[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Aromatase inhibitors](https://durgical.com/en/pharmacology/classes/aromatase-inhibitors/) › Exemestane

[Pharmacology](https://durgical.com/en/pharmacology/) · [Aromatase inhibitors](https://durgical.com/en/pharmacology/classes/aromatase-inhibitors/)

# Exemestane

A steroidal breast cancer tablet that permanently disables the enzyme making oestrogen after menopause. Bone loss is its main long-term risk.

Updated 2026-11-01

- Class: [Aromatase inhibitors](https://durgical.com/en/pharmacology/classes/aromatase-inhibitors/)
- Enzyme: Aromatase (CYP19A1)
- ATC code: L02BG06

✂**Aromatase (CYP19A1)**Exemestane

ⓘ The figure shows exemestane bound in the active site of human placental aromatase, above the heme.

**Target in 3D:** Aromatase (CYP19A1). PDB structure 3S7S (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/3S7S) · Drag to rotate · pinch to zoom

## Mechanism of action

Exemestane is a steroid that resembles androstenedione, the natural substrate of aromatase. The enzyme takes it as a false substrate and converts it into an intermediate that binds irreversibly to the active site, inactivating the enzyme (suicide inhibition). New enzyme must be made before oestrogen synthesis recovers.

- Enters the aromatase active site as a false substrate
- The enzyme turns it into a reactive intermediate
- The intermediate binds irreversibly: aromatase is inactivated
- Oestrogen falls; receptor-positive tumours stop growing

## Pharmacokinetics

**Absorption**
Taken by mouth after a meal

**Metabolism**
In the liver, by CYP3A4 among other pathways

**Elimination**
About equally in urine and faeces, as metabolites

**Half-life**
About 24 hours

## Indications

- Adjuvant treatment of oestrogen receptor-positive early breast cancer in postmenopausal women after several years of tamoxifen [Breast cancer →](https://durgical.com/en/conditions/breast-cancer/)
- Advanced breast cancer in postmenopausal women that progressed on tamoxifen [Breast cancer →](https://durgical.com/en/conditions/breast-cancer/)

## Adverse effects

### Common

- Hot flashes
- Joint pain
- Fatigue
- Sweating
- Insomnia and headache

### Serious (rare, important)

- Reduced bone mineral density and fractures
- Fetal harm

## Contraindications

- Hypersensitivity to exemestane or any excipient

## Key interactions

**Strong CYP3A4 inducers (rifampicin, phenytoin, carbamazepine)**
Lower exemestane exposure.

**Systemic oestrogen-containing products**
Interfere with its action; not given together.

## What is monitored

- Bone mineral density
- Vitamin D (25-hydroxyvitamin D) before starting
- Joint symptoms

## Administration and safety

- Oral tablet once a day after a meal.
- Hazardous drug: people who are pregnant avoid handling broken tablets.

## Nursing care

- Check that the patient is postmenopausal; it is not used for breast cancer before menopause.
- Ask about rifampicin, phenytoin, carbamazepine and other inducers.
- Support bone health: vitamin D, calcium, exercise and bone density checks.
- Teach about hot flashes and joint pain.

## Pregnancy and breastfeeding

Can cause fetal harm; women who could become pregnant use effective contraception.

## Memory aid

EXemestane EXecutes aromatase: a steroid decoy that the enzyme swallows and cannot spit out.

## Test yourself

Think of the answer, then tap the question to see it.

## Why is exemestane called a suicide inhibitor of aromatase?

The enzyme processes it like its own substrate, and the product binds irreversibly to the active site, so the enzyme destroys itself.

## What do rifampicin and phenytoin do to exemestane?

As strong CYP3A4 inducers they lower exemestane exposure, which can weaken its effect.

## Which laboratory value is checked before starting exemestane, and why?

25-hydroxyvitamin D, because aromatase inhibitors reduce bone density and vitamin D deficiency adds to the risk.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/exemestane/)

## Related drugs

- [Anastrozole](https://durgical.com/en/pharmacology/anastrozole/)
- [Letrozole](https://durgical.com/en/pharmacology/letrozole/)
- [Tamoxifen](https://durgical.com/en/pharmacology/tamoxifen/)

## Related conditions

- [Breast cancer](https://durgical.com/en/conditions/breast-cancer/)

[← Back to the class: Aromatase inhibitors](https://durgical.com/en/pharmacology/classes/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: [Exemestane: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a607006.html) (MedlinePlus (U.S. National Library of Medicine), 2022); [DailyMed - EXEMESTANE tablet, film coated](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=1841ec12-3f4f-4b87-b719-fd0b4d9eaffb) (DailyMed (U.S. National Library of Medicine), 2024); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=L02BG06) (WHO Collaborating Centre for Drug Statistics Methodology, 2026); [Crystal structure of human placental aromatase complexed with breast cancer drug exemestane](https://www.rcsb.org/structure/3S7S) (RCSB Protein Data Bank, 2012).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/pharmacology/exemestane/
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