Crysvita Dosage

Generic name: BUROSUMAB 10mg in 1mL
Dosage form: injection
Drug class: Miscellaneous metabolic agents

Medically reviewed by Drugs.com. Last updated on Nov 20, 2023.

Important Dosage and Administration Information

Discontinue oral phosphate and/or active vitamin D analogs (e.g. calcitriol, paricalcitol, doxercalciferol, calcifediol) 1 week prior to initiation of treatment [see Contraindications (4)].

Fasting serum phosphorus concentration should be below the reference range for age prior to initiation of treatment [see Contraindications (4)].

CRYSVITA is administered by subcutaneous injection and should be administered by a healthcare provider.

The maximum volume of CRYSVITA per injection is 1.5 mL. If multiple injections are required, administer at different injection sites.

Pediatric Patients with X-linked Hypophosphatemia (6 months to less than 18 years of age)

For patients who weigh less than 10 kg, the recommended starting dose is 1 mg/kg of body weight, rounded to the nearest 1 mg, administered every two weeks.

For patients who weigh 10 kg and greater, the recommended starting dose regimen is 0.8 mg/kg of body weight, rounded to the nearest 10 mg, administered every two weeks. The minimum starting dose is 10 mg up to a maximum dose of 90 mg.

After initiation of treatment with CRYSVITA, measure fasting serum phosphorus every 4 weeks for the first 3 months of treatment, and thereafter as appropriate. If serum phosphorus is above the lower limit of the reference range for age and below 5 mg/dL, continue treatment with the same dose. Follow dose adjustment schedule below to maintain serum phosphorus within the reference range for age.

Dose Adjustment

Reassess fasting serum phosphorus level 4 weeks after dose adjustment.

Do not adjust CRYSVITA more frequently than every 4 weeks.

Dose Increase:

For patients who weigh less than 10 kg, if serum phosphorus is below the reference range for age, the dose may be increased to 1.5 mg/kg, rounded to the nearest 1 mg, administered every two weeks. If additional dose increases are needed, the dose may be increased to the maximum dose of 2 mg/kg, rounded to the nearest 1 mg, administered every two weeks.

For patients who weigh 10 kg or greater, if serum phosphorus is below the reference range for age, the dose may be increased stepwise up to approximately 2 mg/kg, administered every two weeks (maximum dose of 90 mg) according to the dosing schedule shown in Table 1.

Table 1: XLH Pediatric Dose Schedule for Stepwise Dose Increase for Patients Weighing 10 kg or More
Body Weight (kg)	Starting Dose (mg)	First Dose Increase to (mg)	Second Dose Increase to (mg)
10 – 14	10	15	20
15 – 18	10	20	30
19 – 31	20	30	40
32 – 43	30	40	60
44 – 56	40	60	80
57 – 68	50	70	90
69 – 80	60	90	90
81 – 93	70	90	90
94 – 105	80	90	90
106 and greater	90	90	90

Dose Decrease:

If serum phosphorus is above 5 mg/dL, withhold the next dose and reassess the serum phosphorus level in 4 weeks. The patient must have serum phosphorus below the reference range for age to reinitiate CRYSVITA. Once serum phosphorus is below the reference range for age, treatment may be restarted.

For patients who weigh less than 10 kg, restart CRYSVITA at 0.5 mg/kg of body weight, rounded to the nearest 1 mg, administered every two weeks. For patients who weigh 10 kg or more, restart CRYSVITA according to the dose schedule shown in Table 2.

Table 2: XLH Pediatric Dose Schedule for Re-Initiation of Therapy for Patients Weighing 10 kg or More
Previous Dose (mg)	Re-Initiation Dose (mg)
10	5
15	10
20	10
30	10
40	20
50	20
60	30
70	30
80	40
90	40

After a dose decrease, reassess serum phosphorus level 4 weeks after the dose adjustment. If the level remains below the reference range for age after the re-initiation dose, the dose can be adjusted as outlined under Dose Increase.

Adult Patients with X-linked Hypophosphatemia (18 years of age and older)

The recommended dose regimen in adults is 1 mg/kg body weight, rounded to the nearest 10 mg up to a maximum dose of 90 mg, administered every four weeks.

