burosumab
Crysvita (burosumab) is a monoclonal antibody from Kyowa Kirin that neutralises FGF23, the hormone that wastes phosphate through the kidneys. By restoring phosphate balance it treats X-linked hypophosphataemia and tumour-induced osteomalacia, conditions that weaken bones.
This page is based on FDA prescribing information and the EMA medicine record for burosumab, cross-checked with DailyMed and the National Cancer Institute dictionary; the mechanism is explained in plain language, and analogies are used only where they stay accurate.
How it works
Explains what the medicine does in the body, not dosing, side effects, or safety.
An analogy
In these diseases a faulty signal, FGF23, keeps opening the drain plug in the kidneys so phosphate, the building material for bone, pours out with the urine. Burosumab is a cap that fits over the signal and silences it, the plug closes, phosphate stays in the blood, and bones can harden again.
In simple terms
Phosphate is a mineral the body needs to build strong bones. In X-linked hypophosphataemia and tumour-induced osteomalacia, too much of the hormone FGF23 makes the kidneys discard phosphate, so bones stay soft and painful. Burosumab is an antibody that binds FGF23 and stops it working. The kidneys then reabsorb phosphate, blood levels rise, and bones can mineralise normally.
In depth
Burosumab is a recombinant fully human IgG1 monoclonal antibody that binds FGF23 with high affinity, blocking its interaction with FGFR-Klotho receptor complexes in the renal tubule. This restores expression of sodium-phosphate cotransporters, increasing tubular phosphate reabsorption, and raises 1,25-dihydroxyvitamin D production by lifting FGF23-mediated suppression of 1-alpha hydroxylase. The combined effect normalises serum phosphate and supports bone mineralisation in XLH and TIO.
See it in motion
A schematic animation of the mechanism — simplified for clarity, not drawn to scale.
Burosumab is a cap that fits over the signal and silences it, the plug closes, phosphate stays in the blood, and bones can harden again.
- Phosphate is a mineral the body needs to build strong bones.
- In X-linked hypophosphataemia and tumour-induced osteomalacia, too much of the hormone FGF23 makes the kidneys discard phosphate, so bones stay soft and painful.
- Burosumab binds FGF23 and stops it working.
- The kidneys then reabsorb phosphate, blood levels rise, and bones can mineralise normally.
Target: Fibroblast growth factor 23 (FGF23)
A hormone that tells the kidneys to excrete phosphate and suppresses active vitamin D; when it is in excess, the body loses phosphate and bones cannot mineralise properly.
Approved uses
Approved uses differ by country and change over time. Always follow your local prescribing information.
Approved uses in United States
FDA- Treatment of X-linked hypophosphatemia (XLH) in adults and children 6 months of age and older
- Treatment of FGF23-related hypophosphatemia in tumor-induced osteomalacia (TIO) associated with phosphaturic mesenchymal tumors that cannot be curatively resected or localized, in adults and children 2 years of age and older
Approved uses in European Union
EMA- Treatment of X-linked hypophosphataemia in children and adolescents aged 1 to 17 years with radiographic evidence of bone disease, and in adults
- Treatment of FGF23-related hypophosphataemia in tumour-induced osteomalacia associated with phosphaturic mesenchymal tumours that cannot be curatively resected or localised, in children and adolescents aged 1 to 17 years and in adults
Official sources
The statements on this page trace back to these records.
- Crysvita (burosumab) — Summary of product characteristics and package leaflet, English version
European Medicines Agency
- DailyMed: Crysvita (burosumab) label
DailyMed, U.S. National Library of Medicine
- U.S. Food and Drug Administration: burosumab prescribing information
U.S. Food and Drug Administration
- National Cancer Institute: burosumab
National Cancer Institute
This page explains how the medicine works — it isn’t the patient leaflet. For anything that applies to you, read the leaflet that came with your medicine or ask your pharmacist.
MedUnfold provides educational content and is not medical advice. Always follow your local prescribing information and healthcare professional.