Generic name: letrozole
Brand name: Femara
Dosage form: oral tablet (2.5 mg)
Drug classes: Aromatase inhibitors, Hormones / antineoplastics
Medically reviewed by A Ras MD.
What is letrozole used for?
Letrozole is a prescription medicine that is used to treat breast cancer in women after menopause (change of life). Letrozole may be given to you for other reasons.
Letrozole Tablets, USP for oral administration contain 2.5 mg of letrozole, a nonsteroidal aromatase inhibitor (inhibitor of estrogen synthesis). It is chemically described as 4,4′-(1H-1,2,4-Triazol-1-ylmethylene) dibenzonitrile, and its structural formula is
Letrozole, USP is a white to yellowish crystalline powder, practically odorless, freely soluble in dichloromethane, slightly soluble in ethanol, and practically insoluble in water. It has a molecular weight of 285.31, empirical formula C 17H 11N 5, and a melting range of 184°C to 185°C.
Letrozole Tablets, USP are available as 2.5 mg tablets for oral administration.
Inactive Ingredients: colloidal silica dioxide, hypromellose, lactose monohydrate, magnesium stearate, microcrystalline cellulose, polyethylene glycol/macrogol, polyvinyl alcohol, sodium starch glycolate, talc, titanium dioxide, and the following color additives: yellow iron oxide, FD&C Yellow #5/Tartrazine Aluminum Lake, FD&C Yellow #6/Sunset Yellow FCF Aluminum Lake, FD&C Blue #2/Indigo Carmine Aluminum Lake.
Mechanism of Action
The growth of some cancers of the breast is stimulated or maintained by estrogens. Treatment of breast cancer thought to be hormonally responsive (i.e., estrogen and/or progesterone receptor positive or receptor unknown) has included a variety of efforts to decrease estrogen levels (ovariectomy, adrenalectomy, hypophysectomy) or inhibit estrogen effects (antiestrogens and progestational agents). These interventions lead to decreased tumor mass or delayed progression of tumor growth in some women.
In postmenopausal women, estrogens are mainly derived from the action of the aromatase enzyme, which converts adrenal androgens (primarily androstenedione and testosterone) to estrone and estradiol. The suppression of estrogen biosynthesis in peripheral tissues and in the cancer tissue itself can therefore be achieved by specifically inhibiting the aromatase enzyme.
Letrozole is a nonsteroidal competitive inhibitor of the aromatase enzyme system; it inhibits the conversion of androgens to estrogens. In adult nontumor- and tumor-bearing female animals, letrozole is as effective as ovariectomy in reducing uterine weight, elevating serum LH, and causing the regression of estrogen-dependent tumors. In contrast to ovariectomy, treatment with letrozole does not lead to an increase in serum FSH. Letrozole selectively inhibits gonadal steroidogenesis but has no significant effect on adrenal mineralocorticoid or glucocorticoid synthesis.
Letrozole inhibits the aromatase enzyme by competitively binding to the heme of the cytochrome P450 subunit of the enzyme, resulting in a reduction of estrogen biosynthesis in all tissues. Treatment of women with letrozole significantly lowers serum estrone, estradiol and estrone sulfate and has not been shown to significantly affect adrenal corticosteroid synthesis, aldosterone synthesis, or synthesis of thyroid hormones.
Before taking letrozole, tell your doctor:
- If you are allergic to letrozole; any part of this medicine; or any other drugs, foods, or substances. Tell your doctor about the allergy and what signs you had.
- If you are pregnant or may be pregnant. Do not take letrozole if you are pregnant.
- If you are breast-feeding. Do not breast-feed while you take letrozole and for 3 weeks after your last dose.
This is not a list of all drugs or health problems that interact with letrozole.
Tell your doctor and pharmacist about all of your drugs (prescription or OTC, natural products, vitamins) and health problems. You must check to make sure that it is safe for you to take letrozole with all of your drugs and health problems. Do not start, stop, or change the dose of any drug without checking with your doctor.
What are some things I need to know or do while I take letrozole?
- Tell all of your health care providers that you take letrozole. This includes your doctors, nurses, pharmacists, and dentists.
- Avoid driving and doing other tasks or actions that call for you to be alert until you see how letrozole affects you.
- This medicine may cause weak bones. This may happen more often if used for a long time. This may raise the chance of broken bones. Call your doctor right away if you have bone pain.
- Have a bone density test as you have been told by your doctor. Talk with your doctor.
- Have blood work checked as you have been told by the doctor. Talk with the doctor.
- Take calcium and vitamin D as you were told by your doctor.
- If you are 65 or older, use letrozole with care. You could have more side effects.
- This medicine may affect fertility. Fertility problems may lead to not being able to get pregnant or father a child.
- This medicine may cause harm to the unborn baby if you take it while you are pregnant.
- If you are able to get pregnant, a pregnancy test will be done to show that you are NOT pregnant before starting letrozole. Talk with your doctor.
- Use birth control that you can trust to prevent pregnancy while taking letrozole and for at least 3 weeks after your last dose.
- If you get pregnant while taking letrozole or within 3 weeks after your last dose, call your doctor right away.
How is letrozole best taken?
Use letrozole as ordered by your doctor. Read all information given to you. Follow all instructions closely.
- Take with or without food.
- Keep taking letrozole as you have been told by your doctor or other health care provider, even if you feel well.
- Take letrozole at the same time of day.
What do I do if I miss a dose?
- Take a missed dose as soon as you think about it.
- If it is close to the time for your next dose, skip the missed dose and go back to your normal time.
- Do not take 2 doses at the same time or extra doses.
What are the side effects of letrozole that I need to call my doctor about immediately?
WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:
- Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.
- Signs of high blood pressure like very bad headache or dizziness, passing out, or change in eyesight.
- Signs of a urinary tract infection (UTI) like blood in the urine, burning or pain when passing urine, feeling the need to pass urine often or right away, fever, lower stomach pain, or pelvic pain.
- Swollen gland.
- Chest pain or pressure.
- Shortness of breath.
- Vaginal bleeding that is not normal.
- Low mood (depression).
- Not able to pass urine or change in how much urine is passed.
What are some other side effects of letrozole?
All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away:
- Feeling tired or weak.
- Hot flashes.
- Upset stomach or throwing up.
- Back pain.
- Muscle or joint pain.
- Night sweats.
- Sweating a lot.
- Not able to sleep.
- Weight gain or loss.
- Belly pain.
- Hair loss.
These are not all of the side effects that may occur. If you have questions about side effects, call your doctor. Call your doctor for medical advice about side effects.
You may report side effects to the FDA at 1-800-332-1088. You may also report side effects at https://www.fda.gov/medwatch.
If overdose is suspected:
If you think there has been an overdose, call your poison control center or get medical care right away. Be ready to tell or show what was taken, how much, and when it happened.
How do I store and/or throw out letrozole?
- Store at room temperature.
- Store in a dry place. Do not store in a bathroom.
- Keep all drugs in a safe place. Keep all drugs out of the reach of children and pets.
- Throw away unused or expired drugs. Do not flush down a toilet or pour down a drain unless you are told to do so. Check with your pharmacist if you have questions about the best way to throw out drugs. There may be drug take-back programs in your area.
PRINCIPAL DISPLAY PANEL
- Package Label – 2.5 mg
- Rx Only NDC 69117-0004-1
- Letrozole tablets, USP
- 2.5 mg per tablet
- 30 Tablets
SRC: NLM .