Flutamide is a nonsteroidal antiandrogen that was developed in the 1970s and introduced into clinical use in the 1980s for the treatment of prostate cancer. It works by blocking androgen receptors, thereby preventing testosterone and dihydrotestosterone from stimulating the growth of androgen-dependent prostate cancer cells. Flutamide is typically used in combination with other hormonal therapies, such as luteinizing hormone–releasing hormone (LHRH) analogs, as part of androgen deprivation therapy. Its clinical development was significant in advancing hormonal treatment strategies for prostate cancer, offering an oral option to suppress androgen action at the receptor level. Over time, its use has declined in many settings due to the availability of newer antiandrogens with improved safety profiles, but it remains an important historical and pharmacological example of early androgen receptor antagonism in oncology.
BRAND NAMES
Eulexin (most well-known original brand name)
Drogenil (used in some international markets)
Flutamid / Flutamide (generic brands) (widely available under different manufacturers globally).
MECHANISM OF ACTION
Flutamide is a nonsteroidal antiandrogen that works by competitively blocking androgen receptors in target tissues, particularly in the prostate. After oral administration, flutamide is rapidly metabolized in the liver to its active form, 2-hydroxyflutamide, which has a much higher affinity for the androgen receptor. This active metabolite binds to androgen receptors without activating them, thereby preventing endogenous androgens such as testosterone and dihydrotestosterone from exerting their biological effects.
PHARMACOKINETICS
Absorption:
Flutamide is rapidly absorbed after oral administration and undergoes extensive first-pass metabolism in the liver to its active metabolite, 2-hydroxyflutamide. Peak plasma concentrations of the active metabolite are typically reached within a few hours.
Distribution:
Flutamide and its active metabolite are moderately bound to plasma proteins. The drug is widely distributed in tissues, including those of the prostate, where it exerts its therapeutic effect. Its lipophilic nature allows adequate tissue penetration.
Metabolism:
Flutamide is extensively metabolized in the liver, primarily to its active metabolite 2-hydroxyflutamide, which is responsible for most of its antiandrogenic activity. Further metabolism involves oxidation and hydrolysis pathways, producing inactive metabolites.
Elimination:
Flutamide metabolites are excreted mainly via the kidneys in urine, with a smaller portion eliminated in feces. The elimination half-life of flutamide itself is short, but the active metabolite has a longer duration of action, supporting its therapeutic effect.
PHARMACODYNAMICS
Flutamide is a nonsteroidal antiandrogen that competitively inhibits androgen binding to androgen receptors in target tissues such as the prostate. Its active metabolite, 2-hydroxyflutamide, binds to androgen receptors without activating them, thereby blocking the effects of endogenous androgens like testosterone and dihydrotestosterone.
ADMINISTRATION
Flutamide is administered orally in tablet form and is usually given in divided doses throughout the day. It is commonly used as part of combination therapy for advanced prostate cancer, often alongside agents that suppress testosterone production.
DOSAGE AND STRENGTH
Flutamide is commonly available in 250 mg tablets. The usual adult dosage for prostate cancer is 250 mg taken three times daily (every 8 hours). Dosage may vary depending on treatment regimen, patient tolerance, and combination with other hormonal therapies.
DRUG INTERACTIONS
Flutamide may interact with drugs that are metabolized by the liver, particularly those involving hepatic enzyme systems, potentially altering their blood levels. Concurrent use with anticoagulants like warfarin may increase bleeding risk. Alcohol and other hepatotoxic drugs may increase the risk of liver toxicity when used with flutamide.
FOOD INTERACTIONS
Flutamide does not have significant clinically relevant food interactions. However, it is generally recommended to take it consistently with respect to meals to maintain stable drug absorption.
CONTRAINDICATIONS
Flutamide is contraindicated in patients with severe hepatic impairment or active liver disease due to its potential hepatotoxicity. It should also be avoided in individuals with known hypersensitivity to the drug or its components.
SIDE EFFECTS
Gynecomastia (breast enlargement in males)
Hot flashes
Diarrhea
Nausea and vomiting
Decreased libido
Fatigue
Elevated liver enzymes
Hepatotoxicity (rare but potentially serious)
Anemia (less common)
OVER DOSAGE
Flutamide overdose is rare but may lead to an intensification of its known adverse effects, particularly involving the gastrointestinal tract and liver. Early symptoms can include nausea, vomiting, diarrhea, abdominal discomfort, dizziness, and marked fatigue. In more severe cases, significant hepatotoxicity may occur, presenting as elevated liver enzymes, jaundice, acute hepatitis, and in rare instances, progression to liver failure.
TOXICITY
Flutamide toxicity is primarily associated with liver injury, which can range from mild elevation of liver enzymes to severe, potentially fatal hepatitis. Symptoms of overdose or toxicity may include severe gastrointestinal upset, jaundice, fatigue, and signs of liver failure. Management involves immediate discontinuation of the drug, supportive care, and monitoring of liver function, as there is no specific antidote.
