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Selective oestrogen receptor degrader (SERD) Pregnancy: Contraindicated in pregnancy and during breast-feeding. Patients of childbearing potential should use effective contraception during treatment and for 2 years after the last dose. Animal studies have shown reproductive toxicity including an increased incidence of foetal abnormalities and deaths; fulvestrant crosses the placenta in rat and rabbit.

Fulvestrant

Brand names: Faslodex

Fulvestrant is a selective oestrogen receptor degrader used to treat hormone-receptor-positive, locally advanced or metastatic 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: 500 mg (given as two 250 mg / 5 ml injections)
Route: Intramuscular — two consecutive 5 ml injections by slow intramuscular injection (1-2 minutes per injection), one in each buttock (gluteal area)
Frequency: Once monthly (at intervals of one month), with an additional 500 mg dose given two weeks after the initial dose
UK SPC (Faslodex 250 mg solution for injection) §4.2. Applies to adult females including the elderly. Caution should be taken if injecting at the dorsogluteal site due to the proximity of the underlying sciatic nerve. COMBINATION THERAPY: when used with palbociclib or with capivasertib, also refer to the SPC of that agent; pre/perimenopausal women (and, with capivasertib, men) should be treated with LHRH agonists according to local clinical practice / current clinical practice standards. HEPATIC IMPAIRMENT: no dose adjustment recommended in mild to moderate hepatic impairment, but exposure may be increased so use with caution; no data in severe hepatic impairment (contraindicated). PAEDIATRIC: safety and efficacy in children from birth to 18 years have not been established and no recommendation on a posology can be made. US labelling (openFDA, cross-check only) additionally recommends a reduced dose of 250 mg (one 5 mL injection) on Days 1, 15, 29 and once monthly thereafter for moderate hepatic impairment (Child-Pugh class B) — this hepatic dose reduction is NOT in the UK SPC.

Dose adjustments

Renal

No dose adjustments recommended for mild to moderate renal impairment (creatinine clearance >= 30 ml/min). Safety and efficacy have not been evaluated in severe renal impairment (creatinine clearance < 30 ml/min) — caution is recommended.

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
  • Pregnancy and lactation
  • Severe hepatic impairment

Side effects

  • Injection site reactions (very common)
  • Nausea (very common)
  • Asthenia (very common)
  • Elevated hepatic enzymes — ALT, AST, ALP (very common)
  • Hot flushes (very common)
  • Joint and musculoskeletal pain, rash, hypersensitivity reactions (very common)

Interactions

  • No clinically relevant interaction with CYP3A4 inhibitors or inducers — a study with midazolam showed fulvestrant does not inhibit CYP3A4, and studies with rifampicin (inducer) and ketoconazole (inhibitor) showed no clinically relevant change in fulvestrant clearance; dose adjustment is not necessary (§4.5)
  • Anticoagulants / bleeding diatheses / thrombocytopenia — use with caution because of the intramuscular route (§4.4)
  • May interfere with antibody-based estradiol immunoassays, giving falsely increased estradiol levels (§4.4)

Clinical monograph

How it works

It binds the oestrogen receptor and promotes its degradation, downregulating receptor levels and abolishing oestrogen-driven tumour signalling.

Prescribing in practice

  • Administer by slow intramuscular injection into the buttock and avoid in significant hepatic impairment without specialist assessment.
  • Caution and additional monitoring are needed in patients on anticoagulants because of the intramuscular route and bleeding risk.
  • It is increasingly given in combination with a CDK4/6 inhibitor; check compatibility and interactions against current prescribing references.

Monitoring

Periodically assess liver function and disease response, and watch injection sites for local reactions.

Counselling the patient

  • Injection-site discomfort, hot flushes, joint pain and fatigue are common.
  • Report any new or worsening bruising or bleeding, particularly if you take blood thinners.
  • Attend appointments for your injections on schedule as directed by your oncology team.

Evidence & guidelines

Fulvestrant's role in advanced hormone-receptor-positive breast cancer is supported by trials such as FALCON and is reflected in NICE guidance.

Reference: NICE TA503/TA836; 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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