Lidocaine/Lignocaine

Usage

Lidocaine/Lignocaine is prescribed for a variety of medical conditions, primarily for its local anesthetic and antiarrhythmic properties. It is used to numb tissues in specific areas of the body and to treat certain types of abnormal heart rhythms (ventricular arrhythmias).

Its pharmacological classifications include:

• Local anesthetic: It works by blocking nerve signals in the body, preventing the sensation of pain.
• Antiarrhythmic (Class IB): It helps restore normal heart rhythm by suppressing abnormal electrical activity in the ventricles.

Lidocaine’s mechanism of action involves blocking sodium channels in nerve cells. This action prevents the transmission of pain signals and stabilizes the cell membranes of cardiac muscle cells, thus suppressing abnormal heart rhythms.

Alternate Names

• Lignocaine (International Nonproprietary Name)
• Xylocaine (Brand Name)
• Numerous other brand names exist depending on the formulation and country.

How It Works

Pharmacodynamics: Lidocaine blocks voltage-gated sodium channels in nerve and cardiac cells. This action prevents depolarization and subsequent signal propagation, leading to localized numbness and suppression of abnormal cardiac impulses.

Pharmacokinetics:

• Absorption: Absorption varies depending on the route of administration. Topical application results in minimal systemic absorption. Injection, intravenous, and mucous membrane application lead to faster and more extensive absorption.
• Metabolism: Primarily metabolized in the liver by CYP enzymes, producing several metabolites, including monoethylglycinexylidide (MEGX), which can contribute to toxicity in some cases.
• Elimination: Excreted primarily by the kidneys, with a small portion eliminated in the bile. The half-life is approximately 1.5 to 2 hours, but this can be prolonged in patients with hepatic impairment.

Mode of Action: Lidocaine binds to the intracellular portion of voltage-gated sodium channels. This binding preferentially occurs in activated or inactivated channels, effectively blocking further sodium influx and thus inhibiting depolarization.

Receptor Binding/Enzyme Inhibition/Neurotransmitter Modulation: Lidocaine’s primary effect is on sodium channels, not receptors, enzymes, or neurotransmitters.

Elimination Pathways: Hepatic metabolism via CYP enzymes (primarily CYP3A4 and CYP1A2), followed by renal excretion. Some biliary excretion also occurs.

Dosage

Standard Dosage

Adults: Dosage varies depending on the indication and route of administration. Common dosages include:

• IV: 1-1.5 mg/kg bolus, followed by a continuous infusion of 1-4 mg/minute.
• Local infiltration: Up to 4.5 mg/kg (maximum 300 mg) without epinephrine or up to 7 mg/kg (maximum 500 mg) with epinephrine.
• Topical: Varies depending on the formulation and the area to be treated.

Children: Pediatric dosing is usually based on weight, typically not exceeding 3mg/kg for local infiltration. Use cautiously in children under 3 years old.

Special Cases:

• Elderly Patients: May require lower doses due to age-related decline in hepatic and renal function.
• Patients with Renal Impairment: Dosage adjustments are generally unnecessary for topical use but may be required for systemic administration.
• Patients with Hepatic Dysfunction: Reduced doses are usually necessary.
• Patients with Comorbid Conditions: Dosage adjustments may be required depending on the specific condition.

Clinical Use Cases

• Intubation: 2% jelly applied topically to the endotracheal tube.
• Surgical Procedures: Local infiltration or regional nerve blocks using various concentrations (0.5% - 2%).
• Mechanical Ventilation: Endotracheal tube lubrication using 2% jelly.
• Intensive Care Unit (ICU) Use: IV infusion for ventricular arrhythmias.
• Emergency Situations: IV or IM administration for ventricular fibrillation, ventricular tachycardia, and cardiac arrest.

Dosage Adjustments

Dose modifications are necessary for patients with renal or hepatic dysfunction. For other metabolic disorders or genetic polymorphisms, consult appropriate resources.

