Drug Update · Rare Disease

FDA Approves Elamipretide for Barth Syndrome: 63 N Knee Strength Gain

July 22, 2026

Drug

Elamipretide (Forzinity)

Indication

Improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg

Approval date

09/19/2025

Primary supportive endpoint (extension)

Median knee extensor muscle strength change 63 N at Week 168 (min 38, max 78; N=8) [12]

Randomized trial size

12 subjects randomized; 10 entered extension; 8 reached Week 168 [12][1]

Recommended dose

40 mg subcutaneously once daily in patients ≥30 kg [12]

Clinical Perspective

Clinicians treating patients with Barth syndrome — including pediatric specialists and cardiologists managing males and others with genetically confirmed Barth syndrome who weigh at least 30 kg — now have an FDA‑approved therapy indicated to improve muscle strength ^[2]^[3]. The accelerated approval supports use to improve knee extensor muscle strength based on extension‑period increases (median 63 newtons at Week 168), while a confirmatory randomized, double‑blind, placebo‑controlled trial is required to verify broader clinical benefit ^[2]^[3]. How the observed strength gains will translate into long‑term functional outcomes or changes in cardiac course remains an open question?

Editorial Team · Rare Disease

The FDA approved elamipretide (Forzinity) injection to improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg on September 19, 2025, based on data from a randomized, double‑blind, placebo‑controlled crossover trial and its open‑label extension showing increases in knee extensor muscle strength (median change 63 newtons at Week 168 in the extension) ^[2]^[3].

Clinical Context

Elamipretide (Forzinity) is described in the label as a mitochondrial cardiolipin binder that localizes to the inner mitochondrial membrane and improves mitochondrial morphology and function ^[3]. The therapy was developed by Stealth BioTherapeutics and received accelerated approval as the first FDA‑approved treatment for Barth syndrome, a rare mitochondrial disease that primarily affects males and presents with early cardiac involvement and life‑long functional impairment according to the FDA announcement ^[2]. The approval used an intermediate clinical endpoint—knee extensor muscle strength—under the accelerated approval pathway; the FDA required a post‑approval randomized, double‑blind, placebo‑controlled confirmatory trial to verify clinical benefit ^[2]^[3].

Key Findings

In the randomized, double‑blind, placebo‑controlled crossover trial, FORZINITY was not superior to placebo on the trial's primary endpoints: distance walked during the 6‑minute walk test (6MWT) and Barth Syndrome Symptom Assessment (BTHS‑SA) Total Fatigue score ^[3].
Knee extensor muscle strength (a secondary endpoint) increased during the open‑label extension: median change from pre‑dose baseline to Week 168 was 63 newtons (min 38, max 78) in the 8 subjects who reached Week 168 of the extension period ^[3].
The randomized portion enrolled 12 subjects ≥12 years old and >30 kg and evaluated once‑daily subcutaneous FORZINITY 40 mg for 12 weeks; 10 subjects entered the open‑label extension and 8 participated through Week 168 in the extension ^[3]^[1].
Clinicians should consult current prescribing information for full dosing guidance.
The FDA granted accelerated approval on the basis that the observed increase in knee extensor strength is a reasonably likely predictor of patient benefit; the agency is requiring a confirmatory randomized, double‑blind, placebo‑controlled trial to demonstrate clinical benefit ^[2]^[3].

Safety & Tolerability

Injection‑site reactions were the most common adverse events reported in clinical trials and were described as mild to moderate in the label ^[1]^[3].
Serious reactions to Forzinity have also been reported in clinical trials and safety submissions ^[2]^[3].

Study Design

FORZINITY was evaluated in a randomized, double‑blind, placebo‑controlled, crossover trial that tested once‑daily subcutaneous FORZINITY 40 mg for 12 weeks in 12 subjects ≥12 years and >30 kg; the trial included a 192‑week open‑label, single‑arm extension period ^[3]. Clinicians should consult current prescribing information for full dosing guidance. Primary endpoints of the randomized trial were distance walked during the 6‑minute walk test and BTHS‑SA Total Fatigue score; FORZINITY was not superior to placebo on those primary endpoints. Knee extensor muscle strength was assessed as a secondary endpoint and increased in the open‑label extension, with descriptive median changes reported through Week 168 ^[3]^[1].

FAQ

Q1 What is Forzinity (elamipretide) approved for?

Forzinity (elamipretide) injection is approved to improve muscle strength in adult and pediatric patients with Barth syndrome who weigh at least 30 kg. The approval was granted under the FDA’s accelerated approval pathway on September 19, 2025, based on increases in knee extensor muscle strength observed in the clinical development program.

Q2 How does elamipretide work?

Elamipretide is described in the FDA label and press release as a mitochondrial cardiolipin binder that localizes to the inner mitochondrial membrane and improves mitochondrial morphology and function. The drug’s proposed mechanism is restoration of mitochondrial structure and function via cardiolipin interaction, as stated in the prescribing information and FDA announcement.

Q3 What is the recommended dose of Forzinity?

The recommended dosage in patients weighing at least 30 kg is 40 mg administered subcutaneously once daily; the FDA label includes dosage modification guidance for adults with reduced renal function (for example, a 20 mg once daily recommendation for adults with eGFR less than 30 mL/minute who are not on dialysis) and notes insufficient information to recommend dosing regimens in certain pediatric renal impairment scenarios. Clinicians should consult current prescribing information for complete dosing guidance.

Q4 What are the most common side effects of Forzinity?

The most commonly identified adverse events in trials were mild‑to‑moderate injection‑site reactions. The FDA press release and label note that serious reactions have also been reported in clinical trials and safety submissions; the label also instructs clinicians to review the full prescribing information for detailed safety and monitoring recommendations.

Clinicians should consult current prescribing information for full dosing guidance.

FDA Approves Elamipretide for Barth Syndrome: 63 N Knee Strength Gain

FDA Approves Elamipretide for Barth Syndrome: 63 N Knee Strength Gain

Clinical Perspective

Clinical Context

Key Findings

Safety & Tolerability

Study Design

FAQ

References

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