Population pharmacokinetics of gentamicin in haemodialysis patients: modelling, simulations and recommendations

Individual pharmacokinetic parameter estimation of gentamicin in an obese hemodialysis patient using non-linear mixed effect model

This study aimed to estimate individual pharmacokinetic (PK) parameters in an obese hemodialysis (HD) patient receiving gentamicin and to assess the impact of obesity on gentamicin clearance (CL). A 53-year-old obese Korean woman underwent HD and received gentamicin. To estimate individual PK parameters, we employed the POSTHOC option using NONMEM® 7.4.4. A priori model contained HD as a covariate for CL during HD, and creatinine CL (CrCL), normalized by the group mean value from the a priori model, as a covariate for non-HD CL (CLNHD). Individual CLNHD exhibited a substantial reduction from the population CLNHD, with the value corresponding to 36% of the a priori model's population PK (popPK) parameter. The patient's CrCL exceeded the group maximum of the a priori information, suggesting inaccurate renal function representation. After adjusting CrCL to the group mean from the a priori model, the patient's CLNHD was 138% of the population's typical value. The objective function value for each run was 0.53 and -4.49, respectively. The patient's CLNHD was greater than the popPK parameter value but less than the popPK parameter value when estimated using the patient's original CrCL. Meanwhile, another software (Monolix®; version 2024R1) gave similar results. This study shows the importance of individualized PK parameter estimation, particularly in obese HD patients, and highlights the potential impact of factors including obesity on gentamicin CL.

Gentamicin Administration in Dialysis Patients: Before or After Hemodialysis?

BACKGROUND

Gentamicin is used to treat severe infections and has a small therapeutic window. This study aimed to optimize the dosing strategy of gentamicin in intermittently hemodialyzed patients by simulating concentration-time profiles during pre- and postdialysis dosing, based on a published pharmacokinetic model.

METHODS

Pharmacokinetic simulations were performed with virtual patients, including septic patients, who were treated with gentamicin and received weekly hemodialysis with an interval of 48 h-48 h-72 h. The following dosing regimens were simulated: for nonseptic patients, 5 mg/kg gentamicin was given 1 h or 2 h before dialysis or a starting dose of 2.5 mg/kg and a maintenance dose of 1.5 mg/kg immediately after dialysis were given; for septic patients, 6 mg/kg gentamicin was given 1 h or 2 h before dialysis or a starting dose of 3 mg/kg and a maintenance dose of 1.8 mg/kg immediately were given after dialysis. The mean maximum concentration (C max ), area under the curve (AUC) 24 h , and target attainment (TA) of pharmacodynamic targets were calculated and compared. The following targets were adopted from the literature: C max >8 mg/L and <20 mg/L and AUC 24 h >70 mg·h/L and <120 mg·h/L.

RESULTS

In nonseptic patients, postdialysis dosing resulted in a TA of 35% for C max of >8 mg/L, 100% for <20 mg/L and AUC 24 h >70 mg·h/L, and 45% for <120 mg·h/L. Dosing 2 h before dialysis resulted in a TA of 100% for C max of >8 mg/L, 40% for <20 mg/L, 65% for AUC 24 h >70 mg·h/L, and 77% for <120 mg·h/L. Simulations of septic patients resulted in comparable outcomes with higher TAs for C max <20 mg/L (96%), AUC 24 h >70 mg·h/L (90%), and AUC 24 h <120 mg·h/L (53%) for dosing 1 h before dialysis.

CONCLUSIONS

Postdialysis dosing resulted in a low TA of C max >8 mg/L; however, predialysis dosing ensured a high TA of C max >8 mg/L and acceptable TA of C max <20 mg/L, AUC 24 h >70 mg·h/L, and AUC 24 h <120 mg·h/L, which could increase the efficacy of gentamicin. Therefore, clinicians should consider predialysis dosing of gentamicin in patients undergoing intermittent hemodialysis.

