Antibacterial Dosing in Intensive Care

Therapeutic drug monitoring of amikacin in septic patients

INTRODUCTION

Use of higher than standard doses of amikacin (AMK) has been proposed during sepsis, especially to treat less susceptible bacterial strains. However, few data are available on drug concentrations during prolonged therapy and on potential adverse events related to this strategy.

METHODS

Sixty-three critically ill patients who required AMK administration for the treatment of severe infection were included in this study. After a loading dose (LD, 18 to 30 mg/kg), the daily regimen was adapted using therapeutic drug monitoring (TDM) of both peak (Cpeak) and trough (Cmin) concentrations. Target concentrations had to give a ratio of at least 8 between Cpeak and the minimal inhibitory concentration (MIC) of the isolated pathogen. A Cmin >5 mg/L was considered as potentially nephrotoxic. We recorded clinical and microbiological responses, the development of acute kidney injury (AKI) during therapy and ICU mortality.

RESULTS

The median AMK LD was 1500 (750 to 2400) mg, which resulted in a Cpeak/MIC ≥8 in 40 (63%) patients. Increasing the dose in the 23 patients with a Cpeak/MIC <8 resulted in optimal Cpeak/MIC in 15 of these patients (79%). In 23 patients (37%), Cmin was >5 mg/L after the LD, notably in the presence of altered renal function at the onset of therapy, needing prolongation of drug administration. Overall, only 11 patients (17%) required no dose or interval adjustment during AMK therapy. Clinical cure (32/37 (86%) vs. 16/23 (70%), P = 0.18)) and microbiological eradication (29/35 (83%) vs. 14/23 (61%), P = 0.07) were higher in patients with an initial optimal Cpeak/MIC than in the other patients. The proportion of patients with clinical cure significantly improved as the Cpeak/MIC increased (P = 0.006). Also, increased time to optimal Cpeak was associated with worse microbiological and clinical results. AKI was identified in 15 patients (24%) during AMK therapy; 12 of these patients already had altered renal function before drug administration. Survivors (n = 47) had similar initial Cpeak/MIC ratios but lower Cmin values compared to nonsurvivors.

CONCLUSIONS

TDM resulted in adjustment of AMK therapy in most of our septic patients. Early achievement of an optimal Cpeak/MIC ratio may have an impact on clinical and microbiological responses, but not on outcome. In patients with impaired renal function prior to treatment, AMK therapy may be associated with a further decline in renal function.

The clinical relevance of plasma protein binding changes

Controversy reigns as to how protein binding changes alter the time course of unbound drug concentrations in patients. Given that the unbound concentration is responsible for drug efficacy and potential drug toxicity, this area is of significant interest to clinicians and academics worldwide. The present uncertainty means that many questions relating to this area exist, including "How important is protein binding?", "Is protein binding always constant?", "Do pH and temperature changes alter binding?" and "How do protein binding changes affect dosing requirements?". In this paper, we seek to address these questions and consider the data associated with altered pharmacokinetics in the presence of changes in protein binding and the clinical consequences that these may have on therapy, using examples from the critical care area. The published literature consistently indicates that a change in the protein binding and unbound concentrations of some drugs are common in certain specific patient groups such as the critically ill. Changes in pharmacokinetic parameters, including clearance and apparent volume of distribution (V(d)), may be dramatic. Drugs with high protein binding, high intrinsic clearance (e.g. clearance by glomerular filtration) and where dosing is not titrated to effect are most likely to be affected in a clinical context. Drugs such as highly protein bound antibacterials with multiple half-lives within a dosing interval and that have some level of renal clearance, such as ertapenem, teicoplanin, ceftriaxone and flucloxacillin, are commonly affected. In response to these challenges, clinicians need to adapt dosing regimens rationally based on the pharmacokinetic/pharmacodynamic characteristics of the drug. We propose that further pharmacokinetic modelling-based research is required to enable the design of robust dosing regimens for drugs affected by altered protein binding.

Evaluating amikacin dosage regimens in intensive care unit patients: a pharmacokinetic/pharmacodynamic analysis using Monte Carlo simulation

The objectives of this study were to conduct a comparative pharmacokinetic/pharmacodynamic (PK/PD) evaluation using Monte Carlo simulation of conventional versus high-dose extended-interval dosage (HDED) regimens of amikacin (AMK) in intensive care unit (ICU) patients for an Acinetobacter baumannii infection model. The simulation was performed in five populations (a control population and four subpopulations of ICU patients). Using a specific AMK PK/PD model and Monte Carlo simulation, the following were generated: simulated AMK steady-state plasma level curves; PK/PD efficacy indexes [time during which the serum drug concentration remains above the minimum inhibitory concentration (MIC) for a dosing period (%T>MIC) and ratio of peak serum concentration to MIC (Cmax/MIC)]; evolution of bacterial growth curves; and adaptive resistance to treatment. A higher probability of bacterial resistance was observed with the HDED regimen compared with the conventional dosage regimen. A statistically significant increase in Cmax/MIC and a statistically significant reduction in %T>MIC with the HDED regimen were obtained. A multiple linear relationship between CFU values at 24h with Cmax/MIC and %T>MIC was obtained. In conclusion, with the infection model tested, the likelihood of resistance to treatment may be higher against pathogens with a high MIC with the HDED regimen, considering that in many ICU patients the %T>MIC may be limited. If a sufficient value of %T>MIC (≥60%) is not reached, even though the Cmax/MIC is high, the therapeutic efficacy of the treatment may not be guaranteed. This study indicates that different AMK dosing strategies could directly influence the efficacy results in ICU patients.

