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      Does Beta-lactam Pharmacokinetic Variability in Critically Ill Patients Justify Therapeutic Drug Monitoring? A Systematic Review

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          Abstract

          The pharmacokinetics of beta-lactam antibiotics in intensive care patients may be profoundly altered due to the dynamic, unpredictable pathophysiological changes that occur in critical illness. For many drugs, significant increases in the volume of distribution and/or variability in drug clearance are common. When “standard” beta-lactam doses are used, such pharmacokinetic changes can result in subtherapeutic plasma concentrations, treatment failure, and the development of antibiotic resistance. Emerging data support the use of beta-lactam therapeutic drug monitoring (TDM) and individualized dosing to ensure the achievement of pharmacodynamic targets associated with rapid bacterial killing and optimal clinical outcomes. The purpose of this work was to describe the pharmacokinetic variability of beta-lactams in the critically ill and to discuss the potential utility of TDM to optimize antibiotic therapy through a structured literature review of all relevant publications between 1946 and October 2011. Only a few studies have reported the utility of TDM as a tool to improve beta-lactam dosing in critically ill patients. Moreover, there is little agreement between studies on the pharmacodynamic targets required to optimize antibiotic therapy. The impact of TDM on important clinical outcomes also remains to be established. Whereas TDM may be theoretically rational, clinical studies to assess utility in the clinical setting are urgently required.

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          Most cited references113

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          Pharmacokinetic issues for antibiotics in the critically ill patient.

          To discuss the altered pharmacokinetic properties of selected antibiotics in critically ill patients and to develop basic dose adjustment principles for this patient population. PubMed, EMBASE, and the Cochrane-Controlled Trial Register. Relevant papers that reported pharmacokinetics of selected antibiotic classes in critically ill patients and antibiotic pharmacodynamic properties were reviewed. Antibiotics and/or antibiotic classes reviewed included aminoglycosides, beta-lactams (including carbapenems), glycopeptides, fluoroquinolones, tigecycline, linezolid, lincosamides, and colistin. Antibiotics can be broadly categorized according to their solubility characteristics which can, in turn, help describe possible altered pharmacokinetics that can be caused by the pathophysiological changes common to critical illness. Hydrophilic antibiotics (e.g., aminoglycosides, beta-lactams, glycopeptides, and colistin) are mostly affected with the pathphysiological changes observed in critically ill patients with increased volumes of distribution and altered drug clearance (related to changes in creatinine clearance). Lipophilic antibiotics (e.g., fluoroquinolones, macrolides, tigecycline, and lincosamides) have lesser volume of distribution alterations, but may develop altered drug clearances. Using antibiotic pharmacodynamic bacterial kill characteristics, altered dosing regimens can be devised that also account for such pharmacokinetic changes. Knowledge of antibiotic pharmacodynamic properties and the potential altered antibiotic pharmacokinetics in critically ill patients can allow the intensivist to develop individualized dosing regimens. Specifically, for renally cleared drugs, measured creatinine clearance can be used to drive many dose adjustments. Maximizing clinical outcomes and minimizing antibiotic resistance using individualized doses may be best achieved with therapeutic drug monitoring.
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            Evaluation of area under the inhibitory curve (AUIC) and time above the minimum inhibitory concentration (T>MIC) as predictors of outcome for cefepime and ceftazidime in serious bacterial infections.

