THE NMDA RECEPTOR ANTAGONIST AMANTADINE REDUCES SURGICAL NEUROPATHIC PAIN IN CANCER-PATIENTS - A DOUBLE-BLIND, RANDOMIZED, PLACEBO-CONTROLLED TRIAL

Neuropathic pain is often severe, persistent, and responds poorly to a nalgesic medications. Recent evidence suggests that N-methyl-D-asparta te (NMDA) receptor antagonists may be effective in the treatment of ne uropathic pain. The present trial was designed to test the efficacy of acute administration of the NMDA receptor antagonist amantadine in re lieving surgical neuropathic pain in patients with cancer. The study s ample consisted of 15 cancer patients with the diagnosis of surgical n europathic pain. Two 500 ml infusions of either 200 mg amantadine or p lacebo were administered over a 3 h period, in a randomized order, 1 w eek apart from each other. Spontaneous and evoked pain were measured f or 48 h before treatment, during treatment, and for 48 h following tre atment. An average pain reduction of 85% was recorded at the end of am antadine infusion vs. 45% following placebo administration. The differ ence in pain relief between the two treatments was statistically signi ficant (P = 0.009). Mean pain intensity remained significantly lower d uring the 48 h following amantadine treatment as compared with the 48 h prior to treatment (31% reduction; P = 0.006), whereas no such effec t was found with the placebo (6% reduction; P = 0.40), Amantadine, but not the placebo, also reduced 'wind up' like pain (caused by repeated pinpricking) in four patients. We conclude that amantadine infusion i s a safe and effective acute treatment for surgical neuropathic pain i n cancer patients. Further trials with long-term oral or parenteral am antadine treatment should be conducted. (C) 1998 International Associa tion for the Study of Pain. Published by Elsevier Science B.V.