Pain relief postherpetic neuralgia

King RB. 1993. Topical aspirin in chloroform and the relief of pain due to herpes zoster and postherpetic neuralgia. Arch Neurol 50 1046-1053. 

Capsaicin (Zostrix) is approved for the relief of pain following herpes zoster infection (postherpetic neuralgia). The drug depletes neurons of substance P, an endogenous neuropeptide that may mediate cutaneous pain. It is applied to affected skin after open lesions have healed. Local irritation is common. 

Unlabeled Uses Relief of neuropathic pain, such as that experienced by patients with diabetic neuropathy or postherpetic neuralgia treatment of anxiety, bulimia nervosa, migraine, nocturnal enuresis, panic disorder, peptic ulcer, phantom limb pain... 

Finally, local anesthetics can be administered via a transdermal patch.1 In particular, transdermal patches containing 5% lidocaine have been used to treat localized pain in musculoskeletal conditions (osteoarthritis, low back pain, myofascial pain)22,25,26 and various types of neuropathic pain (postherpetic neuralgia, diabetic neuropathy).2,24,58 As indicated in Chapter 2, transdermal patches provide a convenient and predictable method for administering drugs to a given anatomical site, and lidocaine patches are now being used to provide symptomatic relief in many conditions involving fairly localized pain. 

This pungent product is responsible for the intense irritant effects of topical Capsicum preparations. Repeated application of capsaicin can deplete and prevent reaccumulation of substance P, an endogenous mediator of pain impulses from the periphery to the CNS. Since the early 1990s, capsaicin cream has been available in the U.S. as an approved drug for relief of postherpetic neuralgia and pain due to diabetic neuropathy and osteoarthritis. 

The local anesthetic lidocaine provides significant relief of neuropathic pain in the clinic when administered systemically at subanesthetic doses. In several placebo-controlled studies, intravenous infusions of lidocaine significantly reduced neuropathic pain at plasma concentrations of 1.5-5 pgmL 1 [59-61]. Lightheadedness is a common side effect at therapeutic doses, whereas cardiac depression is associated with plasma concentrations of 20-25 xgmL 1. A transdermal formulation of lidocaine is approved in the United States for the treatment of postherpetic neuralgia [62]. Orally available state-dependent Nayl blockers have shown efficacy in the clinic when appropriate plasma concentrations are achieved. 

Topical 5% lidocaine to 33 patients with postherpetic neuralgia in a crossover trial provided significantly more pain relief than a vehicle patch placebo (41). There was no difference in reported adverse effects skin redness or rash was reported by 9 in the lidocaine patch phase and 11 in the placebo phase. One patient stopped using the placebo patch owing to red irritated skin, which resolved after the application of lidocaine patches. 

In a phase IV trial, 66% patients with postherpetic neuralgia gained relief from a 5% hdocaine patch applied to the most painful area of the body (43). The lidocaine patch was well tolerated, a rash being the most common adverse effect, in 14% of patients. 

A lidocaine transdermal palch (Lidoderm) is used in relief of pain associated with postherpetic neuralgia. The combination of lidocaine (2.59%) and prilocaine (2.5%) in an occlusive dressing (Emla anesthetic disc) is used as an anesthetic prior to venipuncture, skin graft harvesting, and infiltration of anesthetics into genitalia. 

Greenway, F. L., Frome, B. M., Engels, T. M., McLellan, A. 2003. Temporary relief of postherpetic neuralgia pain with topical geranium oil [letter], 115 586-587. 

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