Flutamide

Introduction Overview

Generic Name

flutamide

Brand Name

Eulexin

Dosage Form

Oral capsule

Drug Class

Antiandrogens; Hormones / antineoplastics

Pharmacokinetics

Absorption: Flutamide is well absorbed via the gastrointestinal tract after oral administration, with peak plasma concentrations typically reached within 2 hours. Absorption is efficient and rapid; however, its bioavailability can be affected by first-pass metabolism in the liver. Food intake does not significantly alter the rate or extent of absorption but might delay the time to peak levels. Clinical considerations include maintaining consistent administration times to avoid fluctuation in plasma levels that could affect therapeutic outcomes.

Distribution: After absorption, flutamide is extensively distributed throughout the body, binding moderately to plasma proteins (~94-95%). It crosses biological membranes effectively, reaching target tissues including the prostate and metastatic sites. Volume of distribution is moderate, indicating distribution beyond the plasma compartment. The drug and its active metabolites accumulate in androgen target tissues, facilitating its antiandrogenic effect. Tissue penetration is an important consideration for its efficacy in controlling prostate cancer.

Metabolism: Flutamide undergoes rapid and extensive hepatic metabolism primarily by cytochrome P450 enzymes, predominantly CYP1A2. The main active metabolite, 2-hydroxyflutamide, is pharmacologically more potent than the parent compound and responsible for most of its antiandrogenic effects. Subsequent metabolism involves conjugation pathways leading to inactive metabolites. Metabolic clearance is an important factor influencing plasma levels and therapeutic effects; thus, hepatic impairment can significantly alter the drug’s pharmacokinetics and increase toxicity risk.

Elimination: The elimination of flutamide and its metabolites is primarily via renal excretion, with a smaller fraction excreted in feces. The elimination half-life of flutamide is approximately 6-8 hours, whereas its active metabolite has a longer half-life of about 6-10 hours, contributing to sustained antiandrogenic activity. Renal clearance and hepatic metabolism efficiency influence elimination kinetics. In patients with severe hepatic impairment, elimination may be reduced, raising the possibility of accumulation and necessitating caution or dose adjustment.

Dosage Forms

Available Dosage Forms:
Eulexin is available as oral capsules, specifically formulated for administration in prostate cancer therapy.

Dosages for Adults and Adolescents:
The standard adult dose for metastatic prostate cancer is two 125 mg capsules taken orally three times a day (every eight hours), totaling 750 mg daily. This dosing regimen ensures consistent plasma concentration of the active metabolite for effective androgen receptor antagonism.

Specific Patient Populations:
Pediatric use has not been established, and safety and efficacy data are lacking in this group. No specific geriatric dosing adjustments have been standardized, but consideration of hepatic function is important due to metabolism via the liver. In patients with severe hepatic impairment, flutamide is contraindicated due to risk of hepatotoxicity. Close monitoring of liver function tests is advised for all patients initiating therapy.

Capsule Strength:
- Oral capsule: 125 mg per capsule

Clinical guidelines emphasize the importance of strict adherence to dosing intervals to maintain effective plasma levels and reduce the risk of side effects. Dose adjustments or discontinuation should be considered in the presence of elevated liver enzymes or hepatic adverse effects.

Mechanism Of Action

Flutamide functions as a nonsteroidal antiandrogen by competitively inhibiting the androgen receptor (AR) on target cells, particularly in prostate tissue. It binds to the cytoplasmic androgen receptor, preventing endogenous androgens such as testosterone and dihydrotestosterone (DHT) from binding and activating the receptor. This blockade inhibits androgen-driven gene expression that stimulates prostate cancer cell proliferation and survival.

At the cellular level, flutamide's active metabolite, 2-hydroxyflutamide, exhibits higher affinity for the androgen receptor than the parent compound, enhancing its antagonistic potency. By preventing receptor activation, flutamide disrupts androgen receptor signaling pathways that regulate transcription of genes involved in cell cycle progression and anti-apoptotic mechanisms. This results in reduced tumor growth and progression.

Biochemically, flutamide does not inhibit androgen production but exerts its effects downstream by blocking androgen receptor-mediated transcriptional regulation. Compared with other antiandrogens such as bicalutamide, flutamide has a shorter half-life and distinct metabolic profile but similarly inhibits AR activity, making it effective as part of combined androgen blockade regimens.

