Previous studies have shown that generation of free radicals is increased following pentylenetetrazol kindling, due to increased cytosolic Ca(2+) concentrations. Topiramate, a voltage-gated calcium channel inhibitor, has an evident effect in the treatment of childhood epilepsy; however, topiramate may cause nephrotoxicity. We investigated the effects of topiramate and vitamin E administration on pentylenetetrazol-induced nephrotoxicity in rats by evaluation of lipid peroxidation, nitric oxide, glutathione peroxidase, catalase and superoxide dismutase values. Forty male Wistar rats were randomly divided into five equal groups. Group 1 was used as control and group II received a single dose of pentylenetetrazol. Fifty and 100 mg/kg topiramate daily were intragastrically administered to rats in groups III and IV for 7 days, respectively. Intragastric 100 mg topiramate (daily for 7 days) and intraperitoneal vitamin E (150 mg/kg, daily for 3 days) combination were given to animals in group V before a single-dose pentylenetetrazol administration. Serum and kidney samples were taken after 3 hr of pentylenetetrazol administration. Pentylenetetrazol resulted in a significant increase in nitric oxide levels of serum and kidney, and lipid peroxidation levels of kidney although superoxide dismutase and catalase activities in the kidney was reduced by pentylenetetrazol administration. The lipid peroxidation levels in serum and kidneys and the nitric oxide levels in kidneys of groups III, IV and V were decreased by topiramate although the superoxide dismutase and catalase activities in the kidneys were increased. Lipid peroxidation and nitric oxide levels were reduced by the topiramate and vitamin E combination compared to only topiramate. Glutathione peroxidase activity was not affect by pentylenetetrazol, topiramate and vitamin E administrations. In conclusion, topiramate and vitamin E have protective effects on pentylenetetrazol-induced nephrotoxicity by inhibition of free radicals and by support of the antioxidant redox system.