Area under the concentration–time curve to minimum inhibitory concentration ratio as a predictor of vancomycin treatment outcome in methicillin-resistant Staphylococcus aureus bacteraemia

There have been few clinical studies on the association between the 24-h area under the concentration–time curve (AUC₂₄) to minimum inhibitory concentration (MIC) ratio and vancomycin treatment outcomes in methicillin-resistant Staphylococcus aureus (MRSA) infections. Patients with MRSA bacteraemia between July 2009 and January 2012 were analysed retrospectively. All adult patients treated with vancomycin for ≥72 h without dialysis were included. The MIC was determined by Etest and broth microdilution (BMD). Initial steady-state AUC₂₄ was estimated using a Bayesian model, and the AUC₂₄/MIC cut-off value for differentiating treatment success and failure was calculated by classification and regression tree (CART) analysis. In total, 76 patients were enrolled; vancomycin treatment failure occurred in 20 patients (26.3%). Catheter-related infection was the most frequent (35.5%), followed by surgical site infection (26.3%), whilst 25 (32.9%) had complicated infections. In univariate analysis, decreased MRSA vancomycin susceptibility (MIC ≥ 1.5 mg/L) and vancomycin trough levels (15–20 mg/L) were not associated with treatment outcomes. In the CART analysis, low initial vancomycin AUC₂₄/MIC (<430 by Etest; <398.5 by BMD) was associated with a higher treatment failure rate (50.0% vs. 25.0%, P = 0.039 by Etest; 45.0% vs. 23.2%; P = 0.065 by BMD). In multivariate analysis, low initial vancomycin AUC₂₄/MIC was a significant risk factor for treatment failure [adjusted odds ratio (aOR) = 4.39, 95% confidence interval (CI), 1.26–15.35 by Etest; aOR = 3.73, 95% CI 1.10–12.61 by BMD]. In MRSA bacteraemia, a low initial vancomycin AUC₂₄/MIC is an independent risk factor for vancomycin treatment failure.     

Integration of pharmacokinetic/pharmacodynamic modeling and simulation in the development of new anti-infective agents – minimum inhibitory concentration versus time-kill curves

The selection of appropriate doses and dosing regimens is extremely important in antimicrobial therapy in order to increase the chances of clinical success and decrease the likelihood of toxic side effects and the development of resistance. Therefore, empirical treatment of bacterial infections is not reliable enough and more rational approaches are needed. Pharmacokinetic/pharmacodynamic (PK/PD) modeling provides a powerful tool to systematically link PK and PD properties in order to predict antimicrobial efficacy. However, commonly used minimum inhibitory concentration (MIC) based PK/PD indices, although easy to obtain, have a number of limitations. Thus, more reliable PK/PD indices need to be developed. The following article provides an overview of the present PK/PD approaches used in anti-infective therapy and discusses their role in improving drug therapy.     

Semi-physiological pharmacokinetic–pharmacodynamic modeling and simulation of 5-fluorouracil for the whole time course of alterations in leukocyte,neutrophil and lymphocyte counts in rats

Abstract

1. We aimed to develop a simple pharmacokinetic–pharmacodynamic (PK–PD) model to predict the onset and degree of severe toxic side effects that severely limit the use of many anticancer agents, such as myelosuppression, in rats.

2. Our PK–PD model consisted of a two-compartment PK model, with one compartment representing proliferative cells and some transit compartments consisting of maturing cells, while the other compartment represented circulating blood cells for the PD model.

3. The semi-physiological PK–PD model effectively captured the features of myelosuppression and the degree of the off-target toxicities observed after 5-fluorouracil (5-FU) chemotherapy, and helped simultaneously simulate the whole time course for alterations in leukocyte, neutrophil and lymphocyte counts after 5-FU treatment in rats. Interestingly, by plotting the nadir period of leukocyte, neutrophil and lymphocyte counts as determined by PK–PD analytical simulation curves against the area under the plasma 5-FU concentration–time curve (AUC_0–∞) after intravenous administration of 5-FU, a linear relationship was inferred, with r^2?=?0.989, 0.877 and 0.956, respectively.

4. The semi-physiological PK–PD model is a valuable tool for evaluating a variety of novel cancer chemopreventive agents or emerging therapeutic strategies that are difficult to address in humans.     

Bactericidal activity of daptomycin versus vancomycin in the presence of human albumin against vancomycin-susceptible but tolerant methicillin-resistant Staphylococcus aureus (MRSA) with daptomycin minimum inhibitory concentrations of 1–2 μg/mL

This study explored the influence of vancomycin tolerance and protein binding on the bactericidal activity of vancomycin versus daptomycin (protein binding 36.9% vs. 91.7%, respectively) against four vancomycin-tolerant methicillin-resistant Staphylococcus aureus (MRSA) [minimum inhibitory concentration/minimum bactericidal concentration (MIC/MBC) = 0.5/16, 1/32, 2/32 and 1/32 μg/mL for vancomycin and 1/1, 1/2, 2/2 and 2/4 μg/mL for daptomycin]. Killing curves were performed with vancomycin/daptomycin concentrations equal to serum peak concentrations (C_max) (65.70/98.60 μg/mL) and trough concentrations (C_min) (7.90/9.13 μg/mL) in the presence and absence of a physiological human albumin concentration (4 g/dL), controlled with curves with the theoretical free drug fraction of vancomycin/daptomycin C_max (41.45/8.18 μg/mL) and C_min (4.98/0.76 μg/mL). Vancomycin C_max and C_min concentrations, regardless of the media, showed a bacteriostatic profile not reaching a reduction of 99% or 99.9% of the initial inocula during the 24-h experimental time period. Daptomycin antibacterial profiles significantly differed when testing C_max and C_min. C_max was rapidly bactericidal (≤4 h) with >5 log₁₀ reduction in the initial inocula for all strains, regardless of the presence or not of albumin or the use of concentrations similar to free C_max. C_min exhibited similar final colony counts at 0 h and 24 h in curves with albumin, but with >3 log colony-forming units (CFU)/mL reduction at ≤4 h for strains with an MIC of 1 μg/mL and ca. 2 log CFU/mL reduction at ≤6 h for strains with an MIC of 2 μg/mL. This activity was significantly higher than the activity of the free C_min fraction. The results of this study reinforce the idea that pharmacodynamics using concentrations calculated using reported protein binding are unreliable. Daptomycin exhibited rapid antibacterial activity against vancomycin-tolerant MRSA isolates even against those with high daptomycin MICs in the presence of physiological albumin concentrations.