Diagnosis and management for urosepsis

Urosepsis is defined as sepsis caused by a urogenital tract infection. Urosepsis in adults comprises approximately 25% of all sepsis cases, and is in most cases due to complicated urinary tract infections. The urinary tract is the infection site of severe sepsis or septic shock in approximately 10-30% of cases. Severe sepsis and septic shock is a critical situation, with a reported mortality rate nowadays still ranging from 30% to 40%. Urosepsis is mainly a result of obstructed uropathy of the upper urinary tract, with ureterolithiasis being the most common cause. The complex pathogenesis of sepsis is initiated when pathogen or damage-associated molecular patterns recognized by pattern recognition receptors of the host innate immune system generate pro-inflammatory cytokines. A transition from the innate to the adaptive immune system follows until a T(H2) anti-inflammatory response takes over, leading to immunosuppression. Treatment of urosepsis comprises four major aspects: (i) early diagnosis; (ii) early goal-directed therapy including optimal pharmacodynamic exposure to antimicrobials both in the plasma and in the urinary tract; (iii) identification and control of the complicating factor in the urinary tract; and (iv) specific sepsis therapy. Early adequate tissue oxygenation, adequate initial antibiotic therapy, and rapid identification and control of the septic focus in the urinary tract are critical steps in the successful management of a patient with urosepsis, which includes early imaging, and an optimal interdisciplinary approach encompassing emergency unit, urological and intensive-care medicine specialists.

Systemic inflammatory response syndrome criteria and vancomycin dose requirement in patients with sepsis

PURPOSE

Vancomycin has been used in patients with sepsis infected by MRSA and shows large interindividual variability in its dosing. In this observational study the potential influence of sepsis status on the vancomycin dose requirement in relation to systemic inflammatory response syndrome (SIRS) criteria was assessed.

METHODS

From about 250 patients receiving serum vancomycin monitoring from May 2006 to April 2011 at the Osaka National Hospital, 105 adult patients who had been assessed using the SIRS criteria were identified. Patients on chemotherapy or intermittent positive pressure ventilation in whom the SIRS criteria could not accurately evaluate inflammatory status were excluded. Using two vancomycin serum concentrations at peak and trough, individual pharmacokinetic parameters were calculated by the Bayesian estimation method using a two-compartment model. Creatinine clearance rate was estimated by the Cockcroft-Gault formula (eCcr).

RESULTS

Patients with SIRS had a significantly higher vancomycin clearance than those without SIRS, indicating that SIRS patients had a higher elimination capacity. The vancomycin clearance was positively correlated with the SIRS score defined as the number of positive items in the criteria, and negatively with age, except in patients with renal dysfunction. A linear relationship between the vancomycin clearance and eCcr remained even in the supernormal eCcr phase (more than approximately 120 mL/min).

CONCLUSIONS

This study provides a new insight into the need for quick prediction of dose requirement. That is, an increased vancomycin dosage would be needed in patients with a higher SIRS score to maintain the therapeutic target concentration, in particular in those with a high eCcr value.

Continuous versus intermittent infusions of antibiotics for the treatment of severe acute infections

BACKGROUND

Intravenous broad-spectrum antibiotics are indicated for the treatment of severe infections. However, the emergence of infections caused by multi-drug resistant organisms in conjunction with a lack of novel antibiotics has prompted the investigation of alternative dosing strategies to improve clinical efficacy and tolerability. To optimise pharmacokinetic and pharmacodynamic antibiotic parameters, continuous antibiotic infusions have been compared to traditional intermittent antibiotic infusions.

OBJECTIVES

To compare the clinical efficacy and safety of continuous intravenous administration of concentration-dependent and time-dependent antibiotics to traditional intermittent intravenous administration in adults with severe acute bacterial infections.

SEARCH METHODS

The following electronic databases were searched in September 2012: The Cochrane Injuries Group Specialised Register, Cochrane Central Register of Controlled Trials (The Cochrane Library), MEDLINE (OvidSP), EMBASE (OvidSP), CINAHL, ISI Web of Science: Science Citation Index Expanded (SCI-EXPANDED), ISI Web of Science: Conference Proceedings Citation Index-Science (CPCI-S). The reference lists of all relevant material, the Internet and the trials registry www.clinicaltrials.gov for completed and ongoing trials were also searched.

SELECTION CRITERIA

Randomized controlled trials in adults with a bacterial infection requiring intravenous antibiotic therapy comparing continuous versus intermittent infusions of antibiotics were included. Both time-dependent and concentration-dependent antibiotics were considered.

DATA COLLECTION AND ANALYSIS

Three independent authors performed data extraction for the included studies. All data was cross-checked and disagreements resolved by consensus. An intention to treat analysis was conducted using a random-effects model.

MAIN RESULTS

Twenty-nine studies met inclusion criteria with a combined total of over 1,600 patients. The majority of included studies were judged to be at unclear or high risk of bias with regard to randomisation sequence generation, allocation concealment, blinding, management of incomplete outcome data, selective outcome reporting, and other potential threats to validity. No studies were judged to be at low risk of bias for all methodological quality items assessed. There were no differences in all-cause mortality (n=1241, RR 0.89, 95% CI 0.67 - 1.20, p=0.45), infection recurrence (n=398, RR 1.22, 95% CI 0.35 - 4.19, p=0.76), clinical cure (n=975, RR 1.00, 95% CI 0.93 - 1.08, p=0.98), and superinfection post-therapy (n=813, RR 1.08, 95% CI 0.60 - 1.94, p=0.79). There were no differences in safety outcomes including adverse events (n=575, RR 1.02, 95% CI 0.94 - 1.12, p=0.63), serious adverse events (n=871, RR 1.36, 95% CI 0.80 - 2.30, p=0.26), and withdrawal due to adverse events (n=871, RR 2.03, 95% CI 0.52 - 7.95, p=0.31). A difference was observed in the subgroup analyses of clinical cure in septic versus non-septic patients, where intermittent antibiotic infusions were favoured for clinical cure in septic patients. However, this effect was not consistent between random-effects and fixed-effects analyses. No differences were found in sensitivity analyses conducted.

