Objectives Early detection of aminoglycoside-induced acute kidney injury (AKI) is crucial in intensive care unit (ICU) patients, but it is not adequately reflected by serum creatinine (SrCr) levels. This study proposed investigating the relationship between amikacin trough levels and the development of nephrotoxicity using both conventional markers and a new biomarker of renal function in critically ill elderly patients.

Methods Thirty-three critically ill patients aged ≥65 years with normal SrCr who received once-daily amikacin were evaluated. Trough levels of amikacin, creatinine clearance (CrCL) and urinary neutrophil gelatinase-associated lipocalin (uNGAL) were measured during the 10-day study period. The patients were divided into three groups and were compared based on the trough levels on both day 3 and day 7: <3 µg/mL (low trough (LT)), 3–6 µg/mL (moderate trough (MT)) and >6 µg/mL (high trough (HT)).

Results In the LT group, neither CrCL nor uNGAL levels significantly changed from baseline (p=0.364 and p=0.562, respectively). In the MT group, the CrCL level altered significantly over time from baseline (p=0.007), but the uNGAL level did not change significantly over the study period (p=0.916). In the HT group, both CrCL and uNGAL levels significantly changed from baseline during the study period (p=0.002 and p=0.046, respectively).

Conclusions In critically ill elderly patients with MT, the mean uNGAL level changed at least 4 days earlier than the SrCr level. Instead, the trough level of amikacin demonstrated a potential value for predicting subclinical AKI for implementing necessary interventions. Amikacin trough levels <3 µg/mL in the once-daily dosing regimen appeared safe, even in geriatric patients. Further studies are needed to confirm this finding.