Lidocaine
Lidocaine
Generic Name
Lidocaine
Mechanism
Lidocaine is a *class Ib* local anesthetic and anti‑arrhythmic.
• Voltage‑gated sodium channel blockade: Inactivates sodium channels in neuronal membranes, preventing action‑potential propagation and providing local anesthesia.
• Cardiac effect: In cardiac myocytes, it preferentially inhibits rapid Na⁺ channels, shortening the action‑potential plateau, thus diminishing conduction through the atrioventricular node and ventricular tissue.
• Potentiation of GABAergic transmission: At high concentrations, it modestly increases inhibitory interneuron activity.
• Metabolism: Rapid hydrolysis by plasma cholinesterases to monoethylglycinexylidide (MEGX) and local tissue esterases.
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Pharmacokinetics
| Parameter | Typical Values (IV) | Notes |
| Absorption | Rapid IV entry; topical/epidural absorption varies with tissue perfusion. | Sublingual 10 % oral systemic exposure. |
| Distribution | Protein binding ~85%; crosses blood–brain barrier; widely distributed. | Penetrates target tissues quickly (~1–3 min). |
| Metabolism | *Carboxylation* to MEGX by plasma cholinesterase; ~80 % of dose; MEGX further glucuronidated. | Liver‑potent enzyme *CYP3A4* minor contribution. |
| Half‑life | IV ~1.5–2 hr; topical or low dose ~2–3 hr. | Short; supports frequent dosing. |
| Elimination | Renal excretion of metabolites; ~80 % as MEGX glucuronide. | Reduced clearance in renal failure. |
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Indications
- Local anesthesia:
- Topical: skin, mucosa, oropharynx, ENT, dermatology.
- Infiltration: dental procedures, minor skin excisions.
- Regional blocks: epidural, spinal, peripheral nerve.
- Anti‑arrhythmic:
- IV *anti‑arrhythmic* therapy for ventricular tachyarrhythmias or supraventricular tachyarrhythmias.
- Emergency treatment of premature ventricular contractions (PVCs).
- Vasoconstrictor adjunct:
- Combined with epinephrine for diluted topical use.
- Other uses:
- Suppressing cough reflex in laryngology.
- As a component of wound‑healing dressings.
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Contraindications
- Contraindications:
- Severe cardiac conduction disease (e.g., complete heart block without pacing).
- Hypersensitivity to lidocaine or other amide local anesthetics.
- Pregnancy: Category C; judicious use if essential.
- Warnings:
- Neurotoxicity with high plasma levels (≥5 µg/mL).
- Cardiotoxicity in overdose, especially in patients with impaired hepatic/renal function.
- Drug interactions:
- Potentiation of *CYP3A4* inhibitors (ketoconazole, clarithromycin).
- Synergistic CNS depression when combined with alcohol, benzodiazepines, barbiturates.
- Breathing difficulties in local application near airway.
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Dosing
| Route | Typical Dose | Frequency | Comments |
| IV (anti‑arrhythmic) | 1–2 mg/kg bolus over 2 min; then 1–2 mg/kg/hr infusion. | Continuous | Rapid titration; monitor ECG. |
| Topical (skin) | 1–2 % lidocaine gel; 10–20 min prior to incision. | Single | Avoid contact with eye; use eye drop formulation for ocular surface. |
| Infiltration | 1–2 % solution; 0.5–2 mL per site. | One-time | Max total dose 4.5 mg/kg (IV) or 500 mg (total). |
| Epidural | 0.25–0.5 % 2 mL bolus; continuous infusion 5–10 mL/hr. | Titrated | Monitor for hypotension, urinary retention. |
| Spinal | 0.5–1 % 1–2 mL (60–100 mg). | Single | Rapid onset; avoid high intrathecal doses. |
Maximum daily dose (IV): 3 mg/kg (≈150 mg total) to avoid systemic toxicity.
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Adverse Effects
- Common
- Burning or itching at use site.
- Transient dysesthesia (paresthesia).
- Palpitations (occasionally).
- Serious
- Neurologic: seizures, CNS depression, headache, vertigo.
- Cardiovascular: hypotension, bradycardia, arrhythmias (ventricular tachycardia), cardiac arrest.
- Allergic: urticaria, anaphylaxis.
- Metabolic: hypoglycemia (rare).
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Monitoring
- Vital signs: pulse, BP, RR, SpO₂.
- ECG: PR and QRS intervals, arrhythmia detection for IV dosing.
- Serum levels (if available): keep <4 µg/mL to reduce CNS toxicity.
- Renal/hepatic function: serum creatinine, AST/ALT prior to high-dose therapy.
- Neurologic status: signs of seizures or altered consciousness.
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Clinical Pearls
1. “3‑5‑10” rule: Lidocaine’s therapeutic window (3–5 µg/mL) with a steep rise in toxicity beyond 10 µg/mL.
2. “Burn‑and‑GUM”: Burning sensation is typical; Rare GUM (guanylate kinase) mutations predispose to rapid metabolism and tolerance.
3. Avoid *etomidate* co‑administration: Potentiates CNS depression leading to respiratory arrest.
4. Subcutaneous vs. Intramuscular: Subcutaneous infiltration yields slower onset (≈10 min) but longer duration (≈60 min), whereas IM infiltration gives faster onset but can cause local burn.
5. Nicotine patch compatibility: Patch should be removed 15 min before infiltration to prevent systemic absorption spike.
6. AKIN‑Grade: When considering postoperative epidural infusion in patients with kidney injury, use a reduced loading dose (≤30 mg) to stay within the AKIN‑Grade 1.
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