AUTHORS' CONCLUSIONS

There were no differences in mortality, infection recurrence, clinical cure, superinfection post-therapy, and safety outcomes when comparing continuous infusions of intravenous antibiotics to traditional intermittent infusions of antibiotics. However, the wide confidence intervals suggest that beneficial or harmful effects cannot be ruled out for all outcomes. Therefore, the current evidence is insufficient to recommend the widespread adoption of continuous infusion antibiotics in the place of intermittent infusions of antibiotics. Further large prospective randomised trials, with consistent and complete reporting of clinical outcome measures, conducted with concurrent pharmacokinetic and pharmacodynamic studies in special populations are required to determine whether adoption of continuous antibiotic infusions is warranted in specific circumstances.

Anti-MRSA drug use and antibiotic susceptibilities of MRSA at a university hospital in Japan from 2007 to 2011

The purpose of this study is to examine the use of anti-methicillin-resistant Staphylococcus aureus (MRSA) drugs, such as vancomycin (VCM), teicoplanin (TEIC), arbekasin (ABK) and linezolid (LZD), and the antibiotic susceptibilities of MRSAs in Kobe University Hospital. We investigated MRSA isolation and use of anti-MRSA drugs and susceptibilities of MRSA, using linear regression analysis, from 2007 to 2011, and checked for correlation between the use of these drug and the antibiotic susceptibilities of MRSA. The overall monthly isolation rates of MRSA decreased from a mean of 84.8% in 2007 to 70.0% in 2011 (r=0.946, P=0.015, b=-0.220), and the monthly isolation rate of MRSA in inpatients decreased from a mean of 78.6% in 2007 to 57.7% in 2011 (r=0.952, P=0.012, b=-0.160). From 2007 to 2011, VCM consumption significantly increased (r=0.916, P=0.029, b=0.055), whereas TEIC and LZD use remained stable during the study period. In addition, ABK use significantly decreased from 23.8 defined daily dose (DDD) per 1000 patient-days in 2007 to 5.2 DDD per 1000 in 2011 (r=0.902, P=0.036, b=-0.216). Susceptibility rates of MRSA were almost 100% to TEIC and VCM. The rates of MRSA to ABK and LZD significantly increased (r=0.959, P=0.010, b=2.137 for ABK and r=0.933, P=0.020, b=3.111 for LZD). In conclusion, our findings indicated a decreased MRSA isolation rate and the effective use of anti-MRSA drugs (VCM, TEIC, ABK and LZD), and improved susceptibility rates to anti-MRSA drugs, suggesting the possibilities that appropriate and early use of anti-MRSA drugs may cause the decrease of MRSA isolation.

β-lactam pharmacokinetics and pharmacodynamics in critically ill patients and strategies for dose optimization: a structured review

1. Infections and related sepsis are two of the most prevalent issues in the care of critically ill patients, with mortality as high as 70%. Appropriate antibiotic selection, as well as adequate dosing, is important to improve the clinical outcome for these patients. 2. β-Lactams are the most common antibiotic class used in critically ill sepsis patients because of their broad spectrum of activity and high tolerability. β-Lactams exhibit time-dependent antibacterial activity. Therefore, concentrations need to be maintained above the minimum inhibitory concentration (MIC) of pathogenic bacteria. β-Lactams are hydrophilic antibiotics with small distribution volumes similar to extracellular water and are predominantly excreted through the renal system. 3. Critically ill patients experience a myriad of physiological changes that result in changes in the pharmacokinetics (PK) of hydrophilic drugs such as β-lactams. A different approach to dosing with β-lactams may increase the likelihood of positive outcomes considering the pharmacodynamics (PD) of β-lactams, as well as the changes in PK in critically ill patients. 4. The present review describes the strategies for dose optimization of β-lactams in critically ill patients in line with the PK and PD of these drugs.

The ECMO PK Project: an incremental research approach to advance understanding of the pharmacokinetic alterations and improve patient outcomes during extracorporeal membrane oxygenation

Background

Extracorporeal membrane oxygenation (ECMO) is a supportive therapy and its success depends on optimal drug therapy along with other supportive care. Emerging evidence suggests significant interactions between the drug and the device resulting in altered pharmacokinetics (PK) of vital drugs which may be further complicated by the PK changes that occur in the context of critical illness. Such PK alterations are complex and challenging to investigate in critically ill patients on ECMO and necessitate mechanistic research. The aim of this project is to investigate each of circuit, drug and critical illness factors that affect drug PK during ECMO.

Methods/design

An incremental research plan that encompasses ex vivo experiments for drug stability testing in fresh human and ovine whole blood, ex vivo drug disposition studies in standard and modified adult ECMO circuits primed with fresh human or ovine whole blood, PK studies in healthy and critically ill ovine models of ECMO with appropriate non ECMO controls and an international mutli-centre clinical population PK study will be utilised to comprehensively define the PK alterations that occur in the presence of ECMO. Novel drug assays that will allow quantification of multiple drugs in small volumes of plasma will also be developed. Mixed-effects regression models will be used to estimate the drug loss over time in ex vivo studies. Data from animal and clinical studies will be analysed using non-linear mixed-effects models. This will lead to generation of PK data that enables the development evidence based guidelines for antibiotic, sedative and analgesic drug therapy during ECMO.

Discussion

Systematic research that integrates both mechanistic and clinical research is desirable when investigating the complex area of pharmacokinetic alterations during ECMO. The above research approach will provide an advanced mechanistic understanding of PK during ECMO. The clinical study when complete will result in development robust guidelines for prescription of 18 commonly used antibiotic, sedative and analgesic drugs used in ECMO patients. This research may also pave the way for further refinements in circuitry, drug chemistry and drug prescriptions during ECMO.

Trial registration

ACTRN12612000559819.

Effect of blood protein concentrations on drug-dosing regimes: practical guidance

In this article the importance of blood proteins for drug dosing regimes is discussed. A simple mathematical model is presented for estimating recommended drug doses when the concentration of blood proteins is decreased. Practical guidance for drug dosing regimes is discussed and given in the form of a figure. It is demonstrated that correction of drug dosing regimes is needed only for when there is a high level of drug conjugation with blood proteins and a high degree of hypoalbuminaemia. An example of the use of this model is given.

