Contemporary activity of meropenem and comparator broad-spectrum agents: MYSTIC program report from the United States component (2005)

Rationale and Logistics of Continuous Infusion Cephalosporin Antibiotics

Cephalosporins have traditionally been administered as an intermittent infusion. With the knowledge that cephalosporins demonstrate a time-dependent pharmacodynamic profile, administration via continuous infusion may provide more effective antibiotic exposure for successful therapy. Proposed benefits of administration via continuous infusion include less IV manipulation, decreased potential for antibiotic resistance, and potential cost savings. The objective of this review was to provide a detailed assessment of available evidence for the use of continuous infusion cephalosporins and practical dosing and administration recommendations. Studies were gathered and assessed for inclusion via a literature search of PubMed and Ovid MEDLINE using mesh terms ["continuous infusion" and "cephalosporin"], "intermittent infusion", ["intermittent versus continuous" and "cephalosporin"], "continuous infusion cephalosporin", as well as specific drug names. References from included studies were also evaluated for inclusion. Data which compared the two administration methods (continuous infusion vs. intermittent infusion) were evaluated. Thirty-five studies were analyzed among several cephalosporins with variable delivery. Dosing regimens utilized in the selected studies were assessed with known compatibility and stability data and further summarized.

How to treat severe Acinetobacter baumannii infections

PURPOSE OF REVIEW

To update the management of severe Acinetobacter baumannii infections (ABI), particularly those caused by multi-resistant isolates.

RECENT FINDINGS

The in vitro activity of the various antimicrobial agents potentially helpful in treating ABI is highly variable and has progressively decreased for many of them, limiting current therapeutic options. The combination of more than one drug is still advisable in most circumstances. Ideally, two active first-line drugs should be used. Alternatively, a first-line and a second-line drug and, if this is not possible, two or more second-line drugs in combination. The emergence of new agents such as Cefiderocol, the combination of Sulbactam and Durlobactam, and the new Tetracyclines offer therapeutic options that need to be supported by clinical evidence.

SUMMARY

The apparent limitations in treating infections caused by this bacterium, the rapid development of resistance, and the serious underlying situation in most cases invite the search for alternatives to antibiotic treatment, the most promising of which seems to be bacteriophage therapy.

Multidrug-resistant Acinetobacter baumannii infection in lung transplant recipients: risk factors and prognosis

Backgrounds: Infectious complication is an important cause of poor outcome of lung transplantation (LT). Infections with Acinetobacter baumannii (A. baumannii) are problematic, because of limited therapeutic option due to increasing resistance to antibiotics. However, there are few studies on A. baumannii infection in lung transplant recipients. Thus, we aimed to investigate epidemiology and risk factors for infection with A. baumannii in lung transplant recipients. Methods: Lung transplant recipients ≥18 years of age in a university hospital were enrolled in this retrospective cohort study. Risk factors for infection with multidrug resistant A. baumannii and 90-day mortality were analysed. Results: Fifty-one of 96 lung transplant recipients experienced A. baumannii infection. Infected patients had a significantly higher 90-day mortality rate than uninfected (19.6% vs. 2.2%, p = .009). High blood urea nitrogen (BUN) before transplantation (odds ratio [OR] 1.16; p = .008), long duration of surgery (OR 1.16; p = .029) and hypoalbuminemia before transplantation (OR 4.01; p = .037) were independent risk factors for infection with multidrug resistant A. baumannii. On multivariate analysis, severe thrombocytopenia (OR 28.69; p = .005), high serum creatinine (OR 1.48; p = .042) and infection with multidrug resistant A. baumannii (OR 22.58; p = .031) were independent risk factors for 90-day mortality. Conclusions: Prolonged surgery, high BUN and hypoalbuminemia before LT were significant risk factors for infection with multidrug resistant A. baumannii. Severe thrombocytopenia, high serum creatinine and infection with multidrug resistant A. baumannii infection were independent risk factors for 90-day mortality.

Phenotypic Detection of Extended Spectrum Beta lactamase and Carbapenemase Co-producing Clinical Isolates from Two Tertiary Hospitals in Kano, North West Nigeria

BACKGROUND

Continue rise in unprofessional use of antibiotics in our hospitals and communities is worrisome. A research study was therefore conducted to detect extended spectrum beta-lactamase (ESBL), carbapenemase, metallobeta lactamase and their co-production phenotypically from isolates obtained from patients admitted to or attending two tertiary hospitals in Kano, Nigeria.

METHOD

A total of 248 isolates of Escherichia coli and Klebsiella pneumoniaewere screened phenotypically for ESBL production and carbapenemase production according to CLS1 2012 breakpoints using double disk synergy test and modified Hodge test (MHT) respectively. Antibiotic susceptibility of the organisms was tested against colistin, tigecycline and 3 flouroquinolones.

RESULTS

The result shows that 58.0% of the isolates were ESBL producers with higher percentage in K. pneumoniae (62.9%). Further, about 40.3% and 36.6% of the isolates were resistant to meropenem and imipenem respectively. However, E. coli showed higher resistance to meropenem (47.1%) while K. pneumoniae showed higher resistance to imipenem (44.4%). Co-productions of carbapenemase and ESBL were observed in both E. coli and K. pneumoniae. Carbapenemase producing isolates were more obtained from uro-pathogens and wound isolates, with almost all the cases of co-production of the β lactamases occurring in urine and cathertips isolates. Overall susceptibilities of the isolates to colistin and tigecycline were 64.6and70.0% respectively, but isolates were less susceptible to flouroquinolones.

CONCLUSION

The finding of the study therefore indicates that carbapenem resistance is mediated by carbapenemase production and or overproduction of ESBL coupled with reduced porins. Co-production of carbapenemase, MBLs and ESBLs by some of the isolates is worrisome. Susceptibility to colistin and tigecycline was still promising, but increasing resistance to flouroquinolones has been observed.

