Divalproex sodium in the management of post-herpetic neuralgia: a randomized double-blind placebo-controlled study.

BACKGROUND Post-herpetic neuralgia is difficult to treat. Divalproex sodium (valproic acid and sodium valproate in molar ratio 1:1) has been used successfully in the management of various painful neuropathies. AIM To study the effectiveness and safety of divalproex sodium in the management of post-herpetic neuralgia. DESIGN Randomized double-blind placebo-controlled trial. METHODS We enrolled 48 consecutively attending out-patients with post-herpetic neuralgia, out of whom three were excluded (two had insufficient pain, one withdrew consent). Quantification of pain was by Short Form-McGill pain questionnaire (SF-MPQ), visual analogue scale (VAS), present pain intensity score (PPI) and 11 point Likert scale (11 PLS) at the beginning of the study, after 2 weeks, 4 weeks and at the end of the study (8 weeks). We also assessed patients' global impression of change by questionnaire at the end of the study. RESULTS After 8 weeks treatment with 1000 mg/day divalproex sodium, there was significant reduction in pain: SF-MPQ, 20.47 +/- 2.29 to 11.90 +/- 6.52 (p < 0.0001); PPI 4.0 +/- 0.52 to 1.95 +/- 1.29 (p < 0.0001); VAS 70.17 +/- 9.21 to 31.27 +/- 29.74 (p < 0.0001) and 11 PLS 6.97 +/- 0.73 to 3.63 +/- 2.34 (p < 0.0001) in comparison to placebo (means +/- SEM). The 'global impression of change' questionnaire showed much or moderate improvement in pain in 58.2% of patients receiving divalproex vs. 14.8% of those receiving placebo. The drug was well tolerated by all patients, except one who developed severe vertigo after 10 days of treatment. DISCUSSION Divalproex sodium provides significant pain relief in patients of post-herpetic neuralgia, with very little incidence of adverse reactions. These data provide a basis for longer trials in a larger group of patients.