Trastuzumab is used to treat breast cancer. Trastuzumab belongs to a class of medications known as monoclonal antibodies. It works by slowing or stopping the growth of cancer cells. This product also contains hyaluronidase, which helps your body absorb trastuzumab given by injection under the skin.

This monograph is about the following trastuzumab products: trastuzumab (subcutaneous) and trastuzumab-hyaluronidase-oysk. These products are not the same as other trastuzumab products, including trastuzumab emtansine, or trastuzumab given by injection into a vein, and should not be used in place of each other.

This medication is given by slow injection (over 2 to 5 minutes) under the skin by a health care professional. It is given as directed by your doctor, usually once every 3 weeks. The injection is given in the thigh and the injection site and side are changed each time to lessen injury under the skin. The dosage is based on your medical condition and response to treatment.

Use this medication regularly to get the most benefit from it. To help you remember, mark your calendar with a reminder.

Serious reactions, including an allergic reaction, may happen with your injection, usually within 24 hours after your dose. Your doctor may prescribe other medications (such as acetaminophen, diphenhydramine) before each dose to help prevent these side effects. Get medical help right away if you have any symptoms of serious reactions such as fever, chills, flushing, headache, nausea/vomiting, coughing, chest pain, trouble breathing, itching/swelling (especially of the face/tongue/throat), dizziness, weakness, or feeling faint.

See also Warning and How to Use sections.

Redness/irritation at the injection site, diarrhea, muscle/joint/back pain, stomach/abdominal pain, trouble sleeping, mouth sores, and loss of appetite may occur. Headache, nausea, and vomiting may also happen outside of the 24 hours after your injection. 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:

• bone pain
• numbness/tingling
• mental/mood changes
• fast/pounding heartbeat

This medication may raise your blood pressure. Check your blood pressure regularly and tell your doctor if the results are high.

Get medical help right away if you have any very serious side effects, including:

• weakness on one side of the body
• trouble speaking
• vision changes
• confusion

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, cough).

This medication 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. Tell your doctor 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 subcutaneous trastuzumab, tell your doctor or pharmacist if you are allergic to trastuzumab or hyaluronidase; or to any trastuzumab, trastuzumab deruxtecan, or trastuzumab emtansine 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:

• current/recent infection
• heart problems (such as heart failure, irregular heartbeat)
• high blood pressure
• lung problems
• previous cancer treatments (including radiation treatment)

This medication 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 before having any immunizations/vaccinations. Avoid contact with people who have recently received live vaccines (such as flu vaccine inhaled through the nose).

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 at greater risk for heart problems (such as heart failure) while using this drug.

Tell your doctor if you are pregnant or plan to become pregnant. You should not become pregnant while using trastuzumab. Trastuzumab may harm an unborn baby. Your doctor should order a pregnancy test before you start this medication. Ask about reliable forms of birth control while using this medication and for 7 months after the last dose. If you become 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. Consult your doctor before breastfeeding while using this medication and for 7 months after stopping treatment.

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.

Trastuzumab is very similar to trastuzumab deruxtecan and trastuzumab emtansine. Do not use a trastuzumab deruxtecan or trastuzumab emtansine product while using a trastuzumab 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 heart exams, complete blood count, blood pressure) should be done before you start using this medication and while you are using it. Keep all medical and lab appointments.

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 hospital or clinic 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).