Data edition of
Residue An evidence-graded reference for peptide science

Monograph in Mitochondria-targeted peptides

Elamipretide

SS-31, a four-residue peptide that binds cardiolipin in the inner mitochondrial membrane — approved in 2025 for Barth syndrome after a mixed trial record elsewhere.

Also called SS-31 · MTP-131 · Bendavia · Forzinity

A

Best evidence: Approved / regulatory-grade

FDA accelerated approval (Forzinity, 2025) for Barth syndrome, contingent on confirmatory evidence. A phase 3 trial in primary mitochondrial myopathy failed its endpoints.

FDA accelerated approval — Forzinity (2025)

Residue Editorial Team · updated

What is Elamipretide?

Elamipretide (SS-31) is a synthetic tetrapeptide that binds cardiolipin, a lipid of the inner mitochondrial membrane. In September 2025 it received FDA accelerated approval as Forzinity to improve muscle strength in people with Barth syndrome weighing at least 30 kg1FDAFORZINITY prescribing information: Indications and Usage. FDA-approved labeling via openFDA/DailyMed, version effective 2025-12-10.,2PubMedElamipretide: First Approval. Shirley M Drugs. 2026.. In primary mitochondrial myopathy, the phase 3 MMPOWER-3 trial did not meet its endpoints3PubMedEfficacy and Safety of Elamipretide in Individuals With Primary Mitochondrial Myopathy: The MMPOWER-3 Randomized Clinical Trial. Karaa A et al. Neurology. 2023..

PubMed records
47097 reviews
Trial publications
2119 tagged RCT
Registered studies
293 active · 4 phase 3
Molecular weight
639.8g/mol · PubChem
Evidence grade
AApproved / regulatory-grade

Key findings

  1. FDA granted accelerated approval in September 2025 for Barth syndrome (≥30 kg), based on knee-extensor strength; continued approval may require confirmatory evidence1,2.
  2. In the TAZPOWER phase 2/3 trial in Barth syndrome, part 1 missed both primary endpoints; in part 2 at 36 weeks, 6-minute walk distance improved by 95.9 m4PubMedA phase 2/3 randomized clinical trial followed by an open-label extension to evaluate the effectiveness of elamipretide in Barth syndrome, a genetic disorder of mitochondrial cardiolipin metabolism. Reid Thompson W et al. Genet Med. 2021..
  3. In the open-label extension, 8 of 10 patients reached week 168, with a cumulative 96.1 m 6-minute-walk improvement; injection-site reactions were the most common adverse event5PubMedLong-term efficacy and safety of elamipretide in patients with Barth syndrome: 168-week open-label extension results of TAZPOWER. Thompson WR et al. Genet Med. 2024..
  4. MMPOWER-3 (218 adults with primary mitochondrial myopathy) found no difference from placebo in 6-minute walk (−3.2 m) or fatigue at 24 weeks3.
  5. A single infusion in heart failure with reduced ejection fraction was well tolerated and reduced left-ventricular volumes at the highest dose6PubMedNovel Mitochondria-Targeting Peptide in Heart Failure Treatment: A Randomized, Placebo-Controlled Trial of Elamipretide. Daubert MA et al. Circ Heart Fail. 2017..

Written by Residue Editorial Team

Reviewed by Residue Editorial Team · source-by-source check,

First published

Last updated

Registry data · How we grade · Markdown + sources

What is Elamipretide, chemically?

Identifiers retrieved from PubChem.
PubChem CID11764719 “Elamipretide”
FormulaC32H49N9O5
Molecular weight639.8 g/mol
CAS (as listed)736992-21-5
FDA UNII87GWG91S09
InChIKeySFVLTCAESLKEHH-WKAQUBQDSA-N
Length4 residues
Route in trialsDaily subcutaneous injection (Barth trials); IV infusion studied in heart failure
OriginatorStealth BioTherapeutics
MechanismMitochondrial cardiolipin binder
  • Hydrophobic
  • Basic (+)
  • Non-standard
Figure 1. Residue sequence of Elamipretide (4 positions) as recorded in PubChem CID 11764719 — H-D-Arg-Tyr(2,6-diMe)-Lys-Phe-NH2. “X” marks 1 non-standard, D-form or chemically modified position; see the condensed notation.

