Tucatinib is used with trastuzumab (Herceptin) and capecitabine (Xeloda) to treat a certain type of hormone receptor–positive breast cancer that has spread to other parts of the body and cannot be treated with surgery in adults who have already been treated with at least one other chemotherapy medication. Tucatinib is also used with trastuzumab to treat a certain type of colorectal cancer (cancer that begins in the large intestine) that has spread to other parts of the body and cannot be treated with surgery in adults who have already been treated with other chemotherapy medications and have not improved or worsened. Tucatinib 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.

Tucatinib comes as a tablet to take by mouth. It is usually taken with or without food twice daily, about 12 hours apart. Take tucatinib at around the same times 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 tucatinib 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. Do not take tablets that are broken, cracked, or damaged in any way.

If you vomit after taking tucatinib, do not take another dose. Continue your regular dosing schedule.

Your doctor may decrease your dose or temporarily or permanently stop your treatment if you experience certain side effects. This depends on how well the medication works for you and the side effects you experience. Be sure to tell your doctor how you are feeling during your treatment with tucatinib.

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

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

Before taking tucatinib,

• tell your doctor and pharmacist if you are allergic to tucatinib, any other medications, or any of the ingredients in tucatinib tablets. Ask your pharmacist for a list of the ingredients.
• tell your doctor and pharmacist what other prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
• The following nonprescription or herbal product may interact with tucatinib: St. John’s wort. Be sure to let your healthcare provider know that you are taking this medication before you start taking tucatinib. Do not start this medication while receiving taking tucatinib without discussing with your healthcare provider.
• tell your doctor if you have or have ever had diabetes, or liver or kidney disease.
• tell your doctor if you are pregnant, plan to become pregnant, or if you plan on fathering a child. If you are female, you will need to take a pregnancy test before you start treatment and use birth control to prevent pregnancy during your treatment and for at least 1 week after your final dose. If you are a male, you and your partner should use 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 or your partner become pregnant while taking tucatinib, call your doctor immediately. Tucatinib may harm the fetus.
• tell your doctor if you are breastfeeding. You should not breastfeed while you are taking tucatinib and for 1 week after your final dose.
• you should know that this medication may decrease fertility in men and women. Talk to your doctor about the risks of taking tucatinib.

Unless your doctor tells you otherwise, continue your normal diet.

Skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.

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

• nausea
• vomiting
• constipation
• abdominal pain
• loss of appetite
• weight loss
• fatigue
• rash
• headache
• mouth ulcers
• nose bleeding
• numbness, burning, or tingling in the hands or feet
• joint, muscle, or back pain
• redness or blisters on hands or feet
• pale skin, fatigue, or shortness of breath
• fever
• chills
• cough
• shortness of breath
• anxiety

Some side effects can be serious. If you experience any of these symptoms, call your doctor immediately or get emergency medical treatment:

• diarrhea
• pain or discomfort in right upper stomach area; loss of appetite; bleeding or bruising more easily than normal; yellowing of skin and eyes; fatigue; or dark urine
• seizure

Tucatinib may cause other side effects. Call your doctor if you have any unusual problems while 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 (http://www.fda.gov/Safety/MedWatch) or by phone (1-800-332-1088).

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. Do not remove the desiccant (drying agent) from the bottle. Properly dispose of any unused tablets 3 months after opening the bottle.

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. http://www.upandaway.org

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 (http://goo.gl/c4Rm4p) for more information if you do not have access to a take-back program.

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.

Keep all appointments with your doctor and the laboratory. Your doctor will order certain lab tests before and during your treatment to check your body’s response to tucatinib. Your doctor may order a lab test before you begin your treatment to see whether your cancer can be treated with tucatinib.

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.

• Tukysa^®