OBJECTIVES: Cumulative evidence support a beneficial effect of botulinum toxin A (BTX-A) in postherpetic neuralgia (PHN). We aimed to assess efficacy, safety, and tolerability of BTX-A in the management of PHN, performing a randomized, double-blind, single-dose, placebo-controlled trial.METHODS: Thirty adults with PHN were randomized either to BTX-A or placebo. Severity of pain was evaluated by patients using a visual analogue scale (VAS) and quality of sleep was assessed using a 5-item questionnaire. Primary outcome was reduction in VAS score, with a greater than 50% reduction being considered clinically significant. Secondary outcomes were reduction in sleep score and maintenance of VAS score after treatment, with over 50% maintenance considered clinically meaningful.RESULTS: Thirteen patients from the experimental arm achieved an at least 50% reduction in VAS score, compared with none of the placebo patients (NNT=1.2, 95% CI, 2-1; ARR=0.87, 95% CI, 055-096; P<0.001). BTX-A patients showed significant reduction in VAS pain scores between baseline and week 2, which persisted for a median period of 16 weeks. BTX-A patients showed significant reduction in sleep scores between baseline and week 2, which remained unchanged until 16th week (P<0.001). Treatment was well tolerated.DISCUSSION: Data confirm that BTX-A is effective and well tolerated in the treatment of PHN.