US regulators have issued a green light for Marathon Pharmaceuticals' Emflaza to treat patients age five years and older with Duchenne muscular dystrophy (DMD), a rare genetic disorder affecting around 15,000 people in the country that causes progressive muscle deterioration and weakness.

Emflaza (deflazacort) is a corticosteroid that works by decreasing inflammation and reducing the activity of the immune system.

Corticosteroids are commonly used to treat DMD across the world, but Emflaza is the first to be approved by the US Food and Drug Administration specifically for the condition, following a fast-track designation and priority review.

"This is the first treatment approved for a wide range of patients with Duchenne muscular dystrophy," said Billy Dunn, director of the Division of Neurology Products in the FDA's Center for Drug Evaluation and Research. "We hope that this treatment option will benefit many patients with DMD."

Approval was based on data from 17 preclinical and clinical studies, including one involving 196 male patients who were five to 15 years old at the beginning of the trial with documented mutation of the dystrophin gene and onset of weakness before age five.

This trial showed that, at week 12, patients taking the drug had improvements in a clinical assessment of muscle strength across a number of muscles compared to those taking a placebo, while overall stability in average muscle strength was maintained through the end of study at week 52 in the deflazacort-treated patients.

On the safety side, the drug's profile is similar to that of other corticosteroids, the most common side effects including facial puffiness, weight gain, increased appetite, upper respiratory tract infection, cough, extraordinary daytime urinary frequency (pollakiuria), unwanted hair growth (hirsutism) and excessive fat around the stomach, the regulator noted.

"We are in a new era in the treatment of Duchenne muscular dystrophy. For the first time, patients in the US with Duchenne will have widespread access to an FDA approved medicine that is indicated for all genetic forms of the condition. We are pleased that this development will help patients with this disease stay stronger longer," said Timothy M. Cunniff, executive vice president, R&D, at Marathon. "This is only the first of our products to treat Duchenne muscular dystrophy and we are committed to serving this community of patients, researchers and advocates until a cure is found."

The firm said additional post-market research will be carried out to further advance the science of the drug and the care of patients with the condition. One planned study will look at various dosage regimens in younger patients to determine if earlier intervention is safe and effective and ultimately impacts the course of the disease. A second will examine various dosage regimens in non-ambulatory patients with Duchenne and characterise the pulmonary and cardiac effects of the drug.