Genetic Mechanisms of Antimicrobial Resistance of Acinetobacter baumannii

OBJECTIVE

To summarize published data identifying known genetic mechanisms of antibiotic resistance in Acinetobacter baumannii and the correlating phenotypic expression of antibiotic resistance.

DATA SOURCES

MEDLINE databases (1966-July 15, 2010) were searched to identify original reports of genetic mechanisms of antibiotic resistance in A. baumannii.

DATA SYNTHESIS

Numerous genetic mechanisms of resistance to multiple classes of antibiotics are known to exist in A. baumannii, a gram-negative bacterium increasingly implicated in nosocomial infections. Mechanisms may be constitutive or acquired via plasmids, integrons, and transposons. Methods of resistance include enzymatic modification of antibiotic molecules, modification of antibiotic target sites, expression of efflux pumps, and downregulation of cell membrane porin channel expression. Resistance to β-lactams appears to be primarily caused by β-lactamase production, including extended spectrum β-lactamases (b/aTEM, blaSHV, b/aTX-M,b/aKPC), metallo-β-lactamases (blaMP, blaVIM, bla, SIM), and most commonly, oxacillinases (blaOXA). Antibiotic target site alterations confer resistance to fluoroquinolones (gyrA, parC) and aminoglycosides (arm, rmt), and to a much lesser extent, β-lactams. Efflux pumps (tet, ade, abe) contribute to resistance against β-lactams, tetracyclines, fluoroquinolones, and aminoglycosides. Finally, porin channel deletion (carO, oprD) appears to contribute to β-lactam resistance and may contribute to rarely seen polymyxin resistance. Of note, efflux pumps and porin deletions as solitary mechanisms may not render clinical resistance to A. baumannii.

CONCLUSIONS

A. baumannii possesses copious genetic resistance mechanisms. Knowledge of local genotypes and expressed phenotypes for A. baumannii may aid clinicians more than phenotypic susceptibilities reported in large epidemiologic studies.

Pseudomonas aeruginosa: arsenal of resistance mechanisms, decades of changing resistance profiles, and future antimicrobial therapies

Antimicrobial resistance is one of the most serious public health issues facing humans since the discovery of antimicrobial agents. The frequent, prolonged, and uncontrolled use of antimicrobial agents are major factors in the emergence of antimicrobial-resistant bacterial strains, including multidrug-resistant variants. Pseudomonas aeruginosa is a leading cause of nosocomial infections. The abundant data on the increased resistance to antipseudomonal agents support the need for global action. There is a paucity of new classes of antibiotics active against P. aeruginosa. Here, we discuss recent antibacterial resistance profiles and mechanisms of resistance by P. aeruginosa. We also review future potential methods for controlling antibiotic-resistant bacteria, such as phage therapy, nanotechnology and antipseudomonal vaccines.

Multidrug-resistant Acinetobacter baumannii infections in lung transplant patients in the cardiothoracic intensive care unit

BACKGROUND

Multidrug-resistant (MDR) gram-negative bacteria are a growing threat to solid organ transplantation (SOT) patients in the intensive care unit (ICU). We aimed to examine the mortality rates of gram-negative MDR bacterial infection in SOT patients compared with patient population undergoing other cardiothoracic surgeries and hospitalized under similar ICU conditions.

METHODS

A retrospective study from a single medical center, including patients with MDR Acinetobacter baumannii and carbapenem-resistant Klebsiella pneumoniae infection, hospitalized in the cardiothoracic ICU. Data were collected from computerized databases, and data were verified using the hospitalization files. Microbiological data were provided by the microbiology laboratory.

RESULTS

During the study period, 205 SOT patients and 5031 other patients were hospitalized in the cardiothoracic ICU. Active infection with gram-negative MDR bacteria was identified in 147 patients, of which 37 underwent SOT (18% of total transplant recipients) and 110 underwent another cardiothoracic surgery (2% of total patients who are not transplant recipients). Mortality rates were high among both groups of patients, with no significant difference between them.

CONCLUSIONS

Infection with resistant bacteria is more prevalent among patients following SOT compared with patients following other cardiothoracic surgeries. Mortality is high in all patients regardless of the immunocompromised condition.

Solid-state stability study of meropenem - solutions based on spectrophotometric analysis

Background

B-Lactam antibiotics are still the most common group of chemotherapeutic drugs that are used in the treatment of bacterial infections. However, due to their chemical instability the potential to apply them as oral pharmacotherapeutics is often limited and so it is vital to employ suitable non-destructive analytical methods. Hence, in order to analyze such labile drugs as β-lactam analogs, the application of rapid and reliable analytical techniques which do not require transferring to solutions or using organic solvents, following the current green approach to pharmaceutical analysis, is necessary. The main objective of the present research was to develop analytical methods for the evaluation of changes in meropenem in the solid state during a stability study.

Results

The UV, FT-IR and Raman spectra of meropenem were recorded during a solid-state stability study. The optimum molecular geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities were calculated according to the density-functional theory (DFT/B3LYP method) with a 6-31G(d,p) basis set. As the differences between the observed and scaled wavenumber values were small, a detailed interpretation of the FT-IR and Raman spectra was possible for non-degraded and degraded samples of meropenem. The problem of the overlapping spectra of meropenem and ring-containing degradation products was solved by measuring changes in the values of the first-derivative amplitudes of the zero-order spectra of aqueous solutions of meropenem. Also, molecular electrostatic potential (MEP), front molecular orbitals (FMOs) and the gap potential between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were determined.

Conclusions

Based on the findings of this work, it appears possible to use time-saving and reliable spectrophotometric analytical methods, supported by quantum-chemical calculations, for solid-state stability investigations of meropenem. The methods developed for this study may be considered a novel, green solution to pharmaceutical analysis of labile drugs – an alternative for the recommended chromatographic procedures.

