亜鉛 (酢酸亜鉛、硫酸亜鉛、グルコン酸亜鉛)
亜鉛は必須微量元素および栄養剤であり、体内の200以上の金属酵素の機能に不可欠です。細胞膜や核酸の構造的完全性を維持する上で重要な役割を果たし、細胞の成長、免疫応答、創傷治癒、視覚に必要です。 獣医学において、亜鉛は主に以下の目的で使用されます： * **亜鉛反応性皮膚疾患**： * *タイプI*：主に北方犬種（シベリアン・ハスキー、アラスカン・マラミュートなど）に見られる亜鉛吸収の遺伝的欠陥。 * *タイプII*：フィチン酸やカルシウムを多く含む食事を与えられた急成長中の大型犬の幼犬に発生し、これらが食事中の亜鉛と結合して吸収を妨げます。 * **肝臓の銅蓄積症（銅毒性）**：感受性の高い犬種（ベドリントン・テリア、ウェスト・ハイランド・ホワイト・テリア、ラブラドール・レトリバーなど）において、腸管からの銅の吸収を阻害するために使用されます。 * **肝線維症および肝リピドーシス**：補助的な肝保護剤および抗線維化剤として使用されます。 > **臨床のポイント**：用量を計算する際、**元素亜鉛 (elemental zinc)**と**亜鉛塩 (zinc salts)**を区別することが極めて重要です。例えば、硫酸亜鉛には23%の元素亜鉛が含まれていますが、グルコン酸亜鉛には14.3%しか含まれていません。投与プロトコルがどの形態を指しているかを常に確認してください。
作用機序: 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**.
動物種別の用量
- 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.
投与経路
禁忌
- Patients with pre-existing copper deficiency
- Patients with copper deficiency
有害事象
- 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)
薬物相互作用
- 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
モニタリング
- 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
過量投与
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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