Trastuzumab: uses, dosing, side effects & brands

How trastuzumab is dosed

From the FDA label for Herceptin (application BLA103792). Other trastuzumab products — different forms, different strengths — are dosed differently. Follow the label for the one you were prescribed.

For intravenous (IV) infusion only. Do not administer as an IV push or bolus. Herceptin has different dosage and administration instructions than subcutaneous trastuzumab products. ( 2.3 ) Do not substitute Herceptin (trastuzumab) for or with ado-trastuzumab emtansine or fam-trastuzumab deruxtecan. ( 2.3 ) Perform HER2 testing using FDA-authorized tests by laboratories with demonstrated proficiency. ( 1 , 2.2 ) Adjuvant Treatment of HER2-Overexpressing Breast Cancer ( 2.2 ) Administer at either: Initial dose of 4 mg/kg over 90 minutes IV infusion, then 2 mg/kg over 30 minutes IV infusion weekly for 12 weeks (with paclitaxel or docetaxel) or 18 weeks (with docetaxel and carboplatin). One week after the last weekly dose of Herceptin, administer 6 mg/kg as an IV infusion over 30–90 minutes every three weeks to complete a total of 52 weeks of therapy, or Initial dose of 8 mg/kg over 90 minutes IV infusion, then 6 mg/kg over 30–90 minutes IV infusion every three weeks for 52 weeks. Metastatic HER2-Overexpressing Breast Cancer ( 2.3 ) Initial dose of 4 mg/kg as a 90 minutes IV infusion followed by subsequent weekly doses of 2 mg/kg as 30 minutes IV infusions. Metastatic HER2-Overexpressing Gastric Cancer ( 2.3 ) Initial dose of 8 mg/kg over 90 minutes IV infusion, followed by 6 mg/kg over 30 to 90 minutes IV infusion every 3 weeks. 2.1 Evaluation and Testing Before Initiating…

Trastuzumab side effects

Who shouldn’t take trastuzumab

Trastuzumab drug interactions

Combination products containing trastuzumab

A combination is a different drug — different dosing, different warnings. It is listed here so you can find it, not so you can substitute it.

• Phesgo

How long trastuzumab keeps

The date on a sealed pack is not the only one: some trastuzumab labels start a second clock once the product is opened or mixed, as short as 24 hours.

Trastuzumab and breastfeeding

From LactMed, the US National Library of Medicine’s Drugs and Lactation Database — quoted, not rewritten.

Trastuzumab milk concentrations were collected in one mother. Concentrations were low, consistent with it being a large protein molecule with a molecular weight of about of 145,531 Da. It is also likely to be partially destroyed in the infant's gastrointestinal tract and absorption by the infant is probably minimal. Until more data become available, trastuzumab should be used with caution during breastfeeding, especially while nursing a newborn or preterm infant. The manufacturer recommends that breastfeeding be discontinued during trastuzumab therapy and for 7 months after the last dose.

National Institute of Child Health and Human Development, record revised June 15, 2026. LactMed states its information is not a substitute for professional judgement.

What people report to the FDA about trastuzumab

The FDA Adverse Event Reporting System (FAERS) collects reports from patients and clinicians. It holds 36,591 reports naming trastuzumab, and the FDA flagged 95% of those reports as serious. The effects reported most often — leaving out reports about overdose, misuse or the condition being treated, which dominate the raw list for common medicines:

• diarrhoea3,821 reports
• nausea2,842 reports
• fatigue2,497 reports
• myelosuppression2,211 reports
• vomiting1,867 reports
• neutropenia1,690 reports
• dyspnoea1,538 reports
• pyrexia1,486 reports

Source: openFDA drug/event (FAERS), retrieved July 26, 2026.

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