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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 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. Take all of the tablets for your daily dose at this time each day. Lapatinib is usually taken once a day for 21 days before beginning the next treatment cycle. 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.

Capecitabine is taken in combination with lapatinib, but on a different schedule. Be sure that you understand how and when to take capecitabine. Talk to your doctor and pharmacist if you have any questions about taking capecitabine.

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.

Lapatinib may cause side effects. Tell your doctor if any of these symptoms or those mentioned in the Special Precautions section are severe or do not go away:

• nausea
• vomiting
• heartburn
• loss of appetite
• red, painful hands and feet
• rash
• dry skin
• sores on the lips, mouth, or throat
• 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, call your doctor immediately:

• shortness of breath
• cough
• coughing up pink or bloody mucus
• fast, irregular, or pounding heartbeat
• tiredness or weakness
• swelling of the hands, feet, ankles, or lower legs

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

• tell your doctor and pharmacist if you are allergic to lapatinib or any other medications.
• 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, Rimactane), rifapentine (Priftin), sparfloxacin (Zagam) (not available in the US), telithromycin (Ketek),and troleandomycin (TAO) (not available in the US); antifungals such as itraconazole (Sporanox), ketoconazole (Nizoral), and voriconazole (Vfend); certain benzodiazepines such as alprazolam (Xanax), diazepam (Valium), midazolam (Versed)and triazolam (Halcion); buspirone (BuSpar);calcium channel blockers such as amlodipine (Norvasc), diltiazem (Cardizem, Dilacor, Tiazac, others), felodipine (Plendil), nifedipine (Adalat, Procardia), nisoldipine (Sular), and verapamil (Calan, Isoptin, Verelan); certain cholesterol-lowering medications (statins) including atorvastatin (Lipitor), lovastatin (Mevacor),and simvastatin (Zocor); chlorpheniramine (Chlor-Trimeton, other cough and cold products); cimetidine (Tagamet); cisapride (Propulsid) ; dexamethasone (Mymethasone); certain medications for depression such as fluvoxamine nefazodone,and trazodone (Desyrel); certain chemotherapy medications including daunorubicin (Cerubidine), doxorubicin (Adriamycin, Doxil), epirubicin (Ellence),imatinib (Gleevec), idarubicin (Idamycin), tamoxifen, vinblastine, and vincristine; certain medications for human immunodeficiency virus (HIV) or acquired immunodeficiency syndrome (AIDS) including amprenavir (Agenerase), atazanavir (Reyataz), indinavir (Crixivan), nelfinavir (Viracept), ritonavir (Norvir, in Kaletra), and saquinavir (Invirase); medications for irregular heartbeat including amiodarone (Cordarone), digoxin (Lanoxin), disopyramide (Norpace), dofetilide (Tikosyn), procainamide (Procanbid, Pronestyl), quinidine (Quinidex), and sotalol (Betapace, Betapace AF); methadone (Dolophine, Methadose);certain medications for seizures such as carbamazepine (Equetro, Carbatrol, Tegretol), phenobarbital, and phenytoin (Dilantin, Phenytek); medications that weaken the immune system such as cyclosporine (Neoral, Sandimmune), mycophenolate (Cellcept), sirolimus (Rapamune), and tacrolimus (Prograf); pimozide (Orap); sildenafil (Revatio, Viagra);and thioridazine (Mellaril). Your doctor may need to change the doses of your medications or monitor you carefully for side effects. 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. Your doctor may tell you not to take St. John's wort while taking lapatinib.
• tell your doctor if you have or have ever had angina (chest pain); an arrhythmia (slow, fast, or irregular heartbeat); heart failure; or heart or liver disease.
• tell your doctor if you are pregnant or plan to become pregnant. You should not become pregnant while you are taking lapatinib 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 breast-feeding. You should not breast-feed while you are taking lapatinib.
• 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 and take medication to control the diarrhea and prevent dehydration (condition from losing 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 it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.

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

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). Throw away any medication that is outdated or no longer needed. Talk to your pharmacist about the proper disposal of your medication.

In case of overdose, call your local poison control center at 1-800-222-1222. If the victim has collapsed or is not breathing, call local emergency services at 911.

Symptoms of overdose may include:

• diarrhea
• vomiting

Keep all appointments with your doctor and the laboratory. Your doctor will order certain lab tests to check your body's response to lapatinib.

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.