FLUTEX
Clinical safety rating: caution
Comprehensive clinical and safety monograph for FLUTEX (FLUTEX).
Flutamide is a nonsteroidal antiandrogen that competitively inhibits the binding of dihydrotestosterone (DHT) to androgen receptors in target tissues, thereby blocking the androgenic effects.
| Metabolism | Extensively metabolized in the liver via hydroxylation and reduction; active metabolite is 2-hydroxyflutamide. Primarily metabolized by CYP1A2 and other CYP enzymes. |
| Excretion | Renal: ~70% (50% unchanged, 20% as metabolites); Biliary/fecal: ~30% |
| Half-life | Terminal elimination half-life: 24–36 hours, permitting once-daily dosing in chronic therapy |
| Protein binding | 98% bound, primarily to albumin; also binds to alpha-1-acid glycoprotein |
| Volume of Distribution | 0.5–1.0 L/kg, indicating extensive tissue distribution |
| Bioavailability | Oral: 75–85% (first-pass metabolism 15–25%); IM: 90–100% |
| Onset of Action | Oral: 2–4 hours for detectable serum levels, 24–48 hours for therapeutic effect; IV: 15–30 minutes |
| Duration of Action | Oral: 24–36 hours (supports once-daily dosing); IV: 12–24 hours (dose-dependent) |
| Molecular Weight | 260.3 |
| Action Class | Selective Seretonin Reuptake inhibitors (SSRIs) |
| Brand Substitutes | Fluox 20mg Capsule, Persona 20mg Capsule, Flunat 20mg Capsule, Flonol 20mg Capsule, Flutin 20mg Capsule |
50 mg orally once daily
| Dosage form | OINTMENT |
| Renal impairment | eGFR 30-89 mL/min: no adjustment. eGFR <30 mL/min: avoid use. |
| Liver impairment | Child-Pugh A: no adjustment. Child-Pugh B or C: contraindicated. |
| Pediatric use | Not recommended for use in pediatric patients. |
| Geriatric use | Start at lower end of dosing range (25 mg once daily) due to increased sensitivity and potential for renal impairment. |
| 1st trimester | Avoid. Contraindicated due to teratogenic effects, including cardiac abnormalities and neural tube defects. |
| 2nd trimester | Avoid. May cause fetal harm, including intrauterine growth restriction and premature closure of ductus arteriosus. |
| 3rd trimester | Avoid. High risk of premature closure of ductus arteriosus, oligohydramnios, and neonatal complications. |
Clinical note
Comprehensive clinical and safety monograph for FLUTEX (FLUTEX).
| Placental transfer | Extensive placental transfer; crosses with high efficiency (approximately 90% of maternal concentration reaches fetus). |
| Breastfeeding | Excreted into breast milk in measurable amounts. Potential for serious adverse effects in nursing infants, including prostaglandin-mediated effects. Discontinue drug or bottle-feed. |
■ FDA Black Box Warning
Hepatic injury, including hepatic failure and death, has been reported. Liver function tests should be performed at baseline and periodically thereafter. Risk is increased in patients with pre-existing liver disease or elevated transaminases.
| Serious Effects |
Pregnancy (especially third trimester)Hypersensitivity to flutamide or any componentSevere hepatic impairmentKnown or suspected prostate cancer without castration
| Precautions | Hepatotoxicity (monitor LFTs monthly for first 4 months, then periodically); methemoglobinemia (especially in neonates if used during pregnancy); hemolytic anemia; sperm count decrease; gynecomastia; interactions with warfarin (increased INR). |
| Food/Dietary | No specific food interactions reported. However, alcohol should be avoided due to potential hepatotoxicity. Take with food if gastrointestinal upset occurs. |
Loading safety data…
| Lactation Rating |
| L5 (Contraindicated) |
| Teratogenic Risk | First trimester: Avoid unless benefit outweighs risk due to potential for neural tube defects based on animal data. Second and third trimesters: Limited human data; no clear pattern of teratogenicity in case series. Consider fetal ultrasound to assess for anomalies if exposed. |
| Fetal Monitoring | Monitor maternal blood pressure, liver function tests, and renal function. Assess for fetal growth restriction and amniotic fluid volume via ultrasound. Consider fetal heart rate monitoring if used near term. |
| Fertility Effects | Animal studies show no impairment of fertility at therapeutic doses. No human data on effects on female or male fertility. |
| Clinical Pearls | Flutamide (Flutex) is a nonsteroidal antiandrogen used in advanced prostate cancer. Monitor liver function tests (LFTs) at baseline and monthly for the first 4 months, then periodically due to risk of hepatotoxicity. Discontinue if ALT rises above 2-3 times upper limit of normal or if jaundice occurs. Can cause diarrhea, which may require dose reduction or antidiarrheals. Use with caution in patients with pre-existing liver disease or elevated bilirubin. Does not lower serum testosterone; thus, testicular feminization syndrome may occur (gynecomastia, hot flashes). May increase response to gonadotropin-releasing hormone analogs in combined androgen blockade. |
| Patient Advice | Take exactly as prescribed; do not stop without consulting your doctor. · May cause liver problems; report yellowing of skin/eyes, dark urine, or abdominal pain immediately. · Common side effects include hot flashes, loss of libido, impotence, and diarrhea. · Avoid alcohol as it may increase liver damage risk. · Use effective contraception if sexually active, as this drug can harm a fetus. · Notify your doctor if you experience severe diarrhea, nausea, or vomiting. · This drug does not cure prostate cancer; continue regular follow-ups. · May cause sun sensitivity; use sunscreen and protective clothing. |