Another important action mechanism of the topical lidocaine patch is the skin protection effect. Especially for patients with allodynia, the patch may act as a barrier of protection from mechanical stimu­lation such as the rubbing of clothing and inadver­tent touching. This skin barrier effect may explain why the use of a vehicle patch provided significant pain relief compared with no treatment in multiple controlled trials, including our study.

The 5% lidocaine patch is currently approved in the US FDA for the treatment of PHN at a dosage of up to three patch application to the painful area for up to 12 hours/day. However, recent phar­macokinetic studies have shown that 4 patches applied for up to 24 hours on 3 consecutive days can produce analgesia without systemic side effects or significant skin irritation.

For the present, there have been no clinical trials that have compared the efficacy of the lidocaine patch with another active treatment. In addition, as pointed out in our study, the effect of pain relief effect the subjects experienced through the use of the lidocaine patches was substantial, although not complete. Most of the other studies have shown the same limited treatment efficacy. Nevertheless, because of the ease of administration, the continuous dosing, the safety and the moderate efficacy of the 5% lidocaine patch, several recent treatment guidelines published by international authorities have recommended the lidocaine patch as a first-line treatment for PHN.
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Whether the patch is accepted as the first-line therapy or not, it can afford clinicians a therapeutic option that works well, either alone or in combina­tion with other analgesics, and it does so without systemic adverse effect and undesirable drug-to-drug interactions.

In conclusion, our study along with a review of the literature suggests that the 5% lidocaine patch can be considered as a useful and safe therapeutic option for managing the pain of PHN, either alone or in combination with systemic agents. However, further investigations need to be conducted to identify whether certain characteristics increase the likelihood of response to the lidocaine patch, which agents are more effective and for which patient comparing the topical lidocaine patch and the other therapies, and what combination of therapeutic agents provide the best pain relief and under what conditions.