Clinical studies have demonstrated that adjunctive flutamide therapy with luteinizing hormone-releasing hormone (LHRH) agonists improves outcomes in metastatic prostate cancer by both reducing testosterone production and blocking residual androgen receptor activation. However, flutamide’s use is tempered by hepatotoxicity risk, necessitating monitoring and balancing therapeutic benefits with safety.

Pharmacological Actions

Competitive androgen receptor antagonist inhibiting the binding of endogenous androgens.
Blocks androgen-mediated stimulation of prostate cancer cell growth.
Reduces androgen-induced gene expression critical for tumor cell survival.
Exerts antiandrogenic effects primarily through its active metabolite, 2-hydroxyflutamide.
Does not inhibit androgen synthesis but antagonizes androgen receptor signaling.
Utilized as part of combination hormonal therapy in advanced prostate cancer.
Modulates hormonal feedback loops in the hypothalamic-pituitary-gonadal axis when combined with LHRH agonists.
Embodies a nonsteroidal chemical structure distinct from steroidal antiandrogens.
Potential to induce gynecomastia due to hormonal imbalance.
Metabolized hepatically with potential for liver enzyme elevation and hepatotoxicity.

Therapeutic Or Clinical Uses

Treatment of metastatic prostate cancer in combination with LHRH agonists.
Management of androgen-dependent prostate carcinoma by blocking androgen receptor.
Adjunct hormonal therapy to surgical or medical castration.
Investigated for potential use in other androgen-dependent conditions (off-label).
Used to reduce tumor progression in patients with advanced or recurrent prostate cancer.
Helpful in controlling symptoms related to prostate cancer progression.
May be utilized in clinical settings where antiandrogen therapy is indicated.
Research ongoing for combination therapies enhancing antiandrogen effects.

Side Or Adverse Effects

Elevated liver enzymes and hepatotoxicity including liver failure and hepatic encephalopathy.
Gynecomastia and breast tenderness in males.
Gastrointestinal disturbances such as diarrhea, indigestion, and stomach discomfort.
Flushing and redness of the face and upper body.
Decreased libido, erectile dysfunction, and sexual dysfunction.
Fatigue, weakness, and unusual tiredness.
Black, tarry stools and unusual bleeding or bruising due to potential bleeding risk.
Urinary symptoms including painful urination and frequent urge to urinate.
Neurological symptoms like dizziness, headache, and nervousness.
Rare but serious: jaundice, dark urine, clay-colored stools indicating cholestasis.
Skin reactions including rash, itching, blistering, or peeling.
Respiratory symptoms such as cough or difficulty breathing.
Cardiac symptoms including palpitations, chest pain, and abnormal heartbeat.
Rare reports of severe allergic reactions or swelling.
Symptoms of overdose may include tremors, unsteadiness, and weight loss.

Precautions

Monitor liver function tests prior to initiation and monthly for first 4 months of therapy.
Discontinue therapy if ALT exceeds twice the upper limit of normal or if jaundice occurs.
Avoid use in patients with severe liver disease or hepatic function impairment.
Use cautiously in patients with glucose-6-phosphate dehydrogenase deficiency or hemoglobin M disease due to aniline content.
Inform healthcare providers about all concurrent medications to avoid interactions.
Do not abruptly discontinue antiandrogen therapy without medical supervision.
Potential increased risk of bleeding or bruising; use cautiously in bleeding disorders.
Advise patients about potential for gynecomastia and breast tenderness.
Use with caution in patients with cardiovascular disease and monitor for cardiac symptoms.
Evaluate benefit-risk carefully in elderly patients due to limited data.
Weight monitoring recommended due to potential weight loss side effect.
Avoid alcohol or substances that may increase hepatotoxicity risk during treatment.
Patient education on recognizing signs of liver injury is essential.
Consider drug interactions with methotrexate, levoketoconazole, and pexidartinib.
Regular clinical monitoring advised to assess therapeutic effect and adverse reactions.

