Evaluation of Amikacin Pharmacokinetics in Critically Ill Patients with Intra-abdominal Sepsis

Failure to predict amikacin elimination in critically ill patients with cancer based on the estimated glomerular filtration rate: applying PBPK approach in a therapeutic drug monitoring study

PURPOSE

The aim of this work was to integrate the Therapeutic Drug Monitoring (TDM) with the model-informed precision dosing (MIPD) approach, using Physiologically-based Pharmacokinetic/Pharmacodynamic (PBPK/PD) modelling and simulation, to explore the relationship between amikacin exposure and estimated glomerular filtration rate (GFR) in critically ill patients with cancer.

METHODS

In the TDM study, samples from 51 critically-ill patients with cancer treated with amikacin were analysed. Patients were stratified according to renal function based on GFR status. A full-body PBPK model with 12 organs model was developed using Simcyp V. 21, including steady-state volume of distribution of 0.21 L/kg and renal clearance of 6.9 L/h in healthy adults. PK parameters evaluated were within the 2-fold error range.

RESULTS

During the validation step, predicted vs observed amikacin clearance values after single infusion dose in patients with normal renal function, mild and moderate renal impairment were 7.6 vs 8.1 L/h (7.5 mg/kg dose); 3.8 vs 4.5 L/h (1500 mg dose) and 2.2 vs 3.1 L/h (25 mg/kg dose), respectively. However, predicted vs observed amikacin clearance after a single dose infusion of 1400 mg in critically-ill patients with cancer were 1.46 vs 1.63 (P = 0.6406) L/h (severe), 2.83 vs 1.08 (P < 0.05) L/h (moderate), 4.23 vs 2.49 (P = 0.0625) L/h (mild) and 7.41 vs 3.36 (P < 0.05) L/h (normal renal function).

CONCLUSION

This study demonstrated that estimated GFR did not predict amikacin elimination in critically-ill patients with cancer. Further studies are necessary to find amikacin PK covariates to optimize the pharmacotherapy in this population. Therefore, TDM of amikacin is imperative in cancer patients.

Detection of subclinical nephrotoxicity induced by aminoglycosides in critically ill elderly patients using trough levels and urinary neutrophil gelatinase-associated lipocalin

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.

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

OBJECTIVES

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Area under the Curve-Based Dosing of Vancomycin in Critically Ill Patients Using 6-Hour Urine Creatinine Clearance Measurement

BACKGROUND

The area under the curve- (AUC-) guided vancomycin dosing is the best strategy for individualized therapy in critical illnesses. Since AUC can be calculated directly using drug clearance (CLvan), any parameter estimating CLvan will be able to achieve the goal of 24-hour AUC (AUC24 h). The present study was aimed to determine CLvan based on 6-hour urine creatinine clearance measurement in critically ill patients with normal renal function.

METHOD

23 adult critically ill patients with an estimated glomerular filtration rate (eGFR) ≥60 mL/min who received vancomycin infusion were enrolled in this pilot study. Vancomycin pharmacokinetic parameters were determined for each patient using serum concentration data and a one-compartment model provided by MONOLIX software using stochastic approximation expectation-maximization (SAEM) algorithm. Correlation of CLvan with the measured creatinine clearance in 6-hour urine collection (CL6 h) and estimated creatinine clearance by the Cockcroft-Gault formula (CLCG) was investigated.

RESULTS

Data analysis revealed that CL6 h had a stronger correlation with CLvan rather than CLCG (r = 0.823 vs. 0.594; p < 0.001 vs. 0.003). The relationship between CLvan and CL6 h was utilized to develop the following equation for estimating CLvan: CLvan (mL/min) = ─137.4 + CL6 h (mL/min) + 2.5 IBW (kg) (R 2  = 0.826, p < 0.001). Regarding the described model, the following equation can be used to calculate the empirical dose of vancomycin for achieving the therapeutic goals in critically ill patients without renal impairment: total daily dose of vancomycin (mg) = (─137.4CL6-h (mL/min) + 2.5 IBW (kg)) × 0.06 AUC24 h (mg.hr/L).

CONCLUSION

For AUC estimation, CLvan can be obtained by collecting urine in a 6-hour period with good approximation in critically ill patients with normal renal function.