1. Clinical Overview
Bicalutamide is a non-steroidal, orally active, pure antiandrogen used primarily in the treatment of advanced prostate cancer. It competitively inhibits androgen binding at the androgen receptor, blocking the action of androgens (like testosterone and dihydrotestosterone) that stimulate prostate cancer growth. In India, it is a cornerstone of combined androgen blockade (CAB) therapy when used with a GnRH analogue or as monotherapy in specific cases.
| Onset | Duration | Bioavailability |
|---|---|---|
| Absorption is rapid; however, clinical anti-androgenic effects (e.g., reduction in PSA) are typically observed within several weeks of initiating therapy. | Due to its long half-life, it provides sustained receptor blockade over 24 hours, supporting once-daily dosing. | Well absorbed from the GI tract. Absolute bioavailability is high but not precisely quantified in humans; it is estimated to be >90%. |
2. Mechanism of Action
Bicalutamide is a competitive antagonist at the androgen receptor. It binds to the cytosolic androgen receptor in target tissues (like the prostate), preventing the natural androgens (testosterone and DHT) from binding and activating the receptor. This inhibits androgen-stimulated cell proliferation and promotes apoptosis in androgen-sensitive prostate cancer cells.
3. Indications & Uses
- Treatment of advanced (metastatic) prostate cancer in combination with a Gonadotropin-Releasing Hormone (GnRH) agonist (e.g., Leuprolide, Goserelin) as part of Combined Androgen Blockade (CAB).
- Adjuvant treatment to radical prostatectomy or radiotherapy in high-risk localized prostate cancer (in combination with GnRH therapy).
4. Dosage & Administration
Adult Dosage: 50 mg once daily, taken orally at the same time each day, with or without food. When used for prostate cancer, it is started concurrently with or after the initiation of a GnRH agonist.
Administration: Tablet should be swallowed whole with a glass of water. Can be taken with or without food. If a dose is missed, it should be taken as soon as remembered unless it is almost time for the next dose. Do not double the dose.
5. Side Effects
Common side effects may include:
- Hot flushes (very common with CAB)
- Breast tenderness (gynecomastia) and/or breast pain
- Asthenia (weakness, fatigue)
- Constipation
- Nausea
- Peripheral edema
- Weight gain
- Decreased libido
- Impotence
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Warfarin and other Coumarin Anticoagulants | Bicalutamide may potentiate the anticoagulant effect, increasing INR and risk of bleeding. | Major |
| CYP3A4 Inducers (e.g., Rifampicin, Carbamazepine, Phenytoin, St. John's Wort) | May increase the metabolism of bicalutamide, reducing its plasma concentration and efficacy. | Moderate |
| CYP3A4 Inhibitors (e.g., Ketoconazole, Itraconazole, Clarithromycin, Ritonavir) | May decrease the metabolism of bicalutamide, potentially increasing its plasma concentration and risk of toxicity. | Moderate |
| Midazolam, Triazolam | Bicalutamide may inhibit CYP3A4, potentially increasing levels of these drugs. | Moderate |
7. Patient Counselling
- DO take the tablet at the same time every day, with or without food.
- DO report any signs of liver problems immediately: yellowing of skin/eyes (jaundice), dark urine, severe nausea, vomiting, abdominal pain, unusual fatigue.
- DO keep all scheduled appointments for blood tests (PSA, LFTs).
- DO inform all your doctors and dentists that you are taking bicalutamide, especially before any surgery or new prescription.
- DONT stop taking this medicine without consulting your oncologist.
- DONT take over-the-counter medicines, herbal supplements (like St. John's Wort), or start new prescriptions without checking with your doctor or pharmacist.
8. Toxicology & Storage
Overdose: Expected to be an extension of its pharmacological effects: severe gynecomastia, breast pain, hepatotoxicity signs (nausea, vomiting, abdominal pain, jaundice). No specific reports of acute overdose in humans.
Storage: Store at room temperature (15°C to 30°C). Protect from light and moisture. Keep in the original blister pack or container. Keep out of reach of children and pets. Do not use after the expiry date printed on the pack.