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Aromatase inhibitor (non-steroidal) Pregnancy: Contraindicated — embryotoxic. Confirm postmenopausal status before initiation. Effective contraception for any premenopausal user (off-label).

Anastrozole

Brand names: Arimidex

Adult dose

Dose: 1 mg OD
Route: Oral
Frequency: Once daily
Max: 1 mg/day
Used in postmenopausal women only. Adjuvant endocrine therapy for ER+ breast cancer; also licensed for advanced disease.

Dose adjustments

Renal

No adjustment required.

Hepatic

Mild–moderate: no adjustment. Severe: not studied — avoid.

Clinical pearls

  • First-line adjuvant endocrine therapy for ER+ breast cancer in postmenopausal women — superior DFS vs tamoxifen (ATAC trial Lancet 2002).
  • Standard duration 5 years adjuvant; extended therapy to 10 years (with letrozole) reduces contralateral recurrence (MA.17R).
  • Bisphosphonate (zoledronate) co-prescription if T-score ≤−2.0 or one fragility fracture.
  • Arthralgia is the leading cause of discontinuation — switching between AIs (anastrozole ↔ letrozole ↔ exemestane) helps in ~50% of patients.
  • For chemoprevention in high-risk postmenopausal women: 5-year course (IBIS-II — risk reduction ~50%).

Contraindications

  • Premenopausal women
  • Pregnancy and breastfeeding
  • Severe hepatic impairment
  • Hypersensitivity to anastrozole

Side effects

  • Hot flushes (very common)
  • Arthralgia, myalgia (often dose-limiting — try evening dose, exercise, swap to letrozole/exemestane)
  • Osteoporosis / fracture risk (DEXA at baseline and 2-yearly)
  • Vaginal dryness, dyspareunia
  • Mood changes, fatigue
  • Hyperlipidaemia, hypercholesterolaemia
  • Increased risk of ischaemic heart disease vs tamoxifen (ATAC follow-up)
  • Carpal tunnel syndrome
  • Alopecia (mild)

Interactions

  • Tamoxifen: do not co-prescribe — tamoxifen ↓ anastrozole concentration
  • Oestrogens (HRT, vaginal oestrogens): antagonise efficacy — avoid systemic; topical oestriol may be acceptable after discussion with oncologist for severe vaginal atrophy
  • GnRH analogues (in premenopausal): used to combine with AI in ovarian-suppression regimens — specialist

Monitoring

  • DEXA scan at baseline and every 2 years
  • Lipid profile annually
  • LFTs annually
  • Bone health — calcium 1g/day + vitamin D 800–1000 units/day

Reference: BNF 90; SmPC Arimidex; ATAC trial Lancet 2002;359:2131-39; MA.17R NEJM 2016; IBIS-II Lancet 2014;383:1041-48; NICE NG101 (Early breast cancer); ESMO Breast Cancer Guidelines 2024. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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