Lapatinib Newbury (Lapatinib)

Lapatinib acts on HER2‑driven cancers by inhibiting intracellular tyrosine kinase signaling.

• HER2‑positive metastatic breast cancer: improves disease control when used alone or with other HER2‑targeted agents.
• HER2‑positive advanced gastric or gastro‑oesophageal junction adenocarcinoma: provides an additional therapeutic option after prior treatment.
• HER2‑positive breast cancer in combination therapy: used together with capecitabine and trastuzumab to enhance antitumor efficacy.

• Lapatinib binds to the intracellular ATP‑binding sites of the epidermal growth factor receptor (EGFR/ErbB1) and HER2 (ErbB2) tyrosine kinases, preventing their autophosphorylation. This blockade disrupts downstream signaling cascades such as the MAPK and PI3K/AKT pathways, thereby inhibiting tumor cell proliferation, survival, and angiogenesis.

Lapatinib may cause a range of adverse reactions that vary in frequency and severity.

Common Side Effects

• Diarrhea: watery stools occurring in many patients.
• Rash or skin erythema: often mild to moderate.
• Nausea and vomiting: gastrointestinal discomfort.
• Fatigue: reduced energy levels.
• Headache: intermittent mild pain.

Serious or Rare Side Effects

• Hepatotoxicity: elevated liver enzymes or hepatitis.
• Cardiac dysfunction: decreased left‑ventricular ejection fraction.
• Interstitial lung disease/pneumonitis: breathing difficulty and cough.
• Severe skin reactions: Stevens‑Johnson syndrome or toxic epidermal necrolysis.
• QT interval prolongation: risk of cardiac arrhythmia.

Before initiating therapy, clinicians should evaluate patient‑specific risk factors and monitor for potential complications.

• Liver function monitoring: check ALT/AST regularly.
• Cardiac assessment: baseline and periodic echocardiograms.
• Skin examination: watch for severe rashes or desquamation.
• Avoid in severe hepatic impairment: dose adjustment may be required.
• Pregnancy and breastfeeding: safety unknown, use only if benefit outweighs risk.
• Store at ambient temperature: keep in the original container, protect from moisture and light.

Lapatinib's metabolism and cardiac effects can be altered by co‑administered drugs.

Major Interactions (Avoid)

• Strong CYP3A4 inducers (e.g., rifampin, carbamazepine): markedly reduce exposure.
• Strong CYP3A4 inhibitors (e.g., ketoconazole, clarithromycin): increase plasma levels and toxicity risk.
• QT‑prolonging agents (e.g., amiodarone, sotalol): may precipitate arrhythmias.

Moderate Interactions (Monitor Closely)

• Antacids containing aluminum or magnesium: may affect absorption; separate dosing by at least 2 hours.
• Warfarin: potential alteration of INR; monitor coagulation parameters.
• Other HER2‑targeted therapies (e.g., trastuzumab): may increase dermatologic and cardiac toxicity.