Lapatinib is a 4-anilinoquinazoline kinase inhibitor of the intracellular tyrosine kinase domains of both EGFR and of HER2 receptors.

Recommended dose is 1,250 mg (5 tablets) given orally once daily on days 1–21 continuously in combination with capecitabine 2,000 mg/m²/day (administered orally in two doses approximately 12 hours apart) on days 1–14 in a repeating 21-day cycle.

Indicated in combination with capecitabine, for the treatment of patients with advanced or metastatic breast cancer whose tumors overexpress HER2 and who have received prior therapy including an anthracycline, a taxane, and trastuzumab.

Most common adverse reactions during treatment of lapatinib plus capecitabine were diarrhea, palmar-plantar erythrodysesthesia, nausea, rash, vomiting, and fatigue.

Should be taken at least one hour before or one hour after a meal. However, capecitabine should be taken with food or within 30 minutes of food.

Should be taken once daily. Do not divide the daily dose.

Modify the dose for cardiac and other toxicities, severe hepatic impairment, and CYP3A4 drug interactions. Decreases in left ventricular ejection fraction (LVEF) have been reported. Confirm normal LVEF function before therapy begins. May prolong QT interval in some patients. Monitor with ECG as needed. Consider dose reduction in patients with severe hepatic impairment. Multiple CYP3A4 drug interactions exist.

Severe diarrhea may be managed with antidiarrheal agents, and replace fluids and electrolytes if severe.

Lapatinib may cause fetal harm when administered to pregnant women. Advise women not to become pregnant while on lapatinib.