Lidocaine 5% w/w is a high-potency topical amide local anesthetic, primarily formulated as a medicated plaster or patch for targeted, localized pain relief. It works by stabilizing neuronal membranes and inhibiting the ionic fluxes required for the initiation and conduction of nerve impulses, specifically targeting abnormal sodium channels in damaged or sensitized nociceptors. In the Indian context, it is a cornerstone in the management of post-herpetic neuralgia (PHN) and other localized neuropathic pain conditions, offering a non-systemic, well-tolerated option with minimal systemic absorption.
Adult: Apply one plaster (up to a maximum of 3 plasters) to the most painful area(s) of intact skin. Apply once daily for up to 12 hours, followed by a 12-hour plaster-free period.
Note: 1. Apply to intact, dry, non-hairy skin. 2. Cut plaster to size if needed, before removing release liner. 3. Apply firmly, ensuring good contact. 4. Wash hands after handling. 5. After 12 hours, remove plaster, fold adhesive sides together, and dispose safely. 6. Allow skin to rest for 12 hours before next application. Avoid external heat sources (heating pads) over the plaster.
Lidocaine acts by blocking voltage-gated sodium channels (Nav) on neuronal cell membranes. By binding preferentially to inactivated channels, it stabilizes the neuronal membrane and inhibits depolarization, thereby preventing the generation and propagation of action potentials, specifically in sensory nerves. The 5% topical formulation provides a high local concentration that penetrates the dermis to reach subcutaneous nociceptors.
Pregnancy: Category B (US FDA). Animal studies show no risk, but no adequate, well-controlled studies in pregnant women. Use only if clearly needed, weighing benefit against potential fetal risk. Systemic absorption is minimal with topical use.
Driving: May cause dizziness or somnolence in some patients. Patients should be cautioned about operating machinery or driving until they know how the medication affects them.
| Class I Antiarrhythmics (e.g., Mexiletine, Tocainide) | Additive cardiotoxic and neurotoxic effects; increased risk of arrhythmias and seizures. | Major |
| CYP1A2 & CYP3A4 Inhibitors (e.g., Fluvoxamine, Ciprofloxacin, Ketoconazole, Erythromycin) | May increase lidocaine plasma levels, increasing toxicity risk. | Moderate |
| CYP1A2 Inducers (e.g., Omeprazole, Smoking) | May decrease lidocaine plasma levels, potentially reducing efficacy. | Moderate |
| Other Local Anesthetics | Additive toxic effects if administered concurrently via other routes (e.g., injection). | Major |
| Drugs causing Methemoglobinemia (e.g., Sulfonamides, Dapsone, Nitrates, Primaquine) | Increased risk of developing methemoglobinemia. | Moderate |
Same composition (Lidocaine (5% w/w)), different brands: