Anastrozole prevents the conversion of adrenal androgens (e.g. [testosterone]) to estrogen in peripheral and tumour tissues. As the growth of many breast cancers is stimulated and/or maintained by the presence of estrogen, anastrozole helps to treat these cancers by decreasing the levels of circulating estrogens. Anastrozole has a relatively long duration of action allowing for once daily dosing – serum estradiol is reduced by approximately 70% within 24 hours of beginning therapy with 1mg once daily, and levels remain suppressed for up to 6 days following cessation of therapy. The incidence of ischemic cardiovascular events was increased during anastrozole therapy and patients with pre-existing ischemic heart disease should consider the risks and benefits of anastrozole before beginning therapy. Anastrozole has also been reported to decrease spine and hip bone mineral density (BMD), so consideration should be given to monitoring of BMD in patients receiving long-term therapy.
Anastrozole prevents the conversion of adrenal androgens (e.g. testosterone) to estrogen in peripheral and tumour tissues. As the growth of many breast cancers is stimulated and/or maintained by the presence of estrogen, anastrozole helps to treat these cancers by decreasing the levels of circulating estrogens. Anastrozole has a relatively long duration of action allowing for once daily dosing – serum estradiol is reduced by approximately 70% within 24 hours of beginning therapy with 1mg once daily, and levels remain suppressed for up to 6 days following cessation of therapy.
The incidence of ischemic cardiovascular events was increased during anastrozole therapy and patients with pre-existing ischemic heart disease should consider the risks and benefits of anastrozole before beginning therapy. Anastrozole has also been reported to decrease spine and hip bone mineral density (BMD), so consideration should be given to monitoring of BMD in patients receiving long-term therapy.
Anastrazole exerts its anti-estrogenic effects via selective and competitive inhibition of the aromatase enzyme found predominantly in the adrenal glands, liver, and fatty tissues. Many breast cancers are hormone receptor-positive, meaning their growth is stimulated and/or maintained by the presence of hormones such as estrogen or progesterone. In postmenopausal women, estrogen is primarily derived from the conversion of adrenally-produced androgens into estrogens by the aromatase enzyme – by competitively inhibiting the biosynthesis of estrogen at these enzymes, anastrozole effectively suppresses circulating estrogen levels and, subsequently, the growth of hormone receptor-positive tumours.
Anastrozole is primarily metabolized in the liver via oxidation and glucuronidation to a number of inactive metabolites, including hydroxyanastrozole (both free and glucuronidated) and anastrozole glucuronide. Oxidation to hydroxyanastrozole is catalyzed predominantly by CYP3A4 (as well as CYP3A5 and CYP2C8, to a lesser extent) and the direct glucuronidation of anastrozole appears to be catalyzed mainly by UGT1A4.
Anastrozole may also undergo N-dealkylation to form triazole and 3,5-Bis-(2-methylpropiononitrile)-benzoic acid. Labels for anastrozole state the main metabolite found in plasma following administration is triazole, but a recent pharmacokinetic study was unable to detect any products of N-dealkylation in vitro.
Anastrozole is used with other treatments, such as surgery or radiation, to treat early breast cancer in women who have experienced menopause (change of life; end of monthly menstrual periods). This medication is also used in women, who have experienced menopause, as a first treatment of breast cancer that has spread within the breast or to other areas of the body. This medication is also used to treat breast cancer in women whose breast cancer has worsened after taking tamoxifen (Nolvadex). Anastrozole is in a class of medications called nonsteroidal aromatase inhibitors. It works by decreasing the amount of estrogen the body makes. This can slow or stop the growth of many types of breast cancer cells that need estrogen to grow.
What special precautions should I follow?
- tell your doctor and pharmacist if you are allergic to anastrozole, or any other medications, or any of the ingredients in anastrozole. Ask your pharmacist for a list of the ingredients.
