Elamipretide (SS-31/Bendavia/Forzinity): first FDA-approved mitochondria-targeted drug
A synthetic four-amino-acid drug that stabilizes energy-producing structures inside cells; FDA-approved for Barth syndrome, a rare inherited heart and muscle disorder.
- Class
- Mitochondria-targeted cardiolipin-binding tetrapeptide
- Status
- FDA accelerated approval — Barth syndrome in adults and pediatric patients weighing at least 30 kg (Forzinity); no other FDA-approved indications
- Best-supported effect
- Functional improvement in Barth syndrome patients (human Phase 2/3 RCT and 168-week open-label extension); mechanistically specific to cardiolipin defect underlying Barth disease
- Main caveat
- Approval is based on a surrogate endpoint in a small rare-disease population with confirmatory studies required; broader clinical programs in heart failure, dry AMD, and primary mitochondrial myopathy have failed or been mixed; longevity and anti-aging use is not supported by controlled clinical evidence
A researcher, an agent, or an algorithm wrote down the sequence and picked a target to hit.
An AI model like OpenFold3 or AlphaFold built a 3D structure and scored how well it fits the binding site.
A second contributor repeated the computation on their own hardware and the scores matched.
A chemistry service or a researcher ordered the sequence, it was manufactured, and mass spectrometry confirmed the right molecule was produced.
A binding or activity measurement confirmed that it actually does what the computer predicted — or didn't.
What this is
Elamipretide is a synthetic four-amino-acid peptide designed to localize inside mitochondria — the energy-producing compartments of the cell — and stabilize the inner membrane lipid called cardiolipin. Marketed by Stealth BioTherapeutics as Forzinity, it became the first mitochondria-targeted peptide ever approved by the FDA and the first drug approved specifically for Barth syndrome, a rare X-linked disorder of cardiolipin remodeling affecting roughly 150 patients in the United States. The same molecule is widely known to researchers as SS-31, and earlier in its development was called MTP-131 and Bendavia.
Structurally, elamipretide is an aromatic cationic tetrapeptide (D-Arg–2′,6′-dimethylTyr–Lys–Phe–NH₂): the first residue is a D-amino acid, the second tyrosine carries two methyl substitutions on its aromatic ring, and the C-terminus is amidated — none of which are visible in a raw single-letter sequence. These modifications are what allow the molecule to penetrate cell membranes, transiently localize to the inner mitochondrial membrane, and bind cardiolipin in a voltage-independent manner (Tung et al. 2025, Int. J. Mol. Sci.; Mitchell et al. 2020, J. Biol. Chem.).
Beyond Barth syndrome, elamipretide has been tested in heart failure, dry age-related macular degeneration, primary mitochondrial myopathy, and ischemia–reperfusion injury. Most of those programs were negative or mixed, so the FDA approval is narrow and the broader "mitochondrial therapy" framing should not be confused with demonstrated clinical benefit in other indications.
History
Elamipretide originated in the Szeto–Schiller peptide program at Cornell University, where Hazel Szeto and Peter Schiller designed a series of small cationic aromatic peptides (the "SS peptides") to concentrate selectively at the inner mitochondrial membrane. SS-31 was the lead compound of that program and was later licensed for clinical development.
Stealth BioTherapeutics (initially Stealth Peptides) advanced the molecule under the codename MTP-131 and the trial name Bendavia, beginning with cardiac ischemia–reperfusion studies in the late 2000s and early 2010s. Early animal work showed that the peptide reduced myocardial infarct size when given before reperfusion in rabbit and rat models (Cho et al. 2007, Coronary Artery Disease; Brown et al. 2014, J. Cardiovasc. Pharmacol. Ther.).
The pivot to Barth syndrome was driven by the mechanistic match between the drug's cardiolipin pharmacology and the underlying TAFAZZIN defect of the disease. After the TAZPOWER Phase 2/3 crossover trial and its 168-week open-label extension (Thompson et al. 2024, Genetics in Medicine) and the EMBRACE natural-history comparison (Hornby et al. 2022, Orphanet J. Rare Dis.), the FDA granted accelerated approval in September 2025 under the brand name Forzinity — the first cardiolipin-directed mitochondrial therapeutic to reach market (Zhao et al. 2025, Drug Discoveries & Therapeutics; Shirley 2025, Drugs).
What it does
Inside cells, elamipretide concentrates in mitochondria and binds cardiolipin, a phospholipid that only appears in the inner mitochondrial membrane. By binding cardiolipin, the peptide helps preserve the tightly folded architecture (cristae) of that membrane, stabilizes the protein complexes of the electron transport chain, and reduces the leak of electrons that would otherwise generate reactive oxygen species (Sabbah et al. 2025, Biomedicine & Pharmacotherapy; Nhu et al. 2022, Frontiers in Integrative Neuroscience).
