Pharmacodynamic modeling of carbapenems andfluoroquinolones against bacteria that produce extended-spectrum beta-lactamases

Pharmacodynamics of Moxifloxacin, Meropenem, Caspofungin and their Combinations Against In Vitro Polymicrobial Inter-kingdom Biofilms

Biofilms colonize medical devices and are often recalcitrant to antibiotics. Inter-kingdom biofilms, when at least a bacterium and a fungus are co-isolated, increase the likelihood of therapeutic failures. In this work, a three-species in vitro biofilm model including S. aureus, E. coli and C. albicans was used to study the activity of the antibiotics moxifloxacin and meropenem, the antifungal caspofungin, and combinations of them against inter-kingdom biofilms. The culturable cells and total biomass were evaluated to determine the pharmacodynamic parameters of the drug response for the incubation with the drugs alone. The synergic or antagonistic effects (increased/decreased effects) of the combination of drugs were analysed with the highest single agent method. Biofilms were imaged in confocal microscopy after live/dead staining. The drugs had limited activity when used alone against single-, dual- or three-species biofilms. When used in combination, additive effects were observed against single- or dual-species biofilms, and increased effects (synergy) against biomass of three-species biofilms. In addition, the two antibiotics showed different patterns, moxifloxacin being more active when targeting S. aureus and meropenem when targeting E. coli. All these observations were confirmed by confocal microscopy images. Our findings highlight the interest in combining caspofungin with antibiotics against inter-kingdom biofilms.

Antibiotics for adults with acute cholecystitis or acute cholangitis or both

This is a protocol for a Cochrane Review (intervention). The objectives are as follows:

To assess the benefits and harms of antibiotics treatment versus placebo, no intervention, or another antibiotic for people with cholecystitis or cholangitis, or both.

Delafloxacin: design, development and potential place in therapy

Delafloxacin (DLX) is a new fluoroquinolone pending approval, which has shown a good in vitro and in vivo activity against major pathogens associated with skin and soft tissue infections and community-acquired respiratory tract infections. DLX also shows good activity against a broad spectrum of microorganisms, including those resistant to other fluoroquinolones, as methicillin-resistant Staphylococcus aureus. Its pharmacokinetic properties and excellent activity in acidic environments make DLX an alternative in the treatment of these and other infections. In this manuscript, a detailed analysis of this new fluoroquinolone is performed, from its chemical structure to its in vivo activity in recently published clinical trials. Its possible place in the current antimicrobial outlook and in other infectious models is also discussed.

Study of extended spectrum β-lactamase producing Enterobacteriaceae and antibiotic coresistance in a tertiary care teaching hospital

Aims:

To study the prevalence of extended spectrum β-lactamase (ESBL) producing Enterobacteriaceae and coresistance to other commonly used antibiotics from the Bhopal region of Central India.

Settings and Design:

A prospective study was conducted from September 2011 to August 2012 in Microbiology Department of our tertiary health care center.

Materials and Methods:

A total of 1044 Enterobacteriaceae isolates were recovered from various specimens. ESBL production was detected by using Clinical Laboratory Standard Institute (CLSI) that described the phenotypic confirmatory test along with routine antibiotic susceptibility testing.

Statistical Analysis:

Two-tailed Z-test.

Results:

Escherichia coli was the most common isolate (65.32%). ESBL production was confirmed in 504 (48.27%) isolates. The isolates of E. coli (50.14%) were the most common ESBL producers. Maximum ESBL isolates were obtained from urine samples (52.28%) and male patients (52.54%). Sensitivity to imipenem was 100% followed by piperacillin–tazobactam (89.28%), meropenem (87.5%), and amikacin (83.92%). Significant resistance was detected against trimethoprim–sulfomethoxazole, fluoroquinolones, and gentamicin.

Conclusion:

This is the only study conducted from Central India and shows high prevalence of ESBL production among Enterobacteriaceae. Imipenem seems to be more sensitive than meropenem. Piperacillin–tazobactam combination was found to be the best among the β-lactam–β-lactamase inhibitor combinations. Prevalence of ESBL producers were more in males than females.

