Letrozole belongs to the group of cancer-fighting medications known as antineoplastics, and specifically to the type of antineoplastics known as nonsteroidal aromatase inhibitor.

Letrozole can be used after surgery to treat postmenopausal women with hormone receptor-positive early breast cancer, including those who have received approximately 5 years of tamoxifen therapy. Letrozole can also be used to treat postmenopausal women with advanced breast cancer. It can also be used to treat women who have gone through natural or artificially induced menopause who have breast cancer that has spread to other parts of the body and whose cancer has progressed following anti-estrogen therapy.

Letrozole fights breast cancer by inactivating an enzyme known as aromatase. This prevents the enzyme from supplying the estrogen that allows certain types of breast cancers to grow and survive.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

The recommended dose of letrozole is 2.5 mg once daily. It should be taken at the same time each day and may be taken with or without food.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important to take this medication exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store the tablets in a dry place at room temperature, out of reach of children and pets.

2.5 mg
Each dark yellow, standard convex, round, film-coated tablet, debossed with "93" on one side and "B1" on the other side of the tablet, contains 2.5 mg of letrozole. Nonmedicinal ingredients: colloidal anhydrous silica (Aerosil 200), FD & C Yellow No. 5 Aluminum Lake, FD & C Blue No. 2 Aluminum Lake, iron oxide yellow, lactose monohydrate (spray dried), magnesium stearate, macrogol, microcrystalline cellulose, polyvinyl alcohol, sodium starch glycolate (Type A), maize starch, talc, and titanium dioxide.

Do not take letrozole if you:

• are allergic to letrozole or any ingredients of the medication
• are allergic to any other aromatase inhibitor medications (e.g., anastrozole, exemestane)
• are breast-feeding
• are pregnant
• are premenopausal
• are under 18 years of age

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• abdominal or back pain
• anxiety
• breast pain
• changed sense of taste
• constipation
• cough
• diarrhea
• dizziness
• dry mouth, eyes, nose
• dry skin
• eye irritation
• falls
• fatigue
• fever
• general feeling of being unwell
• hair loss
• headache
• heartburn
• hot flushes
• increase or loss of appetite
• increased sweating
• joint stiffness
• nausea
• night sweats
• pain in muscles, bones, or joints
• rash
• spinning sensation
• swelling or puffiness due to retained body fluid
• thirst
• tiredness
• trigger finger (a condition in which the finger or thumb catches in a bent position)
• trouble sleeping
• weight increase or decrease
• urinary incontinence (i.e., involuntary leakage of urine)
• vaginal discharge or dryness
• vomiting

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• bone fractures
• carpal tunnel syndrome (e.g., pain or burning sensation in the hands or wrists)
• decreased sense of touch
• fast or pounding heartbeat
• increased blood pressure
• increased cholesterol levels
• signs of infection (e.g., severe fever, chills, mouth ulcers, shortness of breath, sudden lack of energy)
• signs of depression (such as feeling sad, losing interest in things you used to enjoy, weight changes, changes in sleep habits, feelings of guilt or worthlessness, thoughts of suicide)
• signs of high blood sugar (e.g., frequent urination, increased thirst, excessive eating, unexplained weight loss, poor wound healing, infections, fruity breath odour)
• signs of liver problems (e.g., yellow skin and eyes, nausea, loss of appetite, dark-coloured urine)
• signs of tendon inflammation or tears (e.g., a snap or pop when the tear happens, severe pain, swelling)
• symptoms of a urinary tract infection (e.g., burning when passing urine, blood in the urine, or increased urgency to urinate)
• unusual vaginal bleeding
• vision changes

Stop taking the medication and seek immediate medical attention if any of the following occur:

• signs of a blood clot in the arm or leg (tenderness, pain, swelling, warmth, or redness in the arm or leg) or lungs (difficulty breathing, sharp chest pain that is worse when breathing in, coughing, coughing up blood, sweating, or passing out)
• signs of a heart attack (e.g., tightness or feeling of heaviness in your chest or pain radiating to your arms or shoulders, neck, teeth, jaw, abdomen, or back)
• signs of a serious allergic reaction (e.g., abdominal cramps, difficulty breathing, nausea and vomiting, or swelling of the face and throat)
• signs of a severe skin reaction such as blistering, peeling, a rash covering a large area of the body, a rash that spreads quickly, or a rash combined with fever or discomfort
• signs of a stroke (e.g., numbness or weakness in arm, leg or any part of the body, loss of coordination, vision changes, sudden headache, difficulty speaking or breathing)
• swelling of the arms, hands, feet, ankles, or other parts of the body

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin taking a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should take this medication.

Blood clots: Letrozole may cause an increase in the formation of blood clots in blood vessels, reducing the blood flow to organs or the extremities. In the arms or legs this is experienced as pain, swelling, warmth, or redness in the limb. In the lungs, you may experience difficulty breathing, sharp chest pain, coughing, or coughing up blood. If you experience any of these symptoms, contact your doctor immediately.

Bone mineral density: Long-term use of letrozole may decrease the density of bones, thereby increasing the risk of osteoporosis. Your doctor will order bone mineral density tests periodically while you are taking letrozole.

Cholesterol: Letrozole may increase cholesterol levels. If you have increased blood cholesterol levels or a history of increased cholesterol, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Drowsiness/dizziness: Letrozole may cause dizziness or drowsiness. If you experience either or both of these side effects, you should not drive, use machinery, or perform any other activities that require alertness.

Heart disease: This medication may increase the risk of heart attack or increased blood pressure. If you are at risk for heart disease or high blood pressure, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed. If you experience signs of a heart attack, such as tightness or heaviness in your chest, sudden chest pain spreading to your arms or shoulders, sweating, nausea, or anxiety, seek medical help immediately.

Kidney function: If you have reduced kidney function, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Liver function: If you have liver disease or reduced liver function, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Premenopausal women: Letrozole should not be taken by women who have not reached menopause (either naturally or surgically), unless the potential benefits outweigh the risks.

Stroke: This medication increases the risk of a stroke or "mini-strokes" occurring as a result of blood clots forming in the blood vessels. If you experience signs of a stroke or mini-stroke, such as confusion, difficulty speaking, loss of coordination, sudden headache or vision changes, contact your doctor immediately.

Pregnancy: It is suspected that the use of letrozole during pregnancy could cause miscarriages and other serious problems. It is not intended to be taken by women who have not reached menopause.

This medication should not be taken during pregnancy. Any woman taking this medication who may become pregnant should practice effective birth control and contact her doctor immediately if pregnancy is suspected while taking this medication.

Breast-feeding: It is not known if letrozole passes into breast milk. If you are breast-feeding and are taking this medication, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of this medication have not been established for children. Children under 18 years of age should not use this medication.

There may be an interaction between letrozole and any of the following:

• birth control pills containing estrogen
• any estrogen-containing medications (e.g., conjugated estrogen, estradiol, ethinyl estradiol)
• methadone
• tamoxifen

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications that you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.