PwPepwise

SS-31 / Elamipretide

Energy & Cells

a.k.a. Bendavia

Cardiolipin-binding tetrapeptide

SS-31, also known as elamipretide or by its brand name FORZINITY™, is a synthetic tetrapeptide designed to protect and stabilize mitochondria.

§Dosing at a glance

2 protocols · from the research
What it's forDoseHow oftenHowFor how long
under the skin (approved and most studied route)40 mgOnce dailySubcutaneousInjected just under the skin, into the fat layer.72 wks
into a vein (early-phase and acute-use protocols)0.25 mg/kgOnce dailySubcutaneousInjected just under the skin, into the fat layer.28 days

Approximate values pulled from the research — double-check before dosing.

§01Summary

SS-31, also known as elamipretide or by its brand name FORZINITY™, is a synthetic tetrapeptide designed to protect and stabilize mitochondria — the energy-producing compartments inside cells. It works by binding to a key lipid called cardiolipin on the inner mitochondrial membrane, helping to maintain the membrane's structure and support efficient energy production. This mechanism makes it relevant to a wide range of conditions where mitochondrial dysfunction plays a role, from rare inherited muscle diseases to heart failure and age-related eye disease.

In clinical development, elamipretide has received FDA accelerated approval for Barth syndrome, a rare genetic disorder of cardiolipin metabolism, based on improvements in muscle strength7. In early human studies, it may improve functional capacity and reduce fatigue in patients with primary mitochondrial myopathy5,6, and preliminary evidence suggests it may support cardiac function in heart failure4. Research into dry age-related macular degeneration is actively advancing, with a pivotal Phase 3 trial currently underway3. Elamipretide is generally well tolerated across its studied routes of administration, with injection site reactions being the most commonly reported side effect with subcutaneous dosing6.

This is the layperson summary. Mechanism, dosing, the evidence base, and the published literature are in the sections below — every claim links to its source.

§02In depth

Elamipretide (SS-31) is a synthetic aromatic-cationic tetrapeptide with the sequence D-Arg-2′,6′-Dmt-Lys-Phe-NH₂, where 2′,6′-Dmt is 2′,6′-dimethyltyrosine. Its primary molecular target is cardiolipin, a unique dimeric phospholipid found almost exclusively in the inner mitochondrial membrane (IMM). Cardiolipin plays an indispensable structural role: it stabilizes the electron transport chain (ETC) supercomplexes (respirasomes), supports the membrane curvature required for cristae architecture, and anchors cytochrome c in a configuration optimized for electron shuttling between Complexes III and IV. In conditions of mitochondrial stress — including genetic mitochondrial disease, ischemia-reperfusion injury, heart failure, and aging — cardiolipin undergoes peroxidation and remodeling defects that destabilize these supercomplexes and impair ATP synthesis efficiency.

Elamipretide selectively concentrates at the IMM due to its alternating aromatic and cationic residues, which interact electrostatically with the negatively charged phosphate head groups of cardiolipin and through hydrophobic insertion into the lipid bilayer. By binding and stabilizing cardiolipin, elamipretide preserves ETC supercomplex integrity, reduces electron leak and mitochondrial reactive oxygen species (mROS) generation, and restores the proton gradient necessary for efficient oxidative phosphorylation. In Barth syndrome, where the tafazzin enzyme is mutated and cardiolipin remodeling is directly impaired, this mechanism is particularly well-matched to the underlying pathophysiology7,12,14.

Downstream effects of improved mitochondrial bioenergetics observed in clinical and preclinical contexts include reductions in left ventricular volumes in heart failure — suggesting improved myocardial energetics supporting acute cardiac remodeling4 — and improvements in skeletal muscle functional capacity in mitochondrial myopathy5,6. Pharmacokinetic data from the IV heart failure study indicate rapid clearance, with peak plasma concentrations undetectable by 24 hours post-infusion, implying a short plasma half-life consistent with peptide metabolism4. Subcutaneous administration at 40 mg/day achieves sustained systemic exposure sufficient for tissue-level mitochondrial engagement across multiple organ systems1,6,14. Oral formulations have been explored in Phase 1 studies to characterize bioavailability via the gastrointestinal route15,18, an area of active pharmacokinetic research given the challenge of peptide absorption across the intestinal epithelium.

