Effect of gabapentin and lamotrigine on mechanical allodynia-like behaviour in a rat model of trigeminal neuropathic pain

Injury to the trigeminal nervous system may induce severe pain states. This study examined the antinociceptive effect of the novel anticonvulsants, ga bapentin and lamotrigine, in a rat model of trigeminal neuropathic pain pro duced by chronic constriction of one infraorbital nerve. Responsiveness to von Frey filament stimulation of the vibrissal pad was evaluated 2 weeks po st-operation. Hyper-responsive rats received acute and repeated (five injec tions separated by the half-life of the compound) injections with gabapenti n and lamotrigine. 76% of the nerve-injured rats displayed pronounced hyper -responsiveness (median 0.217 g (lower-upper percentiles 0.217-0.217) vs. 1 2.5 g preoperative), that was resistant to both single (5-100 mg/kg) and re peated (5-30 mg/kg) injections with i.p. lamotrigine. Repeated (30 and 50 m g/kg), but not single (30-100 mg/kg) injections of i.p. gabapentin partiall y alleviated the mechanical allodynia-like behaviour. Repeated injections o f gabapentin at 50 but not at 30 mg/kg produced motor deficits. The results indicate that gabapentin rather than lamotrigine may be a better therapeut ic approach for the clinical management of some trigeminal neuropathic pain disorders. (C) 2001 International Association for the Study of Pain. Publi shed by Elsevier Science B.V. All rights reserved.