Gabapentin

To define the analgesic pharmacology of the K/BxN allodynic state, groups of 16-week-old K/BxN transgenic arthritic mice (n = 6/sex) received a single i.p. injection of gabapentin (100 mg/kg; Pfizer), or the NSAID, ketorolac (7.5 mg/kg; Sigma). Mice were measured for changes in tactile allodynia 1 h following treatment. Drugs were allowed to wash out for 48 h before the same procedure was repeated with a different drug. gabapentin^{50 (link),51 (link)}, and ketorolac^{24 (link)} were dissolved in normal saline, dosages were based on previous reports demonstrating anti-allodynic efficacy, absent motor or general behavioral effects, in murine models of mono / poly and inflammatory neuropathy, respectively.

Gabapentin—1-(aminomethyl)-cyclohexaneacetic acid—was kindly donated by Pfizer, Inc., New York, NY, USA. A dose of 100 mg/Kg was chosen based on previous works [76 (link),77 (link),78 (link)] for intraperitoneal (IP) injection. The drug was in its pure state, which avoided additional experiments to monitor the potential effects of excipients. This was the lowest effective dose when used in our acute pilot experiments with C57BL/6 tumor-bearing mice (data not shown here for space reasons). Its maximum effect (at 30 min post-injection) was determined in previous acute experiments of 120-min duration; in those experiments, the behavioral tests (see below) were applied with an interval of 15 min between timepoints. During this observation period, neither sedation nor motor impairment was observed in the injected mice, similarly to a previous report from another group [76 (link)]. Gabapentin was dissolved in physiological solution (0.9% NaCl; Laboratorios Behrens, Caracas, Venezuela), and 0.2 mL was the injection volume. An equivalent volume of saline was administered IP to control animals.