Class: Nonsteroidal antiandrogen (NSAA)
Mechanism of Action:
Blocks androgen receptors by competitively inhibiting testosterone and dihydrotestosterone (DHT) binding in prostate cancer cells. Used in combination with ADT to achieve maximal androgen blockade.
Indications
- Metastatic prostate cancer (usually combined with orchiectomy or LHRH therapy)
- Flare prevention when initiating LHRH agonists (less common than bicalutamide)
Adult Dose
- Loading: 300 mg daily PO divided in 2–3 doses for first 30 days
- Maintenance: 150 mg daily PO thereafter (can be once daily)
- Absorption: Well absorbed orally
- Metabolism: Hepatic
- Half-life: ~56 hours (long) → allows once-daily dosing after loading phase
- Excretion: Urine and feces
Toxicities / Adverse Effects
- Visual disturbances: Delayed adaptation to darkness; patients may have trouble driving at night initially.
- Pulmonary toxicity: Interstitial pneumonitis, cough, dyspnea (rare but serious).
- Hepatotoxicity (monitor LFTs).
- Gynecomastia, breast tenderness, hot flashes.
- Alcohol intolerance (flushing, nausea, vomiting with alcohol ingestion).
Monitoring
- Baseline and periodic liver function tests (LFTs).
- Monitor for pulmonary symptoms, especially cough or shortness of breath.
- Advise patients to avoid or limit alcohol intake.
- Monitor disease progression (PSA, imaging).
Clinical Pearls
- Long half-life permits once-daily maintenance dosing after loading.
- Visual and pulmonary toxicities are unique compared to other NSAAs; patient counseling is essential.
- Alcohol intolerance can affect patient quality of life; discuss upfront.
- Less commonly used now due to side effect profile and availability of better-tolerated agents like bicalutamide.