Evaluation of amikacin dosing schedule in critically ill elderly patients with different stages of renal dysfunction

Amikacin is still a widely used aminoglycoside for the treatment of life-threatening infections. The pharmacokinetic parameters of this antibiotic may be altered in critically ill conditions. Moreover, in the elderly population, pathophysiological changes affect these pharmacokinetic variables, making it difficult to predict the appropriate dose and dosing schedule for amikacin. This study aimed to characterise the pharmacokinetics of amikacin in critically ill elderly patients with renal dysfunction, and to evaluate if the available dose adjustment schedules dependent on renal function would be appropriate for empirical dosing.

Critically ill patients aged >60 years with a creatinine clearance of >20 mL/min in need of treatment with amikacin were randomly enrolled. All the patients received approximately 25 mg/kg amikacin. The patients were then divided into three groups according to the stages of their renal dysfunction based on creatinine clearance, and the optimum time to re-dosing was calculated for each group. The pharmacokinetic parameters of the patients were calculated and estimated as population pharmacokinetic data.

Of 30 patients, only 20% attained the target peak levels of amikacin of >64 mg/L. In addition, the mean volume of distribution was 0.47 L/kg. There was a poor correlation between amikacin clearance and creatinine clearance. The difference in amikacin half-life was not statistically significant among any of the stages of renal impairment.

The initial dosing of amikacin in critically ill elderly patients should not be reduced, even in the context of renal impairment. Regarding the dose adjustment in renal impairment, dosing intervals estimation, no decision can be made based on the creatinine clearance and the first dose individualisation method in terms of the two-sample measurements may be considered as an appropriate strategy.