Use of Carbapenems against clinical, nontyphoid Salmonella isolates: results from in vitro and in vivo animal studies

The emergence of multidrug-resistant Salmonella isolates has created the need for new therapeutic agents. We evaluated the intracellular activity of four carbapenem compounds against clinical nontyphoid Salmonella (NTS) isolates in vitro and ex vivo. Subsequently, the efficacy of carbapenem treatment against selected Salmonella isolates in vivo was assessed using a murine peritonitis model. The MIC(50) and MIC(90) for doripenem, ertapenem, imipenem, and meropenem against 126 NTS isolates were found to be 0.062 and 0.062, 0.015 and 0.015, 0.5 and 1, and 0.031 and 0.031 μg/ml, respectively. The intracellular killing effect of ertapenem was sustained for 24 h and was superior to that of imipenem, meropenem, and doripenem; its effect was comparable to that of ceftriaxone. Ertapenem demonstrated an excellent pharmacokinetic profile with a percent time above the MIC of 75.5% and an area under the concentration-time curve/MIC ratio of 20,733. When peritoneal exudate cells were examined directly ex vivo from mice with Salmonella-induced peritonitis, cells from mice treated with ertapenem and ceftriaxone had intracellular and extracellular bacterial counts reduced 10(2)- to 10(4)-fold and exhibited killing effects similar to each other. The survival rates of mice inoculated with 1 × 10(5) and 10(6) CFU of a ceftriaxone-susceptible Salmonella isolate that were subsequently treated with ertapenem or ceftriaxone were 100% and 90%, respectively. When mice were inoculated with 5 × 10(4) and 10(5) CFU of a ceftriaxone-resistant and ciprofloxacin-resistant Salmonella isolate, mice treated with ertapenem had a higher survival rate than mice treated with ceftriaxone (70% versus 0% and 50% versus 0%, respectively; P < 0.001). Our results suggest that ertapenem is at least as effective as ceftriaxone in treating murine Salmonella infections and show that further clinical investigations on the potential use of ertapenem in treatment of human Salmonella infections are warranted.

[Available carbapenems: Properties and differences]

Carbapenems are β-lactam antibiotics endowed with a broader spectrum, activity and resistance to β-lactamases than other β-lactams. Due to their qualities, these antibiotics are crucial in empirical therapy, in the monotherapy of several severe hospital-acquired infections -and even that of some community-acquired infections- as well as in the directed therapy of infections due to multiresistant Gram-negative bacteria. All the available carbapenems have a similar spectrum, although there are significant differences in their antimicrobial activity, which in the long run determines the clinical indications of each carbapenem. The spectrum of ertapenem does not cover eminently nosocomial pathogens such as Pseudomonas aeruginosa and Acinetobacter spp., and hence this antibiotic is indicated in community-acquired infections requiring hospital treatment. In contrast, doripenem shows greater intrinsic activity than other carbapenems in extended spectrum beta-lactamase-producing enterobacteria and AmpC P. aeruginosa, Acinetobacter spp. and other non-fermentative and anaerobic microorganisms. Additionally, like the remaining carbapenems, doripenem has adequate pharmacokinetic characteristics and a favorable safety profile.

Evaluation of updated interpretative criteria for categorizing Klebsiella pneumoniae with reduced carbapenem susceptibility

