ENHERTU is formulated with the active ingredient fam-trastuzumab deruxtecan-nxki, a HER2-directed antibody and topoisomerase inhibitor conjugate. It acts as an antibody-drug conjugate, combining an anti-HER2 monoclonal antibody linked to a topoisomerase inhibitor, DXd. The drug is presented as a lyophilized powder, available in single-dose vials with 100 mg strength, reconstituted to a 20 mg/mL solution for intravenous infusion. Key inactive ingredients include L-histidine, L-histidine hydrochloride monohydrate, polysorbate 80, and sucrose.

How should I use this medication?

This medication is injected into a vein. It is given by your care team in a hospital or clinic setting. A special MedGuide will be given to you before each treatment. Be sure to read this information carefully each time. Talk to your care team about the use of this medication in children. Special care may be needed.

Overdosage: If you think you have taken too much of this medicine contact a poison control center or emergency room at once. NOTE: This medicine is only for you. Do not share this medicine with others.

What if I miss a dose?

It is important not to miss your dose. Call your care team if you are unable to keep an appointment.

Where should I keep my medication?

This medication is given in a hospital or clinic. It will not be stored at home.

NOTE: This sheet is a summary. It may not cover all possible information. If you have questions about this medicine, talk to your doctor, pharmacist, or health care provider.

What side effects may I notice from receiving this medication?

Side effects that you should report to your care team as soon as possible: -Allergic reactions—skin rash, itching, hives, swelling of the face, lips, tongue, or throat -Dry cough, shortness of breath or trouble breathing -Infection—fever, chills, cough, sore throat, wounds that don't heal, pain or trouble when passing urine, general feeling of discomfort or being unwell -Heart failure—shortness of breath, swelling of the ankles, feet, or hands, sudden weight gain, unusual weakness or fatigue -Unusual bruising or bleeding Side effects that usually do not require medical attention (report these to your care team if they continue or are bothersome): -Constipation -Diarrhea -Hair loss -Muscle pain -Nausea -Vomiting

This list may not describe all possible side effects. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What should I tell my care team before I take this medication?

They need to know if you have any of these conditions: -Heart disease -Heart failure -Infection, especially a viral infection, such as chickenpox, cold sores, or herpes -Liver disease -Lung or breathing disease, such as asthma or COPD -An unusual or allergic reaction to fam-trastuzumab deruxtecan, other medications, foods, dyes, or preservatives -Pregnant or trying to get pregnant -Breast-feeding

What may interact with this medication?

Interactions are not expected.

This list may not describe all possible interactions. Give your health care provider a list of all the medicines, herbs, non-prescription drugs, or dietary supplements you use. Also tell them if you smoke, drink alcohol, or use illegal drugs. Some items may interact with your medicine.

What should I watch for while using this medication?

Visit your care team for regular checks on your progress. Tell your care team if your symptoms do not start to get better or if they get worse. This medication may increase your risk of getting an infection. Call your care team for advice if you get a fever, chills, sore throat, or other symptoms of a cold or flu. Do not treat yourself. Try to avoid being around people who are sick. Avoid taking medications that contain aspirin, acetaminophen, ibuprofen, naproxen, or ketoprofen unless instructed by your care team. These medications may hide a fever. Be careful brushing or flossing your teeth or using a toothpick because you may get an infection or bleed more easily. If you have any dental work done, tell your dentist you are receiving this medication. This medication may cause dry eyes and blurred vision. If you wear contact lenses, you may feel some discomfort. Lubricating eye drops may help. See your care team if the problem does not go away or is severe. Talk to your care team if you may be pregnant. Serious birth defects can occur if you take this medication during pregnancy and for 7 months after the last dose. If your partner can get pregnant, use a condom during sex while taking this medication and for 4 months after the last dose. Do not breastfeed while taking this medication and for 7 months after the last dose. This medication may cause infertility. Talk to your care team if you are concerned about your fertility.

What are the most serious risks of this medication?

If you can become pregnant, you will need a test to make sure you are not pregnant before starting this medication. You must use contraception while taking this medication. You may need to keep using contraception even after you stop taking the medication. This depends on the medication. It is important to talk to your care team about how long to use contraception. Call your care team right away if you think you may be pregnant, have unprotected sex, or if you think your contraception did not work. This medicine may cause serious, life threatening lung damage.