FDA Okays Asfotase Alfa (Strensiq) for Rare Bone Disorder

October 23, 2015

The US Food and Drug Administration (FDA) today approved asfotase alfa (Strensiq, Alexion Pharmaceuticals) as the first-ever therapy for patients who develop hypophosphatasia, a rare metabolic bone disorder, in childhood.

Caused by mutations in the alkaline phosphatase gene, hypophosphatasia is a hereditary and potentially life-threatening condition characterized by early loss of teeth, malformed bones, and frequent bone fractures. Complications include profound muscle weakness that can lead to respiratory failure and premature death.

The FDA said in a news release that severe forms of hypophosphatasia affect an estimated 1 in 100,000 newborns per year. Milder cases, which may emerge as late as adulthood, can occur more frequently, according to the agency.

Current treatments, which are merely supportive, include plaster casts for broken bones, calcium supplements, and painkillers.

Asfotase alfa replaces the defective alkaline phosphatase enzyme to improve bone health. Patients receive three to six injections of the drug each week.

The FDA determined that asfotase alfa was safe and effective based on four prospective, open-label studies involving 99 patients who developed hypophosphatasia in utero, as an infant, or as a juvenile. They received the drug for up to 6.5 years. Patients with either perinatal or infant onset of the disease who were treated with asfotase alfa showed improvement in overall survival as well as ventilator-free survival. Ninety-seven percent of patients receiving the drug were alive at 1 year of age compared with 42% of control patients selected from a natural history study group. The ventilator-free survival rates for both groups followed much the same pattern.

The FDA said that patients with juvenile onset of hypophosphatasia experienced improved growth and bone health compared with patients in a natural history database.

Injection-site reactions, hypersensitivity reactions such as difficulty breathing and nausea, lipodystrophy at the injection site, and ectopic calcifications of the eyes and kidneys were among the most common adverse events.

In 2013, the FDA granted asfotase alfa its "breakthrough therapy" designation, designed to speed up the development and approval of new drugs for serious or life-threatening diseases. The drug also was designated an orphan drug, a status that gives manufacturers economic benefits to make commercializing a product for a small number of patients more feasible.

Following a positive recommendation from the European Medicines Agency, the European Commission approved asfotase alfa for hypophosphatasia in September.

More information on today's FDA decision is available on the agency's website.


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