Letrozole and ribociclib are used together in combination to treat HR-positive, HER2-negative breast cancer.

letrozole and ribociclib is used when the cancer has spread to other parts of the body (metastatic).

Letrozole and ribociclib are two different medicines that are packaged together. Letrozole tablets are yellow and ribociclib tablets are violet.

Letrozole and ribociclib may also be used for purposes not listed in this medication guide.

letrozole and ribociclib can cause a serious heart rhythm or lung problem. Call your doctor at once if you have fast or pounding heartbeats, severe dizziness, chest pain, or shortness of breath.

Letrozole and ribociclib may also affect your liver or blood cells. Tell your doctor if you have right-sided stomach pain, tiredness, flu-symptoms, easy bruising or bleeding, dark urine, or yellowing of the skin or eyes.

This medicine may also cause a severe skin reaction. Get emergency medical help if you have a fever, sore throat, burning eyes, skin pain, or red or purple skin rash with blistering and peeling.

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

It is best to take letrozole and ribociclib in the morning, but take it at the same time each day. You may take letrozole and ribociclib with or without food.

Letrozole and ribociclib is given in a 28-day treatment cycle. On days 1 through 21, you will take both ribociclib and letrozole together at the same time each day. During the last 7 days you will take only letrozole each day.

Your doctor may occasionally change the number of tablets in your dose. Follow all dosing instructions very carefully.

Swallow each tablet whole and do not crush, chew, or break it. Do not take any tablet that is broken or cracked.

If you vomit shortly after taking a tablet, do not take another dose. Wait until your next scheduled dose time to take the medicine again.

This medicine can cause a serious heart rhythm or lung problem. Call your doctor at once if you have fast or pounding heartbeats, severe dizziness, or trouble breathing, and shortness of breath.

You will need frequent medical tests while taking letrozole and ribociclib. Your cancer treatments may be delayed based on the results of these tests.

Do not change your dose or stop taking this medicine without your doctor's advice.

Store each medicine in its original container at room temperature, away from moisture and heat.

Usual Adult Dose for Breast Cancer:

Letrozole: 2.5 mg orally once a day throughout the 28-day cycle
Ribociclib: 600 mg orally once a day for 21 consecutive days followed by 7 days off for a 28-day cycle

Use: Initial endocrine-based therapy for the treatment of pre/perimenopausal or postmenopausal women with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced or metastatic breast cancer

You should not use this medicine if you are allergic to letrozole (Femara) or ribociclib (Kisqali).

Your doctor will perform medical tests to make sure you do not have conditions that would prevent you from safely using this medicine.

Tell your doctor if you have any signs of infection, such as fever or chills, or if you have ever had:

• heart disease, heart failure;

• a heart attack;

• heart rhythm problems, including slow heartbeats;

• long QT syndrome;

• low levels of calcium, phosphorus, potassium, or magnesium in your blood; or

• liver disease.

If you have not gone through menopause, you may need an additional hormonal medication while taking letrozole and ribociclib. Tell your doctor if you have begun having symptoms of menopause such as irregular menstrual periods, hot flashes, night sweats, sleep problems, or vaginal dryness.

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

Letrozole and ribociclib may harm an unborn baby. Use effective birth control to prevent pregnancy while you are using this medicine and for at least 3 weeks after your last dose. Tell your doctor right away if you become pregnant.

This medicine may affect fertility (ability to have children) in both men and women. However, it is important for women to use birth control to prevent pregnancy because letrozole and ribociclib may harm the baby if a pregnancy does occur.

You should not breastfeed while using this medicine and for at least 3 weeks after your last dose.

Skip the missed dose and use your next dose at the regular time. Do not use two doses at one time.

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

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

Get emergency medical help if you have signs of an allergic reaction (hives, difficult breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning eyes, skin pain, red or purple skin rash with blistering and peeling).

Letrozole and ribociclib may cause serious side effects. Call your doctor at once if you have:

• trouble breathing, shortness of breath, cough with or without mucus, chest pain;

• fast or pounding heartbeats, fluttering in your chest, and sudden dizziness (like you might pass out);

• liver problems--loss of appetite, right-sided stomach pain, tiredness, easy bruising or bleeding, dark urine, jaundice (yellowing of the skin or eyes);

• low red blood cells (anemia)--pale skin, unusual tiredness, feeling light-headed or short of breath, cold hands and feet; or

• low white blood cell counts--fever, mouth sores, skin sores, sore throat, cough, trouble breathing.

Your cancer treatments may be delayed or permanently discontinued if you have certain side effects.

Common side effects of letrozole and ribociclib may include:

• low white blood cells, infections;

• anemia;

• tiredness;

• nausea, vomiting, diarrhea, constipation;

• headache;

• rash;

• back pain; or

• hair loss.

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.

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.

Letrozole and ribociclib can cause a serious heart problem. Your risk may be higher if you also use certain other medicines for infections, asthma, heart problems, high blood pressure, depression, mental illness, cancer, malaria, or HIV.

Many drugs can affect letrozole and ribociclib. 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.