Burosumab improves phosphate levels, rickets for children with X-linked hypophosphatemia
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Sustained burosumab therapy for more than 3 years for children with X-linked hypophosphatemia resulted in clinically meaningful improvements across several clinical outcomes and demonstrated an acceptable benefit-risk profile, data show.
The end-of-study results from the phase 2, open-label trial of burosumab-twza (Crysvita, Ultragenyx) for children aged 5 to 12 years with X-linked hypophosphatemia (XLH) is the longest treatment duration reported to date in this patient population, Agnès Linglart, MD, PhD, professor of pediatrics at the Bicêtre Paris Sud Paris Saclay University and Hospital in Paris, and colleagues wrote.
“Sustained burosumab treatment of children with XLH for 160 weeks improved phosphorus metabolism, rickets, leg deformities, mobility and growth, and decreased their pain scores,” the researchers wrote. “Improved rickets was first demonstrated radiographically after 40 weeks of burosumab therapy and was maintained through 160 weeks of treatment.”
After a 1-week washout period, researchers randomly assigned participants to
burosumab once every 2 weeks (n = 26) or once every 4 weeks (n = 26) for 64 weeks, with dosing titrated based on fasting serum phosphorus levels between baseline and week 16. From week 66 through week 160, all patients received burosumab once every 2 weeks.
Among 41 children with open distal femoral and proximal tibial growth plates from both treatment groups, total Rickets Severity Score significantly decreased by a least squares mean of 0.9 from baseline to week 160 (P < .0001). Fasting serum phosphorus level increases were sustained with burosumab therapy throughout the study, with an overall population mean of 3.35 mg/dL, within the pediatric normal range of 3.2 mg/dL to 6.1 mg/dL at week 160 (mean change from baseline, P < .0001). Most adverse events were mild to moderate.
“It should be noted that while burosumab was effective in improving phosphorus metabolism, improvement in some features of XLH may take longer than 160 weeks to be fully realized; consequently, the long-term data management plan is ongoing to explore such effects,” the researchers wrote. “For example, standing height z score improved significantly at 160 weeks compared with baseline, but the changes were modest.”
The researchers noted that improvements associated with burosumab administration continued at week 160, suggesting that early XLH diagnosis and treatment can improve outcomes.
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