ペントバルビタール
**ペントバルビタール**は、獣医学において主に全身麻酔、化学的保定、および難治性てんかん重積状態の管理に使用される短時間作用型のオキシバルビツール酸系薬物です。 歴史的には全身麻酔薬として普及していましたが、治療域が狭く、強力な心肺抑制作用があるため、現在ではより安全で用量調整が容易な薬剤（プロポフォールやアルファキサロンなど）に大部分が取って代わられています。 **臨床のポイント:** * **てんかん重積状態:** 難治性てんかん患者を「バルビツール酸昏睡」に導入するためによく使用されます。ただし、標準用量では真の抗てんかん作用は乏しく、全身麻酔薬として機能します。発作の身体的症状は止めますが、脳内の潜在的な発作活動を停止させない可能性があります。 * **呼吸管理:** ペントバルビタールで治療を受ける患者は、強力な呼吸抑制のため、通常、人工呼吸器と集中治療室でのモニタリングが必要です。 * **安楽死:** 非常に高用量では、ほとんどの獣医用安楽死液の主成分となります。 * **酵素誘導:** 長期使用は肝臓のシトクロムP450酵素を強力に誘導し、併用薬の代謝を促進します。
作用機序: Pentobarbital exerts its profound central nervous system (CNS) depressant effects by interacting with the inhibitory neurotransmitter system. * **GABA_A Receptor Modulation:** Binds to the barbiturate site on the **GABA_A receptor** → increases the *duration* of chloride channel opening → enhances chloride influx → hyperpolarization of the postsynaptic neuronal membrane. * **Glutamate Inhibition:** At higher anesthetic doses, it also depresses the actions of the excitatory neurotransmitter glutamate via **AMPA receptors**. * **Result:** Dose-dependent CNS depression ranging from mild sedation to general anesthesia, coma, and fatal respiratory depression.
動物種別の用量
- For chemical restraint for ventilatory support · 1-3 mg/kg/hour · IV · CRI · Switch to shorter acting drug like propofol ~12 hours prior to weaning. Adjunctive drugs: Midazolam 0.3-0.5 mg/kg/hr; Medetomidine 0.3-1 mcg/kg/hr (caution with medetomidine).
- As a sedative · 2-4 mg/kg · IV · single dose
- As a sedative · 2-4 mg/kg · PO · q6h
- For status epilepticus · 5-15 mg/kg to effect · IV · single dose
- For status epilepticus · 3-15 mg/kg SLOWLY to effect · IV · single dose · Goal is heavy sedation, not surgical planes of anesthesia. May need to repeat in 4-8 hours.
- For anesthesia · 25 mg/kg · IV · single dose · An additional 10 mg/kg IV may be given if initial dose is inadequate.
- Euthanasia · 80 mg/kg in debilitated animals, up to 120-160 mg/kg in younger and fitter animals · IV · once · single dose · Rapid IV injection. Premedication recommended to prevent narcotic excitement.
- General · 30 mg/kg to effect · IV · single dose
- As an anesthetic · 15-30 mg/kg · IV · single dose
- As an anesthetic · 20-30 mg/kg · IV · single dose
投与経路
禁忌
- Severe hepatic impairment
- Severe respiratory depression or airway obstruction
- Porphyria
- Hypovolemia or severe cardiovascular instability (relative contraindication)
- Intramuscular (IM) administration (painful and slow to act)
- Use of euthanasia-specific solutions for seizure control or anesthesia
有害事象
- Profound respiratory depression (apnea)
- Depression of myocardial metabolism
- Vasodilation and decreased venous return
- Hypotension and decreased cardiac perfusion
- Poikilothermia (hypothermia)
- Decreased urinary output
- Seizure-like movements or excitement during recovery from anesthesia
- Excitement and injury during induction/recovery in large animals (especially horses)
- Narcotic excitement (if not premedicated)
- Agonal gasping (reflexive, not a sign of pain)
- Muscle twitching
- Vocalization (rare, usually associated with excitement phase)
薬物相互作用
- Oral Anticoagulants (Warfarin) · Decreased effect by lowering serum concentration (due to hepatic enzyme induction)
- Beta-blockers · Decreased effect by lowering serum concentration
- Chloramphenicol · Decreased effect by lowering serum concentration
- Clonazepam · Decreased effect by lowering serum concentration
- Corticosteroids · Decreased effect by lowering serum concentration
- Cyclosporine · Decreased effect by lowering serum concentration
- Doxorubicin · Decreased effect by lowering serum concentration
- Doxycycline · Decreased effect (may persist for weeks after barbiturate is discontinued)
- Estrogens · Decreased effect by lowering serum concentration
- Griseofulvin · Decreased effect by lowering serum concentration
- Methadone · Decreased effect by lowering serum concentration
- Metronidazole · Decreased effect by lowering serum concentration
- Quinidine · Decreased effect by lowering serum concentration
モニタリング
- Levels of consciousness and/or seizure control
- Respiratory rate, rhythm, and depth (capnography and pulse oximetry highly recommended)
- Cardiac signs (heart rate, blood pressure, ECG)
- Body temperature (monitor for poikilothermia)
- Routine blood counts and liver function tests (if used chronically)
- Absence of heartbeat (auscultation)
- Absence of respiration
- Loss of corneal reflex
- Pupillary dilation
過量投与
**Overdose** of pentobarbital leads to profound central nervous system depression, progressing rapidly to coma, severe respiratory depression (apnea), cardiovascular collapse, and death. * **Treatment:** There is no specific reversal agent for barbiturates. Treatment is entirely supportive. * **Interventions:** Immediate intubation and mechanical ventilation are required. Intravenous fluids and vasopressors (e.g., dopamine) should be administered to support blood pressure and cardiac output. Maintain body temperature to prevent severe hypothermia.
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。