1 What is this medicine
and what is it used for?
Lapatinib is an oral dual tyrosine kinase inhibitor that
blocks both EGFR (HER1) and HER2 receptor tyrosine kinases simultaneously. HER2
overexpression drives tumour growth in approximately 20–25% of breast cancers;
lapatinib blocks the intracellular signalling downstream of both receptors,
inhibiting cancer cell proliferation and survival.
It is used in combination (never as monotherapy) for:
HER2-positive advanced or metastatic breast cancer — in combination with
capecitabine (after prior treatment with anthracycline, taxane, and
trastuzumab); or in combination with letrozole in post-menopausal women with
HER2-positive, hormone receptor-positive metastatic breast cancer.
2 How to take this
medicine
The usual dose is 1250 mg (5 tablets of 250 mg) once daily
when combined with capecitabine, OR 1500 mg (6 tablets) once daily when
combined with letrozole. Take on an EMPTY STOMACH — at least 1 hour before or 1
hour after a meal. Take all tablets at the same time each day. Do not crush or
chew.
|
IMPORTANT DOSING INSTRUCTIONS: Take on an EMPTY STOMACH — food significantly
increases lapatinib absorption and toxicity risk. A high-fat meal can
increase exposure by 327%. Taking with food is not acceptable for this
medicine. Avoid grapefruit, grapefruit juice, and Seville
oranges throughout treatment. Missing a dose: if remembered on the same day,
take it. If the next day has started, skip it — never double up. |
3 Possible side effects
|
Frequency |
Side Effect |
What to Do |
|
Very Common (>10%) |
Diarrhoea |
Start loperamide at
the first loose stool; stay hydrated. Contact team if > 4 stools above
baseline. |
|
Very Common (>10%) |
Hand-foot syndrome
(palmar-plantar erythrodysaesthesia) |
Apply thick emollient
cream daily from start; cushioned footwear; report early. |
|
Very Common (>10%) |
Nausea / vomiting |
Anti-emetics as
prescribed; take on empty stomach. |
|
Very Common (>10%) |
Fatigue |
Rest; assess for
underlying anaemia. |
|
Very Common (>10%) |
Rash (acneiform) |
Gentle skin care;
sunscreen; report severe rash. |
|
Common (1–10%) |
Cardiac left
ventricular dysfunction (LVEF decrease) |
Baseline LVEF
required; monitoring during treatment. Discontinue if symptomatic or
significant drop. |
|
Common (1–10%) |
Elevated liver enzymes
/ hepatotoxicity |
Regular LFT
monitoring; report jaundice or dark urine. |
|
Seek help urgently |
QT prolongation, chest
pain, palpitations |
Stop and seek urgent
cardiology review. |
4 Contraindications
Lapatinib must not be used in: known hypersensitivity; severe
hepatic impairment (Child-Pugh C) — contraindicated; known QT prolongation; and
with strong CYP3A4 inhibitors or inducers without dose adjustment.
5 Drug interactions
• Strong CYP3A4 inhibitors
(ketoconazole, itraconazole, ritonavir, clarithromycin): markedly increase
lapatinib — avoid or reduce lapatinib dose to 500 mg/day.
• Strong CYP3A4 inducers (rifampicin,
carbamazepine, dexamethasone, St John's Wort): markedly reduce lapatinib levels
— avoid; if unavoidable, increase lapatinib dose gradually.
• QT-prolonging agents: additive risk —
avoid or monitor ECG.
• Substrates of CYP3A4, CYP2C8 and
P-glycoprotein (digoxin, warfarin, ciclosporin): lapatinib inhibits these —
monitor levels.
6 Storage
Store below 30°C. Original packaging, protect from moisture.
Keep out of reach of children.
7 Prescription
requirement
|
PRESCRIPTION ONLY MEDICINE (POM) — Specialist
oncology prescription required. Pre-treatment: LVEF by ECHO or MUGA; LFTs; ECG
(QTc interval); electrolytes. Monitoring during treatment: LVEF every 8
weeks; LFTs monthly. |
8 Guidance for patients
& caregivers
Lapatinib must always be taken on an empty stomach — this is
one of the most important instructions. Food dramatically increases drug
absorption and worsens side effects. Plan your daily schedule so you take the
tablets at least 1 hour before or 1 hour after eating.
Diarrhoea and hand-foot syndrome are the most common reasons
for dose reductions. Both are more manageable with early action: start
loperamide at the very first loose stool; apply thick emollient cream to hands
and feet every day from the start of treatment.
9 Pharmacist &
prescriber notes
Lapatinib 1250 mg/day (5 × 250 mg) with capecitabine is the
EMA-approved combination for trastuzumab-pretreated HER2+ MBC. The 1500 mg/day
(6 × 250 mg) dose is used with letrozole in hormone
receptor-positive/HER2-positive MBC.
LVEF monitoring is mandatory — discontinue permanently if
absolute LVEF decrease ≥ 20% below baseline and below institutional lower limit
of normal.
Hepatotoxicity: severe (Grade 3+) in ~2% — monitor LFTs
monthly; reduce dose to 750 mg/day in severe hepatic impairment (Child-Pugh C).
150-tablet pack = 30 days at 5 tablets/day. QTc baseline essential — do not
start if QTc > 480 ms.
10 Frequently asked
questions
My heart scan showed a change — what does that mean?
Lapatinib can reduce the heart's pumping function (LVEF) in
some patients. Your oncologist will discuss whether a dose adjustment or
temporary break in treatment is needed based on the degree of change.
Can I take ibuprofen for pain?
Consult your oncologist before taking any over-the-counter
medicines. NSAIDs can interact with capecitabine (your combination partner) and
should generally be avoided.
Why do I need an ECG before starting?
Lapatinib can prolong the QT interval on ECG — a measure of
heart electrical recovery. Prolonged QT can lead to dangerous arrhythmias.
Baseline ECG checks ensure it is safe to start.
What do I do if I have very bad diarrhoea?