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trastuzumab, Herceptin

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GENERIC NAME: trastuzumab

BRAND NAME: Herceptin

DRUG CLASS AND MECHANISM: Trastuzumab is an intravenous drug that is used to treat breast cancer that has spread (metastasized). It belongs to a class of drugs called monoclonal antibodies. Other monoclonal antibodies include rituximab (Rituxan) and gemtuzumab ozogamicin (Mylotarg). The cells of tumors have various receptors on their surfaces. Chemicals bind to these receptors and cause changes within the tumor cells. One of the receptors which occurs in about one-third of all breast cancers is called HER2. HER2 is known to control the growth and development of the tumor cells and the production of new tumor cells. If HER2 receptors are present in large numbers on the tumor cells (often referred to as overexpression of HER2), then the tumor cells may multiply and grow quickly. Normally, the immune system produces antibodies that will detect and attack HER2 receptors to slow the growth of tumor cells However, if HER2 is present in large numbers, the immune system may be unable to control HER2. Trastuzumab is a man-made antibody developed using molecular cloning and recombinant DNA technology. Trastuzumab is thought to block the HER2 receptors when there is overexpression and thereby block tumor growth and development. Trastuzumab was approved by the FDA in 1998.

GENERIC AVAILABLE: no

PRESCRIPTION: yes

PREPARATIONS: Trastuzumab is available as a powder in a vial containing 440 mg of drug. It must be mixed with a liquid before intravenous injection.

STORAGE: Trastuzumab should be stored at 2-8°C (36-46°F) and should not be frozen.

PRESCRIBED FOR: Trastuzumab is used to treat metastatic breast cancer among patients who overexpress HER2. There are two situations in which trastuzumab may be used. In the first, trastuzumab is used as the only drug for patients who already have received one or more regimens of chemotherapy. In the second, trastuzumab is used in combination with paclitaxel (Taxol) for patients who have not yet received chemotherapy for their metastatic breast cancer.

DOSING: Trastuzumab usually is administered intravenously with an initial dose of 4 mg per kilogram of body weight followed by a weekly dose of 2 mg per kilogram of body weight.

DRUG INTERACTIONS: There have been no studies of drug interactions with trastuzumab.

PREGNANCY: There are not enough studies to draw conclusions about the safety and efficacy of trastuzumab in pregnant women.

NURSING MOTHERS: Nursing mothers should avoid trastuzumab therapy and not begin nursing for six months after discontinuing the drug. Since trastuzumab is a type of antibody that can be secreted into breast milk and absorbed by the infant, it has the potential for harming nursing infants.

SIDE EFFECTS: The most common side effects with trastuzumab alone include diarrhea (25% of patients), a prickling or burning sensation in the skin (9% of patients), either an upper respiratory or a catheter related infection (26% of patients), increased cough (26% of patients), nausea and vomiting (23-33% of patients), rash (18% of patients), and infusion related side effects including mild to moderate chills and/or fever (40% of patients). More patients experience these side effects when trastuzumab is given in combination with paclitaxel. Back pain may occur in 22% of patients receiving trastuzumab alone. More serious but less-common side effects may develop if trastuzumab is given with paclitaxel other chemotherapeutic drugs, for example, cyclophosphamide (Cytoxan) or doxorubicin (Rubex). Damage to the heart including congestive heart failure (CHF) or ventricular dysfunction may occur in 19% of patients receiving trastuzumab with another chemotherapeutic drug in contrast to 2-20% of patients receiving only one of the drugs. Other less-common side effects of trastuzumab alone or combined with paclitaxel include decreased red and/or white blood cells, increased heart rate, body swelling, acne, and herpes simplex infections.

Reference: FDA Prescribing Information

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