Determinants of amikacin first peak concentration in critically ill patients

Amikacin in emergency surgery: How to dose it optimally?

Amikacin is still a recommended option in emergency surgery. Current guidelines have suggested an amikacin dose of 15-20 mg/kg/24 h for intra-abdominal infections (IAI). Our objectives were to analyse amikacin pharmacokinetics (PK) and dosage requirements in patients who underwent emergency surgery, and to identify an optimal dosing approach. We performed a retrospective data analysis of patients who received amikacin for emergency surgery over 2.5 years, with measurement of both peak (C_max) and trough (C_min) concentration after the first dose. The BestDose software was used to analyse amikacin concentrations and simulate various alternative dosage regimens in each patient. We compared concentration estimates with target values: C_max > 64 mg/L and C_min < 2.5 mg/L at 24 h. Classification and regression tree analysis was used to identify determinants of C_max target attainment (TA) and optimal dose. Data from 84 patients, including 62 with IAI, were analysed. Despite a median initial dose of 25 mg/kg, 32% of patients did not achieve the C_max target. An amikacin dose ≤ 21.5 mg/kg was the primary predictor of failure to achieve the target. A dose of 30 mg kg of total or corrected body weight, as well as a fixed dose of 2500 mg would result in the highest TA. The primary determinants of the optimal dose were ideal body weight, age, and renal function. To conclude, recommended dosages of amikacin in emergency surgery are not optimal. A fixed initial dose of 2500 mg could simplify and optimise dosing in this setting.

An international survey on aminoglycoside practices in critically ill patients: the AMINO III study

BACKGROUND

While aminoglycosides (AG) have been used for decades, debate remains on their optimal dosing strategy. We investigated the international practices of AG usage specifically regarding dosing and therapeutic drug monitoring (TDM) in critically ill patients. We conducted a prospective, multicentre, observational, cohort study in 59 intensive-care units (ICUs) in 5 countries enrolling all ICU patients receiving AG therapy for septic shock.

RESULTS

We enrolled 931 septic ICU patients [mean ± standard deviation, age 63 ± 15 years, female 364 (39%), median (IQR) SAPS II 51 (38-65)] receiving AG as part of empirical (761, 84%) or directed (147, 16%) therapy. The AG used was amikacin in 614 (66%), gentamicin in 303 (33%), and tobramycin in 14 (1%) patients. The median (IQR) duration of therapy was 2 (1-3) days, the number of doses was 2 (1-2), the median dose was 25 ± 6, 6 ± 2, and 6 ± 2 mg/kg for amikacin, gentamicin, and tobramycin respectively, and the median dosing interval was 26 (23.5-43.5) h. TDM of C_max and C_min was performed in 437 (47%) and 501 (57%) patients, respectively, after the first dose with 295 (68%) patients achieving a C_max/MIC > 8 and 353 (71%) having concentrations above C_min recommended thresholds. The ICU mortality rate was 27% with multivariable analysis showing no correlation between AG dosing or pharmacokinetic/pharmacodynamic target attainment and clinical outcomes.

CONCLUSION

Short courses of high AG doses are mainly used in ICU patients with septic shock, although wide variability in AG usage is reported. We could show no correlation between PK/PD target attainment and clinical outcome. Efforts to optimize the first AG dose remain necessary. Trial registration Clinical Trials, NCT02850029, registered on 29th July 2016, retrospectively registered, https://www.clinicaltrials.gov.

