鋅 (醋酸鋅、硫酸鋅、葡萄糖酸鋅)
鋅是一種必需的微量元素和營養劑，對於體內超過200種金屬酶的功能至關重要。它在維持細胞膜和核酸的結構完整性方面扮演重要角色，並且是細胞生長、免疫反應、傷口癒合和視覺所必需的。 在獸醫學中，鋅主要用於： * **鋅反應性皮膚病**： * *第一型*：主要見於北方犬種（如西伯利亞哈士奇、阿拉斯加雪橇犬）的鋅吸收遺傳缺陷。 * *第二型*：發生於生長快速的大型幼犬，因餵食高植酸或高鈣飲食，結合了飲食中的鋅並阻礙其吸收。 * **肝銅中毒症**：用於易感犬種（如貝林登梗、西高地白梗、拉布拉多犬），以阻斷腸道對銅的吸收。 * **肝纖維化與脂肪肝**：作為輔助性保肝和抗纖維化藥物。 > **臨床要點**：在計算劑量時，區分**元素鋅 (elemental zinc)**和**鋅鹽 (zinc salts)**至關重要。例如，硫酸鋅含有23%的元素鋅，而葡萄糖酸鋅僅含14.3%。請務必確認劑量方案所指的具體形式。
作用機制: Zinc acts as a critical cofactor for numerous metalloenzymes, including **alkaline phosphatase**, **alcohol dehydrogenase**, **carbonic anhydrase**, and **RNA polymerase**. **Mechanism in Copper Toxicosis**: When administered orally in large doses, zinc induces the synthesis of **metallothionein** in intestinal enterocytes. Metallothionein is a cysteine-rich protein that has a much higher binding affinity for copper than for zinc. Dietary zinc → Induces enterocyte metallothionein → Binds dietary and biliary copper → Traps copper within the enterocyte → Enterocyte is sloughed into the feces (normal turnover) → **Negative copper balance**.
各物種劑量
- Adjunctive therapy of severe hepatic lipidosis · 7-10 mg/kg PO once daily, in B-Complex mixture if possible · PO · q24h
- Appetite stimulant · 1 mg/kg of elemental zinc PO once a day · PO · q24h
- Zinc-responsive dermatoses, copper storage disease · 1-2 mg elemental zinc p.o. q24h (zinc sulphate: 5 mg/kg p.o. q24h or in divided doses; zinc gluconate: 2 mg/kg p.o. q24h; zinc acetate: 1 mg/kg p.o. q24h) · PO · q24h · Not specified · Give with food to minimize vomiting.
- Adjunctive treatment and prophylaxis of hepatic copper toxicosis · Initially, give a loading dose of 100 mg elemental zinc (zinc acetate used in this study) twice daily (separate doses by at least 8 hours) for about 3 months; then reduce dose to 50 mg (elemental zinc) twice daily. · PO · q12h · Lifetime/Maintenance · If animal vomits, give doses with a small piece of meat. Do not give within one hour of a meal. Target zinc levels are 200-500 micrograms/dL.
- Adjunctive treatment and prophylaxis of hepatic copper toxicosis · 5-10 mg/kg elemental zinc q12h; use high end of dosage range initially for 3 months, then 50 mg PO q12h for maintenance. · PO · q12h · Lifetime/Maintenance · Separate dosage from meals by 1-2 hours. In dogs with active copper-induced hepatitis, do not use zinc alone, but in combination with a chelator.
- Adjunctive treatment and prophylaxis of hepatic copper toxicosis · 10 mg/kg elemental zinc (given as zinc acetate or zinc gluconate) PO twice daily. · PO · q12h · Give one hour before each meal.
- Adjunctive treatment and prophylaxis of hepatic copper toxicosis · 1.5-2.5 mg/kg zinc gluconate PO three times daily; 0.67 mg/kg zinc sulfate PO three times daily; or 100 mg (total dose) elemental zinc (as zinc acetate) PO twice daily. · PO · q8h or q12h · 3-6 month loading, then half dose · Goal is to achieve zinc plasma concentrations of 200-600 micrograms/dL.
給藥途徑
禁忌症
- Patients with pre-existing copper deficiency
- Patients with copper deficiency
不良反應
- Gastrointestinal disturbances (vomiting, nausea, anorexia)
- Hematologic abnormalities (hemolytic anemia, particularly at serum levels >1000 mcg/dL)
- Hypotension (with overdose)
- Jaundice (with overdose)
- Pulmonary edema (with overdose)
- Nausea
- Vomiting
- Diarrhoea
- Haemolysis (at high doses)
藥物相互作用
- Copper · Large doses of zinc inhibit copper absorption in the intestine; separate supplements by at least 2 hours. · moderate
- Fluoroquinolones (e.g., enrofloxacin, ciprofloxacin) · Zinc salts may reduce the oral absorption of fluoroquinolones.
- Penicillamine · May potentially inhibit zinc absorption; clinical significance is not clear. · minor
- Tetracyclines · Zinc salts may chelate oral tetracycline and reduce its absorption; separate doses by at least 2 hours. · major
- Ursodiol · May potentially inhibit zinc absorption; clinical significance is not clear.
- Iron · Long-term administration of zinc may lead to decreased iron stores and functional deficiency · moderate
- Ursodeoxycholic acid · May potentially inhibit zinc absorption · minor
- Fluoroquinolones · Zinc salts may reduce the absorption of fluoroquinolone antibiotics · major
監測
- Serum zinc levels (Target 200-500 mcg/dL for copper toxicosis; do not exceed 1000 mcg/dL)
- Gastrointestinal signs (vomiting, anorexia)
- Complete Blood Count (CBC) to monitor for hemolysis/anemia
- Clinical response (resolution of dermatosis or hepatic signs)
- Serum zinc levels
- Serum copper levels
- Complete Blood Count (CBC) / PCV to monitor for haemolysis
過量
Signs associated with overdoses of zinc in mammals include **hemolytic anemia**, hypotension, jaundice, vomiting, and pulmonary edema. > **Toxicity Alert**: Ingestion of U.S. pennies minted after 1982 is a common cause of severe zinc toxicosis in dogs, as these coins are 97.5% zinc. **Treatment in Mammals**: * Remove the source (e.g., endoscopic or surgical removal of coins). * Dilution with milk or water. * Chelation therapy using edetate calcium disodium (Calcium EDTA). **Avian Toxicity**: Zinc intoxication in birds is relatively common (often from cage wire or hardware). Clinical signs are varied and nonspecific: lethargy, anorexia, regurgitation, polyuria, polydipsia, hematuria, hematochezia, pallor, dark or bright green diarrhea, foul-smelling feces, paresis, seizures, and sudden death. Treatment involves removing the source, chelation therapy (Calcium EDTA or succimer), and supportive care.
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