Exondys 51 works by helping the body produce a protein called dystrophin. Dystrophin is a protein that helps stabilize the structure of muscle tissue and is necessary for proper muscle development and function. Without dystrophin, muscle fibers can become weak and easily damaged. This can affect voluntary movement such as walking.

Children with Duchenne muscular dystrophy have a mutation of a gene that would normally cause the body to produce dystrophin.

Exondys 51 is used in children with Duchenne muscular dystrophy (DMD). This medicine is not a cure for DMD, but Exondys 51 may lessen muscle weakness and muscle wasting caused by this disease.

Exondys 51 was approved by the US Food and Drug Administration (FDA) on an "accelerated" basis. In clinical studies, some children responded to this medicine. However, further studies are needed to determine if this medicine is generally effective in treating DMD.

Exondys 51 may also be used for purposes not listed in this medication guide.

Before your child receives Exondys 51, tell the doctor about all your child's medical conditions or allergies, and all the medicines the child uses.

Exondys 51 is given as an infusion into a vein. A healthcare provider will give you this injection.

To make the injection more comfortable, a numbing medicine may be applied to the skin area where the IV needle will be placed.

Exondys 51 is given once per week. This medicine must be injected slowly, and the infusion can take up to 1 hour to complete.

Tell your caregivers if you feel itchy, warm, light-headed, or have chest tightness or trouble breathing when Exondys 51 is injected.

Tell your doctor if your child has any changes in weight. Exondys 51 doses are based on weight, and any changes may affect the dose.

Tell your child's doctor if any prior Exondys 51 injections caused a severe allergic reaction in your child.

Before your child receives Exondys 51, tell the doctor about all your child's medical conditions or allergies, and all the medicines the child uses.

Although Exondys 51 has been used mainly in children, it is not known whether Exondys 51 could be harmful if used during pregnancy or while nursing.

Call your child's doctor for instructions if you miss an appointment for your child's Exondys 51.

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Follow your doctor's instructions about any restrictions on food, beverages, or activity.

Get emergency medical help if your child has signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Common side effects of Exondys 51 may include:

• pain, bruising, itching, skin rash, or other irritation where the medicine was injected;

• vomiting;

• joint pain;

• problems with balance; or

• cold symptoms such as stuffy nose, sneezing, sore throat.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.