Pharmacology · Aromatase inhibitors
Anastrozole !
A breast cancer tablet for postmenopausal women that blocks the enzyme making oestrogen. It can thin the bones and cause joint pain.
Updated 2026-11-01
No structure with anastrozole is available. The figure shows exemestane, another aromatase inhibitor, bound in the same active site of human placental aromatase, above the heme.
Mechanism of action
Anastrozole is a non-steroidal triazole that binds reversibly to aromatase, the cytochrome P450 that converts androgens into oestrogens. In postmenopausal women, where peripheral aromatase supplies most oestrogen, it lowers estradiol strongly. Hormone receptor-positive breast cancer cells lose the oestrogen signal that drives their growth.
- Binds reversibly to the heme pocket of aromatase
- Androgens are no longer converted into estrone and estradiol
- Oestrogen levels fall sharply after menopause
- Oestrogen-dependent breast cancer cells stop growing
Pharmacokinetics
- Absorption
- Well absorbed by mouth
- Metabolism
- Mostly in the liver, which accounts for most of its elimination
- Elimination
- A small fraction leaves unchanged through the kidneys
- Half-life
- About 50 hours, so it is given once a day
Indications
- Adjuvant treatment of hormone receptor-positive early breast cancer in postmenopausal women Breast cancer →
- First-line treatment of hormone receptor-positive or unknown advanced breast cancer in postmenopausal women Breast cancer →
- Advanced breast cancer that progressed on tamoxifen Breast cancer →
Adverse effects
Common
- Hot flashes
- Joint pain and stiffness
- Weakness and fatigue
- Rise in total cholesterol
- Low mood
Contraindications
- Hypersensitivity to anastrozole or any excipient
Key interactions
- Tamoxifen
- Not used together: the combination adds no benefit over tamoxifen alone.
- Oestrogen-containing products
- May weaken the effect of anastrozole.
What is monitored
- Bone mineral density
- Cholesterol
- Joint symptoms and quality of life
Administration and safety
- Oral tablet, taken at the same time each day with or without food.
- Hazardous drug: people who are pregnant should avoid handling crushed or broken tablets.
- Look-alike names: anastrozole and letrozole are both aromatase inhibitors, but their tablets are not interchangeable.
Nursing care
- Ask about menopausal status: the drug is meant for postmenopausal women.
- Teach about joint pain and hot flashes, which are common and often manageable.
- Encourage calcium, vitamin D, weight-bearing exercise and bone density checks as planned.
- Ask about chest pain in women with known heart disease.
- Ask about oestrogen products, including some herbal or vaginal products, and report them.
Pregnancy and breastfeeding
Can cause fetal harm; women who could become pregnant use effective contraception during treatment.
Test yourself
Think of the answer, then tap the question to see it.
Which enzyme does anastrozole inhibit?
Aromatase (CYP19A1), which converts androstenedione and testosterone into estrone and estradiol.
A woman on anastrozole asks why she needs a bone density scan. What is the reason?
Lowering oestrogen speeds bone loss; anastrozole decreases bone mineral density and raises fracture risk, so bone density is checked.
Why is anastrozole not given together with tamoxifen?
In the trial that compared them, the combination gave no extra benefit over tamoxifen alone.
Related drugs
Related conditions
← Back to the class: Aromatase inhibitors
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Anastrozole: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2018); DailyMed - ANASTROZOLE tablet (DailyMed (U.S. National Library of Medicine), 2024); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); Crystal structure of human placental aromatase complexed with breast cancer drug exemestane (RCSB Protein Data Bank, 2012).
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Representative model, for educational purposes only.