Analgesic effect of subanesthetic intravenous ketamine in refractory neuropathic pain: a case report.

A 59-year-old male patient with progressive neuropathic pain secondary to chronic idiopathic axonal polyneuropathy responded poorly to conventional therapies including gabapentin, tricyclic antidepressants, serotonin-norepinephrine reuptake inhibitors and opioids. Following continuous intravenous administration of low dose ketamine, an N-methyl-D-aspartic acid receptor antagonist, 20 mg/h for 5 days, almost complete pain relief was obtained without significant side effects. The analgesic effect lasted 10-12 weeks and the ketamine infusion was repeated, with this pattern being maintained for 3.5 years. This supports the growing body of evidence that ketamine may be useful in the management of refractory chronic neuropathic pain. We discuss chronic idiopathic axonal polyneuropathy, neuropathic pain mechanisms, and the use of ketamine in this report.