美索比妥
美索比妥（Methohexital）是一種超短效的甲基氧巴比妥類麻醉劑。雖然在現代獸醫學中已很大程度上被異丙酚（Propofol）取代，但它在特定情況下仍具實用性，特別是對於**視覺獵犬**（如靈緹犬），因為其作用的終止依賴於快速的肝臟代謝，而非重新分佈到脂肪組織。它也有利於胃部充滿食物的病患進行快速插管，以防止嘔吐物吸入。 **臨床要點**： - 本藥不具鎮痛或肌肉鬆弛作用。 - 對組織具強烈刺激性；若發生血管外滲漏會導致嚴重的局部組織壞死。 - 其效力約為硫噴妥（Thiopental）的兩倍，但作用時間僅為其一半。
作用機制: Methohexital produces dose-dependent CNS depression by depressing the **reticular activating system** in the brainstem. - **Mechanism**: Binds to the **GABA_A receptor** complex → prolongs the opening of **chloride channels** → increases intracellular chloride influx → cellular hyperpolarization → profound inhibition of neuronal firing. - **Termination of Effect**: Unlike thiobarbiturates, methohexital is rapidly metabolized by the liver and does not depend on redistribution to fat to reverse its effects.
各物種劑量
- Induction or sole anesthetic in non-premedicated cats · 11 mg/kg · IV · once · give approximately 1/2 the dose rapidly and then titrate to effect.
- Induction or sole anesthetic in premedicated cats · 5.5-6.6 mg/kg · IV · once · 10-30% is given rapidly IV and then the remainder titrated to effect.
- Induction with premedication · 5 mg/kg · IV · once · give 1/2 to 3/4 of dose over 10 seconds. In 30 seconds if adequate plane is not reached to allow intubation, give additional drug. Delay will result in poor induction due to rapid redistribution.
- Induction or sole anesthetic in non-premedicated dogs · 11 mg/kg · IV · once · give approximately 1/2 the dose rapidly and then titrate to effect.
- Induction or sole anesthetic in premedicated dogs · 5.5-6.6 mg/kg · IV · once · 10-30% is given rapidly IV and then the remainder titrated to effect.
劑量為持牌獸醫專業人員的臨床參考。請務必對照最新藥品說明書及個別病患確認。
給藥途徑
禁忌症
- Absence of suitable veins for IV administration
- History of hypersensitivity reactions to barbiturates
- Status asthmaticus
- Cattle (due to unpredictable effects)
不良反應
- Apnea
- Hypotension
- Muscle tremors
- Seizures during recovery
- Rough recoveries (especially in dogs)
- Profound respiratory depression
- Tissue necrosis (if extravasated)
藥物相互作用
- CNS Depressants (e.g., alpha2-agonists, opioids) · Additive CNS and respiratory depression; premedication is usually preferred to reduce methohexital dosage required for inductions and to decrease rough recoveries.
監測
- Plane of anesthesia
- Respiratory rate and depth
- Cardiac rate, rhythm, and blood pressure
- CNS stimulation (seizures) upon recovery
過量
**Narrow Safety Margin**: The lethal dose may only be 2-3 times the anesthetic dose. - **Clinical Signs**: Profound respiratory depression, apnea, hypotension, and cardiovascular collapse. - **Treatment**: Requires immediate mechanical ventilation and cardiovascular support. Postoperative seizures have been reported and can be treated with IV diazepam.
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。