The biological effect — at least in Barth syndrome — is a gradual improvement in cardiac and skeletal-muscle function, including measures such as the six-minute walk distance, fatigue scores, and indices of cardiac performance (Thompson et al. 2024, Genetics in Medicine; Sabbah 2022, Heart Failure Reviews). A single-dose pharmacodynamic study in older adults without Barth syndrome reported an increase in in vivo mitochondrial ATP production measured by phosphorus magnetic resonance spectroscopy, but this was a one-time acute readout, not a demonstration of long-term clinical benefit (PLOS ONE 2021).
Evidence
- Human: FDA accelerated approval (September 2025) for Barth syndrome in adults and pediatric patients weighing at least 30 kg, based on the TAZPOWER Phase 2/3 crossover RCT and its 168-week open-label extension, with supporting evidence from the EMBRACE natural-history comparison (Thompson et al. 2024, Genetics in Medicine; Hornby et al. 2022, Orphanet J. Rare Dis.; Shirley 2025, Drugs). Phase 2 in heart failure with reduced ejection fraction (PROGRESS-HF) missed its primary endpoint (Butler et al. 2020, J. Cardiac Failure). Phase 3 in primary mitochondrial myopathy (MMPOWER-3) missed its primary endpoint, with post-hoc signals only in a nuclear-DNA-mutation subgroup (Karaa et al. 2023, Neurology; Karaa et al. 2024, Orphanet J. Rare Dis.). The MMPOWER-2 crossover precursor and the original dose-escalation study reported safety and some functional signals in mitochondrial myopathy (Karaa et al. 2018, Neurology; Karaa et al. 2020, J. Cachexia, Sarcopenia and Muscle). A topical ophthalmic formulation has been tested in Leber hereditary optic neuropathy (Karanjia et al. 2024, Ophthalmology). Studies in acute ST-elevation myocardial infarction reported a biomarker effect (decreased circulating HtrA2) without meeting clinical primary endpoints (Hortmann et al. 2019, Eur. Heart J. Acute Cardiovasc. Care), and the dry age-related macular degeneration programs (ReCLAIM, ReNEW) were not successful.
- Animal: Strong and varied — cardiac ischemia–reperfusion (Cho et al. 2007, Coronary Artery Disease; Brown et al. 2014, J. Cardiovasc. Pharmacol. Ther.), heart failure, renal protection, and neurodegeneration / lipopolysaccharide-induced cognitive impairment models (Zhao et al. 2019, J. Neuroinflammation; Nhu et al. 2022, Frontiers in Integrative Neuroscience).
- In vitro: Cardiolipin-binding characterization, mitochondrial supercomplex stabilization, and surface-electrostatics modulation of lipid bilayers as a core component of mechanism (Mitchell et al. 2020, J. Biol. Chem.).
The TAZPOWER program reported functional improvement in Barth patients over 168 weeks of open-label exposure; the EMBRACE natural-history comparison anchored that signal against an untreated cohort because the rare-disease population is too small for a conventional placebo-controlled Phase 3 (Hornby et al. 2022; Thompson et al. 2024). A hierarchical-clustering analysis of TAZPOWER wearable-device data has further attempted to identify responders within the small treated population (Van den Eynde et al. 2023, Orphanet J. Rare Dis.).
A large share of the elamipretide clinical literature derives from trials sponsored by or closely associated with Stealth BioTherapeutics; independent academic replication of the Barth program is limited by the rarity of the disease.
Known effects
- Functional improvement in Barth syndrome — FDA-approved (Thompson et al. 2024; Shirley 2025).
- Cardiomyopathy stabilization in Barth syndrome — supported by the TAZPOWER extension and dedicated cardiac-phenotype analyses (Sabbah et al. 2023, Future Cardiology).
- Reduction of myocardial infarct size in ischemia–reperfusion models — preclinical (Cho et al. 2007; Brown et al. 2014).
- Improved mitochondrial ATP synthesis after a single dose in older adults — Phase 2 pharmacodynamic only (PLOS ONE 2021).
- Heart failure with reduced ejection fraction — Phase 2 negative (Butler et al. 2020).
- Primary mitochondrial myopathy — Phase 3 negative overall, with a post-hoc nDNA-subgroup signal (Karaa et al. 2023; Karaa et al. 2024).
- Dry age-related macular degeneration — Phase 2 (ReCLAIM, ReNEW) unsuccessful.
