Lapatinib Pharos (Lapatinib)

Lapatinib is indicated for HER2‑driven cancers and is used as part of targeted therapy regimens.

• HER2‑positive metastatic breast cancer: improves progression‑free survival when combined with chemotherapy or other HER2‑targeted agents.
• HER2‑positive advanced gastric or gastro‑oesophageal junction adenocarcinoma: inhibits tumor growth in patients with HER2 overexpression.
• HER2‑positive solid tumors (investigational): evaluated in clinical trials for potential benefit in other HER2‑expressing malignancies.

• Lapatinib reversibly binds to the intracellular tyrosine kinase domains of epidermal growth factor receptor (EGFR/ErbB1) and human epidermal growth factor receptor 2 (HER2/ErbB2). By blocking autophosphorylation, it prevents activation of downstream signaling pathways such as MAPK and PI3K/AKT, which are critical for cell proliferation, survival and angiogenesis in HER2‑driven tumors. The inhibition reduces tumor cell signaling, leading to cell cycle arrest and apoptosis in susceptible cancer cells.

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

Common Side Effects

• Diarrhea: frequent watery stools that may require supportive care.
• Rash: skin eruptions, often on the trunk or extremities.
• Nausea: mild to moderate feeling of sickness.
• Fatigue: general tiredness affecting daily activities.

Serious or Rare Side Effects

• Cardiac dysfunction: reduced left ventricular ejection fraction or heart failure.
• Severe skin reactions: Stevens‑Johnson syndrome or toxic epidermal necrolysis.
• Hepatotoxicity: elevated liver enzymes or hepatitis.
• Interstitial lung disease: inflammation of lung tissue causing breathing difficulty.

When prescribing Lapatinib, clinicians should consider several safety precautions to minimize risk.

• Cardiac monitoring: assess baseline and periodic left ventricular function.
• Hepatic function: evaluate liver enzymes before initiation and during therapy.
• Dermatologic assessment: monitor for severe rash or skin reactions.
• Drug interactions: review concomitant medications that affect CYP3A4 metabolism.
• Pregnancy and lactation: avoid use in pregnant or breastfeeding women unless benefits outweigh risks.
• Store at ambient temperature: keep below 25 °C, in original packaging, protected from moisture and light.

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

Major Interactions (Avoid)

• Strong CYP3A4 inducers (e.g., rifampin, carbamazepine): may markedly reduce lapatinib exposure.
• Strong CYP3A4 inhibitors (e.g., ketoconazole, clarithromycin): can increase lapatinib levels and risk of adverse events.

Moderate Interactions (Monitor Closely)

• Antacids containing aluminum or magnesium: may decrease absorption; separate dosing by at least 2 hours.
• Warfarin: potential for altered anticoagulant effect; monitor INR closely.
• Hormonal contraceptives: may reduce efficacy; consider alternative non‑hormonal methods.
• Other HER2‑targeted agents: combined use may increase cardiac toxicity; monitor cardiac function.