What is the recommended dosage and application time for a lidocaine (local anesthetic) patch in treating post-herpetic neuralgia?

Lidocaine Patch Dosage and Application Time for Postherpetic Neuralgia

For postherpetic neuralgia, apply up to 3 lidocaine 5% patches to cover the painful area for 12 hours per day, removing the patches for the remaining 12 hours in a 24-hour period. 1

Dosage Specifications

• Strength: 5% lidocaine patch (prescription strength) is recommended over the 4% OTC version 2, 1
• Number of patches: Up to 3 patches may be used simultaneously 2, 1
• Coverage area: Apply to cover the painful area as completely as possible, up to a maximum of 420 cm² 3
• Duration: Apply for 12 hours, then remove for 12 hours in each 24-hour period 1

Application Instructions

1. Clean and dry the affected area
2. Apply patches directly to the most painful areas
3. Patches can be cut to fit the specific painful region if needed
4. Ensure good adhesion to the skin
5. Remove after 12 hours and leave off for 12 hours before reapplying new patches

Clinical Evidence

The lidocaine patch works by blocking sodium ion channels required for the initiation and conduction of neuronal impulses, resulting in local anesthesia after topical application 2. This mechanism provides targeted pain relief with minimal systemic absorption.

Clinical studies have demonstrated that the 5% lidocaine patch significantly reduces pain intensity compared to vehicle patches or no treatment 3. Pain relief begins as early as 30 minutes after application and continues throughout the 12-hour application period 3.

Efficacy and Safety

• The lidocaine patch is considered a first-line topical treatment for postherpetic neuralgia by the American Geriatrics Society 1
• Studies show significant reduction in pain intensity and improved quality of life with consistent use 4
• Minimal systemic absorption occurs, with blood levels typically not exceeding 0.1 μg/mL 3
• Long-term studies demonstrate sustained efficacy and continued tolerability for extended treatment periods 5

Common Side Effects and Precautions

• Most common adverse effects are mild skin reactions at the application site:
  • Skin redness
  • Irritation
  • Itching
• These reactions typically occur at similar rates to vehicle patches 6
• No significant systemic side effects have been reported in clinical trials 3, 4

Treatment Duration

• An adequate trial period should be at least 4 weeks to properly assess efficacy 2
• For patients who respond, treatment can be continued long-term with maintained efficacy and tolerability 5
• Earlier initiation of treatment may lead to better outcomes, though the patch is effective even in longstanding postherpetic neuralgia 4

Practical Considerations

• Patches are particularly practical for use on flat surfaces like the dorsal or plantar surface of the feet 2
• The patch delivery system may be more effective than lidocaine gel formulations as it provides gradual release over hours 2
• For patients with refractory pain, lidocaine patches can be used as part of a multimodal approach in combination with other treatments 1