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Lapatinib (Generic Name)

UPMC Content 2

About This Drug

Lapatinib is used to treat cancer. It is given by mouth.

Possible Side Effects (More Common)

  • Bone marrow depression. This is a decrease in the number of white blood cells, red blood cells, and platelets. This may raise your risk of infection, make you tired and weak (fatigue), and raise your risk of bleeding
  • Loose bowel movements (diarrhea) that may last for a few days
  • Nausea and throwing up (vomiting). These symptoms may happen within a few hours after your treatment. Medicines are available to stop or lessen these side effects.
  • Soreness of the mouth and throat. You may have red areas, white patches, or sores that hurt
  • Rash
  • Indigestion
  • Fatigue (feeling very tired)
  • Weakness
  • Loss of appetite
  • Headache
  • Dry skin
  • Changes to fingernails and toenails
  • Hair loss (mild)
  • Back pain
  • Trouble sleeping

 Possible Side Effects (Less Common)

  • Changes in the tissue of the heart. Some changes may happen that can cause your heart to have less ability to pump blood. Your heart function will be checked as needed.
  • Heart beat that is fast or not normal
  • Changes in your liver function.  Your doctor will check your liver function as needed.
  • Inflammation (swelling) of the lungs. You may have a dry cough or trouble breathing.

Treating Side Effects

  • Drink 6-8 cups of fluids each day unless your doctor has told you to limit your fluid intake due to some other health problem. A cup is 8 ounces of fluid. If you throw up or have loose bowel movements, you should drink more fluids so that you do not become dehydrated (lack water in the body from losing too much fluid).
  • Ask your doctor or nurse about medicine that is available to help stop or lessen the loose bowel movements.
  • If you get a rash do not put anything on it unless your doctor or nurse says you may. Keep the area near the rash clean and dry.
  • Mouth care is very important. Your mouth care should consist of routine, gentle cleaning of your teeth or dentures and rinsing your mouth with a mixture of 1/2 teaspoon of salt in 8 ounces of water or ½ teaspoon of baking soda in 8 ounces of water. This should be done at least after each meal and at bedtime.
  • Talk with your doctor or nurse about options for birth control

Important Information

  • Take lapatinib on an empty stomach, at least 1 hour before eating or 1 hour after eating.
  • Take this drug at the same time each day.
  • Swallow the pills whole, do not crush, split, or dissolve the tablets.
  • Missed dose: If you miss a dose of lapatinib, take your next dose at your normal scheduled time the next day. Do not take more than 1 dose at a time. Do not take extra doses.

Food and Drug Interactions

  • Do not eat grapefruit or drink grapefruit juice while taking this medicine.
  • Do not take St. John’s Wort while taking this medicine.
  • This drug may interact with other medicines. Tell your doctor and pharmacist about all the medicines and dietary supplements (vitamins, minerals, herbs and others) that you are taking at this time. The safety and use of dietary supplements and alternative diets are often not known. Using these might affect your cancer or interfere with your treatment. Until more is known, you should not use dietary supplements or alternative diets without your cancer doctor's help.

When to Call the Doctor

Call your doctor or nurse right away if you have any of these symptoms:

  • Trouble breathing or feeling short of breath
  • Dry cough
  • Feeling your heart beat rapidly (palpitations)
  • Loose bowel movements
  • Nausea that stops you from eating or drinking
  • Throwing up more than 3 times in one day
  • Rash
  • Pain, swelling, or redness in your hands and/or feet
  • Signs of liver problems: dark urine, pale stools, severe stomach pain, feeling very tired and weak, unusual itching, or yellowing of the eyes

Call your doctor or nurse as soon as possible if you have any of these symptoms:

  • Nausea, throwing up, indigestion, and/or loose bowel movements that is not relieved by prescribed medicines
  • Pain in your mouth or throat, or if you are not able to eat or drink
  • Feel tired all the time even if doing nothing. 
  • Fatigue
  • Loss of appetite that stops you from eating
  • Fast weight loss, such as 5 pounds in 1 week
  • Trouble sleeping

Reproduction Concerns

  • Pregnancy warning: This drug may have harmful effects on the unborn child, so effective methods of birth control should be used during your cancer treatment.
  • Genetic counseling is available for you to talk about the effects of this drug therapy on future pregnancies. Also, a genetic counselor can look at the possible risk of problems in the unborn baby due to this medicine if an exposure happens during pregnancy.
  • Breast feeding warning: It is not known if this drug passes into breast milk. For this reason, women should talk to their doctor about the risks and benefits of breast feeding during treatment with this drug because this drug may enter the breast milk and badly harm a breast feeding baby. 


Revised August 2014