Lapatinib Eg (Lapatinib)

Lapatinib is used in HER2‑driven cancers, targeting pathways that promote tumor growth.

• HER2‑positive metastatic breast cancer: Used with capecitabine or other chemotherapy to extend progression‑free survival.
• HER2‑positive gastric cancer: Combined with chemotherapy to improve disease control.
• HER2‑positive breast cancer after trastuzumab resistance: Provides an alternative targeted therapy option.

• Lapatinib blocks the intracellular tyrosine kinase domains of both epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor‑2 (HER2). By preventing autophosphorylation, it inhibits downstream signaling pathways such as MAPK and PI3K/AKT, reducing cellular proliferation and survival in tumor cells that depend on EGFR/HER2 signaling. The inhibition is reversible and selective, allowing concurrent use with other agents that target complementary mechanisms.

Lapatinib may cause a range of adverse reactions, which are categorized by frequency and severity.

Common Side Effects

• Diarrhea: frequent watery stools.
• Rash: skin irritation often on trunk.
• Nausea: mild to moderate feeling of sickness.
• Fatigue: general tiredness.

Serious or Rare Side Effects

• Cardiotoxicity: decreased left ventricular ejection fraction.
• Severe skin reactions: Stevens‑Johnson syndrome or toxic epidermal necrolysis.
• Liver injury: elevated transaminases or hepatitis.
• Interstitial lung disease: breathing difficulties and cough.

When prescribing Lapatinib, clinicians should observe several precautionary measures to minimize risk.

• Cardiac monitoring: baseline and periodic assessment of left ventricular function.
• Liver function: check transaminases before starting and during therapy.
• Dermatologic assessment: monitor for severe rash or hand‑foot syndrome.
• Drug interactions: avoid concomitant use with strong CYP3A4 inhibitors.
• Pregnancy and lactation: contraindicated; advise effective contraception.
• Store at ambient temperature: keep below 25 °C in original packaging, protect from moisture.

Lapatinib interacts with several medicines that can alter its plasma concentration or increase toxicity.

Major Interactions (Avoid)

• Strong CYP3A4 inhibitors (e.g., ketoconazole, clarithromycin): may raise Lapatinib levels and risk severe toxicity.
• Strong CYP3A4 inducers (e.g., rifampicin, carbamazepine): can lower exposure, reducing efficacy.

Moderate Interactions (Monitor Closely)

• Antacids or proton pump inhibitors: may affect absorption; separate dosing by at least 2 hours.
• Warfarin: potential increase in INR; monitor coagulation parameters.
• St. John’s wort: may modestly reduce Lapatinib concentrations; observe therapeutic response.