Lidocaine (10% w/v) is a high-potency topical formulation of the prototypical amide-type local anesthetic. It acts by blocking voltage-gated sodium channels on neuronal membranes, preventing the initiation and conduction of nerve impulses, thereby producing reversible loss of sensation (anesthesia) in a localized area. The 10% w/v (100 mg/mL) concentration is specifically designed for surface anesthesia on mucous membranes and is a key agent for procedures requiring profound, rapid-onset topical anesthesia in outpatient and surgical settings.
Adult: Dose is highly individualized based on procedure and application area. Apply the smallest amount necessary. For oropharyngeal use: 1-5 sprays (10-50 mg) or 1-5 mL of solution/gel (100-500 mg). For urethral instillation: 5-10 mL (500-1000 mg) is common. MAXIMUM RECOMMENDED DOSE: 4.5 mg/kg, not to exceed 300 mg in a single application for normal healthy adults.
Note: For Spray: Apply directly to the target mucosal surface. Avoid spraying deeply into the pharynx to prevent aspiration. For Solution/Gel: Apply with a cotton swab, syringe (without needle), or as a gargle (expectorated). For Urethral Use: Instill slowly using a urethral syringe or catheter-tipped applicator; clamp the urethral meatus for several minutes. NEVER INJECT. Avoid contact with eyes. Do not apply to large areas or under occlusive dressings.
Lidocaine stabilizes the neuronal membrane by reversibly binding to and inhibiting voltage-gated sodium channels in their inactivated state. This binding prevents the transient influx of sodium ions (Na+) required for the depolarization phase of the action potential. Consequently, the threshold for electrical excitability is increased, the rate of depolarization is decreased, and the propagation of the action potential along the nerve fiber is effectively blocked.
Pregnancy: Category B (US FDA). No well-controlled studies in pregnant women. Use only if clearly needed. Should be used in lowest effective dose for essential procedures. Avoid high doses near term due to theoretical risk of fetal bradycardia.
Driving: Patients should be advised not to drive or operate machinery until the effects of numbness and any potential CNS effects (dizziness) have completely worn off.
| Other Local Anesthetics (e.g., Bupivacaine, Prilocaine) | Additive toxic effects (CNS, cardiac). Increased risk of methemoglobinemia with prilocaine. | Major |
| Antiarrhythmics (Class I: e.g., Mexiletine, Tocainide) | Additive cardiac effects (negative inotropy, conduction delays). | Major |
| Beta-blockers (e.g., Propranolol) | Reduced hepatic blood flow, decreased lidocaine clearance, increased risk of toxicity. | Moderate |
| CYP1A2 & CYP3A4 Inhibitors (e.g., Ciprofloxacin, Fluconazole, Amiodarone) | Decreased lidocaine metabolism, increased plasma levels and toxicity risk. | Moderate |
| CYP1A2 Inducers (e.g., Smoking, Omeprazole) | Increased lidocaine metabolism, potentially reduced efficacy. | Minor |
| Drugs causing Methemoglobinemia (e.g., Dapsone, Nitrates, Sulfonamides) | Increased risk of clinically significant methemoglobinemia. | Major |