Methohexital
Methohexital is an ultra-short-acting methylated oxybarbiturate anesthetic agent. While largely replaced by propofol in modern veterinary medicine, it retains niche utility, particularly in **sight hounds** (e.g., Greyhounds) because its termination of effect relies on rapid hepatic metabolism rather than redistribution to fat. It is also advantageous for rapid sequence intubation in patients with a full stomach, allowing an endotracheal tube to be placed rapidly before aspiration of vomitus can occur. **Clinical Pearls**: - It lacks analgesic and muscle relaxant properties. - It is highly irritating to tissues; perivascular extravasation can cause severe localized necrosis. - It is about twice as potent as thiopental with half the duration of action.
กลไกการออกฤทธิ์: 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.
ขนาดยาตามชนิดสัตว์
- Induction or sole anesthetic in non-premedicated cats · 11 mg/kg · IV · once · give approximately 1/2 the dose rapidly and then titrate to effect.
- Induction or sole anesthetic in premedicated cats · 5.5-6.6 mg/kg · IV · once · 10-30% is given rapidly IV and then the remainder titrated to effect.
- Induction with premedication · 5 mg/kg · IV · once · give 1/2 to 3/4 of dose over 10 seconds. In 30 seconds if adequate plane is not reached to allow intubation, give additional drug. Delay will result in poor induction due to rapid redistribution.
- Induction or sole anesthetic in non-premedicated dogs · 11 mg/kg · IV · once · give approximately 1/2 the dose rapidly and then titrate to effect.
- Induction or sole anesthetic in premedicated dogs · 5.5-6.6 mg/kg · IV · once · 10-30% is given rapidly IV and then the remainder titrated to effect.
ขนาดยาเป็นข้อมูลอ้างอิงทางคลินิกสำหรับสัตวแพทย์ผู้มีใบอนุญาต โปรดตรวจสอบกับฉลากล่าสุดและผู้ป่วยแต่ละรายเสมอ
วิธีการให้ยา
ข้อห้ามใช้
- Absence of suitable veins for IV administration
- History of hypersensitivity reactions to barbiturates
- Status asthmaticus
- Cattle (due to unpredictable effects)
อาการไม่พึงประสงค์
- Apnea
- Hypotension
- Muscle tremors
- Seizures during recovery
- Rough recoveries (especially in dogs)
- Profound respiratory depression
- Tissue necrosis (if extravasated)
อันตรกิริยาระหว่างยา
- CNS Depressants (e.g., alpha2-agonists, opioids) · Additive CNS and respiratory depression; premedication is usually preferred to reduce methohexital dosage required for inductions and to decrease rough recoveries.
การติดตาม
- Plane of anesthesia
- Respiratory rate and depth
- Cardiac rate, rhythm, and blood pressure
- CNS stimulation (seizures) upon recovery
การได้รับยาเกินขนาด
**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.
ข้อมูลอ้างอิงยาของ VetSheet มีไว้สำหรับสัตวแพทย์ผู้มีใบอนุญาตเพื่อช่วยในการตัดสินใจทางคลินิก ไม่ใช่สิ่งทดแทนการวินิจฉัยของผู้เชี่ยวชาญหรือฉลากล่าสุดของผู้ผลิต