フィナステリド
フィナステリドは、5-α還元酵素の競合的かつ特異的な阻害薬として作用する合成4-アザステロイド化合物です。 獣医学においては、主に未去勢の雄犬における**前立腺肥大症（BPH）**の内科的治療に使用されます。特に繁殖用の種牡犬にとって、生殖能力や血中テストステロン濃度に大きな影響を与えることなく前立腺を縮小させるため、外科的去勢に代わる非常に有効な選択肢となります。 さらに、フェレットの**副腎疾患**に対する補助療法として適応外使用され、雄フェレットにおけるアンドロゲン由来の臨床症状（前立腺肥大や尿道閉塞など）の管理に役立ちます。
作用機序: Finasteride specifically and totally inhibits the intracellular enzyme **5-alpha-reductase** (predominantly Type II). * **Pathway**: Testosterone → (via **5-alpha-reductase**) → **Dihydrotestosterone (DHT)** DHT is a highly potent androgen and is the primary hormone responsible for the development and enlargement of the prostate gland. By blocking this conversion, finasteride significantly reduces DHT concentrations in the prostate, liver, and skin. This leads to prostatic involution and a reduction in clinical signs of BPH. Because it does not directly block testosterone or its receptors, normal testosterone-dependent functions (such as spermatogenesis and libido) are largely preserved.
動物種別の用量
- Adjunctive treatment of adrenal disease · 5 mg (total dose) · PO · once daily · tablet
- Benign prostatic hyperplasia · 0.1-0.5 mg/kg · PO · once daily · for a 10-50 kg dog, one 5 mg tablet daily
- Benign prostatic hyperplasia · <15 kg: 1.5 mg (approx. 1/3 of a 5 mg tablet); 15-30 kg: 2.5 mg (1/2 tablet); >30 kg: 5 mg (one tablet) · PO · daily
- Benign prostatic hypertrophy · 5 mg per dog · PO · q24h · Extended treatment course (<8 weeks) may be required for full efficacy · Alternative to castration. Use when delmadinone or osaterone are not appropriate.
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
- Hypersensitivity to finasteride
- Sexually developing animals
- Females (especially pregnant females)
- Sexually-developing dogs
- Breeding dogs (due to secretion in semen and teratogenic potential)
有害事象
- Decreased libido
- Decreased ejaculate volume
- Impotence (rare/mild)
- Secreted into semen
- Causes fetal anomalies (teratogenic)
薬物相互作用
- Anticholinergic drugs · May precipitate or aggravate urinary retention thereby negating the effects of the drug when used for BPH
モニタリング
- Prostate exam (to evaluate efficacy and reduction in size)
- Prostate size (via palpation or ultrasound)
- Resolution of clinical signs (e.g., tenesmus, dysuria, hematuria)
過量投与
Limited information is available regarding acute toxicity. Mild **gastrointestinal effects** (such as vomiting or diarrhea) may be noted in the event of an overdose. Supportive care is recommended.
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。