Methyltestosterone
**Methyltestosterone** is a synthetic androgenic and anabolic steroid hormone. It is a 17-alpha-alkylated derivative of testosterone, which significantly reduces its first-pass hepatic metabolism, allowing for effective oral administration. In veterinary medicine, it is primarily utilized for: * **Hormone-responsive dermatoses**: Particularly **Alopecia X** (hair cycle arrest) in dogs, when melatonin therapy has failed. * **Reproductive management**: Suppression of estrus or treatment of pseudopregnancy in female dogs. * **Hormone-dependent tumors**: Adjunctive treatment for certain estrogen-dependent mammary tumors. > **Clinical Pearl**: Its use in veterinary medicine, particularly in cats, is highly controversial and generally discouraged due to a significant risk of **severe hepatotoxicity**. Cats appear to be uniquely susceptible to hepatic injury from 17-alpha-alkylated androgens.
Mecanismo: Methyltestosterone acts as an exogenous androgen, binding to intracellular **androgen receptors (AR)** in target tissues. * **Mechanism**: Free methyltestosterone enters cells → binds to cytosolic **AR** → the receptor-ligand complex translocates to the nucleus → binds to specific DNA sequences (androgen response elements) → modulates gene transcription. * **Anabolic Effects**: Stimulates erythropoiesis (increases red blood cell production), enhances nitrogen balance, promotes protein anabolism (requires adequate caloric and protein intake), and increases retention of potassium, sodium, and phosphorus. * **Pharmacokinetic Advantage**: The addition of a **methyl group at the C-17 alpha position** sterically hinders hepatic degradation, providing higher oral bioavailability compared to native testosterone.
Dosificación por especie
- Anti-estrogenic activity, anabolic effects, negative feedback on gonadotropin release · 0.5 mg/kg · PO · once daily · Dose may need to be adjusted, but should not exceed 1 mg/kg. Use is highly controversial due to hepatotoxicity.
- Alopecia X (when melatonin fails) · 1 mg/kg to a maximum dose of 30 mg (total dose) · PO · once daily · Stop after maximal hair re-growth is noted · Get baseline liver profile and then again one and two months after starting treatment. Can cause hepatotoxicity, aggressive behavior and/or seborrhea.
- Testosterone-responsive dermatosis · 1 mg/kg to a maximum dose of 30 mg · PO · every other day · Once dog responds, then every 4-7 days
- Suppress estrus in Greyhounds · 5 mg (total dose) · PO · once weekly or divided, two times a week
- Estrus suppression · 25-50 mg (total dose) · PO · twice weekly
- Anti-estrogenic activity, anabolic effects, negative feedback on gonadotropin release · 0.5 mg/kg · PO · once daily · Dose may need to be adjusted, but should not exceed 1 mg/kg.
Las dosis son una referencia clínica para médicos veterinarios. Confirme siempre con la información vigente del producto y el paciente individual.
Vías de administración
Contraindicaciones
- Hepatic dysfunction or pre-existing liver disease
- Pregnancy (Category X - causes fetal masculinization)
- Prostate cancer or severe prostatic hypertrophy
Efectos adversos
- Hepatotoxicity (elevated liver enzymes, icterus, periportal hepatocyte enlargement)
- Virilization of females (clitoral hypertrophy, vaginitis)
- Vaginal discharge
- Prostatic hyperplasia in males
- Increased aggression or behavioral changes
- Seborrhea
- Premature epiphyseal closure in young animals
Interacciones farmacológicas
- Cyclosporine · Methyltestosterone may increase serum cyclosporine levels, potentially leading to toxicity.
- Insulin · Methyltestosterone may decrease serum glucose levels, reducing insulin requirements.
- Oral Antidiabetic Agents · May decrease serum glucose levels, increasing the risk of hypoglycemia.
- Warfarin · Methyltestosterone may increase anticoagulant effects, increasing bleeding risk.
Monitoreo
- Baseline and serial hepatic function panels (ALT, AST, ALP, Bilirubin)
- Clinical signs of hepatotoxicity (icterus, anorexia, weight loss, vomiting)
- Behavioral changes (aggression)
- Prostatic evaluation in intact males
Sobredosis
Information on acute toxicity in veterinary species is limited. * **Acute signs**: Nausea, vomiting, and edema are the most likely effects of a single massive overdose. * **Management**: Consider gastrointestinal decontamination if ingestion is recent. Monitor liver function closely with large overdoses and provide supportive care.
La referencia de fármacos de VetSheet está destinada a médicos veterinarios como apoyo a la decisión clínica; no sustituye el juicio profesional ni la información vigente del fabricante.