Characterization of Amikacin Drug Exposure and Nephrotoxicity in an Animal Model.

Despite excellent in vitro activity, aminoglycosides are used conservatively to treat multidrug resistant bacterial infections due to their associated nephrotoxicity. Aminoglycosides are known to accumulate in the kidneys, but the quantitative relationship between drug exposures and nephrotoxicity is not well established. To bridge the knowledge gap, the objective of this study was to develop an animal model with clinically relevant conditions to mimic human disease progression. Single dose pharmacokinetics were studied in Sprague-Dawley rats dosed either with 100 or 500 mg/kg of amikacin subcutaneously. Serial blood samples were collected and serum amikacin concentrations were measured using liquid chromatography tandem mass spectrometry. Rats were also dosed with amikacin once daily for up to 10 days; blood samples were taken at baseline and daily to detect nephrotoxicity (defined as doubling of serum creatinine from baseline). Kidneys from both studies were harvested from selected rats and amikacin concentrations in renal tissues were measured. A dose-dependent increase in systemic AUC was observed, which ranged from approximately 1/3 (AUC=53 mg*h/L) to 3 times (AUC=650 mg*h/L) the expected exposure resulting from standard dosing in humans. Nephrotoxicity was significantly higher in rats given 500 mg/kg (100% vs. 30%, p=0.003). Kaplan-Meier analysis also showed a significant difference in nephrotoxicity onset between the two groups (p=0.001). Finally, analysis of the renal tissues showed that accumulation of amikacin could be associated with nephrotoxicity. These results are consistent with clinical observations, which support using this model in the future to investigate intervention(s) that can be used clinically to alleviate nephrotoxicity.