醋酸甲地孕酮
醋酸甲地孕酮是一種強效的合成**黃體素**，具有顯著的抗雌激素和內在糖皮質激素特性。 在過去，它廣泛應用於獸醫學（特別是貓）以治療各種皮膚和行為問題。然而，由於其引發嚴重且有時不可逆副作用（如嚴重的腎上腺皮質抑制和醫源性糖尿病）的高風險，**目前在貓的臨床使用已大幅減少**。 在狗中，它仍獲 FDA 批准用於母狗的發情延遲和假孕緩解，並標示外用於公狗的良性前列腺肥大 (BPH)。在人類醫學中，它被用作食慾促進劑以及晚期乳腺癌或子宮內膜癌的姑息治療。
作用機制: Megestrol acetate exerts its effects through multiple receptor pathways: * **Progesterone Receptors**: Binds to progestin receptors → provides negative feedback to the hypothalamus and pituitary → inhibits the release of **GnRH**, **LH**, and **FSH** → suppresses estrus and ovulation. * **Glucocorticoid Receptors**: Possesses significant intrinsic glucocorticoid activity → binds to glucocorticoid receptors → causes profound suppression of the **hypothalamic-pituitary-adrenal (HPA) axis** and induces insulin resistance. * **Anti-estrogenic Activity**: Modifies target tissue response to estrogens. *Clinical Pearl*: Unlike some other progestins, megestrol acetate does not possess significant anabolic or masculinizing effects on the developing fetus.
各物種劑量
- Suppression of estrus (in anestrus) · 5 mg/cat PO every 2 weeks or 2.5 mg/cat per week (better if divided into 2 doses given every 3.5 days) · PO · q7-14d · Variable
- Suppression of estrus (in proestrus) · 5 mg/cat per day for 4 days, then 5 mg PO every 2 weeks. · PO · q24h then q14d · Variable
- Suppression of estrus (behavioral estrus) · 5 mg/day PO until estrus stops (generally within 3-5 days), then 2.5-5 mg PO once weekly for 10 weeks · PO · q24h then q7d · 10+ weeks
- Postponement of estrus (started during diestrus) · 2.5 mg PO daily for 8 weeks · PO · q24h · 8 weeks
- Postponement of estrus (started during anestrus) · 2.5 mg PO once weekly for up to 18 months. · PO · q7d · Up to 18 months · Recommend allowing cat to have a cycle (unmedicated) before beginning another treatment cycle.
- Prevention of estrus · 5 mg daily PO for 3 days as soon as behavioral signs of estrus are seen · PO · q24h · 3 days · Next estrus period will occur in approximately 4 weeks.
- Idiopathic feline miliary dermatitis · 2.5-5 mg once every other day, followed by weekly maintenance dosages. · PO · q48h then q7d · Variable · Reserve use for severe cases; explain risks to owner and do not exceed 2.5 mg per week during maintenance phase.
- Appetite stimulant · 0.25-0.5 mg/kg q24h for 3-5 days, then q48-72h · PO · q24h then q48-72h · Variable
- Alternative treatment for immune-mediated skin diseases · 2.5-5 mg PO once daily for 10 days, then every other day · PO · q24h then q48h · Variable
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
- Pregnancy
- Uterine disease (e.g., pyometra, endometritis)
- Diabetes mellitus
- Mammary neoplasias
- Prior to the first estrous cycle in dogs
- Anestrus therapy in dogs with abnormal cycles
- During diestrus or in the presence of uterine hemorrhage
- Treatment of pseudopregnancy in bitches (per manufacturer, though off-label protocols exist)
不良反應
- Profound adrenocortical suppression (especially in cats)
- Transient or permanent diabetes mellitus
- Cystic endometrial hyperplasia (CEH) and pyometra
- Mammary hypertrophy and neoplasia
- Increased appetite and weight gain
- Polydipsia and polyuria (PU/PD)
- Lethargy and personality changes
- Hepatotoxicity (rare)
- Acromegaly (dogs)
- Lactation (rare)
藥物相互作用
- Corticosteroids · Concurrent long-term use may exacerbate adrenocortical suppression and increase the risk of diabetes mellitus.
- Rifampin · May decrease progestin activity due to microsomal enzyme induction, resulting in increased progestin metabolism.
監測
- Body weight
- Blood glucose (draw baseline before therapy)
- Mammary gland development and appearance (nodules/hypertrophy)
- Adrenocortical function (ACTH stimulation test if indicated)
- Liver enzymes (especially with long-term treatment)
- Clinical efficacy
過量
Acute toxicity from overdosage has not been reported. In humans, massive doses (up to 800 mg/day) caused no observable acute adverse reactions. **Chronic Toxicity in Dogs**: * Dosages of 0.1-0.25 mg/kg/day PO for 36 months yielded no gross abnormalities, but histologically, **cystic endometrial hyperplasia (CEH)** was noted (resolved when therapy was discontinued). * Dosages of 0.5 mg/kg/day PO for 5 months caused reversible uterine hyperplasia. * Dosages of 2 mg/kg/day demonstrated early cystic endometritis within 64 days.
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。