We studied the accuracy of various susceptibility testing methods, including the 2009, 2010, and updated 2010 CLSI recommendations, to identify Klebsiella pneumoniae isolates with reduced susceptibility to carbapenems associated with different mechanisms of resistance. Forty-three wild-type (WT) strains, 42 extended-spectrum β-lactamase (ESBL) producers, 18 ESBL producers with outer membrane porin protein loss (ESBL/Omp strains), and 42 blaKPC-possessing K. pneumoniae (KPC-Kp) isolates were evaluated. Imipenem (IPM), meropenem (MEM), ertapenem (ERT), and doripenem (DOR) were tested by broth microdilution (BMD), Etest, and disk diffusion (DD), and the modified Hodge test (MHT) was performed using IPM and MEM disks. Results were interpreted according to original as well as recently updated interpretative criteria. MHT was positive for all 42 KPC-Kp isolates and 10 of 18 ESBL/Omp strains and therefore had poor specificity in differentiating between KPC-Kp and ESBL/Omp isolates. Based on the updated CLSI standards, phenotypic susceptibility testing by BMD and DD differentiated most carbapenem-susceptible from carbapenem-nonsusceptible K. pneumoniae isolates without the need for MHT, while the Etest method characterized many KPC-Kp isolates as susceptible, and breakpoints may need to be lowered for this method. However, both the original and updated CLSI criteria do not adequately differentiate between isolates in the KPC-Kp group, which are unlikely to respond to carbapenem therapy, and those in the ESBL/Omp group, which are likely to respond to carbapenem therapy if MICs are within pharmacokinetic/pharmacodynamic targets. Further studies are required to determine if there is a clinical need to differentiate between KPC-Kp and ESBL/Omp groups.

Peritoneal pharmacokinetics and pharmacodynamic target attainment of meropenem in patients undergoing abdominal surgery

Although meropenem is commonly used for intra-abdominal infections, its penetration into the abdominal cavity is not well understood. Meropenem (500 mg) was administered intravenously to 8 patients with inflammatory bowel diseases undergoing laparotomy. The drug concentrations were analyzed and used for a Monte Carlo simulation with minimum inhibitory concentration (MIC) data. Meropenem concentrations in peritoneal fluid (PF) and plasma were similar at 1 h after the end of a 0.5-h infusion. The probabilities of target achievement of drug concentrations over the MIC in PF for 40% of the dosing interval with 500 mg every 8 h and 1000 mg every 8 h, were 84% and 90% against Bacteroides spp., 98% and 99% against Escherichia coli , and 76% and 83% against Pseudomonas aeruginosa, respectively. In conclusion, meropenem penetrated PF well, and 500 mg every 8 h or 1000 mg every 8 h would be suitable for the therapy for intraabdominal infections.

The use of carbapenems in the treatment of serious infections

Inadequate initial antimicrobial treatment in serious infections leads to increased mortality. Achieving adequate treatment is increasingly difficult because of the increasing prevalence of multidrug-resistant (MDR) pathogens. The carbapenems are potent, broad-spectrum antibiotics that have been shown to be safe and efficacious therapies in the treatment of serious infections. This review is intended to compare the 4 major members of the carbapenem class, which include imipenem, meropenem, ertapenem, and doripenem, with other widely used antimicrobial agents in the intensive care unit (ICU). The carbapenems are potent, broad-spectrum antibiotics that have been shown to be safe and efficacious therapies in the treatment of serious infections. They provide better gram-negative coverage than other beta-lactams and are stable against extended-spectrum beta-lactamases and AmpC beta-lactamases, making them effective in the treatment of many MDR bacteria. The newly approved carbapenem, doripenem, may help preserve the utility of the carbapenem class.

Effect of concomitant administration of meropenem and valproic acid in an elderly Chinese patient

BACKGROUND

Meropenem is a carbapenem with a broad spectrum of activity against beta-lactamase-producing organisms. Valproic acid is widely used in the treatment of generalized tonic-clonic and partial seizures. Concomitant administration of meropenem and valproic acid reportedly leads to a rapid decline in serum concentrations of valproic acid, which is sometimes associated with seizures.

CASE SUMMARY

This report describes an 85-year-old Chinese male inpatient who twice received concomitant administration of meropenem and valproic acid for the treatment of pneumonia and poststroke epilepsy, respectively. Rapid declines in valproic acid concentrations were observed both times after meropenem administration. No seizures occurred in the first treatment period; however, when the patient suffered pneumonia again 3 months later, the same concomitant therapy was prescribed, and seizures occurred. It is difficult to identify a single etiology of the seizures. Based on a score of 7 on the Naranjo adverse drug reaction probability scale, the seizures were considered to be probably related to the concomitant administration of meropenem and valproic acid.

