lapatinib

What is the most important information I should know about lapatinib?

What is lapatinib?

Lapatinib is used to treat advanced hormone-related breast cancer that has progressed or spread after treatment with other cancer medicines.

Lapatinib is used for this condition only if your tumor tests positive for a protein called human epidermal growth factor receptor 2 (HER2). HER2 protein can speed the growth of cancer cells.

In postmenopausal women, lapatinib is given in combination with a hormonal medicine called letrozole (Femara). In others, lapatinib is given together with a cancer medicine called capecitabine (Xeloda).

Lapatinib may also be used for purposes not listed in this medication guide.

What should I discuss with my healthcare provider before taking lapatinib?

Tell your doctor if you have ever had:

• heart disease;
• liver disease (lapatinib can cause severe or fatal liver problems);
• an electrolyte imbalance (such as low levels of potassium or magnesium in your blood); or
• long QT syndrome (in you or a family member).

You may need to have a negative pregnancy test before starting this treatment.

Tell your doctor right away if a pregnancy occurs while either the mother or the father is using lapatinib.

How should I take lapatinib?

Follow all directions on your prescription label and read all medication guides or instruction sheets. Use the medicine exactly as directed.

When used with letrozole, the usual dose of lapatinib is 6 tablets taken once daily every day. Letrozole is also taken every day.

When used with capecitabine, the usual dose of lapatinib 5 tablets taken once daily for 21 days in a row. Capecitabine is also taken twice daily for only the first 14 days. This 21-day cycle is then repeated.

Follow your doctor's dosing instructions very carefully.

You may swallow each lapatinib tablet one at a time, but take the entire dose (all 5 or 6 tablets) at the same time each day.

You will need blood tests every 4 to 6 weeks to check your liver function. Your heart function may also need to be checked using an electrocardiograph or ECG (sometimes called an EKG).

What happens if I miss a dose?

Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

What happens if I overdose?

What should I avoid while taking lapatinib?

Grapefruit may interact with lapatinib and lead to unwanted side effects. Avoid the use of grapefruit products.

What are the possible side effects of lapatinib?

• fast or pounding heartbeats, fluttering in your chest, shortness of breath, and sudden dizziness (like you might pass out);
• severe or ongoing diarrhea; or
• new or worsening cough, wheezing, chest pain, feeling short of breath.

Common side effects may include:

• indigestion, loss of appetite;
• nausea, vomiting, diarrhea;
• rash, itching, dry skin, acne;
• pain or redness on the palms of your hands or the soles of your feet;
• problems with your fingernails or toenails;
• feeling weak or tired;
• nosebleeds, mouth sores;
• thinning hair; or
• headache.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What other drugs will affect lapatinib?

Sometimes it is not safe to use certain medications at the same time. Some drugs can affect your blood levels of other drugs you take, which may increase side effects or make the medications less effective.

Many drugs can affect lapatinib. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed here. Tell your doctor about all your current medicines and any medicine you start or stop using.

Where can I get more information?

Your doctor or pharmacist can provide more information about lapatinib.