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Gentamicin (GM) is an effective aminoglycoside antibiotic against life-threatening Gram-negative bacteria. However, a major complication of therapeutic doses of GM is nephrotoxicity, which is believed to be related to the generation of reactive oxygen species. The present study was therefore aimed to investigate the protective effect of eugenol, a phenolic antioxidant, on GM-induced nephrotoxicity in Sprague-Dawley rats. Intramuscular injection of rats with GM (80 mg/kg body weight/day) for six consecutive days induced marked acute renal failure, manifested by a sharp significant increase in serum urea and creatinine levels, along with a significant depletion of serum potassium level, compared to normal controls. GM-induced renal dysfunction was attributable to enhanced oxidative stress, as revealed by decreased superoxide dismutase and catalase activities, glutathione depletion and increased lipid peroxidation. Furthermore, kidney lactate dehydrogenase activity, as an indicator of hypoxia, was significantly increased by GM administration. Eugenol (100 mg/kg body weight, per os) administered four days before and six days concurrently with GM (80 mg/kg body weight, i.m.) restored normal renal functions and suppressed GM-induced oxidative stress and hypoxia. Light microscopical examination of the renal tissues of GM-treated animals demonstrated severe tubular necrosis at the cortex and increased cellular inflammatory processes. However, these alterations were considerably reduced with eugenol coadministration. In conclusion, eugenol ameliorates GM-induced nephrotoxicity and oxidative damage by scavenging oxygen free radicals, decreasing lipid peroxidation and improving intracellular antioxidant defense.