# Elamipretide - Canonical: https://residue.info/c/elamipretide/ - Also called: SS-31, MTP-131, Bendavia, Forzinity - Evidence grade: A (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. - Status: FDA accelerated approval — Forzinity (2025) - PubChem CID: 11764719 - Updated: 2026-10-19 · Reviewed by: Residue Editorial Team 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 kg [1][2]. In primary mitochondrial myopathy, the phase 3 MMPOWER-3 trial did not meet its endpoints [3]. ## Key findings - FDA granted accelerated approval in September 2025 for Barth syndrome (≥30 kg), based on knee-extensor strength; continued approval may require confirmatory evidence [1][2]. (anchor: https://residue.info/c/elamipretide/#kf-label-nda215244) - 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 m [4]. (anchor: https://residue.info/c/elamipretide/#kf-pmid-33077895) - 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 event [5]. (anchor: https://residue.info/c/elamipretide/#kf-pmid-38602181) - MMPOWER-3 (218 adults with primary mitochondrial myopathy) found no difference from placebo in 6-minute walk (−3.2 m) or fatigue at 24 weeks [3]. (anchor: https://residue.info/c/elamipretide/#kf-pmid-37268435) - A single infusion in heart failure with reduced ejection fraction was well tolerated and reduced left-ventricular volumes at the highest dose [6]. (anchor: https://residue.info/c/elamipretide/#kf-pmid-29217757) ## Effects by system - Muscle strength (Barth syndrome) (grade A): Approved use under accelerated approval [1]; knee-extensor strength improved in TAZPOWER [4]. (anchor: https://residue.info/c/elamipretide/#effect-muscle-strength-barth-syndrome) - Exercise capacity (Barth) (grade B): 6MWT +95.9 m (part 2) and +96.1 m over 168 weeks open-label [4][5]. (anchor: https://residue.info/c/elamipretide/#effect-exercise-capacity-barth) - Mitochondrial myopathy (grade B): No improvement versus placebo in a 218-person phase 3 trial [3]. (anchor: https://residue.info/c/elamipretide/#effect-mitochondrial-myopathy) - Heart (grade B): Acute reduction in LV volumes after a single high-dose infusion in HFrEF [6]. (anchor: https://residue.info/c/elamipretide/#effect-heart) - Injection site (adverse) (grade C): Injection-site reactions were the most common adverse events in long-term use [5]. (anchor: https://residue.info/c/elamipretide/#effect-injection-site-adverse) ## How does Elamipretide work? Elamipretide is described in its approval profile and label as a mitochondrial cardiolipin binder [2][1]. Cardiolipin is a phospholipid of the inner mitochondrial membrane, and Barth syndrome is a genetic disorder of cardiolipin metabolism [4]. PubChem's sequence for the peptide includes a non-standard residue, shown as X in Figure 1 [7]. ## 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 parameters [4]. 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 improvement [5]. FDA's accelerated approval rests on knee-extensor strength as an intermediate endpoint [1]. **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 tolerated [3]. **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-infusion [6]. ## What adverse events were reported? Injection-site reactions were the most common adverse event over 168 weeks in Barth syndrome [5], and most adverse events in MMPOWER-3 were mild to moderate [3]. Barth syndrome is an ultra-rare X-linked recessive disorder [2], and TAZPOWER randomized 12 people [4], so the safety record in that population is small. Forzinity's application is listed in Drugs@FDA with a September 2025 original approval [8]. 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 trial [1]. ## What is still unknown? - **Confirmatory evidence** for clinical benefit in Barth syndrome [1]. - **Other indications**, including dry AMD, remain investigational [2]. ## Frequently asked questions **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 trial [1]. **Is SS-31 the same as elamipretide?** Yes. SS-31 is the research code; elamipretide is the generic name and Forzinity the brand [2]. **What are the side effects of elamipretide?** Injection-site reactions were the most common adverse events in the Barth syndrome extension [5]. In MMPOWER-3, most adverse events were mild to moderate [3]. The prescribing information carries the complete safety information [1]. **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 weeks [3]. **What else is elamipretide being studied for?** A 2026 profile lists phase 3 development in dry age-related macular degeneration and mitochondrial myopathies [2]. ## Sources [1] FORZINITY prescribing information: Indications and Usage. FDA-approved labeling via openFDA/DailyMed, version effective 2025-12-10. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=146bf34c-76f2-48db-ac07-fb29cce2cd75 [2] Elamipretide: First Approval. Shirley M Drugs. 2026. https://pubmed.ncbi.nlm.nih.gov/41335372/ [3] Efficacy and Safety of Elamipretide in Individuals With Primary Mitochondrial Myopathy: The MMPOWER-3 Randomized Clinical Trial. Karaa A et al. Neurology. 2023. https://pubmed.ncbi.nlm.nih.gov/37268435/ [4] 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. Reid Thompson W et al. Genet Med. 2021. https://pubmed.ncbi.nlm.nih.gov/33077895/ [5] Long-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. https://pubmed.ncbi.nlm.nih.gov/38602181/ [6] Novel Mitochondria-Targeting Peptide in Heart Failure Treatment: A Randomized, Placebo-Controlled Trial of Elamipretide. Daubert MA et al. Circ Heart Fail. 2017. https://pubmed.ncbi.nlm.nih.gov/29217757/ [7] PubChem compound record: Elamipretide. C32H49N9O5 · MW 639.8 g/mol. https://pubchem.ncbi.nlm.nih.gov/compound/11764719 [8] Drugs@FDA: FORZINITY (NDA215244). STEALTH BIOTHERAPS; original approval 2025-09-19; Prescription. https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm?event=overview.process&ApplNo=215244 --- From Residue. Research and education only; not medical advice. Quote with attribution and a link to the canonical page.