A biotech company developing a Duchenne muscular dystrophy drug has suffered a setback with the U.S. Food and Drug Administration. The company in trouble is Santhera Pharmaceuticals (SANN.SW), not Sarepta Therapeutics (SRPT - Get Report) , so breathe.

Santhera's timetable to seek approval in the U.S. for its Duchenne drug Raxone is now pushed back to 2020 after the FDA said a second, successful phase III study will be required, the company said Thursday.

The company had hoped to persuade the FDA to accept an accelerated approval filing for Raxone based on a single, already completed phase III study. After meeting with Santhera, however, the FDA turned down the company's request.

Santhera intends to start enrolling Duchenne patients into the second phase III study soon, but doesn't anticipated having results until the second half of 2019.

European regulators are reviewing Raxone based on the single, phase III study, with an approval decision likely early next year.

Santhera shares are down 38% on the Swiss stock exchange in Thursday trading.

Raxone, also known as idebenone, is a pill designed to stimulate mitochondria, the energy-producing organelle found inside cells. Santhera is developing Raxone to improve the lung function of Duchenne patients. The progressive weakening of muscles in the chest of Duchenne patients leads to respiratory disease and breathing problems.

Santhera's focus with Raxone is symptomatic improvement for Duchenne patients. The drug isn't intended to be disease modifying like the "exon skipper" eteplirsen being developed Sarepta. But eteplirsen is suitable only in patients with a specific genetic mutation, where Raxone has the potential to benefit all Duchenne patients and could be used in combination with disease-modifying drugs, if approved.

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