Four Year Trend of Carbapenem-Resistance in Newly Opened ICUs of a University-Affiliated Hospital of South Korea

Background

Carbapenem-resistance is rapidly evolving among the pathogenic microbes in intensive care units (ICUs). This study aimed to determine annual trend of carbapenem-resistance in the ICU for 4 years, since the opening of a university-affiliated hospital in South Korea.

Methods

From 2005 to 2008, microbial samples from consecutive 6,772 patients were screened in the ICU. Three hundred and ninety-seven patients (5.9%) and their first isolates of carbapenem-resistant pathogens were analyzed.

Results

The percentage of patients infected with carbapenem-resistant organisms increased constantly during the initial three years (2.3% in 2005, 6.2% in 2006, 7.8% in 2007), then it declined to 6.5% in 2008. Acute Physiology and Chronic Health Evaluation (APACHE) III score at admission was 58.0±23.5, the median length of the ICU stay was 37 days, and the mortality rate was 37.5%. The sampling sites were endotracheal suction (67%), catheterized urine (17%), wound (6%) and others (10%). Bacteria with carbapenem-resistance were Pseudomonas aeruginosa (247 isolates, 62%), Acinetobacter baumannii (117 isolates, 30%), Enterobacteriaceae (12 isolates, 3%), and others (21, 5%). Of note, peak isolation of carbapenem-resistant microorganisms in medical ICU was followed by the same epidemic at surgical ICU.

Conclusion

Taken together, carbapenem-resistant pathogens are of growing concern in the ICU.

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.

Steady-state pharmacokinetics and pharmacodynamics of cefepime administered by prolonged infusion in hospitalised patients

The objective of this study was to evaluate the steady-state pharmacokinetics and pharmacodynamics of cefepime administered by prolonged infusion in hospitalised patients requiring antimicrobial therapy. Nine patients received 1g every 8h (q8h), infused over 4h, and steady-state pharmacokinetic parameters were determined by non-compartmental and compartmental methods. Using these pharmacokinetic parameters, 5000-patient Monte Carlo simulations were performed to estimate the pharmacokinetic profiles for six prolonged-infusion dosing regimens. The probability of target attainment (PTA) was calculated at minimum inhibitory concentrations (MICs) ranging from 0.06 μg/mL to 32 μg/mL, and the cumulative fraction of response (CFR) was calculated for six Gram-negative pathogens using MIC data from the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) (2005-2007, USA). The pharmacodynamic target was free cefepime concentrations remaining above the MIC for 60% of the dosing interval (60% fT>MIC). Mean ± standard deviation maximum and minimum serum concentrations, terminal elimination half-life, elimination rate constant, volume of distribution and systemic clearance of cefepime were 32.5 ± 13.5 μg/mL, 9.5 ± 5.2 μg/mL, 2.4 ± 0.7h, 0.316 ± 0.116 h(-1), 21.3 ± 6.5L and 6.6 ± 3.6L/h, respectively. At the susceptibility breakpoint of 8 μg/mL, the PTA was >90% for 1g and 2g q8h (4-h infusion) and 1g and 2g every 6h (q6h) (3-h infusion). For Pseudomonas aeruginosa, the CFR was 88.6% for 1g q8h (4-h infusion) and ≥ 92.7% for 2g q8h (4-h infusion) and 1g and 2g q6h (3-h infusion). Cefepime 1g q8h infused over 4h provides excellent target attainment for susceptible bacterial pathogens with MICs ≤8 μg/mL.

Comparative in vitro activity of Meropenem, Imipenem and Piperacillin/tazobactam against 1071 clinical isolates using 2 different methods: a French multicentre study

BACKGROUND

Meropenem is a carbapenem that has an excellent activity against many gram-positive and gram-negative aerobic, facultative, and anaerobic bacteria. The major objective of the present study was to assess the in vitro activity of meropenem compared to imipenem and piperacillin/tazobactam, against 1071 non-repetitive isolates collected from patients with bacteremia (55%), pneumonia (29%), peritonitis (12%) and wound infections (3%), in 15 French hospitals in 2006. The secondary aim of the study was to compare the results of routinely testings and those obtained by a referent laboratory.

METHOD

Susceptibility testing and Minimum Inhibitory Concentrations (MICs) of meropenem, imipenem and piperacillin/tazobactam were determined locally by Etest method. Susceptibility to meropenem was confirmed at a central laboratory by disc diffusion method and MICs determined by agar dilution method for meropenem, imipenem and piperacillin/tazobactam.

RESULTS

Cumulative susceptibility rates against Escherichia coli were, meropenem and imipenem: 100% and piperacillin/tazobactam: 90%. Against other Enterobacteriaceae, the rates were meropenem: 99%, imipenem: 98% and piperacillin/tazobactam: 90%. All Staphylococci, Streptococci and anaerobes were susceptible to the three antibiotics. Against non fermeters, meropenem was active on 84-94% of the strains, imipenem on 84-98% of the strains and piperacillin/tazobactam on 90-100% of the strains.

CONCLUSIONS

Compared to imipenem, meropenem displays lower MICs against Enterobacteriaceae, Escherichia coli and Pseudomonas aeruginosa. Except for non fermenters, MICs90 of carbapenems were <4 mg/L. Piperacillin/tazobactam was less active against Enterobacteriaceae and Acinetobacter but not P. aeruginosa. Some discrepancies were noted between MICs determined by Etest accross centres and MICs determined by agar dilution method at the central laboratory. Discrepancies were more common for imipenem testing and more frequently related to a few centres. Overall MICs determined by Etest were in general higher (0.5 log to 1 log fold) than MICs by agar dilution.

