Before you begin using a medication, be sure to inform your doctor of any medical conditions or Allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use Tykerb (Lapatinib).

Diarrhea: Tykerb (Lapatinib) can cause diarrhea that can lead to dehydration. Dehydration can cause many symptoms, including decreased urine production, dry and sticky mouth, sleepiness, dizziness, headache, thirst, and confusion. In some cases, dehydration can become a medical emergency. If you have diarrhea or any of these symptoms while taking Tykerb (Lapatinib), let your doctor know.

Heart effects: Tykerb (Lapatinib) can affect heart function. Your doctor will monitor you for these effects while you are taking Tykerb (Lapatinib). If heart problems occur, your doctor may stop Tykerb (Lapatinib) and restart it if your heart function improves.

Tykerb (Lapatinib) can also have an effect on the electrical activity of the heart called QT prolongation. If you experience an abnormal heartbeat, dizziness, palpitations, seizures, or fainting while taking Tykerb (Lapatinib), get immediate medical attention.

If you are at risk of complications due to QT prolongation (e.g., seniors, women, heart disease, abnormal heart rhythms, Stroke, Eating Disorders, Diabetes, a family history of sudden cardiac death) or are taking other medications that can cause QT prolongation (see the section "What medications can interact with Tykerb (Lapatinib)?"), discuss with your doctor how Tykerb (Lapatinib) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Tykerb (Lapatinib), and whether any special monitoring is needed.

Liver problems: Tykerb (Lapatinib) can cause reduced liver function and can cause liver failure, which can be fatal. Your doctor will monitor your liver function with blood tests while you are taking Tykerb (Lapatinib). If your liver function worsens, your doctor may stop Tykerb (Lapatinib).

If you have liver problems, discuss with your doctor how Tykerb (Lapatinib) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Tykerb (Lapatinib), and whether any special monitoring is needed.

If you experience symptoms of liver problems such as fatigue, feeling unwell, loss of appetite, nausea, yellowing of the skin or whites of the eyes, dark urine, pale stools, abdominal pain or swelling, and itchy skin, contact your doctor immediately.

Lung effects: Tykerb (Lapatinib) can cause lung problems. Your doctor will monitor you for these effects while you are taking Tykerb (Lapatinib). If you experience shortness of breath or difficulty breathing while taking Tykerb (Lapatinib), contact your doctor immediately. If lung problems occur, your doctor may need to stop Tykerb (Lapatinib).

Pregnancy: Tykerb (Lapatinib) should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking Tykerb (Lapatinib), contact your doctor immediately. Women who may become pregnant should use contraception and avoid becoming pregnant while they are taking Tykerb (Lapatinib) and for at least 5 days after the last dose.

Breast-feeding: It is not known if Tykerb (Lapatinib) passes into breast milk. If you are a breast-feeding mother and are taking Tykerb (Lapatinib), it may affect your baby. Talk to your doctor about whether you should continue breast-feeding. Breast-feeding while taking Tykerb (Lapatinib) is not recommended.

Children: The safety and effectiveness of using Tykerb (Lapatinib) have not been established for children.