地塞米松
**地塞米松 (Dexamethasone)** 是一種高效、長效的合成糖皮質激素，在獸醫學中廣泛用於其強大的抗發炎和免疫抑制特性。 * **效力：** 其效力大約是氫化可的松 (皮質醇) 的 25-30 倍，且幾乎沒有鹽皮質激素 (保水) 活性。 * **劑型：** 可作為醇基或磷酸鹽衍生物 (懸浮液、溶液或軟膏) 使用。醇基形式的抗發炎功效通常優於磷酸鹽衍生物。 > **臨床重點：** 由於其較長的生物半衰期 (>36-72 小時) 且缺乏鹽皮質激素活性，地塞米松非常適合用於高劑量免疫抑制治療、急性過敏反應或診斷測試。但由於有嚴重抑制下丘腦-垂體-腎上腺 (HPA) 軸的風險，**不適合**用於隔日維持治療。
作用機制: Dexamethasone exerts its effects by diffusing across cell membranes and binding to specific cytosolic **glucocorticoid receptors (GR)**. * **Transactivation:** The receptor-ligand complex translocates to the nucleus → binds to glucocorticoid response elements (GREs) on DNA → upregulates the expression of anti-inflammatory proteins like **lipocortin-1** (annexin A1). Lipocortin-1 inhibits **phospholipase A2**, thereby blocking the release of arachidonic acid and the subsequent synthesis of inflammatory prostaglandins and leukotrienes. * **Transrepression:** It inhibits transcription factors such as **NF-κB** and **AP-1** → downregulates the production of pro-inflammatory cytokines (e.g., IL-1, IL-6, TNF-α).
給藥途徑
禁忌症
- Systemic fungal infections
- Active viral infections
- Corneal ulcers (especially for ophthalmic preparations)
- Concurrent use of NSAIDs
- Known hypersensitivity to the drug
不良反應
- Polyuria (PU) and Polydipsia (PD)
- Polyphagia (increased appetite)
- Panting (especially in dogs)
- Gastrointestinal ulceration or bleeding
- Iatrogenic hyperadrenocorticism (Cushing's syndrome) with chronic use
- Secondary infections due to immunosuppression
- Delayed wound healing
- Muscle wasting and weakness
藥物相互作用
- NSAIDs (e.g., carprofen, meloxicam) · Significantly increased risk of severe gastrointestinal ulceration and bleeding.
- Insulin · Dexamethasone induces insulin resistance, antagonizing the hypoglycemic effect of insulin and increasing requirements in diabetic patients.
- Phenobarbital · May induce hepatic enzymes, increasing the metabolism and clearance of dexamethasone.
- Diuretics (potassium-depleting) · Increased risk of hypokalemia.
監測
- Clinical signs of disease resolution
- Water intake and urination (PU/PD)
- Appetite and body weight
- Blood glucose levels (especially in predisposed patients)
- Signs of gastrointestinal bleeding (melena, hematemesis)
- ACTH stimulation test (if assessing HPA axis suppression)
過量
Acute overdose is rarely life-threatening but may cause significant gastrointestinal upset, profound PU/PD, and panting. Chronic overdosage leads to **iatrogenic hyperadrenocorticism (Cushing's syndrome)**, characterized by alopecia, pot-bellied appearance, muscle wasting, and immunosuppression. Treatment is supportive and requires gradual tapering of the drug.
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