Dose Decrease

Reassess fasting serum phosphorus level 2 weeks after dose adjustment.

Do not adjust CRYSVITA more frequently than every 4 weeks.

If serum phosphorus is above the normal range, withhold the next dose and reassess the serum phosphorus level after 4 weeks. The patient must have serum phosphorus below the normal range to be able to reinitiate CRYSVITA. Once serum phosphorus is below the normal range, treatment may be restarted at approximately half the initial starting dose up to a maximum dose of 40 mg every 4 weeks according to the dose schedule shown in Table 3. Reassess serum phosphorus 2 weeks after any change in dose.

Table 3: XLH Adult Dose Schedule for Re-Initiation of Therapy
Previous Dose (mg)	Re-Initiation Dose (mg)
40	20
50	20
60	30
70	30
80 and greater	40

Pediatric Patients with Tumor-induced Osteomalacia (2 years to less than 18 years of age)

The recommended starting dose for pediatrics is 0.4 mg/kg body weight administered every 2 weeks, rounded to the nearest 10mg, up to a maximum dose of 2 mg/kg not to exceed 180mg, administered every 2 weeks.

After initiation of treatment with CRYSVITA, assess fasting serum phosphorus on a monthly basis, measured 2 weeks post-dose, for the first 3 months of treatment, and thereafter as appropriate. If serum phosphorus is within the reference range for age, continue with the same dose. Follow the dose adjustment schedule below to maintain serum phosphorus within the reference range for age.

Dose Adjustment

Reassess fasting serum phosphorus level 4 weeks after dose adjustment.

Do not adjust CRYSVITA more frequently than every 4 weeks.

Dose Increase

If serum phosphorus is below the reference range for age, the dose should be titrated in accordance with Table 4 up to the maximum dose of 2 mg/kg every 2 weeks. The maximum dose should not exceed 180 mg.

Table 4: TIO Pediatric Dose Schedule for Stepwise Dose Increase for Patients Weighing 10 kg or more
Body Weight (kg)	Starting Dose (mg)	First Dose Increase to (mg)	Second Dose Increase to (mg)	Third Dose* Increase to (mg)
* The table shows a dose increase up to 1.5 mg/kg. Further dose increases to a maximum of 2 mg/kg not to exceed 180 mg, administered every 2 weeks should be calculated by the physician.
10 – 14	5	10	15	20
15 – 18	5	10	20	25
19 – 31	10	20	25	30
32 – 43	10	30	40	50
44 – 56	20	40	50	70
57 – 68	20	50	70	90
69 – 80	30	60	80	100
81 – 93	30	70	100	120
94 – 105	40	80	110	140
106 and greater	40	90	130	160

Dose Decrease

If serum phosphorus is above the reference range for age, withhold the next dose and reassess the serum phosphorus level in 4 weeks. The patient must have serum phosphorus below the reference range for age to reinitiate CRYSVITA. Once serum phosphorus is below the reference range for age, treatment may be restarted at approximately half the initial starting dose, up to a maximum dose of 180 mg administered every 2 weeks for pediatrics. After a dose decrease, reassess serum phosphorus level 4 weeks after the dose adjustment. If the level remains below the reference range for age after the re-initiation dose, the dose can be adjusted as outlined per Table 4.

Dose Interruption

If a patient undergoes treatment of the underlying tumor (i.e., surgical excision or radiation therapy) CRYSVITA treatment should be interrupted and serum phosphorus reassessed after treatment has been completed. CRYSVITA dose should be restarted at the patient's initiation dose if serum phosphorus remains below the lower limit of normal. Follow dose adjustment per Table 4 to maintain serum phosphorus within the reference range for age.

Adult Patients with Tumor-induced Osteomalacia (18 years of age and older)

The recommended starting dose for adults is 0.5 mg/kg body weight administered every 4 weeks, rounded to the nearest 10 mg, up to a maximum dose of 2 mg/kg not to exceed 180mg, administered every 2 weeks.

After initiation of treatment with CRYSVITA, assess fasting serum phosphorus on a monthly basis, measured 2 weeks post-dose, for the first 3 months of treatment, and thereafter as appropriate. If serum phosphorus is within the normal range, continue with the same dose. Follow the dose adjustment schedule below to maintain serum phosphorus within the reference range.

