Stealth BioTherapeutics, a clinical-stage biopharmaceutical company developing therapeutics to treat mitochondrial dysfunction, announced that the FDA Office of Orphan Products Development (OOPD) has granted Orphan Drug Designation to Stealth's investigational drug candidate, elamipretide, for the treatment of patients with primary mitochondrial myopathy (PMM).

"We are thrilled to achieve this key regulatory milestone for the treatment of PMM, a debilitating condition characterized by muscle weakness and fatigue with no FDA-approved treatments," said Reenie McCarthy, Stealth's chief executive officer. "We will continue to work closely with the FDA as we advance into our phase III trial of elamipretide in patients with PMM." 

The Orphan Drug Act was enacted in 1983 to encourage development of drugs for rare diseases, which are diseases that affect fewer than 200,000 persons in the United States. Once granted, Orphan Drug Designation provides various development benefits for an investigational drug, including seven-year exclusivity after marketing approval is received.

In June 2017, Stealth announced results from MMPOWER-2, a phase II continuation trial evaluating safety, tolerability and efficacy of treatment with elamipretide for PMM, which showed benefit of elamipretide across multiple endpoints assessed and supports a phase III trial in this patient population. Stealth is currently recruiting for the RePOWER trial, an observational study of patients with PMM. Patients enrolled in RePOWER may have the opportunity to participate in the phase III trial to further evaluate the potential efficacy, safety and tolerability of elamipretide for patients with PMM.