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

This study aimed to evaluate the potential efficacy and safety of the amikacin dosage proposed by the main guidelines and to develop an interactive nomogram, especially focused on the potential impact of albumin on initial dosage recommendation. The probability of target attainment (PTA) for each of the different dosing recommendations was calculated through stochastic simulations based on pharmacokinetic/pharmacodynamic (PKPD) criteria. Large efficacy and safety differences were observed for the evaluated amikacin dosing guidelines together with a significant impact of albumin concentrations on efficacy and safety. For all recommended dosages evaluated, efficacy and safety criteria of amikacin dosage proposed were not achieved simultaneously in most of the clinical scenarios evaluated. Furthermore, a significant impact of albumin was identified: The higher is the albumin, (i) the higher will be the PTA for maximum concentration/minimum inhibitory concentration (Cmax/MIC), (ii) the lower will be the PTA for the time period with drug concentration exceeding MIC (T_>MIC) and (iii) the lower will be the PTA for toxicity (minimum concentration). Thus, accounting for albumin effect might be of interest for future amikacin dosing guidelines updates. In addition, AMKnom, an amikacin nomogram builder based on PKPD criteria, has been developed and is freely available to help evaluating dosing recommendations.

Amikacin pharmacokinetic/pharmacodynamic in intensive care unit: a prospective database

Background

Aminoglycosides have a concentration-dependent therapeutic effect when peak serum concentration (C_max) reaches eight to tenfold the minimal inhibitory concentration (MIC). With an amikacin MIC of 8 mg/L, the C_max should be 64–80 mg/L. This objective is based on clinical breakpoints and not on measured MIC. This study aimed to assess the proportion of patients achieving the pharmacokinetic/pharmacodynamic (PK/PD) target C_max/MIC ≥ 8 using the measured MIC in critically ill patients treated for documented Gram-negative bacilli (GNB) infections.

Methods

Retrospective analysis from February 2016 to December 2017 of a prospective database conducted in 2 intensive care units (ICU). All patients with documented severe GNB infections treated with amikacin (single daily dose of 25 mg/kg of total body weight (TBW)) with both MIC and C_max measurements at first day of treatment (D1) were included. Results are expressed in n (%) or median [min–max].

Results

93 patients with 98 GNB-documented infections were included. The median C_max was 55.2 mg/L [12.2–165.7] and the median MIC was 2 mg/L [0.19–16]. C_max/MIC ratio ≥ 8 was achieved in 87 patients (88.8%) while a C_max ≥ 64 mg/L was achieved in only 38 patients (38.7%). Overall probability of PK/PD target attainment was 93%. No correlation was found between C_max/MIC ratio and clinical outcome at D8 and D28.

Conclusion

According to PK/PD parameters observed in our study, single daily dose of amikacin 25 mg/kg of TBW appears to be sufficient in most critically ill patients treated for severe GNB infections.

Amikacin Initial Dose in Critically Ill Patients: a Nonparametric Approach To Optimize A Priori Pharmacokinetic/Pharmacodynamic Target Attainments in Individual Patients

Amikacin is commonly used for probabilistic antimicrobial therapy in critically ill patients with sepsis. Its narrow therapeutic margin makes it challenging to determine the right individual dose that ensures the highest efficacy target attainment rate (TAR) in this setting. This study aims to develop a new initial dosing approach for amikacin by optimizing the a priori TAR in this population. A population pharmacokinetic model was built with a learning data set from critically ill patients who received amikacin. It was then used to design an initial dosing approach maximizing a priori TAR for a target ratio of ≥8 for the peak concentration to the MIC (C _max/MIC) or of ≥75 for the ratio of the area under the concentration-time curve from 0 to 24 h to the MIC (AUC_0-24/MIC). In the 166 patients included, 53% had amikacin C _max of ≥64 mg/liter with a median dose of 23.4 mg/kg. A two-compartment model with creatinine clearance and body surface area as covariates best described the data and showed good predictive performance. Our dosing approach was successful in optimizing TAR for C _max/MIC, with a rate of 92.9% versus 67.9% using a 30-mg/kg regimen, based on an external subset of data and assuming a MIC of 8 mg/liter. Mean optimal doses were higher (3.5 ± 0.5 g) than with the 30-mg/kg regimen (2.1 ± 0.3 g). Suggested doses varied with the MIC, the target index, and desired TAR threshold. A dosing algorithm based on the method is proposed for a large range of patient covariates. Clinical studies are necessary to confirm efficacy and safety of this optimized dosing approach.