When This Medicine Should Not Be Used:
This medicine is not right for everyone. Do not use it if you had an allergic reaction to lapatinib or you are pregnant.

How to Use This Medicine:
Tablet

• Your doctor will tell you how much medicine to use. Do not use more than directed.
• Take lapatinib at least 1 hour before or 1 hour after a meal. Take all the tablets at the same time.
• This medicine is given together with capecitabine or letrozole. Follow your doctor's instructions on when to take these medicines.
• Read and follow the patient instructions that come with this medicine. Talk to your doctor or pharmacist if you have any questions.
• Missed dose: Take a dose as soon as you remember. If it is almost time for your next dose, wait until then and take a regular dose. Do not take extra medicine to make up for a missed dose.
• Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light.

Drugs and Foods to Avoid:
Ask your doctor or pharmacist before using any other medicine, including over-the-counter medicines, vitamins, and herbal products.

• Some foods and medicines can affect how lapatinib works. Tell your doctor if you are using any of the following:
  
  • Dexamethasone, digoxin, midazolam, nefazodone, paclitaxel, or St John's wort
  • Medicine to treat heart rhythm problems or lower blood pressure
  • Medicine to treat an infection (such as clarithromycin, itraconazole, ketoconazole, rifabutin, rifampin, rifapentine, voriconazole)
  • Medicine to treat HIV infection (such as atazanavir, indinavir, nelfinavir, ritonavir, saquinavir, telithromycin)
  • Medicine to treat seizures (such as carbamazepine, phenytoin, phenobarbital)
• Do not eat grapefruit or drink grapefruit juice while you are using this medicine.

Warnings While Using This Medicine:

• It is not safe to take this medicine during pregnancy. It could harm an unborn baby. Tell your doctor right away if you become pregnant.
• Tell your doctor if you are breastfeeding, or if you have liver disease, heart disease, heart rhythm problems (such as QT prolongation), or lung disease.
• This medicine may cause the following problems:
  
  • Heart problems, including changes in heart rhythm
  • Liver problems
  • Lung problems
  • Serious skin reactions
• Medicines used to treat cancer are very strong and can have many side effects. Before receiving this medicine, make sure you understand all the risks and benefits. It is important for you to work closely with your doctor during your treatment.
• Your doctor will do lab tests at regular visits to check on the effects of this medicine. Keep all appointments.
• Keep all medicine out of the reach of children. Never share your medicine with anyone.

Possible Side Effects While Using This Medicine:
Call your doctor right away if you notice any of these side effects:

• Allergic reaction: Itching or hives, swelling in your face or hands, swelling or tingling in your mouth or throat, chest tightness, trouble breathing
• Blistering, peeling, or red skin rash
• Chest pain, cough, trouble breathing
• Dark urine or pale stools, nausea, vomiting, loss of appetite, stomach pain, yellow skin or eyes
• Dizziness, lightheadedness, unusual tiredness
• Fast, slow, pounding, or uneven heartbeat
• Severe diarrhea or diarrhea with cramps, nausea, vomiting, or fever

If you notice these less serious side effects, talk with your doctor:

• Mild diarrhea, nausea, or vomiting, stomach upset
• Rash
• Red, painful hands and feet, rash

If you notice other side effects that you think are caused by this medicine, tell your doctor.
Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088