SS-31

What is SS-31 approved to do?

SS-31 is the development code for elamipretide, which FDA approved under accelerated approval in September 2025, branded Forzinity, to improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg [1][2]. Barth syndrome is described as "an ultra-rare X-linked recessive genetic disorder," and Forzinity is its first disease-specific approved product [2]. Forzinity's label describes it as a mitochondrial cardiolipin binder, given as a 40 mg subcutaneous injection once daily [1]. Because the approval is accelerated, continued approval "may be contingent upon verification and description of clinical benefit in a confirmatory trial" [1].

What does the trial evidence show?

In the TAZPOWER open-label extension, 10 patients continued daily 40 mg elamipretide after a 28-week placebo-controlled trial, and 8 reached week 168; six-minute walk distance improved cumulatively by 96.1 meters by week 168 (P = .003) [3]. Injection-site reactions were the most common adverse event in both the label and the extension study, reported in 100% of Forzinity patients versus 67% on placebo in the label [1]. Elamipretide is also in phase III testing for dry age-related macular degeneration and mitochondrial myopathies [2].

Is compounded "SS-31" the same as Forzinity?

No. "SS-31" sold online as a research or compounding product is not the FDA-approved Forzinity formulation. Elamipretide does not appear on FDA's May 2026 list of bulk substances nominated for compounding under section 503A [4]. Under 503A, a pharmacy may compound from a bulk substance that is a component of an FDA-approved drug, a condition that could be relevant here since an approved elamipretide product exists, but whether a specific compounded "SS-31" product satisfies that or any other condition is a question for the pharmacy and its counsel.