Objectives: There is an abundance of literature on the efficacy of gabapentin for the treatment of neuropathic pain. Two studies have demonstrated an effect of a single dose of gabapentin on experimental cutaneous hyperalgesia. This study evaluated the effect of chronic delivery of oral gabapentin on experimentally induced cutaneous hyperalgesia.
Methods: A randomized, double-blinded, placebo-controlled crossover design methodology was conducted. Participants took part in two 10-day study sessions, separated by a 7-day washout period. One session was with gabapentin and one with placebo. Study drug was administered 300 mg b.i.d. from day 1 to 3, 300 mg q.i.d. from day 4 to 6 and 600 mg t.i.d. from day 7 to 10. At baseline, day 4, day 7, and day 10, quantitative sensory testing was performed to thermal and mechanical stimuli. On day 10, only intradermal capsaicin was injected on the volar aspect of the forearm followed by an assessment of pain and hyperalgesia. Side effects were recorded by the participants each evening.
Results: Thirteen participants were enrolled into the study. Three dropped out because of intolerable side effects. Ten participants completed the study and were able to tolerate the highest dose of gabapentin. Oral gabapentin had no significant effect on acute sensory thresholds, pain, secondary hyperalgesia, or flare response induced by intradermal capsaicin. There were significantly more side effects associated with gabapentin with sedation and dizziness being the most common.
Discussion: This study demonstrated a lack of effect of the chronic delivery of oral gabapentin on experimentally induced cutaneous hyperalgesia. The discrepancy of this finding with other studies using single oral doses may be the result of differences in the models used and differences in drug kinetics and plasma levels. The results of this study do not correlate with the clinical studies on gabapentin, which demonstrate efficacy at 1800 mg/d.