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X-linked hypophosphataemia Clinical criteria: Treatment Phase: Initial treatment - New patient Patient must have a documented confirmation of PHEX pathogenic variant; OR Patient must have a confirmed diagnosis of X-linked hypophosphataemia demonstrated by the presence of all of the following: (i) a serum phosphate concentration below the age adjusted lower limit of normal; (ii) current or historical (for those with growth plate fusion) radiographic X-ray evidence of rickets; (iii) elevated (or inappropriately normal) serum or plasma FGF-23 levels of above the mean of the assay-specific reference range; (iv) renal phosphate wasting demonstrated by a ratio of tubular maximum reabsorption rate of phosphate to glomerular filtration rate (TmP/GFR) according to age specific normal ranges using the second morning urine void and paired serum sample measuring phosphate and creatinine. Treatment criteria: Must be treated by a medical practitioner identifying as at least one of the following specialists: (i) paediatric endocrinologist, (ii) paediatric nephrologist, (iii) endocrinologist, (iv) nephrologist. At the time of authority application, medical practitioners must request the appropriate number of vials of appropriate strength(s) to provide sufficient drug, based on the weight of the patient, adequate for 4 weeks, according to the specified dosage in the approved Product Information (PI). A separate authority prescription form must be completed for each strength requested. Up to a maximum of 5 repeats will be authorised. Confirmation of eligibility for treatment with diagnostic reports must be documented in the patient's medical records.
“Burosumab is a recombinant human monoclonal IgG1 antibody that binds to and inhibits the biological activity of fibroblast growth factor 23 (FGF23), present in excess in X-linked hypophosphataemia.”
“The clearance of burosumab is dependent on body weight and estimated to be 0.278 l/day in a typical adult (70kg) XLH patient with corresponding disposition half-life (t 1/2 ) in the serum of approximately 18 days.”
A plain-language summary of the cited sources below. Informational only — not medical advice.
Here is a plain-language explainer for families and guardians about burosumab.
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Understanding Burosumab: A Guide for Families
This guide explains what burosumab is, how it works, and what to expect. It's important to remember that your child's doctor and healthcare team are your best source of information for your specific situation.
What is Burosumab?
Burosumab (often known by its brand name, Crysvita) is a prescription medicine used to treat a rare genetic condition called X-linked hypophosphataemia (XLH) .
People with XLH have a problem with a hormone called FGF23. Their bodies produce too much of it, which causes them to lose too much phosphate through their urine. Phosphate is a mineral that is essential for building strong bones and teeth. This loss of phosphate can lead to weak, soft bones (a condition called rickets in children and osteomalacia in adults), bone pain, and other problems.
Burosumab is also used to treat a similar phosphate-wasting condition called tumour-induced osteomalacia (TIO) in certain adults and children.
How Does Burosumab Work?
Think of the excess FGF23 hormone as a "blocker" that stops the kidneys from keeping phosphate in the body. Burosumab is a type of medicine called a monoclonal antibody.
It works like a "key" that finds and sticks to the FGF23 "blocker." By doing this, it stops FGF23 from working. This allows the kidneys to do their job properly and keep more phosphate in the blood, which helps to build stronger bones.
How is it Given?
Burosumab is not a pill. It is given as an injection under the skin (subcutaneously), usually in the stomach, thigh, or upper arm. This is often done by a parent or caregiver after training from a healthcare professional.
- Dosing Schedule: The injections are typically given once every two weeks for children, and once every four weeks for adults. Your doctor will determine the exact dose and schedule. - Monitoring: Before each dose, your doctor will likely order a blood test to check the phosphate level. The dose of burosumab may be adjusted based on these results.
A plain-language summary of the cited sources below. Informational only — not medical advice.
Here is a clinical summary framing for prescribers based on the provided source facts.
