Burosumab-twza (Crysvita)

Number: 0932

Policy

Note: REQUIRES PRECERTIFICATIONFootnotes*

Aetna considers burosumab-twza (Crysvita) medically necessary for the treatment of X-linked hypophosphatemia (XLH) in adult and pediatric members 1 year of age and older who meet the following criteria:

  • Member has a documented diagnosis of X-linked hypophophatemia (XLH) as defined by either of the following

    • Confirmed phosphate regulating gene with homology to endopeptidases located on the X chromosome (PHEX) mutation in the member or a directly related family member with appropriate X-linked inheritance; OR
    • Serum fibroblast growth factor 23 (FGF23) level greater than 30 pg/mL by Kainos assay; and

  • Member has serum phosphorus less than or equal to 2.8 mg/dL (0.904 mmol/L) or below the normal range for age; and

  • Member will not be taking Crysvita with an oral phosphate or active vitamin D analogs; and

  • Member does not have severe renal impairment or end stage renal disease.

Aetna considers burosumab-twza experimental and investigational for all other indications.

Footnotes*Precertification of burosumab-twza is required of all Aetna participating providers and members in applicable plan designs. For precertification of burosumab-twza call (866) 503-0857, or fax (866) 267-3277.

 

Background

Hereditary hypophosphatemic rickets is characterized by hypophosphatemia and rickets (and/or osteomalacia) that resembles vitamin D deficiency but does not respond to vitamin D replacement or pharmacologic doses of vitamin D because the underlying cause is renal phosphate wasting rather than true vitamin D resistance. X-linked hypophosphatemia (XLH) is the most common heritable form of rickets and osteomalacia, with a prevalence of approximately one case per 20,000 live births. XLH causes low levels of phosphorus in the blood. X-linked hypophosphatemia is caused by excess fibroblast growth factor 23 (FGF23) which suppresses renal tubular phosphate reabsorption and the renal production of 1,25 dihydroxy vitamin D. Most children with XLH experience bowed or bent legs, short stature, bone pain and severe dental pain. Some adults with XLH experience persistent discomfort or complications, such as joint pain, impaired mobility, tooth abscesses and hearing loss. 

The FDA approved burosumab-twza (Crysvita) on April 17, 2018 with a Breakthrough Therapy designation, under which the FDA provides intensive guidance to the company on efficient drug development, and expedites its review of drugs that are intended to treat serious conditions where clinical evidence shows the drug may represent a substantial improvement over other available therapies. Burosumab-twza also received Orphan Drug designation, which provides incentives to assist and encourage the development of drugs for rare diseases. Burosumab-twza binds to and inhibits the biological activity of FGF23 restoring renal phosphate reabsorption and increasing the serum concentration of 1,25 dihydroxy vitamin D. 

The safety and efficacy of burosumab-twza were studied in four clinical trials, two in pediatric patients (Study 1 and Study 2) and two in adult patients (Study 3 and Study 4). Radiographs from 52 burosumab-twza-treated XLH patients in Study 1 and 13 patients in Study 2 were examined to assess XLH-related rickets using the 10-point Thacher Rickets Severity Score (RSS) and the 7-point Radiographic Global Impression of Change (RGI-C). The RSS score is assigned based on images of the wrist and knee from a single time-point, with higher scores indicating greater rickets severity. The RGI-C score is assigned based on side-by-side comparisons of wrist and knee radiographs from two time-points, with higher scores indicating greater improvement in radiographic evidence of rickets. A RGI-C score of +2.0 was defined as radiographic evidence of substantial healing.