How does Elamipretide work?

Elamipretide is described in its approval profile and label as a mitochondrial cardiolipin binder2,1. Cardiolipin is a phospholipid of the inner mitochondrial membrane, and Barth syndrome is a genetic disorder of cardiolipin metabolism4. PubChem's sequence for the peptide includes a non-standard residue, shown as X in Figure 17PubChemPubChem compound record: Elamipretide. C32H49N9O5 · MW 639.8 g/mol..

What did the clinical trials find?

Barth syndrome (TAZPOWER). This phase 2/3 trial had a randomized, placebo-controlled crossover part followed by an open-label part. In part 1, neither primary endpoint was met. At 36 weeks in part 2, the 6-minute walk test improved by 95.9 m and the Barth Syndrome Symptom Assessment by 2.1 points, alongside gains in knee-extensor strength, patient global impression and some cardiac parameters4. The 168-week extension followed 10 patients, 8 to the end, reporting a cumulative 96.1 m improvement with left-ventricular volumes showing significant trends toward improvement5. FDA's accelerated approval rests on knee-extensor strength as an intermediate endpoint1.

Primary mitochondrial myopathy (MMPOWER-3). In 218 adults randomized 1:1, the trial did not meet its primary endpoints: the difference in 6-minute walk at 24 weeks was −3.2 m (p=0.69), and fatigue scores did not differ. Treatment was well tolerated3.

Heart failure. In a double-blind, ascending-dose trial in heart failure with ejection fraction ≤35%, a single 4-hour infusion caused no serious adverse events; blood pressure and heart rate were stable, and the highest dose reduced end-diastolic (−18 mL) and end-systolic (−14 mL) volumes at end-infusion6.

What adverse events were reported?

Injection-site reactions were the most common adverse event over 168 weeks in Barth syndrome5, and most adverse events in MMPOWER-3 were mild to moderate3. Barth syndrome is an ultra-rare X-linked recessive disorder2, and TAZPOWER randomized 12 people4, so the safety record in that population is small.

Is Elamipretide FDA-approved?

Table 1. Regulatory status of Elamipretide in the United States — from Drugs@FDA (openFDA) and FDA’s bulk-substance compounding categories, as fetched.
RecordStatusSource
FORZINITY
NDA215244 · STEALTH BIOTHERAPS		 FDA-approved original approval 2025-09-19
SOLUTION SUBCUTANEOUS		 8

Forzinity's application is listed in Drugs@FDA with a September 2025 original approval8FDADrugs@FDA: FORZINITY (NDA215244). STEALTH BIOTHERAPS; original approval 2025-09-19; Prescription.. The label states that the indication is approved under accelerated approval and that continued approval may be contingent upon verification and description of clinical benefit in a confirmatory trial1.

What is still unknown?

  • Confirmatory evidence for clinical benefit in Barth syndrome1.
  • Other indications, including dry AMD, remain investigational2.

What effects has Elamipretide shown, by body system?

Each row is graded separately using the Residue evidence scale: a compound can carry an A for one use and a D for another.

Table 2. Research-observed effects of Elamipretide by body system, with the strongest evidence available for each.
SystemWhat was observedGrade
Muscle strength (Barth syndrome)Approved use under accelerated approval1; knee-extensor strength improved in TAZPOWER4. A
Exercise capacity (Barth)6MWT +95.9 m (part 2) and +96.1 m over 168 weeks open-label4,5. B
Mitochondrial myopathyNo improvement versus placebo in a 218-person phase 3 trial3. B
HeartAcute reduction in LV volumes after a single high-dose infusion in HFrEF6. B
Injection site (adverse)Injection-site reactions were the most common adverse events in long-term use5. C

How much research is there on Elamipretide?

