Ultragenyx Pharmaceutical has won FDA approval for its enzyme replacement therapy Mepsevii™ (vestronidase alfa), the first treatment authorized by the agency for children and adults with mucopolysaccharidosis VII (MPS VII).

Mepsevii is an enzyme-replacement therapy designed to replace the deficient lysosomal enzyme beta-glucuronidase in patients with MPS VII, a rare genetic metabolic lysosomal storage disorder (LSD) caused by the deficiency of beta-glucuronidase.

MPS VII—which according to the FDA affects fewer than 150 patients worldwide—is also called Sly syndrome, for William Sly, M.D., who originally described the condition in 1972.

Mepsevii is the first approved treatment for Ultragenyx, a biopharma focused on developing products to treat rare and ultrarare diseases.

“The approval of Mepsevii is a pivotal moment for Ultragenyx and for patients suffering from ultrarare genetic diseases for which the investment and development of treatments has not happened yet,” Ultragenyx CEO and president Emil D. Kakkis, M.D., Ph.D., said yesterday in a statement. “Our development program sought to create a new paradigm in study design and endpoint evaluations to help accommodate the difficulties of studying extremely heterogeneous ultrarare diseases to fulfill the promise that the science we have all invested in over many years actually becomes something available for patients.”

Mepsevii won FDA approval following Priority Review, reserved for drugs deemed to offer major advances in treatment or provide a treatment where no adequate therapy exists.

23 Patients Enrolled

The FDA said it based its approval of Mepseviion clinical studies and expanded access protocols enrolling a total of 23 patients ranging from 5 months to 25 years of age. Patients received treatment with Mepsevii at doses up to 4 mg/kg once every two weeks for up to 164 weeks.

Efficacy was primarily assessed via the six-minute walk test in 10 patients who could perform the test. After 24 weeks of treatment, the mean difference in distance walked relative to placebo was 18 meters. Additional follow-up for up to 120 weeks suggested continued improvement in three patients and stabilization in the others. Two patients in the Mepsevii development program experienced marked improvement in pulmonary function.

The most common side effects after treatment with Mepsevii include infusion site reactions, diarrhea, rash, and anaphylaxis, the FDA added.

Ultragenyx has cautioned that the effect of Mepsevii on the central nervous system manifestations of MPS VII has not been determined.

“This approval underscores the agency’s commitment to making treatments available to patients with rare diseases,” Julie Beitz, M.D., director of the Office of Drug Evaluation III in the FDA’s Center for Drug Evaluation and Research (CDER), said in a separate statement issued by the agency. “Prior to today’s approval, patients with this rare, inherited condition had no approved treatment options.”

With its approval, the FDA issued a Rare Pediatric Disease Priority Review Voucher that confers priority review to a subsequent drug application that would not otherwise qualify for such status. The rare pediatric disease review voucher program is designed to encourage development of new drugs and biologics for the prevention or treatment of rare pediatric diseases.

Ultragenyx said Mepsevii will be available to U.S. patients later this month. The price of Mepsevii has not been disclosed—but has been projected publicly to run as high as $400,000 annually.

To support Mepsevii patients, Ultragenyx said, it has launched its UltraCare™ service for patients and caregivers, and will help patients obtain coverage and assist with financial support for both medication and administration of medication.

Ultragenyx is awaiting European Medicines Agency (EMA) review of its marketing authorization application for the enzyme-replacement therapy under the name vestronidase alfa. An opinion from the EMA’s Committee for Medicinal Products for Human Use (CHMP) is expected in the first half of 2018.


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