乙醯半胱胺酸
乙醯半胱胺酸（常被稱為 NAC）在獸醫學中是一種用途廣泛的治療藥物。它最主要被用作**普拿疼（對乙醯氨基酚）中毒的救命解毒劑**，特別是在貓和狗身上，能預防嚴重的肝臟壞死和變性血紅素血症。 除了作為解毒劑外，乙醯半胱胺酸也是一種強效的**祛痰劑（黏液溶解劑）**。當投予至呼吸道時，它能有效分解濃稠的黏液，幫助清除呼吸道分泌物。 **臨床應用：** * **毒物學：** 治療對乙醯氨基酚、木糖醇和苯酚中毒的主要藥物。 * **呼吸系統：** 透過霧化或氣管內滴注，治療慢性上呼吸道疾病或黏液過多的情況。 * **眼科：** 局部應用於抑制膠原蛋白酶，阻止「融化性」角膜潰瘍的惡化。 * **馬科醫學：** 局部使用以溶解喉囊內的軟骨樣凝塊，並作為灌腸劑治療新生小馬頑固性胎便阻塞。 * **內科：** 作為貓脂肪肝的輔助治療，以及犬退化性脊髓病的軼事性療法。
作用機制: **Antidote Mechanism (Hepatoprotection):** Acetaminophen is metabolized in the liver to a highly reactive and toxic intermediate called **NAPQI** (N-acetyl-p-benzoquinone imine). Normally, NAPQI is safely conjugated by endogenous **glutathione**. In an overdose, glutathione is rapidly depleted, allowing NAPQI to cause severe oxidative stress and hepatocellular necrosis. Acetylcysteine acts as a **glutathione precursor** and provides an alternate sulfhydryl substrate to conjugate directly with NAPQI, thereby neutralizing the toxin and restoring cellular antioxidant defenses. **Mucolytic Mechanism:** The free **sulfhydryl group (-SH)** on the acetylcysteine molecule directly interacts with mucoproteins in respiratory secretions. It cleaves the **disulfide bonds** linking these proteins, which drastically reduces the viscosity of both purulent and non-purulent mucus. This effect is optimal in an alkaline environment (pH 7-9). It has no effect on living tissue or fibrin.
各物種劑量
- Acetaminophen toxicity · 140 mg/kg PO loading dose, followed by 70 mg/kg PO q6h · PO · q6h · For 7 treatments (up to 12-17 doses for massive ingestions) · Dilute to 5% in dextrose or sterile water. May also be given slow IV over 15-20 minutes. Wait 2-3 hours after activated charcoal if giving PO.
- Acetaminophen toxicity · 150 mg/kg PO or IV initially, then 50 mg/kg q4h · PO/IV · q4h · For 17 additional doses
- Acetaminophen toxicity · 140 mg/kg PO loading dose, then 70 mg/kg PO every 6 hours · PO · q6h · For 7 treatments
- Phenol toxicity · 140 mg/kg PO or IV initially, then 50 mg/kg q4h · PO/IV · q4h · For 3 days · May be partially effective to reduce hepatic and renal injury.
- Hepatotoxicity secondary to xylitol poisoning · 140-280 mg/kg loading dose IV or PO; followed by 70 mg/kg four times daily · IV/PO · q6h · Used as part of a comprehensive protocol including vitamin K, plasma, SAMe, vitamin E, and silymarin.
- Degenerative myelopathy (anecdotal) · 25 mg/kg PO q8h for 2 weeks, then q8h every other day · PO · q8h · Indefinitely (every other day after 2 weeks) · Dilute 20% solution to 5% with chicken broth. Used in conjunction with aminocaproic acid. Note: No treatment has been shown to be effective in published trials.
- Mucolytic · nebulize 50 mg as a 2% (dilute with saline) solution over 30-60 min or instil directly into the trachea 1-2 ml of a 20% solution · Nebulization/Intratracheal · prn · As needed · Dilute with saline for nebulization.
- Paracetamol poisoning · 140-280 mg/kg diluted to a 5% solution using 5% dextrose by slow i.v. infusion over 15-20 min, followed by further slow infusions of 70 mg/kg (similarly diluted) every 6 hours · IV · q6h · for at least 7 doses · Administer after inducing emesis if appropriate (within 2 hours of ingestion). IV preferred for serious intoxications. Can be given PO but must be diluted to improve palatability.
給藥途徑
禁忌症
- Hypersensitivity to the drug (specifically for pulmonary indications)
不良反應
- Nausea and vomiting (especially with oral administration due to poor palatability)
- Urticaria (rare)
- Bronchospasm, chest tightness, and bronchial/tracheal irritation (when inhaled)
- Blood pressure changes and allergic reactions (reported with IV boluses in humans)
藥物相互作用
- Activated Charcoal · May adsorb orally administered acetylcysteine, potentially reducing its systemic absorption and efficacy. A 2-3 hour wait between charcoal and oral acetylcysteine is recommended, or acetylcysteine should be given intravenously. · moderate
監測
- Hepatic enzymes (especially in dogs)
- Acetaminophen levels (if available)
- Hemogram, specifically monitoring methemoglobin values (especially critical in cats)
- Serum electrolytes
- Hydration status
過量
Acetylcysteine is considered quite safe in overdose situations. The LD50 in dogs is reported to be 1 g/kg orally and 700 mg/kg intravenously. Massive overdoses may result in gastrointestinal distress (nausea, vomiting) or hypersensitivity reactions, but life-threatening toxicity from the drug itself is rare.
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