布托啡諾
**布托啡諾 (Butorphanol)** 是一種合成的鴉片類部分促效劑，廣泛應用於多種動物的獸醫學中。 * **鎮痛作用**：提供輕至中度的內臟鎮痛。由於其「天花板效應 (ceiling effect)」，增加劑量並不會增強鎮痛效果，因此不適用於嚴重疼痛（如大型骨科手術）。 * **鎮咳作用**：對抑制犬隻的慢性非生產性咳嗽（如傳染性氣管支氣管炎、氣管塌陷）非常有效。 * **逆轉劑**：能獨特地逆轉純粹的 mu-促效劑（如芬太尼、美沙酮或嗎啡）所引起的嚴重呼吸和中樞神經抑制，同時仍保留一定程度由 kappa 受體介導的鎮痛效果。 * **鎮靜作用**：常與 alpha-2 促效劑（如右美托咪啶或甲苯噻嗪）及苯二氮平類藥物合併使用，以達到協同鎮靜和化學保定的效果。 > **臨床要點**：雖然布托啡諾在小動物中是極佳的鎮咳劑和輕度鎮靜劑，但其作用時間極短（犬隻的鎮痛作用通常小於 1 小時），限制了它作為主要鎮痛劑的實用性。相反地，它在馬匹（例如治療疝痛）中是一種非常有效且常用的內臟鎮痛劑。
作用機制: Butorphanol exerts its effects by interacting with specific opioid receptors in the central nervous system: * **Kappa (κ) and Sigma (σ) Agonist**: Activation of κ-receptors in the limbic system and spinal cord provides visceral analgesia and sedation. * **Mu (μ) Antagonist**: Competitively binds to and blocks μ-receptors. This antagonism is responsible for its ability to reverse pure μ-agonist drugs and is the reason for its analgesic "ceiling effect." * **Antitussive Mechanism**: Directly suppresses the **medullary cough center**, elevating the threshold to stimuli (like CO2) without depressing respiratory center sensitivity as profoundly as pure agonists. * **Cellular Pathway**: Binds to κ-receptors → inhibits adenylate cyclase → decreases intracellular cAMP → closes voltage-gated calcium channels and opens potassium channels → hyperpolarization and reduced neuronal excitability.
各物種劑量
- As an analgesic · 0.1-0.5 mg/kg IV, IM, SQ · IV/IM/SC · PRN · Provides only mild to moderate analgesia; duration of sedative action 2-4 hours, but analgesic action may be 1 hour or less.
- As a postoperative CRI · Loading dose of 0.1-0.2 mg/kg IV, then a CRI of 0.1-0.2 mg/kg/hr · IV · CRI · Usually in combination with ketamine (loading dose 0.1 mg/kg IV, CRI 0.4 mg/kg/hr).
- As an epidural analgesic · 0.25 mg/kg diluted with preservative-free saline (0.2 mL) or local anesthetic epidurally · Epidural · Once · 2-4 hours · Onset of action less than 30 minutes.
- As reversal agent for mu-agonist opiates · 0.05-0.1 mg/kg IV · IV · Once · Does not completely reverse analgesic effects.
- In combination as an immobilizing agent (short procedures) · butorphanol 0.2 mg/kg; medetomidine 0.001-0.015 mg/kg; midazolam 0.05-0.2 mg/kg · IM · Once · For difficult cats and short procedures.
- In combination as an immobilizing agent (more sedation) · butorphanol 0.2 mg/kg; medetomidine 0.015-0.02 mg/kg; midazolam 0.05-0.2 mg/kg; add ketamine 1-5 mg/kg when insufficient sedation · IM · Once
- As a sedative/analgesic · Butorphanol alone 0.05-0.1 mg/kg IM, SC. Butorphanol/Xylazine: Butorphanol 0.2 mg/kg + Xylazine 2 mg/kg IM · IM/SC · Once
- For injectable anesthesia · Butorphanol 0.1 mg/kg, Ketamine 5 mg/kg, medetomidine 80 micrograms/kg. Combine in one syringe and give IM. · IM · Once · May need to supplement with isoflurane (0.5-1.5%) for abdominal surgery.
給藥途徑
禁忌症
- Known hypersensitivity to butorphanol
- Lower respiratory tract conditions with copious mucous production (suppressing cough prevents clearance)
- Caution in patients with head trauma, increased CSF pressure, or severe CNS dysfunction (e.g., coma)
- Caution in severe liver disease, renal insufficiency, hypothyroidism, or Addison's disease
- Caution in dogs with heartworm disease (safety not established)
不良反應
- Sedation and ataxia
- Anorexia or diarrhea (rare in small animals)
- Respiratory depression (mild compared to pure agonists)
- CNS excitement, head tossing, and increased ambulation (especially in horses at high doses or rapid IV administration)
- Decreased gastrointestinal motility and potential ileus (horses)
- Nystagmus, salivation, seizures, and hyperthermia (at massive overdoses in horses)
藥物相互作用
- Other CNS Depressants (anesthetics, antihistamines, phenothiazines, barbiturates, tranquilizers) · May cause increased CNS or respiratory depression; dosage may need to be decreased.
- Erythromycin · Could potentially decrease the metabolism of butorphanol, prolonging its effects.
- Fentanyl (and other pure opiate agonists) · Butorphanol may antagonize analgesic effects, but will also reverse sedative and respiratory depressant effects.
- Pancuronium · May cause increased conjunctival changes when used concurrently.
- Theophylline · Could potentially decrease the metabolism of butorphanol.
- Anaesthetic agents · Reduces the doses of other drugs required for induction and maintenance of anaesthesia · moderate
- Full mu-opioid agonists (e.g., methadone, fentanyl) · Addition of butorphanol will reduce analgesia produced from the full mu agonist; combination is not recommended for analgesia · major
- Acepromazine · Synergistic sedation · moderate
- Alpha-2 agonists · Synergistic sedation and analgesia · moderate
- Full mu-agonist opioids (e.g., methadone, fentanyl) · Butorphanol's mu-antagonist properties may block or partially reverse the analgesic effects of full mu-agonists. Higher doses of full mu-agonists may be required. · major
監測
- Analgesic and/or antitussive efficacy
- Respiratory rate and depth
- Appetite and bowel function
- CNS effects (sedation vs. excitement)
過量
Acute life-threatening overdoses are unlikely (LD50 in dogs is 50 mg/kg). However, because veterinary injection comes in two highly different strengths (0.5 mg/mL and 10 mg/mL), inadvertent overdoses can occur in small animals. **Clinical Signs**: CNS effects (profound sedation or excitement), cardiovascular changes, and respiratory depression. **Treatment**: * Administer **intravenous naloxone** immediately to reverse opioid effects. * Provide supportive measures: IV fluids, oxygen therapy, vasopressors, and mechanical ventilation if required. * If seizures occur and persist, use **diazepam** for control.
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