Crysvita (burosumab-twza)
An approved treatment for X-Linked Hypophosphatemia.
Drug facts
The same compound appears under different names depending on the context. Here is how to identify Burosumab-twza wherever you encounter it, plus the key facts at a glance.
- Generic name
- Burosumab-twza
- Brand name
- Crysvita
- Development codes
- KRN23, UX023
- Drug class
- FGF23-blocking antibody
- Manufacturer
- Kyowa Kirin
- How it's taken
- Given as an injection under the skin by a healthcare provider, with no more than 1.5mL per injection site.
An injection under the skin, given by a healthcare provider every 2 or 4 weeks, and the only approved drug that targets the cause of X-linked hypophosphatemia (XLH). It is approved for XLH in adults and children 6 months and older, and for tumor-induced osteomalacia from age 2.
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Where Burosumab-twza fits
The only FDA-approved drug that targets FGF23, the cause of phosphate loss in XLH. The older approach of oral phosphate several times a day plus calcitriol is still used. The 2 are never combined, because phosphate can climb too high.
How Burosumab-twza works
In XLH, a change in the PHEX gene leads to too much FGF23. This hormone tells the kidneys to dump phosphate into the urine and to make less active vitamin D. Bones need phosphate to harden, so children develop rickets and bowed legs, and adults get soft bones, pain and fractures. Burosumab is an antibody that attaches to FGF23 and blocks it. The kidneys then hold on to phosphate and make more active vitamin D, which raises blood phosphate toward normal.
Side effects and safety
- Allergic reactions. Rash and hives have been reported. Crysvita is stopped for a serious reaction.
- Phosphate too high. High phosphate may raise the risk of calcium deposits in the kidneys. When a child's phosphate goes above 5mg/dL, the next dose is skipped and treatment restarts at a lower dose.
- High blood calcium. The risk is higher with overactive parathyroid glands, long periods without moving, dehydration, high vitamin D levels or kidney problems. Calcium and parathyroid hormone are checked in people at higher risk.
- Injection site reactions. Redness, swelling, itching, bruising or pain at the shot site. Crysvita is stopped for a severe reaction.
- Oral phosphate and active vitamin D stopped 1 week before the first dose
- Fasting blood phosphate every 4 weeks for the first 3 months, then as needed
- Calcium and parathyroid hormone before and during treatment in people at higher risk
Crysvita has no boxed warning, and it must not be used with oral phosphate or active vitamin D such as calcitriol, when blood phosphate is already normal or high, or with severe kidney disease. Its warnings cover allergic reactions, phosphate climbing too high, which may raise the risk of calcium deposits in the kidneys, high blood calcium and injection site reactions.
In children, the most common side effects were fever, injection site reactions, cough, vomiting, arm or leg pain, headache and dental abscesses or cavities. In adults they were back pain, headache, tooth infection, restless legs and low vitamin D. Narrowing of the spinal canal is common in adults with XLH, and pressure on the spinal cord has been reported on Crysvita. It is not known whether the drug makes this worse.
This is not a complete list of side effects. Talk to your doctor or pharmacist about what to expect and when to seek medical attention.
Taking Burosumab-twza
Given as an injection under the skin by a healthcare provider, with no more than 1.5mL per injection site. Children with XLH start at 0.8mg/kg every 2 weeks, or 1mg/kg for babies under 10kg, with a minimum of 10mg and a maximum of 90mg per dose. The dose can be raised in steps to about 2mg/kg if phosphate stays low. Adults with XLH start at 1mg/kg every 4 weeks, up to 90mg.
Since April 2026, adults whose phosphate stays low after 3 months can move to 0.5mg/kg every 2 weeks, then to 1mg/kg every 2 weeks if needed, still up to 90mg. Oral phosphate and active vitamin D are stopped 1 week before the first dose, and fasting phosphate must be below normal for age to start.
Availability and cost
Only available as the brand-name product.
Help paying for Crysvita
Pick your insurance to see which help fits. Drugmaker copay cards can't be used with Medicare, Medicaid or TRICARE; charity funds are the usual route there.
- Insurance and case manager help
After the doctor submits the enrollment form, a Case Manager runs a benefits investigation, helps with prior authorization and the specialty pharmacy, and a Clinical Educator explains XLH and treatment.
The official page does not say who qualifies. Ask the program. · source - Copay help
Kyowa Kirin Cares Co-Pay Assistance Program for commercially insured US residents, covering out-of-pocket costs for Crysvita and its administration up to a yearly maximum; 95% of enrolled patients paid $0. Not valid with Medicare, Medicaid, TRICARE, VA, DoD or other federal or state programs. People in Massachusetts or Rhode Island may not get help with administration costs.
For: private insurance · source
Good to know: Call 833-KK-CARES (833-552-2737), weekdays 8am-8pm ET. Case Managers can discuss other financial assistance for people who qualify.
- From a charity · The Assistance FundHypophosphatemia fundOpen
Pays for: Copays, coinsurance, deductibles and other health-related expenses.
Every program and charity fund for X-Linked Hypophosphatemia →
Clinical trial results
In children, a 64-week trial (NCT02915705) randomly assigned 61 children aged 1-12 to Crysvita or standard oral phosphate plus active vitamin D. After 40 weeks, rickets scores on X-rays fell from 3.2 to 1.1 on Crysvita and from 3.2 to 2.5 on standard treatment. Substantial healing was seen in 21 of 29 children on Crysvita and 2 of 32 on standard treatment, and blood phosphate rose from 2.4 to 3.3mg/dL.