Study 1 (NCT 02163577) was a randomized, phase 2, open-label study in 52 prepubescent XLH patients, 5 to 12 years old, which compared treatment with burosumab-twza administered every 2 weeks versus every 4 weeks. Following an initial 16-week dose titration phase, patients completed 48-weeks of treatment with burosumab-twza every 2 weeks. All 52 patients completed at least 64 weeks on study; no patient discontinued. Burosumab-twza dose was adjusted to target a fasting serum phosphorus concentration of 3.5 to 5.0 mg/dL based on the fasting phosphorus level the day of dosing. Twenty-six of 52 patients received burosumab-twza every two weeks up to a maximum dose of 2 mg/kg. The average dose was 0.73 mg/kg (range: 0.3, 1.5) at week 16, 0.98 mg/kg (range: 0.4, 2.0) at week 40 and 1.04 mg/kg (range: 0.4, 2.0) at week 60. The remaining 26 patients received burosumab-twza every four weeks. At study entry, the mean age of patients was 8.5 years and 46% were male. Ninety-six percent had received oral phosphate and active vitamin D analogs for a mean (SD) duration of 7 (2.4) years. Oral phosphate and active vitamin D analogs were discontinued prior to study enrollment. Ninety-four percent of patients had radiographic evidence of rickets at baseline. Burosumab-twza increased mean (SD) serum phosphorus levels from 2.4 (0.40) at baseline to 3.3 (0.40) and 3.4 (0.45) mg/dL at week 40 and week 64 in the patients who received burosumab-twza every 2 weeks. The ratio of renal tubular maximum reabsorption rate of phosphate to glomerular filtration rate (TmP/GFR) increased in these patients from mean (SD) of 2.2 (0.49) at baseline to 3.3 (0.60) and 3.4 (0.53) mg/dL at week 40 and week 64. The baseline mean (SD) RSS total score was 1.9 (1.17) in patients receiving burosumab-twza every two weeks. After 40 weeks of treatment with burosumab-twza, mean total RSS decreased from 1.9 to 0.8. After 40 weeks of treatment with burosumab-twza, the mean RGI-C Global score was +1.7 in patients receiving burosumab-twza every two weeks. Eighteen out of 26 patients achieved an RGI-C score of ≥ +2.0. These findings were maintained at week 64. The mean (SD) serum total alkaline phosphatase activity was 462 (110) U/L at baseline and decreased to 354 (73) U/L at Week 64 (-23%, p < 0.0001) in the patients who received burosumab-twza every 2 weeks. Burosumab-twza treatment for 64 weeks increased standing mean (SD) height Z score from -1.72 (1.03) at baseline to -1.54 (1.13) in the patients who received burosumab-twza every two weeks (LS mean change of +0.19 (95% CI: 0.09 to 0.29).

Study 2 (NCT 02750618) was a 64-week open-label study in 13 pediatric XLH patients, 1 to 4 years old. Patients received burosumab-twza at a dose of 0.8 mg/kg every two weeks with titration up to 1.2 mg/kg based on serum phosphorus measurements. All patients completed at least 40 weeks on study; no patients discontinued. At study entry, the mean age of patients was 2.9 years and 69% were male. All patients had radiographic evidence of rickets at baseline and had received oral phosphate and active vitamin D analogs for a mean (SD) duration of 16.9 (13.9) months. Oral phosphate and active vitamin D analogs were discontinued prior to study enrollment. Burosumab-twza increased mean (SD) serum phosphorus levels from 2.5 (0.28) mg/dL at baseline to 3.5 (0.49) mg/dL at week 40. Baseline mean (SD) total RSS was 2.9 (1.37) in 13 patients. After 40 weeks of treatment with burosumab-twza, mean total RSS decreased from 2.9 to 1.2 and the mean (SE) RGI-C Global score was +2.3 (0.08). All 13 patients achieved a RGI-C global score ≥ +2.0. The mean (SE) lower limb deformity as assessed by RGI-C, using standing long leg radiographs, was +1.3 (0.14). The mean (SD) serum total alkaline phosphatase activity was 549 (194) U/L at baseline and decreased to 335 (88) U/L at Week 40 (mean change: -36%).

Study 3 (NCT 02526160) was a randomized, double-blind, placebo-controlled study in 134 adult XLH patients. The study comprised a 24-week placebo-controlled treatment phase. Burosumab-twza was administered at a dose of 1 mg/kg every 4 weeks. At study entry, the mean age of patients was 40 years (range 19 to 66 years) and 35% were male. All patients had skeletal pain associated with XLH/osteomalacia at baseline. The baseline mean (SD) serum phosphorus concentration was below the lower limit of normal at 1.98 (0.31) mg/dL. Oral phosphate and active vitamin D analogs were not allowed during the study. One patient in the burosumab-twza group discontinued treatment. At baseline, mean (SD) serum phosphorus was 1.9 (0.32) and 2.0 (0.30) mg/dL in the placebo and burosumab-twza groups respectively. During the initial 24 weeks of treatment, mean (SD) serum phosphorus across the midpoints of dose intervals (2 weeks post dose) was 2.1 (0.30) and 3.2 (0.53) mg/dL in the placebo and burosumab-twza groups, and mean (SD) serum phosphorus across the ends of dose intervals was 2.0 (0.30) and 2.7 (0.45) mg/dL in the placebo and burosumab-twza groups. A total of 94% of patients treated with burosumab-twza achieved a serum phosphorus level above the lower limit of normal (LLN) compared to 8% in the placebo group through week 24. At baseline, the mean (SD) ratio of renal tubular maximum reabsorption rate of phosphate to glomerular filtration rate (TmP/GFR) was 1.60 (0.37) and 1.68 (0.40) mg/dL in the placebo and burosumab-twza groups respectively. At week 22 (midpoint of a dose interval), mean (SD) TmP/GFR was 1.69 (0.37) and 2.73 (0.75) mg/dL in the placebo and burosumab-twza groups. At week 24 (end of a dose interval), mean (SD) TmP/GFR was 1.73 (0.42) and 2.21 (0.48) mg/dL in the placebo and burosumab-twza groups. A skeletal survey was conducted at baseline to identify osteomalacia-related fractures and pseudofractures. Osteomalacia-related fractures are defined as atraumatic lucencies extending across both bone cortices and pseudofractures are defined as atraumatic lucencies extending across one cortex. There were 52% of patients who had either active (unhealed) fractures (12%) or active pseudofractures (47%) at baseline. The active fractures and pseudofractures were predominantly located in the femurs, tibia/fibula, and metatarsals of the feet. Assessment of these active fracture/pseudofracture sites at week 24 demonstrated a higher rate of complete healing in the burosumab-twza group compared to placebo. During treatment through week 24, a total of 6 new fractures or pseudofractures appeared in 68 patients receiving burosumab-twza, compared to 8 new abnormalities in 66 patients receiving placebo.

