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Trade/other name(s): Tykerb, GW572016

Why would this drug be used?

This drug is used to treat some types of breast cancer. It is also being studied for use against cancers of the prostate, brain, liver, and ovaries, as well as other cancers.

How does this drug work?

Lapatinib is a type of targeted therapy known as a tyrosine kinase inhibitor. Tyrosine kinases are proteins at the surface of a cell that signal its control center to divide and grow. Lapatinib blocks the signals from the HER2 tyrosine kinase. Some breast (and other) cancers have higher than normal amount of HER2 on their cells. Having too much HER2 signals the cells to grow and divide in an out-of-control way. Blocking HER2 helps stop the growth of those cancer cells.

Not all breast cancers have too much of the HER2 protein on the cell surfaces. Your doctor will test your cancer cells to be sure they have this before starting treatment with this drug. (Most likely this will already have been done before if you received other treatments aimed at HER2.)

Before taking this medicine

Tell your doctor…

  • If you are allergic to anything, including medicines, dyes, additives, or foods.
  • If you have any history of liver disease (including hepatitis). This drug is cleared from the body mainly by the liver. Reduced liver function may result in more drug staying in the body, which could lead to unwanted side effects. Your doctor may need to adjust the drug's dose.
  • If you have ever been diagnosed with heart problems, especially long QT syndrome, an abnormal heart rhythm, congestive heart failure, or if you have been told you have low blood levels of potassium, calcium, or magnesium (which can affect the heart). This drug can affect the rhythm of the heart, which might lead to irregular heartbeats and can even lead to death. It can also cause the heart to weaken, which can lead to congestive heart failure.
  • If you have any other medical conditions such as kidney disease, high blood pressure, diabetes, gout, or infections. These conditions may require that your medicine dose, regimen, or timing be changed.
  • If you are pregnant, trying to get pregnant, or if there is any chance of pregnancy. This drug may cause problems with the fetus if taken at the time of conception or during pregnancy (see “Precautions” below).
  • If you are breast-feeding. While no studies have been done, this drug may pass into breast milk and affect the baby. Breast-feeding is not recommended during treatment with this drug.
  • If you think you might want to have children in the future. It is not known whether this drug can affect fertility. Talk with your doctor about the possible risk with this drug and the options that may preserve your ability to have children.
  • About any other prescription or over-the-counter medicines you are taking, including vitamins and herbs. In fact, keeping a written list of each of these medicines (including the doses of each and when you take them) with you in case of emergency may help prevent complications if you get sick.

Interactions with other drugs

Lapatinib can interact with a number of drugs and supplements. The following drugs can cause lapatinib to build up in the body, raising the risk of serious side effects:

  • The antidepressant nefazodone (Serzone)
  • The antibiotics erythromycin (EES), clarithromycin (Biaxin) and telithromycin (Ketek)
  • Anti-fungal drugs such as ketoconazole (Nizoral), itraconazole (Sporanox), voriconazole (Vfend)
  • HIV drugs such as indinavir, ritonavir, saquinavir, nelfinavir, atazanavir, and others
  • The cholesterol drug gemfibrozil (Lopid)
  • Trimethoprim (Proloprim; also in Bactrim, Septra, and Co-trimoxazole)

Lapatinib can raise the level of digoxin (a heart medicine) in the body and your doctor may need to change your dose.

Lapatinib can also raise the levels of tranquilizers or “nerve pills” such as diazepam (Valium), alprazolam (Xanax), and Midazolam (Versed), as well as triazolam (Halcion), a sleeping pill. Using these drugs with lapatinib can raise your risk of serious side effects.

