Table 1.

Summary of the use of burosumab solution for injection (Crysvita^®) in the treatment of X-linked hypophosphatemia in adults and pediatric patients aged ≥ 1 year in the USA [5]

How is burosumab available, what is its route of administration, how should it be stored?
Availability	Single-dose vials containing 10, 20 or 30 mg of burosumab in 1 mL of solution for injection
Administration route	Subcutaneous injection into upper arms or thighs, buttocks, or any quadrant of abdomen; rotate injection site with each injection
Storage	Refrigerate at 2–8 °C (36–46 °F) in the original package (to protect from light)
What steps need to be taken prior to initiating treatment with burosumab?
1 week prior to initiation: discontinue the use of oral phosphate and active vitamin D analogs (concomitant use of such agents with burosumab is contraindicated due to the ↑ risk of hyperphosphatemia and hypercalcemia)
Measure fasting serum phosphorus: should be < RRA prior to initiation (the use of burosumab is contraindicated if the level is ≥ RRA)
How should the dosage of burosumab be determined in pediatric patients (aged ≥ 1 to <18 years)?
Starting dosage	0.8 mg/kg rounded to the nearest 10 mg (minimum 10 mg; maximum 90 mg) every 2 weeks
Monitor fasting serum phosphorus levels	Measure every 4 weeks during the first 3 months of treatment, and thereafter as appropriate (including 4 weeks after any dosage adjustment)
Dosage adjustment based on fasting serum phosphorus levels	Serum phosphorus > the lower limit of RRA and < 5 mg/dL: no dosage change needed
	Serum phosphorus < RRA: ↑ dosage stepwise to ≈ 2 mg/kg (maximum 90 mg) every 2 weeks
	Serum phosphorus > 5 mg/dL: withhold the next dose and assess serum phosphorus in 4 weeks; once serum phosphorus is < RRA, restart burosumab at a ↓ dosage than previously received; reassess in 4 weeks and adjust as required
	Do not adjust dosage more frequently than every 4 weeks
How should the dosage of burosumab be determined in adult patients (aged ≥ 18 years)?
Starting dosage	1 mg/kg rounded to the nearest 10 mg (maximum dose 90 mg) administered every 4 weeks
Monitor fasting serum phosphorus levels	Measure 2 weeks post-dose on a monthly basis for the first 3 months of treatment, and thereafter as appropriate (including 2 weeks after any dosage adjustment)
Dosage adjustment based on fasting serum phosphorus levels	Serum phosphorus within normal range: no dosage change needed
	Serum phosphorus > normal range: withhold the next dose and assess serum phosphorus in 4 weeks; once serum phosphorus is < normal range, restart burosumab at ≈ 50% of the dosage previously received (maximum 40 mg every 4 weeks); reassess in 2 weeks and adjust as required
	Do not adjust dosage more frequently than every 4 weeks
How should burosumab be used in special populations?
Women of child-bearing potential	Monitor serum phosphorus levels throughout pregnancy (lack of human data regarding risks)
Breast-feeding women	Consider the benefits of breastfeeding, the mother’s clinical need for treatment, and the potential adverse effects on the breastfed infant from burosumab or XLH (lack of data regarding risks)
Patients with renal impairment	Severe or end-stage renal disease: use is contraindicated
What other precautions should be taken with burosumab?
Hyperphosphatemia	Serum phosphorus levels > ULN may ↑ the risk of nephrocalcinosis: interrupt treatment and/or ↓ dosage
Serious hypersensitivity or injection-site reactions	Discontinue burosumab and initiate appropriate medical treatment
Restless leg syndrome	Advise patients to contact their physician if symptoms of restless leg syndrome occur or worsen

RRA reference range for age, ULN upper limit of normal, XLH X-linked hypophosphatemia, ↑ increase(d) greater, ↓ reduce/lower