Crysvita (burosumab) is a treatment for people with X-linked hypophosphatemia (XLH) developed by Kyowa Kirin and Ultragenyx. It is the only U.S. Food and Drug Administration-approved treatment for XLH that targets the underlying cause of the progressive inherited disorder.
The following are some frequently asked questions — FAQs — about Crysvita, and their answers.
How does Crysvita work?
Crysvita is an antibody that targets the protein FGF23, reducing its activity. FGF23 plays an important role in the regulation of phosphate ions in the body. In XLH patients, its activity is abnormally high. By reducing FGF23 activity, Crysvita can increase the amount of phosphate reabsorbed by the kidneys. It also can lead to higher levels of active vitamin D, which can increase the absorption of calcium and phosphate by the intestines.
How do I or my child take Crysvita?
A healthcare professional must administer Crysvitam which is given as an under-the-skin (subcutaneous) injection. The injections will be rotated to different locations for each dose. The acceptable areas include the upper arms, upper legs, and the abdomen.
Your doctor will monitor your phosphate levels to determine whether or not your dose Crysvita needs to be adjusted. Initial doses are 1 mg/kg of body weight for adults, rounded to the nearest 10 mg (not to exceed 90 mg). For children who weigh less than 10 kg or 22 pounds, the dose is 1 mg/kg rounded to the nearest 1 mg. Children weighing more than 10 kg should receive 0.8 mg/kg bodyweight rounded to the nearest 10 mg.
How often do I or my child take it?
Children receive injections every two weeks while adults are given the medication every four weeks.
What are the side effects?
Crysvita can lead to allergic reactions such as hives, rash, swelling, bruising, pain, and itching. It also can result in blood collecting outside of the blood vessels.
The most common side effects in children include fever, diarrhea, reactions at the site of injection, low vitamin D levels, cough, toothache, cavities, and tooth infections. Nausea, vomiting, headache, muscle pain, rash, and dizziness are other common side effects.
For adults, the most common side effects are back pain, dizziness, headache, constipation, muscle spasms, and tooth infections. Other common adverse effects in adults are low vitamin D levels, high phosphorus levels in the blood, and restless legs syndrome.
Are there reasons I shouldn’t take Crysvita?
You should not take Crysvita if you are still taking phosphate and active forms of vitamin D — such as calcitriol or paricalcitol — since this can lead to levels of phosphate that are too high. If you are planning to take Crysvita, you should stop taking these supplements a week before starting treatment. You should not take Crysvita if your phosphate levels are within the normal range.
Taking Crysvita also is not recommended if you have severe kidney impairment or end-stage kidney disease.
There is no data on Crysvita’s use in pregnant or breast-feeding women so you should consult your physician before becoming pregnant or nursing your baby.
Last updated: Dec. 4, 2020
XLH News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.