By: Irene Li, PharmD Candidate c/o 2016

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Postherpetic neuralgia is the most common chronic complication of herpes zoster that affects one million people annually in the United States.¹ It is defined as dermatomal pain lasting at least 90 days after the appearance of an acute herpes zoster rash. The rash is usually unilateral. Although the most common sites are the face, back, and neck, it can involve any area. Itchiness, pain, or tingling occurs continuously or intermittently for two to three days at an area before the presentation of the rash. New lesions then appear over a period of three to five days. Within seven to ten days, the rash dries over with crusting. Some risk factors for postherpetic neuralgia include the older age, those with multiple chronic diseases, and rash and pain during the acute phase.² Since there is currently no cure for postherpetic neuralgia, treatment is primarily based on symptom control, which may require treatment for many years. Topical analgesics are considered to be first-line treatment for postherpetic neuralgia.

The use of topical analgesics is especially recommended for those who have more than one chronic health condition, cardiovascular and gastrointestinal risk factors, for those who suffer from renal or hepatic organ dysfunction, as well as the elderly.³ Topical analgesics limit many drug-drug interactions and bypass first pass metabolism. Compared with opioids, which have side effects such as constipation and sedation, the most common adverse effect of topical analgesics is minor local irritation. It is also important to differentiate between topical and transdermal medications. Topical me­dications are applied to the affected area and provide a local effect, preventing the occurrence of systemic side effects.³ Transdermal medications are not required to be applied on the area of pain and are systemically absorbed.

Lidocaine 5% patch is approved for treatment of postherpetic neuralgia.⁴ It alleviates local pain by blocking voltage-gated sodium channels, which are upregulated during chronic inflammation. Up to three patches can be applied daily to intact skin areas for up to 12 hours.⁵ When removing the patch, patients should remember to fold the adhesive sides of the patch to each other before disposal.⁴ A meta analysis pooled 12 randomized double-blind studies of at least two weeks duration comparing topical lidocaine with placebo or another active treatment for neuropathic pain.⁶ Most of the studies reflected third tier evidence, which means that there was a high risk of bias due to small study size or incomplete outcome assessment, or both. Only one multiple dose study reported that the primary outcome, > 50% or > 30% pain intensity reduction, was obtained.  Although there has been case reports that show benefits with lidocaine patches in neuropathic pain, more randomized clinical trials need to be conducted in this patient population.⁷

Although postherpetic neuralgia is debilitating and painful, healthcare professionals may consider the use of lidocaine given its minimal systemic side effects, ease of administration, and bypass of the first pass metabolism.

 

SOURCES:

1. Johnson RW, Rice AC. Postherpetic neuralgia. New Engl J Med. 2014;371:1526-33.
2. Drolet M, Brisson M, Schmader K, et al. Predictors of postherpetic neuralgia among patients with herpes zoster: a prospective study. J Pain 2010;11:1211-1221.
3. D’Arcy Y. Targeted topical analgesics for acute pain. Pain Medication News. http://www.painmedicinenews.com/ViewArticle.aspx?d=Educational Reviews&d_id=95&i=December 2014&i_id=1129&a_id=28992. Published 12/2014.
4. Stanos S. Overview of topical analgesics. Pain Medication News. http://www.painmedicinenews.com/download/Topical_PMNSE09_WM.pdf. Published 12/2009.
5. Lidocaine. In: Lexi-Drugs Online. Hudson, OH: Lexi-Comp, Inc.; [Updated January 23, 2015; Accessed June 2, 2015]. http://online.lexi.com.jerome.stjohns.edu:81/lco/action/doc/retrieve/docid/patch_f/1797833.
6. Derry S, Wiffen PJ, Quinlan J. Topical lidocaine for neuropathic pain in adults. Cochrane Database Syst Rev. 2014;7:CD010958.
7. Hans G, Robert D, Verhust J, et al. Lidocaine 5% patch for localized neuropathic pain: progress for the patient, a new approach for the physician. Clin Pharmacol. 2010;2:65-70.

[pubmed_related keyword1=’lidocaine’ keyword2=’postherpetic’ keyword3=’neuralgia’]

Published by Rho Chi Post