June 18, 2020
The U.S. FDA has approved a new indication for Crysvita® (burosumab), manufactured by Ultragenyx and Kyowa Kirin. The drug is now indicated to treat patients who are at least two years of age and have FGF23-related hypophosphatemia in tumor-induced osteomalacia (TIO) associated with phosphaturic mesenchymal tumors that cannot be curatively resected or localized. Crysvita is the first and only therapy granted FDA approval specifically for the treatment of TIO.
TIO is a rare bone disease caused by slow-growing tumors that produce an excess of fibroblast growth factor 23 (FGF23), a hormone-like substance that regulates phosphate levels in the body. Normal phosphate levels help to maintain bone health. Although TIO tumors are usually benign, the extra FGF23 they produce causes low phosphate levels. This in term causes osteomalacia, a pronounced softening of the bones, as well as bone lesions.
In clinical studies, up to 69% of patients who received Crysvita achieved normal phosphate levels through week 24 of treatment and maintained normal or near normal phosphate levels through week 88. Patient bone scans also suggested healing of osteomalacia-related bone lesions.
The recommended starting dose for pediatric patients is 0.4mg/kg of body weight (rounded to the nearest 10mg) administered once every two weeks. For adults, Crysvita should be initiated at a dose of 0.5mg/kg of body weight given once every four weeks. In both patient populations, the dosage can be increased to a maximum of 2mg/kg, not to exceed a total dose of 180mg, given once every two weeks. Crysvita is administered via subcutaneous injection by a healthcare provider.
First FDA approved in 2018, Crysvita is also indicated to treat X-linked hypophosphatemia (XLH) in patients who are at least six months of age.