Lapatinib

HER2 tyrosine kinase inhibitors
HER2 tyrosine kinase inhibitors
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: a pregnancy test is done before starting, effective contraception is used during treatment and for a time afterwards (by women and by men…

An oral dual HER2 and EGFR kinase inhibitor for HER2-positive breast cancer, with capecitabine or letrozole. Boxed warning: liver damage.

Updated Nov 1, 2026

Also called: lapatinib ditosylate, GW572016

Quick facts

Group: HER2 tyrosine kinase inhibitors
Target: HER2 (ERBB2) and EGFR tyrosine kinases
Used for: HER2-positive advanced · Hormone receptor-positive
Key effects: Diarrhoea · Acne-like rash and dry skin · Nausea
Monitor: Liver tests before and during treatment
ATC: L01EH01

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

Mechanism of action

HER2 (ERBB2) and EGFR tyrosine kinasesLapatinib

The figure shows lapatinib (GW572016) in the ATP pocket of the human EGFR kinase domain; it binds the matching site of HER2.

Target in 3D: HER2 (ERBB2) and EGFR tyrosine kinases. PDB structure 1XKK (RCSB PDB, public domain). View the structure at RCSB PDB

Lapatinib reversibly blocks the ATP site of both HER2 and EGFR kinases. In HER2-overexpressing breast cancer this switches off the receptor signal from inside the cell, so it still works in tumours that have become resistant to trastuzumab.

HER2 overexpression drives breast cancer growth
Lapatinib blocks the ATP site of HER2 and EGFR
Works from inside, even after trastuzumab resistance

Indications

HER2-positive advanced or metastatic breast cancer previously treated with an anthracycline, a taxane and trastuzumab, with capecitabine. Breast cancer →
Hormone receptor-positive, HER2-positive metastatic breast cancer in postmenopausal women, with letrozole. Breast cancer →

Adverse effects

Common

Diarrhoea, which can be severe (worse with capecitabine)
Acne-like rash and dry skin
Nausea, vomiting, heartburn and reflux
Red, painful or tingling hands and feet
Mouth sores, decreased appetite, trouble sleeping

Contraindications

Used with caution in heart disease, long QT and low potassium or magnesium

Key interactions

Strong CYP3A4 inhibitors (clarithromycin, itraconazole, ketoconazole, ritonavir) and grapefruit: Raise its levels and its toxicity.
Strong CYP3A4 inducers (rifampicin, carbamazepine, phenytoin, St John's wort): Lower its levels and can make it fail.
Other QT-prolonging drugs (some antiarrhythmics, macrolides, antipsychotics): Additive risk of QT prolongation and arrhythmia.

What is monitored

Liver tests before and during treatment
Heart function (ejection fraction) and ECG
Potassium and magnesium
Stool frequency and hydration

Administration and safety

Oral tablets once daily, at least an hour away from a meal, swallowed whole.
Grapefruit, its juice and St John's wort are avoided because they change its levels.

Pregnancy and breastfeeding

Avoid in pregnancy. Can harm the fetus: a pregnancy test is done before starting, effective contraception is used during treatment and for a time afterwards (by women and by men with partners who could conceive), and breastfeeding is avoided.

Nursing care

Check liver tests before refills as ordered; teach to report jaundice, dark urine or itching.
Teach a diarrhoea plan and the signs of dehydration.
Report breathlessness, swelling or palpitations.
Confirm a negative pregnancy test before the first dose and teach contraception during treatment and afterwards.

Pharmacokinetics

Absorption: Oral tablets, once daily, away from meals.
Metabolism: Liver, CYP3A4.
Half-life: About 14 hours.

Test yourself

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

Which two kinases does lapatinib inhibit?

HER2 (ERBB2) and EGFR.

What is lapatinib's boxed warning?

Severe, possibly fatal hepatotoxicity; liver tests are checked before and during treatment.

With which oral chemotherapy is lapatinib combined, and which side effect gets worse?

Capecitabine; diarrhoea becomes worse.

Add to my cards (3)

Connections

← Back to the class: HER2 tyrosine kinase inhibitors

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

Sources: Lapatinib: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2019); Lapatinib Ditosylate - NCI (National Cancer Institute, 2024); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.