苯妥英
Phenytoin
Diphenylhydantoin
別名: pro-Epanutin · Dilantin · Diphenylhydantoin · DPH
由 VetSheet 獸醫團隊審訂更新於 2026年4月5日本內容以實證獸醫文獻為本
各物種劑量
此藥的劑量資料尚未收錄於 VetSheet 藥典，以下其他章節資料完整。開立處方前請參閱最新仿單。
概覽
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。
作用機轉
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.
安全性與警告
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)
注意事項
Warning: Highly toxic in cats. Warning: Rapid IV administration can cause severe hypotension, bradycardia, and cardiovascular collapse. Always administer IV slowly and monitor ECG.
藥物交互作用
Unpredictable effects on serum concentrations of both drugs due to CYP450 induction
Inhibits hepatic metabolism of phenytoin, leading to increased levels and toxicity
Inhibits metabolism of phenytoin, increasing risk of toxicity
Phenytoin induces hepatic enzymes, increasing the clearance and reducing the efficacy of corticosteroids
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
藥物動力學
半衰期
吸收
Variable and unpredictable oral absorption in dogs.
分佈
Highly protein-bound (70-90%). Distributes rapidly into the CNS.
代謝
Undergoes extensive hepatic metabolism via CYP450 enzymes. Dogs metabolize phenytoin extremely rapidly, whereas cats metabolize it extremely slowly due to deficient glucuronidation.
排除
Excreted primarily in the urine as inactive metabolites.
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.
可用產品
劑型
- Oral capsules: 25 mg, 50 mg, 100 mg, 300 mg
- Oral tablets: 100 mg
- Oral chewable tablets: 50 mg
- Oral suspension: 30 mg/5 ml
- Injectable solution: 50 mg/ml
- Injectable fosphenytoin: 75 mg/ml (equivalent to 50 mg/ml phenytoin)
人用標示
- Epanutin capsules (25 mg, 50 mg, 100 mg, 300 mg)
- Epanutin Infatabs (50 mg chewable)
- Epanutin suspension (30 mg/5 ml)
- pro-Epanutin injection (fosphenytoin 75 mg/ml)
各地核准狀態
POM (Prescription Only Medicine). Primarily human-authorized products used off-label under the cascade.
POM (Prescription Only Medicine). Primarily human-authorized products used off-label under the cascade.
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儲存與穩定性
Store at room temperature (15-30°C) in tight, light-resistant containers. Do not freeze the oral suspension or injectable solutions.
飼主須知
請嚴格按照獸醫指示給藥。切勿突然停藥，否則可能引發嚴重癲癇發作。
如果您的寵物出現黃疸（牙齦或眼白發黃）、嚴重嗜睡、嘔吐或步態不穩，請立即聯繫獸醫。
極度危險： 絕對不可將此藥物給予貓咪。
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