Lapatinib Pharos (Lapatinib)

Lapatinib is used to target HER2‑driven cancers, particularly in breast and gastric malignancies.

• HER2‑positive breast cancer: improves progression‑free survival when combined with chemotherapy.
• Metastatic breast cancer: delays disease progression in patients whose tumours overexpress HER2.
• Gastric cancer: used in HER2‑positive advanced gastric adenocarcinoma to extend survival.

• Lapatinib binds to the intracellular ATP‑binding sites of the HER2/ErbB2 and EGFR (ErbB1) tyrosine kinases, preventing autophosphorylation and downstream signaling through the MAPK and PI3K/AKT pathways. This inhibition reduces cellular proliferation, induces apoptosis, and limits tumor growth in HER2‑driven malignancies.

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

Common Side Effects

• Diarrhea: watery stools that may require antidiarrheal therapy.
• Rash: maculopapular skin eruptions, often on the trunk.
• Nausea: sensation of queasiness, sometimes with vomiting.
• Fatigue: persistent tiredness affecting daily activities.

Serious or Rare Side Effects

• Hepatotoxicity: elevated liver enzymes or hepatitis requiring monitoring.
• Cardiac dysfunction: decreased left‑ventricular ejection fraction or heart failure.
• Interstitial lung disease: dyspnea and cough with infiltrates on imaging.

Before initiating therapy, clinicians should assess baseline organ function and monitor patients regularly.

• Monitor liver function: obtain baseline and periodic LFTs during treatment.
• Assess cardiac status: perform baseline echocardiogram and repeat as indicated.
• Check for skin reactions: report severe or worsening rash promptly.
• Avoid in patients with known hypersensitivity to lapatinib or its excipients.
• Store at ambient temperature: keep in the original pack, protect from moisture.

Lapatinib interacts with several drug classes that can alter its exposure or increase toxicity.

Major Interactions (Avoid)

• Strong CYP3A4 inducers (e.g., rifampin, carbamazepine): may markedly reduce lapatinib levels.
• QT‑prolonging agents (e.g., sotalol, quinidine): increase risk of cardiac arrhythmias.
• Antacids containing aluminum or magnesium: can decrease absorption if taken simultaneously.

Moderate Interactions (Monitor Closely)

• CYP3A4 inhibitors (e.g., ketoconazole, clarithromycin): may raise lapatinib concentrations.
• Warfarin: potential for altered INR, requiring closer coagulation monitoring.
• Hormonal contraceptives: reduced efficacy, consider alternative non‑hormonal methods.