Warnings

Risk of severe and potentially fatal hepatotoxicity, especially within the first 3 months of treatment.
Immediate discontinuation required if signs of liver injury such as jaundice or elevated liver enzymes develop.
Not recommended for use in patients with pre-existing severe liver disease.
May cause significant hormonal side effects including gynecomastia.
Use with caution in patients with blood disorders or G6PD deficiency due to risk of adverse effects.
Potential for serious drug interactions that may alter drug levels and toxicity.
Pregnancy category not established; avoid use in women who are or may become pregnant.
Not studied adequately in pediatrics or geriatrics; use under strict medical supervision.
Alcohol consumption may exacerbate hepatotoxic risk and should be avoided.
Increased risk of bleeding and bruising necessitates caution with anticoagulant use.
Monitor cardiac function for patients manifesting arrhythmias or other cardiac symptoms.
Patients should be advised to report any symptoms of liver toxicity or allergic reactions immediately.
Use in combination with other antiandrogens or hormonal therapies requires careful monitoring.
Do not use as monotherapy in prostate cancer; part of combined androgen blockade regimen.
Adherence to dosing schedule is critical to avoid suboptimal therapeutic effects or toxicity.

Contraindication

Known hypersensitivity to flutamide or any component of the formulation.
Severe hepatic impairment or active liver disease.
Patients with a history of serious hypersensitivity reactions to antiandrogens.
Use in pediatric patients due to lack of established safety and efficacy data.
Concurrent use with drugs having major interactions such as levoketoconazole, methotrexate, and pexidartinib without physician oversight.
Patients with blood disorders like hemoglobin M disease or G6PD deficiency requiring caution; contraindicated if severe.
Pregnant or breastfeeding women due to unknown risk to infants.
Patients with known bleeding disorders without medical supervision.
Patients unable to adhere to monitoring requirements for liver function.
Contraindicated as monotherapy for prostate cancer; not indicated for non-androgen-dependent tumors.
Use avoided in patients with severe cardiovascular complications without close supervision.
Patients with known aniline sensitivity due to risk of adverse hematologic reactions.
Patients with elevated liver enzymes (>2 times upper limit of normal) prior to therapy.
Known drug-drug interactions where risk outweighs benefit according to clinical assessment.
Patients with serious skin reactions or history of skin hypersensitivity disorders to flutamide.

Drug Interactions

Levoketoconazole may increase risk of hepatotoxicity when combined with flutamide.
Methotrexate interaction potentially increases toxicity; use with caution and monitor closely.
Pexidartinib may have unestablished interactions; coadministration requires careful consideration.
Co-administration with other hepatotoxic drugs may exacerbate liver injury risk.
Drugs that induce cytochrome P450 enzymes (CYP1A2) may decrease flutamide levels reducing effectiveness.
Inhibitors of CYP1A2 may increase flutamide and metabolite plasma concentrations, increasing toxicity risk.
Anticoagulants or antiplatelet agents may have enhanced bleeding risk when used with flutamide.
Alcohol consumption increases potential for hepatotoxicity and should be avoided.
Combination with other hormonal therapies requires dose adjustment and monitoring for additive effects.
Concurrent use with agents affecting androgen metabolism or receptor activity may alter therapeutic outcomes.
Avoid simultaneous use with drugs causing QT prolongation without cardiac monitoring.
Interactions with drugs affecting renal clearance can impact metabolite elimination.
Nonsteroidal anti-inflammatory drugs (NSAIDs) may increase risk of bleeding when used concomitantly.
Monitor for increased adverse effects when used with medications known to cause gastrointestinal irritation.
Herbal supplements affecting hepatic enzymes may alter flutamide metabolism and efficacy.

Preparations Of The Drug

Oral capsules containing 125 mg of flutamide as active ingredient.
Formulated for oral administration with excipients ensuring stability and bioavailability.
Available only via prescription due to potential severe adverse effects and need for monitoring.
Manufactured under Good Manufacturing Practices ensuring quality and consistency.
Packaging includes patient information leaflets detailing dosing and safety information.
Storage instructions specify room temperature, protection from moisture, heat, and light.
Discontinued brand name 'Eulexin' in the U.S., but generic flutamide formulations may be available.
Capsule shell designed to mask taste and facilitate ease of swallowing.
Production batch tested for purity, potency, and absence of contaminants.
Prepared for use in combination with LHRH agonists for maximal therapeutic efficacy.
Manufactured in unit doses to prevent dosing errors and enhance patient compliance.
Includes labeling with warnings about hepatotoxicity, contraindications, and drug interactions.
Limited availability may require sourcing through specialty pharmacies.
Formulation stability supported for prescribed expiration period when stored properly.
No topical or injectable formulations currently available; oral capsules are the sole preparation.