Lignocaine (Lidocaine)

Lignocaine (Lidocaine) is a widely used amide local anesthetic and Class IB antiarrhythmic agent. It stabilizes neuronal membranes by inhibiting sodium ion influx, which prevents nerve signal transmission. As an antiarrhythmic, it reduces cardiac excitability and electrical conduction in ischemic tissues.

Uses

Local Anesthetic: Used for local and regional anesthesia in minor surgeries, dental procedures, and nerve blocks.
Antiarrhythmic: Effective in the management of ventricular tachycardia and ventricular fibrillation.
Adjunct in Intubation: Reduces intracranial pressure during tracheal intubation.
Pain Management: Utilized for postoperative and chronic pain relief.

Dosage and Administration

Local Anesthesia (Plain)

Adults: 2-3 mg/kg (maximum dose: 300 mg).
Pediatrics: 1-1.5 mg/kg.

Local Anesthesia (With Epinephrine)

Adults: 5-7 mg/kg (maximum dose: 500 mg).
Pediatrics: 3-4 mg/kg.

Antiarrhythmic Use

Adults (IV): 1-1.5 mg/kg IV bolus. Repeat doses of 0.5-0.75 mg/kg every 5-10 minutes if needed (maximum 3 mg/kg).
Pediatrics: 1 mg/kg IV bolus followed by infusion at 20-50 mcg/kg/min.

Toxic Dose

Plain: >3 mg/kg.
With Epinephrine: >7 mg/kg.
Toxic Plasma Concentration: >5 mcg/mL.

Dose Adjustment in Different Diseases

Hepatic Impairment: Reduced clearance; lower doses recommended.
Renal Impairment: Minimal impact, but accumulation may occur with long-term use.
Heart Failure: Use with caution due to decreased hepatic perfusion.

Presentation or Form

Injectables: 0.5%, 1%, and 2% solutions in 5 mL and 10 mL ampoules.
Topical: 5% lidocaine patches, EMLA cream (2.5% lidocaine + 2.5% prilocaine).
Other Forms: Lidocaine gels, sprays, and ointments.

Pharmacokinetics

Absorption: Rapid absorption when administered parenterally.
Distribution: Widely distributed; 60-80% plasma protein binding.
Metabolism: Primarily in the liver by CYP1A2 and CYP3A4 enzymes.
Excretion: Renal; 90% excreted as metabolites.
Half-life: 90-120 minutes.

Pharmacodynamics

Mechanism of Action: Inhibits voltage-gated sodium channels, blocking nerve signal transmission. In cardiac tissue, it reduces excitability and conduction, particularly in ischemic areas.
Onset: 2-5 minutes.
Duration: 30 minutes to 3 hours (longer with epinephrine).

Drug Interactions

CYP3A4 Inhibitors (e.g., ketoconazole): Increase the risk of toxicity.
Phenytoin: Decreases lidocaine efficacy by enhancing metabolism.
Beta-blockers: May reduce lidocaine clearance.
Other Local Anesthetics: Increased risk of systemic toxicity.

Comparison with Other Drugs in the Same Category

Bupivacaine: Longer duration but higher cardiotoxicity.
Ropivacaine: Similar duration with a better safety profile for cardiac toxicity.
Mepivacaine: Faster onset but shorter duration compared to lidocaine.

Precautions and Special Considerations

Allergic Reactions: Avoid in patients with hypersensitivity to amide-type local anesthetics.
Cardiac Conditions: Use cautiously in heart block and bradycardia.
Pregnancy: Category B; safe when used appropriately.
Elderly: Lower doses recommended due to reduced hepatic metabolism.
Liver Disease: Dose adjustments are necessary.

Side Effects

Common: Dizziness, drowsiness, nausea, paresthesia.
Serious: Seizures, hypotension, bradycardia, arrhythmias.
Local Anesthesia Systemic Toxicity (LAST):
- Early Symptoms: Tinnitus, circumoral numbness, metallic taste.
- Advanced Symptoms: Seizures, coma, bradycardia, arrhythmias.
- Management: Lipid rescue therapy (20% lipid emulsion)
  - Bolus: 1.5 mL/kg over 1 minute.
  - Infusion: 0.25 mL/kg/min for 30-60 minutes.

Recent Updates and Guidelines

American Heart Association (AHA) Guidelines: Lidocaine is recommended as an alternative to amiodarone for refractory ventricular fibrillation or pulseless ventricular tachycardia.
Enhanced Formulations: Development of extended-release lidocaine patches for chronic pain management.
FDA Updates: Emphasis on appropriate dosing to prevent systemic toxicity.

Facts to Remember

Maximum safe dose: 3 mg/kg (plain) and 7 mg/kg (with epinephrine).
Onset within 2-5 minutes; duration up to 3 hours.
Effective in managing ischemia-induced ventricular arrhythmias.
Lipid rescue therapy is crucial for LAST management.

References

Stoelting’s Pharmacology and Physiology in Anesthetic Practice, 5th Edition.
NCBI StatPearls - Lidocaine: https://www.ncbi.nlm.nih.gov/books/NBK539881/
Local Anesthetic Systemic Toxicity - BJA Education: https://bjaed.org/article/S2058-5349(19)30040-0/fulltext
American Heart Association Guidelines for Advanced Cardiac Life Support.
FDA Drug Safety Communications on Lidocaine Formulations.

Pages

Lignocaine