Antibacterial-resistant Pseudomonas aeruginosa: clinical impact and complex regulation of chromosomally encoded resistance mechanisms

Treatment of infectious diseases becomes more challenging with each passing year. This is especially true for infections caused by the opportunistic pathogen Pseudomonas aeruginosa, with its ability to rapidly develop resistance to multiple classes of antibiotics. Although the import of resistance mechanisms on mobile genetic elements is always a concern, the most difficult challenge we face with P. aeruginosa is its ability to rapidly develop resistance during the course of treating an infection. The chromosomally encoded AmpC cephalosporinase, the outer membrane porin OprD, and the multidrug efflux pumps are particularly relevant to this therapeutic challenge. The discussion presented in this review highlights the clinical significance of these chromosomally encoded resistance mechanisms, as well as the complex mechanisms/pathways by which P. aeruginosa regulates their expression. Although a great deal of knowledge has been gained toward understanding the regulation of AmpC, OprD, and efflux pumps in P. aeruginosa, it is clear that we have much to learn about how this resourceful pathogen coregulates different resistance mechanisms to overcome the antibacterial challenges it faces.

Summary trends for the Meropenem Yearly Susceptibility Test Information Collection Program: a 10-year experience in the United States (1999-2008)

The Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program was a global, longitudinal antimicrobial resistance surveillance network of more than 100 medical centers worldwide monitoring the susceptibility of meropenem and selected other broad-spectrum comparator agents. In 1999, and from 2000 through 2008, a total of 10 or 15 United States (USA) medical centers each forwarded 200 nonduplicate clinical isolates from serious infections to a central processing laboratory. Over the 10-year period of this surveillance program, the activity of meropenem and an average of 11 other antimicrobial agents were assessed against a total of 27 289 bacterial isolates using Clinical and Laboratory Standards Institute reference methods. Meropenem consistently demonstrated low resistance rates against Enterobacteriaceae species isolates through 2008 and did not exhibit a widespread change in resistance rates over the monitored interval. In fact, the incidence of emerging carbapenemase-producing (KPC-type) Klebsiella spp. showed a decline in 2008 compared to the steeply increasing rates observed from 2004 to 2007. Moreover, the KPC serine carbapenemases have spread to other Enterobacteriaceae species monitored by the MYSTIC Program. Greatest increases in antimicrobial resistance rates were observed for the fluoroquinolones (ciprofloxacin, levofloxacin) among all species monitored by the MYSTIC Program. Current susceptibility rates for meropenem when tested against prevalent pathogens were Pseudomonas aeruginosa (439 strains, 85.4% susceptible), Enterobacteriaceae (1537 strains, 97.3% susceptible), methicillin-susceptible staphylococci (460 strains, 100.0% susceptible), Streptococcus pneumoniae (125 strains, 80.2% at meningitis susceptibility breakpoints), other streptococci (159 strains, 90.0-100.0% susceptible), and Acinetobacter spp. (127 strains, 45.7% susceptible), the widest spectrum among beta-lactams tested in 2008 and throughout the last decade. Continued local surveillance of broad-spectrum agents following the completion of the MYSTIC Program (USA) appears critical to detect emerging resistances among pathogens causing the most serious infections requiring carbapenem agents.

Attributable hospital cost and length of stay associated with health care-associated infections caused by antibiotic-resistant gram-negative bacteria

Determination of the attributable hospital cost and length of stay (LOS) are of critical importance for patients, providers, and payers who must make rational and informed decisions about patient care and the allocation of resources. The objective of the present study was to determine the additional total hospital cost and LOS attributable to health care-associated infections (HAIs) caused by antibiotic-resistant, gram-negative (GN) pathogens. A single-center, retrospective, observational comparative cohort study was performed. The study involved 662 patients admitted from 2000 to 2008 who developed HAIs caused by one of following pathogens: Acinetobacter spp., Enterobacter spp., Escherichia coli, Klebsiella spp., or Pseudomonas spp. The attributable total hospital cost and LOS for HAIs caused by antibiotic-resistant GN pathogens were determined by comparison with the hospital costs and LOS for a control group with HAIs due to antibiotic-susceptible GN pathogens. Statistical analyses were conducted by using univariate and multivariate analyses. Twenty-nine percent of the HAIs were caused by resistant GN pathogens, and almost 16% involved a multidrug-resistant GN pathogen. The additional total hospital cost and LOS attributable to antibiotic-resistant HAIs caused by GN pathogens were 29.3% (P < 0.0001; 95% confidence interval, 16.23 to 42.35) and 23.8% (P = 0.0003; 95% confidence interval, 11.01 to 36.56) higher than those attributable to HAIs caused by antibiotic-susceptible GN pathogens, respectively. Significant covariates in the multivariate analysis were age >or=12 years, pneumonia, intensive care unit stay, and neutropenia. HAIs caused by antibiotic-resistant GN pathogens were associated with significantly higher total hospital costs and increased LOSs compared to those caused by their susceptible counterparts. This information should be used to assess the potential cost-efficacy of interventions aimed at the prevention of such infections.

Antibacterial-resistant Pseudomonas aeruginosa: clinical impact and complex regulation of chromosomally encoded resistance mechanisms

Treatment of infectious diseases becomes more challenging with each passing year. This is especially true for infections caused by the opportunistic pathogen Pseudomonas aeruginosa, with its ability to rapidly develop resistance to multiple classes of antibiotics. Although the import of resistance mechanisms on mobile genetic elements is always a concern, the most difficult challenge we face with P. aeruginosa is its ability to rapidly develop resistance during the course of treating an infection. The chromosomally encoded AmpC cephalosporinase, the outer membrane porin OprD, and the multidrug efflux pumps are particularly relevant to this therapeutic challenge. The discussion presented in this review highlights the clinical significance of these chromosomally encoded resistance mechanisms, as well as the complex mechanisms/pathways by which P. aeruginosa regulates their expression. Although a great deal of knowledge has been gained toward understanding the regulation of AmpC, OprD, and efflux pumps in P. aeruginosa, it is clear that we have much to learn about how this resourceful pathogen coregulates different resistance mechanisms to overcome the antibacterial challenges it faces.