Clinical Pharmacokinetics of Gentamicin in Various Patient Populations and Consequences for Optimal Dosing for Gram-Negative Infections: An Updated Review

Gentamicin is an aminoglycoside antibiotic with a small therapeutic window that is currently used primarily as part of short-term empirical combination therapy. Gentamicin dosing schemes still need refinement, especially for subpopulations where pharmacokinetics can differ from pharmacokinetics in the general adult population: obese patients, critically ill patients, paediatric patients, neonates, elderly patients and patients on dialysis. This review summarizes the clinical pharmacokinetics of gentamicin in these patient populations and the consequences for optimal dosing of gentamicin for infections caused by Gram-negative bacteria, highlighting new insights from the last 10 years. In this period, several new population pharmacokinetic studies have focused on these subpopulations, providing insights into the typical values of the most relevant pharmacokinetic parameters, the variability of these parameters and possible explanations for this variability, although unexplained variability often remains high. Both dosing schemes and pharmacokinetic/pharmacodynamic (PK/PD) targets varied widely between these studies. A gentamicin starting dose of 7 mg/kg based on total body weight (or on adjusted body weight in obese patients) appears to be the optimal strategy for increasing the probability of target attainment (PTA) after the first administration for the most commonly used PK/PD targets in adults and children older than 1 month, including critically ill patients. However, evidence that increasing the PTA results in higher efficacy is lacking; no studies were identified that show a correlation between estimated or predicted PK/PD target attainment and clinical success. Although it is unclear if performing therapeutic drug monitoring (TDM) for optimization of the PTA is of clinical value, it is recommended in patients with highly variable pharmacokinetics, including patients from all subpopulations that are critically ill (such as elderly, children and neonates) and patients on intermittent haemodialysis. In addition, TDM for optimization of the dosing interval, targeting a trough concentration of at least < 2 mg/L but preferably < 0.5–1 mg/L, has proven to reduce nephrotoxicity and is therefore recommended in all patients receiving more than one dose of gentamicin. The usefulness of the daily area under the plasma concentration–time curve for predicting nephrotoxicity should be further investigated. Additionally, more research is needed on the optimal PK/PD targets for efficacy in the clinical situations in which gentamicin is currently used, that is, as monotherapy for urinary tract infections or as part of short-term combination therapy.

Aminoglycosides in Critically Ill Septic Patients With Acute Kidney Injury Receiving Intermittent Hemodialysis: A Multicenter, Observational Study

PURPOSE

Data on aminoglycoside stewardship in critically ill septic patients with acute kidney injury (AKI) needing intermittent hemodialysis (IH) are scarce. The first objective of the study was to evaluate whether aminoglycoside administration occurs before vs after IH in the real-life management of critically ill septic patients with AKI needing IH. The second objective was to assess the delay in achieving a potential reinjection window for a second dose of aminoglycoside, which should be obtained with a postdialysis vs predialysis regimen.

METHODS

A post hoc observational analysis of a multicenter randomized trial of critically ill patients with AKI needing renal replacement therapy was conducted. Inclusion criteria consisted of any patients receiving IH for AKI during an antimicrobial therapy for a septic episode.

FINDINGS

Among 206 of 341 septic patients (60%) receiving aminoglycosides, 90 underwent IH (46 with previous continuous renal replacement therapy and 44 without). Amikacin and gentamicin were administered for a mean (SD) of 2.2 (1.5) and 2.5 (2.1) days with mean (SD) doses of 20.6 (6.6) and 5.4 (2.5) mg/kg, respectively. In the 44 patients undergoing exclusive IH, aminoglycosides were administered in a predialysis in 53% of episodes versus 35% in a postdialysis schedule. The first C_min target was obtained earlier with a predialysis vs postdialysis schedule (33.9 [14.2] hours vs 50.9 [12.2] hours, P = 0.009).

IMPLICATIONS

Despite being less frequently used than a predialysis schedule, the postdialysis administration of aminoglycosides remains a regular practice in the intensive care unit. A predialysis schedule of administration in IH reduces the interval time to tolerable aminoglycoside redosing.