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 right away 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.
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. Lapatinib may also be used together with another medication (letrozole) to treat HER2-positive breast cancer in women after menopause. It works by slowing or stopping the growth of cancer cells.
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.
See also Warning section.
Diarrhea is a common side effect and may become severe. Tell your doctor right away if diarrhea occurs or if you have signs of a severe loss of body water (dehydration) such as dizziness or decreased urination. 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 right away 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 right away if any of these unlikely but serious side effects occur: unusual tiredness, shortness of breath, swelling ankles/feet.
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 or at www.fda.gov/medwatch.
In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.
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.
Lapatinib may cause a condition that affects the heart rhythm (QT prolongation). QT prolongation can rarely cause serious (rarely fatal) fast/irregular heartbeat and other symptoms (such as severe dizziness, fainting) that need medical attention right away.
The risk of QT prolongation may be increased if you have certain medical conditions or are taking other drugs that may cause QT prolongation. Before using lapatinib, tell your doctor or pharmacist of all the drugs you take and 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.
Older adults may be more sensitive to the side effects of this drug, especially QT prolongation (see above).
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 the use of 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 right away.
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.
Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (including prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor's approval.
This medication can slow down the removal of other medications from your body, which may affect how they work. Examples of affected drugs include certain "statin" cholesterol medications (simvastatin, lovastatin, atorvastatin), tacrolimus, trazodone, digoxin, among others.
Other medications can affect the removal of lapatinib from your body, which may affect how lapatinib works. Examples include dexamethasone, cimetidine, St. John's wort, azole antifungals (such as itraconazole, ketoconazole), macrolide antibiotics (such as erythromycin, clarithromycin), HIV protease inhibitors (such as ritonavir, saquinavir), rifamycins (such as rifabutin), certain anti-seizure medicines (such as phenytoin), among others.
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.
If someone has overdosed and has serious symptoms such as passing out or trouble breathing, call 911. Otherwise, call a poison control center right away. US residents can call their local poison control center at 1-800-222-1222. Canada residents can call a provincial poison control center. Symptoms of overdose may include: severe diarrhea/vomiting.
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.
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.
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.Information last revised December 2016. Copyright(c) 2016 First Databank, Inc.
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