美替拉酮
美替拉酮是一種**腎上腺類固醇合成抑制劑**，在獸醫學中主要用於控制貓的腎上腺皮質機能亢進（庫興氏症候群）。 * **臨床用途**：最常用於外科手術（腎上腺切除術）前的短期醫療穩定治療。 * **併發糖尿病**：貓的庫興氏症候群較罕見，且常伴隨具胰島素阻抗的糖尿病。藉由解決皮質醇過高的問題，美替拉酮能減少胰島素拮抗作用，從而顯著降低甚至消除對外源性胰島素的需求。 * **物種特異性**：雖然臨床經驗有限，但貓對此藥物的耐受性似乎良好。它也可能對雪貂和小型哺乳動物（如倉鼠）有效，但缺乏這些物種的藥代動力學和安全性數據。 * **人類用途**：在人類醫學中，它被用於診斷評估下視丘-腦下垂體-腎上腺 (HPA) 軸的功能，以及標示外用於治療庫興氏症候群。
作用機制: Metyrapone exerts its effects by directly interfering with the steroidogenic pathway within the adrenal cortex: * **Enzyme Inhibition**: It reversibly inhibits the enzyme **11-β-hydroxylase** (CYP11B1). * **Pathway Blockade**: **11-deoxycortisol** → [Blocked by Metyrapone] → **Cortisol**. This prevents the final hydroxylation step, leading to a rapid reduction in circulating cortisol and corticosterone levels. * **Feedback Loop**: The sudden drop in cortisol removes negative feedback on the pituitary gland, leading to a compensatory surge in **ACTH** secretion. Over time, this ACTH surge can override the enzymatic blockade, limiting the drug's long-term efficacy. * **Mineralocorticoid Effects**: It can also suppress aldosterone synthesis, causing mild natriuresis. However, long-term use leads to the accumulation of 11-desoxycorticosterone (a precursor with mineralocorticoid activity), which prevents Addisonian crises but can induce hypertension.
各物種劑量
- Hyperadrenocorticism · 65 mg/kg PO every 8 to 12 hours · PO · q8-12h · Alternatively, dosages ranging from 195-250 mg/cat/day (divided) have been used without observed toxicity (Bruyette 2010).
劑量為合格獸醫專業人員的臨床參考。請務必對照最新藥品仿單及個別病患確認。
給藥途徑
禁忌症
- Known hypersensitivity to metyrapone
- Primary adrenal cortical insufficiency (Addison's disease)
不良反應
- Nausea
- Vomiting
- Abdominal pain
- Headache (reported in humans)
- Dizziness (reported in humans)
- Sedation (reported in humans)
- Allergic rash (reported in humans)
- Bone marrow depression (rare)
藥物相互作用
- Acetaminophen · Increased risk for acetaminophen toxicity. Note: Acetaminophen is strictly contraindicated in cats due to fatal methemoglobinemia and hepatotoxicity.
- Corticosteroids · Decreases the efficacy of metyrapone by suppressing ACTH and interfering with the diagnostic or therapeutic intent.
監測
- Blood glucose levels (critical in diabetic cats)
- Clinical signs of hyperadrenocorticism (to assess efficacy)
- Clinical signs of hypoadrenocorticism/Addisonian crisis (lethargy, vomiting, collapse)
- Electrolytes (sodium, potassium)
過量
Acute toxicity data indicates an oral LD50 in rats of 521 mg/kg. **Clinical Signs of Overdose**: * Gastrointestinal distress (severe vomiting/nausea) * **Acute adrenocortical insufficiency (Addisonian crisis)** * Hypoglycemia, hyponatremia, hypochloremia, hyperkalemia * Cardiac arrhythmias, hypotension, dehydration, and altered mentation **Treatment**: * No specific antidote exists. * Standard gastrointestinal decontamination protocols if ingestion is recent. * Intravenous fluid therapy (saline) supplemented with **glucose**. * Administration of **intravenous hydrocortisone** or dexamethasone to replace depleted corticosteroids. * Intensive monitoring and supportive care for several days may be required.
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。