Study 4 (NCT 02537431) was a 48-week, open-label, single-arm study in 14 adult XLH patients to assess the effects of CRYSVITA on improvement of osteomalacia as determined by histologic and histomorphometric evaluation of iliac crest bone biopsies. Patients received 1 mg/kg burosumab-twza every four weeks. At study entry, the mean age of patients was 40 years (range 25 to 52 years) and 43% were male. Oral phosphate and active vitamin D analogs were not allowed during the study. After 48 weeks of treatment, healing of osteomalacia was observed in ten patients as demonstrated by decreases in Osteoid volume/Bone volume (OV/BV) from a mean (SD) score of 26% (12.4) at baseline to 11% (6.5), a change of -57%. Osteoid thickness (O.Th) declined in eleven patients from a mean (SD) of 17 (4.1) micrometers to 12 (3.1) micrometers, a change of -33%. Mineralization lag time (MLt) declined in 6 patients from a mean (SD) of 594 (675) days to 156 (77) days, a change of -74%.

The most common adverse reactions in adults taking burosumab-twza were back pain, headache, restless leg syndrome, decreased vitamin D, dizziness and constipation. The most common adverse reactions in children were headache, injection site reaction, vomiting, decreased vitamin D and pyrexia (fever). Patients taking burosumab-twza may need dose interruption and/or dose reduction based on their serum phosphorus levels.

Appendix 

Oral phosphate and active vitamin D analogs should be discontinued 1 week prior to initiation of treatment. Fasting serum phosphorus concentration should be below the reference range for age prior to initiation of treatment.

For subcutaneous use only

Pediatric XLH:

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. Dose may be increased up to approximately 2 mg/kg (maximum 90 mg), administered every two weeks to achieve normal serum phosphorus.



Adult XLH:

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


Table: CPT Codes / HCPCS Codes / ICD-10 Codes
Code Code Description

Information in the [brackets] below has been added for clarification purposes.   Codes requiring a 7th character are represented by "+" :

Other CPT codes related to the CPB:

84100 Phosphorus inorganic (phosphate)
96372 Therapeutic, prophylactic, or diagnostic injection (specify substance or drug); subcutaneous or intramuscular

Other HCPCS codes related to the CPB:

J0636 Injection, calcitriol, 0.1 mcg
J1270 Injection, doxercalciferol, 1 mcg
J2501 Injection, paricalcitol, 1 mcg
J8562 Fludarabine phosphate, oral, 10 mg
S0169 Calcitrol, 0.25 microgram

ICD-10 codes covered if selection criteria are met:

E83.31 Familial hypophosphatemia [for X-linked hypophosphatemia (XLH)]

ICD-10 codes contraindicated for this CPB:

N18.4 Chronic kidney disease, stage 4 (severe)
N18.5 Chronic kidney disease, stage 5
N18.6 End stage renal disease

The above policy is based on the following references:

  1. Scheinman SJ and Drezner MK. Hereditary hypophosphatemic rickets and tumor-induced osteomalacia. UpToDate [online serial]. Waltham, MA: UpToDate; reviewed Septembe 2017.
  2. U.S. Food and Drug Administration (FDA). FDA approves first therapy for rare inherited form of rickets, x-linked hypophosphatemia. Silver Spring, MD: FDA; April 21, 2018. Available at: https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm604810.htm. Accessed April 24, 2018.
  3. Ultragenyx Pharmaceutical Inc. CRYSVITA (burosumab-twza) injection, for subcutaneous use. Prescribing Information. Novato, CA: Ultragenyx Pharmaceutical Inc; revised April 2018.
  4. Kaplon H, Reichert JM. Antibodies to watch in 2018. MAbs. 2018;10(2):183-203.