Effects of gabapentin on experimental somatic pain and temporal summation

Background and objectives: Gabapentin is used for treatment of neuropathic pain, but its effect on different somatic pain modalities and integrative mechanisms are not completely understood. The aim of this double-blind, placebo-controlled experimental pain study, conducted on 20 healthy volunteers, was to examine the effect of a single dose of 1200 mg gabapentin on multi-modal experimental cutaneous and muscle pain models. Methods: The following pain models were applied: (1) pain thresholds to single and repeated cutaneous and intramuscular electrical stimulation (temporal sununation to 5 stimuli delivered at 2 Hz); (2) stimulus-response function relating pain intensity scores (visual analog scale, VAS) to increasing current intensities for electrical skin and muscle stimuli (single and repeated, determined at baseline); and (3) the pain intensity (VAS) and pain areas after intramuscular injection of hypertonic saline. Pain assessments were performed prior to, and at 4, 6, and 8 hours after medication. Results: When responses were averaged across the post-dose times, gabapentin: (1) significantly increased the temporal summation pain threshold in skin compared with placebo (P =.03); (2) significantly reduced the area under the pain intensity curve to hypertonic saline injections in the muscle (P =.02); and (3) significantly reduced the area of pain evoked by hypertonic saline (P =.03). Conclusions: Gabapentin reduces temporal summation of skin stimuli at pain threshold intensities; this may have potential as a biomarker for drugs with efficacy on neurogenic pain. The data also suggest that tonic muscle pain is responsive to gabapentin treatment and suggest further clinical studies.