- Leber hereditary optic neuropathy — topical ophthalmic formulation tested in a randomized trial (Karanjia et al. 2024, Ophthalmology).
- Longevity or anti-aging use in healthy adults — not established; no controlled chronic trials in healthy populations identified in the source literature.
Safety signals
Across the elamipretide development program, the most commonly reported adverse events have been injection-site reactions (erythema, pain, pruritus), followed by headache and infrequent gastrointestinal symptoms such as nausea or diarrhea (Karaa et al. 2020, J. Cachexia, Sarcopenia and Muscle; Thompson et al. 2024, Genetics in Medicine; Shirley 2025, Drugs). Dizziness has been reported uncommonly.
The Forzinity label lists known hypersensitivity to elamipretide or the product's excipients as a contraindication. Use in pediatric patients weighing less than 30 kg is not covered by the current US labeling, even though weight-adjusted dosing was studied during development. Human pregnancy data and transfer into breast milk have not been well characterized (Shirley 2025, Drugs).
Long-term safety beyond the approximately 168-week TAZPOWER open-label extension in a small Barth cohort has not been characterized, and safety in non-Barth populations (heart failure, healthy adults, longevity-seeking use) is not established by the approved dataset. Elamipretide is not metabolized by cytochrome P450 enzymes; formal drug-interaction data are limited, but cardiac co-medications were used concomitantly in trials without reported clinically meaningful interaction signals (Sabbah et al. 2025, Biomedicine & Pharmacotherapy).
Regulatory status
- US: FDA accelerated approval (September 2025) for Barth syndrome in adults and pediatric patients ≥30 kg, marketed as Forzinity by Stealth BioTherapeutics. No other FDA-approved indications. Confirmatory clinical-benefit studies are required under the accelerated-approval commitment (Shirley 2025, Drugs; Zhao et al. 2025, Drug Discoveries & Therapeutics).
- US compounding: The FDA's 2023 peptide compounding review categorized elamipretide as ineligible for standard 503A compounding. The approved product is distributed through a manufacturer-managed specialty pharmacy network rather than through retail or compounding pharmacies.
- EU: As of early 2026, Forzinity's approval is US-specific; EMA evaluation under a rare-disease pathway has been described in source literature; international availability depends on local approval and reimbursement.
- WADA: Not currently named on the Prohibited List as an approved human therapeutic; athletes using Forzinity for its approved Barth syndrome indication would seek a Therapeutic Use Exemption. Research-chemical SS-31 sold outside the regulated pharmacy supply chain is a different matter and should be treated as high-risk for athletes subject to anti-doping programs.
Mechanism
Elamipretide is a cationic aromatic tetrapeptide whose key chemistry — a D-arginine at position 1, a 2′,6′-dimethyltyrosine at position 2, and a C-terminal phenylalanine amide — is what determines its biophysical behavior. The combination of two basic residues (D-Arg, Lys) and two aromatic residues (dmTyr, Phe) gives the molecule both a net positive charge and amphiphilic character, allowing it to cross the plasma membrane and then concentrate at the inner mitochondrial membrane. Unlike older mitochondria-targeting molecules such as MitoQ that rely on the inner-membrane voltage gradient, elamipretide binds cardiolipin in a voltage-independent manner, so it accumulates even in depolarized or dysfunctional mitochondria (Mitchell et al. 2020, J. Biol. Chem.; Tung et al. 2025, Int. J. Mol. Sci.).
Cardiolipin is a dimeric phospholipid found almost exclusively in the inner mitochondrial membrane. It organizes the supercomplexes of Complexes I, III, and IV of the electron transport chain and stabilizes the tight curvature of the cristae folds where ATP synthase is concentrated. By binding cardiolipin, elamipretide:
1. preserves cristae architecture, 2. stabilizes electron transport chain supercomplexes and improves electron flux and ATP output, and 3. reduces reactive oxygen species generation by limiting electron leak (Sabbah et al. 2025, Biomedicine & Pharmacotherapy; Nhu et al. 2022, Frontiers in Integrative Neuroscience).
It also protects cardiolipin itself from peroxidation, an early event in mitochondrial dysfunction across several disease contexts (Sabbah 2022, Heart Failure Reviews; Obi et al. 2022, Heart Failure Reviews).
In Barth syndrome, loss-of-function mutations in TAFAZZIN (encoding the phospholipid-remodeling acyltransferase tafazzin) result in immature, monolyso-cardiolipin-enriched inner-membrane lipids, disorganized cristae, and impaired oxidative phosphorylation. Elamipretide's cardiolipin-binding pharmacology is an unusually direct mechanistic match to that underlying defect, which is the rationale that supported accelerated approval (Sabbah 2022, Heart Failure Reviews; Zhao et al. 2025, Drug Discoveries & Therapeutics).