In adults, a trial of 134 people aged 20-63 (NCT02526160) found that 94% on Crysvita had average phosphate in the normal range midway between doses during the 24-week blinded period, against 8% on placebo.
Development history
Kyowa Kirin and Ultragenyx developed burosumab, and the FDA approved it on April 17, 2018 for XLH in adults and children 1 and older. On September 27, 2019 the FDA lowered the starting age to 6 months. On June 18, 2020 it added tumor-induced osteomalacia, a rare condition where a hidden tumor makes FGF23. An April 2026 update let adults whose phosphate stays low move to dosing every 2 weeks, raised in steps.
Explore X-Linked Hypophosphatemia trials
Common questions about Burosumab-twza
▸What is Burosumab-twza (Crysvita)?
An injection under the skin, given by a healthcare provider every 2 or 4 weeks, and the only approved drug that targets the cause of X-linked hypophosphatemia (XLH). It is approved for XLH in adults and children 6 months and older, and for tumor-induced osteomalacia from age 2.
▸How does Burosumab-twza work?
In XLH, a change in the PHEX gene leads to too much FGF23. This hormone tells the kidneys to dump phosphate into the urine and to make less active vitamin D. Bones need phosphate to harden, so children develop rickets and bowed legs, and adults get soft bones, pain and fractures. Burosumab is an antibody that attaches to FGF23 and blocks it. The kidneys then hold on to phosphate and make more active vitamin D, which raises blood phosphate toward normal.
▸What are the side effects of Burosumab-twza?
Crysvita has no boxed warning, and it must not be used with oral phosphate or active vitamin D such as calcitriol, when blood phosphate is already normal or high, or with severe kidney disease. Its warnings cover allergic reactions, phosphate climbing too high, which may raise the risk of calcium deposits in the kidneys, high blood calcium and injection site reactions. In children, the most common side effects were fever, injection site reactions, cough, vomiting, arm or leg pain, headache and dental abscesses or cavities. In adults they were back pain, headache, tooth infection, restless legs and low vitamin D. Narrowing of the spinal canal is common in adults with XLH, and pressure on the spinal cord has been reported on Crysvita. It is not known whether the drug makes this worse.
▸How is Burosumab-twza taken?
Given as an injection under the skin by a healthcare provider, with no more than 1.5mL per injection site. Children with XLH start at 0.8mg/kg every 2 weeks, or 1mg/kg for babies under 10kg, with a minimum of 10mg and a maximum of 90mg per dose. The dose can be raised in steps to about 2mg/kg if phosphate stays low. Adults with XLH start at 1mg/kg every 4 weeks, up to 90mg. Since April 2026, adults whose phosphate stays low after 3 months can move to 0.5mg/kg every 2 weeks, then to 1mg/kg every 2 weeks if needed, still up to 90mg. Oral phosphate and active vitamin D are stopped 1 week before the first dose, and fasting phosphate must be below normal for age to start.
▸Is Burosumab-twza FDA approved?
Yes, Burosumab-twza (Crysvita) is FDA approved (2018) for the treatment of X-Linked Hypophosphatemia.
▸Can my child take phosphate and calcitriol with Crysvita?
No, the label forbids combining Crysvita with oral phosphate or active vitamin D such as calcitriol, because phosphate can climb too high. These are stopped 1 week before the first Crysvita dose.
▸How often is Crysvita given?
Children get a shot every 2 weeks, with the dose based on weight. Adults usually get a shot every 4 weeks, and since April 2026 adults whose phosphate stays low can move to every 2 weeks. Each injection is given by a healthcare provider, usually at a clinic or infusion center.
▸Does Crysvita help adults with XLH or only children?
It helps both. In a trial of 134 adults, 94% on Crysvita had average blood phosphate in the normal range midway between doses over 24 weeks, against 8% on placebo. Adults start at 1mg/kg every 4 weeks, up to 90mg.
Sources and references
Every factual claim on this page is drawn from the public sources listed below. Click any reference to open the original document.
- U.S. National Library of Medicine, DailyMed · 2026-04-22. CRYSVITA (burosumab-twza) injection: prescribing information. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=102f96a0-6e3a-4fc1-b204-34d604683af6
- U.S. Food and Drug Administration · 2018-04-17. BLA 761068 approval letter. https://www.accessdata.fda.gov/drugsatfda_docs/appletter/2018/761068Orig1s000ltr.pdf
- U.S. Food and Drug Administration · 2019-09-27. BLA 761068 supplement S-004 approval letter (age 6 months and older). https://www.accessdata.fda.gov/drugsatfda_docs/appletter/2019/761068Orig1s004ltr.pdf
- U.S. Food and Drug Administration · 2020-06-18. BLA 761068 supplement S-005 approval letter (tumor-induced osteomalacia). https://www.accessdata.fda.gov/drugsatfda_docs/appletter/2020/761068Orig1s005ltr.pdf
- U.S. Food and Drug Administration · 2026-04-23. BLA 761068 supplement S-011 approval letter (adult dose increase). https://www.accessdata.fda.gov/drugsatfda_docs/appletter/2026/761068Orig1s011ltr.pdf
- ClinicalTrials.gov. Efficacy and Safety of Burosumab Versus Oral Phosphate and Active Vitamin D Treatment in Pediatric Patients With XLH. https://clinicaltrials.gov/study/NCT02915705
- Kyowa Kirin. Accessing patient support for CRYSVITA. https://www.crysvita.com/patient-support/