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Response of chronic neuropathic pain syndromes to ketamine: a preliminary study
Miroslav Backonja1, George Arndt, Kathy A Gombar
1Department of Neurology University of Wisconsin Hospital and Clinics, Madison, WI 53792 USA Department of Anesthesiology University of Wisconsin Hospital and Clinics, Madison, WI 53792 USA Department of Pain clinic University of Wisconsin Hospital and Clinics, Madison, WI 53792 USA Department of Pharmacy Service, University of Wisconsin Hospital and Clinics, Madison, WI 53792 USA.
Abstract:
Hyperactivity of N-methyl-D-aspartate (NMDA) receptors may be one of the factors in the genesis of neuropathic pain. Ketamine is an NMDA-blocking agent widely used in human medicine. Ketamine (at 250 mcg/kg i.v. slow push) was administered to 6 patients for control of chronic neuropathic pain syndromes in double-blind placebo-controlled fashion. All 3 patients with peripheral nervous system (PNS) disease-related pain, and 2 of 3 patients with central pain and dysesthesia syndromes responded with a temporary decrease in the rating of ongoing pain. The allodynia, hyperalgesia and after-sensation present in 5 patients improved after the administration of ketamine. Dose-response estimation in 2 patients with PNS-related neuropathic pain revealed that ketamine was effective in dose-related fashion. Continuous subcutaneous infusion of ketamine administered to 1 patient with PNS-related neuropathic pain caused no additional improvement in pain control but caused intolerable cognitive and memory side effects. In contrast, side effects during single-dose injections were mild and well tolerated. Ketamine affected the evoked pain and associated after-sensation in chronic neuropathic pain syndromes more than the ongoing constant pain.