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By Bronwyn Mixter
Oct. 26 — The FDA Oct. 23 approved Strensiq (asfotase alfa) as the first treatment for perinatal, infantile and juvenile-onset hypophosphatasia (HPP).
HPP is a rare, genetic, progressive, metabolic disease in which patients experience devastating effects on multiple systems of the body, leading to severe disability and life-threatening complications, the agency said. It is characterized by defective bone mineralization that can lead to rickets and softening of the bones that results in skeletal abnormalities. It also can cause complications such as profound muscle weakness with loss of mobility, seizures, pain, respiratory failure and premature death.
Strensiq is administered via injection three or six times per week, the FDA said. It works by replacing the enzyme (known as tissue-nonspecific alkaline phosphatase) responsible for forming an essential mineral in normal bone, which has been shown to improve patient outcomes. Strensiq is manufactured by Alexion Pharmaceuticals Inc., which is based in Cheshire, Conn.
Alexion said in a statement that Strensiq will be available commercially by Oct. 27.
“For the first time, the HPP community will have access to an approved therapy for this rare disease,” said Amy G. Egan, deputy director of the Office of Drug Evaluation III in the FDA's Center for Drug Evaluation and Research (CDER). “Strensiq's approval is an example of how the breakthrough therapy designation program can bring new and needed treatments to people with rare diseases.”
Strensiq received a breakthrough therapy designation as it is the first and only treatment for perinatal, infantile and juvenile-onset HPP, the agency said. The designation, enacted as part of the FDA Safety and Innovation Act of 2012 (FDASIA), is intended to facilitate and expedite the development and review of drugs for serious or life-threatening conditions.
The agency also said it granted orphan drug designation to Strensiq because it treats a disease affecting fewer than 200,000 patients in the U.S. Orphan drug designation provides financial incentives, like clinical trial tax credits, user fee waivers and eligibility for market exclusivity to promote rare disease drug development.
Also, Strensiq was granted priority review, which is granted to drug applications that show a significant improvement in safety or effectiveness in the treatment of a serious condition.
Alexion also was granted a rare pediatric disease priority review voucher for the drug.
FDASIA created the program under which a sponsor who receives an approval for a drug or biologic to treat or prevent a rare pediatric disease may, if the statute's criteria are met, qualify for a voucher that can be used to receive a priority review for a subsequent marketing application for a different product. These vouchers can be sold or transferred for use to another sponsor any number of times before the voucher is used, as long as the sponsor making the transfer hasn't yet submitted the application.
The FDA said development of Strensiq was supported in part by the FDA Orphan Products Grants Program, which provides grants for clinical studies on safety and/or effectiveness of these products.
The safety and efficacy of Strensiq were established in 99 patients with perinatal (disease occurs in utero and is evident at birth), infantile-onset or juvenile-onset HPP who received treatment for up to 6.5 years during four prospective, open-label studies, the agency said. Study results showed that patients with perinatal-onset and infantile-onset HPP treated with Strensiq had improved overall survival and survival without the need for a ventilator (ventilator-free survival).
Ninety-seven percent of treated patients were alive at one year old compared to 42 percent of control patients selected from a “natural history study group,” the FDA said. Similarly, the ventilator-free survival rate at one year old was 85 percent for treated patients compared to less than 50 percent for the natural history control patients.
Patients with juvenile-onset HPP treated with Strensiq showed improvements in growth and bone health compared to control patients selected from a natural history database, the agency said. All treated patients had improvement in low weight or short stature or maintained normal height and weight. In comparison, about 20 percent of control patients had growth delays over time, with shifts in height or weight from the normal range for children their age to heights and weights well below normal for their age.
Juvenile-onset patients also showed improvements in bone mineralization, as measured on a scale that evaluates the severity of rickets and other HPP-related skeletal abnormalities based on X-ray images, the agency said. All treated patients demonstrated substantial healing of rickets on X-rays while some natural history control patients showed increasing signs of rickets over time.
The FDA said the most common side effects in patients treated with Strensiq include injection site reactions, hypersensitivity reactions (such as difficulty breathing, nausea, dizziness and fever), lipodystrophy (a loss of fat tissue resulting in an indentation in the skin or a thickening of fat tissue resulting in a lump under the skin) at the injection site and ectopic calcifications of the eyes and kidney.
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