lidocaine
Local anesthetic· Brands: Xylocaine, Lignocaine, Dentocaine, Anestacon, LidodermIMIVNEBPOSCTOP
Mechanism of action
Lidocaine blocks voltage-gated sodium channels in nerve cell membranes, preventing the influx of sodium ions during depolarization. This stabilizes the membrane and raises the threshold for excitation, thereby blocking conduction of nerve impulses. It preferentially affects small, unmyelinated fibers and has a rapid onset of action.
Pharmacokinetics
Lidocaine is well absorbed after parenteral and topical administration, but undergoes extensive first-pass hepatic metabolism after oral ingestion, limiting oral use. It is metabolized by cytochrome P450 enzymes, primarily CYP1A2 and CYP3A4, to active metabolites that can accumulate. The elimination half-life is approximately 1.5 to 2 hours, but may be prolonged in hepatic impairment or heart failure. It is distributed widely, including to the brain and myocardium, and is about 60-80% protein bound.
Indications & dosing
Local infiltration anaesthesia for minor surgical procedures
Maximum 300 mg or 4.5 mg/kg with epinephrine; use 0.5% to 1% solution.
- adult · SC: 1–5 mg/kg single dose · Maximum 300 mg or 4.5 mg/kg without epinephrine (500 mg or 7 mg/kg with epinephrine); use 0.5% to 1% solution.
Peripheral nerve block (e.g. brachial plexus, femoral)
Use 1% to 2% solution; max 300 mg or 4.5 mg/kg with epinephrine.
- adult · SC: 1–5 mg/kg single dose · Use 1% to 2% solution; max 300 mg or 4.5 mg/kg without epinephrine (500 mg or 7 mg/kg with epinephrine).
Intravenous regional anaesthesia (Bier block)
Dilute to 0.5% solution; max volume 50 mL (40 mL for upper limb).
- adult · IV: 3 mg/kg single dose · Dilute to 0.5% solution; max volume 50 mL (40 mL for upper limb).
Ventricular arrhythmias (e.g. in cardiac arrest)
Follow with 1-4 mg/min infusion; only for shock-refractory VT/VF.
- adult · IV: 1–1.5 mg/kg initial bolus · Follow with 1-4 mg/min infusion; only for shock-refractory VT/VF.
Contraindications & precautions
- Hypersensitivity to lidocaine or other amide local anaesthetics · History of allergic reaction to lidocaine or related agents.
- Complete heart block without a functioning pacemaker · Lidocaine may suppress ventricular escape rhythms.
- Severe hepatic impairment · Risk of accumulation because lidocaine is extensively metabolised in the liver.
- Use the lowest effective dose and concentration, especially in the elderly and those with cardiac disease.
- Aspirate before injection to prevent accidental intravascular administration, which can cause systemic toxicity.
- Monitor ECG and blood pressure during prolonged or high-dose administration, particularly when using lidocaine with adrenaline.
- Ensure resuscitation equipment and anticonvulsants are immediately available when using lidocaine for regional anaesthesia.
- Caution in patients with hepatic impairment, hypovolaemia, or poor peripheral perfusion, as clearance is reduced.
Adverse effects
- Pain or local tissue reaction at injection site
- Dizziness or lightheadedness
- Hypotensionserious
- Bradycardia or other arrhythmiasserious
- Seizures or CNS toxicityserious
- Anaphylaxisserious
Renal & hepatic adjustment
- eGFR 0+: No dose adjustment required. Caution in severe renal impairment (eGFR < 30) due to metabolite accumulation.
- Hepatic impairment (mild): No dose adjustment usually required. Monitor for toxicity.
- Hepatic impairment (moderate): Reduce dose and monitor closely. Consider alternative if possible.
- Hepatic impairment (severe): Avoid or use with extreme caution. Reduce dose significantly and monitor for CNS toxicity. (avoid)
Monitoring, pregnancy & toxicity
- ECG and vital signs · Continuous during IV infusion
- Neurological status · Regularly during infusion
- Serum lidocaine concentration · If prolonged infusion or hepatic impairment
- Pregnancy: Lidocaine may be used in pregnancy when clinically indicated. It crosses the placenta but is generally considered safe at recommended doses. Use the lowest effective dose and monitor for fetal effects.
- Toxicity: CNS toxicity: light-headedness, confusion, paresthesia, seizures, respiratory depression · Stop infusion, provide supportive care, monitor vital signs. For seizures, give benzodiazepines. Consider lipid emulsion therapy for severe toxicity.
- Toxicity: Cardiovascular toxicity: hypotension, bradycardia, arrhythmias (e.g., wide-complex tachycardia), cardiovascular collapse · Stop infusion, give IV fluids, vasopressors, and lipid emulsion therapy. For bradycardia, consider atropine. Follow ACLS protocols.
- Toxicity: Methemoglobinemia (rare) · Administer methylene blue (1-2 mg/kg IV) if symptomatic.
- Toxicity: Allergic reactions (rare) · Stop drug, treat anaphylaxis with epinephrine, antihistamines, and corticosteroids.
Antidotes & reversal
- 20% lipid emulsion ( Intralipid ) · For systemic toxicity (seizures, cardiovascular collapse): lipid emulsion per LAST protocol.
Clinical notes
Lidocaine is used for local anesthesia, nerve blocks, and as an antiarrhythmic for ventricular arrhythmias. It is commonly used with epinephrine to prolong duration and reduce systemic absorption. Careful calculation of maximum doses is essential to prevent toxicity, which may manifest as perioral numbness, confusion, seizures, and cardiovascular collapse. Dosage adjustments are needed in liver disease, heart failure, or elderly patients. Always check local guidelines for maximum safe doses.
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BNF; local formulary