Elamipretide

What is Elamipretide?

Elamipretide is a cationic, water-soluble tetrapeptide (D-Arg-2',6'-dimethylTyr-Lys-Phe-NH2) that concentrates at the inner mitochondrial membrane, where it binds cardiolipin and stabilizes the structural architecture required for efficient oxidative phosphorylation. Developed by Stealth BioTherapeutics, it received FDA accelerated approval on September 19, 2025 under the brand name Forzinity — the first mitochondria-targeted peptide ever to clear FDA review. The labelled indication is narrower than 'treatment of Barth syndrome' as it is often reported: Forzinity is indicated specifically to improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg, and the accelerated approval rests on an improvement in knee extensor muscle strength, which FDA classes as an intermediate clinical endpoint rather than a surrogate. Barth syndrome is an X-linked disorder of cardiolipin remodeling characterized by cardiomyopathy, skeletal myopathy, neutropenia, and growth delay; the Barth Syndrome Foundation's intake database holds 502 affected individuals worldwide, which it estimates is more than 80% of the known global population, with the United States the largest single share. The widely repeated figure of 'about 150 in the US' traces to older counts of cases reported in the literature. It is important to note that elamipretide is chemically identical to the research-grade peptide widely known as SS-31; the two names refer to the same molecule at different stages of its regulatory life. This entry focuses on the approved-drug context — label, indication, access — while the broader clinical-development story and off-label discussion live on the SS-31 page.

What Elamipretide Is Investigated For

Elamipretide's approved use case is narrow and specific: improving muscle strength in adult and pediatric Barth syndrome patients weighing at least 30 kg, granted FDA accelerated approval on September 19, 2025 as Forzinity — the first mitochondria-targeted peptide ever to clear FDA review. The strongest evidence is the TAZPOWER Phase 2/3 crossover in 12 patients, its open-label extension running to 192 weeks, and a retrospective natural-history-controlled comparison against untreated individuals; the cardiolipin-binding mechanism is an unusually direct match for Barth's underlying tafazzin defect. Importantly, elamipretide's broader clinical record is mixed to negative: PROGRESS-HF in heart failure failed, the Phase 2 ReCLAIM-2 trial in dry AMD missed its primary endpoints (the Phase 3 ReNEW trial has completed enrollment at 313 participants and is scheduled for primary completion in August 2027), and MMPOWER-3 in broader primary mitochondrial myopathy missed its primary endpoint. The honest framing is that approval rests on an intermediate clinical endpoint — knee extensor muscle strength — in an ultra-rare population, with a safety database of just 12 patients and confirmatory studies pending, and that use outside Barth syndrome — including the longevity and anti-aging marketing that surrounds the chemically identical research peptide SS-31 — is not supported by controlled clinical evidence.

History & Discovery

Elamipretide's scientific origin is the Szeto-Schiller peptide program at Cornell University in the late 1990s and early 2000s, where Hazel Szeto and Peter Schiller systematically engineered small cationic peptides that could penetrate cell membranes and concentrate in mitochondria without depending on membrane potential. SS-31 — the fourth generation of that series — distinguished itself by its ability to bind cardiolipin on the inner mitochondrial membrane with unusual selectivity, independent of the mitochondrial membrane potential that had limited earlier triphenylphosphonium-based targeting strategies. Stealth BioTherapeutics (originally Stealth Peptides) licensed the molecule and advanced it through clinical development under multiple names — Bendavia for cardiovascular indications, MTP-131 in early trial documentation, and ultimately elamipretide as the International Nonproprietary Name. The program's regulatory arc spanned more than a decade: EMBRACE-STEMI in acute ST-elevation myocardial infarction missed its primary endpoint, PROGRESS-HF in heart failure with reduced ejection fraction was negative, the Phase 2 ReCLAIM-2 trial in dry age-related macular degeneration missed its primary endpoints (the Phase 3 ReNEW trial in dry AMD is ongoing), and MMPOWER-3 in broader primary mitochondrial myopathy missed its primary endpoint despite signals in genotype-defined subgroups. The Barth syndrome program — TAZPOWER and its 168-week open-label extension, paired with a retrospective, propensity-matched natural-history-controlled comparison against untreated individuals — produced the package that ultimately persuaded the FDA. Regulatory review was itself protracted, though the sequence is often misreported. Stealth's first submission in August 2021 drew a Refuse-to-File decision that October rather than a Complete Response Letter. A new application was filed in January 2024 and accepted that April; an advisory committee voted in its favour in October 2024; FDA issued a single Complete Response Letter on May 15, 2025; and Stealth's August 2025 amendment constituted the complete response that led to accelerated approval for Forzinity on September 19, 2025 made elamipretide the first FDA-approved mitochondria-targeted peptide and, in a broader sense, the first drug ever approved specifically for Barth syndrome. Confirmatory studies are required under the accelerated-approval commitment. The randomized, double-blind, placebo-controlled confirmatory trial (4TAZPower, also designated SPIBA-401, NCT07531251) began on July 2, 2026, and aims to enroll about 48 patients against a composite functional primary endpoint; its primary completion date is September 2029, so the data that will decide whether this approval converts to full approval are years away. Stealth BioTherapeutics began operating as Mighty Therapeutics in June 2026, though the legal entity named on the FDA label and on trial registrations remains Stealth BioTherapeutics Inc.

