FLUOXYMESTERONE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for FLUOXYMESTERONE (FLUOXYMESTERONE).
Synthetic androgen receptor agonist; binds to androgen receptors, modulating gene expression and promoting protein synthesis, muscle growth, and secondary sexual characteristic development.
| Metabolism | Primarily hepatic metabolism via reduction and conjugation; excreted in urine. |
| Excretion | Renal: 90% as glucuronide and sulfate conjugates; fecal: 10% |
| Half-life | Terminal elimination half-life: 9.2 hours; clinical context: supports once-daily dosing for androgen replacement, with steady-state achieved in ~2 days |
| Protein binding | 98% bound to sex hormone-binding globulin (SHBG) and albumin |
| Volume of Distribution | Vd: 1.5 L/kg (range 0.5-3.0 L/kg); clinical meaning: moderate to large distribution into tissues, including muscle and liver |
| Bioavailability | Oral: approximately 75-80%, with interindividual variability due to first-pass metabolism; not administered parenterally |
| Onset of Action | Oral: 1-2 hours for androgenic effects (e.g., voice deepening); maximum effect at 4-6 hours |
| Duration of Action | Oral: Androgenic effects persist for 24-48 hours; clinical note: duration of action sufficient for daily dosing in hypogonadism, but short half-life may require multiple daily doses for some effects |
| Molecular Weight | 336.44 |
Adults: 5-20 mg orally once daily. For replacement therapy, 5-10 mg daily; for hypogonadism, 5-20 mg daily for several months.
| Dosage form | TABLET |
| Renal impairment | No specific guidelines; use with caution in patients with severe renal impairment (CrCl <30 mL/min) due to potential fluid retention. |
| Liver impairment | Contraindicated in patients with severe hepatic impairment (Child-Pugh class C). For mild to moderate impairment (Child-Pugh A or B), consider dose reduction (e.g., 50% of usual dose) and monitor liver function. |
| Pediatric use | Not recommended for use in children due to risk of premature epiphyseal closure and virilization. If used for specific conditions (e.g., delayed puberty in males), dose: 2.5-5 mg orally once daily for 4-6 months. |
| Geriatric use | Use with caution; lower initial doses (e.g., 2.5-5 mg orally once daily) due to increased risk of prostatic hypertrophy, fluid retention, and cardiovascular events. |
| 1st trimester | Avoid; androgenic effects may cause fetal masculinization. Contraindicated in pregnancy. |
| 2nd trimester | Avoid; androgenic effects may cause fetal masculinization. Contraindicated in pregnancy. |
| 3rd trimester | Avoid; androgenic effects may cause fetal masculinization. Contraindicated in pregnancy. |
Clinical note
Comprehensive clinical and safety monograph for FLUOXYMESTERONE (FLUOXYMESTERONE).
| Placental transfer | Crosses placenta; can cause virilization of female fetus. |
| Breastfeeding | Excreted in breast milk; may cause virilization in female infants. Avoid breastfeeding. |
| Lactation Rating |
■ FDA Black Box Warning
Hepatotoxicity: Prolonged use at high doses associated with severe hepatic effects including peliosis hepatis, hepatocellular carcinoma, and hepatic necrosis. Contraindicated in patients with existing liver disease.
| Serious Effects |
PregnancyNursing mothersProstate cancerBreast cancer in males
| Precautions | Monitor liver function; risk of cholestatic hepatitis. May cause fluid retention, hypercalcemia, gynecomastia, prostatic hypertrophy, and polycythemia. In females, virilization; in prepubertal males, premature epiphyseal closure. Use in athletes for performance enhancement is banned. |
| Food/Dietary | No significant food interactions. Maintain a balanced diet; avoid excessive salt intake to minimize fluid retention. Avoid grapefruit juice if on medications metabolized by CYP3A4, though not specifically contraindicated. |
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| L5 |
| Teratogenic Risk | Fluoxymesterone is contraindicated in pregnancy. It is an androgen and can cause virilization of the female fetus. First trimester exposure risks clitoral enlargement, labial fusion, and other ambiguous genitalia. Second and third trimester exposure may cause clitoral enlargement and other masculinizing effects. There is also potential for growth retardation and adverse pregnancy outcomes. |
| Fetal Monitoring | Monitor maternal signs of virilization (e.g., hirsutism, deepening voice, acne) and liver function tests. In case of inadvertent exposure during pregnancy, fetal ultrasound should be performed to assess for ambiguous genitalia and growth parameters. Long-term follow-up may be necessary. |
| Fertility Effects | Fluoxymesterone may suppress gonadotropin secretion, leading to decreased spermatogenesis in males and ovulatory dysfunction in females. Reversible infertility may occur. Use in women may cause menstrual irregularities and anovulation. |
| Clinical Pearls | Fluoxymesterone is a synthetic androgen with anabolic activity; monitor liver function due to risk of hepatotoxicity, including peliosis hepatis and hepatocellular carcinoma. Contraindicated in prostate or male breast cancer. Use with caution in patients with cardiac, renal, or hepatic disease due to fluid retention. May cause virilization in women and premature epiphyseal closure in children. |
| Patient Advice | Take exactly as prescribed; do not adjust dose without consulting doctor. · Report signs of liver toxicity: jaundice, dark urine, abdominal pain, persistent nausea. · Women may experience masculinizing effects (deepening voice, hirsutism); notify doctor if these occur. · Monitor blood pressure and weight regularly due to possible fluid retention. · Avoid concurrent alcohol consumption to reduce hepatotoxicity risk. |