Amikacin population pharmacokinetics in critically ill Kuwaiti patients

Amikacin pharmacokinetic data in Kuwaiti (Arab) intensive care unit (ICU) patients are lacking. Fairly sparse serum amikacin peak and trough concentrations data were obtained from adult Kuwaiti ICU patients. The data were analysed using a nonparametric adaptive grid (NPAG) maximum likelihood algorithm. The estimations of the developed model were assessed using mean error (ME) as a measure of bias and mean squared error (MSE) as a measure of precision. A total of 331 serum amikacin concentrations were obtained from 56 patients. The mean (± SD) model parameter values found were Vc = 0.2302 ± 0.0866 L/kg, kslope = 0.004045 ± 0.00705 min per unit of creatinine clearance, k12 = 2.2121 ± 5.506 h(-1), and k21 = 1.431 ± 2.796 h(-1). The serum concentration data were estimated with little bias (ME = -0.88) and good precision (MSE = 13.08). The present study suggests that amikacin pharmacokinetics in adult Kuwaiti ICU patients are generally rather similar to those found in other patients. This population model would provide useful guidance in developing initial amikacin dosage regimens for such patients, especially using multiple model (MM) dosage design, followed by appropriate Bayesian adaptive control, to optimize amikacin dosage regimens for each individual patient.

Dose modulation: a new concept of antibiotic therapy in the critically ill patient?

Considerable evidence has shown that adequate antibiotic therapy is of utmost importance in the critically ill septic patient. However, antibiotic concentration may be insufficient early in infection course. We propose the concept of dose modulation, meaning front-line variability of antibiotic dose, according to patient and microorganism characteristics, followed by its reduction after clinical response and patient recovery. Therefore, dose modulation means concentrating the largest weight of antibiotics at the front-end, when the microbial load is higher and the pharmacokinetic changes poses the highest risk of underdosing and nibbling off antibiotic dose, when the sepsis syndrome is improving, guided by pharmacokinetic and pharmacodynamic data.

Optimum Use of Therapeutic Drug Monitoring and Pharmacokinetics-Pharmacodynamics in the NICU

Therapeutic drug monitoring is increasingly giving way to dosing drugs based on population-based pharmacokinetic parameters, even when pharmacokinetic values vary quite a bit in individual patients. Further, drug concentrations are often considered appropriate if they are within a defined therapeutic range, even if the patient response is suboptimal. This lecture discusses the limitations of therapeutic ranges in neonates, and proposes greater emphasis on pharmacodynamic curves to individualize drug therapy. Examples are provided using methylxanthines, indomethacin, antiepileptic drugs and aminoglycosides. The potential to use pharmacokinetic findings to describe physiologic changes and occasionally assist with diagnosis is also discussed.

A comparison of pulse contour wave analysis and ultrasonic cardiac output monitoring in the critically ill

Cardiac output (CO) is a key determinant of major organ blood flow and solute delivery to drug eliminating organs. As such, CO assessment is a key covariate in understanding altered drug handling in the critically ill. Newer minimally-invasive devices are providing unique platforms for such an application, although comparison data are currently lacking. In this study we evaluated the Vigileo (Edwards Lifesciences, Irvine, CA, USA) and USCOM (USCOM Ltd, Sydney, NSW) devices in 62 critically ill patients requiring antibacterial therapy. The mean COVigileo and COUSCOM for the first paired measurements were 8.20±2.65 l/minute and 6.84±2.57 l/minute respectively (P <0.001). A significant correlation was evident in all patients (r=0.537, P <0.001) although the recorded bias was large (1.36±2.51 l/minute, limits of agreement -3.6 to±6.3 l/minute). The overall percentage error was 65%. There was an improved correlation in those admitted with sepsis (r=0.639, P <0.001), compared to trauma (r=0.373, P=0.066), although bias, precision and percentage error were similar in both subgroups. In 54 patients a second paired assessment was obtained at three hours. A weak, although significant correlation (r=0.377, P=0.005) was observed suggesting that gross trends over time were similar. In conclusion, our findings demonstrate poor agreement between these techniques suggesting that these devices are not simply interchangeable when assessing CO in a research or clinical setting.

Initial vancomycin dosing recommendations for critically ill patients undergoing continuous venovenous hemodialysis

BACKGROUND

Delaying appropriate antimicrobial therapy for critically ill patients increases the risk of death. Currently, there are insufficient data to guide initial vancomycin dosing for patients undergoing continuous venovenous hemodialysis (CVVHD).

OBJECTIVE

To develop practical recommendations for initial dosing of vancomycin, based on the pharmacokinetics of this drug in critically ill patients undergoing CVVHD.

METHODS

A chart review was conducted for 24 critically ill adult patients who had undergone concurrent CVVHD and vancomycin therapy. Mean pharmacokinetic parameters were determined, along with practical recommendations for initial vancomycin dosing that targeted steady-state trough concentrations for patients receiving intermittent infusions and steady-state levels for those receiving continuous infusions between 15 and 20 mg/L. Monte Carlo simulation was used to develop the initial vancomycin dosing recommendations.

RESULTS

The mean (95% confidence interval) pharmacokinetic parameters for vancomycin (elimination rate constant 0.0315 [0.0254-0.0391], half-life 22.0 h [17.72-27.24 h], volume of distribution 0.96 L/kg [0.77-1.20 L/kg], and clearance 2.4 L/h [1.97-2.92 L/h]) indicated that initial intermittent IV dosing of 1.25-1.5 g q24h or 15 mg/kg q24h would be suitable. For continuous infusion, a 1.5-g IV loading dose followed by continuous infusion of 1-1.5 g IV over 24 h (42-62 mg/h) would be recommended. However, Monte Carlo simulation revealed that the probability of achieving desired concentrations between 15 and 20 mg/L with any of these initial regimens is low.

CONCLUSIONS

There was considerable variation in vancomycin pharmacokinetics in this patient population. The observations reported here raise concerns about the reliability of numerous empiric dosing recommendations derived from small pharmacokinetic studies in heterogeneous populations. Follow-up therapeutic drug monitoring is essential to ensure that concentrations remain within the target range.