The following drugs and supplements can lower the levels of lapatinib in the blood and make it less effective:

  • Anti-seizure drugs carbamazepine (Tegretol), phenobarbital (Luminal), and phenytoin (Dilantin)
  • TB drugs rifampin (Rifadin, Rimactane; also in Rifamate and Rifater), rifapentin (Priftin), and rifabutin (Mycobutin)
  • The steroid drug dexamethasone (Decadron)
  • St. John's wort (herbal dietary supplement)

If you need to take these drugs, your doctor may need to adjust your dose of lapatinib. Do not start or stop taking any medicines or supplements while on lapatinib without talking with the prescribing doctor(s) about everything you take, including lapatinib.

This drug may change your heart rhythm. Medicines that can affect heart rhythm or the heart's electrical system may increase the risk of harmful effects:

  • Antibiotics such as ciprofloxacin (Cipro), levofloxacin Levaquin), sparfloxacin (Zagam), moxifloxacin (Avelox), erythromycin (E.E.S., E-Mycin, Erythrocin), clarithromycin (Biaxin), or pentamidine (Pentam, nebupent)
  • The anti-fungal drug amphotericin B
  • Heart rhythm drugs such as amiodorone (Cordarone, Pacerone), disopyrmide (Norpace), dofetilide (Tikosyn), flecainide (Tambocor), mexiletine (Mexitil), moricizine (Ethmozine), procainamide (Procanbid, Pronestyl), propafenone (Rythmol), quinidine (Quinidex), sotalol (Betapace, Betapace AF), and tocainide (Tonocard)
  • Mental health drugs such as haloperidol (Haldol), thioridazine (Mellaril), pimozide (Orap), mesoridazine (Serentil), chlorpromazine (Thorazine)
  • Methadone (Dolophine, Methadose)
  • The anti-nausea drug droperidol (Inapsine)
  • Anti-malaria drugs halofantrine (Halfan) and chloroquine (Aralen)
  • Bepridil (Vascor), a drug for angina or heart pain

Other medicines may affect lapatinib, such as drugs for stomach ulcers and more. Check with your doctor, nurse, or pharmacist about any other medicines, herbs, and supplements you are taking, and whether alcohol can cause problems with this medicine.

Interactions with foods

Avoid grapefruit or grapefruit juice. Grapefruit may raise the level of lapatinib in your blood and cause worse side effects. Check with your doctor, nurse, or pharmacist about whether these or other foods may be a problem.

Tell all the doctors, dentists, nurses, and pharmacists you visit that you are taking this drug.

How is this drug taken or given?

Lapatinib comes in pill form. These pills are taken once a day, at least one hour before or one hour after a meal. (Do not save part of the dose and take it later.) The usual starting dose is 5 or 6 pills per day (1250 to 1500 milligrams). The dose may need to be changed if you have certain health problems, are taking certain medicines, or have side effects.

Take this drug exactly as directed by your doctor. If you do not understand the instructions, ask your doctor or nurse to explain them to you. Keep the medicine in a tightly closed container away from heat and moisture and out of the reach of children and pets.


This drug may interact with a number of other drugs or supplements in the body. (See "Interactions" above.) Be sure your doctor is aware of all drugs and supplements you are taking. Do not start or stop taking any medicine without discussing all your medicines with the doctor who prescribed lapatinib.

This drug can cause a change in heart rhythm called prolonged QT interval. Tell your doctor if you have ever been diagnosed with any type of heart disease, especially an abnormal heart rhythm or long QT syndrome. Your doctor may need to test your heart rhythm with an EKG and test your blood levels of certain minerals that could affect heart rhythm during treatment. Tell your doctor or nurse right away if you notice a fast or irregular heartbeat, very slow heartbeat, lightheadedness, dizziness, fainting, or shortness of breath to your doctor right away. Tell your doctor if you start to take or have any changes in heart or blood pressure medicines.

This drug can cause heart damage and weaken the heart muscle. Tell your doctor if you have had any heart problems, such as a heart attack or congestive heart failure before starting treatment. He or she may order tests of heart function before treatment begins. Possible symptoms of heart damage can include increased coughing, trouble breathing (especially at night), heart palpitations, rapid weight gain (5 pounds or more in less than a week), dizziness, fainting, or swelling in the ankles or legs. Tell your doctor right away if you notice any of these symptoms once you start treatment.

