Lapatinib

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), digoxin, irinotecan, tacrolimus, trazodone, among others.

Other medications can affect the removal of lapatinib from your body, which may affect how lapatinib works. Examples include cimetidine, dexamethasone, ritonavir, St. John's wort, azole antifungals (such as itraconazole, ketoconazole), macrolide antibiotics (such as erythromycin, clarithromycin), HIV protease inhibitors (such as 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. Before using lapatinib, report all medications you are currently using to your doctor or pharmacist.

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 nausea that doesn't stop, 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.

Read the Patient Information Leaflet if available from your pharmacist before you start using lapatinib and each time you get a refill. If you have any questions, ask your doctor or pharmacist.

Take this medication by mouth 1 hour before or 1 hour after a meal as directed by your doctor, usually once daily. 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 other medications you may be taking. Be sure to tell your doctor and pharmacist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).

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 using this medication unless your doctor or pharmacist says you may do so safely. Grapefruit can increase the chance of side effects with this medicine. Ask 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 or letrozole with lapatinib.

See also Warning section.

Nausea, vomiting, upset stomach, mouth sores, mild rash, dry skin, and trouble sleeping may occur. If any of these effects last or get worse, tell your doctor or pharmacist promptly.

Diarrhea is a common side effect and may become severe. Tell your doctor right away if diarrhea occurs or if you have signs of 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 (such as hot dishwater, long hot baths). Use a sunscreen and wear protective clothing when outdoors. Avoid pressure on elbows, knees, and soles of feet (such as 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 this medication has been prescribed because your doctor 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 you have any serious side effects, including: unusual tiredness, shortness of breath, swelling ankles/feet.

Get medical help right away if you have any very serious side effects, including: fast/pounding/irregular heartbeat, dizziness, fainting.

A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including: 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/safety/medwatch-fda-safety-information-and-adverse-event-reporting-program.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

It is important to take each dose of this medication as scheduled. 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. Take your next dose at the regular time. Do not double the dose to catch up.

Store at room temperature away from light and moisture. Do not store in the bathroom. Keep all medications 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.

Do not share this medication with others.

Lab and/or medical tests (such as EKG, electrolyte levels, heart/liver function) should be done while you are taking this medication. Keep all medical and lab appointments. Consult your doctor for more details.

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.