The Food and Drug Administration (FDA) has approved Crysvita (burosumab-twza; Ultragenyx and Kyowa Kirin) as the first treatment for patients aged ≥1 year with x-linked hypophosphatemia (XLH). 

XLH is a rare, inherited form of rickets that causes low levels of serum phosphorous. Crysvita, a recombinant fully human monoclonal IgG1 antibody, works by blocking fibroblast growth factor 23 (FGF23), a hormone that causes phosphate urinary excretion and suppresses vitamin D production by the kidney. This results in increased phosphate reabsorption from the kidney and increased vitamin D production, enhancing intestinal absorption of phosphate and calcium. 

The FDA approval was supported by data from 2 pediatric studies (Study CL201 [N=52] and Study CL205 [N=13]), 2 adult studies (Study CL303 [N=134] and an open-label bone biopsy study [N=14]). In the placebo-controlled trial, 94% of adults who received Crysvita once monthly achieved normal phosphorous levels vs 8% of adults who received placebo. Normal phosphorous levels were achieved in 94–100% of pediatric patients who received Crysvita every 2 weeks. X-ray findings associated with XLH improved with Crysvita in both adults and children. The study data, when compared to a natural history cohort, further confirmed the efficacy of Crysvita.

Back pain, headache, restless leg syndrome, decreased vitamin D, dizziness, and constipation were the most frequent adverse reactions among adults, while headache, injection site reaction, vomiting, decreased vitamin D, and pyrexia were the most frequent adverse reactions among children. 

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The FDA had previously granted Crysvita a Breakthrough Therapy designation and an Orphan Drug designation. 

Crysvita will be available as 10mg/mL, 20mg/mL, and 30mg/mL strength solutions for subcutaneous (SC) injection in single-dose vials. 

For more information call (888) 756-8657 or visit