Fam-trastuzumab deruxtecan-nxki injection may cause serious or life-threatening lung damage, including interstitial lung disease (a condition in which there is scarring of the lungs) or pneumonitis (swelling of lung tissue). Tell your doctor if you have lung disease or breathing problems. If you experience any of the following symptoms, call your doctor immediately: new or worsening cough, difficulty breathing, wheezing, chest tightness, fever, or shortness of breath.

Tell your doctor if you are pregnant, plan to become pregnant, or if you plan to father a child. You or your partner should not become pregnant while you are receiving fam-trastuzumab deruxtecan-nxki injection. If you are able to become pregnant, your doctor may perform a pregnancy test to be sure that you are not pregnant before you receive fam-trastuzumab deruxtecan-nxki injection. If you are female, you should use birth control during your treatment and for 7 months after your final dose. If you are male, you and your female partner should use birth control during your treatment and for 4 months after your final dose. Talk to your doctor about birth control methods that will work for you. If you or your partner becomes pregnant while receiving fam-trastuzumab deruxtecan-nxki injection, call your doctor. Fam-trastuzumab deruxtecan-nxki may harm the fetus.

Keep all appointments with your doctor and the laboratory. Your doctor will order certain tests before and during treatment to check your body’s response to fam-trastuzumab deruxtecan-nxki.

Your doctor or pharmacist will give you the manufacturer’s patient information sheet (Medication Guide) when you begin treatment with fam-trastuzumab deruxtecan-nxki. You can also visit the Food and Drug Administration (FDA) website (http://www.fda.gov/Drugs/DrugSafety/ucm085729.htm) or the manufacturer’s website to obtain the Medication Guide.

Talk to your doctor about the risk(s) of receiving fam-trastuzumab deruxtecan-nxki.

Fam-trastuzumab deruxtecan-nxki injection is used to treat a certain type of breast cancer that cannot be removed by surgery, that has spread to other parts of the body, or has come back after another breast cancer treatment. It is also used to treat certain types of gastric cancer (cancer of the stomach) in adults that has spread to nearby tissues or to other parts of the body after receiving another treatment. Fam-trastuzumab deruxtecan-nxki injection is also used to treat a certain type of non-small cell lung cancer (NSCLC) in adults that cannot be removed by surgery or that has spread to other parts of the body after receiving another treatment. Fam-trastuzumab deruxtecan-nxki is in a class of medications called antibody-drug conjugates. It works by killing cancer cells.

Fam-trastuzumab deruxtecan-nxki comes as a powder to be mixed with liquid and injected intravenously (into a vein) over 30 or 90 minutes by a doctor or nurse in a hospital or medical facility. It is usually injected once every 3 weeks for as long as your doctor recommends that you receive treatment.

Your doctor may delay or stop your treatment with fam-trastuzumab deruxtecan-nxki injection, or treat you with additional medications, depending on your response to the medication and any side effects that you experience. Talk to your doctor about how you are feeling during your treatment.

Fam-trastuzumab deruxtecan-nxki injection may cause nausea and vomiting during and after treatment with the medication. Your doctor may give you another medication to help prevent nausea and vomiting.

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

Before receiving fam-trastuzumab deruxtecan-nxki injection,

• tell your doctor and pharmacist if you are allergic to fam-trastuzumab deruxtecan-nxki, medications made from Chinese hamster ovary cell protein, any other medications, or any of the ingredients in fam-trastuzumab deruxtecan-nxki injection. Ask your pharmacist or check the Medication Guide for a list of the ingredients.
• tell your doctor and pharmacist what other 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 or have ever had any of the conditions mentioned in the IMPORTANT WARNING section, a fever or any other signs of an infection, if you have or have ever had heart failure, heart disease, liver or kidney problems.
• tell your doctor if you are breast-feeding. You should not breast-feed while you are receiving fam-trastuzumab deruxtecan-nxki injection and for 7 months after your final dose.
• you should know that this medication may decrease fertility in men. Talk to your doctor about the risks of receiving fam-trastuzumab deruxtecan-nxki injection.

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

Fam-trastuzumab deruxtecan-nxki may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

• nausea
• vomiting
• constipation
• diarrhea
• sores on the lips, mouth, or throat
• stomach pain
• heartburn
• loss of appetite
• decreased weight
• hair loss
• headache
• dizziness
• tiredness
• muscle and bone pain
• dry eye(s)
• numbness or tingling of the hands or feet
• rash

Some side effects can be serious. If you experience any of these symptoms or those listed in the IMPORTANT WARNING section, call your doctor immediately or get emergency medical treatment:

• pale skin or shortness of breath
• new or worsening shortness of breath, cough, tiredness, swelling of ankles or legs, irregular heart beat, weight gain, dizziness, or fainting
• nose bleeds or other unusual bleeding or bruising
• fever, chills, cough, or other signs of infection

Fam-trastuzumab deruxtecan-nxki 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).

Ask your pharmacist any questions you have about fam-trastuzumab deruxtecan-nxki.

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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