Burosumab was found to be superior to conventional therapy of oral phosphate and active vitamin D in children with X-linked hypophosphatemia (XLH), according to an abstract presented at the Endocrine Society’s Annual Meeting, ENDO 2019, held March 23-26, in New Orleans, Louisiana.1

In this phase 3, multicenter, international study (ClinicalTrials.gov identifier: NCT02915705), 61 children (ages 1-12 years) with XLH were randomly assigned 1:1 to receive either subcutaneous burosumab (n = 29) starting at 0.8 mg/kg every 2 weeks or to continue with conventional oral phosphate/vitamin D treatment (n = 32) titrated and individualized for each patient. The primary end point was healing of rickets at 40 weeks, as assessed by radiologists using the Radiographic Global Impression of Change (RGI-C) scale. All pediatric radiologists were blinded to treatment.

While rickets improved in both groups at week 40, RGI-C score was significantly higher with burosumab vs conventional therapy (mean change ± standard error: +1.9 ± 0.1 vs +0.8 ± 0.1; P <.0001). RGI-C scores also showed substantial healing of rickets (RGI-C ≥+2.0) in more children receiving burosumab vs conventional therapy (72% vs 6%; P <.0001).

In addition, improvement in the RGI-C lower limb deformity score was greater with burosumab vs conventional therapy (mean ± standard error: +0.62 ± 0.12 vs +0.21 ± 0.12; P =.02). Participants treated with burosumab showed greater improvements in height and mobility as measured by a 6-minute walking test and had larger increases in serum phosphorus and active vitamin D levels.

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There were 4 serious adverse events (3 in the burosumab group, 1 in the conventional therapy group) but none were related to treatment and all resolved. The study drug was not discontinued in either group.

“We now know the magnitude of benefit from the new medication, burosumab, versus the prior approach with conventional therapy,” said study principal investigator Erik Imel, MD, associate professor of medicine and pediatrics at Indiana University School of Medicine, Indianapolis, in a press release.2 “This information is critical for doctors making treatment decisions for their patients with XLH.”

Burosumab is the first approved medication by the United States Food and Drug Administration for the treatment of XLH.3

Ultragenyx Pharmaceutical Inc. funded the study in partnership with Kyowa Kirin International of Japan.

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References

1. Imel EA, Whyte MP, Munns CF, et al. Burosumab resulted in greater improvement in rickets than conventional therapy in children with X-linked hypophosphatemia (XLH). Presented at: ENDO 2019; March 23-26, 2019; New Orleans, LA. Abstract OR13-2.

2. Genetic rickets improves more with burosumab than standard care, study finds [press release]. Washington, DC: Endocrine Society; March 24, 2019. Accessed March 24, 2019.

3. FDA approves first therapy for rare inherited form of rickets, x-linked hypophosphatemia [press release]. Silver Spring, MD: US Food and Drug Administration; April 17, 2018. https://www.fda.gov/newsevents/newsroom/pressannouncements/ucm604810.htm. Accessed March 24, 2019.