Side Effects

Common Side Effects

• Lightheadedness, dizziness, drowsiness
• Nausea, vomiting
• Localized reactions (redness, swelling, pain) at the application/injection site.

Rare but Serious Side Effects

• Seizures
• Cardiac arrest
• Anaphylaxis
• Methemoglobinemia

Long-Term Effects

Chronic complications from prolonged use are rare but can include local tissue damage with topical or injected formulations.

Adverse Drug Reactions (ADR)

Clinically significant ADRs include severe allergic reactions, cardiac arrest, seizures, and methemoglobinemia. These require immediate intervention.

Contraindications

• Known hypersensitivity to lidocaine or other amide-type local anesthetics.
• Severe heart block (unless a pacemaker is present)
• Wolff-Parkinson-White syndrome
• Severe heart failure or cardiogenic shock

Drug Interactions

Lidocaine interacts with a significant number of medications, including:

• Beta-blockers: Can enhance lidocaine’s effects.
• Cimetidine: Increases lidocaine levels.
• Antiarrhythmics: May increase the risk of arrhythmias.
• CYP3A4 and CYP1A2 inhibitors or inducers: Can alter lidocaine metabolism.

It’s crucial to check for potential interactions before prescribing or administering lidocaine.

Pregnancy and Breastfeeding

• Pregnancy Safety Category: B (FDA). Generally considered safe for use during pregnancy but should only be used when clearly needed and the benefits outweigh the risks. Monitor fetal heart rate.
• Breastfeeding: Lidocaine is excreted in breast milk in small amounts, and adverse effects in infants are rare. Caution is recommended.

Drug Profile Summary

• Mechanism of Action: Sodium channel blocker
• Side Effects: Drowsiness, dizziness, nausea, local reactions, seizures (rare), cardiac arrest (rare).
• Contraindications: Hypersensitivity, severe heart block, WPW syndrome.
• Drug Interactions: Beta-blockers, cimetidine, antiarrhythmics.
• Pregnancy & Breastfeeding: Category B; caution advised during breastfeeding.
• Dosage: Varies by route and indication.
• Monitoring Parameters: Heart rate, blood pressure, ECG (for IV administration), respiratory status.

Popular Combinations

Lidocaine is often combined with epinephrine to prolong its anesthetic effects and reduce bleeding at the injection site.

Precautions

• General Precautions: Check for allergies and assess cardiovascular and hepatic function.
• Specific Populations: Exercise caution in pregnant/breastfeeding women, children, and the elderly.
• Lifestyle Considerations: Alcohol and other CNS depressants can potentiate lidocaine’s sedative effects.

FAQs (Frequently Asked Questions)

Q1: What is the recommended dosage for Lidocaine/Lignocaine?

A: Dosage varies based on indication, route of administration, and patient factors. Consult the detailed dosage guidelines provided above.

Q2: How is lidocaine metabolized?

A: Primarily metabolized in the liver via CYP enzymes, specifically CYP3A4 and CYP1A2.

Q3: Can lidocaine be used during pregnancy?

A: Generally considered safe (Category B) but use with caution and monitor fetal heart rate.

Q4: What are the major drug interactions with lidocaine?

A: Beta-blockers, cimetidine, certain antiarrhythmics, and drugs that affect CYP3A4 or CYP1A2 activity.

Q5: What are the signs of lidocaine toxicity?

A: Lightheadedness, dizziness, confusion, seizures, cardiac arrhythmias, respiratory depression.

Q6: How is lidocaine administered for local anesthesia?

A: Via injection, topical application (cream, ointment, gel, patch), or as a spray.

Q7: Can lidocaine be used for dental procedures?

A: Yes, commonly used for local anesthesia during dental procedures.

Q8: What is the duration of action of lidocaine?

A: Varies depending on the route of administration but generally lasts 1-2 hours for local anesthesia.

Q9: How should lidocaine be stored?

A: Store at room temperature, away from light and moisture.