Thiopental Sodium
Thiopental sodium is an ultra-short-acting thiobarbiturate used primarily for the induction of general anesthesia or as a sole anesthetic for very brief procedures. **Clinical Pearls:** * **Redistribution Kinetics:** Its short duration of action (10-30 minutes) is due to rapid redistribution from the highly perfused CNS to muscle and adipose tissue, rather than rapid metabolism. * **Sight Hound Sensitivity:** Greyhounds and other sight hounds exhibit prolonged recoveries due to differences in metabolic handling and lower body fat; alternative induction agents (e.g., propofol, alfaxalone, or methohexital) are generally preferred. * **Tissue Toxicity:** Thiopental solutions are highly alkaline (pH > 10). **Perivascular extravasation causes severe tissue irritation and necrosis.** It must be administered via a secure IV catheter. * **Arrhythmogenic:** It can sensitize the myocardium to catecholamines, commonly causing transient ventricular bigeminy in dogs.
กลไกการออกฤทธิ์: 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.
ขนาดยาตามชนิดสัตว์
- 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
วิธีการให้ยา
ข้อห้ามใช้
- 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
อาการไม่พึงประสงค์
- 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
อันตรกิริยาระหว่างยา
- 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
การติดตาม
- Level of hypnosis/anesthesia
- Respiratory status (rate, depth, apnea)
- Cardiac status (heart rate, rhythm, blood pressure)
การได้รับยาเกินขนาด
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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