Pharmacology of Bicalutamide (Casodex) ; Pharmacokinetics, Mechanism of Action, Uses, Effects

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Bicalutamide (brand name: Casodex) is a non-steroidal anti-androgen (NSAA) medication primarily used in the treatment of advanced prostate cancer. It is effective as part of androgen deprivation therapy (ADT) due to its ability to block the action of male sex hormones (androgens). Here's an overview of its pharmacology:

Mechanism of Action
Androgen Receptor Antagonist:

Bicalutamide binds competitively to androgen receptors, preventing androgens like testosterone and dihydrotestosterone (DHT) from activating the receptors.

This inhibition blocks androgen-mediated growth signals in androgen-dependent prostate cancer cells, leading to their apoptosis and suppression of tumor growth.

It is often combined with LHRH agonists or antagonists or surgical castration to achieve maximum androgen blockade.

Pharmacokinetics
Administration:

Administered orally as a single daily dose, usually 50 mg.

Absorption:

Well-absorbed after oral administration, with peak plasma concentrations reached within 1–2 hours.

Distribution:

Highly protein-bound and widely distributed in body tissues.

Metabolism:

Extensively metabolized in the liver by cytochrome P450 enzymes, primarily CYP3A4.

Excretion:

Excreted primarily in feces, with a small fraction eliminated in the urine.

Half-Life:

The elimination half-life of bicalutamide is approximately 6 days, allowing for once-daily dosing.

Indications
Prostate Cancer:

Used in combination with LHRH agonists (e.g., leuprolide) or after surgical castration to treat advanced or metastatic prostate cancer.

Off-Label Uses (less common):

Management of hirsutism or androgen-related disorders in females.

Adverse Effects
Common Side Effects:

Hot flashes.

Gynecomastia (breast enlargement) and breast tenderness.

Decreased libido and erectile dysfunction.

Nausea and diarrhea.

Hepatotoxicity:

Rare but can cause elevated liver enzymes or hepatocellular damage.

Liver function monitoring is recommended during therapy.

Other Effects:

Fatigue and weakness.

Anemia.

Rash or pruritus.

Contraindications and Precautions
Contraindications:

Females, particularly during pregnancy or lactation, as it can cause harm to the fetus.

Severe hepatic impairment.

Precautions:

Regular monitoring of liver function and complete blood counts is advised.

Use with caution in patients with pre-existing cardiovascular disease due to potential risks of fluid retention or anemia.

Drug Interactions
CYP3A4 Inhibitors:

Drugs like ketoconazole may increase bicalutamide plasma levels, increasing the risk of toxicity.

Anticoagulants (e.g., Warfarin):

Bicalutamide may enhance the effects of warfarin, increasing the risk of bleeding.

Other Hepatotoxic Drugs:

Combining with drugs that have hepatotoxic potential may exacerbate liver toxicity.

Clinical Considerations
Bicalutamide is primarily used for maximum androgen blockade (MAB) in prostate cancer treatment, aiming to enhance the efficacy of LHRH analogs.

Its favorable side effect profile compared to older anti-androgens (e.g., flutamide) makes it a preferred choice in many cases.

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