戊巴比妥
**戊巴比妥 (Pentobarbital)** 是一種短效的氧巴比妥類藥物，在獸醫學中主要用於全身麻醉、化學保定以及難治性癲癇重積狀態的處理。 雖然過去常作為全身麻醉劑，但由於其治療指數狹窄且具有強烈的心肺抑制作用，目前已大多被更安全、更易滴定的藥物（如丙泊酚 Propofol 或阿法沙龍 Alfaxalone）所取代。 **臨床要點：** * **癲癇重積狀態：** 戊巴比妥常被用於誘導難治性癲癇患者進入「巴比妥昏迷」狀態。然而，在標準劑量下，它主要作為全身麻醉劑，缺乏真正的抗癲癇特性；它能停止癲癇的肢體表現，但可能無法阻止大腦內潛在的異常放電。 * **呼吸支持：** 因嚴重癲癇而接受戊巴比妥治療的病患，通常會出現嚴重的呼吸抑制，需要機械通氣和加護病房監測。 * **安樂死：** 在極高劑量下，戊巴比妥是大多數獸醫安樂死溶液的主要活性成分。 * **酵素誘導：** 長期使用會強烈誘導肝臟細胞色素 P450 酵素，加速許多併用藥物的代謝。
作用機制: 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.
各物種劑量
- 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
給藥途徑
禁忌症
- 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
不良反應
- 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)
藥物相互作用
- 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
監測
- 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
**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.
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