Trastuzumab

Class:

• HER2-targeted monoclonal antibody (humanized IgG1)

Mechanism of Action:

• Binds to the extracellular domain IV of the HER2 receptor on cancer cells.
• Blocks HER2 receptor signaling pathways that promote cell growth and survival.
• Induces antibody-dependent cellular cytotoxicity (ADCC), enhancing immune-mediated tumor cell killing.

Indications:

• HER2-positive breast cancer in early-stage, locally advanced, and metastatic settings.
• Used in combination with chemotherapy or as monotherapy in certain settings.

Administration:

• Intravenous infusion (initial loading dose followed by maintenance doses every 1–3 weeks)
• Also available as a subcutaneous formulation.

Key Toxicities:

• Cardiotoxicity (reduced left ventricular ejection fraction, congestive heart failure)
• Infusion-related reactions (fever, chills, rash)
• Pulmonary toxicity (rare)

Pharmacist Considerations

• Monitor cardiac function (LVEF) regularly before and during treatment.
• Educate patients on signs/symptoms of heart failure and infusion reactions.
• Coordinate administration with chemotherapy schedules.
• Minimal drug interactions due to monoclonal antibody nature.
• Counsel on adherence to treatment duration, which may extend up to 1 year in the adjuvant setting.