メチルテストステロン
**メチルテストステロン**は、合成アンドロゲンおよびアナボリックステロイドホルモンです。テストステロンの17-α-アルキル化誘導体であり、肝臓での初回通過効果を大幅に減少させることで、経口投与を有効にします。 獣医学では主に以下の目的で使用されます： * **ホルモン反応性皮膚疾患**：特にメラトニン療法が無効な犬の**脱毛症X（Alopecia X）**（毛周期停止）。 * **繁殖管理**：雌犬の発情抑制や偽妊娠の治療。 * **ホルモン依存性腫瘍**：特定のエストロゲン依存性乳腺腫瘍の補助治療。 > **臨床上のポイント**：獣医学、特に猫での使用は非常に議論の余地があり、**重篤な肝毒性**のリスクがあるため一般的には推奨されません。猫は17-α-アルキル化アンドロゲンによる肝障害に対して特異的に感受性が高いと考えられています。
作用機序: 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.
動物種別の用量
- 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.
用量は獣医療従事者向けの臨床リファレンスです。必ず最新の添付文書と個々の患者で確認してください。
投与経路
禁忌
- Hepatic dysfunction or pre-existing liver disease
- Pregnancy (Category X - causes fetal masculinization)
- Prostate cancer or severe prostatic hypertrophy
有害事象
- 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
薬物相互作用
- 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.
モニタリング
- 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
過量投与
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 の薬剤リファレンスは、獣医療従事者向けの臨床意思決定支援を目的としており、専門的判断やメーカーの最新添付文書に代わるものではありません。