Burosumab-twza injection is used to treat X-linked hypophosphatemia (XLH; an inherited disease where the body doesn't maintain phosphorus and that leads to weak bones) in adults and children 6 months of age and older. It is also used to treat tumor-induced osteomalacia (a tumor that causes a loss of phosphorus in the body that leads to weak bones) that cannot be surgically removed in adults and children 2 years of age and older, Burosumab-twza injection is in a class of medications called fibroblast growth factor 23 (FGF23) blocking antibodies. It works by blocking the action of a certain natural substance in the body which causes the symptoms of XLH.

Burosumab-twza injection comes as a solution (liquid) to be injected subcutaneously (under the skin) by a doctor or nurse. For the treatment of X-linked hypophosphatemia, it is usually injected once every 2 weeks for children 6 months to 17 years of age, and once every 4 weeks for adults. For the treatment of tumor-induced osteomalacia, in children 2 to 17 years of age, it is usually injected once every 2 weeks. For the treatment of tumor-induced osteomalacia in adults, it is usually injected every 4 weeks and as the dose is increased it may be injected every 2 weeks. Your doctor or nurse will inject the medication in either your upper arm, upper thigh, buttocks, or stomach area, and use a different injection site each time.

Tell your doctor if you are taking any phosphate supplements or certain vitamin D supplements such as calcitriol (Rocaltrol) or paricalcitol (Zemplar). You will need to stop taking these 1 week before you start treatment.

Your doctor may increase your dose (not more than once every 4 weeks), or may skip a dose, depending on the results of your lab tests.

Before using burosumab-twza injection,

• tell your doctor and pharmacist if you are allergic to burosumab-twza, any other medications, or any of the ingredients in burosumab-twza injection. Ask your pharmacist for a list of the ingredients.
• tell your doctor and pharmacist what prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
• tell your doctor if you have kidney disease. Your doctor may tell you not to use burosumab-twza injection.
• tell your doctor if you have or have ever had restless leg syndrome (RLS; a condition that causes discomfort in the legs and a strong urge to move the legs, especially at night and when sitting or lying down).
• tell your doctor if you are pregnant, plan to become pregnant, or are breastfeeding. If you become pregnant while receiving burosumab-twza injection, call your doctor.

If you miss an appointment to receive a dose, make another appointment as soon as possible.

Unless your doctor tells you otherwise, continue your normal diet.

Burosumab-twza injection may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

• headache
• vomiting
• fever
• pain in arms, legs, or back
• muscle pain
• constipation
• dizziness

Some side effects can be serious. If you experience any of these symptoms, call your doctor:

• redness, rash, hives, itching, swelling, pain, or bruising near or at the spot that the medication was injected
• rash or hives
• discomfort in the legs; a strong urge to move the legs, especially at night and when sitting or lying down

Burosumab-twza injection may cause other side effects. Call your doctor if you have any unusual problems while receiving this medication.

If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting program online (http://www.fda.gov/Safety/MedWatch) or by phone (1-800-332-1088).

This medication may be prescribed for other uses; ask your doctor or pharmacist for more information.

Keep all appointments with your doctor and the laboratory. Your doctor will order certain lab tests before and during your treatment to check your body's response to burosumab-twza injection.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.

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