Lapatinib may cause liver damage which can be severe or life-threatening. Liver damage can occur as soon as several days or as late as several months after the start of treatment with lapatinib. Tell your doctor if you have or have ever had liver disease. If you experience any of the following symptoms, call your doctor immediately: itching, yellowing of the skin or eyes, dark urine, pain in the upper right part of the stomach, unusual bleeding or bruising, or pale or dark stools.

Keep all appointments with your doctor and the laboratory. Your doctor will order certain laboratory tests before and during your treatment to see whether your liver is likely to be damaged or has been damaged by lapatinib.

Talk to your doctor about the risks of taking lapatinib.

Lapatinib is used with capecitabine (Xeloda) to treat a certain type of advanced breast cancer in people who have already been treated with other chemotherapy medications. Lapatinib is also used with letrozole (Femara) to treat a certain type of breast cancer in postmenopausal women (women who have experienced a change of life; end of menstrual periods) that has spread to other parts of the body. Lapatinib is in a class of medications called kinase inhibitors. It works by blocking the action of the abnormal protein that signals cancer cells to multiply. This helps stop or slow the spread of cancer cells.

Lapatinib comes as a tablet to take by mouth. It is usually taken once a day, at least 1 hour before or 1 hour after a meal. When lapatinib is used to treat advanced or metastatic breast cancer, it is usually given once daily on days 1 to 21 (along with capecitabine on days 1 to 14) of a 21-day cycle. The cycle may be repeated as recommended by your doctor. When lapatinib is used to treat breast cancer in postmenopausal women, it is usually given once daily along with letrozole. Take all of the lapatinib tablets for your daily dose at one time each day; do not divide the tablets to take as separate doses. Take lapatinib at around the same time every day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take lapatinib exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

Swallow the tablets whole; do not split, chew, or crush them.

Your doctor may gradually increase or decrease your dose of lapatinib during your treatment. This depends on how well the medication works for you and any side effects you may experience. Continue to take lapatinib even if you feel well. Do not stop taking lapatinib without talking to your doctor.

Ask your pharmacist or doctor for a copy of the manufacturer’s information for the patient.

This medication may be prescribed for other uses; ask your doctor or pharmacist for more information.

