Comparative activity of the anti-convulsants oxcarbazepine, carbamazepine, lamotrigine and gabapentin in a model of neuropathic pain in the rat and guinea-pig

Anti-epileptic drugs (AEDs) are increasingly used for the treatment of neuropathic pain. Oxcarbazepine is a recently introduced AED that is effective in treating epilepsy and has an improved side-effect profile compared to existing therapies. Here we have examined the effect of oxcarbazepine and other AEDs in a model of neuropathic pain in the rat and guinea-pig. Oxcarbazepine and carbamazepine (3–100 mg kg −1) did not affect mechanical hyperalgesia or tactile allodynia induced by partial sciatic nerve ligation in the rat following oral administration. However, in the same model in the guinea-pig, both drugs produced up to 90% reversal of mechanical hyperalgesia with respective D 50 values of 10.7 and 0.8 mg kg −1. The active human metabolite of oxcarbazepine, monohydroxy derivative, was similarly active against mechanical hyperalgesia in the guinea-pig but not the rat. Lamotrigine (3–100 mg kg −1, p.o.) was effective against mechanical hyperlagesia in both species although it showed greater efficacy and potency in the guinea-pig (D 50 4.7 mg kg −1) compared to the rat (D 50 27 mg kg −1). Lamotrigine produced slight inhibition of tactile allodynia in the rat only at the highest dose tested of 100 mg kg −1. Gabapentin was poorly active against mechanical hyperalgesia in both the rat and guinea-pig following a single oral administration (100 mg kg −1), although upon repeated administration it produced up to 70 and 90% reversal in rat and guinea-pig, respectively. Gabapentin did however produce significant dose-related reversal of tactile allodynia in the rat following a single administration. These data show that oxcarbazepine and other AEDs are effective anti-hyperalgesic or anti-allodynic agents in an animal model of neuropathic pain, and provide further support for their use in the treatment of neuropathic pain in the clinic.