Comparative Pharmacodynamics of Intermittent and Prolonged Infusions of Piperacillin/Tazobactam Using Monte Carlo Simulations and Steady-State Pharmacokinetic Data from Hospitalized Patients

Background:

Prolonging the infusion of a β-lactam antibiotic enhances the time in which unbound drug concentrations remain above the minimum inhibitory concentration (fT>MIC).

Objective:

To compare the pharmacodynamics of several dosing regimens of piperacillin/tazobactam administered by intermittent and prolonged infusion using pharmacokinetic data from hospitalized patients.

Methods:

Steady-state pharmacokinetic data were obtained from 13 patients who received piperacillin/tazobactam 4.5 g every 8 hours, infused over 4 hours. Monte Carlo simulations (10,000 pts.) were performed to calculate pharmacodynamic exposures at 50% fT>MIC for 4 intermittent-infusion regimens (3.375 g every 4 and 6 h, 4.5 g every 6 and 8 h) and 4 prolonged-infusion regimens (2.25 g, 3.375 g. 4.5 g, and 6.75 g every 8 h [4-h infusion]) of piperacillin/tazobactam using pharmacokinetic data for piperacillin. Cumulative fraction of response (CFR) was calculated using MIC data for 6 gram-negative pathogens (Meropenem Yearly Susceptibility Test Information Collection, 2004-2007), and probability of target attainment (PTA) was calculated at MICs ranging from 1 μg/mL to 64 μ/g/mL

Results:

The CFR for 3.375 g every 4 hours (intermittent infusion) and 3.375–4.5 g every 8 hours (prolonged infusion) greater than or equal to 90.3% for Escherichia coli, Serratia marcescens, and Citrobacter spp. Increasing the prolonged-infusion dose to 6.75 g improved the CFR to greater than 90% for Enterobacter spp. For every regimen evaluated, the CFR was less than 90% for Klebsiella pneumoniae and Pseudomonas aeruginosa. At an MIC of 16 μg/mL, PTA was greater than 90% for one intermittent-infusion regimen (3.375 g every 4 h) and 3 prolonged-infusion regimens (≥3.375 g every 8 h). but no regimen achieved a PTA greater than 90% at an MIC of 64 μ/g/mL.

Conclusions:

At doses greater than or equal to 3.375 g every 8 hours, 4-hour infusions of piperacillin/tazobactam achieved excellent target attainment with lower daily doses compared with standard regimens at MICs less than or equal to 16 μg/mL

Steady-state pharmacokinetics and pharmacodynamics of piperacillin/tazobactam administered by prolonged infusion in hospitalised patients

The objective of this study was to evaluate the steady-state pharmacokinetics and pharmacodynamics of piperacillin/tazobactam, administered by prolonged infusion, in hospitalised patients requiring antimicrobial therapy. Thirteen patients received 4.5 g every 8 h (q8h), infused over 4 h, and pharmacokinetic parameters were determined by non-compartmental methods. Monte Carlo simulations (10,000 patients) were performed to calculate the cumulative fraction of response (CFR) for seven gram-negative pathogens using minimum inhibitory concentration (MIC) data from the Meropenem Yearly Susceptibility Test Information Collection (2004-2007, USA) as well as the probability of target attainment (PTA) at MICs ranging from 1 microg/mL to 64 microg/mL. The pharmacodynamic target was free piperacillin concentration remaining above the MIC for 50% of the dosing interval. Mean+/-standard deviation maximum and minimum serum concentrations, half-life, volume of distribution at steady-state and systemic clearance of piperacillin were 108.2+/-31.7 microg/mL, 27.6+/-26.3 microg/mL, 2.1+/-1.2 h, 22.1+/-4.0 L and 8.6+/-3.0 L/h, respectively. The CFR was > 90% for Escherichia coli, Serratia marcescens and Citrobacter spp., 88.6% for Enterobacter spp., 87% for Klebsiella pneumoniae, 85.5% for Pseudomonas aeruginosa and 52.8% for Acinetobacter spp. The PTA was 100%, 81.1% and 12.3% at MICs of < or = 16 microg/mL, 32 microg/mL and 64 microg/mL, respectively. Piperacillin/tazobactam 4.5 g q8h infused over 4 h provides excellent target attainment for bacterial pathogens with MICs < or = 16 microg/mL. However, the CFR was < 90% for four of the seven gram-negative pathogens evaluated.

Intravenous doripenem at 500 milligrams versus levofloxacin at 250 milligrams, with an option to switch to oral therapy, for treatment of complicated lower urinary tract infection and pyelonephritis

The prospective, multicenter, double-blind study presented in this report evaluated whether or not intravenous (IV) administration of doripenem, a carbapenem with bactericidal activity against gram-negative and gram-positive uropathogens, is inferior to IV administration of levofloxacin in the treatment of complicated urinary tract infection (cUTI). Patients (n = 753) with complicated lower UTI or pyelonephritis were randomly assigned to receive IV doripenem at 500 mg every 8 h (q8h) or IV levofloxacin at 250 mg q24h. Patients in both treatment arms were eligible to switch to oral levofloxacin after 3 days of IV therapy to complete a 10-day treatment course if they demonstrated significant clinical and microbiological improvements. The microbiological cure rate (primary end point) was determined at the test-of-cure (TOC) visit occurring 5 to 11 days after the last dose of antibiotic. For the microbiologically evaluable patients (n = 545), the microbiological cure rates were 82.1% and 83.4% for doripenem and levofloxacin, respectively (95% confidence interval [CI] for the difference, -8.0 to 5.5%); in the microbiological modified intent-to-treat cohort (n = 648), the cure rates were 79.2% and 78.2%, respectively. Clinical cure rates at the TOC visit were 95.1% in the doripenem arm and 90.2% in the levofloxacin arm (95% CI around the difference in cure rates [doripenem cure rate minus levofloxacin cure rate], 0.2% to 9.6%). Both treatment regimens were generally well tolerated. Doripenem was found not to be inferior to levofloxacin in terms of therapeutics and is now approved for use in the United States and Europe for the treatment of adults with cUTI, including pyelonephritis. As fluoroquinolone resistance increases, doripenem may become a more important option for successful treatment of cUTIs, including treatment of pyelonephritis.

