Abstract
 Purpose: Gentamicin is an antibiotic, used to treat infections caused by microorganisms. Endogenous antioxidants are strengthened by using antioxidant protectors against the toxic effects caused by drugs. Rosmarinic acid has antioxidative, anti-inflammatory, antiapoptotic, and antitumoral effects. In our study, we aimed to investigate the protective effect, immunohistochemical changes, oxidative markers, histopathological changes and inflammation related Ifi44 expression of rosmarinic acid against gentamicin induced nephrotoxicity in rats.
 Materials and methods: In our study, 32 rats randomly divided into four groups. These groups are consisted of control group, gentamicin group received gentamicin 100 mg/kg/day, gentamicin + rosmarinic group acid received gentamicin 100 mg/kg/day and rosmarinic acid 50 mg/kg/day, and rosmarinic acid group received rosmarinic acid 50 mg/kg/day. At the end of the study, histopathological, immunohistochemical, and biochemical changes in kidney tissues evaluated. 
 Results: Rosmarinic acid reduced creatine, urea, blood urea nitrogen, and total oxidative stress in blood serum. The toxic effect of gentamicin caused severe histopathological changes in the kidneys. A slight decrease in histopathological changes observed in the gentamicin + rosmarinic acid group. Antiproliferative Ifi44 expression was higher in the gentamicin group and gentamicin + rosmarinic acid group.
 Conclusion: As a result of the application of rosmarinic acid, a decrease in oxygen radicals and an increase in antioxidant levels observed. When used in combination with gentamicin and rosmarinic acid, the protective effect of rosmarinic acid was partially observed, but it could not provide full protection.