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> Burosumab Heavy Chain Sequence QVQLVQSGAEVKKPGASVKVSCKASGYTFTNHYMHWVRQAPGQGLEWMGIINPISGSTSN AQKFQGRVTMTRDTSTSTVYMELSSLRSEDTAVYYCARDIVDAFDFWGQGTMVTVSSAST KGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLY SLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSV FLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTY RVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTK NQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQG NVFSCSVMHEALHNHYTQKSLSLSPGK
> Burosumab Light Chain Sequence AIQLTQSPSSLSASVGDRVTITCRASQGISSALVWYQQKPGKAPKLLIYDASSLESGVPS RFSGSGSGTDFTLTISSLQPEDFATYYCQQFNDYFTFGPGTKVDIKRTVAAPSVFIFPPS DEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTL SKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC
QVQLVQSGAE VKKPGASVKV SCKASGYTFT NHYMHWVRQA PGQGLEWMGI INPISGSTSN
AQKFQGRVTM TRDTSTSTVY MELSSLRSED TAVYYCARDI VDAFDFWGQG TMVTVSSAST
KGPSVFPLAP SSKSTSGGTA ALGCLVKDYF PEPVTVSWNS GALTSGVHTF PAVLQSSGLY
SLSSVVTVPS SSLGTQTYIC NVNHKPSNTK VDKKVEPKSC DKTHTCPPCP APELLGGPSV
FLFPPKPKDT LMISRTPEVT CVVVDVSHED PEVKFNWYVD GVEVHNAKTK PREEQYNSTY
RVVSVLTVLH QDWLNGKEYK CKVSNKALPA PIEKTISKAK GQPREPQVYT LPPSRDELTK
NQVSLTCLVK GFYPSDIAVE WESNGQPENN YKTTPPVLDS DGSFFLYSKL TVDKSRWQQG
NVFSCSVMHE ALHNHYTQKS LSLSPGK
AIQLTQSPSS LSASVGDRVT ITCRASQGIS SALVWYQQKP GKAPKLLIYD ASSLESGVPS
RFSGSGSGTD FTLTISSLQP EDFATYYCQQ FNDYFTFGPG TKVDIKRTVA APSVFIFPPS
DEQLKSGTAS VVCLLNNFYP REAKVQWKVD NALQSGNSQE SVTEQDSKDS TYSLSSTLTL
SKADYEKHKV YACEVTHQGL SSPVTKSFNR GEC
(dimer; disulfide bridge:H22-H96, H144-H200, H220-L213, H220-H’226, H229-H’229, H261-H321, H367-H425, H’22-H’96, H’144-H’200, H’220-L’213, H’261-H’321, H’367-H’425, L23-L88, L133-L193, L’23-L’88, L’133-L’193)
Burosumab-twza, KRN 23
Protein chemical formulaC6388H9904N1700O2006S46
Protein average weight144100.0 Da
Protein Based Therapies
Monoclonal antibody (mAb)
Approval Status:Approved April 2018
Specific Treatments:X-linked hypophosphatemia
Crysvita (burosumab-twza) is a fibroblast growth factor 23 (FGF23) blocking antibody.
This drug is indicated for the treatment of X-linked hypophosphatemia with radiological evidence of bone disease in children of 1 year of age and older and adolescents with growing skeletons .
Burosumab (INN, trade name Crysvita) known as KRN23 is a human monoclonal antibody designed for the treatment of X-linked hypophosphatemia. Burosumab was approved by the FDA for its intended purpose, in patients aged 1 year and older, on 17 April 2018. The FDA approval fell under both the breakthrough therapy and orphan drug designations.
This drug was developed by Ultragenyx and is in a collaborative license agreement with Kyowa Hakko Kirin.
Burosumab (KRN23) is an entirely human monoclonal IgG1 antibody that binds excess fibroblast growth factor 23 (FGF23) and has been successfully tested in clinical trials in children with X-linked hypophosphatemic rickets .
The U.S. Food and Drug Administration approved Crysvita (burosumab) in April 2018. This is the first drug approved to treat adults and children ages 1 year and older with X-linked hypophosphatemia (XLH), which is a rare, inherited form of rickets. X-linked hypophosphatemia causes low circulating levels of phosphorus in the blood. It causes impaired bone growth and development in children and adolescents and issues with bone mineralization throughout a patient’s life .
XLH is a serious disease which affects about 3,000 children and 12,000 adults in the United States. Most children with XLH suffer from bowed or bent legs, short stature, bone pain and severe dental pain. Some adults with this condition suffer from persistent, unrelenting discomfort and complications, such as joint pain, impaired mobility, tooth abscesses and hearing loss 
Crysvita is specifically indicated for the treatment of X-linked hypophosphatemia (XLH) in adult and pediatric patients 1 year of age and older.
Crysvita is supplied as a subcutaneous injection. The recommended starting dose for pediatrics 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 per the drug label. 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. 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. See drug label for specific dose adjustments.
Mechanism of Action
Crysvita (burosumab-twza) is a fibroblast growth factor 23 (FGF23) blocking antibody. 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. 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.
- Kutilek S: Burosumab: A new drug to treat hypophosphatemic rickets. Sudan J Paediatr. 2017;17(2):71-73. doi: 10.24911/SJP.2017.2.11. [PubMed:29545670]
- Kinoshita Y, Fukumoto S: X-linked hypophosphatemia and FGF23-related hypophosphatemic diseases -Prospect for new treatment. Endocr Rev. 2018 Jan 26. pii: 4825438. doi: 10.1210/er.2017-00220. [PubMed:29381780]
- FDA approves first therapy for rare inherited form of rickets, x-linked hypophosphatemia [Link]
- Crysvita Drug Label [Link]
- Burosumab for a rare bone disease [Link]
- DRUG: Burosumab [Link]
- NHS document [Link]
- Burosumab for XLH [Link]
|Chemical and physical data|
|Molar mass||144.1 kDa|
- Statement On A Nonproprietary Name Adopted By The USAN Council – Burosumab, American Medical Association.[permanent dead link]
- World Health Organization (2016). “International Nonproprietary Names for Pharmaceutical Substances (INN). Proposed INN: List 115”(PDF). WHO Drug Information. 30 (2): 255.
- “Burosumab (KRN23) for X-Linked Hypophosphatemia (XLH)” (PDF). n.d. Retrieved 2018-04-18.
- “FDA approves first therapy for rare inherited form of rickets, x-linked hypophosphatemia” (Press release). FDA. 17 April 2018.
- “Collaboration with Ultragenyx to Develop and Commercialize KRN23 for X-linked Hypophosphatemia” (Press release). Kyowa Kirin. 4 September 2013. Retrieved 2018-04-17.