What are the uses and dosages of lidocaine (local anesthetic/antiarrhythmic agent)?

Lidocaine: Uses and Dosages

Lidocaine is a versatile amide local anesthetic and Class Ib antiarrhythmic agent with multiple clinical applications, each requiring specific dosing protocols to maximize efficacy while minimizing toxicity risk.

Primary Clinical Uses

Local Anesthesia

Lidocaine serves as a first-line local anesthetic for infiltration, nerve blocks, and topical applications, with maximum safe doses dependent on the presence of epinephrine. 1

• Without epinephrine: Maximum dose is 4.5 mg/kg (not exceeding 300 mg total) in adults 2, 1
• With epinephrine: Maximum dose increases to 7.0 mg/kg (not exceeding 500 mg total) in adults due to vasoconstriction reducing systemic absorption 2, 3
• Pediatric dosing: For children, maximum is 1.5-2.0 mg/kg without epinephrine and 3.0-4.5 mg/kg with epinephrine 4
• Practical conversion: 1% lidocaine = 10 mg/mL; 2% lidocaine = 20 mg/mL 2

Antiarrhythmic Use

Lidocaine remains the drug of choice for ventricular arrhythmias in acute myocardial infarction settings, despite being supplanted by amiodarone in many protocols. 5, 6

• Initial bolus: 1.0-1.5 mg/kg (75-100 mg) administered intravenously 5
• Additional boluses: 0.5-0.75 mg/kg (25-50 mg) every 5-10 minutes as needed, up to total of 3 mg/kg 5
• Maintenance infusion: Following bolus dosing for sustained ventricular tachycardia or fibrillation 5
• Mechanism: Blocks voltage-gated sodium channels preferentially in ischemic tissue, interrupting re-entrant tachycardias and raising ventricular fibrillatory threshold 6

Perioperative Analgesia (Intravenous Infusion)

For postoperative pain management, intravenous lidocaine should only be initiated by experienced consultant anesthetists, as the clinical benefit is limited in most patients and requires careful risk-benefit assessment. 5

• Loading dose: 1.5 mg/kg administered over 10 minutes (too rapid infusion increases toxicity risk) 5, 3
• Maintenance infusion: 1.5 mg/kg/hour intraoperatively, reducing to 1.33 mg/kg/hour postoperatively 2
• Absolute maximum: 120 mg/hour regardless of patient weight 5, 4
• Weight calculation: Use ideal body weight (IBW): men = height(cm) - 100; women = height(cm) - 105 5
• Minimum patient weight: Do not use in patients <40 kg 5, 4
• Monitoring requirements: Continuous ECG, pulse oximetry, and blood pressure every 5 minutes during initial infusion and first 15 minutes thereafter 5, 3

Airway Anesthesia

• Transtracheal injection: 2-3 mL (80-120 mg) injected rapidly during inspiration 1
• Topical pharyngeal spray: 1-5 mL (40-200 mg), with combined spray and injection not exceeding 5 mL (200 mg) or 3 mg/kg 1
• Maximum for airway topicalization: Do not exceed 9 mg/kg of lean body weight 2

Ophthalmic Surgery

• Retrobulbar injection: 3-5 mL (120-200 mg) for a 70 kg adult, equivalent to 1.7-3 mg/kg 1
• Critical caveat: Corneal anesthesia occurs before adequate external ocular muscle akinesia; do not rely on corneal sensation alone to determine surgical readiness 1

Dental Anesthesia

2% lidocaine with 1:100,000 epinephrine provides 90-200 minutes of pulpal anesthesia, making it ideal for most dental procedures. 3

• Adult maximum: 7.0 mg/kg with epinephrine (not exceeding 500 mg) 3
• Pediatric example: For a 5-year-old weighing 50 lbs, maximum dose should not exceed 75-100 mg 3, 1
• Administration technique: Inject slowly (approximately 1 mL per minute) and aspirate before injection to avoid intravascular administration 3

Critical Safety Considerations

Contraindications and Relative Contraindications

Exercise extreme caution or avoid lidocaine in patients with cardiac disease, electrolyte disorders, seizure disorders, renal or hepatic impairment, pregnancy/breastfeeding, and neurological disorders. 5

• Hepatic disease: Lidocaine is metabolized by the liver; severe hepatic disease dramatically increases toxicity risk due to reduced clearance 1
• Cardiac disease: Patients with impaired cardiovascular function may be unable to compensate for A-V conduction prolongation 1
• Advanced liver failure: Lidocaine is contraindicated due to decreased clearance 4

Cumulative Dose Toxicity Prevention

The total dose of ALL local anesthetics administered must be considered when calculating maximum safe dosage, regardless of route (regional infiltration, surgical, topical, or nerve blocks). 4, 2

• Do not start IV lidocaine within 4 hours of any nerve block, fascial plane block, or laparoscopic port site infiltration 5, 4
• Do not perform nerve/fascial plane blocks until 4 hours after completing IV lidocaine infusion 5
• Remove topical 5% lidocaine patches before starting IV lidocaine infusion 5
• Single-shot spinal blockade does not pose cumulative toxicity problems given the small dose used 5
• Epidural/wound catheter boluses: Must not be given until 4 hours after IV lidocaine completion; continuous infusions (without boluses) may start 30 minutes after stopping IV lidocaine 5

Recognition and Management of Toxicity

Early signs of lidocaine toxicity include circumoral numbness, facial tingling, tinnitus, light-headedness, and slurred speech; progression leads to muscle twitching, seizures, respiratory arrest, cardiac arrhythmias, myocardial depression, and potentially ventricular arrest. 5

• Plasma concentration correlation: Toxicity typically begins at concentrations >5 μg/mL, with severe effects at >10 μg/mL and death risk at >25 μg/mL 5
• CNS toxicity precedes cardiac toxicity: Restlessness, anxiety, dizziness, blurred vision, tremors, and drowsiness are early warning signs 1
• Immediate management: Discontinue lidocaine, provide airway support, manage seizures with benzodiazepines, and use lipid emulsion therapy for cardiovascular collapse 2, 3, 7
• Resuscitative equipment: Must be immediately available whenever lidocaine is administered 1

Special Populations

• Elderly and debilitated patients: Require reduced doses commensurate with age and physical status 1
• Patients with shock: Use lidocaine with extreme caution 5
• Repeated dosing: May cause significant blood level increases with each dose due to slow drug/metabolite accumulation 1

Informed Consent Requirements

Where possible, explicit consent should be obtained from patients if IV lidocaine is to be used, clearly explaining the limited clinical benefit in most patients along with risks and possible advantages. 5

• Patients should be informed about symptoms of local anesthetic toxicity as well as commonly experienced feelings such as euphoria and facial flushing 5
• This follows standard guidance for use of medicine for unlicensed indications 5

Drug Interactions

• Monoamine oxidase inhibitors, tricyclic antidepressants, or phenothiazines: When lidocaine contains epinephrine, may produce severe, prolonged hypotension or hypertension; concurrent use should generally be avoided 1
• Ketamine: Concurrent administration is acceptable and often used before lidocaine is considered for difficult-to-manage pain 5

Additional Clinical Pearls

• Epinephrine benefit: Adding epinephrine provides local vasoconstriction that prolongs anesthetic effect and reduces systemic absorption 3
• Vascular areas: Use lower doses in highly vascular areas due to increased systemic absorption 4
• Intramuscular injection: May increase creatine phosphokinase levels, potentially confounding acute myocardial infarction diagnosis 1
• Oral anesthesia precaution: When used in the mouth, patients should not eat for 60 minutes due to impaired swallowing and aspiration risk; particularly important in children 1