Management of meningitis due to antibiotic-resistant Acinetobacter species

Acinetobacter meningitis is becoming an increasingly common clinical entity, especially in the postneurosurgical setting, with mortality from this infection exceeding 15%. Infectious Diseases Society of America guidelines for therapy of postneurosurgical meningitis recommend either ceftazidime or cefepime as empirical coverage against Gram-negative pathogens. However, assessment of the pharmacodynamics of these cephalosporins in cerebrospinal fluid suggests that recommended doses will achieve pharmacodynamic targets against fewer than 10% of contemporary acinetobacter isolates. Thus, these antibiotics are poor options for suspected acinetobacter meningitis. From in vitro and pharmacodynamic perspectives, intravenous meropenem plus intraventricular administration of an aminoglycoside may represent a superior, albeit imperfect, regimen for suspected acinetobacter meningitis. For cases of meningitis due to carbapenem-resistant acinetobacter, use of tigecycline is not recommended on pharmacodynamic grounds. The greatest clinical experience rests with use of polymyxins, although an intravenous polymyxin alone is inadvisable. Combination with an intraventricularly administered antibiotic plus removal of infected neurosurgical hardware appears the therapeutic strategy most likely to succeed in this situation. Unfortunately, limited development of new antibiotics plus the growing threat of multidrug-resistant acinetobacter is likely to increase the problems posed by acinetobacter meningitis in the future.

Meropenem dosing in critically ill patients with sepsis and without renal dysfunction: intermittent bolus versus continuous administration? Monte Carlo dosing simulations and subcutaneous tissue distribution

OBJECTIVES

To compare the plasma and subcutaneous tissue concentration-time profiles of meropenem administered by intermittent bolus dosing or continuous infusion to critically ill patients with sepsis and without renal dysfunction, and to use population pharmacokinetic modelling and Monte Carlo simulations to assess the cumulative fraction of response (CFR) against Gram-negative pathogens likely to be encountered in critical care units.

PATIENTS AND METHODS

We randomized 10 patients with sepsis to receive meropenem by intermittent bolus administration (n = 5; 1 g 8 hourly) or an equal dose administered by continuous infusion (n = 5). Serial subcutaneous tissue concentrations were determined using microdialysis and compared with plasma data for first-dose and steady-state pharmacokinetics. Population pharmacokinetic modelling of plasma data and Monte Carlo simulations were then undertaken with NONMEM.

RESULTS

It was found that continuous infusion maintains higher median trough concentrations, in both plasma (intermittent bolus 0 versus infusion 7 mg/L) and subcutaneous tissue (0 versus 4 mg/L). All simulated intermittent bolus, extended and continuous infusion dosing achieved 100% of pharmacodynamic targets against most Gram-negative pathogens. Superior obtainment of pharmacodynamic targets was achieved using administration by extended or continuous infusion against less susceptible Pseudomonas aeruginosa and Acinetobacter species.

CONCLUSIONS

This is the first study to compare the relative concentration-time data of bolus and continuous administration of meropenem at the subcutaneous tissue and plasma levels. We found that the administration of meropenem by continuous infusion maintains higher concentrations in subcutaneous tissue and plasma than by intermittent bolus dosing. Administration by extended or continuous infusion will achieve superior CFR against less-susceptible organisms in patients without renal dysfunction.

Rapid emergence of blaCTX-M among Enterobacteriaceae in U.S. Medical Centers: molecular evaluation from the MYSTIC Program (2007)

A total of 220 gram-negative isolates showing distinct beta-lactam resistance profiles recovered in U.S. medical centers during the MYSTIC Program 2007 were evaluated to determine the presence of selected beta-lactamase genes. CTX-M-encoding genes, considered rare in the United States, were detected in 38.8% (28/70; three species) of the extended spectrum beta-lactamase-positive isolates and were observed in 80.0% of the participating hospitals. CTX-M-14 and -15 were found in multiple institutions (eight and nine medical centers, respectively), and CTX-M-3 was detected in only one isolate. The OXA-2 and -10 were identified in nine Enterobacteriaceae strains, and plasmid-mediated AmpC enzymes CMY-2 and FOX-5 were identified in six and four isolates, respectively, displaying negative clavulanate inhibition. Genes encoding OXA-23 and -24 were detected in 30.0% (15/50) of carbapenem-resistant Acinetobacter spp. strains. Retrospective sampling showed that these OXA enzymes were present since 2004 in the MYSTIC Program isolates. The KPC serine carbapenemases were observed in the majority of the carbapenem-resistant Enterobacteriaceae (usually Klebsiella pneumoniae), confirming an epidemic problem in the New York City area. The association of beta-lactamase production and transferable quinolone resistance genes (qnr; 6.7%) in Enterobacteriaceae strains was higher than previously reported. This study illustrates the emergence and rapid dissemination of some beta-lactamases, such as CTX-M, broad-spectrum oxacillinases, and serine carbapenemases, that compromised the treatment of gram-negative infections in numerous U.S. hospitals participating in the MYSTIC Program in 2007.

