Fulvestrant
SERDs
Selective oestrogen receptor degraders (SERDs)High alert
An error with this medicine can cause serious harm: double checks and protocols are used.
Pure antioestrogen given into the buttock muscle. It blocks the oestrogen receptor and makes the cell destroy it; for hormone-receptor-positive breast cancer.
Quick facts
- Group
- Selective oestrogen receptor degraders (SERDs)
- Target
- Oestrogen receptor alpha (ERα), ligand-binding domain
- Used for
- Hormone-receptor-positive advanced · The same cancer
- Key effects
- Pain at the injection site · Hot flushes · Nausea
- Monitor
- Pain · Liver tests and signs of liver injury
- ATC
- L02BA03
No doses: the clinician sets them by the current guideline.
Mechanism of action
No public structure shows fulvestrant in the human oestrogen receptor. The figure shows elacestrant, another SERD, in the same ligand-binding pocket of human ERα.
Fulvestrant is a steroidal antioestrogen that binds the oestrogen receptor competitively and with high affinity. It blocks oestrogen binding, hinders receptor dimerisation and changes the receptor's shape so that the cell tags it for destruction in the proteasome. With fewer receptors left, oestrogen-dependent genes are no longer switched on. Unlike tamoxifen, it has no oestrogen-like (agonist) effect in any tissue, and it still works in tamoxifen-resistant tumours.
- Fulvestrant binds the oestrogen receptor in place of oestrogen
- The changed receptor is degraded in the proteasome
- Oestrogen-driven genes stay off: the tumour stops growing
Indications
- Hormone-receptor-positive advanced or metastatic breast cancer in postmenopausal women, alone (first line or after other endocrine therapy). Breast cancer →
- The same cancer, HER2-negative, in combination with a CDK4/6 inhibitor (palbociclib, ribociclib or abemaciclib). Breast cancer →
Adverse effects
Common
- Pain at the injection site
- Hot flushes
- Nausea, vomiting, constipation, loss of appetite
- Bone, joint, back and limb pain
- Headache, tiredness, weakness, cough, breathlessness
Contraindications
- Allergy to fulvestrant or its ingredients
Key interactions
- Anticoagulants (e.g., warfarin), thrombocytopenia or bleeding disorders
- Not a drug interaction but a risk: bleeding at the intramuscular site; it is used with caution.
- Estradiol immunoassays
- Fulvestrant resembles estradiol and can give falsely high estradiol results.
What is monitored
- Pain, numbness or weakness in the lower back or legs after injections
- Liver tests and signs of liver injury
- Platelets and anticoagulant use before injecting
- Pregnancy test before starting in women who could be pregnant
Administration and safety
- Intramuscular only, given slowly into the gluteal muscle as two injections, one in each buttock.
- Care is taken at the dorsogluteal site because the sciatic nerve lies beneath it.
- Given by a doctor or nurse in a clinic; it comes in prefilled syringes.
Pregnancy and breastfeeding
Can cause fetal harm; pregnancy and breastfeeding are avoided during treatment and for a year after the last dose, and it may reduce fertility.
Nursing care
- Ask about anticoagulants and bleeding problems before each injection.
- Teach the patient to report leg pain, numbness or weakness after the injections.
- Tell the laboratory before an estradiol test.
- Teach to report yellow skin, upper-right abdominal pain or painful urination.
Pharmacokinetics
- Absorption
- Slow intramuscular injection into the buttocks; it is released slowly from the muscle.
- Distribution
- Wide, mostly outside the blood vessels; about 99% bound to plasma lipoproteins.
- Metabolism
- Like natural steroids: oxidation, hydroxylation and conjugation; CYP3A4 is the only CYP involved, with an unclear share.
- Elimination
- Mostly in the faeces through the bile; almost none in the urine. Exposure rises in moderate liver impairment, so the dose is adjusted.
- Half-life
- Very long after intramuscular injection, about 40 days.
Test yourself
Think of the answer, then tap the question to see it.
How does fulvestrant differ from tamoxifen at the oestrogen receptor?
Fulvestrant is a pure antagonist that causes the receptor to be degraded; tamoxifen is a modulator with agonist effects in some tissues and stabilises the receptor.
Which nerve must be avoided when fulvestrant is injected?
The sciatic nerve, which lies beneath the dorsogluteal site.
Why can a patient on fulvestrant show a falsely high estradiol level?
Fulvestrant has a steroid structure like estradiol and cross-reacts in immunoassays.
With which drug group is fulvestrant combined in HER2-negative advanced breast cancer?
CDK4/6 inhibitors (palbociclib, ribociclib, abemaciclib).
Connections
← Back to the class: Selective oestrogen receptor degraders (SERDs)
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - FULVESTRANT injection, solution (DailyMed (U.S. National Library of Medicine), 2026); Fulvestrant Injection: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2024); Estrogen Receptor Alpha Ligand Binding Domain in Complex with RAD1901 (RCSB Protein Data Bank, 2022).
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Representative model, for educational purposes only.