial myopathy and age-related macular degeneration, and in earlier-stage trials for heart failure, Friedreich's ataxia, and renal artery stenosis. Its selectivity for dysfunctional mitochondria (no adverse effects on healthy mitochondria) is a key safety advantage.
| Weeks | Dosage | Syringe units (U-100) |
|---|---|---|
| Weeks 1–2 | 5 mg | 50 units0.5 mL |
| Weeks 3–8 | 10 mg | 100 units1 mL |
FrequencyOnce daily, subcutaneous.
For review — a quarter of the amount used in the cited trials. The elamipretide programme dosed 40 mg a day subcutaneously; the schedule in the chart tops out at 10 mg. Both figures are once daily, but they are not the same treatment. The concentration strip above the chart is calculated from the vial and water volume and is correct.
SS-31 is elamipretide, which reached human trials for primary mitochondrial myopathy and Barth syndrome under regulatory oversight at 40 mg once daily — four times the top amount charted here, which is why the schedule is flagged for review rather than presented as matching the trial. Those trials produced mixed results and the compound is not approved for general use, and research-grade SS-31 is not the same material as the clinical formulation that was tested. Athena lists one strength: a 10 mg vial made up with 1 mL is 10 mg/mL, so the 10 mg maintenance amount is 100 units — twice the 0.5 mL a 50-unit syringe holds, and marked as such — while the 5 mg step is exactly one full syringe, which leaves no room for measurement error at that concentration.
Measurement note. At this strength and water volume one or more of the amounts above is larger than the 0.5 mL a 50-unit U-100 syringe holds, so it would be drawn with a 100-unit syringe rather than in a single 50-unit fill.
What this evidence establishes. SS-31 is elamipretide, which has been through human trials for primary mitochondrial myopathy and Barth syndrome under regulatory oversight. The dose below is from that programme. Trial results have been mixed and the compound is not approved for general use; research-grade SS-31 is not the same material as the clinical formulation.
Sources: Elamipretide clinical trial programme, as reported on this site's SS-31 profile
For educational and laboratory research purposes only. It does not provide medical advice, dosing recommendations, or instructions for human or veterinary use. Syringe units assume a U-100 syringe, on which 1 mL is 100 units and a 50-unit syringe holds 0.5 mL.
SS-31 selectively interacts with cardiolipin on the inner mitochondrial membrane, producing cascading improvements in structure and bioenergetics:
Binds cardiolipin via electrostatic (D-Arg, Lys) and hydrophobic (Dmt, Phe) interactions. Concentrates 1000-5000x in the IMM vs. cytoplasm.
Maintains cristae membrane curvature essential for respiratory supercomplex assembly and efficient electron transport chain function.
Improves ETC efficiency by preserving supercomplex organization, increasing ATP synthesis while reducing electron leak and energy waste.
Decreases mitochondrial reactive oxygen species by optimizing electron flow, reducing oxidative damage to lipids, proteins, and mtDNA.
Promotes cytochrome c electron carrier function over peroxidase activity, favoring cell survival over apoptotic signaling pathways.
No adverse effects on healthy mitochondria. Preferentially benefits dysfunctional mitochondria where cardiolipin is compromised.
Elamipretide has clinical safety data from the Barth syndrome program and multiple Phase 2/3 trials:
| Condition / Factor | Risk Level | Rationale |
|---|---|---|
| Injection site reactions | LOW (common) | Most common adverse event. Includes redness, pain, induration at SC site. Generally mild. |
| GI symptoms (nausea, diarrhea) | LOW | Reported in some trials. Mild and transient. |
| Pregnancy / breastfeeding | HIGH (insufficient data) | Limited reproductive toxicology data. Standard precaution. |
| Active malignancy | MODERATE (theoretical) | Enhanced mitochondrial function could theoretically benefit tumor metabolism. Not studied in cancer patients. |
| Healthy mitochondria | NO EFFECT | SS-31 has no adverse effects on healthy mitochondria. Selectively benefits dysfunctional mitochondria. |
| Opioid activity | ELIMINATED | Opioid receptor activity was specifically engineered out during development. |
| Drug interactions | LOW | No significant interactions identified. No CYP450 involvement. |
| Long-term safety (Barth) | FAVORABLE | Open-label extension data up to 168 weeks (3+ years). Well-tolerated with sustained efficacy. |
| Overall profile | WELL-CHARACTERIZED | FDA approval reflects acceptable benefit-risk profile. Most AEs are mild injection site reactions. |
FDA: Elamipretide (Forzinity) received accelerated approval September 19, 2025, for Barth syndrome. First FDA-approved mitochondria-targeted therapeutic. Developed by Stealth BioTherapeutics. 40 mg/day SC injection.
Orphan Drug: Designated for Barth syndrome and Friedreich's ataxia. Fast Track for mitochondrial myopathy and LHON.
Expanded Access: Available for patients with confirmed genetic mitochondrial disease and serious clinical manifestations.
Key distinction: SS-31's FDA approval validates mitochondrial membrane biology as a druggable therapeutic target. The cardiolipin-binding mechanism is entirely distinct from conventional antioxidant approaches. Whether this breakthrough extends beyond rare disease into common conditions (heart failure, AMD, aging) depends on ongoing Phase 3 results.
Test your understanding of SS-31's mitochondrial mechanism, clinical development, and FDA milestone.
This profile is for educational and research purposes only. It is not medical advice, and nothing on it is a protocol, a recommendation, or an instruction for use in a person or an animal.
Athena Peptides Education does not prescribe, sell, or recommend any compound. Compounds discussed here are for laboratory research only and are not for human consumption. Always consult a qualified physician before making any decision about your health.