The negative outcomes in heart failure (PROGRESS-HF), broader primary mitochondrial myopathy (MMPOWER-3), and dry AMD (ReCLAIM, ReNEW) illustrate that a well-characterized mechanism — even one as specific as cardiolipin binding — does not guarantee clinical benefit across every mitochondria-related condition. Target confidence for the primary mechanism is high; translation to clinical benefit outside Barth syndrome is not established.
Open questions
- Confirmatory clinical benefit in Barth syndrome. As an accelerated-approval drug, Forzinity's post-marketing confirmatory studies will determine whether full approval is granted or the indication is narrowed or withdrawn.
- Pediatric access below 30 kg. Weight-adjusted dosing was explored in development but is not covered by the current US label; pathways to extend labeling to younger patients remain unresolved.
- Long-term safety profile. Continuous-use safety beyond the ~168-week TAZPOWER extension in a small Barth cohort is not characterized.
- Broader mitochondrial-disease indications. Whether genotype-defined subgroup signals from MMPOWER-3 or new formulations will eventually support label expansion beyond Barth syndrome is not resolved (Karaa et al. 2024, Orphanet J. Rare Dis.).
- Non-Barth and healthy-population use. No controlled chronic trials of elamipretide in healthy adults or longevity-seeking populations are identified in the source literature. The single-dose pharmacodynamic ATP study in older adults does not establish chronic efficacy.
- EU and international access. EMA evaluation is ongoing as of early 2026.
Related peptides
Elamipretide is the lead compound of the Szeto–Schiller (SS) peptide series of mitochondria-targeted aromatic cationic tetrapeptides. Within the broader mitochondria-targeted field it sits alongside non-peptide compounds such as MitoQ and SkQ1, which use a covalently attached triphenylphosphonium cation to concentrate at the inner membrane via the membrane potential rather than via cardiolipin binding. No other mitochondria-targeted peptide has been approved by the FDA to date.
Research directions for this peptide, selected from the current sources — hypotheses you can explore and model. None of it is proven yet; tap any one to see the full thinking.
When a severe infection scrambles the brain, could a peptide already approved for a rare heart disease undo the damage?
Up to 70% of ICU patients with sepsis suffer confusion and lasting cognitive harm, and there is currently no approved treatment. If this hypothesis holds, a well-tolerated existing drug could be repurposed for this acute crisis, addressing a large unmet need in critical care.
Could a small structural tweak make the drug stick around in cells long enough to stop requiring daily injections?
Children with Barth syndrome currently need a daily injection under the skin, which is hard on patients and families. If adding a fatty tail to the molecule makes it lodge in the cell's energy machinery for days instead of hours, a once-weekly dose might become possible, meaningfully improving everyday life.
Does the drug's effect wear off because it simply lets go of its target, the way a loosely bound key leaves a lock?
If the drug acts as a short-lived surface stabilizer rather than building something lasting, doctors would need to design dosing schedules around that window to keep benefit continuous. For patients on long-term therapy, like those with Barth syndrome, getting this right could mean the difference between steady improvement and cycling on and off.
Could a large failed trial actually be hiding a real benefit in a smaller, better-defined group of patients?
A Phase 3 trial found no overall benefit, but a closer look suggested improvement in patients whose mutations came from nuclear DNA rather than mitochondrial DNA. If that distinction is confirmed, it could rescue a failed drug for a subset of patients who have almost no other options, by targeting the right people from the start.
Is one specially shaped ingredient in the drug responsible for locking onto the right fat molecule inside the cell's power plant?
Cardiolipin is a fat found almost exclusively in the inner wall of mitochondria, and elamipretide seems to seek it out specifically. If one modified amino acid is the key to that selectivity, chemists could use that insight to build better versions of the drug with stronger or more precise binding, potentially raising effectiveness in diseases caused by cardiolipin deficiency.
▸full evidence table1 metrics
| metric | value | tool |
|---|---|---|
| ranking score | 0.7652245759963989 | boltz-2 |
▸3-letter notation
▸recipeboltz-2 2.2.1
| parameter | value |
|---|---|
| model | boltz-2 2.2.1 |
| weights | — |
| hardware | vast_v100_32gb |
| mlx version | — |
| python | — |
| random seed | 1 |
| msa strategy | none_monomer |
| runtime | — |
| predicted by | — |
| predicted at | 2026-05-23 |
▸citationbibtex
@peptide{pep11002,
sequence = {RXKF},
target = {cardiolipin},
author = {peptidemodel},
year = {2026},
status = {computed}
}