CONCLUSIONS

Various factors make the effect of concomitant administration of meropenem and valproic acid unpredictable, even in the same patient. Caution should be used when administering meropenem and valproic acid concomitantly, especially in elderly patients with central nervous system disorders, even if the patient has had a successful prior experience with these 2 drugs. If concomitant administration is essential, very close serum concentration monitoring and clinical observation are necessary.

New developments in carbapenems

Antibiotic resistance among Gram-negative pathogens in hospitals is a growing threat to patients and is driving the increased use of carbapenems. Carbapenems are potent members of the beta-lactam family of antibiotics, with a history of safety and efficacy for serious infections that exceeds 20 years. Original and review articles were identified from a Medline search (1979-2008). Reference citations from identified publications, abstracts from the Interscience Conferences on Antimicrobial Agents and Chemotherapy and package inserts were also used. Carbapenems are effective in treating severe infections at diverse sites, with relatively low resistance rates and a favourable safety profile. Carbapenems are the beta-lactams of choice for the treatment of infections caused by multidrug-resistant organisms. Optimized dosing of carbapenems should limit the emergence of resistance and prolong the utility of these agents. The newly approved doripenem should prove to be a valuable addition to the currently available carbapenems: imipenem, meropenem and ertapenem.

Breakpoints for extended-spectrum beta-lactamase-producing Enterobacteriacae: pharmacokinetic/pharmacodynamic considerations

An understanding of antibacterial pharmacokinetics and pharmacodynamics is central to setting clinical breakpoints. It is important to understand any impact that a resistance mechanism may have on these basic drug properties. With extended-spectrum beta-lactamase (ESBL)-producing strains of Enterobacteriacae, it is known that MIC, and hence T>MIC, for beta-lactams predicts outcome. Therefore, pharmacodynamic modelling can be used to set breakpoints for ESBL-producing bacteria with beta-lactams.

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.

Carbapenems: a potent class of antibiotics

The purpose of this review is to assess the relative strengths and weaknesses of individual members of the carbapenem class of antibiotics. Clinical trials and review articles were identified from a Medline search (1979 - July 2006), in addition to, reference citations from identified publications, abstracts from the Interscience Conferences on Antimicrobial Agents and Chemotherapy and the 12th International Congress on Infectious Disease, and package inserts. Articles in English were reviewed, with emphasis on those containing efficacy or safety data. Carbapenems bind to critical penicillin-binding proteins, disrupting the growth and structural integrity of bacterial cell walls. They provide enhanced anaerobic and Gram-negative coverage as compared with other beta-lactams and their stability against extended-spectrum beta-lactamases (ESBLs) makes them an effective treatment option. The most common adverse effects are infusion-site complications and gastrointestinal distress. Ertapenem has limited efficacy against non-fermenting, Gram-negative bacteria, restricting its use to community-acquired infections. Imipenem is slightly more effective against Gram-positive organisms and meropenem slightly more effective against Gram-negative organisms. However, both have broad-spectrum activity, including non-fermenting, Gram-negative bacteria. Among non-fermenting, Gram-negatives, resistance to imipenem in particular is increasing. Doripenem is in late-stage clinical development and combines the broad-spectrum coverage of imipenem and meropenem, and more potent activity against Pseudomonas aeruginosa. Due to the increasing challenges represented by ESBLs and multi-drug resistant organisms, the carbapenems are assuming a greater role in the treatment of serious infections. Imipenem and meropenem are presently available and have been shown to be effective against nosocomial infections. Doripenem is an investigational carbapenem that has completed Phase III clinical trials and that has the potential to improve on this efficacy and minimize the emergence of resistance to the carbapenem class.

Efficacy of Ertapenem for Consolidation Therapy of Extended-Spectrum β-lactamase-Producing Gram-Negative Infections: A Case Series Report

Background:

Infections caused by extended-spectrum β-lactamase (ESBL)-producing gram-negative organisms are becoming increasingly common and present significant challenges in terms of treatment. Carbapenems is the antibiotic class of choice for treatment of these types of infections. Ertapenem is the newest carbapenem, capable of being dosed once daily, and has some in vitro but little in vivo evidence supporting its use for the treatment ol these resistant infections.