Clinical Equivalency of Ciprofloxacin 750 mg Enterally and 400 mg Intravenously for Patients Receiving Enteral Feeding: Systematic Review

BACKGROUND

Concomitant enteral administration of ciprofloxacin with products containing magnesium, aluminum, and calcium (e.g., as enteral feeds) decreases the oral bioavailability of this antibiotic. The manufacturer currently recommends holding enteral feeds for a total of 8 h after ciprofloxacin is given, but this is not feasible for patients who are receiving continuous enteral feeding. A previous study demonstrated that a higher dose of oral ciprofloxacin (750 mg BID) may compensate for the reduced bioavailability associated with this drug-food interaction, allowing adequate concentrations for effective bactericidal activity.

OBJECTIVE

To evaluate whether ciprofloxacin 750 mg administered enterally is a clinically feasible alternative to ciprofloxacin 400 mg administered intravenously for adults receiving enteral feeds.

METHODS

A literature search was conducted in EMBASE (January 1980 to April 2008) and MEDLINE (January 1949 to April 2008), with no language restrictions, using the key words "ciprofloxacin", "fluoroquinolone", "tube feed", and "enteral". For trials that remained after screening of the abstract, the full text was reviewed and the reference lists were hand-searched to identify additional trials. The following outcomes were prespecified: death, serious adverse events, clinical cure, microbiological cure, re-infection, total adverse events, ratio of area under the curve (AUC, in microgram-hours per millilitre) to minimum inhibitory concentration (MIC, in micrograms per millilitre), ratio of maximum serum concentration (C(max), in micrograms per millilitre) to MIC, and C(max).

RESULTS

The search identified 121 potentially eligible studies, which were screened on the basis of information provided in the abstract. From this initial screening, it was clear that 113 studies did not meet the inclusion criteria. The remaining 8 studies were subjected to a full-text review, which revealed that only 1 study met the inclusion criteria. In that study, ciprofloxacin 750 mg given enterally yielded an AUC similar to that achieved with 400 mg given parentally, but the C(max) was lower. No clinical outcomes were reported.

CONCLUSIONS

There is insufficient evidence from this systematic review to determine whether patients receiving enteral feeds concomitantly with enteral ciprofloxacin 750 mg BID will achieve clinical outcomes similar to those receiving parenteral ciprofloxacin 400 mg BID.

Continuous beta-lactam infusion in critically ill patients: the clinical evidence

There is controversy over whether traditional intermittent bolus dosing or continuous infusion of beta-lactam antibiotics is preferable in critically ill patients. No significant difference between these two dosing strategies in terms of patient outcomes has been shown yet. This is despite compelling in vitro and in vivo pharmacokinetic/pharmacodynamic (PK/PD) data. A lack of significance in clinical outcome studies may be due to several methodological flaws potentially masking the benefits of continuous infusion observed in preclinical studies. In this review, we explore the methodological shortcomings of the published clinical studies and describe the criteria that should be considered for performing a definitive clinical trial. We found that most trials utilized inconsistent antibiotic doses and recruited only small numbers of heterogeneous patient groups. The results of these trials suggest that continuous infusion of beta-lactam antibiotics may have variable efficacy in different patient groups. Patients who may benefit from continuous infusion are critically ill patients with a high level of illness severity. Thus, future trials should test the potential clinical advantages of continuous infusion in this patient population. To further ascertain whether benefits of continuous infusion in critically ill patients do exist, a large-scale, prospective, multinational trial with a robust design is required.

DALI: Defining Antibiotic Levels in Intensive care unit patients: a multi-centre point of prevalence study to determine whether contemporary antibiotic dosing for critically ill patients is therapeutic

Background

The clinical effects of varying pharmacokinetic exposures of antibiotics (antibacterials and antifungals) on outcome in infected critically ill patients are poorly described. A large-scale multi-centre study (DALI Study) is currently underway describing the clinical outcomes of patients achieving pre-defined antibiotic exposures. This report describes the protocol.

Methods

DALI will recruit over 500 patients administered a wide range of either beta-lactam or glycopeptide antibiotics or triazole or echinocandin antifungals in a pharmacokinetic point-prevalence study. It is anticipated that over 60 European intensive care units (ICUs) will participate. The primary aim will be to determine whether contemporary antibiotic dosing for critically ill patients achieves plasma concentrations associated with maximal activity. Secondary aims will compare antibiotic pharmacokinetic exposures with patient outcome and will describe the population pharmacokinetics of the antibiotics included. Various subgroup analyses will be conducted to determine patient groups that may be at risk of very low or very high concentrations of antibiotics.

Discussion

The DALI study should inform clinicians of the potential clinical advantages of achieving certain antibiotic pharmacokinetic exposures in infected critically ill patients.

Continuous infusion of antibiotics in the critically ill: The new holy grail for beta-lactams and vancomycin?

The alarming global rise of antimicrobial resistance combined with the lack of new antimicrobial agents has led to a renewed interest in optimization of our current antibiotics. Continuous infusion (CI) of time-dependent antibiotics has certain theoretical advantages toward efficacy based on pharmacokinetic/pharmacodynamic principles. We reviewed the available clinical studies concerning continuous infusion of beta-lactam antibiotics and vancomycin in critically ill patients. We conclude that CI of beta-lactam antibiotics is not necessarily more advantageous for all patients. Continuous infusion is only likely to have clinical benefits in subpopulations of patients where intermittent infusion is unable to achieve an adequate time above the minimal inhibitory concentration (T > MIC). For example, in patients with infections caused by organisms with elevated MICs, patients with altered pharmacokinetics (such as the critically ill) and possibly also immunocompromised patients. For vancomycin CI can be chosen, not always for better clinical efficacy, but because it is practical, cheaper, associated with less AUC_24h (area under the curve >24 h)-variability, and easier to monitor.

