FDA approves Crysvita for X-linked hypophosphatemia.- Ultragenyx Pharma + Kyowa Kirin.

Ultragenyx Pharmaceutical, Kyowa Hakko Kirin Co, and Kyowa Kirin Int announced that the FDA has approved Crysvita (burosumab-twza) for the treatment of X-linked hypophosphatemia (XLH) in adult and pediatric patients one year of age and older. Crysvita is an antibody that blocks fibroblast growth factor 23 (FGF23), a hormone that causes phosphate urinary excretion and suppresses active vitamin D production by the kidney.

For the pediatric XLH population, the FDA approval is supported by 64-week data from Study CL201, a randomized, open-label study in 52 patients ages 5 to 12, which showed that treatment with Crysvita improved rickets, increased serum phosphorus levels, decreased serum alkaline phosphatase activity, and increased growth. The indication is also supported by 40-week data from Study CL205, an open-label study in 13 patients ages 1 to 4. In these patients, Crysvita improved rickets and lower-limb deformity, increased serum phosphorus levels and decreased serum alkaline phosphatase activity.

For the adult XLH indication, the FDA approval is supported by 24-week data from Study CL303, a randomized, double-blind, placebo-controlled study in 134 adult XLH patients. Crysvita treatment resulted in a higher proportion of patients achieving serum phosphorus levels above the lower limit of normal, and a higher rate of complete healing of active fractures and pseudofractures, compared to placebo. The adult indication is also supported by data from the 48-week, open-label, single-arm bone biopsy study in 14 adult XLH patients, which showed healing of osteomalacia as demonstrated by decreases in osteoid volume/bone volume, osteoid thickness and mineralization lag time.

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