1. Clinical Overview
Lidocaine (2%) is a widely used amide-type local anesthetic agent, primarily employed for surface anesthesia, infiltration, and nerve block. It stabilizes neuronal membranes by inhibiting the ionic fluxes required for the initiation and conduction of nerve impulses, thereby producing local anesthetic, antiarrhythmic, and anticonvulsant effects. In the Indian market, it is a cornerstone drug for minor surgical procedures, dental work, and topical analgesia.
| Onset | Duration | Bioavailability |
|---|---|---|
| Topical/Infiltration: 2-5 minutes; Nerve Block: 5-10 minutes. | Topical/Infiltration: 30-90 minutes; Nerve Block: 60-120 minutes (varies with addition of vasoconstrictor like epinephrine). | Topical: ~3%; Parenteral: 100%. |
2. Mechanism of Action
Lidocaine acts by blocking voltage-gated sodium channels in the neuronal cell membrane. It binds preferentially to activated and inactivated channels, stabilizing them in their inactive state. This prevents the transient increase in sodium ion permeability required for the depolarization phase of the action potential, thereby halting the initiation and propagation of nerve impulses.
3. Indications & Uses
- Local anesthesia for minor surgical procedures (e.g., suturing, incision & drainage).
- Infiltration anesthesia in dental procedures.
- Topical anesthesia for mucous membranes (oral, laryngeal, urethral).
- Peripheral nerve block (e.g., digital, intercostal).
4. Dosage & Administration
Adult Dosage: Dose varies by procedure and site. Maximum recommended dose without epinephrine: 4.5 mg/kg (not to exceed 300 mg). With epinephrine: 7 mg/kg (not to exceed 500 mg). For infiltration: 1-5 mL (20-100 mg) of 2% solution. For nerve block: 1-30 mL (20-600 mg) depending on the nerve.
Administration: For injection: Use aseptic technique. Aspirate before injection to avoid intravascular administration. Inject slowly. For topical use: Apply to clean, dry mucous membrane as a spray, gel, or solution. Do not swallow topical preparations meant for oral mucosa. Never inject into infected or inflamed tissue.
5. Side Effects
Common side effects may include:
- Transient burning or stinging at application site.
- Localized erythema or edema.
- Numbness beyond the target area.
- Mild dizziness or lightheadedness.
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Beta-blockers (e.g., Propranolol) | Decreased hepatic clearance of lidocaine, increasing risk of toxicity. | Major |
| Cimetidine | Inhibits CYP enzymes, reduces lidocaine metabolism, increases plasma levels and toxicity risk. | Major |
| Class I Antiarrhythmics (e.g., Mexiletine, Tocainide) | Additive cardiac effects, increased risk of arrhythmias and toxicity. | Major |
| CYP3A4 Inhibitors (e.g., Ketoconazole, Erythromycin) | Increased lidocaine levels. | Moderate |
| CYP1A2 Inducers (e.g., Smoking, Omeprazole) | May decrease lidocaine levels. | Moderate |
| Succinylcholine | Lidocaine may enhance neuromuscular blockade. | Moderate |
| Vasoconstrictors (e.g., Epinephrine in formulation) | Prolongs duration, reduces systemic absorption. Contraindicated in areas with end-arteries (fingers, toes, penis, ears). | Moderate |
7. Patient Counselling
- Do inform your doctor about all allergies, especially to local anesthetics.
- Do report any history of heart, liver, or kidney disease.
- Do not eat or chew gum until numbness wears off after oral/dental procedures to avoid biting injury.
- Do not rub or scratch the numbed area.
- Do not apply heat to the anesthetized area.
8. Toxicology & Storage
Overdose: Manifests as CNS excitation (tinnitus, metallic taste, perioral numbness, dizziness, tremors, seizures) followed by CNS depression (drowsiness, coma, respiratory arrest). Cardiovascular toxicity includes hypotension, bradycardia, heart block, and ultimately ventricular fibrillation or asystole.
Storage: Store at room temperature (15-30°C). Protect from light. Do not freeze. Keep out of reach of children. Do not use if solution is discolored or contains particulate matter. For multi-dose vials, maintain aseptic technique and discard as per hospital/institution policy (typically 28 days after first use).