The NMDA (N-methyl-D-aspartate) receptor antagonist memantine in the treatment of postherpetic neuralgia: a double-blind, placebo-controlled study

A double-blind, randomized, placebo-controlled trial was conducted to study the analgesic efficacy of the NMDA (N-methyl-D-aspartate) receptor antagonist memantine (1-amino-3,5-dimethyladamantane hydrochloride) in relieving postherpetic neuralgia (PHN). Memantine (or an identical-looking placebo; n = 12/group) was administered at a dose of 10 mg/day for one week, and 20 mg/day for an additional 4 weeks. All patients were required to record their pain level twice daily during the entire study period, with the use of a 0-10 numerical pain scale (NPS). The McGill Pain Questionnaire (MPQ), spontaneous pain, and a series of mechanical and thermal stimuli-induced pain were measured with the use of a 0-100 visual analogue scale (VAS), on six office visits. Quantitative thermal testing (QTT) and routine blood tests were performed at the beginning and at the end of the study. Although reduction in spontaneous pain, mechanical and cold allodynia, mechanical hyperalgesia, and 'wind-up' like pain were found in both groups, there were no significant differences between memantine and the placebo on any of the outcome measures. No changes were found in either group in MPQ scores or in quantitative thermal thresholds. Although three patients were withdrawn from the memantine group and only one from the control group, no differences in incidence of adverse effects between the two groups were found. Study results show that memantine is ineffective in reducing spontaneous and evoked pain in patients with PHN.