Avapritinib is used in adults to treat a certain type of cancer that affects the stomach, esophagus, or intestines. avapritinib is used when the cancer has spread to other parts of the body (metastatic) or cannot be removed with surgery.

Avapritinib is used if your cancer has a specific genetic marker (an abnormal "PDGFRA" gene). Your doctor will test you for this gene.

Avapritinib can also be used in adults to treat certain rare blood disorders, including advanced systemic mastocytosis, aggressive systemic mastocytosis, systemic mastocytosis with an associated hematological neoplasm, and mast cell leukemia.

Avapritinib is not recommended for the treatment of advanced systemic mastocytosis in people with low platelet counts.

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

Use only as directed. Tell your doctor if you use other medicines or have other medical conditions or allergies.

Follow all directions on your prescription label and read all medication guides or instruction sheets. Use the medicine exactly as directed.

Take avapritinib on an empty stomach, at least 1 hour before or 2 hours after a meal.

If you vomit shortly after taking avapritinib, do not take another dose. Wait until your next scheduled dose time to take the medicine again.

Do not change your dose or stop taking avapritinib without your doctor's advice.

Your blood may need to be tested often.

Store at room temperature away from moisture and heat.

Usual Adult Dose for Stomach Cancer:

300 mg orally once a day until disease progression or unacceptable toxicity

Use: For the treatment of adults with unresectable or metastatic GIST harboring a
platelet-derived growth factor receptor alpha (PDGFRA) exon 18 mutation, including PDGFRA D842V mutations

Tell your doctor if you:

• have low platelets counts;

• have bulging or weakening of a blood vessel wall (aneurysm);

• have ever had bleeding in your brain; or

• had a stroke within the last year.

You may need to have a negative pregnancy test before starting this treatment.

Both men and women using avapritinib should use effective birth control to prevent pregnancy. Avapritinib can harm an unborn baby or cause birth defects if the mother or father is using this medicine.

Keep using birth control for at least 6 weeks after your last dose. Tell your doctor right away if a pregnancy occurs while either the mother or the father is using avapritinib.

Do not breastfeed while using this medicine, and for at least 2 weeks after your last dose.

Take the medicine as soon as you can, but skip the missed dose if your next dose is due in less than 8 hours. Do not take two doses at one time.

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

Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from light excess heat and moisture (not in the bathroom).

It is important to keep all medication out of sight and reach of children as many containers (such as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in a safe location – one that is up and away and out of their sight and reach. http://www.upandaway.org

Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA's Safe Disposal of Medicines website (http://goo.gl/c4Rm4p) for more information if you do not have access to a take-back program.

Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medication.

Avoid driving or hazardous activity until you know how avapritinib will affect you. Your reactions could be impaired.

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

Avapritinib may cause serious side effects. Call your doctor at once if you have:

• a severe headache, vision problems;

• unusual changes in mood or behavior;

• problems with speech, thinking, or memory;

• confusion, hallucinations (seeing objects or hearing things that are not real);

• severe drowsiness or dizziness;

• trouble sleeping; or

• severe weakness on one side of your body.

Your cancer treatments may be delayed or permanently discontinued if you have certain side effects.

Common side effects of avapritinib may include:

• nausea, vomiting, loss of appetite, stomach pain;

• diarrhea, constipation;

• fluid retention, swelling;

• feeling dizzy, weak, or tired;

• muscle weakness;

• watery eyes;

• rash; or

• hair color changes.

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.

Sometimes it is not safe to use certain medications at the same time. Some drugs can affect your blood levels of other drugs you take, which may increase side effects or make the medications less effective.

Other drugs may affect avapritinib, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell your doctor about all your current medicines and any medicine you start or stop using.

Keep all appointments with your doctor and the laboratory. Your doctor will order a lab test before you begin your treatment to see whether your cancer can be treated with avapritinib. Your doctor may order certain lab tests to check your body's response to avapritinib.

Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.

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.