Ceftazidime dosage regimen in intensive care unit patients: from a population pharmacokinetic approach to clinical practice via Monte Carlo simulations

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

The large variability in drug pharmacokinetic disposition has already been described in ICU patients leading to important variations in drugs concentrations. The usual recommended dosage of ceftazidime is not adapted for all ICU situations and ceftazidime should be monitored closely. New recommendations have to be given for some specific cases.

WHAT THIS STUDY ADDS

Our results propose individual therapeutic drug monitoring taking into account: For the patient: the reason of admission in the ICU, the mechanical ventilation status and the creatinine clearance calculated by the modified diet in renal disease (MDRD). • For the antibiotics: the lung distribution, the minimal inhibitory concentration (MIC) of the strain to eradicate and the potential toxicity. AIM To predict the ceftazidime dosage regimen as a function of the glomerular filtration rate expressed by the modification of the diet in renal disease (MDRD), reason for admission and mechanical ventilation in intensive care unit (ICU) patients to treat Pseudomonas aeruginosa pneumonia.

METHOD

A published and qualified population pharmacokinetic model was used to perform Monte Carlo simulations of ceftazidime concentrations. The serum target of 40-100 mg l(-1) was defined based on the minimal inhibitory concentration (MIC), the European break point (EBP), the pulmonary drug diffusion and toxicity. The recommended dosage regimens were based on the maximum percentile of the patients with simulated steady state concentrations reaching the target.

RESULTS

Steady-state was reached at 72 h whatever the MDRD. The simulations of serum concentrations generated higher percentiles of the population reaching the target after continuous administration. We recommend a 4 g continuous dose after the usual 2 g loading dose for patients with MDRD from 10 to 30 ml min(-1) , 6 g for MDRD between 40 and 80 ml min(-1) , 8 g for MDRD from 90 to 110 ml min(-1) , 10 g for MDRD from 120 to 190 ml min(-1) and 12 g day(-1) for patients with MDRD higher than 200 ml min(-1) .

CONCLUSION

Our study demonstrated that in ICU patients for a given MDRD, steady-state takes longer to reach in polytrauma patients than in patients with medical or post surgery reasons for admission. Continuous infusion ensures that a higher percentage of patients reaches the target than the same dose given by discontinuous administration and this only depends on MDRD.

Clinical and microbiological efficacy of continuous versus intermittent application of meropenem in critically ill patients: a randomized open-label controlled trial

Introduction

Meropenem bactericidal activity depends on the time when the free drug concentrations remain above the minimum inhibitory concentration of pathogens. The goal of this study was to compare clinical and bacteriological efficacy of continuous meropenem infusion versus bolus administration in critically ill patients with severe infection, and to evaluate the safety of both dosing regimens.

Methods

Patients admitted to the interdisciplinary Intensive Care Unit (ICU) who suffered from severe infections and received meropenem were randomized either in the Infusion group (n = 120) or in the Bolus group (n = 120). Patients in the Infusion group received a loading dose of 2 g of meropenem followed by a continuous infusion of 4 g of meropenem over 24 hours. Patients in the Bolus group were given 2 g of meropenem over 30 minutes every 8 hours. Clinical and microbiological outcome, safety, meropenem-related length of ICU and hospital stay, meropenem-related length of mechanical ventilation, duration of meropenem treatment, total dose of meropenem, and ICU and in-hospital mortality were assessed.

Results

Clinical cure at the end of meropenem therapy was comparable between both groups (83.0% patients in the Infusion vs. 75.0% patients in the Bolus group; P = 0.180). Microbiological success rate was higher in the Infusion group as opposed to the Bolus group (90.6% vs. 78.4%; P = 0.020). Multivariate logistic regression identified continuous administration of meropenem as an independent predictor of microbiological success (OR = 2.977; 95% CI = 1.050 to 8.443; P = 0.040). Meropenem-related ICU stay was shorter in the Infusion group compared to the Bolus group (10 (7 to 14) days vs. 12 (7 to 19) days; P = 0.044) as well as shorter duration of meropenem therapy (7 (6 to 8) days vs. 8 (7 to 10) days; P = 0.035) and lower total dose of meropenem (24 (21 to 32) grams vs. 48 (42 to 60) grams; P < 0.0001). No severe adverse events related to meropenem administration in either group were observed.

Conclusions

Continuous infusion of meropenem is safe and, in comparison with higher intermittent dosage, provides equal clinical outcome, generates superior bacteriological efficacy and offers encouraging alternative of antimicrobial therapy in critically ill patients.

Introduction to drug pharmacokinetics in the critically ill patient

Despite regular use of drugs for critically ill patients, overall data are limited regarding the impact of critical illness on pharmacokinetics (PK). Designing safe and effective drug regimens for patients with critical illness requires an understanding of PK. This article reviews general principles of PK, including absorption, distribution, metabolism, and elimination, and how critical illness can influence these parameters. In the area of drug absorption, we discuss the impact of vasopressor use, delayed gastric emptying and feeding tubes, and nutrient interactions. On the topic of drug distribution, we review fluid resuscitation, alterations in plasma protein binding, and tissue perfusion. With drug metabolism, we discuss hepatic enzyme activity, protein binding, and hepatic blood flow. Finally, we review drug elimination in the critically ill patient and discuss the impact of augmented renal clearance and acute kidney injury on drug therapies. In each section, we highlight select literature reviewing the PK impact of these conditions on a drug PK profile and, where appropriate, provide general suggestions for clinicians on how to modify drug regimens to manage PK challenges.

