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Lapatinib is used together with another medication (capecitabine) to treat a certain type of breast cancer (HER2-positive) that has not responded to the standard treatment. It works by slowing or stopping the growth of cancer cells.

For the best possible benefit, it is important to take each scheduled dose of this medication as directed. If you miss a dose, take it as soon as you remember. If it is near the time of the next dose, skip the missed dose and resume your usual dosing schedule. Do not double the dose to catch up.

Read the Patient Information Leaflet provided by your pharmacist before you start using lapatinib and each time you get a refill. If you have any questions, consult your doctor or pharmacist. Take this medication by mouth 1 hour before or 1 hour after a meal, usually once daily or as directed by your doctor. It is important that you do not take this medication more than once daily. The dosage is based on your medical condition, response to treatment, and certain other drugs you may be taking. Do not increase your dose or take this medication more often than prescribed. Your condition will not improve any faster, and the risk of serious side effects may be increased. Avoid eating grapefruit or drinking grapefruit juice while being treated with this medication unless your doctor instructs you otherwise. Grapefruit can increase the amount of certain medications in your bloodstream. Consult your doctor or pharmacist for more details. Since this drug can be absorbed through the skin and lungs, women who are pregnant or who may become pregnant should not handle this medication or breathe the dust from the tablets. Follow your doctor's instructions on how to correctly take capecitabine with this medication.

Your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with them first. Before using this medication, tell your doctor or pharmacist of all prescription and nonprescription/herbal products you may use, especially of: drugs affecting liver enzymes that remove lapatinib from your body (such as dexamethasone, cimetidine, St. John's wort, azole antifungals including itraconazole/ketoconazole, macrolide antibiotics including erythromycin/clarithromycin, HIV protease inhibitors including ritonavir/saquinavir, rifamycins including rifabutin, certain anti-seizure medicines including carbamazepine/phenytoin). This drug can slow down the removal of other drugs from your body by affecting certain liver enzymes. These affected drugs include certain "statin" cholesterol medications (simvastatin, lovastatin, atorvastatin), tacrolimus, trazodone, digoxin, and cyclosporine, among others. Tell your doctor if you also take any of these medications. Many drugs besides lapatinib may affect the heart rhythm (QT prolongation), including dofetilide, pimozide, procainamide, amiodarone, quinidine, sotalol, macrolide antibiotics (such as erythromycin), among others. Therefore, before using lapatinib, report all medications you are currently using to your doctor or pharmacist. This document does not contain all possible interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share the list with your doctor and pharmacist.

Your condition can cause complications in a medical emergency. For information about enrolling in MedicAlert, call 1-800-854-1166 (USA) or 1-800-668-1507 (Canada).

Do not share this medication with others. Laboratory and/or medical tests (e.g., EKG, electrolyte levels, heart/liver function) should be performed periodically to monitor your progress or check for side effects. Consult your doctor for more details.

If overdose is suspected, contact your local poison control center or emergency room immediately. US residents can call the US National Poison Hotline at 1-800-222-1222. Canada residents can call a provincial poison control center. Symptoms of overdose may include: severe diarrhea/vomiting.

Before taking lapatinib, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details. Before using this medication, tell your doctor or pharmacist your medical history, especially of: heart disease (e.g., irregular heartbeat), liver disease. Lapatinib may cause a condition that affects the heart rhythm (QT prolongation). QT prolongation can infrequently result in serious (rarely fatal) fast/irregular heartbeat and other symptoms (such as severe dizziness, fainting) that require immediate medical attention. The risk of QT prolongation may be increased if you have certain medical conditions or are taking other drugs that may affect the heart rhythm (see also Drug Interactions section). Before using lapatinib, tell your doctor or pharmacist if you have any of the following conditions: certain heart problems (heart failure, slow heartbeat, QT prolongation in the EKG), family history of certain heart problems (QT prolongation in the EKG, sudden cardiac death). Low levels of potassium or magnesium in the blood may also increase your risk of QT prolongation. This risk may increase if you use certain drugs (such as diuretics/"water pills") or if you have conditions such as severe sweating, diarrhea, or vomiting. Talk to your doctor about using lapatinib safely. This medication is not recommended for use during pregnancy. It may harm an unborn baby. Therefore, it is important to prevent pregnancy while taking this medication. Consult your doctor for more details and to discuss using at least 2 reliable forms of birth control (e.g., condoms, birth control pills) while taking this medication. If you become pregnant or think you may be pregnant, tell your doctor immediately. It is not known whether this drug passes into breast milk. Because of the possible risk to the infant, breast-feeding while using this drug is not recommended. Consult your doctor before breast-feeding.

Store at room temperature at 77 degrees F (25 degrees C) away from light and moisture. Brief storage between 59-86 degrees F (15-30 degrees C) is permitted. Do not store in the bathroom. Keep all medicines away from children and pets. Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer needed. Consult your pharmacist or local waste disposal company for more details about how to safely discard your product.

See also Warning section. Nausea, vomiting, upset stomach, mouth sores, mild rash, dry skin, and trouble sleeping may occur. If any of these effects persist or worsen, tell your doctor or pharmacist promptly. Diarrhea is a common side effect and may become severe. Tell your doctor immediately if diarrhea occurs or if you have signs of a severe loss of body water (dehydration) such as dizziness or decreased amount of urine. Your doctor should prescribe additional medication to help control your symptoms. If your diarrhea becomes severe, your doctor may need to stop or delay your lapatinib treatment. Treatment with this drug may sometimes cause your hands/feet to develop a skin reaction called hand-foot syndrome (palmar-plantar erythrodysesthesia). Tell your doctor immediately if you experience swelling, pain, redness, peeling, blisters, or tingling/burning of the hands/feet. The symptoms can be made worse by heat/pressure on your hands/feet. Avoid prolonged sun exposure, tanning booths, and sunlamps, as well as unnecessary exposure to heat (e.g., hot dishwater, long hot baths). Use a sunscreen and wear protective clothing when outdoors. Avoid pressure on elbows, knees, and soles of feet (e.g., leaning on elbows, kneeling, taking long walks). Wear loose clothing and comfortable shoes. Depending on how severe your hand-foot syndrome is, your doctor may give you an additional medication to reduce the symptoms, or stop or delay your lapatinib treatment. Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects. Tell your doctor immediately if any of these unlikely but serious side effects occur: unusual tiredness, shortness of breath, swelling ankles/feet. Seek immediate medical attention if any of these rare but serious side effects occur: fast/pounding/irregular heartbeat, dizziness, fainting. A very serious allergic reaction to this drug is rare. However, seek immediate medical attention if you notice any of the following symptoms of a serious allergic reaction: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing. This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist. In the US - Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088. In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Rarely, people taking lapatinib have developed serious (possibly fatal) liver problems. Your doctor will perform liver function tests before and during treatment to monitor for this side effect. Keep all medical/lab appointments. Tell your doctor immediately if you develop symptoms of liver disease such as persistent nausea, stomach/abdominal pain, dark urine, or yellowing eyes/skin. Do not restart this medication if you have previously stopped taking it due to liver problems.