Trastuzumab emtansine is used to treat breast cancer. This medication is called a monoclonal antibody. It works by slowing or stopping the growth of cancer cells.

This monograph is about the following trastuzumab emtansine products: trastuzumab emtansine, ado-trastuzumab emtansine.

This medication is given by slow injection into a vein by a health care professional. It is given as directed by your doctor, usually once every 3 weeks. Your first infusion will be given over at least 90 minutes.

The dosage, the speed of your injection, and the length of time you receive trastuzumab emtansine is based on your body weight, medical condition, and response to treatment.

Infusion reactions may happen during the infusion of this drug and for up to 24 hours afterward. Your doctor may prescribe other medications (such as acetaminophen, diphenhydramine) before each treatment to help prevent these side effects. Tell your doctor right away if you have any symptoms of infusion reactions such as chills, fever, flushing, wheezing, shortness of breath, dizziness, or fast heartbeat. Your doctor may slow down or stop your treatment for some time.

To get the most benefit from this medication, do not miss any doses. To help you remember, mark your calendar with a reminder.

See also Warning and How to Use sections.

Diarrhea, dizziness, muscle/joint/back pain, stomach/abdominal pain, constipation, trouble sleeping, nausea, vomiting, mouth sores, dry mouth, changes in taste, and loss of appetite may occur. Nausea and vomiting can be severe. In some cases, your doctor may prescribe medication to prevent or relieve nausea and vomiting. Eating several small meals, not eating before treatment, or limiting activity may help lessen some of these effects. If any of these effects last or get worse, tell your doctor or pharmacist promptly.

Remember that this medication has been prescribed because your doctor has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Tell your doctor right away if you have any serious side effects, including:

• pain/swelling/redness/irritation at the injection site
• bone pain
• increased coughing
• severe headache
• tingling/numbness (such as in the hands, feet, leg)
• mental/mood changes
• fast/pounding heartbeat
• muscle cramps
• easy bruising/bleeding

This drug has caused very serious (rarely fatal) bleeding. Get medical help right away if you develop symptoms of very serious bleeding, including:

• weakness on one side of the body
• trouble speaking
• vision changes
• confusion
• severe stomach/abdominal pain
• vomit that is bloody or looks like coffee grounds
• black/tarry stool

This medication may lower your ability to fight infections. This may make you more likely to get a serious (rarely fatal) infection or make any infection you have worse. Tell your doctor right away if you have any signs of infection (such as sore throat that doesn't go away, fever, chills).

Trastuzumab emtansine can commonly cause a rash that is usually not serious. However, you may not be able to tell it apart from a rare rash that could be a sign of a severe reaction. Get medical help right away if you develop any rash.

A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including:

• rash
• itching/swelling (especially of the face/tongue/throat)
• severe dizziness
• trouble breathing

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US - Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

See also Warning section.

Before using trastuzumab emtansine, tell your doctor or pharmacist if you are allergic to it; or to any trastuzumab deruxtecan, trastuzumab emtansine, trastuzumab, or trastuzumab-hyaluronidase products; or if you have any other allergies. This product may contain inactive ingredients which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Before using this medication, tell your doctor or pharmacist your medical history, especially of:

• previous cancer treatments (including radiation therapy to the chest)
• current infection
• heart disease
• high blood pressure
• lung problems
• liver disease

Trastuzumab emtansine can make you more likely to get infections or may make current infections worse. Stay away from anyone who has an infection that may easily spread (such as chickenpox, COVID-19, measles, flu). Talk to your doctor if you have been exposed to an infection or for more details.

Tell your health care professional that you are using trastuzumab emtansine before having any immunizations/vaccinations. Avoid contact with people who have recently received live vaccines (such as flu vaccine inhaled through the nose).

To lower the chance of getting cut, bruised, or injured, use caution with sharp objects like razors and nail cutters, and avoid activities such as contact sports.

This drug may make you dizzy. Alcohol or marijuana (cannabis) can make you more dizzy. Do not drive, use machinery, or do anything that needs alertness until you can do it safely. Limit alcoholic beverages. Talk to your doctor if you are using marijuana (cannabis).

Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).

Older adults may be more sensitive to the side effects of this drug, especially heart problems (such as heart failure).

Tell your doctor if you are pregnant or plan to become pregnant. You should not become pregnant while using trastuzumab emtansine. Trastuzumab emtansine may harm an unborn baby. Your doctor should order a pregnancy test before you start this medication. Women using this medication should ask about the use of reliable forms of birth control during treatment and for 7 months after the last dose. Men using this medication should ask about the use of reliable forms of birth control during treatment and for 4 months after the last dose. If you or your partner becomes pregnant, talk to your doctor right away about the risks and benefits of this medication.

It is unknown if this drug passes into breast milk. Because of the possible risk to the infant, breastfeeding is not recommended while using this drug and for 7 months after the last dose. Consult your doctor before breastfeeding.

See also Warning section.

Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (including prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor's approval.

Other medications can affect the removal of trastuzumab emtansine from your body, which may affect how trastuzumab emtansine works. Examples include adagrasib, azole antifungals (such as itraconazole, ketoconazole), ceritinib, clarithromycin, cobicistat, mifepristone, nefazodone, HIV protease inhibitors (such as atazanavir), ritonavir, telithromycin, tucatinib, among others.

Trastuzumab emtansine is very similar to trastuzumab, trastuzumab deruxtecan, and trastuzumab-hyaluronidase. Do not use a trastuzumab, trastuzumab deruxtecan, or trastuzumab-hyaluronidase product while using a trastuzumab emtansine product.

If someone has overdosed and has serious symptoms such as passing out or trouble breathing, call 911. Otherwise, call a poison control center right away. US residents can call 1-800-222-1222. Canada residents can call 1-844-764-7669.

Lab and/or medical tests (such as complete blood count, heart/liver function, bilirubin level) should be done before you start using this medication and while you are using it. Keep all medical and lab appointments. Consult your doctor for more details.

It is important to get each dose of this medication as scheduled. If you miss a dose, ask your doctor or pharmacist right away for a new dosing schedule.

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

Your condition can cause complications in a medical emergency. For information about enrolling in MedicAlert, call 1-888-633-4298 (US) or 1-800-668-1507 (Canada).