甲基睪酮
**甲基睪酮 (Methyltestosterone)** 是一種合成的雄性激素與同化類固醇。它是睪酮的 17-α-烷基化衍生物，這項結構改變顯著降低了肝臟的首過代謝效應，使其能透過口服有效吸收。 在獸醫學中，主要用於： * **荷爾蒙反應性皮膚病**：特別是當褪黑激素治療無效時，用於犬隻的 **X型脫毛症 (Alopecia X)**（毛髮生長週期停滯）。 * **生殖管理**：抑制母犬發情或治療假孕。 * **荷爾蒙依賴性腫瘤**：作為某些雌激素依賴性乳腺腫瘤的輔助治療。 > **臨床要點**：在獸醫臨床上（尤其是貓）使用此藥物極具爭議，且通常不建議使用，因為有引發**嚴重肝毒性**的高風險。貓似乎對 17-α-烷基化雄性激素引起的肝損傷特別敏感。
作用機制: 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.
各物種劑量
- 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.
劑量為持牌獸醫專業人員的臨床參考。請務必對照最新藥品說明書及個別病患確認。
給藥途徑
禁忌症
- Hepatic dysfunction or pre-existing liver disease
- Pregnancy (Category X - causes fetal masculinization)
- Prostate cancer or severe prostatic hypertrophy
不良反應
- 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
藥物相互作用
- 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.
監測
- 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
過量
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.
VetSheet 藥物參考供持牌獸醫專業人員作臨床決策輔助之用,不能取代專業判斷或廠方最新藥品說明書。