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Non-steroidal aromatase inhibitor

Letrozole

Brand names: Femara

Letrozole is a non-steroidal aromatase inhibitor used chiefly in the treatment of hormone receptor-positive breast cancer in postmenopausal women, and in some fertility settings for ovulation induction.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

Clinical monograph

How it works

It reversibly inhibits the aromatase enzyme, blocking peripheral conversion of androgens to oestrogens and thereby lowering circulating oestrogen in postmenopausal women.

Prescribing in practice

  • Oestrogen depletion accelerates bone loss and increases fracture risk, so bone health should be assessed and managed during treatment.
  • Arthralgia, hot flushes and fatigue are common and may affect adherence.
  • It is contraindicated in pregnancy and is ineffective as adjuvant breast cancer therapy in women with intact premenopausal ovarian function.

Monitoring

Monitor bone mineral density and lipid profile, alongside clinical assessment for musculoskeletal symptoms, during treatment.

Counselling the patient

  • Report new or worsening bone, joint or muscle pain.
  • Maintain adequate calcium, vitamin D and weight-bearing activity to protect your bones.
  • Hot flushes are common; discuss persistent or troublesome symptoms with your team.

Evidence & guidelines

Aromatase inhibitors including letrozole are established adjuvant therapy in postmenopausal hormone receptor-positive breast cancer, supported by the BIG 1-98 trial.

Reference: NICE TA112/NG3; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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