Clinical review: balancing the therapeutic, safety, and economic issues underlying effective antipseudomonal carbapenem use

Antipseudomonal carbapenems have played a useful role in our antimicrobial armamentarium for 20 years. However, a review of their use during that period creates concern that their clinical effectiveness is critically dependent on attainment of an appropriate dosing range. Unfortunately, adequate carbapenem dosing is missed for many reasons, including benefit/risk misconceptions, a narrow therapeutic window for imipenem and meropenem (due to an increased rate of seizures at higher doses), increasingly resistant pathogens requiring higher doses than are typically given, and cost containment issues that may limit their use. To improve the use of carbapenems, several initiatives should be considered: increase awareness about appropriate treatment with carbapenems across hospital departments; determine optimal dosing regimens for settings where multidrug resistant organisms are more likely encountered; use of, or combination with, an alternative antimicrobial agent having more favorable pharmacokinetic, pharmacodynamic, or adverse event profile; and administer a newer carbapenem with lower propensity for resistance development (for example, reduced expression of efflux pumps or greater stability against carbapenemases).

Acinetobacter baumannii: emergence of a successful pathogen

Acinetobacter baumannii has emerged as a highly troublesome pathogen for many institutions globally. As a consequence of its immense ability to acquire or upregulate antibiotic drug resistance determinants, it has justifiably been propelled to the forefront of scientific attention. Apart from its predilection for the seriously ill within intensive care units, A. baumannii has more recently caused a range of infectious syndromes in military personnel injured in the Iraq and Afghanistan conflicts. This review details the significant advances that have been made in our understanding of this remarkable organism over the last 10 years, including current taxonomy and species identification, issues with susceptibility testing, mechanisms of antibiotic resistance, global epidemiology, clinical impact of infection, host-pathogen interactions, and infection control and therapeutic considerations.

Antimicrobial lock solutions for the prevention of infections associated with intravascular catheters in patients undergoing hemodialysis: systematic review and meta-analysis of randomized, controlled trials

BACKGROUND

Prevention of catheter-related bloodstream infections in patients undergoing hemodialysis by use of antimicrobial catheter lock solutions has been examined in several trials, but no consensus is available for clinical practice.

METHODS

A systematic review and meta-analysis were performed of randomized controlled trials that compared single or combination antimicrobial catheter lock solutions with heparin or another antimicrobial for the prevention of infections in patients undergoing hemodialysis. The primary outcomes assessed were bloodstream infections, catheter-related bloodstream infections, and the need for catheter removal. Relative risks with 95% confidence intervals (CIs) for individual trials were pooled.

RESULTS

Eleven trials (924 patients) that assessed antibiotic catheter lock solutions and 5 trials (661 patients)that assessed non antibiotic antimicrobial catheter lock solutions met inclusion criteria. None of the trials assessed all bloodstream infections. Antibiotic catheter lock solutions significantly reduced catheter-related bloodstream infections (relative risk, 0.44; 95% CI, 0.38-0.50). Significant heterogeneity for this outcome could be explained by smaller effect estimates in larger trials that reported adequate randomization methods (relative risk, 0.60; 95%CI, 0.54-0.67). Efficacy was higher when additional preventive measures were used and to prevent the first episode of catheter-related bloodstream infection. Catheter removal rates were significantly reduced (relative risk, 0.35;95% CI, 0.23-0.55). Resistance development was documented in a single patient. Data concerning nonantibiotic antimicrobial lock solutions were limited and heterogeneous. High-quality trials that used additional preventive measures showed a significant reduction in catheter-related bloodstream infections (relative risk, 0.25; 95% CI,0.13-0.50).

CONCLUSIONS

Antibiotic catheter lock solutions reduce catheter-related bloodstream infections, with a number needed to treat of 4 patients (95% CI, 4-5), and catheter removal rates in patients undergoing hemodialysis. The use of antibiotic catheter lock solutions should be considered in routine clinical practice in conjunction with other prevention modalities.

Acinetobacter infection in the ICU

Acinetobacter is a formidable challenge to managing critically ill patients. This pathogen's ability to rapidly develop antimicrobial resistance to all currently available antimicrobial agents is concerning because increasing data support attributable mortality to these bacteria when associated with hospitalized patients with comorbidities and severe illness. The role of dual therapy is currently unclear and might be associated with increased toxicities without proven synergy or ability to prevent the development of resistance. Infection control and antibiotic control measures might have the greatest impact on these bacteria. Continued efforts are needed to develop new antimicrobial agents against this pathogen and assess the ideal currently available agents.

The current state of multidrug-resistant gram-negative bacilli in North America

Although much of today's media focuses on multidrug-resistant gram-positive bacteria such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus, resistance within gram-negative bacilli continues to rise, occasionally creating situations in which few or no antibiotics that retain activity are available. Extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli and Klebsiella sp are emerging threats nationally. Although carbapenems are considered the antibiotic class of choice to treat ESBL-producing Enterobacteriaceae, the ability of these organisms to produce carbapenemases has now become apparent in some regions throughout the United States. Although still rare, Klebsiella sp that produce KPC-2 retain susceptibility only to tigecycline, polymyxins, and occasionally aminoglycosides. Multidrug resistance among Pseudomonas aeruginosa and Acinetobacter sp has always been apparent across many hospitals in the United States. Recent surveillance indicates increasing resistance to all currently available antibiotics, including carbapenems, cephalosporins, penicillins, fluoroquinolones, and aminoglycosides. Against many strains, only polymyxins retain activity; however, resistance has also been reported to these agents. Fortunately, resistance mechanisms such as metallo-beta-lactamases are still rare in the United States. As no new antibiotics with novel mechanisms against many of these gram-negative bacilli are expected to be developed in the foreseeable future, careful and conservative use of agents combined with good infection control practices is required.

