Burosumab (Crysvita) is a fibroblast growth factor 23 (FGF-23) blocking antibody that binds to and inhibits the biological activity of FGF-23, restores renal tubular reabsorption of phosphate, and increases serum concentration of 1,23-dihydroxyvitatmin D for patients with X-linked hypophosphatemia (XLH). Burosumab is supplied in single-use vials of 10 mg/mL, 20 mg/mL, and 30 mg/mL for subcutaneous administration. The recommended starting dose regimen for pediatric patients is 0.8 mg/kg of body weight rounded to the nearest 10 mg and administered every two weeks. The recommended dose regimen in adults is 1 mg/kg of body weight rounded to the nearest 10 mg and administered every four weeks. Fasting serum phosphorus should be measured every four weeks for the first three months and thereafter, as appropriate. In pediatric patients, if serum phosphorous is below the expected reference range for age, the dose may be increased stepwise in 0.4 mg/kg intervals up to a maximum of 2 mg/kg administered every two weeks. In both pediatric and adult patients, if the serum phosphorus level is above the reference range for age, the dose of burosumab should be withheld, with serum phosphorus levels reassessed four week later. Once serum phosphorus levels are below the reference range for age, burosumab may be restarted at half the dose level that was previously administered, with serum phosphorus levels reassessed every two weeks or four weeks after dose adjustment for adult and pediatric patients, respectively. At the sponsor’s submitted price of $4,992.29 per 10 mg/mL, and assuming the average weight reported in the respective trials, CADTH calculated that the annual cost of treatment may range from $129,780 to $1,168,196 per pediatric patient and $454,298 to $584,098 per adult patient.
The sponsor-submitted cost-utility analyses comparing burosumab with best supportive care (BSC) in patients greater than one year of age with XLH from the perspective of the Canadian health care payer. Two subgroups of interest were considered in the economic evaluation, defined by the patient’s baseline age: pediatric (i.e., one year to 17 years of age) and adult (i.e., greater than or equal to 18 years of age). Note: the sponsor also submitted a subgroup analysis of patients who had a history of fracture, but the full Health Canada and reimbursement requested population shall be the focus of this review. BSC was defined differently by subgroup: in the pediatric phase, BSC consisted of phosphate and vitamin D; in the adult phase, BSC consisted of phosphate, vitamin D, and/or a calcimimetic.
Funding: CADTH receives funding from Canada’s federal, provincial, and territorial governments, with the exception of Quebec.
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