SIDE EFFECTS: See also Warning section. Diarrhea, redness/irritation at injection (IV) site, muscle/joint/back pain, stomach/abdominal pain, trouble sleeping, nausea, vomiting, mouth sores, 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 these effects persist or worsen, tell your doctor or pharmacist promptly. Remember that your doctor has prescribed this medication because he or she 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: symptoms of heart failure (such as shortness of breath, swelling ankles/feet, unusual tiredness, unusual/sudden weight gain), bone pain, increased coughing, severe headache, tingling/numbness (e.g., in the hands, feet, leg), mental/mood changes, fast/pounding heartbeat, easy bruising/bleeding. Get medical help right away if you have any very serious side effects, including: weakness on one side of the body, slurred speech, vision changes, confusion. This medication can lower the body's ability to fight an infection. Tell your doctor promptly if you develop any signs of an infection such as fever, chills, or persistent sore throat. This medication can sometimes cause a serious infusion (IV) reaction. Immediately tell your doctor of the following side effects that occur while this drug is being given or within 24 hours after your treatment is finished, such as chills, fever, flushing, nausea, headache, dizziness, fainting, rash, and weakness. (See also Warning section.) Trastuzumab 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. Therefore, 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.

PRECAUTIONS: See also Warning section. Before using trastuzumab, tell your doctor or pharmacist if you are allergic to it; or to other mouse protein medications; or if you have any other allergies. This product may contain inactive ingredients (such as benzyl alcohol), 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, virus infection with returning symptoms (e.g., herpes, shingles), heart disease, high blood pressure, lung problems, previous severe reaction to monoclonal antibody treatment. Trastuzumab can make you more likely to get infections or may worsen any current infections. Therefore, wash your hands well to prevent the spread of infection. Avoid contact with people who have infections that may spread to others (such as chickenpox, measles, flu). Consult your doctor if you have been exposed to an infection or for more details. Do not have immunizations/vaccinations without the consent of your doctor. Avoid contact with people who have recently received live vaccines (such as flu vaccine inhaled through the nose). To lower your risk 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 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. Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products). Caution is advised when using this drug in the elderly because they may be at greater risk for heart problems (e.g., heart failure). 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. Ask about reliable forms of birth control while using this medication and for 7 months after stopping treatment. 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 breast-feeding while using this medication and for 7 months after stopping treatment.

DRUG INTERACTIONS: 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. If you will be using an anthracycline (such as doxorubicin) after stopping trastuzumab treatment, if possible, wait at least 7 months.

OVERDOSE: 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 their local poison control center at 1-800-222-1222. Canada residents can call a provincial poison control center.