Lidocaine 4% is a high-potency, amide-type local anesthetic agent primarily formulated for topical application on mucous membranes. It acts by blocking voltage-gated sodium channels, thereby inhibiting the initiation and conduction of nerve impulses, leading to reversible loss of sensation. In the Indian context, it is a cornerstone for procedural anesthesia in dentistry, otolaryngology, and minor surgical interventions.
Adult: Dose is highly site-specific. General Max: 200 mg (5 mL of 4% solution). Common doses: Oropharynx: 1-5 sprays (approx. 10-50 mg) or 2-5 mL gargle/swish & spit. Urethra: 5-15 mL (instilled and retained for 5-10 minutes). MUST NOT exceed 4.5 mg/kg (without epinephrine).
Note: For oral/pharyngeal use: Apply via spray or cotton swab to specific area. Patient should not swallow; must spit out excess. For urethral use: Instill solution into urethra using a syringe (without needle) and clamp meatus for 5-10 minutes. NEVER inject. Apply only to the area required for the procedure. Use the smallest volume and lowest concentration needed.
Lidocaine stabilizes the neuronal membrane by binding to and inhibiting voltage-gated sodium channels in their inactivated state. This prevents the influx of sodium ions required for the depolarization phase of the action potential, thereby halting the initiation and propagation of nerve impulses.
Pregnancy: Category B (US FDA). No well-controlled studies in pregnant women. Use only if clearly needed, especially during first trimester. Should be used at the lowest effective dose for the shortest duration, primarily for essential procedures.
Driving: Patient must NOT drive or operate machinery until full sensation and normal coordination have returned (typically 1-2 hours after procedure). Dizziness and blurred vision are common side effects.
| Other Local Anesthetics (e.g., Bupivacaine, Prilocaine) | Additive toxic effects; increased risk of systemic toxicity. | Major |
| Antiarrhythmics (Class I e.g., Mexiletine, Tocainide) | Additive cardiotoxic effects; potentiation of myocardial depression and arrhythmias. | Major |
| Beta-blockers (e.g., Propranolol) | May reduce hepatic blood flow and inhibit CYP enzymes, increasing lidocaine plasma levels and toxicity risk. | Moderate |
| CYP1A2 & CYP3A4 Inhibitors (e.g., Ciprofloxacin, Erythromycin, Fluconazole, Amiodarone) | Decreased lidocaine metabolism, leading to increased plasma concentrations and risk of toxicity. | Moderate |
| CYP1A2 Inducers (e.g., Smoking, Omeprazole) | Increased lidocaine metabolism, potentially reducing efficacy. | Moderate |
| Succinylcholine | May potentiate neuromuscular blockade. | Moderate |
| Vasoconstrictors (e.g., Epinephrine) - when used in combination injections | Prolongs duration of action and reduces systemic absorption. NOT typically part of topical 4% formulation. | Moderate |
Same composition (Lidocaine (4%)), different brands: