Pharmacology · Antiandrogens and androgen synthesis inhibitors

Flutamide !

An older antiandrogen tablet for prostate cancer, taken with a GnRH analogue. It can cause serious liver damage and turns the urine orange or green.

Updated 2026-11-01

Class: Antiandrogens and androgen synthesis inhibitors
Receptor: Androgen receptor (AR)
ATC code: L02BB01

Androgen receptor (AR)Flutamide

The figure shows hydroxyflutamide, the active metabolite of flutamide, in the ligand-binding domain of a human androgen receptor carrying the T877A mutation.

Target in 3D: Androgen receptor (AR). PDB structure 2AX6 (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

Flutamide is a non-steroidal androgen receptor antagonist. Its active metabolite, hydroxyflutamide, competes with testosterone and dihydrotestosterone for the receptor in prostate cancer cells and blocks androgen-driven growth. It is combined with a GnRH agonist.

Converted in the liver to hydroxyflutamide
Hydroxyflutamide binds the androgen receptor
Androgens cannot activate their genes
Prostate cancer growth slows

Pharmacokinetics

Absorption: Taken by mouth several times a day
Metabolism: In the liver, to the active metabolite hydroxyflutamide
Half-life: Short, about 5 hours, so it is taken several times a day

Indications

Prostate cancer, together with a GnRH (LHRH) agonist Prostate cancer →

Adverse effects

Common

Diarrhoea
Nausea and vomiting
Hot flushes
Breast enlargement and tenderness
Loss of libido
Blue-green or orange urine

Contraindications

Women, especially in pregnancy
Hypersensitivity to flutamide

Key interactions

Alcohol: Its use is discussed with the treating team because of the risk of liver injury.
Other prescription and non-prescription medicines and supplements: The team reviews them because doses may need changes or closer monitoring.

What is monitored

Liver tests before starting and regularly during treatment
PSA

Administration and safety

Oral capsule every 8 hours, at about the same times each day, with or without food.
Taken with a GnRH agonist, not alone.

Nursing care

Make sure liver tests are done before starting and at the scheduled intervals.
Teach to report nausea, vomiting, loss of appetite, tiredness, right upper abdominal pain, yellow skin or dark urine.
Explain that a blue-green or orange urine colour is expected and harmless.
Teach that the GnRH injections continue alongside.
Ask about smoking and inherited blood disorders such as G6PD deficiency or haemoglobin M disease.

Pregnancy and breastfeeding

Only for men; it can harm a fetus if taken during pregnancy.

Test yourself

Think of the answer, then tap the question to see it.

What is the active metabolite of flutamide?

Hydroxyflutamide, formed in the liver; it is the molecule that blocks the androgen receptor.

Which symptoms in a patient on flutamide suggest liver injury?

Nausea, vomiting, loss of appetite, tiredness, right upper abdominal pain, jaundice or dark urine.

Why has bicalutamide largely replaced flutamide?

Bicalutamide is taken once a day and is generally better tolerated; flutamide needs several doses a day and causes more diarrhoea and liver toxicity.

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Prostate cancer

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: Flutamide: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2018); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 73 (McGraw Hill, 2023); Crystal Structure Of The Androgen Receptor Ligand Binding Domain T877A Mutant In Complex With Hydroxyflutamide (RCSB Protein Data Bank, 2005).

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Representative model, for educational purposes only.