Before taking lapatinib,

• tell your doctor and pharmacist if you are allergic to lapatinib, any other medications, or any of the ingredients in lapatinib tablets. Ask your pharmacist for a list of the ingredients.
• tell your doctor and pharmacist what prescription and nonprescription medications, vitamins, and nutritional supplements you are taking or plan to take. Be sure to mention any of the following: certain antibiotics such as clarithromycin (Biaxin, in Prevpac), erythromycin (E.E.S., E-Mycin, Erythrocin), moxifloxacin (Avelox), rifabutin (Mycobutin), rifampin (Rifadin, in Rifamate, in Rifater, Rimactane), rifapentine (Priftin), sparfloxacin (Zagam) (not available in the U.S.), and telithromycin (Ketek); antifungals such as itraconazole (Sporanox), ketoconazole (Nizoral), and voriconazole (Vfend); calcium channel blockers such as amlodipine (Norvasc, in Caduet and Lotrel), diltiazem (Cardizem, Dilacor, Tiazac, others), felodipine (Plendil, in Lexxel), nifedipine (Adalat, Nifedical XL, Procardia, others), nisoldipine (Sular), and verapamil (Calan, Isoptin, Verelan, others); cisapride (Propulsid) (not available in the U.S.); dexamethasone (Decadron, Dexpak); certain medications for depression such as nefazodone; certain chemotherapy medications including daunorubicin (Cerubidine, DaunoXome), doxorubicin (Adriamycin, Doxil, Rubex), epirubicin (Ellence), idarubicin (Idamycin), tamoxifen (Nolvadex), valrubicin (Valstar), vinblastine, and vincristine; certain medications for human immunodeficiency virus (HIV) or acquired immunodeficiency syndrome (AIDS) including atazanavir (Reyataz), indinavir (Crixivan), nelfinavir (Viracept), ritonavir (Norvir, in Kaletra), and saquinavir (Invirase); medications for irregular heartbeat including amiodarone (Cordarone), disopyramide (Norpace), dofetilide (Tikosyn), procainamide (Procanbid), quinidine, and sotalol (Betapace, Betapace AF, Sorine); certain medications for seizures such as carbamazepine (Carbatrol, Epitol, Tegretol), phenobarbital (Luminal), and phenytoin (Dilantin, Phenytek); pimozide (Orap); and thioridazine. Your doctor may need to change the doses of your medications or monitor you carefully for side effects. Many other medications may also interact with lapatinib, so be sure to tell your doctor about all the medications you are taking, even those that do not appear on this list.
• tell your doctor and pharmacist what herbal products you are taking, especially St. John’s wort.
• tell your doctor if you have or have ever had a slow, fast, or irregular heartbeat; a prolonged QT interval (a rare heart problem that may cause irregular heartbeat, fainting, or sudden death); a low level of magnesium or potassium in your blood; or heart or lung disease.
• tell your doctor if you are pregnant or plan to become pregnant. You will have to take a pregnancy test before starting treatment. If you are a woman who is able to become pregnant, you must use effective birth control during your treatment and for 1 week after your final dose. If you are male with a female partner who could become pregnant, you must use effective birth control during your treatment and for 1 week after your final dose. Talk to your doctor about birth control methods that you can use during your treatment. If you become pregnant while taking lapatinib, call your doctor immediately. Lapatinib may harm the fetus.
• tell your doctor if you are breastfeeding or plan to breastfeed. You should not breastfeed while taking lapatinib and for 1 week after your final dose.
• you should know that lapatinib often causes diarrhea, which can be severe. Call your doctor if you have diarrhea while taking lapatinib. Your doctor may tell you to drink plenty of liquids, make changes in your diet, and take medication to control the diarrhea and prevent dehydration (loss of too much water from your body). Call your doctor immediately if you experience any of the following symptoms of dehydration: extreme thirst, dry mouth and/or skin, decreased urination, sunken eyes, or fast heartbeat.

Do not eat grapefruit or drink grapefruit juice while taking this medication.

Take the missed dose as soon as you remember it that day. However, if you do not remember until the next day, if you cannot remember whether you took the medication, or if you vomit your medication, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.

Lapatinib may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

• nausea
• vomiting
• heartburn
• sores on the lips, mouth, or throat
• loss of appetite
• red, painful, numb, or tingling hands and feet
• dry skin
• pain in the arms, legs, or back
• difficulty falling asleep or staying asleep

Some side effects can be serious. If you experience any of these symptoms or those listed in the IMPORTANT WARNING section or the SPECIAL PRECAUTIONS section, call your doctor immediately:

• shortness of breath
• dry cough
• coughing up pink or bloody mucus
• fast, irregular, or pounding heartbeat
• weakness
• swelling of the hands, feet, ankles, or lower legs
• rash
• fever
• blistering or peeling skin

Lapatinib may change the way your heart beats and pumps blood through your body. Your doctor will monitor you carefully to see whether lapatinib has affected your heart. Talk to your doctor about the risks of taking lapatinib.

Lapatinib may cause other side effects. Call your doctor if you have any unusual problems while you are taking this medication.

If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration’s (FDA) MedWatch Adverse Event Reporting program online (http://www.fda.gov/Safety/MedWatch) or by phone (1-800-332-1088).

Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture (not in the bathroom).

Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA’s Safe Disposal of Medicines website (http://goo.gl/c4Rm4p) for more information if you do not have access to a take-back program.

It is important to keep all medication out of sight and reach of children as many containers (such as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in a safe location – one that is up and away and out of their sight and reach. http://www.upandaway.org

In case of overdose, call the poison control helpline at 1-800-222-1222. Information is also available online at https://www.poisonhelp.org/help. If the victim has collapsed, had a seizure, has trouble breathing, or can’t be awakened, immediately call emergency services at 911.

Symptoms of overdose may include the following:

• diarrhea
• vomiting

Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.

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