Anti-HER2 monoclonal antibody Pregnancy: Should be avoided during pregnancy unless the potential benefit for the mother outweighs the potential risk to the foetus. In the post-marketing setting, cases of foetal renal growth and/or function impairment associated with oligohydramnios — some with fatal pulmonary hypoplasia of the foetus — have been reported. Women of childbearing potential should use effective contraception during treatment and for 7 months after treatment concludes; women should not breast-feed during therapy and for 7 months after the last dose. If a pregnant woman is treated, or a patient becomes pregnant during treatment or within 7 months of the last dose, close monitoring by a multidisciplinary team is desirable.

Trastuzumab (Specialist drug)

Brand names: Herceptin, Herzuma, Ontruzant

Trastuzumab is a monoclonal antibody used under specialist supervision for HER2-positive breast cancer and HER2-positive metastatic gastric cancer.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Three-weekly schedule (metastatic breast cancer, early breast cancer and metastatic gastric cancer): initial loading dose 8 mg/kg body weight, then a maintenance dose of 6 mg/kg body weight

Route: Intravenous infusion — the loading dose is given over 90 minutes; do not administer as an intravenous push or bolus. If the loading dose was well tolerated, subsequent doses may be given as a 30-minute infusion

Frequency: Every three weeks, with maintenance beginning three weeks after the loading dose

HER2 testing is mandatory before initiation. Treatment should only be initiated by a physician experienced in the administration of cytotoxic chemotherapy and administered by a healthcare professional only. It is important to check product labels to ensure the correct formulation (intravenous or subcutaneous fixed dose) is given — the intravenous formulation is not intended for subcutaneous administration — and to ensure the product is trastuzumab and not another trastuzumab-containing product (e.g. trastuzumab emtansine or trastuzumab deruxtecan). Weekly schedule (metastatic breast cancer): initial loading dose 4 mg/kg body weight, then weekly maintenance 2 mg/kg body weight beginning one week after the loading dose. Early breast cancer weekly regimen: loading dose 4 mg/kg followed by 2 mg/kg every week, concomitantly with paclitaxel following chemotherapy with doxorubicin and cyclophosphamide. Duration: metastatic breast or gastric cancer — treat until disease progression; early breast cancer — treat for 1 year or until disease recurrence, whichever occurs first (extending beyond one year is not recommended). Dose reduction: no reductions were made during clinical trials; if LVEF drops by 10 percentage points or more from baseline AND to below 50%, suspend treatment and repeat the LVEF assessment within approximately 3 weeks — if LVEF has not improved, has declined further, or symptomatic congestive heart failure has developed, strongly consider discontinuation. Missed doses: if missed by one week or less, give the usual maintenance dose (weekly 2 mg/kg; three-weekly 6 mg/kg) as soon as possible and resume the schedule; if missed by more than one week, give a re-loading dose over approximately 90 minutes (weekly 4 mg/kg; three-weekly 8 mg/kg) as soon as possible, then resume maintenance 7 or 21 days later. Administration must be by a healthcare provider prepared to manage anaphylaxis, with an emergency kit available; observe patients for at least six hours after the start of the first infusion and for two hours after subsequent infusions. Paediatric population: there is no relevant use of this product in the paediatric population.

Dose adjustments

Renal

Dedicated pharmacokinetic studies in the elderly and in those with renal or hepatic impairment have not been carried out. In a population pharmacokinetic analysis, age and renal impairment were not shown to affect trastuzumab disposition.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to trastuzumab, murine proteins, or to any of the excipients
Severe dyspnoea at rest due to complications of advanced malignancy or requiring supplementary oxygen therapy

Side effects

Cardiac dysfunction — very common decreased ejection fraction, decreased or increased blood pressure, irregular heart beat and cardiac flutter; common congestive cardiac failure
Infusion-related reactions and hypersensitivity (common), with rare anaphylactic reaction and anaphylactic shock
Haematotoxicity — very common febrile neutropenia, anaemia, neutropenia, leukopenia and thrombocytopenia; common neutropenic sepsis
Infections — very common infection and nasopharyngitis; common cystitis, influenza, sinusitis, skin infection, rhinitis, upper respiratory tract infection, urinary tract infection and pharyngitis
Pulmonary adverse reactions; also very common tremor, dizziness, headache, paraesthesia, dysgeusia, insomnia, weight loss, anorexia, conjunctivitis and increased lacrimation

Clinical monograph

How it works

It binds the HER2 receptor on tumour cells, blocking HER2-mediated growth signalling and recruiting immune-mediated cytotoxicity.

Prescribing in practice

Cardiotoxicity is the key concern — assess cardiac function before and during treatment and avoid or use cautiously with anthracyclines.
It is reserved for HER2-positive tumours confirmed by validated testing and is prescribed by oncology specialists.
Infusion-related reactions can occur, particularly with the first infusion.

Monitoring

Monitor left ventricular ejection fraction at baseline and at regular intervals throughout therapy.

Counselling the patient

Report breathlessness, ankle swelling, palpitations or a persistent cough.
Tell the team about any reaction during or shortly after an infusion.
Effective contraception is advised during and after treatment.

Evidence & guidelines

Benefit in HER2-positive breast cancer is established by the HERA and pivotal adjuvant trials and supported by NICE guidance.

Reference: NICE TA34/TA208; SmPC; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways