チオペンタールナトリウム
チオペンタールナトリウムは、主に全身麻酔の導入や極めて短時間の処置における単独麻酔薬として使用される超短時間作用型チオバルビツール酸系薬剤です。 **臨床上のポイント：** * **再分布の動態：** 作用時間が短い（10〜30分）のは、急速な代謝によるものではなく、血流の豊富な中枢神経系から筋肉や脂肪組織への急速な再分布によるものです。 * **サイトハウンドの感受性：** グレイハウンドなどのサイトハウンドは、代謝の違いや体脂肪の少なさから回復が遅延します。プロポフォール、アルファキサロン、メトヘキシタールなどの代替導入薬が一般的に推奨されます。 * **組織毒性：** チオペンタール溶液は強アルカリ性（pH > 10）です。**血管外漏出は重度の組織刺激と壊死を引き起こします。** 確実な静脈カテーテルを介して投与する必要があります。 * **不整脈誘発性：** カテコールアミンに対する心筋の感受性を高め、犬では一過性の心室性二段脈をよく引き起こします。
作用機序: Thiopental is a highly lipid-soluble thiobarbiturate. * **Mechanism:** It binds to the **GABA_A receptor** complex in the central nervous system. * **Pathway:** Binding → increases the duration of chloride ion channel opening → enhances chloride influx → hyperpolarization of the postsynaptic neuronal membrane → profound CNS depression, hypnosis, and anesthesia. * Due to its high lipid solubility, it rapidly crosses the blood-brain barrier, resulting in anesthesia within 15-30 seconds of IV injection.
動物種別の用量
- Anesthesia · 9.9-15 mg/kg · IV · once · depending on depth required
- Anesthesia · 20-22 mg/kg · IV · once · Given after atropine (0.7 mg/kg) IM
- Anesthesia · 13.2-26.4 mg/kg · IV · once · depending on duration of anesthesia required
- Anesthesia (unpremedicated) · 22 mg/kg · IV · once
- Anesthesia (after tranquilization) · 15.4 mg/kg · IV · once
- Anesthesia (after narcotic premedication) · 11 mg/kg · IV · once
- Anesthesia induction · 12-15 mg/kg · IV · once · One-third administered rapidly, additional amount to effect
- Anesthesia · 8.14-15.4 mg/kg · IV · once
- Deep surgical anesthesia (unweaned calves fasted 6-12h) · no more than 6.6 mg/kg · IV · once
- Anesthesia (calves under 2 weeks of age) · 15-22 mg/kg · IV · once · 10-12 minutes · Administer slowly until complete muscular relaxation
投与経路
禁忌
- Absence of suitable veins for IV administration (Absolute)
- History of hypersensitivity to barbiturates (Absolute)
- Status asthmaticus (Absolute)
- Preexisting leukopenia in horses
- Use with extreme caution or avoid in greyhounds and other sight hounds
- Relative: Severe cardiovascular disease, ventricular arrhythmias, shock, increased intracranial pressure, myasthenia gravis, severe hepatic disease
有害事象
- Ventricular bigeminy (dogs)
- Apnea (especially in cats)
- Arterial hypotension
- Excitement and severe ataxia during recovery (horses, if used alone)
- Transient leukopenia and hyperglycemia (horses)
- Vascular dilatation and hypoglycemia (with rapid IV administration)
- Severe tissue necrosis (if administered perivascularly)
- Prolonged recovery with repeated doses
薬物相互作用
- Clonidine · IV clonidine prior to induction may reduce thiopental dosage requirements by up to 37%
- CNS Depressants · May enhance respiratory and CNS depressant effects
- Diazoxide · Potential for hypotension
- Epinephrine / Norepinephrine · Ventricular fibrillatory effects may be potentiated when used with thiobarbiturates and halothane
- Metoclopramide · Given prior to induction may reduce thiopental dosage requirements
- Midazolam · May potentiate hypnotic effects
- Opiates · Given prior to induction may reduce thiopental dosage requirements
- Phenothiazines · May potentiate thiopental effects; hypotension possible
- Probenecid · May displace thiopental from plasma proteins
- Sulfonamides · Thiopental and sulfas may displace one another from plasma proteins
モニタリング
- Level of hypnosis/anesthesia
- Respiratory status (rate, depth, apnea)
- Cardiac status (heart rate, rhythm, blood pressure)
過量投与
Treatment of thiobarbiturate overdosage consists of: * **Respiratory Support:** Provide oxygen (O2) and mechanical ventilation. * **Cardiovascular Support:** Provide IV fluids and supportive care. > **Note:** Do NOT use catecholamines (e.g., epinephrine) as they may induce fatal ventricular arrhythmias in the presence of thiobarbiturates.
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