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The Treatment of Topical Drugs for Postherpetic Neuralgia: A Network Meta-Analysis.

BACKGROUND
Postherpetic neuralgia (PHN) is a neuropathic pain that causes a reduction in patients' quality of life. There are many topical drugs for PHN, including topical lidocaine patch, topical application of capsaicin, and others.


OBJECTIVES
This study aims to compare the efficacy and safety of topical drugs for PHN.


STUDY DESIGN
Relevant studies were found by systemically searching for terms including "topical" and "Postherpetic neuralgia" in PubMed, Cochrane library, MEDLINE, and EMBASE databases (inception through June 12, 2019). The primary outcome was the percentage of change in the Numeric Rating Scale or the Visual Analog Scale scores from baseline. The secondary outcome was the number of adverse events.


METHODS
The efficacy and safety of topical drugs for PHN was investigated by the pairwise meta-analysis and Bayesian network meta-analysis, applying Revman 5.3, the Stata 14.0 software, and GeMTC 0.14.3.


RESULTS
Twelve studies met the inclusion criteria, and eligible studies were selected for the ultimate meta-analysis. Our meta-analysis displayed 6 topical drugs for PHN. Lidocaine, high-concentration capsaicin, and aspirin/diethyl ether (ADE) had a higher possibility of bringing pain relief than placebo. Among them, lidocaine had the highest possibility of being the most effective drug for PHN and had the statistical significances compared with diclofenac, high-concentration capsaicin, indomethacin, low-concentration capsaicin, and placebo, and lidocaine was significantly preferable than other effective drugs in the aspect of safety.


LIMITATIONS
(1) The small number of included studies; (2) a small number of patients and short-term trials in progress, including lidocaine and ADE; (3) both randomized controlled trial and crossover randomized trial were included in our network meta-analysis; (4) only studies published in English were evaluated; (5) lack of head-to-head comparisons of some treatments; (6) different measurement methods were used in different trial, which may cause deviation; and (7) with the lack of cycles in the included trials, the inconsistency factors cannot be calculated, and node-splitting method cannot be performed in our network meta-analysis to check the inconsistency.


CONCLUSIONS
Compared with other topical drugs, lidocaine was the most effective and most tolerable drug to be recommended for PHN.