Background : Postherpetic neuralgia (PHN) is a complication of acute herpes zoster, which is emerging as a\r\npreferred clinical trial model for chronic neuropathic pain. Although there are published metaanalyses\r\nof analgesic therapy in PHN, and neuropathic pain in general, the evidence base has\r\nbeen substantially enhanced by the recent publication of several major trials. Therefore, we\r\nhave conducted a systematic review and meta-analysis for both efficacy and adverse events of\r\nanalgesic therapy for PHN.\r\nMethods and Findings : We systematically searched databases (MEDLINE 1966ââ?¬â??2004, EMBASE 1988ââ?¬â??2004, CINAHL\r\n1982ââ?¬â??2002, and PubMed [29 October 2004]) for trials of PHN. We also searched references of\r\nretrieved studies and review articles for further trials. We included trials that examined adult\r\npatients with PHN of greater duration than 3 mo, that were blinded, randomised, and had at\r\nleast one measure of pain outcome. Dichotomous pain outcome data were extracted for 50%\r\ndecrease in baseline pain using a hierarchy of pain/pain-relief measurement tools. Where\r\navailable, dichotomous data were also collected for adverse events. Calculated estimates of\r\nefficacy included relative benefit and number needed to treat.\r\nOf 62 studies identified, 35 were randomised controlled trials. Of these, 31 were placebo\r\ncontrolled and suitable for meta-analysis, from which it was possible to extract dichotomous\r\nefficacy outcome data from 25.\r\nThis meta-analysis revealed that there is evidence to support the use of the following orally\r\nadministered therapies: tricyclic antidepressants, ââ?¬Ë?ââ?¬Ë?strongââ?¬â?¢Ã¢â?¬â?¢ opioids, gabapentin, tramadol, and\r\npregabalin. Topical therapies associated with efficacy were lidocaine 5% patch and capsaicin.\r\nFinally, a single study of spinal intrathecal administration of lidocaine and methyl prednisolone\r\ndemonstrated efficacy, although this has yet to be replicated.\r\nData suggest that the following therapies are not associated with efficacy in PHN: certain\r\nNMDA receptor antagonists (e.g., oral memantine, oral dextromethorphan, intravenous\r\nketamine), codeine, ibuprofen, lorazepam, certain 5HT1 receptor agonists, and acyclovir.\r\nTopical administration of benzydamine, diclofenac/diethyl ether, and vincristine (iontophoresis)\r\nare similarly not associated with efficacy, nor are intrathecal administration of lidocaine alone or\r\nepidural administration of lidocaine and methylprednisolone, intravenous therapy with\r\nlidocaine, subcutaneous injection of Cronassial, or acupuncture. However, many of the trials\r\nthat demonstrated a lack of efficacy represented comparatively low numbers of patient\r\nepisodes or were single-dose studies, so it may be appropriate to regard such interventions as\r\nââ?¬Ë?ââ?¬Ë?not yet adequately testedââ?¬â?¢Ã¢â?¬â?¢ rather than demonstrating ââ?¬Ë?ââ?¬Ë?no evidence of efficacy.ââ?¬â?¢Ã¢â?¬â?¢ Topical\r\naspirin/diethyl ether has not been adequately tested.\r\nConclusion : The evidence base supports the oral use of tricyclic antidepressants, certain opioids, and\r\ngabapentinoids in PHN. Topical therapy with lidocaine patches and capsaicin is similarly\r\nsupported. Intrathecal administration of methylprednisolone appears to be associated with\r\nhigh efficacy, but its safety requires further evaluation
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