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Steroidal aromatase inhibitor Pregnancy: Contraindicated in pregnant women - no clinical data on exposed pregnancies are available and animal studies have shown reproductive toxicity. It is unknown whether exemestane is excreted into human milk; it should not be administered to lactating women. The physician needs to discuss adequate contraception with women who have the potential to become pregnant, including perimenopausal women and those who have recently become postmenopausal, until postmenopausal status is fully established. US labelling: can cause fetal harm; advise females of reproductive potential to use effective contraception.

Exemestane

Brand names: Aromasin

Exemestane is a steroidal aromatase inhibitor used in the treatment of oestrogen-receptor-positive breast cancer in postmenopausal women.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: One 25 mg tablet once daily, preferably after a meal
Route: Oral
Frequency: Once daily, preferably after a meal
UK SPC (Exemestane 25 mg coated tablets) §4.2 - the same dose applies to adult and elderly patients. In patients with early breast cancer, treatment should continue until completion of five years of combined sequential adjuvant hormonal therapy (tamoxifen followed by exemestane), or earlier if tumour relapse occurs. In patients with advanced breast cancer, treatment should continue until tumour progression is evident. No dose adjustments are required for patients with hepatic or renal insufficiency, although §4.4 advises caution in hepatic or renal impairment. Exemestane should not be administered to women with pre-menopausal endocrine status; whenever clinically appropriate the post-menopausal status should be ascertained by assessment of LH, FSH and oestradiol levels. Bone mineral density should be assessed at the commencement of adjuvant treatment in women with osteoporosis or at risk of osteoporosis, and 25-hydroxy vitamin D levels should be assessed routinely before starting aromatase inhibitor treatment, with supplementation if deficient. US labelling cross-check (DailyMed 2024-05-29) gives the same 25 mg once daily after a meal, and adds a dose modification not present in the UK SPC: for patients receiving exemestane with a strong CYP3A4 inducer such as rifampicin or phenytoin, the recommended dose is 50 mg once daily after a meal. PAEDIATRIC: the UK SPC states exemestane is not recommended for use in children; the US label states safety and effectiveness in paediatric patients have not been established. No paediatric dose is given.

Dose adjustments

Renal

No dose adjustments are required for patients with renal insufficiency (§4.2); however §4.4 advises that exemestane should be used with caution in patients with renal impairment.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Hypersensitivity to the active substance or to any of the excipients
  • Pre-menopausal women
  • Pregnant or lactating women

Side effects

  • Hot flushes (very common - 22% in early breast cancer, 14% in advanced breast cancer)
  • Joint and musculoskeletal pain including arthralgia (very common - 18%); fracture and osteoporosis (common); reduction in bone mineral density
  • Fatigue and pain (very common - fatigue 16%); asthenia and peripheral oedema (common)
  • Depression, insomnia, headache and dizziness (very common); carpal tunnel syndrome and paraesthesia (common)
  • Abdominal pain and nausea (very common); vomiting, diarrhoea, constipation, dyspepsia and anorexia (common)
  • Hyperhidrosis (very common); alopecia, rash, urticaria and pruritus (common)
  • Hepatic enzyme increased, blood bilirubin increased and blood alkaline phosphatase increased (very common); leucopenia (very common), thrombocytopenia (common); hepatitis and cholestatic hepatitis (rare)

Interactions

  • CYP3A4 inducers - rifampicin, anticonvulsants (e.g. phenytoin, carbamazepine) and herbal preparations containing Hypericum perforatum (St John's Wort) may reduce the efficacy of exemestane; in an interaction study rifampicin 600 mg daily reduced exemestane AUC by 54% and Cmax by 41%. US labelling recommends increasing the exemestane dose to 50 mg once daily with a strong CYP3A4 inducer
  • CYP3A4 inhibitors - specific inhibition of CYP3A4 by ketoconazole showed no significant effect on the pharmacokinetics of exemestane
  • Medicinal products metabolised via CYP3A4 with a narrow therapeutic window - exemestane should be used cautiously with these
  • Exemestane is metabolised through CYP3A4 and aldoketoreductases and does not inhibit any of the major CYP isoenzymes

Clinical monograph

How it works

It irreversibly inactivates the aromatase enzyme, blocking peripheral conversion of androgens to oestrogens and thereby lowering circulating oestrogen.

Prescribing in practice

  • Oestrogen depletion accelerates bone loss, so bone health should be assessed and managed to reduce fracture risk during treatment.
  • It is only effective in postmenopausal women and should not be used where ovarian function persists.
  • Arthralgia, hot flushes and fatigue are common and may affect adherence.

Monitoring

Monitor bone mineral density and assess fracture risk, and review tolerability of musculoskeletal and vasomotor effects.

Counselling the patient

  • Joint aches and hot flushes are common; discuss troublesome symptoms rather than stopping treatment.
  • Bone-protecting measures, including calcium, vitamin D and exercise, are important.
  • Take the tablet consistently and continue for the full prescribed course.

Evidence & guidelines

Aromatase inhibitors including exemestane are recommended by NICE within adjuvant endocrine therapy for postmenopausal hormone-receptor-positive breast cancer.

Reference: NICE TA112; SmPC; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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