This medication is used to treat certain types of breast, colon, or rectum cancers. Tucatinib belongs to a class of drugs known as kinase inhibitors. It works by slowing or stopping the growth of cancer cells.

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

Take this medication by mouth with or without food as directed by your doctor, usually twice daily (about 12 hours apart). Swallow the medication whole. Do not chew, crush, or split the tablets. Do not take tablets if they are broken, cracked, or damaged.

If you miss a dose or vomit after taking tucatinib, do not take another dose. Take your next dose at the regular time.

Use this medication regularly to get the most benefit from it. To help you remember, take it at the same times each day.

The dosage is based on your medical condition and response to treatment. Do not increase your dose or use this drug more often or for longer than prescribed. Your condition will not improve any faster, and your risk of serious side effects will increase.

Since this drug can be absorbed through the skin and lungs and may harm an unborn baby, women who are pregnant or who may become pregnant should not handle this medication or breathe the dust from the tablets.

Nausea, vomiting, mouth sores/pain, loss of appetite, weight loss, tiredness, or muscle/joint pain may occur. If any of these effects last or get worse, tell your doctor or pharmacist promptly.

Diarrhea is a common side effect and can sometimes be severe. Vomiting/diarrhea that doesn't stop may result in dehydration. Contact your doctor promptly if you notice any symptoms of dehydration, such as unusual decreased urination, unusual dry mouth/thirst, fast heartbeat, or dizziness/lightheadedness. Your doctor may prescribe anti-diarrheal medication to take during treatment with this medication.

People using this medication may have serious side effects. However, you have been prescribed this drug because your doctor has judged that the benefit to you is greater than the risk of side effects. Careful monitoring by your doctor may decrease your risk.

Tucatinib may make you develop a skin problem called hand-foot syndrome. To help prevent this, protect your hands and feet from heat or increased pressure. Avoid activities such as using hot dishwater, taking tub baths, jogging, going on long walks, or using garden or household tools such as screwdrivers. Symptoms may include pain, swelling, redness, blisters, or numbness of the hands/feet. Your doctor may prescribe medication (such as balm) to help with symptoms. If symptoms affect your usual activities, get medical help right away.

Tucatinib may rarely cause serious (possibly fatal) liver disease. Your doctor should check liver function tests before you start taking this medication and every 3 weeks during treatment, or as needed. Get medical help right away if you have any symptoms of liver damage, such as:

• nausea/vomiting that doesn't stop
• stomach/abdominal pain
• yellowing eyes/skin
• dark urine

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/medwatch.

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

Before taking tucatinib, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Before using this medication, tell your doctor or pharmacist your medical history, especially of:

• kidney disease
• liver problems

Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).

Since this drug can be absorbed through the skin and lungs and may harm an unborn baby, women who are pregnant or who may become pregnant should not handle this medication or breathe the dust from the tablets.

Tell your doctor if you are pregnant or plan to become pregnant. You should not become pregnant while using tucatinib. Tucatinib may harm an unborn baby. Your doctor should order a pregnancy test before you start this medication. Men and women using this medication should ask about reliable forms of birth control during treatment and for at least 1 week after the last dose. If you or your partner becomes pregnant, talk to your doctor right away about the risks and benefits of this medication.

It is unknown if this medication passes into breast milk. Because of the possible risk to the infant, breastfeeding is not recommended while using this medication and for at least 1 week after the last dose. Consult your doctor before breastfeeding.

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.

Other medications can affect the removal of tucatinib from your body, which may affect how tucatinib works. Examples include rifamycins (such as rifabutin, rifampin), St. John's wort, drugs used to treat seizures (such as carbamazepine, phenytoin), among others.

This medication can slow down the removal of other medications from your body, which may affect how they work. Examples of affected drugs include avanafil, some benzodiazepines (such as midazolam, triazolam), daridorexant, ergot drugs (such as ergotamine, dihydroergotamine), finerenone, mavacamten, pacritinib, some "statin" drugs (such as lovastatin, simvastatin), ubrogepant, among others.

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 1-800-222-1222. Canada residents can call 1-844-764-7669.

Do not share this medication with others.

Lab and/or medical tests (such as complete blood count, kidney/liver function) should be done before you start taking this medication and while you are taking it. Keep all medical and lab appointments.

If you miss a dose, skip the missed dose. Take your next dose at the regular time. Do not double the dose to catch up.

Store in the original container at room temperature away from light and moisture. Do not store in the bathroom. Keep the drying agent (desiccant) in the bottle. Tightly close the bottle when not in use. Once the bottle is opened, this medication expires after 3 months. 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.