            The objective of this study was to evaluate the relationship of the predicted pharmacodynamic parameters 24-h area under the inhibitory curve (AUIC=area under the concentration-time curve for 24h of dosing/minimum inhibitory concentration (AUC0-24/MIC) and time above the minimum inhibitory concentration (T>MIC) with clinical and microbiological outcomes in patients with bacteraemia and sepsis treated with cefepime or ceftazidime. Pharmacokinetic and pharmacodynamic parameters were derived for 76 of 107 patients enrolled in two prospective, randomised, clinical trials comparing cefepime with ceftazidime for the treatment of sepsis with bacteraemia, lower respiratory tract infection or complicated urinary tract infection. The relationships between the pharmacodynamic parameters and outcomes were examined. Whilst no significant differences in clinical outcomes were observed between cefepime and ceftazidime, there were significant differences in the pharmacodynamic analysis. Patients with an AUIC> or =250 had significantly greater clinical cure (79% vs. 33%; P=0.002) and bacteriological eradication (96% vs. 44%; P MIC of 100% had significantly greater clinical cure (82% vs. 33%; P=0.002) and bacteriological eradication (97% vs. 44%; P MIC of MIC was <100%.
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              Antibiotics in critically ill patients: a systematic review of the pharmacokinetics of β-lactams

              Introduction Several reports have shown marked heterogeneity of antibiotic pharmacokinetics (PK) in patients admitted to ICUs, which might potentially affect outcomes. Therefore, the pharmacodynamic (PD) parameter of the efficacy of β-lactam antibiotics, that is, the time that its concentration is above the bacteria minimal inhibitory concentration (T > MIC), cannot be safely extrapolated from data derived from the PK of healthy volunteers. Methods We performed a full review of published studies addressing the PK of intravenous β-lactam antibiotics given to infected ICU patients. Study selection comprised a comprehensive bibliographic search of the PubMed database and bibliographic references in relevant reviews from January 1966 to December 2010. We selected only English-language articles reporting studies addressing β-lactam antibiotics that had been described in at least five previously published studies. Studies of the PK of patients undergoing renal replacement therapy were excluded. Results A total of 57 studies addressing six different β-lactam antibiotics (meropenem, imipenem, piperacillin, cefpirome, cefepime and ceftazidime) were selected. Significant PK heterogeneity was noted, with a broad, more than twofold variation both of volume of distribution and of drug clearance (Cl). The correlation of antibiotic Cl with creatinine clearance was usually reported. Consequently, in ICU patients, β-lactam antibiotic half-life and T > MIC were virtually unpredictable, especially in those patients with normal renal function. A better PD profile was usually obtained by prolonged or even continuous infusion. Tissue penetration was also found to be compromised in critically ill patients with septic shock. Conclusions The PK of β-lactam antibiotics are heterogeneous and largely unpredictable in ICU patients. Consequently, the dosing of antibiotics should be supported by PK concepts, including data derived from studies of the PK of ICU patients and therapeutic drug monitoring.
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                Author and article information

                Journal
                Ann Intensive Care
                Ann Intensive Care
                Annals of Intensive Care
                Springer
                2110-5820
                2012
                28 July 2012
                : 2
                : 35
                Affiliations
                [1 ]School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, Australia
                [2 ]Therapeutics Research Centre, Basil Hetzel Institute for Translational Health Research, The Queen Elizabeth Hospital, Adelaide, Australia
                [3 ]Therapeutics Research Centre, School of Medicine, The University of Queensland, Brisbane, Australia
                [4 ]Department of Intensive Care Medicine, The Queen Elizabeth Hospital, Adelaide, Australia
                [5 ]Burns, Trauma, and Critical Care Research Centre, The University of Queensland, Herston, Brisbane, QLD, Australia
                [6 ]Department of Intensive Care Medicine, Royal Brisbane and Women’s Hospital, Herston, Brisbane, QLD, Australia
                [7 ]Pharmacy Department, Royal Brisbane and Women’s Hospital, Herston, Brisbane, QLD, Australia
                Article
                2110-5820-2-35
                10.1186/2110-5820-2-35
                3460787
                22839761
                6f44402d-28bd-409e-977c-f8b7618248ef
                Copyright ©2012 Sime et al.; licensee Springer.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 7 June 2012
                : 28 June 2012
                Categories
                Review

                Emergency medicine & Trauma
                pharmacodynamics,therapeutic drug monitoring,antibiotics,critically ill,beta-lactam,pharmacokinetics

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