Objective:

To examine the clinical and microbiologic outcomes associated with ertapenem therapy of ESBL-producing Escherichia coli, Klebsiella pneumoniae. and Proteus mirabilis infections.

Methods:

This was a retrospective case series that examined the clinical and microbiologic outcomes of 22 patients who received ertapenem for treatment of an ESBL infection at Rush University Medical Center in Chicago. IL, during 2003–2005.

Results:

The majority (16/22) of patients received ertapenem (or consolidation rather than initial therapy. Different antibiotics most commonly used were other carbapenems, piperacillin/tazobactam, and aminoglycosides. The most common infections treated were lower urinary tract infections and osteomyelitis. Clinical efficacy was determined in all 22 patients, with 20 (91%) patients having a positive outcome, defined as either clinical improvement or clinical cure. The best clinical cure rate was seen with wound infections, where all 3 patients examined were found to be clinically cured. Microbiologic efficacy was determined in 7 patients, with 6 {85.7%) defined as microbiologic cure. One patient was found to be both a clinical and microbiologic failure and was also found to have developed an ertapenem-resistant strain of E. coli.

Conclusions:

These results demonstrate potential microbiologic and clinical efficacy of ertapenem for treatment of ESBL-producing infections and the need for a prospective, randomized study examining its efficacy versus that of other carbapenems.

High-performance liquid chromatography with ultraviolet detection for real-time therapeutic drug monitoring of meropenem in plasma

A simple, rapid, and precise high-performance liquid chromatography (HPLC) method using ultrafiltration to remove plasma protein was developed to determine meropenem concentrations in human plasma in a clinical setting. Plasma was separated by centrifugation at 4 degrees C from blood collected in heparinized vacuum tubes, and meropenem was stabilized by immediately mixing the plasma with 1M 3-morpholinopropanesulfonic acid buffer (pH 7.0) (1:1). Ultrafiltration was used for plasma deproteinization. Meropenem was detected by ultraviolet absorbance at 300 nm with no interfering plasma peak. The calibration curve of meropenem in human plasma was linear from 0.05 to 100 microg/mL. Intraday and interday precision was less than 7.17% (CV), and accuracy was between 97.7% and 106.3% over 0.05 microg/mL. The limit of detection was 0.01 microg/mL. The assay has been clinically applied to a real-time therapeutic drug monitoring in pediatric patients and pharmacokinetic studies.

Simulated Comparison of the Pharmacodynamics of Ciprofloxacin and Levofloxacin Against Pseudomonas aeruginosa Using Pharmacokinetic Data from Healthy Volunteers and 2002 Minimum Inhibitory Concentration Data

BACKGROUND

Until the 2002 approval of levofloxacin 750 mg QD, ciprofloxacin was the fluoroquinolone of choice against Pseudomonas aeruginosa infections.

OBJECTIVE

This study evaluated the AUC:MIC ratios for ciprofloxacin 400 mg BID and TID and levofloxacin 750 mg QD, all administered intravenously, against P. aeruginosa using a Monte Carlo simulation.

METHODS

Pharmacokinetic data for ciprofloxacin and levofloxacin and 2002 MIC distributions against P. aeruginosa were obtained from studies in healthy volunteers published in the peer-reviewed literature. Pharmacokinetic studies of each agent were identified by separate MEDLINE searches combining the MeSH heading pharmacokinetics with the generic name of the antimicrobial. Only human studies published in English between 1990 and 2001 were included. Included studies also had to meet 3 minimum criteria: evaluation of clinically relevant dosing regimens, use of rigorous study methods, and provision of mean (SD) values for the pharmacokinetic parameters of interest. When multiple studies met these criteria, a single study was selected for each antimicrobial regimen. Pharmacodynamic analysis was performed using a Monte Carlo simulation of 10,000 patients by integrating the pharmacokinetic parameters, their variability, and 2002 MIC distributions for each antimicrobial regimen. The probability of target attainment was determined for each regimen for an AUC:MIC ratio from 0 to 300. A > or =90% probability of target attainment was considered satisfactory.

