Amantadine sulfate reduces experimental sensitization and pain in chronic back pain patients.
We investigated if established psychophysical measures of enhanced experimental sensitization in chronic musculoskeletal pain can be reduced by adjuvant treatment with a N-methyl-d-aspartate receptor antagonist, amantadine sulfate, and whether a reduction in sensitization might be accompanied by a concurrent improvement in clinical pain. Sensitization was evaluated by an experimental tonic heat model of short-term sensitization with concurrent subjective and behavioral psychophysical scaling. Twenty-six patients with chronic back pain were included in the randomized, double-blind, placebo-controlled study and received daily dosages of either placebo or 100 mg of amantadine sulfate during a 1-wk treatment. Participants completed quantitative sensory testing of pain thresholds and experimental sensitization before and after treatment and clinical pain ratings before, during, and after treatment. Experimental sensitization and clinical pain were reduced in patients receiving verum. Initially, experimental sensitization was enhanced in patients, with early sensitization at nonpainful intensities of contact heat and enhanced sensitization at painful intensities, as shown previously. After 1 wk of treatment, experimental sensitization was reduced with amantadine sulfate but not with placebo. We conclude that adjuvant chronic pain treatment with N-methyl-d-aspartate receptor antagonists might be beneficial for chronic pain if enhanced sensitization is involved and that the quantitative sensory test of temporal summation may be used to verify this.