Review of lidocaine patch 5% studies in the treatment of postherpetic neuralgia.

Postherpetic neuralgia (PHN) is a chronic pain syndrome that disproportionately affects the elderly; its incidence is anticipated to increase as the population ages. PHN presents as pain (continuous burning or intense paroxysmal), most often with tactile allodynia, which may be severe and disabling, resulting in poor quality of life and depression. Traditional treatments have included tricyclic antidepressants, anticonvulsants and opioids; however, adverse systemic effects associated with these agents have led to the development of a newer and potentially safer agent, the topical lidocaine patch 5% (Lidoderm), a targeted peripheral analgesic. This article reviews the clinical pharmacology of the lidocaine patch 5% for the treatment of PHN and summarises data from clinical trials of its safety, tolerability and efficacy. The Medline search terms "lidocaine" and "patch" were used to search for English-language articles on the pharmacokinetics of the lidocaine patch 5% and its clinical use for the treatment of PHN. Additional published studies not identified by the database search but performed by the authors or their colleagues were also included in the review. The systemic absorption of lidocaine from the patch was minimal in healthy adults when four patches were applied for up to 24 hours/day, and lidocaine absorption was even lower among PHN patients than healthy adults at the currently recommended dose. Vehicle-controlled and open-label trials found the lidocaine patch 5%, either alone or in combination with other agents, to be effective in the treatment of PHN. Most adverse events were at patch application sites; no clinically significant systemic adverse effects were noted, including when used long term or in an elderly population.In patients with PHN, the lidocaine patch 5% has demonstrated relief of pain and tactile allodynia with a minimal risk of systemic adverse effects or drug-drug interactions. Because of its proven efficacy and safety profile, the lidocaine patch 5% has been recommended as a first-line therapy for the treatment of the neuropathic pain of PHN.