メトヘキシタール
メトヘキシタールは超短時間作用型のメチル化オキシバルビツール酸系麻酔薬です。現代の獣医療では主にプロポフォールに取って代わられていますが、作用の消失が脂肪への再分布ではなく急速な肝代謝に依存するため、特に**サイトハウンド**（グレイハウンドなど）において有用性を保っています。また、胃が満たされている患者の迅速な気管挿管にも有利であり、嘔吐物の誤嚥を防ぐことができます。 **臨床のポイント**: - 鎮痛作用や筋弛緩作用はありません。 - 組織に対する刺激性が非常に強く、血管外に漏出すると重篤な局所組織壊死を引き起こす可能性があります。 - チオペンタールの約2倍の効力を持ちますが、作用時間は半分です。
作用機序: 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.
動物種別の用量
- 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.
用量は獣医療従事者向けの臨床リファレンスです。必ず最新の添付文書と個々の患者で確認してください。
投与経路
禁忌
- Absence of suitable veins for IV administration
- History of hypersensitivity reactions to barbiturates
- Status asthmaticus
- Cattle (due to unpredictable effects)
有害事象
- Apnea
- Hypotension
- Muscle tremors
- Seizures during recovery
- Rough recoveries (especially in dogs)
- Profound respiratory depression
- Tissue necrosis (if extravasated)
薬物相互作用
- 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.
モニタリング
- Plane of anesthesia
- Respiratory rate and depth
- Cardiac rate, rhythm, and blood pressure
- CNS stimulation (seizures) upon recovery
過量投与
**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 の薬剤リファレンスは、獣医療従事者向けの臨床意思決定支援を目的としており、専門的判断やメーカーの最新添付文書に代わるものではありません。