03672 1993: 1 records 1993 1994: 0 records 1995: 0 records 1995 1996: 0 records 1997: 3 records 1998: 0 records 1999: 0 records 2000: 1 records 2000 2001: 0 records 2002: 0 records 2003: 1 records 2004: 1 records 2005: 1 records 2005 2006: 2 records 2007: 2 records 2008: 2 records 2009: 3 records 2010: 2 records 2010 2011: 8 records 2012: 5 records 2013: 10 records 2014: 20 records 2015: 18 records 2015 2016: 18 records 2017: 26 records 2018: 31 records 2019: 30 records 2020: 31 records 2020 2021: 40 records 2022: 40 records 2023: 32 records 2024: 59 records 2025: 72 records 2025 2026: 72 records (year to date) 2026
Figure 2. PubMed records per publication year matching (elamipretide[tiab] OR SS-31[tiab] OR MTP-131[tiab] OR bendavia[tiab]) — 470 in total; peak 72 in 2025. The 2026 bar is year-to-date (hatched). Volume of literature is not evidence of efficacy. Run this query on PubMed.
Registered studies of Elamipretide by phase and status
PhaseStudiesBreakdown
Phase 1 8
7 completed, 0 active or recruiting, 1 stopped, 0 other
Phase 2 15
12 completed, 1 active or recruiting, 2 stopped, 0 other
Phase 3 4
2 completed, 1 active or recruiting, 1 stopped, 0 other
Phase 4 1
0 completed, 1 active or recruiting, 0 stopped, 0 other
Expanded access 1
0 completed, 0 active or recruiting, 0 stopped, 1 other
Figure 3. 29 studies on ClinicalTrials.gov match the registry search elamipretide OR SS-31 OR MTP-131. Multi-phase studies are counted at their highest phase. Open the full trial feed

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Questions readers ask

What is elamipretide approved for?

To improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg, under accelerated approval based on knee-extensor strength. Continued approval may be contingent on a confirmatory trial1.

Is SS-31 the same as elamipretide?

Yes. SS-31 is the research code; elamipretide is the generic name and Forzinity the brand2.

What are the side effects of elamipretide?

Injection-site reactions were the most common adverse events in the Barth syndrome extension5. In MMPOWER-3, most adverse events were mild to moderate3. The prescribing information carries the complete safety information1.

Does elamipretide work for mitochondrial myopathy?

Not in the phase 3 MMPOWER-3 trial, which found no significant difference from placebo on 6-minute walk or fatigue after 24 weeks3.

What else is elamipretide being studied for?

A 2026 profile lists phase 3 development in dry age-related macular degeneration and mitochondrial myopathies2.

References

Every source below was retrieved from its official API or page and cached on the data-edition date. Numbers match the margin notes.

  1. 1 FDA FORZINITY prescribing information: Indications and Usage. FDA-approved labeling via openFDA/DailyMed, version effective 2025-12-10.
  2. 2 PubMed Shirley M. Elamipretide: First Approval. Drugs 2026. PMID 41335372; doi:10.1007/s40265-025-02269-8.
  3. 3 PubMed Karaa A, Bertini E, Carelli V, et al. Efficacy and Safety of Elamipretide in Individuals With Primary Mitochondrial Myopathy: The MMPOWER-3 Randomized Clinical Trial. Neurology 2023. PMID 37268435; doi:10.1212/WNL.0000000000207402.
  4. 4 PubMed Reid Thompson W, Hornby B, Manuel R, et al. A phase 2/3 randomized clinical trial followed by an open-label extension to evaluate the effectiveness of elamipretide in Barth syndrome, a genetic disorder of mitochondrial cardiolipin metabolism. Genet Med 2021. PMID 33077895; doi:10.1038/s41436-020-01006-8.
  5. 5 PubMed Thompson WR, Manuel R, Abbruscato A, et al. Long-term efficacy and safety of elamipretide in patients with Barth syndrome: 168-week open-label extension results of TAZPOWER. Genet Med 2024. PMID 38602181; doi:10.1016/j.gim.2024.101138.
  6. 6 PubMed Daubert MA, Yow E, Dunn G, et al. Novel Mitochondria-Targeting Peptide in Heart Failure Treatment: A Randomized, Placebo-Controlled Trial of Elamipretide. Circ Heart Fail 2017. PMID 29217757; doi:10.1161/CIRCHEARTFAILURE.117.004389.
  7. 7 PubChem PubChem compound record: Elamipretide. C32H49N9O5 · MW 639.8 g/mol.
  8. 8 FDA Drugs@FDA: FORZINITY (NDA215244). STEALTH BIOTHERAPS; original approval 2025-09-19; Prescription.