What is lidocaine

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Here is a thorough overview of lidocaine, drawn from Goodman & Gilman's Pharmacological Basis of Therapeutics, Rosen's Emergency Medicine, and the Harriet Lane Handbook:

Lidocaine

What It Is

Lidocaine (brand names: Xylocaine, Lidoderm, L-M-X, among others) is a Class Ib antiarrhythmic and amide-type local anesthetic. It is one of the most widely used drugs in medicine, appearing in injectable, topical, patch, and IV infusion forms.

Mechanism of Action

Lidocaine blocks voltage-gated sodium (Na+) channels - both the open and inactivated states. This prevents the influx of sodium ions that generates the action potential in nerve and cardiac cells.

Key features of its Na+ channel block:

Recovery from block is rapid, so the drug preferentially affects depolarized or rapidly firing tissue (e.g., ischemic myocardium, active nerve fibers)
It decreases automaticity by reducing the slope of phase 4 depolarization and altering the excitability threshold
It generally does not prolong PR or QRS intervals, and the QT interval is unaltered or slightly shortened
It is not useful in atrial arrhythmias because atrial action potentials are too short for effective Na+ channel binding
Goodman & Gilman's, p. 708

Uses

Route	Indication
IV	Acute ventricular arrhythmias (VT, VF) - alternative to amiodarone
Injection (local)	Local/regional anesthesia for procedures, nerve blocks
Topical (cream, gel, patch)	Pain relief, skin anesthesia (e.g., before IV insertion)
Oral solution	Mouth/throat anesthesia

Lidocaine is the sole Class Ib agent used in emergency rhythm management. It suppresses dysrhythmias from enhanced automaticity (e.g., ventricular tachycardia). It is an alternative to amiodarone in pulseless VT/VF but has no efficacy in supraventricular tachycardia (SVT).

Rosen's Emergency Medicine, p. 1039

Note: Lidocaine is no longer given routinely to all MI patients, because while it reduced VF incidence, survival to discharge tended to be worse, possibly due to exacerbated heart block or CHF.

Pharmacokinetics

Not used orally (as a systemic drug) - undergoes extensive first-pass hepatic metabolism
IV is the preferred systemic route
Distribution half-life: ~8 min (rapid redistribution after IV bolus)
Terminal elimination half-life: ~2 hours (hepatic metabolism)
Metabolized by CYP enzymes in the liver; drugs that inhibit CYP450 (e.g., certain azoles, some antibiotics) can slow clearance and increase toxicity risk
Metabolites: glycine xylidide (GX) and monoethyl-GX - weaker Na+ channel blockers, may compete with parent drug and reduce efficacy over prolonged infusions (>24 h)
Goodman & Gilman's, p. 708-709

Dosing (Pediatric & Adult)

Antiarrhythmic (IV):

Bolus: 1 mg/kg/dose (max 100 mg) slowly IV; may repeat every 10-15 min x2; max total 3-5 mg/kg in first hour
Continuous infusion: 20-50 mcg/kg/min IV

Local anesthetic injection:

Without epinephrine: max 4.5 mg/kg (up to 300 mg); do not repeat within 2 hr
With epinephrine: max 7 mg/kg (up to 500 mg) - epinephrine causes vasoconstriction, slowing systemic absorption and extending duration

Topical/patch: varies by formulation; 4-5% patch applied for up to 12 hr in any 24-hr period

Harriet Lane Handbook, 23rd ed., p. 1213

Adverse Effects / Toxicity

Severity	Signs/Symptoms
Early/mild	Nystagmus (first sign), tremor, dysarthria, altered consciousness
Severe/rapid infusion	Seizures
Cardiac	Rare exacerbation of heart failure; asystole in acute MI/ischemia; heart block

Toxicity is increased when hepatic enzymes are inhibited (drug interactions)
True lidocaine allergy is rare (amide class has lower allergy risk than esters)

Formulations Available

Injection: 0.5%, 1%, 1.5%, 2%, 4%
IV infusion (in D5W): 0.4% and 0.8% premixed bags
Topical: creams, gels, ointments, lotions, aerosol sprays (2-5%)
Transdermal patch: 3.5-5%
Oral solution: 2% and 4% (for mouth/throat)
Combined with epinephrine (1:100,000 or 1:200,000) for local anesthesia

Key Points Summary

Class Ib antiarrhythmic - sodium channel blocker with rapid kinetics
Works best in ischemic/depolarized tissue - targeted action in diseased myocardium
Preferred IV antiarrhythmic for ventricular arrhythmias when amiodarone unavailable or contraindicated
Avoid oral systemic use - high first-pass metabolism renders it ineffective by mouth
Monitor for nystagmus as an early warning sign of toxicity
Reduce dose in patients with hepatic disease, CHF, or shock

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