利多卡因
利多卡因 (Lidocaine) 是一種多功能的**醯胺類 (amide) 局部麻醉劑**與 **IB 類抗心律不整藥物**。在獸醫學中，它不僅廣泛用於局部或區域麻醉，還常以全身性給藥的方式來控制心室心律不整、神經性疼痛以及胃腸道運動障礙。 主要臨床應用包括： * **抗心律不整治療：** 治療犬隻急性、危及生命的心室性心搏過速 (VT) 和心室性早搏 (VPCs) 的首選藥物。 * **全身性鎮痛：** 常以恆速輸注 (CRI) 方式給藥，並經常與鴉片類藥物及氯胺酮 (Ketamine) 併用（例如 **MLK CRI**），以提供深度的輔助鎮痛、降低吸入性麻醉劑的最低肺泡濃度 (MAC)，並減輕神經性疼痛或痛覺過敏。 * **促腸胃蠕動與抗發炎作用：** 在馬匹中，全身性利多卡因常被用於治療或預防術後腸阻塞 (ileus)，並能清除活性氧物質 (ROS)，從而減少再灌注損傷。 > **臨床要點：** 貓對利多卡因的心臟抑制和中樞神經系統 (CNS) 毒性反應明顯更為敏感。其在貓科動物的全身性使用仍具爭議，必須極度謹慎並精確控制劑量。
作用機制: Lidocaine exerts its effects through multiple mechanisms depending on the target tissue: * **Antiarrhythmic Action (Class IB):** Lidocaine binds to and blocks **fast voltage-gated sodium channels (Nav1.5)** in the myocardium. It exhibits *use-dependent* and *state-dependent* blockade, meaning it preferentially binds to sodium channels in their **inactive state** (which occurs during depolarization). This action → attenuates phase 4 diastolic depolarization → decreases automaticity → suppresses ectopic ventricular pacemakers without significantly affecting the SA or AV nodes at therapeutic levels. * **Local Anesthetic/Analgesic Action:** Blocks **neuronal voltage-gated sodium channels**, preventing the influx of sodium required for the initiation and conduction of action potentials in peripheral nerves. Systemically, it reduces ectopic firing from damaged afferent neurons, providing relief from neuropathic pain. * **Prokinetic & Cytoprotective Action:** The exact mechanism for enhancing intestinal motility (especially in equine ileus) is multifactorial, likely involving suppression of sympathetic inhibitory reflexes, direct anti-inflammatory effects, and acting as a **scavenger of reactive oxygen species (ROS)** to prevent lipid peroxidation and reperfusion injury.
各物種劑量
- Antiarrhythmic · Initially, IV bolus of 0.25-0.5 mg/kg given slowly; can repeat at 0.15-0.25 mg/kg in 5-20 minutes; if effective, 10-20 micro-grams/kg/minute (0.01-0.02 mg/kg/min) as a constant rate IV infusion · IV · Bolus then CRI · Caution: Cats are reportedly very sensitive to the CNS effects.
- Antiarrhythmic · 0.25-0.5 mg/kg slow IV, with the possibility of repeating up to twice more if needed. · IV · PRN · If diluting for accurate dosing, use an insulin/tuberculin syringe.
- Epidural · 4-5 mg/kg epidurally. · Epidural · Single dose · Duration 1.5 hours · Onset <10 minutes.
- Ventricular tachyarrhythmias · Initially IV bolus of 1-1.5 mg/kg. To maintain effect, a constant IV infusion will be required. · IV · Bolus then CRI · Will generally distinguish between ventricular tachyarrhythmias (effective) and supraventricular tachyarrhythmias (no effect).
- Ventricular tachyarrhythmias · 0.25-0.5 mg/kg IV (slowly) every 5-10 minutes up to a total dose of 1.5 mg/kg · IV · q5-10m
- Postoperative ileus · Initially, IV bolus of 1.3 mg/kg followed by a IV infusion of 0.05 mg/kg/minute for 24 hours · IV · Bolus then CRI · 24 hours
- Colic patients · Initial IV bolus at 1.4 mg/kg, then as a CRI at 0.03-0.05 mg/kg/min (1.8-3 mg/kg/hr). · IV · Bolus then CRI · Lidocaine has anti-endotoxic, analgesic and anti-ileus properties.
給藥途徑
禁忌症
- Known hypersensitivity to amide-class local anesthetics
- Severe SA, AV, or intraventricular heart block (unless artificially paced)
- Adams-Stokes syndrome
- Intravenous use of lidocaine products containing epinephrine
- Continuous rate infusion (CRI) in cats during the perioperative period (due to negative haemodynamic effects)
- Intravenous administration of lidocaine solutions containing adrenaline
- Use of adrenaline-containing solutions for complete ring block of an extremity (danger of ischaemic necrosis)
不良反應
- CNS toxicity (dose-related): drowsiness, depression, ataxia, nystagmus, muscle tremors, seizures
- Gastrointestinal: nausea and vomiting (usually transient)
- Cardiovascular: hypotension (especially with rapid IV bolus), bradycardia, PR and QRS interval prolongation, circulatory collapse at toxic doses
- Cats: heightened risk of severe cardiodepression and CNS signs
- Depression
- Seizures
- Muscle fasciculations
- Vomiting
- Bradycardia
- Hypotension
- Laryngeal oedema (in cats, associated with CFC propellants in unlicensed aerosols)
藥物相互作用
- Gas Anesthetics (Isoflurane, Sevoflurane) · Lidocaine infusions reduce MAC requirements. Additive cardiodepression may occur, especially in cats.
- Other Antiarrhythmics (Procainamide, Quinidine, Propranolol) · May cause additive or antagonistic cardiac effects; enhanced risk of toxicity.
- Cimetidine · May decrease lidocaine clearance, increasing lidocaine levels and effects. · moderate
- Furosemide · Diuretic-induced hypokalemia may reduce the antiarrhythmic efficacy of lidocaine.
- Phenobarbital / Phenytoin · May induce hepatic enzymes, increasing lidocaine metabolism and decreasing its serum levels.
- Propranolol · May decrease hepatic blood flow and lidocaine clearance, increasing lidocaine levels. · moderate
- Succinylcholine · Large doses of lidocaine may prolong succinylcholine-induced apnea.
- Other antiarrhythmics · May cause increased myocardial depression · major
監測
- Continuous ECG monitoring (especially during IV bolus or CRI)
- Signs of CNS toxicity (ataxia, tremors, seizures)
- Blood pressure (monitor for hypotension)
- Serum lidocaine levels if available (Therapeutic range: 1-6 micrograms/mL)
- ECG (especially during IV therapy for arrhythmias)
- Blood pressure
- Heart rate
- CNS signs (monitor for fasciculations or seizures)
過量
In dogs, toxicity may result if serum levels exceed **8 micrograms/mL**. * **Clinical Signs:** Ataxia, nystagmus, depression, seizures, bradycardia, hypotension, and at very high levels, circulatory collapse. * **Management:** Because lidocaine is rapidly metabolized, simply stopping the infusion or reducing the rate (with close monitoring) is often sufficient for minor signs. * **Seizure Control:** Treat seizures or excitement with **diazepam** or a short/ultrashort-acting barbiturate. > **Warning:** Longer-acting barbiturates (e.g., pentobarbital) should be avoided. * **Cardiovascular Support:** Treat circulatory depression with IV fluids, pressor agents, and initiate CPR if necessary.
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