阿法沙龍
**阿法沙龍 (Alfaxalone)** 是一種神經活性類固醇分子，作為一種速效中樞神經系統抑制劑和全身麻醉藥。它主要用於獸醫病患的麻醉誘導與維持。 **臨床要點與藥理特性：** * **配方演進：** 現代配方 (Alfaxan®) 使用 2-羥丙基-β-環糊精 (HPCD) 作為助溶劑。這比歷史產品 (Saffan®) 有了顯著改進，舊產品含有聚氧乙烯蓖麻油 (Cremophor EL)，會引起嚴重的組織胺釋放和過敏反應（特別是在貓）。 * **心肺影響：** 雖然通常被認為具有較寬的安全範圍，但阿法沙龍會引起劑量依賴性的呼吸抑制和誘導後呼吸中止，特別是如果靜脈注射過快時。心血管參數通常維持良好，儘管可能會出現代償性心搏過速。 * **鎮痛作用：** 阿法沙龍**幾乎沒有鎮痛效果**。對於疼痛性操作，必須結合適當的純鎮痛藥（例如鴉片類藥物）。 * **恢復：** 由於其半衰期短且無蓄積性，恢復通常快速且平穩，但如果受到刺激或術前給藥/鎮痛不足，病患可能會經歷精神運動性興奮（划水動作、發聲、抽搐）。
作用機制: Alfaxalone exerts its anesthetic effects by interacting with **GABA_A (gamma-aminobutyric acid type A) receptors** in the central nervous system. * **Mechanism:** It binds to specific transmembrane domains on the GABA_A receptor complex. * **Pathway:** Binding → Enhances the binding of the inhibitory neurotransmitter GABA to the receptor → Increases the frequency and duration of **chloride (Cl⁻) ion channel** opening → Influx of chloride ions into the neuron → **Hyperpolarization** of the postsynaptic cell membrane → Inhibition of neural action potential transmission → Dose-dependent CNS depression (ranging from sedation to general anesthesia).
各物種劑量
- Anesthesia Induction (Premedicated) · 3 mg/kg · IV · once · Administer over first 60 seconds to effect. If intubation not possible, one further similar dose may be administered.
- Anesthesia Induction (Unpremedicated) · 2 mg/kg · IV · once · Administer over first 60 seconds to effect.
- Anesthesia Induction (Alternative) · 1-2 mg/kg · IV · once · Slowly over 20-30 seconds while assessing degree of anesthesia.
- Anesthesia Maintenance (CRI, Premedicated) · 0.1-0.12 mg/kg/minute · IV · CRI · Up to 1 hour · Equivalent to 6-7 mg/kg/hour.
- Anesthesia Maintenance (CRI, Unpremedicated) · 0.13-0.15 mg/kg/minute · IV · CRI · Up to 1 hour · Equivalent to 8-9 mg/kg/hour.
- Anesthesia Maintenance (Bolus, Premedicated) · 1-1.2 mg/kg · IV · q10m · Up to 1 hour · Administer every 10 minutes as needed.
- Anesthesia Maintenance (Bolus, Unpremedicated) · 1.3-1.5 mg/kg · IV · q10m · Up to 1 hour · Administer every 10 minutes as needed.
- Anesthesia Maintenance (Alternative Bolus) · 5-12 mg/kg total dose · IV · incremental · 5-7 mg/kg total for short procedures; 8-12 mg/kg total for longer procedures.
- Anesthesia Induction · 5 mg/kg · IV · once · Premedicated or unpremedicated. Administer over first 60 seconds to effect.
給藥途徑
禁忌症
- Concurrent use with other injectable general anesthetic agents (e.g., propofol, thiopental)
- Situations where endotracheal intubation, positive pressure ventilation, and oxygen support are unavailable
- Animals less than 12 weeks of age (safety not established)
不良反應
- Respiratory depression
- Post-induction apnea
- Hypotension (dose-dependent)
- Cardiac arrhythmias (primarily secondary to hypoxemia/hypercapnia)
- Psychomotor excitement during recovery (especially if unstimulated or lacking premedication)
藥物相互作用
- CNS Depressants (e.g., acepromazine, opioids, alpha-2 agonists, benzodiazepines) · Potentiates the CNS and respiratory depressant effects. Significantly reduces the required induction and maintenance doses of alfaxalone.
- Propofol · Should not be used concurrently according to the manufacturer label.
- Thiopental · Should not be used concurrently according to the manufacturer label.
- Other IV anaesthetic agents · Increased risk of severe CNS and respiratory depression · major
- Premedicants (e.g., sedatives, opioids) · Synergistic CNS depression; significantly reduces the required induction dose of alfaxalone · moderate
- Opioids (e.g., methadone, buprenorphine) · Synergistic CNS depression; reduces the required induction dose of alfaxalone. · moderate
- Alpha-2 agonists (e.g., dexmedetomidine) · Profound synergy; significantly reduces alfaxalone dose requirements and may exacerbate cardiovascular and respiratory depression. · major
- Phenothiazines (e.g., acepromazine) · Enhanced sedation and increased risk of hypotension. · moderate
- Opioids (e.g., butorphanol, methadone) · Synergistic CNS depression; significantly reduces the required induction dose of alfaxalone. · moderate
- Benzodiazepines (e.g., midazolam) · Synergistic CNS depression; reduces alfaxalone dose requirements. · moderate
監測
- Level of anesthesia / CNS depression (jaw tone, palpebral reflex)
- Respiratory rate, rhythm, and depth (capnography and pulse oximetry highly recommended due to apnea risk)
- Cardiovascular status (heart rate, ECG rhythm, blood pressure)
- Body temperature (monitor for hypothermia during anesthesia)
過量
Overdoses up to 25 mg/kg primarily result in severe cardiorespiratory depression. **Clinical Signs of Toxicity:** * Severe hypoventilation and prolonged apnea * Hypotension * Cardiac arrhythmias **Treatment:** * Immediate endotracheal intubation and positive pressure ventilation with 100% oxygen. * Cardiovascular support (IV fluids, vasopressors/inotropes if hypotension is severe). * Continuous monitoring until the drug is metabolized and cleared.
VetSheet 藥物參考供持牌獸醫專業人員作臨床決策輔助之用,不能取代專業判斷或廠方最新藥品說明書。