Neuropathic pain is caused by nerve damage, often accompanied by changes in the central nervous sytem, and fibromyalgia is a related complex pain syndrome. Many people with these conditions are disabled with moderate or severe pain for many years. Conventional analgesics are usually not effective treatment options. In light of the fact that there are similarities between the pathophysiologic and biochemical mechanisms observed in epilepsy and in neuropathic pain, it is not surprising that antiepileptic agents can be used to treat neuropathic pain. The aim of this review was to investigate the efficacy and adverse events associated with use of sodium valproate and valproic acid for the treatment of chronic neuropathic pain and fibromyalgia. We identified three relevant studies, two in diabetic neuropathy and a third in post-herpetic neuralgia. Two of the three studies report significantly greater reduction in pain for valproate than placebo, but studies were small (≤ 45 participants) and provided insufficient data for pooled analysis, and the methods of analysis used may have overestimated treatment effect. Adverse events such as nausea, sedation, drowsiness, vertigo, and abnormal liver function are more common with valproate than placebo, but these studies were unsuitable to allow for a comprehensive assessment of harm.
There is insufficient evidence to support the use of valproic acid or sodium valproate as a first-line treatment for neuropathic pain.