How It Works

Elamipretide is a small peptide that homes to the inner membrane of your cells' mitochondria — the powerhouses that make cellular energy. Once there, it binds to cardiolipin, a lipid that holds the energy-producing machinery in the right shape. By stabilizing cardiolipin, elamipretide helps mitochondria run more efficiently and produce less oxidative damage. In Barth syndrome, a genetic defect in cardiolipin metabolism causes heart and muscle dysfunction, which is why this mechanism is a particularly close match for the disease.

Elamipretide is chemically identical to the research peptide SS-31, a 4-residue cationic peptide developed in the Szeto-Schiller program at Cornell. Its distinguishing pharmacological property is selective, voltage-independent binding to cardiolipin on the matrix-facing leaflet of the inner mitochondrial membrane. Cardiolipin is a dimeric phospholipid unique to mitochondria (and bacterial membranes) that organizes the supercomplexes of Complex I, III, and IV of the electron transport chain and maintains the tight cristae curvature required for efficient ATP synthesis. By binding cardiolipin, elamipretide (i) preserves cristae architecture, (ii) stabilizes electron transport chain supercomplexes, improving electron flux and ATP synthesis, and (iii) reduces generation of reactive oxygen species by limiting electron leak. It also prevents peroxidation of cardiolipin itself — a cardinal early event in mitochondrial dysfunction across many disease contexts. Barth syndrome is caused by loss-of-function mutations in TAFAZZIN (TAZ), the gene encoding tafazzin, a phospholipid-remodeling acyltransferase. Loss of tafazzin activity leads to immature, monolyso-cardiolipin-enriched membranes, disorganized cristae, and impaired oxidative phosphorylation — producing cardiomyopathy, skeletal myopathy, growth delay, and cyclic neutropenia. Because elamipretide acts directly on cardiolipin architecture, the mechanistic match to Barth biology is unusually direct, which underpins the accelerated-approval rationale where earlier heart-failure and dry-AMD trials (PROGRESS-HF, n=71, which showed no change in left ventricular end-systolic volume at week 4; and the Phase 2 ReCLAIM-2) did not produce convincing benefit, and MMPOWER-3 (n=218) missed both co-primary endpoints in broader primary mitochondrial myopathy — the 6-minute walk test and a patient-reported fatigue score.

Evidence Snapshot

Research Gaps & Open Questions

What the current literature has not yet settled about Elamipretide:

