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Fixed-dose anti-HER2 combination

Pertuzumab with trastuzumab (Specialist drug)

Brand names: Phesgo

This is a combination of two anti-HER2 monoclonal antibodies used in oncology for HER2-positive breast cancer; it is not a rheumatology treatment. A fixed-dose subcutaneous formulation and separate intravenous infusions are both available.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

Clinical monograph

How it works

Pertuzumab blocks HER2 dimerisation (notably HER2–HER3 pairing) while trastuzumab binds a different HER2 epitope; together they give more complete dual HER2 blockade and engage antibody-dependent cellular cytotoxicity against HER2-overexpressing tumour cells.

Prescribing in practice

  • Both antibodies are cardiotoxic and can reduce left ventricular ejection fraction, so assess cardiac function before and regularly during treatment and withhold for significant decline — the central added caution of combining them.
  • Infusion- or administration-related and hypersensitivity reactions can occur and require monitoring.
  • Both are embryotoxic and can cause oligohydramnios, so they must be avoided in pregnancy with effective contraception used.

Monitoring

Monitor left ventricular ejection fraction at baseline and at intervals throughout treatment, alongside observation for infusion reactions and symptoms of heart failure.

Counselling the patient

  • Report breathlessness, ankle swelling or palpitations promptly.
  • Use effective contraception and tell us if pregnancy is possible.
  • Keep all scheduled heart-function scan appointments.

Evidence & guidelines

The dual-blockade combination is supported by randomised trials showing improved survival in HER2-positive breast cancer when added to chemotherapy.

Reference: NICE TA569; SmPC; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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