Population pharmacokinetics of vancomycin in Thai patients

Population pharmacokinetics of vancomycin in Thai adult patients was determined by non-linear mixed-effects approach using 319 vancomycin serum concentrations from 212 patients. The data were best fitted by a two-compartment model and it was used to examine the effect of patient characteristics on the vancomycin pharmacokinetics. In the final model, there was a linear relationship between vancomycin clearance, CL (L/h), and creatinine clearance calculated by Cockcroft-Gault equation, CL_Cr (mL/min): CL  =0.044  ×  CL_Cr. Meanwhile, volume of central compartment, V₁ (L), was linearly related with the age (years old): V₁ = 0.542  × Age. Intercompartment clearance (Q) and volume of peripheral compartment (V₂) was 6.95 L/h and 44.2 L, respectively. The interindividual variability for CL, V₁, Q, and V₂ was 35.78, 20.93, 39.50, and 57.27%, respectively. Whereas, the intraindividual variability was 4.51 mg/L. Final model then was applied to predict serum vancomycin concentrations on validation group. Predictive performance revealed a bias of −1.43 mg/L (95% CI: −5.82–2.99) and a precision of 12.2 mg/L (95% CI: −1.60–26.16). In conclusion, population pharmacokinetic of vancomycin in Thai adult patients was developed. The model could be used to create vancomycin dosage regimen in the type of patient similar with the present study.

Therapeutic drug monitoring of antimicrobials

Optimizing the prescription of antimicrobials is required to improve clinical outcome from infections and to reduce the development of antimicrobial resistance. One such method to improve antimicrobial dosing in individual patients is through application of therapeutic drug monitoring (TDM). The aim of this manuscript is to review the place of TDM in the dosing of antimicrobial agents, specifically the importance of pharmacokinetics (PK) and pharmacodynamics (PD) to define the antimicrobial exposures necessary for maximizing killing or inhibition of bacterial growth. In this context, there are robust data for some antimicrobials, including the ratio of a PK parameter (e.g. peak concentration) to the minimal inhibitory concentration of the bacteria associated with maximal antimicrobial effect. Blood sampling of an individual patient can then further define the relevant PK parameter value in that patient and, if necessary, antimicrobial dosing can be adjusted to enable achievement of the target PK/PD ratio. To date, the clinical outcome benefits of a systematic TDM programme for antimicrobials have only been demonstrated for aminoglycosides, although the decreasing susceptibility of bacteria to available antimicrobials and the increasing costs of pharmaceuticals, as well as emerging data on pharmacokinetic variability, suggest that benefits are likely.

Continuing education: alternative approaches to optimizing antimicrobial pharmacodynamics in critically ill patients

Critical illness results in a constellation of physiologic changes that subsequently impact antibiotic pharmacokinetic and pharmacodynamic parameters. These changes can result in poorly treated infections that in turn lead to longer intensive care unit (ICU) and hospital stays, prolonged use of mechanical ventilation, and higher mortality rates. Research has expanded our understanding of antibiotic pharmacodynamics among ICU patients, and some investigators and clinicians have questioned traditional antibiotic dosing schemes among this population. Alternative dosing strategies to optimize antibiotic pharmacodynamics of aminoglycosides, beta-lactams, fluoroquinolones, and vancomycin have been explored. Appropriate duration of exposure to beta-lactam antibiotics has been recognized as an important parameter associated with successful treatment outcomes. To maximize this exposure, continuous infusions over a 24-hour period have resulted in higher clinical response rates and improved surrogate markers of infection. Equally as promising is the alternative of extending the infusion time to increase exposure while maintaining the same daily beta-lactam dose and frequency. Data from clinical trials have suggested that the area under the concentration-time curve to minimum inhibitory concentration ratio for aminoglycosides, fluoroquinolones, and vancomycin is a better correlate for successful treatment outcomes. Optimizing antibiotic pharmacodynamics by changing dosage methods should be considered in ICU patients to improve treatment response and success.

Urosepsis--from the view of the urologist

Urosepsis accounts for approximately 25% of all sepsis cases and may develop from a community-or nosocomial-acquired urinary tract infection (UTI). The underlying UTI is almost exclusively a complicated one with involvement of parenchymatous urogenital organs (e.g. kidneys, prostate). In urosepsis, as in other types of sepsis, the severity of sepsis depends mostly upon the host response. The urological management of urosepsis comprises early diagnosis, early fluid and oxygen treatment, early antibiotic therapy and early control of the complicating factor in the urinary tract. Time from admission to therapy is critical. The shorter the time to effective treatment, the higher is the success rate. This aspect has to become incorporated into the organisational process, including urologists, radiologists and intensive care specialists amongst others. Adequate initial antibiotic therapy has to be insured. This goal implies, however, a wide array of measures over time to ensure a rational antibiotic policy, including microbiologists and clinical pharmacologists. Dosage of an antibiotic in the septic patient generally has to be high to ensure adequate pharmacological exposure in the individual patient.

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.

Evaluation of the accuracy of a pharmacokinetic dosing program in predicting serum vancomycin concentrations in critically ill patients

BACKGROUND

Optimization of the timing of appropriate antibiotics is crucial to improve the management of patients in severe sepsis and septic shock. Vancomycin is commonly used empirically in cases of nosocomial infections in critically ill patients. Therefore, early optimization of vancomycin pharmacokinetics is likely to improve outcomes.

OBJECTIVE

To evaluate a pharmacokinetic program to predict serum vancomycin concentrations in accordance with administered dose, weight, height, and creatinine clearance in a critically ill population.

METHODS

We conducted a prospective observational single-center study in a 45-bed intensive care unit (ICU). All patients hospitalized in the ICU requiring intravenous treatment with vancomycin for a suspected infection were enrolled. The modalities of vancomycin therapy and the monitoring of serum concentrations were left to the discretion of the treating clinician. We compared the measured serum vancomycin concentrations with those predicted by the MM-USCPACK program and analyzed the factors influencing the prediction.

RESULTS

Fifty-four intravenous vancomycin courses were administered in 48 critically ill patients over the 3-month study. The precision was considered acceptable, based on a relative precision equal to 8.9% (interquartile range 3.5-18.9%) and the relative bias for all predictions was equal to -1.3%. Overall, 77.3% of predictions were within 20% of observed concentrations; factors correlating with a poorer prediction were a change in renal function, obesity, and the magnitude of organ dysfunction on initiation of vancomycin (expressed by a Systemic Organ Failure Assessment score >11).

