Insufficient evidence to recommend topical lidocaine as first-line treatment for postherpetic neuralgia

The Cochrane Pain, Palliative and Supportive Care Group Trials Register, Cochrane Central Register of Controlled Trials, Medline, Embase, LILACS (Latin American and Caribbean Health Sciences), SIGLE (System for Information on Grey Literature in Europe)(for conference proceedings) and Science Citation Index were searched, along with the reference lists of all eligible trials, key textbooks and previous systematic reviews. Authors of all identified trials were contacted.

Studies of interest were randomised controlled trials (RCT) or quasi-RCT comparing all topical applications of lidocaine, including gels and patches in people of all ages suffering from postherpetic neuralgia (PHN; pain persisting at the site of shingles at least 1 month after the onset of the acute rash).

Data were extracted independently by two authors with disputes resolved by a third reviewer. A meta-analysis was conducted using a fixed-effect approach.

Three trials were included, giving a total of 182 individuals who used topical lidocaine and 132 controls. Two trials provided data on pain relief, and the remaining study provided data on secondary outcome measures. The largest trial published as an abstract compared a topical lidocaine patch to a placebo patch and accounted for 150 of the 314 patients (48%). A meta-analysis combining two of the three studies identified a significant difference between the topical lidocaine and control groups for the primary outcome measure: a mean improvement in pain relief according to a pain relief scale. Topical lidocaine relieved pain better than placebo (P 0.003). There was a statistical difference between the groups for the secondary outcome measure of mean score-reduction on a visual analogue scale (P 0.030), but this was only for a single small trial. There were a similar number of adverse skin reactions in both treatment and placebo groups.

There is insufficient evidence to recommend topical lidocaine as a first-line agent in the treatment of PHN with allodynia. Further research should be undertaken on the efficacy of topical lidocaine for other chronic neuropathic pain disorders, and also to compare different classes of drugs (eg, topical anaesthetics versus anti-epileptics).