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 summation 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.
- Drug profiling
- Experimental pain
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This study is supported by an unrestricted grant from Pfizer Ltd. (Sandwich Laboratories, Kent, UK). Pfizer provided the active (gabapentin) and placebo drugs. John P. Huggins, M.Sc. Pharm, and Trevor S. Smart, M.Sc., from Pfizer provided valuable help in designing the study and commenting on the manuscript. Furthermore, they provided help to ensure that all good clinical practice regulations were fulfilled and hence helped submitting the protocol, provided a monitor, and helped design and print the case record forms. None of the other authors have any financial interest in Pfizer or act as consultants for Pfizer.