Lidocaine
Lidocaine is a versatile **amide-class local anesthetic** and **Class IB antiarrhythmic agent**. In veterinary medicine, it is widely utilized not only for local/regional anesthesia but also systemically for the management of ventricular arrhythmias, neuropathic pain, and gastrointestinal motility disorders. Key clinical applications include: * **Antiarrhythmic Therapy:** The drug of choice for acute, life-threatening ventricular tachycardia (VT) and ventricular premature complexes (VPCs) in dogs. * **Systemic Analgesia:** Administered as a constant rate infusion (CRI), often in combination with opioids and ketamine (e.g., **MLK CRI**), to provide profound adjunctive analgesia, reduce MAC (minimum alveolar concentration) of inhalant anesthetics, and mitigate neuropathic pain or hyperalgesia. * **Prokinetic & Anti-inflammatory Effects:** In horses, systemic lidocaine is frequently used to treat or prevent postoperative ileus and to scavenge reactive oxygen species (ROS), thereby reducing reperfusion injury. > **Clinical Pearl:** Cats are significantly more sensitive to the cardiodepressant and central nervous system (CNS) toxic effects of lidocaine. Its systemic use in felines remains controversial and requires extreme caution and precise dosing.
Mechanism: 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 โ attenuates phase 4 diastolic depolarization โ decreases automaticity โ 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.
Dosing by species
- Antiarrhythmic ยท 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 ยท IV ยท Bolus then CRI ยท Caution: Cats are reportedly very sensitive to the CNS effects.
- Antiarrhythmic ยท 0.25-0.5 mg/kg slow IV, with the possibility of repeating up to twice more if needed. ยท IV ยท PRN ยท If diluting for accurate dosing, use an insulin/tuberculin syringe.
- Epidural ยท 4-5 mg/kg epidurally. ยท Epidural ยท Single dose ยท Duration 1.5 hours ยท Onset <10 minutes.
- Ventricular tachyarrhythmias ยท Initially IV bolus of 1-1.5 mg/kg. To maintain effect, a constant IV infusion will be required. ยท IV ยท Bolus then CRI ยท Will generally distinguish between ventricular tachyarrhythmias (effective) and supraventricular tachyarrhythmias (no effect).
- Ventricular tachyarrhythmias ยท 0.25-0.5 mg/kg IV (slowly) every 5-10 minutes up to a total dose of 1.5 mg/kg ยท IV ยท q5-10m
- Postoperative ileus ยท Initially, IV bolus of 1.3 mg/kg followed by a IV infusion of 0.05 mg/kg/minute for 24 hours ยท IV ยท Bolus then CRI ยท 24 hours
- Colic patients ยท 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). ยท IV ยท Bolus then CRI ยท Lidocaine has anti-endotoxic, analgesic and anti-ileus properties.
Routes of administration
Contraindications
- 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)
Adverse effects
- 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)
Drug interactions
- Gas Anesthetics (Isoflurane, Sevoflurane) ยท Lidocaine infusions reduce MAC requirements. Additive cardiodepression may occur, especially in cats.
- Other Antiarrhythmics (Procainamide, Quinidine, Propranolol) ยท May cause additive or antagonistic cardiac effects; enhanced risk of toxicity.
- Cimetidine ยท May decrease lidocaine clearance, increasing lidocaine levels and effects. ยท moderate
- Furosemide ยท Diuretic-induced hypokalemia may reduce the antiarrhythmic efficacy of lidocaine.
- Phenobarbital / Phenytoin ยท May induce hepatic enzymes, increasing lidocaine metabolism and decreasing its serum levels.
- Propranolol ยท May decrease hepatic blood flow and lidocaine clearance, increasing lidocaine levels. ยท moderate
- Succinylcholine ยท Large doses of lidocaine may prolong succinylcholine-induced apnea.
- Other antiarrhythmics ยท May cause increased myocardial depression ยท major
Monitoring
- 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)
Overdose
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.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.