Safety profile of meropenem: an updated review of over 6,000 patients treated with meropenem

Meropenem is a broad-spectrum carbapenem antibacterial with potent antimicrobial activity against a broad range of Gram-negative, Gram-positive and anaerobic bacteria. The second parenteral carbapenem to be introduced worldwide, meropenem has been in clinical use since 1994. Two previous safety reviews have established that meropenem has a favourable and acceptable safety profile. This new review was conducted after the approval of meropenem in the US in 2005 for the treatment of patients with complicated skin and skin-structure infections, in addition to the previously approved indications of intra-abdominal infections and paediatric bacterial meningitis. The analysis includes the clinical trial data from the previous safety reviews, updated with expanded experience across a number of serious bacterial infections, including a large international study in patients with skin or skin-structure infections and further experience in patients with intra-abdominal infections and bacterial meningitis. A total of 6154 patients with 6308 meropenem exposures were compared with 4483 patients treated with comparator agents (4593 exposures), and the paediatric population base for which safety data are available has doubled to over 1000 patients. The data presented reinforce the favourable safety profile of meropenem. In general, the incidence and pattern of adverse events occurring with meropenem were similar to those of the first carbapenem, imipenem/cilastatin, and to those of the cephalosporin- and clindamycin-based regimens to which it had been compared. The most common adverse events reported for meropenem were diarrhoea (2.5%), rash (1.4%) and nausea/vomiting (1.2%). No adverse event occurred in more than 3% of patient exposures to meropenem, indicating a low overall frequency of adverse events as well as excellent gastrointestinal tolerability. Furthermore, no unexpected adverse events were identified, and the very low incidence of seizures in patients with meningitis was not considered to be drug related. In infections other than meningitis, the incidence of seizures considered by investigators to be related to meropenem treatment was 0.07%. In the new studies that updated the earlier safety data, no new cases of drug-related seizure were reported for any treatment or patient group (meningitis/non-meningitis infections). In conclusion, meropenem is well tolerated and has good CNS and gastrointestinal tolerability when used for the treatment of serious bacterial infections in a wide range of adult and paediatric patient populations.

Antimicrobial resistance among Gram-negative bacilli causing infections in intensive care unit patients in the United States between 1993 and 2004

During the 12-year period from 1993 to 2004, antimicrobial susceptibility profiles of 74,394 gram-negative bacillus isolates recovered from intensive care unit (ICU) patients in United States hospitals were determined by participating hospitals and collected in a central location. MICs for 12 different agents were determined using a standardized broth microdilution method. The 11 organisms most frequently isolated were Pseudomonas aeruginosa (22.2%), Escherichia coli (18.8%), Klebsiella pneumoniae (14.2%), Enterobacter cloacae (9.1%), Acinetobacter spp. (6.2%), Serratia marcescens (5.5%), Enterobacter aerogenes (4.4%), Stenotrophomonas maltophilia (4.3%), Proteus mirabilis (4.0%), Klebsiella oxytoca (2.7%), and Citrobacter freundii (2.0%). Specimen sources included the lower respiratory tract (52.1%), urine (17.3%), and blood (14.2%). Rates of resistance to many of the antibiotics tested remained stable during the 12-year study period. Carbapenems were the most active drugs tested against most of the bacterial species. E. coli and P. mirabilis remained susceptible to most of the drugs tested. Mean rates of resistance to 9 of the 12 drugs tested increased with Acinetobacter spp. Rates of resistance to ciprofloxacin increased over the study period for most species. Ceftazidime was the only agent to which a number of species (Acinetobacter spp., C. freundii, E. aerogenes, K. pneumoniae, P. aeruginosa, and S. marcescens) became more susceptible. The prevalence of multidrug resistance, defined as resistance to at least one extended-spectrum cephalosporin, one aminoglycoside, and ciprofloxacin, increased substantially among ICU isolates of Acinetobacter spp., P. aeruginosa, K. pneumoniae, and E. cloacae.

Activity of meropenem as serine carbapenemases evolve in US Medical Centers: monitoring report from the MYSTIC Program (2006)

The Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Surveillance Program was designed to monitor the antimicrobial potency and spectrum of meropenem, and selected broad-spectrum comparison agents against pathogens from hospitalized patients. In the 2006 (year 8 of the study) United States sample, a total of 2841 isolates (94.7% compliance) including 641 Escherichia coli, 619 Klebsiella spp., 606 Pseudomonas aeruginosa, 456 oxacillin-susceptible Staphylococcus aureus, 300 streptococci, 149 Enterococcus faecalis, and 70 Gram-positive anaerobic organisms were tested by reference broth microdilution or agar dilution susceptibility methods. The carbapenems, especially meropenem, consistently demonstrated the lowest resistance rates against Enterobacteriaceae strains, and the fluoroquinolones had the highest and increasing resistance rates. The presence of qnr-mediated fluoroquinolone resistance was investigated using polymerase chain reaction methods but was only observed at very low levels (2.1%) and was not clonally associated. Confirmed extended-spectrum beta-lactamase rates for E. coli and Klebsiella spp. were only 4.8% and 5.0%, respectively, with mobile AmpC (CMY-2 and FOX-5) enzymes shown in 13 additional Enterobacteriaceae isolates. Clonally related KPC-type serine carbapenemase production (57 strains, 9.5%) was observed at a rate 2-fold greater than the prior year among Klebsiella spp. isolates, primarily from 1 geographic region (Middle Atlantic States). These MYSTIC Program (2006) results demonstrate the continued need to monitor the carbapenem class potency and spectrum of activity against Enterobacteriaceae as well as P. aeruginosa because of the documented presence of serine carbapenemases and rare incidence of metallo-beta-lactamases that may further compromise their activity and that of other beta-lactam agents.