磺胺二甲嘧啶
**磺胺二甲嘧啶 (Sulfadimethoxine)** 是一種在獸醫學中廣泛使用的長效、廣效磺胺類抗菌藥物。 **主要臨床重點：** * **主要用途：** 獲 FDA 批准用於治療犬、貓、馬和牛的呼吸道、泌尿生殖道、腸道及軟組織感染。它也常被大量用於治療**球蟲症 (Coccidiosis)**（儘管在某些物種中屬仿單標示外使用）。 * **抗菌譜：** 對許多革蘭氏陽性菌（如鏈球菌、葡萄球菌、諾卡氏菌）及部分革蘭氏陰性菌有效。對球蟲和弓形蟲等原蟲也具有顯著活性。 * **限制：** 單獨使用時為抑菌劑。在有膿液、壞死組織或大量細胞碎屑的環境中，其療效會顯著降低。細菌抗藥性日益普遍。 * **物種特性：** 具有高蛋白結合率且分佈良好。在犬隻體內，主要依賴腎臟排泄而非肝臟代謝，且因腎小管的廣泛再吸收作用而具有較長的半衰期。
作用機制: Sulfonamides are bacteriostatic agents that disrupt bacterial folic acid synthesis. * **Mechanism:** Sulfadimethoxine acts as a structural analog of **para-aminobenzoic acid (PABA)**. * **Pathway:** It competitively inhibits the bacterial enzyme **dihydropteroate synthase** → blocks the incorporation of PABA into **dihydropteroic acid** → prevents the biosynthesis of **tetrahydrofolic acid** (active folic acid). * **Result:** Without tetrahydrofolic acid, susceptible bacteria and protozoa cannot synthesize purines, pyrimidines, and ultimately DNA/RNA, halting replication. * *Note:* Mammalian cells are unaffected because they utilize preformed dietary folic acid rather than synthesizing it de novo.
各物種劑量
- Coccidiosis (Camelids - E. alpacae, E. lamae, E. punoensis, E. peruviana) · 15 mg/kg PO twice daily for 5 days · PO · q12h · 5 days · Monitor for signs of polioencephalomalacia.
- Coccidiosis (Camelids - E. macusaniensis) · 110 mg/kg PO q24h · PO · q24h · 10-15 days · Administer directly to animal, not in water supply.
- Susceptible infections · 25 mg/kg PO, IV, or IM once daily · PO, IV, IM · q24h
- Susceptible infections · 100 mg/kg PO, IV or IM once daily · PO, IV, IM · q24h
- Susceptible infections · 55 mg/kg PO, or IV, or SC initially, then 27.5 mg/kg once daily thereafter · PO, IV, SC · q24h
- Coccidiosis · 50 mg/kg once daily for 10-14 days · PO · q24h · 10-14 days · Will eliminate oocyst excretion in most cats
- Susceptible infections · 25 mg/kg PO, SC or IM once daily · PO, SC, IM · q24h
- Coccidiosis · 25 mg/kg PO once daily for 14 days · PO · q24h · 14 days
- Susceptible infections · 110 mg/kg PO or IV once daily · PO, IV · q24h
給藥途徑
禁忌症
- Hypersensitivity to sulfonamides, thiazides, or sulfonylurea agents
- Severe renal or hepatic impairment
- Doberman Pinschers (highly susceptible to poly-systemic immune complex disease)
- Dehydrated patients (increased risk of crystalluria)
不良反應
- Crystalluria, hematuria, and renal tubule obstruction (especially with acidic/concentrated urine)
- Keratoconjunctivitis sicca (KCS or 'dry eye') in dogs
- Hypersensitivity reactions (rashes, dermatitis, fever)
- Bone marrow depression
- Nonseptic polyarthritis (especially in Doberman Pinschers)
- Focal retinitis
- Vomiting and diarrhea (due to altered gut flora)
- Muscle weakness, blindness, ataxia, and collapse (if injected IV too rapidly)
- Tissue irritation and necrosis (if injected IM or SC)
藥物相互作用
- Antacids · May decrease the oral bioavailability of sulfonamides if administered concurrently.
監測
- Clinical efficacy and resolution of infection/coccidiosis
- Hydration status and urine output
- Schirmer Tear Test (STT) in dogs (monitor for KCS, especially with prolonged use)
- Complete Blood Count (CBC) if used long-term (monitor for bone marrow depression)
- Signs of hypersensitivity (fever, joint pain, rash)
過量
Acute toxicity secondary to overdoses occurs only rarely in veterinary species. In addition to standard adverse effects (crystalluria, GI upset, hypersensitivity), **CNS stimulation** and **myelin degeneration** have been noted after very high dosages.
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