- tell your doctor and pharmacist what other prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention any of the following: medications that contain estrogen such as hormone replacement therapy (HRT) and hormonal contraceptives (birth control pills, patches, rings, and injections); raloxifene (Evista); and tamoxifen (Nolvadex). Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
- tell your doctor if you have or have ever had high cholesterol, osteoporosis (condition in which the bones are fragile and break easily), liver, or heart disease.
- you should know that anastrozole should only be taken by women who have undergone menopause and cannot become pregnant. However, if you are pregnant or breast-feeding, you should tell your doctor before you begin taking this medication. Anastrozole may harm the fetus.
Anastrozole may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:
- hot flashes
- stomach pain
- loss of appetite
- weight gain
- joint, bone, or muscle pain
- breast pain
- mood changes
- difficulty falling asleep or staying asleep
- vaginal bleeding
- vaginal dryness or irritation
- pain, burning, or tingling in the hands or feet
- dry mouth
- hair thinning
Some side effects can be serious. If you experience any of these symptoms, call your doctor immediately:
- chest pain
- sore throat, cough, fever, chills, swollen glands, or other signs of infection
- swelling, redness, or warmth in hand or arm
- difficult, painful, or urgent urination
- blurred vision or vision changes
- yellowing of the skin or eyes
- pain in the upper right part of the stomach
- skin lesions, ulcers, or blisters
- shortness of breath
- difficulty swallowing or breathing
- swelling of the eyes, face, lips, tongue, throat, arms, hands, feet, ankles, or lower legs
Anastrozole may cause or worsen osteoporosis. It can decrease the density of your bones and increase the chance of broken bones and fractures. Talk to your doctor about the risks of taking this medication and to find out what you can do to decrease these risks.
Anastrozole may cause other side effects. Call your doctor if you have any unusual problems while taking this medication.
What should I know about storage and disposal of this medication?
Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture (not in the bathroom).
It is important to keep all medication out of sight and reach of children as many containers (such as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in a safe location – one that is up and away and out of their sight and reach. Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA’s Safe Disposal of Medicines website for more information if you do not have access to a take-back program.
In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For this medicine, the following should be considered:
Tell your doctor if you have ever had any unusual or allergic reaction to this medicine or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.
Appropriate studies performed to date have not demonstrated pediatric-specific problems that would limit the usefulness of anastrozole in children. However, efficacy has not been established to treat teenage boys with pubertal gynecomastia and to treat precocious puberty in teenage girls with McCune-Albright Syndrome.
Appropriate studies performed to date have not demonstrated geriatric-specific problems that would limit the usefulness of anastrozole in the elderly.
There are no adequate studies in women for determining infant risk when using this medication during breastfeeding. Weigh the potential benefits against the potential risks before taking this medication while breastfeeding.
Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. Tell your healthcare professional if you are taking any other prescription or nonprescription (over-the-counter [OTC]) medicine.
Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. Discuss with your healthcare professional the use of your medicine with food, alcohol, or tobacco.
Other Medical Problems
The presence of other medical problems may affect the use of this medicine. Make sure you tell your doctor if you have any other medical problems, especially:
- Bone problems (eg, osteoporosis) or
- Hypercholesterolemia (high cholesterol or fat in the blood) or
- Ischemic heart disease (eg, heart attack, angina), history of, or
- Liver disease—Use with caution. May make these conditions worse.
- Premenopausal women (still having menstrual cycles)—Should not be used in these patients.
Take this medicine only as directed by your doctor. Do not take more of it, do not take it more often, and do not take it for a longer time than your doctor ordered. To do so may increase the chance for side effects.
This medicine comes with a patient information leaflet. Read and follow these instructions carefully. Ask your doctor if you have any questions.
You may take this medicine with or without food.
Anastrozole sometimes causes nausea, vomiting, or diarrhea. However, it is very important that you continue to use the medicine, even if you begin to feel ill. Ask your doctor for ways to prevent these effects or make them less severe.
The dose of this medicine will be different for different patients. Follow your doctor’s orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.
The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.