§04Evidence & efficacy

Evidence base
326Studies
157Human
89Animal

Elamipretide has received FDA accelerated approval for Barth syndrome based on improvement in knee extensor muscle strength as an intermediate clinical endpoint, with confirmatory post-approval data being collected in an ongoing 72-week RCT7. In the earlier Phase 2/3 Barth syndrome crossover trial, the blinded phase did not meet its primary endpoints, though the open-label extension at 36 weeks showed meaningful improvements in 6-minute walk test distance (+95.9 m) and symptom burden scores, along with improvements in muscle strength and cardiac parameters14.

In primary mitochondrial myopathy, the pivotal MMPOWER-3 Phase 3 trial (n=218, 24 weeks) did not demonstrate significant improvement in 6-minute walk test distance (difference: -3.2 m, p=0.69) or fatigue scores (p=0.37) compared to placebo1. In earlier-phase PMM studies, elamipretide may improve walking capacity and fatigue outcomes: a dose-escalation IV trial showed a dose-dependent improvement in 6MWT at the highest dose5, and a 4-week crossover trial showed significant improvements in patient-reported fatigue measures, though the primary 6MWT endpoint was not met6.

In heart failure with reduced ejection fraction, a single IV infusion at the highest tested dose (0.25 mg/kg/h) may support acute reductions in left ventricular volumes4, and early evidence suggests a potential dose-response relationship. However, a Phase 2 trial of subcutaneous elamipretide over 28 days did not demonstrate significant improvements in LVESV or LVEF compared to placebo2.

A Phase 3 trial in dry age-related macular degeneration targeting photoreceptor preservation is currently underway3, and an earlier Phase 2 AMD study with geographic atrophy is in the evidence base10.

§05Safety

Across the clinical trial program, elamipretide has demonstrated a generally favorable tolerability profile. In the largest Phase 3 trial to date (MMPOWER-3, n=218), adverse events were predominantly mild to moderate in severity, and no specific serious safety signals were identified1. In the PROGRESS-HF Phase 2 heart failure trial, rates of study drug-related adverse events were similar across the placebo, 4 mg, and 40 mg elamipretide groups, supporting short-term tolerability at both doses2. The Phase 2/3 Barth syndrome trial completed with the majority of participants continuing through the open-label extension, consistent with acceptable tolerability in a pediatric rare disease population14.

The most consistently reported adverse event with subcutaneous administration is injection site reactions, occurring in approximately 80% of elamipretide-treated participants in the MMPOWER-2 crossover trial, with the majority described as mild in severity6. No serious adverse events or deaths were attributed to elamipretide in this study6. In the IV infusion heart failure study, blood pressure and heart rate remained stable across all dose cohorts with no serious adverse events reported4.

Long-term safety data beyond 36 weeks are actively being generated through the ongoing 72-week confirmatory Barth syndrome trial7 and the Phase 3 dry AMD trial3. No drug interaction data or contraindication signals have been reported in the available study summaries.

§06History

Elamipretide originated from the laboratory of Hazel Szeto at Weill Cornell Medical College in the early 2000s as part of a research program investigating aromatic-cationic peptides with mitochondria-targeting properties. The compound was initially designated MTP-131 and later Bendavia, before being renamed elamipretide during its clinical development phase. Its design was rationally guided by the goal of concentrating a cardiolipin-binding molecule at the inner mitochondrial membrane without requiring the mitochondrial membrane potential as a driving force — distinguishing it mechanistically from earlier cationic mitochondria-targeting agents.

The first-in-human Phase 1 IV infusion study was registered in 2010, establishing the foundational safety and pharmacokinetic profile in healthy volunteers17. Oral Phase 1 studies followed in 2012–2013 to explore alternative delivery routes15,18. Clinical development expanded into cardiovascular indications with Phase 2 ischemia-reperfusion studies in renal artery stenosis16 and heart failure4,8,11, as well as into rare mitochondrial diseases. The MMPOWER dose-escalation trial5 and MMPOWER-2 crossover study6 provided early signals in primary mitochondrial myopathy, advancing the program to the MMPOWER-3 Phase 3 trial1. Stealth BioTherapeutics filed for bankruptcy in 202213, significantly impacting several ongoing programs including the NuPower nPMD trial. Development of elamipretide for Barth syndrome continued and culminated in FDA accelerated approval under the brand name FORZINITY™, a landmark regulatory outcome for mitochondria-targeted therapeutics7. Phase 3 development in dry AMD is currently advancing3, representing the newest pivotal frontier for the compound.

§07References