メトヘキシタール
Methohexital
Methohexital sodium
別名: Brevital · Brevimytal · Brietal · compound 25398 · enallynymalnatrium · methohexitone sodium
VetSheet 獣医チームが監修更新日 2026年4月5日エビデンスに基づく獣医学リファレンス
監査済み v13 用量エビデンス
確認済み・計算対象外のエビデンス確認済み・計算対象外のエビデンス (3)
エビデンス表示のみ（自動計算対象外）
Recovery time of red-sided garter snakes at 21°C (70°F), 125 min; 26°C (79°F), 86 min; 31°C (88°F), 64 min; thinner snakes had longer recovery times; if within 5 wk of parturition, mean recovery time 2 × as long as nongravid; time postfeeding had no effect at 1, 3, 10 days266
TABLE 127.5. Agent: Methohexital (Brevital, Lilly). Dosage: —. Species/Comments: Recovery time of red-sided garter snakes at 21°C (70°F), 125 min; 26°C (79°F), 86 min; 31°C (88°F), 64 min; thinner snakes had longer recovery times; if within 5 wk of parturition, mean recovery time 2 × as long as nongravid; time postfeeding had no effect at 1, 3, 10 days266.
エビデンス表示のみ（自動計算対象外）
Most species/induction, 5–30 min; recovery, 1–5 hr; use at 0.125%–0.5% concentration; much species variability; decrease dose 20%–30% for young animals; avoid use in debilitated animals
TABLE 127.5. Agent: Methohexital (Brevital, Lilly). Dosage: 5–20 mg/kg SC,19 IV89. Species/Comments: Most species/induction, 5–30 min; recovery, 1–5 hr; use at 0.125%–0.5% concentration; much species variability; decrease dose 20%–30% for young animals; avoid use in debilitated animals.
エビデンス表示のみ（自動計算対象外）
Colubrids/induction, ≥ 22 min; recovery, 2–5 hr; does not produce soft-tissue irritation seen with other barbiturates; may need to adjust dosage in obese snakes
TABLE 127.5. Agent: Methohexital (Brevital, Lilly). Dosage: 9–10 mg/kg SC,243 ICe. Species/Comments: Colubrids/induction, ≥ 22 min; recovery, 2–5 hr; does not produce soft-tissue irritation seen with other barbiturates; may need to adjust dosage in obese snakes.
用量は獣医専門家向けの臨床参考資料です。必ず最新の医薬品情報および個別症例に基づいて確認してください。
概要
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.
安全性・警告
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)
注意事項
WARNING: Strictly for IV use. Perivascular extravasation causes severe tissue necrosis. Extravasation injuries can be treated with multiple infiltrates of sterile normal saline and lidocaine for pain.
- Relative Contraindications: Seizure-prone animals, severe cardiovascular disease, preexisting ventricular arrhythmias, shock, increased intracranial pressure, myasthenia gravis, asthma, and conditions with prolonged hypnotic effects (e.g., severe hepatic disease, myxedema, severe anemia).
- Species Warnings: NOT recommended for use in cattle due to unpredictable effects.
- Administration: Repeated dosing or IV infusions are not recommended as recovery times can be significantly prolonged and increase the risk for complications.
医薬品相互作用
Additive CNS and respiratory depression; premedication is usually preferred to reduce methohexital dosage required for inductions and to decrease rough recoveries.
監視
- Plane of anesthesia
- Respiratory rate and depth
- Cardiac rate, rhythm, and blood pressure
- CNS stimulation (seizures) upon recovery
薬物動態
半減期
吸収
Rapid onset of anesthesia (15-60 seconds) after IV injection.
分布
Distribution half-life is 5-6 minutes. Not dependent on redistribution to fat to reverse its effects.
代謝
Rapidly metabolized by the liver.
消失
No drug is detectable in the body 24 hours after administration. Recovery times in small animals average 30 minutes.
過剰投与
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.
製品
製剤
- Powder for injection
ヒト用医薬品
- Methohexital Sodium Powder for Injection: 500 mg & 2.5 grams in 50 mL multiple dose vials
規制ステータス
規制データなし: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
保管・安定性
Store powder at room temperature (<25°C). Reconstitute preferably with sterile water for injection (D5W or 0.9% NaCl may be used for 0.2% concentrations). Do NOT use solutions with bacteriostatic agents. Incompatible with silicone (avoid silicone-treated rubber stoppers/syringes). Do NOT mix with acidic drugs (e.g., atropine, succinylcholine).
飼主向け情報
メトヘキシタールは、手術や短い処置の前にペットを眠らせるために病院内でのみ使用される速効性の麻酔薬です。
- 迅速な作用: 数秒以内に効果が現れ、獣医療チームがペットの気道を素早く確保できます。
- 回復: 特に犬では、目覚める際に「荒い回復」（震え、興奮、鳴き声など）を経験することがあります。獣医療チームは注意深く監視し、この過程をスムーズにするために他の薬を使用することがあります。
- 安全性: この薬の効果が続いている間、ペットの心拍数、呼吸、血圧は継続的に監視されます。
VetSheet医薬品リファレンスは獣医専門家の臨床意思決定支援を目的としており、専門的判断または製造業者の最新医薬品情報の代替にはなりません。