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, plan to become pregnant, or are breast-feeding. 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.
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.