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FDA Approves Strensiq for Rare Metabolic Disorder
The FDA has approved asfotase alfa (Strensiq, Alexion Pharmaceuticals), an injectable drug that treats an ultra-rare metabolic disorder that can result in skeletal abnormalities and severe disabilities.
According to The Wall Street Journal, asfotase alfa is the first approved treatment for perinatal, infantile, and juvenile-onset hypophosphatasia (HPP), a rare genetic disease that can result in skeletal abnormalities and severe disabilities. Severe HPP affects about one in 100,000 newborns, while milder cases happen in childhood or adulthood more frequently. The FDA had granted the drug a breakthrough therapy designation, which helps speed the review process for drugs that treat life-threatening conditions. Asfotase alfa was also granted an orphan drug designation. Approval of the medication was based on data from four clinical trials and supporting extension trials.
In patients (ages 1 day to 6.5 years) with perinatal/infantile-onset HPP, treatment with asfotase alfa resulted in a significant survival benefit compared with historical control patients with similar clinical characteristics. At week 48, the Kaplan-Meier estimate of overall survival was 97% for treated patients (n = 68) compared with 42% for historical control patients (n = 48). In addition, estimated invasive ventilator-free survival was 96% for treated patients (n = 54) compared with 31% for historical control patients (n = 48). Study results also demonstrated substantial improvements in the skeletal manifestations of HPP, as assessed by the Radiographic Global Impression of Change (RGI-C) scale, and improvements in height and weight, as measured by z-scores, in patients treated with asfotase alfa.
In patients (ages 6 to 12 years) with juvenile-onset HPP, treatment with asfotase alfa resulted in significant improvements in the skeletal manifestations of HPP at 24 weeks, as measured by RGI-C, compared with historical controls. Importantly, by month 54, 100% of asfotase alfa–treated juvenile-onset patients were responders to treatment (n = 8), as measured by substantial bone healing, compared with 6% of patients in the historical control group (n = 32) at last assessment.
In addition, patients treated with asfotase alfa had improvements in height and weight, as measured by z-scores, compared with untreated historical controls, as well as improvements in gait and mobility. By four years of treatment, 100% of patients assessed (n = 6) completed the six-minute walk test within the normal range for age-, sex-, and height-matched peers, whereas no patients were in the normal range at baseline.
The most commonly reported adverse events observed in clinical trials were injection-site reactions. Other common adverse reactions included lipodystrophy, ectopic calcifications, and hypersensitivity reactions.
Sources: Alexion, October 26, 2015; and The Wall Street Journal, October 24, 2015.