苯妥英
苯妥英是一種乙內醯脲類抗癲癇藥物和 IB 類抗心律不整藥物。 **臨床提示：** 雖然歷史上曾用於獸醫癲癇治療，但由於其在狗體內的半衰期極短（需要頻繁給藥）且具有高肝毒性風險，目前已很少使用，多被苯巴比妥、左乙拉西坦等更安全的藥物取代。 > **警告：** 由於貓缺乏肝臟葡萄糖醛酸結合代謝途徑，苯妥英對貓具有極高毒性，即使極低劑量也會導致嚴重蓄積和中毒。
作用機制: Diminishes the spread of focal neural discharges by promoting sodium efflux from neurons via the **voltage-gated sodium channels** → stabilizes the neuronal membrane → raises the threshold against hyperexcitability. It also acts on Purkinje fibers in the heart to shorten the action potential duration, functioning as a Class IB antiarrhythmic.
給藥途徑
禁忌症
- Cats (due to severe toxicity)
- Hepatic dysfunction
- Bradycardia
- High-grade AV block
不良反應
- Hepatotoxicity (especially in dogs)
- Ataxia
- Sedation
- Gingival hyperplasia
- Peripheral neuropathy
- Hypotension and arrhythmias (with rapid IV administration)
藥物相互作用
- Phenobarbital · Unpredictable effects on serum concentrations of both drugs due to CYP450 induction · moderate
- Chloramphenicol · Inhibits hepatic metabolism of phenytoin, leading to increased levels and toxicity · major
- Cimetidine · Inhibits metabolism of phenytoin, increasing risk of toxicity · moderate
- Corticosteroids · Phenytoin induces hepatic enzymes, increasing the clearance and reducing the efficacy of corticosteroids · moderate
監測
- Serum drug concentrations (therapeutic range typically 10-20 mcg/mL, though rarely monitored now due to infrequent use)
- Liver enzymes (ALT, AST, ALP) and bilirubin
- ECG and blood pressure during IV administration
過量
Clinical signs of overdose include severe ataxia, tremors, lethargy, vomiting, and paradoxical seizures. Rapid IV overdose leads to hypotension and cardiac arrest. **Treatment:** Consists of supportive care, IV fluid therapy, and cardiovascular monitoring. There is no specific antidote.
VetSheet 藥物參考供持牌獸醫專業人員作臨床決策輔助之用,不能取代專業判斷或廠方最新藥品說明書。