CONCLUSIONS

The MM-USCPACK program is a useful and reliable tool for prediction of serum vancomycin concentrations in patients hospitalized in ICU and likely reflects the close monitoring of renal function in this setting. For some patients (more severely ill, obese, or significant change in renal function during vancomycin therapy), predictions were less precise.

[Monitoring vancomycin in an intensive care unit: A retrospective survey on 66 patients]

OBJECTIVES

The study objectives were to check whether recommended vancomycin doses were related to pharmacological objectives for intensive care patients: steady-state plasma concentration (SSc) and ratio SSc/MIC (Minimal Inhibiting Concentration). The authors tried to identify variability factors for vancomycin plasmatic concentrations at peak.

PATIENTS AND METHODS

This monocentric, observational, and retrospective survey was performed on 66 intensive care patients treated by antibiotics including vancomycin, alone or in combination, as a curative treatment for a severe infection with Gram-positive bacteria. Vancomycin was dosed at 15mg/kg during the first hour, then 40 to 60mg/kg per 24hour. Vancomycin SSc and bacteria MIC were recorded. The SSc/MIC ratio was determined and was considered efficient when superior to 8.

RESULTS

Forty-two percent of vancomycin SSc were within the effectiveness rate. Twenty-three percent of SSc/MIC ratios were superior to 8. The rate of clinical recovery was 71 %. The length of antibiotherapy was identified as positively interacting with biological effectiveness, unlike severe sepsis, a factor of negative interaction on vancomycin SSc in this study.

CONCLUSION

Less than half of the SSc and less than a quarter of the SSc/MIC ratios were at effective rates in our study. Therefore, adequacy between dosage, administration, and monitoring should be reviewed.

Overview of antimicrobial therapy in intensive care units

In the management of a patient with severe sepsis, it is important to suspect the infection early, to collect samples immediately after diagnosis and to promptly initiate a broad-spectrum antibiotic treatment. The choice of this empirical antimicrobial therapy should be based on host characteristics, site of infection, local ecology and pharmacokinetics/pharmacodynamics of antibiotics. In severe infection, guidelines recommend the use of a combination of antibiotics. After results of cultures are obtained, treatment should be re-evaluated to either de-escalate or escalate the antibiotic prescription. This is associated with optimal costs, decreased incidence of superinfection and minimal development of antimicrobial resistance. All these steps should rely on written protocols, and the compliance to these protocols should be continuously monitored in order to detect violations and implement corrective procedures.

Antibiotic dosing in the 'at risk' critically ill patient: Linking pathophysiology with pharmacokinetics/pharmacodynamics in sepsis and trauma patients

Background

Critical illness, mediated by trauma or sepsis, can lead to physiological changes that alter the pharmacokinetics of antibiotics and may result in sub-therapeutic concentrations at the sites of infection. The first aim of this project is to identify the clinical characteristics of critically ill patients with significant trauma that have been recently admitted to ICU that may predict the dosing requirements for the antibiotic, cefazolin. The second aim of this is to identify the clinical characteristics of critically ill patients with sepsis that may predict the dosing requirements for the combination antibiotic, piperacillin-tazobactam.

Methods/Design

This is an observational pharmacokinetic study of patients with trauma (cefazolin) or with sepsis (piperacillin-tazobactam). Participants will have samples from blood and urine, collected at different intervals. Patients will also have a microdialysis catheter inserted into subcutaneous tissue to measure interstitial fluid penetration of the antibiotic. Participants will be administered sinistrin, indocyanine green and sodium bromide as well as have cardiac output monitoring performed and tetrapolar bioimpedance to determine physiological changes resulting from pathology. Analysis of samples will be performed using validated liquid chromatography tandem mass-spectrometry. Pharmacokinetic analysis will be performed using non-linear mixed effects modeling to determine individual and population pharmacokinetic parameters of antibiotics.

Discussion

The study will describe cefazolin and piperacillin-tazobactam concentrations in plasma and the interstitial fluid of tissues in trauma and sepsis patients respectively. The results of this study will guide clinicians to effectively dose these antibiotics in order to maximize the concentration of antibiotics in the interstitial fluid of tissues.

Impact of early oseltamivir treatment on outcome in critically ill patients with 2009 pandemic influenza A

OBJECTIVES

The impact of oseltamivir on mortality in critically ill patients with 2009 pandemic influenza A (2009 H1N1) is not clear. The main objective of this study was to investigate the relationship between the timing of antiviral administration and intensive care unit (ICU) outcomes.

METHODS

Prospective, observational study of a cohort of ICU patients with confirmed 2009 H1N1 infection. Clinical data, treatment and outcome were compared between patients receiving early treatment (ET) with oseltamivir, initiated within 2 days, and patients administered late treatment (LT), initiated after this timepoint. Multivariate analysis and propensity score were used to determine the effect of oseltamivir on ICU mortality.

RESULTS

Six hundred and fifty-seven patients were enrolled. Four hundred and four (61.5%) patients required mechanical ventilation (MV; mortality 32.6%). Among them, 385 received effective antiviral therapy and were included in the study group. All patients received oseltamivir for a median duration of 10 days (interquartile range 8-14 days). Seventy-nine (20.5%) ET patients were compared with 306 LT patients. The two groups were comparable in terms of main clinical variables. ICU length of stay (22.7 ± 16.7 versus 18.4 ± 14.2 days; P = 0.03), hospital length of stay (34.0 ± 20.3 versus 27.2 ± 18.2 days; P = 0.001) and MV days (17.4 ± 15.2 versus 14.0 ± 12.4; P = 0.04) were higher in the LT group. ICU mortality was also higher in LT (34.3%) than in ET (21.5%; OR = 1.9; 95% CI 1.06-3.41). A multivariate model identified ET (OR = 0.44; 95% CI 0.21-0.87) as an independent variable associated with reduced ICU mortality. These results were confirmed by propensity score analysis (OR = 0.44; 95% CI 0.22-0.90; P < 0.001).

CONCLUSIONS

Our findings suggest that early oseltamivir administration was associated with favourable outcomes among critically ill ventilated patients with 2009 H1N1 virus infection.