Dose Adjustment

Reassess fasting serum phosphorus level 2 weeks after dose adjustment.

Do not adjust CRYSVITA more frequently than every 4 weeks.

Dose Increase

If serum phosphorus is below the normal range, the dose should be titrated in accordance with Table 5 up to the maximum dose of 2 mg/kg not to exceed 180 mg, administered every 2 weeks. For those individuals not reaching a serum phosphorus greater than the lower limit of the normal range, physicians may consider dividing total dose administered every 4 weeks and administering every 2 weeks.

Table 5: TIO Dose Schedule* for Stepwise† Dose Increase for Adults (18 years of age and older)
	Starting Dose	First Dose Increase‡	Second Dose Increase‡	Third Dose Increase‡	Fourth Dose Increase	Fifth Dose Increase (maximum dose)
* Rounded to the nearest 10 mg. † Do not adjust CRYSVITA more frequently than every 4 weeks. ‡ For those individuals not reaching a serum phosphorus greater than the lower limit of the normal range, physicians may consider dividing total dose administered every 4 weeks and administering every 2 weeks. § In patients with high body weight, if the calculated dose is greater than 180 mg every 4 weeks, move to a divided dose every 2 weeks.
If serum phosphorus 2 weeks post-dose adjustment is below lower limit of normal	0.5 mg/kg every 4 weeks	Increase to: 1 mg/kg every 4 weeks OR 0.5 mg/kg every 2 weeks	Increase to: 1.5 mg/kg every 4 weeks§ OR 0.75 mg/kg every 2 weeks	Increase to: 2 mg/kg every 4 weeks§ OR 1 mg/kg every 2 weeks	Increase to: 1.5 mg/kg not to exceed 180 mg every 2 weeks	Increase to: 2 mg/kg not to exceed 180 mg every 2 weeks

Dose Decrease

If serum phosphorus is above the normal range, withhold the next dose and reassess the serum phosphorus level in 4 weeks. The patient must have serum phosphorus below the reference range to reinitiate CRYSVITA. Once serum phosphorus is below the reference range, treatment may be restarted at approximately half the initial starting dose, up to a maximum dose of 180 mg administered every 2 weeks for adults. After a dose decrease, reassess serum phosphorus level 2 weeks after the dose adjustment. If the level remains below the reference range after the re-initiation dose, the dose can be adjusted as outlined per Table 5.

Dose Interruption

If a patient undergoes treatment of the underlying tumor (i.e., surgical excision or radiation therapy) CRYSVITA treatment should be interrupted and serum phosphorus reassessed after treatment has been completed. CRYSVITA dose should be restarted at the patient's initiation dose if serum phosphorus remains below the lower limit of normal. Follow dose adjustment per Table 5 to maintain serum phosphorus within the reference range.

Missed Dose

If a patient misses a dose, resume CRYSVITA as soon as possible at the prescribed dose. To avoid missed doses, treatments may be administered 3 days either side of the scheduled treatment date.

25-Hydroxy Vitamin D Supplementation

Monitor 25-hydroxy vitamin D levels. Supplement with cholecalciferol or ergocalciferol to maintain 25-hydroxy vitamin D levels in the normal range for age. Do not administer active Vitamin D analogs during CRYSVITA treatment [see Contraindications (4)].

General Considerations for Subcutaneous Administration

Injection sites should be rotated with each injection administered at a different anatomic location (upper arms, upper thighs, buttocks, or any quadrant of abdomen) than the previous injection. Do not inject into moles, scars, or areas where the skin is tender, bruised, red, hard, or not intact. If a given dose on a dosing day requires multiple vials of CRYSVITA, contents from two vials can be combined for injection. The maximum volume of CRYSVITA per injection is 1.5 mL. If multiple injections are required on a given dosing day, administer at different injection sites. Monitor for signs of reactions [see Warnings and Precautions (5.3)].

Visually inspect CRYSVITA for particulate matter and discoloration prior to administration. CRYSVITA is a sterile, preservative-free, clear to slightly opalescent and colorless to pale brown-yellow solution for subcutaneous injection. Do not use if the solution is discolored or cloudy or if the solution contains any particles or foreign particulate matter.