螺內酯
螺內酯（Spironolactone）是一種合成的**醛固酮拮抗劑**和保鉀利尿劑。在獸醫學中，它主要作為鬱血性心衰竭（CHF）、腹水、全身性高血壓和原發性醛固酮增多症（特別是在貓）的輔助治療藥物。 **臨床重點與藥理背景：** * **醛固酮逃逸（Aldosterone Escape）：** 雖然與呋塞米（Furosemide）等環利尿劑相比，其直接利尿效果較弱，但螺內酯在阻斷腎素-血管張力素-醛固酮系統（RAAS）中扮演著關鍵角色。即使病患正在服用ACE抑制劑，醛固酮水平最終仍可能反彈升高（即「醛固酮逃逸」現象），而螺內酯能有效減輕此現象。 * **心肌保護作用：** 在人類醫學中，螺內酯因其對心肌的抗纖維化作用而受到高度重視，有助於防止有害的心臟重塑。雖然這種益處在獸醫病患（如患有黏液瘤性二尖瓣疾病的狗）中的程度仍有爭議，但它已越來越多地被納入標準的多重藥物CHF治療方案中。 * **生物可用率：** 與食物一起服用可顯著提高其吸收率。
作用機制: Spironolactone acts as a competitive antagonist at the **mineralocorticoid receptor**. * **Mechanism:** It competitively inhibits **aldosterone** binding in the distal renal tubules and collecting ducts. * **Pathway:** Blockade of the receptor → prevents the synthesis of aldosterone-induced proteins (such as Na+/K+ ATPase and epithelial sodium channels) → **decreases sodium and chloride reabsorption** while **decreasing potassium, ammonium, and phosphate excretion**. * **Result:** Mild diuresis with potassium retention. It does not affect carbonic anhydrase or proximal renal transport mechanisms.
各物種劑量
- As a diuretic in CHF (when furosemide and ACE inhibitors alone do not control fluid accumulation) · 1-2 mg/kg PO q12h · PO · q12h · Refractory CHF
- As a diuretic in CHF (when serum potassium is low) · 1 mg/kg q12h PO · PO · q12h
- For adjunctive treatment of hypertension · 1-2 mg/kg PO q12h · PO · q12h
- For adjunctive treatment of hypertension (Step 3 drug) · 1-2 mg/kg twice daily · PO · q12h · When systolic BP >160 mmHg, diastolic >120 mmHg after amlodipine and ACE inhibitor.
- For adjunctive treatment of primary hyperaldosteronism · 1-2 mg/kg PO twice daily · PO · q12h · If potassium supplementation alone does not control clinical signs.
- Congestive heart failure, ascites, hyperaldosteronism · 2-4 mg/kg · PO · q24h · Continuous · Severe ulcerative facial dermatitis has been reported in Maine Coon cats.
- As a diuretic in CHF (when furosemide and ACE inhibitors alone do not control fluid accumulation) · 1-2 mg/kg PO q12h · PO · q12h · Refractory CHF
- As a diuretic in CHF (with other diuretics when hypokalemia is an issue) · 2-4 mg/kg PO once daily · PO · q24h
- As a diuretic in CHF (to allow further reduction of furosemide dose) · 0.5 mg/kg PO once daily to 2 mg/kg twice daily · PO · q24h to q12h · 0.5 mg/kg once daily for aldosterone blockage (weak diuretic effect); 2 mg/kg twice daily for stronger diuretic effect.
給藥途徑
禁忌症
- Hyperkalemia
- Addison's disease (hypoadrenocorticism)
- Anuria
- Acute renal failure
- Significant renal impairment
- Hypoadrenocorticism
- Hyperkalaemia
- Hyponatraemia
- Concurrent use with NSAIDs in animals with renal insufficiency
- Pregnancy
- Lactation
- Animals intended for breeding
不良反應
- Facial dermatitis (notably reported in Maine Coon cats)
- Hyperkalemia
- Hyponatremia
- Dehydration
- Increased BUN and mild acidosis (in patients with renal impairment)
- Gastrointestinal distress (vomiting, anorexia)
- CNS effects (lethargy, ataxia)
- Endocrine changes (anti-androgenic effects, e.g., gynecomastia in humans, feminization of male fetuses)
- Hyponatraemia
- Hyperkalaemia
- Reversible prostatic atrophy (in entire male dogs)
- Severe ulcerative facial dermatitis (in Maine Coon cats)
- Hepatotoxicity (reported in humans)
藥物相互作用
- Digoxin · Spironolactone may increase the half-life of digoxin; enhanced monitoring of digoxin serum levels is warranted. May also cause falsely elevated digoxin values if using a radioimmune assay (RIA). · moderate
- Mitotane · Spironolactone may mute the effects of mitotane if given concurrently; monitor carefully.
- Neuromuscular blockers, non-depolarizing · Possible increase in neuromuscular blockade effects.
- Potassium-sparing diuretics (e.g., triamterene) · Increased risk of hyperkalemia.
- Potassium supplements · Increased risk of hyperkalemia. · major
- Salicylates (e.g., Aspirin) · Spironolactone's diuretic effects may be decreased if administered concomitantly.
- Thiazide diuretics · Potentiates diuretic effects · moderate
- Loop diuretics · Potentiates diuretic effects · moderate
- ACE inhibitors · Increased risk of hyperkalaemia (though generally safe to use concurrently in practice; monitor potassium) · moderate
- NSAIDs · Increased risk of hyperkalaemia and nephrotoxicity · major
- Ciclosporin · Increased risk of hyperkalaemia · moderate
監測
- Serum electrolytes (especially potassium and sodium)
- BUN and creatinine
- Hydration status
- Blood pressure (if indicated)
- Clinical signs of edema/ascites
- Patient weight
- Serum potassium
- Serum sodium
- Renal function (BUN, Creatinine)
- Digoxin levels (if used concurrently)
過量
Information on acute overdosage of spironolactone in veterinary patients is limited. * **Management:** Should an acute overdose occur, follow general guidelines for diuretic overdose (e.g., furosemide or chlorothiazide). * **Treatment:** Empty the stomach if ingestion was recent. Provide supportive care, monitor hydration status, and closely evaluate serum electrolytes (especially potassium and sodium). * Contact an animal poison control center for further guidance.
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