• 01Confirmatory clinical benefit — as an accelerated-approval drug, Forzinity's post-marketing confirmatory studies are a material part of its evidentiary story. Outcomes of those studies over the next several years will determine whether full approval is granted or whether the indication is narrowed or withdrawn.
• 02Pediatric access below 30 kg — still outside the label, but no longer an entirely open question: a regulatory pathway using extrapolation to support patients between 7 and 30 kg, backed by a small open-label pharmacokinetic study, was described at the 2026 Barth Syndrome Foundation conference as the route to a label expansion.
• 03Long-term safety beyond the 168-week extension — larger populations and longer exposures are needed to characterize rare adverse events.
• 04Cardiac imaging and biomarker endpoints — the heterogeneity of Barth cardiomyopathy and the small patient population mean endpoint validation remains an ongoing area of work.
• 05Broader mitochondrial disease indications — whether subgroup signals in MMPOWER-3 or new formulations might eventually support label expansion beyond Barth syndrome is not resolved. NuPower (NCT05162768), a 102-patient placebo-controlled Phase 3 in nuclear-DNA primary mitochondrial disease, completed in September 2024 but has no posted or published results, which is itself a gap.
• 06Non-Barth and healthy-population use — despite marketing adjacent to 'mitochondrial support' in the research-chemical and longevity space, no controlled trial supports any longevity or anti-aging claim. One academically sponsored study is now under way (NCT07275424, University of Washington), but it is an open-label, single-arm Phase 2a safety pilot of about 30 adults aged 65 to 80 with low VO2peak, with Stealth as a collaborator, and its primary outcome is adverse events over four weeks. It is designed to test tolerability, not benefit, and cannot support an efficacy claim — a distinction worth holding onto, because it is exactly the kind of trial that gets cited as though it could.

Forms & Administration

Forzinity is supplied ready to use — a sterile, clear, colorless to yellow aqueous solution at 280 mg/3.5 mL (80 mg/mL) in single-patient-use vials, not a lyophilized powder requiring reconstitution. The 40 mg dose is 0.5 mL. The label provides 40 mg once daily for adult and pediatric Barth patients ≥30 kg, reduced to 20 mg once daily in adults with an eGFR below 30 mL/min who are not on dialysis; there is insufficient information to recommend a dose for adults on dialysis or for renally impaired pediatric patients. Administration is performed at home by patients or caregivers after training, by subcutaneous injection into the abdomen (at least two inches from the navel) or the outer thigh, rotating the site daily — the upper arm is not a labeled injection site. The solution contains benzyl alcohol as a preservative and must not be used in neonates. All injectable peptides should only be administered under the guidance of a qualified healthcare provider. Never self-administer without clinician oversight.

Dosing & Protocols

The ranges below reflect protocols commonly discussed in the literature and by clinicians — not a prescription. Actual dosing for any individual should be determined by a qualified healthcare provider who knows the patient.

Dosing information reflects the FDA-approved Barth syndrome label. Use of elamipretide or SS-31 outside this indication is off-label and is not supported by the approved evidence base.

Timeline of Effects

Monitoring & Measurement

Common Questions

Who Elamipretide Is NOT For

Drug & Supplement Interactions

Elamipretide has a relatively limited published drug-interaction profile, in part because no hepatic metabolism is observed in vitro, so hepatic impairment is not expected to alter its pharmacokinetics. The label confirms it neither inhibits the major CYP enzymes nor induces CYP1A2, CYP2B6 or CYP3A4, and it does not inhibit OCT2, BCRP, OAT1, OAT3, OATP1B1, OATP1B3, P-gp or MATE2-K. There is one transporter exception worth knowing: elamipretide inhibits MATE1 with an IC50 of 3.53 μM. MATE1 handles the renal secretion of several widely used cationic drugs, metformin among them, and no dedicated clinical interaction study with a MATE1 substrate has been published — so this is a theoretical interaction with a measured in vitro basis rather than a documented clinical one. Clearance is essentially renal, which is why the label carries a dose reduction below an eGFR of 30. In Barth syndrome clinical experience, patients are commonly on cardiac medications including beta-blockers, ACE inhibitors, and diuretics; these have been used alongside elamipretide in trials without signals of clinically meaningful interaction. Granulocyte colony-stimulating factor and growth hormone — both used in selected Barth patients — have also been used concomitantly in the development program. Patients and caregivers should disclose all concurrent medications, supplements, and compounded products to the prescribing specialist, who will coordinate with a specialty pharmacy as part of Forzinity initiation.

Safety Profile

Legal Status

Regulatory status changes over time. Verify current local rules with a qualified professional.

Myths & Misconceptions