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Clinical Summary: Burosumab (FGF23 Inhibitor)
Executive Summary for Prescribers
Burosumab is a targeted therapy for FGF23-mediated hypophosphataemia. It is a recombinant human monoclonal antibody that binds and inhibits Fibroblast Growth Factor 23 (FGF23), thereby increasing serum phosphate and improving bone mineralisation. It is indicated for X-linked hypophosphataemia (XLH) and select cases of tumour-induced osteomalacia (TIO). Prescribing requires careful patient selection due to contraindications and the need for monitoring of phosphate, calcium, and parathyroid hormone levels.
Mechanism and Pharmacokinetics
Burosumab directly addresses the underlying pathophysiology of XLH by inhibiting the excess biological activity of FGF23. This action restores renal phosphate reabsorption and increases serum 1,25-dihydroxyvitamin D levels. With a half-life of approximately 18 days, burosumab allows for a convenient dosing schedule (typically every 2 or 4 weeks). Its clearance is weight-dependent.
Indications
Burosumab is indicated for the treatment of: - X-linked hypophosphataemia (XLH) in adults, adolescents, and children aged 1 year and older. - FGF23-related hypophosphataemia in tumour-induced osteomalacia (TIO) associated with phosphaturic mesenchymal tumours that cannot be curatively resected or localised, in adults, adolescents, and children aged 1 year and older.
Key Prescribing Considerations
- Contraindications: - Hypersensitivity to the active substance or excipients. - Concurrent administration with oral phosphate and/or active Vitamin D analogues. These must be discontinued prior to initiating burosumab. - Serum phosphate level within or above the normal range for age at initiation. - Severe renal impairment or end-stage renal disease.
- Dosing and Administration: Administer as a subcutaneous injection. Dosing is weight-based and titrated to target serum phosphate levels within the normal range for age. Adherence to the dosing schedule is important for efficacy.
Curated subset. The full adverse-effect list is in the TGA Product Information; click any citation above to open it.
What Are the Common Side Effects?
Many children and adults experience side effects, but not everyone does. The most common ones include:
- Injection site reactions: Redness, swelling, or pain where the needle went in (this is very common, affecting more than half of patients). - Cough - Headache - Fever (pyrexia) - Pain in the arms or legs
These are often manageable. You should always tell your doctor about any side effects your child experiences.
What Are the Serious Risks?
While rare, burosumab can cause serious side effects that need medical attention. Your doctor will monitor for these.
- High levels of calcium in the blood or urine (Hypercalcaemia / Hypercalciuria): This can happen if phosphate levels get too high. It can cause symptoms like nausea, vomiting, confusion, or kidney problems. - High levels of phosphate in the blood: This is why blood tests before each dose are so important. - Hyperparathyroidism: A condition where the parathyroid glands become overactive. - Septic shock: A severe, life-threatening reaction to infection. This is a medical emergency. Seek help immediately if your child has signs of a severe infection, such as high fever, difficulty breathing, confusion, or a rapid heartbeat.
Important Warnings
- Do Not Take With Certain Other Medicines: Burosumab must
- Monitoring: Before and during treatment, closely monitor: - Serum Phosphate: To assess efficacy and guide dose titration. It is contraindicated to start if phosphate is already normal or high. - Parathyroid Hormone (PTH), Calcium, and Alkaline Phosphatase: To monitor for hyperparathyroidism and hypercalcaemia/hypercalciuria, which are identified serious risks. - Renal Function: As the drug is contraindicated in severe renal impairment.
Safety Profile
- Common Adverse Effects (≥40% incidence): Injection site reactions, cough, headache, pyrexia, and pain in extremity. These are generally manageable and should be discussed with patients.
- Serious Adverse Effects: Prescribers must be vigilant for the following: - Hyperparathyroidism, Hypercalcaemia, and Hypercalciuria: Require monitoring of PTH and calcium levels as part of the treatment plan. - Blood Phosphorus Increased: Reinforces the need for careful dose titration and monitoring. - Septic Shock: While noted, its frequency is not specified; prescribers should