芬太尼
**芬太尼 (Fentanyl)** 是一種高效、合成的苯基哌啶衍生物，屬於**第二級鴉片類鎮痛藥**，在獸醫學中廣泛用於控制中度至重度疼痛。 **主要藥理特徵：** * **效力：** 鎮痛效力約為嗎啡的 75 至 100 倍。 * **脂溶性：** 芬太尼具有高度脂溶性，能迅速穿過血腦屏障（靜脈注射時起效極快），這也使其成為**經皮給藥 (貼片)** 的絕佳選擇。 * **作用時間：** 單次靜脈注射時，由於藥物迅速從大腦重新分佈至其他組織，其作用時間極短（15-30 分鐘）。因此，通常透過**恆速輸注 (CRI)** 或**經皮貼片**來維持鎮痛效果。 **臨床應用：** * 術後疼痛的輔助控制。 * 控制嚴重的慢性、鈍痛或非特異性廣泛性疼痛（例如：癌症、胰臟炎、主動脈血栓栓塞）。 * 圍手術期使用可顯著降低吸入性麻醉劑的最低肺泡有效濃度 (MAC)，為心血管功能受損的病患提供穩定性。 > **臨床要點：** 雖然經皮貼片非常方便，但不同動物個體間的吸收差異極大。依賴芬太尼貼片時，應隨時備妥注射型鎮痛藥物以供「救援」使用。
作用機制: Fentanyl is a highly selective **full agonist at the mu-opioid receptor (MOR)**. **Mechanism Pathway:** 1. **Receptor Binding:** Fentanyl binds to presynaptic and postsynaptic mu-receptors primarily located in the central nervous system (limbic system, spinal cord, thalamus, midbrain) and peripheral tissues. 2. **G-Protein Activation:** Binding activates inhibitory G-proteins (Gi/Go). 3. **Cellular Effects:** * Inhibits **adenylate cyclase**, decreasing intracellular cAMP. * Promotes the opening of **inward-rectifying potassium (K+) channels**, leading to neuronal hyperpolarization. * Inhibits the opening of **voltage-gated calcium (Ca2+) channels** on presynaptic nerve terminals. 4. **Analgesia:** This cascade profoundly inhibits the release of excitatory, nociceptive neurotransmitters (such as **Substance P** and **glutamate**) and decreases the excitability of postsynaptic neurons, effectively blocking pain transmission.
各物種劑量
- Perioperative pain · 2-3 micrograms/kg IV plus 2-3 micrograms/kg/hour IV infusion · IV/CRI · Continuous · Perioperative
- Pain management · 1-3 micrograms/kg IV, followed by a CRI at 1-4 micrograms/kg/hr · IV/CRI · Continuous · Loading dose followed by CRI
- Surgical analgesia · CRI at 10-30 micrograms/kg/hr · CRI · Continuous · Intraoperative
- Analgesia · 2-4 micrograms/kg/hour · CRI · Continuous
- Induction · 0.001-0.002 mg/kg IV · IV · Single dose
- MAC reduction during general anesthesia · 10-20 micrograms/kg/hr CRI · CRI · Continuous · Intraoperative
- Severe to excruciating pain in the emergent patient · Fentanyl at 1050 micrograms/kg, administered IV titrated to effect; use the effective dose as an hourly CRI. · IV/CRI · Titrated to effect · Note: '1050' appears exactly as written in source text, likely a typo for 10-50.
- Epidural for pain control · 0.004 mg/kg (4 micrograms/kg), diluted 0.2 mL with preservative-free saline or local anesthetic. · Epidural · Single dose · 1/2 hour · Onset in less than 10 minutes
- Maintenance analgesia/heavy sedation in critically ill hypotensive animals · fentanyl at 0.5-0.8 micrograms/kg/minute (equivalent to 30-50 micrograms/kg/hr). · CRI · Continuous · Used in addition to a local line block. May combine with midazolam.
- Transdermal Analgesia · 25 mcg/hr or 12.5 mcg/hr · Transdermal · q120h · Up to 5 days · Apply 6-24 hours prior to need. 12 mg patches are available for very small cats.
給藥途徑
禁忌症
- Known hypersensitivity to fentanyl or patch adhesive
- Conditions where additional respiratory or CNS depression would be deleterious
- No specific contraindications available in the monograph (use with caution in patients with respiratory compromise)
不良反應
- Dose-related respiratory depression
- CNS depression (sedation)
- Circulatory depression (bradycardia)
- Dysphoria or agitation (especially in cats)
- Urine retention
- Constipation
- Contact dermatitis/rash at patch site
- Altered thermoregulation (hypothermia or hyperthermia)
- Respiratory depression
- Severe bradycardia
- Asystole (with rapid IV injection)
- Reduction in heart rate
藥物相互作用
- Azole Antifungals (ketoconazole, itraconazole, fluconazole) · May inhibit fentanyl metabolism, increasing risk of toxicity
- CNS Depressants (other) · Additive CNS and respiratory depressant effects
- Diuretics · Opiates may decrease diuretic efficacy in congestive heart failure patients
- Macrolide Antibiotics (erythromycin, clarithromycin) · May inhibit fentanyl metabolism
- Monoamine Oxidase Inhibitors (amitraz, selegiline) · Severe and unpredictable opiate potentiation; generally not recommended within 14 days of MAOI use
- Skeletal Muscle Relaxants · Fentanyl may enhance neuromuscular blockade
- Nitrous Oxide · High fentanyl doses combined with nitrous oxide may cause cardiovascular depression
- Phenobarbital, Phenytoin · May increase the metabolism of fentanyl, reducing its efficacy
- Rifampin · May increase the metabolism of fentanyl
- Tricyclic Antidepressants (clomipramine, amitriptyline) · Fentanyl may exacerbate the effects of tricyclic antidepressants
- Warfarin · Opiates may potentiate anticoagulant activity
- Other anaesthetic drugs · Reduces the dose requirement for other anaesthetic agents · major
監測
- Analgesic efficacy (pain scoring)
- Heart rate (monitor for bradycardia)
- Respiratory rate and depth
- Body temperature (monitor for fever which increases patch absorption)
- Neurologic status (sedation, dysphoria)
- Heart rate and rhythm (monitor for bradycardia)
- Blood pressure
- Adequacy of analgesia
- Body temperature (avoid external heat on patches)
過量
**Clinical Signs of Overdose:** Profound respiratory and/or CNS depression, cardiovascular collapse, bradycardia, hypothermia, tremors, neck rigidity, and seizures. Newborns are particularly susceptible. **Treatment:** * **Naloxone** is the specific reversal agent of choice for treating respiratory depression. * Because naloxone's duration of action is often shorter than fentanyl's, **repeated doses or a CRI of naloxone** may be required. * Patients must be closely monitored for re-narcotization. * Mechanical respiratory support should be instituted in cases of severe respiratory depression.
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