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.