Lapatinib

WHY is this medicine prescribed?

Lapatinib is used with capecitabine (Xeloda) to treat a certain type of advanced breast cancer in people who have already been treated with other chemotherapy medications. Lapatinib is also used with letrozole (Femara) to treat a certain type of breast cancer in postmenopausal women (women who have experienced a change of life; end of menstrual periods) that has spread to other parts of the body. Lapatinib is in a class of medications called kinase inhibitors. It works by blocking the action of the abnormal protein that signals cancer cells to multiply. This helps stop or slow the spread of cancer cells.

HOW should this medicine be used?

Lapatinib comes as a tablet to take by mouth. It is usually taken once a day, at least 1 hour before or 1 hour after a meal. When lapatinib is used to treat advanced or metastatic breast cancer, it is usually given once daily on days 1 to 21 (along with capecitabine on days 1 to 14) of a 21-day cycle. The cycle may be repeated as recommended by your doctor. When lapatinib is used to treat breast cancer in postmenopausal women, it is usually given once daily along with letrozole. Take all of the lapatinib tablets for your daily dose at one time each day; do not divide the tablets to take as separate doses. Take lapatinib at around the same time every day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take lapatinib exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

Swallow the tablets whole; do not split, chew, or crush them.

Your doctor may gradually increase or decrease your dose of lapatinib during your treatment. This depends on how well the medication works for you and any side effects you may experience. Continue to take lapatinib even if you feel well. Do not stop taking lapatinib without talking to your doctor.

Ask your pharmacist or doctor for a copy of the manufacturer's information for the patient.

Are there OTHER USES for this medicine?

This medication may be prescribed for other uses; ask your doctor or pharmacist for more information.

What SPECIAL PRECAUTIONS should I follow?

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 while taking lapatinib. Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
• the following herbal product may interact with lapatinib: St. John's wort. Be sure to let your doctor and pharmacist know that you are taking this medication before you start taking lapatinib. Do not start this medication while taking lapatinib without discussing with your healthcare provider.
• 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 or plan to become pregnant. You will have to take a pregnancy test before starting treatment. If you are a woman who is able to become pregnant, you must use effective birth control during your treatment and for 1 week after your final dose. If you are male with a female partner who could become pregnant, you must use effective birth control during your treatment and for 1 week after your final dose. 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.
• tell your doctor if you are breastfeeding or plan to breastfeed. You should not breastfeed while taking lapatinib and for 1 week after your final dose.
• 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.

What SPECIAL DIETARY instructions should I follow?

Do not eat grapefruit or drink grapefruit juice while taking this medication.

What should I do IF I FORGET to take a dose?

Take the missed dose as soon as you remember it that day. However, if you do not remember until the next day, if you cannot remember whether you took the medication, or if you vomit your medication, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.

What SIDE EFFECTS can this medicine cause?

Lapatinib may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

• nausea
• vomiting
• heartburn
• sores on the lips, mouth, or throat
• loss of appetite
• red, painful, numb, or tingling hands and feet
• dry skin
• pain in the arms, legs, or back
• difficulty falling asleep or staying asleep

Some side effects can be serious. If you experience any of these symptoms or those listed in the IMPORTANT WARNING section or the SPECIAL PRECAUTIONS section, call your doctor immediately:

• shortness of breath
• dry cough
• coughing up pink or bloody mucus
• fast, irregular, or pounding heartbeat
• weakness
• swelling of the hands, feet, ankles, or lower legs
• rash
• fever
• blistering or peeling skin

Lapatinib may change the way your heart beats and pumps blood through your body. Your doctor will monitor you carefully to see whether lapatinib has affected your heart. Talk to your doctor about the risks of taking lapatinib.

Lapatinib may cause other side effects. Call your doctor if you have any unusual problems while you are taking this medication.

If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting program online (https://www.fda.gov/Safety/MedWatch) or by phone (1-800-332-1088).

What should I know about STORAGE and DISPOSAL of this medication?

Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture (not in the bathroom).

Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA's Safe Disposal of Medicines website (https://goo.gl/c4Rm4p) for more information if you do not have access to a take-back program.

It is important to keep all medication out of sight and reach of children as many containers (such as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in a safe location — one that is up and away and out of their sight and reach. https://www.upandaway.org

What should I do in case of OVERDOSE?

In case of overdose, call the poison control helpline at 1-800-222-1222. Information is also available online at https://www.poisonhelp.org/help. If the victim has collapsed, had a seizure, has trouble breathing, or can't be awakened, immediately call emergency services at 911.

Symptoms of overdose may include the following:

• diarrhea
• vomiting

What OTHER INFORMATION should I know?

Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.

This report on medications is for your information only, and is not considered individual patient advice. Because of the changing nature of drug information, please consult your physician or pharmacist about specific clinical use.

The American Society of Health-System Pharmacists, Inc. represents that the information provided hereunder was formulated with a reasonable standard of care, and in conformity with professional standards in the field. The American Society of Health-System Pharmacists, Inc. makes no representations or warranties, express or implied, including, but not limited to, any implied warranty of merchantability and/or fitness for a particular purpose, with respect to such information and specifically disclaims all such warranties. Users are advised that decisions regarding drug therapy are complex medical decisions requiring the independent, informed decision of an appropriate health care professional, and the information is provided for informational purposes only. The entire monograph for a drug should be reviewed for a thorough understanding of the drug's actions, uses and side effects. The American Society of Health-System Pharmacists, Inc. does not endorse or recommend the use of any drug. The information is not a substitute for medical care.

AHFS^® Patient Medication Information™. © Copyright, 2024. The American Society of Health-System Pharmacists^®, 4500 East-West Highway, Suite 900, Bethesda, Maryland. All Rights Reserved. Duplication for commercial use must be authorized by ASHP.

Selected Revisions: June 15, 2019.