[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Antineoplastic monoclonal antibodies](https://durgical.com/en/pharmacology/classes/antineoplastic-monoclonal-antibodies/) › Trastuzumab

# Trastuzumab

## Antineoplastic monoclonal antibodies?

Antineoplastic monoclonal antibodies

## High alert?

An error with this medicine can cause serious harm: double checks and protocols are used.

## Pregnancy: avoid?

Avoid in pregnancy. Can harm the fetus (including too little amniotic fluid); pregnancy is avoided during treatment and for several months after the last dose.

An anti-HER2 antibody for HER2-positive breast and stomach cancer. Its key risk is heart failure, so the heart's pumping is checked before and during treatment.

Updated Nov 1, 2026

Also called: anti-HER2 antibody

## Quick facts

**Group**
[Antineoplastic monoclonal antibodies](https://durgical.com/en/pharmacology/classes/antineoplastic-monoclonal-antibodies/)

**Target**
HER2 (ErbB2) receptor tyrosine kinase, extracellular domain IV

**Used for**
HER2-overexpressing breast cancer

**Key effects**
Infusion reactions · Diarrhoea · Muscle

**Monitor**
Ejection fraction · Baseline ECG

**ATC**
L01FD01

No doses: the clinician sets them by the current guideline.

On this page

- The basics Mechanism of action
- Indications
- Adverse effects
- Pharmacokinetics
- Memory aid

- Clinical What the labels mean

- Safety Contraindications
- Key interactions
- What is monitored
- Administration and safety
- Pregnancy and breastfeeding
- Nursing care

- Study Test yourself

- Connections Connections

## Mechanism of action

◎**HER2 (ErbB2) receptor tyrosine kinase, extracellular domain IV**Trastuzumab

ⓘ The cryo-EM structure shows the HER2 extracellular domain with two antibody arms bound at once: trastuzumab on domain IV and pertuzumab on domain II.

**Target in 3D:** HER2 (ErbB2) receptor tyrosine kinase, extracellular domain IV. PDB structure 6OGE (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/6OGE) · Drag to rotate · pinch to zoom

About one in four or five breast cancers carries many copies of the ERBB2 gene and overexpresses HER2, which signals for growth even without a ligand. Trastuzumab, a humanised IgG1, binds domain IV of the HER2 extracellular region, reduces HER2 signalling and marks the cell for antibody-dependent cellular cytotoxicity. It only helps tumours with HER2 overexpression or amplification. HER2 signalling also keeps heart muscle working, which explains its cardiotoxicity.

- HER2-amplified tumour cells overexpress HER2
- Trastuzumab binds HER2 domain IV
- Growth signalling falls; immune cells kill (ADCC)
- Loss of HER2 signal in heart muscle: cardiotoxicity

## Indications

- HER2-overexpressing breast cancer, early (adjuvant) or metastatic, usually with a taxane or other chemotherapy. [Breast cancer →](https://durgical.com/en/conditions/breast-cancer/)
- HER2-overexpressing metastatic gastric or gastro-oesophageal junction cancer, with chemotherapy. [Gastric cancer →](https://durgical.com/en/conditions/gastric-cancer/)

## Adverse effects

### Common

- Infusion reactions: fever, chills, nausea, headache, rash
- Diarrhoea, abdominal pain
- Muscle, joint and back pain
- Insomnia
- Tingling of hands and feet

### Serious (rare, important)

- Left ventricular dysfunction and heart failure, more frequent with anthracyclines
- Severe infusion reactions up to 24 hours later
- Severe lung toxicity
- Fetal harm, including too little amniotic fluid
- Low blood counts when combined with chemotherapy

## Contraindications

- Symptomatic heart failure or a low ejection fraction before starting
- HER2-negative tumours (no benefit)

## Key interactions

**Anthracyclines (doxorubicin, epirubicin)**
Together they cause much more left ventricular dysfunction; they are usually given one after the other, not at the same time.

**Taxanes (paclitaxel, docetaxel)**
The usual partners; the cardiac risk is much lower than with anthracyclines.

## What is monitored

- Ejection fraction (echocardiogram or radionuclide scan) before starting and regularly during and after treatment
- Baseline ECG
- Symptoms of heart failure: breathlessness, oedema, rapid weight gain
- Pregnancy test before starting

## Administration and safety

- Intravenous infusion only, never as a push or bolus; watch for chills and fever during and after the infusion.
- Look-alike names: trastuzumab, ado-trastuzumab emtansine and fam-trastuzumab deruxtecan are different drugs and are never substituted for one another.
- The intravenous and subcutaneous (with hyaluronidase) products are not interchangeable.
- Confirm that a recent ejection fraction result is on file before each cycle.

## Pregnancy and breastfeeding

Avoid in pregnancy. Can harm the fetus (including too little amniotic fluid); pregnancy is avoided during treatment and for several months after the last dose.

## Nursing care

- Check vital signs and look for infusion reactions during and after the infusion.
- Ask at each visit about breathlessness, cough, ankle swelling and palpitations; weigh the patient.
- Make sure cardiac imaging is scheduled as ordered.
- Teaching: report sudden weight gain, swelling or shortness of breath; use effective contraception during treatment and for months after.

## Pharmacokinetics

**Absorption**
Intravenous infusion (a subcutaneous form with hyaluronidase also exists).

**Elimination**
Removed like other IgG antibodies; levels take months to reach steady state.

**Half-life**
Several days to weeks, depending on the schedule.

## Memory aid

«Trastuzumab = HER-2-heart»: it targets HER2 and, by the same signal, can weaken the heart. Echo before and during; never at the same time as doxorubicin.

## Test yourself

Think of the answer, then tap the question to see it.

## Which test on the tumour decides whether trastuzumab is used?

HER2 testing: protein overexpression (immunohistochemistry) or gene amplification (in situ hybridisation).

## Why does trastuzumab cause heart failure?

HER2 signalling is needed to keep cardiomyocytes contracting normally; blocking it reduces ejection fraction.

## Which combination raises trastuzumab's cardiac risk the most?

Combination with an anthracycline such as doxorubicin.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/trastuzumab/)

[More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology)

## What the labels mean

**High alert**
An error with this medicine can cause serious harm: double checks and protocols are used.

**Pregnancy: avoid**
Avoid in pregnancy. Can harm the fetus (including too little amniotic fluid); pregnancy is avoided during treatment and for several months after the last dose.

## Connections

## Related drugs 3

- [Cetuximab](https://durgical.com/en/pharmacology/cetuximab/)
- [Bevacizumab](https://durgical.com/en/pharmacology/bevacizumab/)
- [Rituximab](https://durgical.com/en/pharmacology/rituximab/)

## Related conditions 2

- [Breast cancer](https://durgical.com/en/conditions/breast-cancer/)
- [Gastric cancer](https://durgical.com/en/conditions/gastric-cancer/)

[← Back to the class: Antineoplastic monoclonal antibodies](https://durgical.com/en/pharmacology/classes/antineoplastic-monoclonal-antibodies/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [Trastuzumab Injection: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a699019.html) (MedlinePlus (U.S. National Library of Medicine), 2025); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=L01FD01) (WHO Collaborating Centre for Drug Statistics Methodology, 2026); [eEML - Electronic Essential Medicines List](https://list.essentialmeds.org/) (World Health Organization, 2025).

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Representative model, for educational purposes only.

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