SS-31: Dosing Protocols

Research Dosing Disclaimer#

SS-31 (elamipretide) is an investigational drug that has not received regulatory approval from the FDA or any other regulatory agency for any indication. The dosing information provided here is derived exclusively from published clinical trial protocols and results. This information is intended for educational and research reference purposes and does not constitute medical advice or a prescribing guide. All dosing decisions in clinical settings must be made by qualified investigators under approved research protocols.

Clinical Trial Dosing Overview#

SS-31 has been evaluated in clinical trials using two primary routes of administration: subcutaneous injection for chronic treatment and intravenous infusion for acute or short-duration applications. The dose selection in clinical trials was informed by preclinical pharmacokinetic and pharmacodynamic studies demonstrating that SS-31 rapidly concentrates in mitochondria after systemic administration.

Barth Syndrome: TAZPOWER Protocol#

The TAZPOWER trial represents the most advanced clinical dosing protocol for elamipretide. This Phase 3, randomized, double-blind, placebo-controlled crossover study evaluated subcutaneous elamipretide in patients with genetically confirmed Barth syndrome.

Dose and Schedule#

Patients received 40 mg of elamipretide administered as a once-daily subcutaneous injection. This dose was selected based on Phase 2 dose-finding data and pharmacokinetic modeling to achieve and maintain mitochondrial concentrations expected to stabilize cardiolipin and optimize electron transport chain function over a 24-hour dosing interval.

Treatment Duration#

The crossover design consisted of two 12-week treatment periods. Each patient received both elamipretide and placebo in a randomized sequence, with a washout period between treatment phases to allow for clearance and assessment of any carryover effects.

Open-Label Extension#

Patients who completed the TAZPOWER trial were eligible to enter an open-label extension study in which all patients received elamipretide 40 mg subcutaneous injection daily. Some patients in the extension study have been treated continuously for multiple years, providing the longest available safety and efficacy data for chronic elamipretide administration.

Administration Technique#

In the TAZPOWER trial, subcutaneous injections were administered in the abdominal, thigh, or upper arm regions. Site rotation was recommended to minimize injection site reactions. Patients or caregivers were trained on self-injection technique following the initial supervised administrations.

Heart Failure: EMBRACE STEMI Protocol#

The EMBRACE STEMI trial (Evaluating Myocardial Effects of Bendavia for Reducing Reperfusion Injury in Patients with Acute Coronary Events) was a Phase 2a, randomized, double-blind, placebo-controlled trial evaluating a single intravenous dose of elamipretide in patients with first-time ST-elevation myocardial infarction undergoing percutaneous coronary intervention.

Dose and Administration#

Patients received elamipretide at a weight-based dose of 0.25 mg/kg administered as an intravenous infusion. The infusion was initiated prior to the percutaneous coronary intervention procedure to ensure that therapeutic concentrations were present at the time of coronary reperfusion, when mitochondrial injury from ischemia-reperfusion is maximal.

Rationale for IV Route#

Intravenous administration was chosen for the acute STEMI setting to ensure rapid achievement of therapeutic plasma and tissue concentrations. The pharmacokinetic advantage of IV dosing in this context is the elimination of the absorption phase associated with subcutaneous injection, allowing immediate delivery to cardiac tissue during the critical window of reperfusion injury.

Timing Considerations#

The timing of elamipretide administration relative to reperfusion was a critical protocol element. Preclinical data demonstrated that maximal cardioprotection was achieved when SS-31 was present in cardiac mitochondria at the time of reperfusion. The protocol specified initiation of the IV infusion before balloon inflation or stent deployment to meet this pharmacological requirement.

Heart Failure with Reduced Ejection Fraction Protocol#

The Phase 2 trial in heart failure with reduced ejection fraction (HFrEF) evaluated subcutaneous elamipretide at 40 mg daily for 4 weeks. This study assessed the effects of SS-31 on cardiac function using imaging endpoints including left ventricular end-systolic volume, left ventricular end-diastolic volume, and ejection fraction.

The 4-week duration was selected as sufficient to detect changes in cardiac remodeling parameters while maintaining a manageable trial duration. The 40 mg daily dose matched the chronic dosing regimen used in the Barth syndrome program, providing consistency across the subcutaneous dosing program.

Primary Mitochondrial Myopathy Protocol#

The Phase 2 trial in primary mitochondrial myopathy (PMM) used a different dosing approach: intravenous elamipretide at 0.25 mg/kg daily for 5 consecutive days. This short-duration, IV-based protocol was designed to evaluate whether rapid, sustained mitochondrial loading of SS-31 could produce measurable improvements in exercise capacity as assessed by the six-minute walk test.

The 5-day IV protocol was intended as a proof-of-concept approach to determine whether mitochondrial bioenergetic improvement could translate to functional benefit in a genetically heterogeneous patient population. The short duration limited the ability to assess longer-term adaptive responses that might require weeks to months of treatment.

Dose Rationale and Pharmacokinetic Basis#

The clinical doses of elamipretide were derived from preclinical pharmacokinetic-pharmacodynamic modeling. Key considerations in dose selection included the following factors.

SS-31 concentrates more than 1,000-fold within the inner mitochondrial membrane relative to cytoplasmic concentrations. This means that relatively modest plasma concentrations can achieve therapeutically relevant mitochondrial concentrations. The 40 mg subcutaneous dose produces plasma concentrations that, based on the known partitioning ratio, are expected to result in sustained cardiolipin-saturating concentrations within mitochondria over the 24-hour dosing interval.

The elimination half-life of approximately 3 to 4 hours following subcutaneous administration means that plasma levels fluctuate over the dosing interval. However, because SS-31 binds to cardiolipin within the inner mitochondrial membrane, the effective tissue residence time may exceed the plasma half-life. The mitochondrial compartment serves as a reservoir that buffers against the decline in plasma concentrations between doses.

Dosing Summary Table#

Related Reading#

• SS-31 overview and research guide
• SS-31 side effects profile
• SS-31 research evidence