Gabapentin, [1-(aminomethyl)cyclohexaneacetic acid withmolecular formula of C9H17NO2, m.w. 171.24; Neurontin; PfizerInc., New York, NY, USA], is an anticonvulsant drug used asadjunctive therapy in humans for the treatment of partial seizuresnot adequately controlled with standard antiseizure drugs (Wolfet al., 1996; Gambelunghe et al., 2005). Gabapentin is a structuralanalog of the inhibitory neurotransmitter gamma-aminobutyricacid (GABA) and therefore, like benzodiazepines and barbiturates,it is very likely that gabapentin has the potential to produceanxiolytic, analgesic, sedative, and ⁄ or tranquilizing, skeletalmuscle relaxant, and anticonvulsant activities in racing horses.Gabapentin is generally used as an add-on therapy for controlof partial seizures in patients who have not achieved satisfactorycontrol with, or who are intolerant to standard anticonvulsants.Although its structure resembles GABA, the actual mode ofaction of gabapentin is still unknown (Goa & Sorkin, 1993; Berryet al., 2003). It has been shown that gabapentin does not possessaffinity for GABAAor GABABreceptors, it is not metabolized to aGABA or GABA agonist, and it does not inhibit GABA uptake ordegradation (Gambelunghe et al., 2005). It has been proposedthat gabapentin may alter the metabolism of amino acids in thebrain and may bind to specific neuronal proteins in the brain(Chadwick, 1994; Taylor, 1994). Several other possible modes ofaction of gabapentin were recently summarized by Stefan andFeuerstein (2007) including augmentation of nonspecific cationchannels like the hyperpolarization-activated cation channel,acting as an agonist of ATP-dependent potassium channels, andbinding with high affinity to the ¥2d type 1 and 2 subunits ofvoltage-gated calcium channels