Lapatinib Newbury (Lapatinib)

Lapatinib is a targeted therapy that inhibits HER2‑driven signaling pathways in certain cancers.

• HER2‑positive metastatic breast cancer: when added to standard chemotherapy, Lapatinib has been shown to extend progression‑free survival and, in some studies, improve overall response rates in adult patients.
• HER2‑positive advanced gastric cancer: Lapatinib is combined with chemotherapy agents to slow tumor growth, providing clinical benefit by prolonging time to disease progression in eligible patients.
• HER2‑positive early breast cancer (adjuvant setting): investigated as part of combination therapy to reduce the risk of disease recurrence after surgery.

• Lapatinib exerts its antineoplastic effect by reversibly binding to the intracellular kinase domains of both epidermal growth factor receptor (EGFR/ErbB1) and HER2/ErbB2. This dual inhibition blocks autophosphorylation and downstream signaling through the MAPK and PI3K/AKT pathways, thereby reducing tumor cell proliferation, survival and angiogenesis. The blockade also impairs cell cycle progression and promotes apoptotic mechanisms in HER2‑driven malignancies.

Lapatinib may cause a range of adverse reactions, varying from mild to severe.

Common Side Effects

• Diarrhea: frequent watery stools that may lead to dehydration.
• Rash: acne‑like skin eruptions, often on the trunk and extremities.
• Nausea: feeling of sickness that may be accompanied by vomiting.
• Fatigue: persistent tiredness affecting daily activities.

Serious or Rare Side Effects

• Hepatotoxicity: elevated liver enzymes or liver failure requiring monitoring.
• Cardiac dysfunction: decreased left ventricular ejection fraction or heart failure.
• Severe skin reactions: Stevens‑Johnson syndrome or toxic epidermal necrolysis.

Before initiating Lapatinib therapy, clinicians should consider several precautionary measures to ensure patient safety.

• Cardiac monitoring: assess baseline and periodic left ventricular function during treatment.
• Liver function: check hepatic enzymes before start and regularly while on therapy.
• Skin assessment: examine for rash or severe dermatologic reactions and manage promptly.
• Diarrhea management: educate patients on early intervention and hydration strategies.
• Drug hypersensitivity: avoid use in individuals with known allergy to Lapatinib or its excipients.
• Store at below 25°C: keep in original packaging, protect from moisture and direct sunlight.

Lapatinib is metabolized primarily by CYP3A4, and several drugs can alter its plasma concentrations.

Major Interactions (Avoid)

• Strong CYP3A4 inhibitors (e.g., ketoconazole, itraconazole): may increase Lapatinib exposure and toxicity.
• Strong CYP3A4 inducers (e.g., rifampin, phenytoin): may reduce efficacy by lowering drug levels.
• Antacids that raise gastric pH (e.g., aluminum‑magnesium hydroxide): can decrease absorption of Lapatinib.

Moderate Interactions (Monitor Closely)

• CYP3A4 substrates with narrow therapeutic index (e.g., warfarin, tacrolimus): monitor plasma levels.
• Statins (e.g., simvastatin, lovastatin): increased risk of myopathy; consider dose adjustment.
• Oral contraceptives: Lapatinib may reduce effectiveness; advise alternative contraception.