Preferential Emergence of Reduced Vancomycin Susceptibility in Health Care-Associated Methicillin-Resistant Staphylococcus aureus Isolates during Continuous-Infusion Vancomycin Therapy in an
            <i>In Vitro</i>
            Dynamic Model

Pathophysiological changes involved in drug disposition in critically ill patients should be considered in order to optimize the dosing of vancomycin administered by continuous infusion, and certain strategies must be applied to reach therapeutic targets on the first day of treatment. The aim of this study was to develop a population pharmacokinetic model of vancomycin to determine clinical covariates, including mechanical ventilation, that influence the wide variability of this antimicrobial. Plasma vancomycin concentrations from 54 critically ill patients were analyzed simultaneously by a population pharmacokinetic approach. A nomogram for dosing recommendations was developed and was internally evaluated through stochastic simulations. The plasma vancomycin concentration-versus-time data were best described by a one-compartment open model with exponential interindividual variability associated with vancomycin clearance and the volume of distribution. Residual error followed a homoscedastic trend. Creatinine clearance and body weight significantly dropped the objective function value, showing their influence on vancomycin clearance and the volume of distribution, respectively. Characterization based on the presence of mechanical ventilation demonstrated a 20% decrease in vancomycin clearance. External validation ( = 18) was performed to evaluate the predictive ability of the model; median bias and precision values were 0.7 mg/liter (95% confidence interval [CI], -0.4, 1.7) and 5.9 mg/liter (95% CI, 5.4, 6.4), respectively. A population pharmacokinetic model was developed for the administration of vancomycin by continuous infusion to critically ill patients, demonstrating the influence of creatinine clearance and mechanical ventilation on vancomycin clearance, as well as the implications for targeting dosing rates to reach the therapeutic range (20 to 30 mg/liter).

Section: Discussionmentioning

confidence: 99%

Influence of Mechanical Ventilation on the Pharmacokinetics of Vancomycin Administered by Continuous Infusion in Critically Ill Patients

Medellín‐Garibay

Romano‐Moreno

Tejedor-Prado

et al. 2017

“…The phenotypic expression of low-level glycopeptide resistance is variable, being significantly influenced by several technical parameters, including the compositions of liquid or solid test media and various time frames and inoculum sizes (24,28,49,51). Since broth microdilution and agar dilution assays use inadequate inocula and too-short incubation periods for reliable detection of some hGISA isolates (25,42,47,51), alternative GISA detection methods, such as the PAP-AUC, Etest macromethod, and Etest GRD, have been proposed (summarized in references 24 and 49) and repeatedly tested in vitro (26,41,45,50,55). Despite their merits, these alternative GISA detection methods have generated complex results that can hardly be integrated into the current schemes of glycopeptide MIC breakpoints.…”

Section: Discussionmentioning

confidence: 99%

High Prevalence of Isolates with Reduced Glycopeptide Susceptibility in Persistent or Recurrent Bloodstream Infections Due to Methicillin-Resistant Staphylococcus aureus

Uçkay¹,

Bernard²,

Buzzi³

et al. 2012

Reduced susceptibility to glycopeptides in methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates is considered a risk factor for failure of glycopeptide therapy. We compared the prevalences of MRSA isolates with reduced glycopeptide susceptibility in patients with versus without persistent or recurrent MRSA bloodstream infections. A retrospective cohort study at the University Hospital of Geneva identified 27 patients with persistent or recurrent clonally related MRSA bacteremic episodes over an 8-year period, which included 208 consecutive nosocomial MRSA bacteremic episodes. Vancomycin and teicoplanin MICs were determined by a modified macrodilution assay allowing improved detection of glycopeptide-intermediate MRSA isolates (GISA), characterized by elevated teicoplanin or/and vancomycin MICs (>4 g/ml). For 16 patients (59%), their pretherapy and/or posttherapy MRSA isolates showed elevated teicoplanin MICs, among which 10 (37%) concomitantly displayed elevated vancomycin MICs. In contrast, 11 other patients (41%) were persistently or recurrently infected with non-GISA isolates. In comparison, only 39 (22%) of 181 single isolates from patients with no microbiological evidence of persistent or recurrent infections showed elevated teicoplanin MICs, among which 14 (8%) concomitantly displayed elevated vancomycin MICs. Clinical, microbiological, and pharmacokinetic variables for patients persistently or recurrently infected with GISA or non-GISA isolates were similar. Bacteremic patients with a poor response to glycopeptide therapy had a 2.8-fold-and 4.8-fold-higher rates of MRSA isolates displaying elevated teicoplanin and vancomycin MICs, respectively, than patients with single isolates (P < 0.0001). Detection of elevated teicoplanin MICs may help to predict a poor response to glycopeptide therapy in MRSA bacteremic patients.