Some people may develop inflammation of the lungs (pneumonitis) during treatment with this drug, which in some cases may be severe. Tell your doctor right away if you notice any possible symptoms of lung problems, such as wheezing, pain in the chest, shortness of breath, or a new or worsening cough.

This drug may affect liver function, which in rare cases may be serious or even life threatening. Your doctor will likely do blood tests to check your liver function before and during treatment. Be sure to tell your doctor if you notice skin itching, yellow eyes or skin, dark urine, or pain or discomfort in the right upper area of the belly, which could be signs of liver problems.

This drug may cause diarrhea. If left unchecked, this could lead to dehydration and imbalances in blood chemistry, which can be serious if not treated quickly. Your doctor may prescribe medicine to help prevent or control this side effect. Call your doctor if the medicine does not control your diarrhea. Your doctor may need to change your dose of lapatinib or stop it for a time if the problem is severe.

This drug can pain, numbness, tingling, redness, or swelling in the hands or feet -- a problem called hand-foot syndrome. When severe this can lead to peeling and blistering of the skin, and even open sores in these areas. Let your doctor know right away if you notice any of these symptoms, even if they are mild.

This drug can rarely cause severe skin problems which can even be fatal. Let your doctor know if you develop a rash with blisters, skin peeling, or sores in your mouth, especially if it gets worse over time.

Your doctor will likely test your blood during your treatment, looking for effects of the drug on blood counts or on blood chemistry levels. Based on the test results, you may be given medicines to help treat any effects. Your doctor may also reduce or delay your next dose of this drug, or even stop it altogether. Keep all your appointments for lab tests and doctor visits.

This drug may lower your red blood cell count. If this occurs, it is usually a few months after starting treatment. A low red blood cell count (known as anemia) can cause shortness of breath, or make you feel weak or tired all the time. Your doctor may give you medicines to help prevent or treat this condition.

Avoid pregnancy while taking this drug and for some time afterward. This drug might cause problems with the fetus if taken at the time of conception or during pregnancy. Women who could become pregnant should check with their doctors about whether birth control should be used and what kinds of birth control can be used with this medicine.

Possible side effects

You will probably not have most of the following side effects, but if you have any talk to your doctor or nurse. They can help you understand the side effects and cope with them.


  • Diarrhea*
  • Rash
  • Hand-foot syndrome (red, swollen, numb, or painful hands and feet)*

Less common

  • Nausea
  • Vomiting
  • Feeling tired
  • Mouth sores
  • Loss of appetite
  • Headaches
  • Itching
  • Hair loss or thinning
  • Nail changes or infections
  • Heartburn or indigestion
  • Shortness of breath*
  • Swelling in the feet or ankles*
  • Dry skin
  • Trouble sleeping


  • Effects on heart rhythm or function*
  • Low red blood cell count (anemia)*
  • Liver problems, which might show up as yellow eyes or skin, skin itching, dark urine, pain in the right side of the belly, or abnormal blood tests*
  • Serious allergic reactions with symptoms such as itching, hives, trouble breathing or swallowing, swelling in the mouth or throat, dizziness, and shock
  • Lung problems (cough, trouble breathing)*
  • Severe skin problems*
  • Death due to liver failure, heart problems, lung problems, skin problems, diarrhea, or other causes

*See "Precautions" section for more detailed information.

There are other side effects not listed above that can also occur in some patients. Tell your doctor or nurse if you develop these or any other problems.

FDA approval

Yes - first approved in 2007

Disclaimer: This information does not cover all possible uses, actions, precautions, side effects, or interactions. It is not intended as medical advice, and should not be relied upon as a substitute for talking with your doctor, who is familiar with your medical needs.

Last Medical Review: 08/26/2013
Last Revised: 01/05/2015