Effective Dosing of Burosumab in XLH

X-linked hypophosphataemia (XLH) is a rare, hereditary condition. The genetic defect leads to low blood phosphate levels and vitamin D suppression. Phosphate is required for strong bones and teeth and to store energy in cells. Low phosphate leads to soft bones (rickets). Patients experience bowed legs, short stature, bone pain and dental pain. Prior to Burosumab, conventional treatment of XLH previously consisted of two medications. On this regimen, patients take oral phosphate supplements 4-6 times a day and an active form of vitamin D daily. This treatment can leave patients with residual symptoms. They report significant disabilities and reduced quality of life. Burosumab (Crysvita, Kyowa Kirin) is now the standard paediatric treatment for XLH. It is given once a fortnight by injection under the skin. Early studies used a starting dose of 0.4mg/kg per dose. NICE recommends a starting dose of 0.4mg/kg, a normal maintenance dose of 0.8mg/kg and a maximum of 2mg/kg (up to 90mg). The British National Formulary for Children (BNFC) gives the same advice. However, the European Medicines Agency recommends a starting dose of 0.8mg/kg per dose which is, therefore, the standard starting dose now. Some patients achieve symptom and biochemical control on less than 0.8 mg/kg per dose. They may be exposed to higher doses than necessary. To date, approximately 200 patients have started on Burosumab in England. They are all managed by specialist centres. The rare status of XLH means there are relatively few patients in each centre. Treatment effects and trends can only be described by collating data from multiple centres. The investigators will undertake a review across multiple English centres of the doses of Burosumab. The review will only collect data already in the patients' health records. It will look at factors affecting the starting dose. The investigators will assess the association between dose, blood markers and growth.

NCT Number	NCT07183579
Lead Sponsor	University of Nottingham Collaborators: Nottingham University Hospitals NHS Trust, Birmingham Women's and Children's NHS Foundation Trust, University Hospitals Bristol and Weston NHS Foundation Trust, University Hospital Southampton NHS Foundation Trust, Sheffield Children's NHS Foundation Trust, Manchester University NHS Foundation Trust, Newcastle-upon-Tyne Hospitals NHS Trust, Alder Hey Children's NHS Foundation Trust
Conditions	X-linked Hypophosphatemia (XLH)
Enrollment	120 participants
Start Date	2025-11-03
Primary Completion	2026-07-01 (estimated)
Study Completion	2026-07-01 (estimated)
Updated on ClinicalTrials.gov	2026-05-11