“…A PD study reasserted that bacterial killing and development of diminished vancomycin susceptibility during CoI therapy were dependent on the AUC/MIC ratio, with values of 480 being bactericidal and suppressing emerging resistance; this target would be achieved with CoI at a steady-state concentration of 20 mg/liter when vancomycin pathogen MICs are 1 mg/liter (40). Other authors have suggested that, given the tendency toward increasing vancomycin MICs in clinical isolates of S. aureus in some centers, a target concentration of 25 mg/liter may be more appropriate (41).…”

Section: Intermittent Versus Continuous Infusion Therapymentioning

confidence: 99%

Optimizing the Clinical Use of Vancomycin

Álvarez

López-Cortés

Molina

et al. 2016

193

124

Pharmacists published specific guidelines about vancomycin dosage and monitoring. However, these guidelines have not been updated in the past 6 years. This review analyzes the new available information about vancomycin published in recent years regarding pharmacokinetics and pharmacodynamics, serum concentration monitoring, and optimal vancomycin dosing in special situations (obese people, burn patients, renal replacement therapy, among others). Vancomycin efficacy is linked to a correct dosage which should aim to reach an area under the curve (AUC)/MIC ratio of >400; serum trough levels of 15 to 20 mg/liter are considered a surrogate marker of an AUC/MIC ratio of >400 for a MIC of <1 mg/liter. For Staphylococcus aureus strains presenting with a MIC >1 mg/liter, an alternative agent should be considered. Vancomycin doses must be adjusted according to body weight and the plasma trough levels of the drug. Nephrotoxicity has been associated with target vancomycin trough levels above 15 mg/liter. Continuous infusion is an option, especially for patients at high risk of renal impairment or unstable vancomycin clearance. In such cases, vancomycin plasma steady-state level and creatinine monitoring are strongly indicated. Vancomycin has traditionally been used as a first-line agent for treating methicillin-resistant Staphylococcus aureus (MRSA) and other Gram-positive beta-lactam-resistant bacteria (1), which are frequent etiologies of severe health-related infections (2, 3).Although the effectiveness of vancomycin is supported by more than 5 decades of use and multiple studies, the clinical and microbiological scenario in which it is used is always changing. Attaining an appropriate dosage of vancomycin for S. aureus infections might be difficult due to the clinical impact of the creep in the MIC of vancomycin and heteroresistance among MRSA strains, or due to complex pharmacokinetic and pharmacodynamic (PK/PD) situations. In this context, the American Society of Health-System Pharmacists (ASHP), the Infectious Diseases Society of America (IDSA), and the Society of Infectious Diseases Pharmacists (SIDP) introduced a practice guideline in 2009 (4), marking a milestone in vancomycin therapy. However, several questions, such as the optimal dosing in some special clinical situations (e.g., with renal replacement therapies or in burn patients or obese patients), the role of continuous infusion, or the renal toxicity when the suggested vancomycin serum levels are achieved, remain unanswered. The present review mainly focuses on these issues. VANCOMYCIN PHARMACODYNAMICS AND ITS IMPLICATIONS FOR DRUG MONITORINGThe killing effect of vancomycin is characterized by a slow mode of action and is further hampered by a large bacterial inoculum, a stationary growth phase, and anaerobic conditions (5, 6). Although several pharmacodynamic parameters have been proposed to determine vancomycin activity, data from experimental and clinical studies have selected the area under the curve (AUC)/ MIC ratio as the best parameter to predict the...