Can a lidocaine 5% patch be applied over the shingles lesions in an elderly patient with post‑herpetic neuralgia?

Can Lidocaine 5% Patches Be Applied Over Shingles Lesions?

No, lidocaine 5% patches should NOT be applied directly over active shingles lesions with broken skin or blisters, but CAN be applied to intact skin areas within the painful dermatome, avoiding any areas with open vesicles, erosions, or damaged skin. 1, 2

Critical Safety Principle: Intact Skin Only

• Application to broken or inflamed skin dramatically increases systemic absorption and creates significant toxicity risk, making this an absolute contraindication regardless of the clinical scenario 3, 1, 2
• The patches must be applied only to intact portions of the painful skin area, carefully avoiding any blisters, erosions, ulcerations, or areas of skin breakdown 4
• This restriction exists because damaged skin barrier function allows exponentially higher lidocaine absorption into systemic circulation, potentially reaching toxic levels 1, 2

Evidence-Based Application Strategy for Post-Herpetic Neuralgia

• For post-herpetic neuralgia with healed lesions and intact skin, lidocaine 5% patches are a first-line therapy with exceptional efficacy (NNT = 2), with approximately 60% of patients achieving moderate to complete pain relief 1
• Apply up to 3-4 patches simultaneously to cover the painful area for 12 hours daily, followed by a mandatory 12-hour patch-free interval 1, 5, 6
• The patches work by blocking peripheral sodium channels and dampening nociceptor sensitization without producing complete sensory block 7, 8

Special Consideration for Acute Herpes Zoster

• One randomized, double-blind study demonstrated that lidocaine patches applied to intact portions of skin (avoiding blisters) in acute herpes zoster (within 4 weeks of onset) provided significant pain relief compared to vehicle patches, with mean pain reduction differences of 14.7 points at rest (P = 0.005) and 10.4 points during movement (P = 0.007) 4
• This study specifically excluded application over damaged skin and blisters, applying patches only to intact painful areas within the affected dermatome 4
• However, this approach requires careful patient selection and meticulous avoidance of any compromised skin 4

Alternative Topical Approach When Patch Adhesion Is Problematic

• Lidocaine cream formulations may be employed as an alternative when patch adhesion is difficult or when the affected area configuration makes patch application impractical, though patches generally provide superior sustained delivery 1
• The 5% prescription strength is preferred over 4% over-the-counter formulation for neuropathic pain conditions 5, 2

Pharmacokinetic Safety Profile

• Even with four patches applied over 24 hours to intact skin, systemic lidocaine levels remain minimal (highest measured at 0.1 micrograms/ml), well below toxic thresholds 1, 6
• This minimal systemic absorption makes patches safer than systemic analgesics in elderly patients or those with organ dysfunction 2

Combination Therapy Algorithm When Patches Alone Are Insufficient

• If inadequate pain relief after 3-4 weeks of patch therapy, add gabapentin starting at 50-100 mg three times daily, titrating to 900-3600 mg daily 1, 5
• Alternatively, consider pregabalin 50 mg three times daily, titrated to 100 mg three times daily if gabapentin fails 1
• Capsaicin 8% patch provides pain relief lasting up to 90 days from single application (NNT = 3.26), with pre-treatment using lidocaine cream for 60 minutes before capsaicin application 1

Monitoring for Systemic Toxicity (Though Rare with Topical Use)

• Monitor for signs of systemic absorption: dizziness, confusion, bradycardia, drowsiness, disorientation, muscle twitching, though these are uncommon with proper topical application 1, 5, 2
• Avoid excessive heat application over patches, as this increases systemic absorption 1, 5

Common Pitfall to Avoid

• The most critical error is applying patches to any area of broken skin, which transforms a safe topical therapy into a potentially dangerous systemic exposure 3, 1, 2
• Do not exceed 12 hours of continuous application to ensure adequate patch-free period and minimize skin irritation 1
• Do not use patches within 4 hours of other local anesthetic interventions to prevent cumulative toxicity 5, 2