Evaluation of Current Amikacin Dosing Recommendations and Development of an Interactive Nomogram: The Role of Albumin

Therapeutic drug monitoring of Amikacin in hospitalized patients: A pilot study

Background

Amikacin, an aminoglycoside, is a widely used parenteral antibiotic. Therapeutic drug monitoring (TDM) is recommended for aminoglycosides to avoid toxicity. However, the lack of infrastructure at most places precludes it. This pilot and novel study attempt to estimate the real-world serum levels of Amikacin in hospitalised patients.

Methods

Thirty admitted patients, given Amikacin injections, were included in the study. In addition, 15 clinical specimens isolated with gram-negative bacteria were tested for minimum inhibitory concentration (MIC) value of Amikacin. Trough and peak serum levels of Amikacin were estimated by high-pressure liquid chromatography (HPLC).

Results

The average MIC value of Amikacin estimated in our laboratory was 3.92 mcg/mL. Peak and trough serum levels of Amikacin ranged from 12.1 to 66.4 mcg/ml and 1.1 to 20.7 mcg/ml, respectively. More than 83% of our patients achieved peak Amikacin levels of 15 mcg/mL, and 37% had trough levels above 5 mcg/mL. These levels are desirable watersheds as per available literature.

Conclusion

Trough levels of Amikacin in all cases and a review of dosing according to MIC values are recommended to achieve drug safety and therapeutic efficacy.

Development of a Predictive Dosing Nomogram to Achieve PK/PD Targets of Amikacin Initial Dose in Critically Ill Patients: A Non-Parametric Approach

French guidelines recommend reaching an amikacin concentration of ≥8 × MIC 1 h after beginning infusion (C_1h), with MIC = 8 mg/L for probabilistic therapy. We aimed to elaborate a nomogram guiding clinicians in choosing the right first amikacin dose for ICU patients in septic shock. A total of 138 patients with 407 observations were prospectively recruited. A population pharmacokinetic model was built using a non-parametric, non-linear mixed-effects approach. The total body weight (TBW) influenced the central compartment volume, and the glomerular filtration rate (according to the CKD-EPI formula) influenced its clearance. A dosing nomogram was produced using Monte Carlo simulations of the amikacin amount needed to achieve a C_1h ≥ 8 × MIC. The dosing nomogram recommended amikacin doses from 1700 mg to 4200 mg and from 28 mg/kg to 49 mg/kg depending on the patient's TBW and renal clearance. However, a C_through ≤ 2.5 mg/L 24 h and 48 h after an optimal dose of amikacin was obtained with probabilities of 0.20 and 0.81, respectively. Doses ≥ 30 mg/kg are required to achieve a C_1h ≥ 8 × MIC with MIC = 8 mg/L. Targeting a MIC = 8 mg/L should depend on local ecology.

Amikacin pharmacokinetics in elderly patients with severe infections

OBJECTIVE

The aim of this study was to characterize the population pharmacokinetics of amikacin in elderly patients by means of nonlinear mixed effects modelling and to propose initial dosing schemes to optimize therapy based on PK/PD targets.

METHOD

A total of 137 elderly patients from 65 to 94 years receiving intravenous amikacin and routine therapeutic drug monitoring at Hospital Universitario Severo Ochoa were included. Concentration-time data and clinical information were retrospectively collected; initial doses of amikacin ranged from 5.7 to 22.5 mg/kg/day and each patient provided between 1 and 10 samples.

RESULTS

Amikacin pharmacokinetics were best described by a two-compartment open model; creatinine clearance (CrCL) was related to drug clearance (2.75 L/h/80 mL/min) and it was augmented 28% when non-steroidal anti-inflammatory drugs were concomitantly administered. Body mass index (BMI) influenced the central volume of distribution (17.4 L/25 kg/m²). Relative absolute prediction error was reduced from 33.2% (base model) to 17.9% (final model) when predictive performance was evaluated with a different group of elderly patients. A nomogram for initial amikacin dosage was developed and evaluated based on stochastic simulations considering final model to achieve PK/PD targets (Cmax/MIC>10 and AUC/MIC>75) and to avoid toxic threshold (Cmin<2.5 mg/L).

CONCLUSION

Initial dosing approach for amikacin was designed for elderly patients based on nonlinear mixed effects modeling to maximize the probability to attain efficacy and safety targets considering individual BMI and CrCL.