1. Clinical Overview
Lidocaine (9.5% w/w) is a high-potency topical formulation of the amide-type local anesthetic, lidocaine. It is primarily used as a topical anesthetic for intact skin to provide dermal analgesia for minor procedures such as venipuncture, intravenous cannulation, and superficial dermatological surgeries. In the Indian context, it is a key agent for procedural pain management in outpatient and dermatology settings. The 9.5% w/w concentration, often formulated as a medicated plaster or patch, is designed for targeted, sustained delivery.
| Onset | Duration | Bioavailability |
|---|---|---|
| 20 to 30 minutes after topical application to intact skin. | 1 to 5 hours post-removal, depending on duration of application. | Approximately 3-5% systemic absorption from intact skin; significantly higher from mucous membranes or damaged skin. |
2. Mechanism of Action
Lidocaine stabilizes neuronal membranes by reversibly inhibiting the ionic fluxes required for the initiation and conduction of nerve impulses. It achieves this by binding to specific voltage-gated sodium channels on the inner portion of the neuronal cell membrane.
3. Indications & Uses
- Topical anesthesia for intact skin prior to minor dermatological procedures (e.g., needle insertion, laser therapy, skin biopsy)
- Management of localized neuropathic pain conditions like post-herpetic neuralgia (PHN) as an adjunct (off-label but common)
4. Dosage & Administration
Adult Dosage: Apply one plaster/patch (typically up to 3 plasters) to intact skin covering the most painful area. Apply for up to 12 hours in a 24-hour period. Maximum application time per day should not exceed 12 hours.
Administration: 1. Apply to intact, non-irritated, non-hairy skin. 2. Clip hair if necessary; do not shave. 3. Apply plaster to dry skin. 4. Press firmly to ensure good contact. 5. Remove after recommended time (e.g., 1-5 hours for procedures, up to 12 hours for pain). 6. Wash hands after application and removal. 7. Do not apply external heat sources (heating pads) over the plaster.
5. Side Effects
Common side effects may include:
- Localized skin reactions: Erythema (redness), edema, pruritus (itching), burning sensation at application site.
- Blanching or pallor of skin.
- Altered sensation (numbness) beyond the target area.
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Class I Antiarrhythmics (e.g., Mexiletine, Tocainide) | Additive cardiotoxic effects; increased risk of arrhythmias. | Major |
| CYP1A2 & CYP3A4 Inhibitors (e.g., Ciprofloxacin, Fluconazole, Amiodarone) | Increased lidocaine plasma levels, risk of toxicity. | Moderate |
| Beta-blockers (e.g., Propranolol) | Reduce hepatic blood flow, decreasing lidocaine clearance, increasing toxicity risk. | Moderate |
| Other Local Anesthetics | Additive toxic effects. | Major |
7. Patient Counselling
- DO apply only to intact, clean, dry skin.
- DO wash hands before and after handling the plaster.
- DO store out of reach of children and pets.
- DO NOT cut or trim the plaster.
- DO NOT apply heat (heating pad, hot water bottle) over the plaster.
- DO NOT apply to eyes, mouth, wounds, or mucous membranes.
- DO NOT use for more than 12 hours in a 24-hour period.
- DO NOT use more plasters than prescribed.
8. Toxicology & Storage
Overdose: CNS: Lightheadedness, tinnitus, metallic taste, blurred vision, tremors, drowsiness, convulsions, respiratory depression. Cardiovascular: Hypotension, bradycardia, heart block, ventricular arrhythmias, asystole.
Storage: Store at room temperature (15°C to 30°C). Protect from moisture and direct sunlight. Keep in the original packaging until use. Do not freeze.