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) |
| 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 | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for FLUTEX (FLUTEX).
| Breastfeeding | No human studies; M/P ratio unknown. Use caution due to potential for adverse effects in nursing infants (e.g., sedation, poor feeding). Weigh benefits against risks. |
| 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 |
■ 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 |
Severe hepatic impairment; hypersensitivity to flutamide or any component of the formulation; pregnancy (teratogenic effects).
| 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). |
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| 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. |