RESULTS

For ciprofloxacin 400 mg TID and levofloxacin 750 mg QD, the AUC:MIC ratio at the corresponding 2002 Clinical Laboratory Standards Institute break points of 1 and 2 microg/mL were 33 and 34, respectively. The probabilities of target attainment for a free AUC:MIC ratio >90 (equivalent to a total AUC:MIC ratio > or =125) were 47% for ciprofloxacin 400 mg BID, 54% for ciprofloxacin 400 mg TID, and 48% for levofloxacin 750 mg QD.

CONCLUSION

When pharmacokinetic data from healthy volunteers and 2002 MIC data were used, none of the simulated fluoroquinolone regimens achieved a high likelihood of target attainment against P. aeruginosa.

[Treatment of respiratory and urinary tract infections in elderly inmates at a nursing home by selective antimicrobial agents based on the sensitivity of the isolated bacteria]

OBJECTIVES

Elderly patients living in nursing homes can easily find themselves unable to carry out their daily activities, once they become ill, even with infectious diseases of a slight to mild degree, and rapid treatment is required to cure them of their malaise. However, treatment is often difficult due to the presence of drug-resistant bacteria. This study was designed to evaluate the efficacy of the selective use of antimicrobial agents based on a sensitivity test of isolated bacteria.

METHODS

Possible pathogenic bacteria were isolated from cultures of pharyngeal swabs or urine obtained from patients with chronic febrile conditions or urinary tract infections, resistant to antimicrobial treatment. The efficacy of the treatment was evaluated based on release from febrile conditions and improvement of activities of daily living (ADL) accompanied by the disappearance of possible pathogenic bacteria following the use of selective antimicrobial agents.

RESULTS

The outcome of 14 cases with sustaining febrile conditions and 3 cases with urinary tract infections was reviewed. Most of them showed a good response to treatment with remarkable improvement in ADL. In some cases, patients were switched from one antimicrobial agent to another each time new pathogenic bacteria were detected in the culture. A combination of rifampicin and sulfamethoxazole/trimethoprim (RFP/ST) was found to be the most convenient and effective treatment in patients with MRSA or drug-resistant Streptococcus pneumoniae. Levofloxacin (LVFX)-resistant Escherichia coli were detected together with MRSA in our 3 patients with urinary tract infections, corresponding to the frequent use of LVFX in our community.

CONCLUSIONS

Identification of possible pathogenic bacteria and the use of proper antibiotic agents based on a sensitivity test are very effective in the treatment of elderly patients with chronic febrile conditions arising from the presence of drug-resistant bacteria. Careful use of fluoroquinolones is required in patients in whom MRSA is or had once been detected. This is beneficial not only for the elderly patients themselves but is also useful in preventing the spread of drug-resistant bacteria.

Bactericidal activities of meropenem and ertapenem against extended-spectrum-beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae in a neutropenic mouse thigh model

The purpose of this study was to examine the in vivo efficacies of meropenem and ertapenem against extended-spectrum-beta-lactamase (ESBL)-producing isolates with a wide range of MICs. Human-simulated dosing regimens in mice were designed to approximate the free drug percent time above the MIC (fT>MIC) observed for humans following meropenem at 1 g every 8 h and ertapenem at 1 g every 24 h. An in vivo neutropenic mouse thigh infection model was used to examine the bactericidal effects against 31 clinical ESBL Escherichia coli and Klebsiella pneumoniae isolates and 2 non-ESBL isolates included for comparison at a standard 10(5) inoculum. Three isolates were examined at a high 10(7) inoculum as well. Meropenem displayed greater in vitro potency, with a median MIC (range) (microg/ml) of 0.125 (0.03 to 32), than did ertapenem, with 0.5 (0.012 to 128). Seven of the 31 ESBL isolates were removed from the efficacy analysis due to their inability to establish infection in the mouse model. When MICs were<or=1.5 microg/ml for ertapenem (<or=0.5 microg/ml for meropenem), similar reductions in CFU (approximately 2-log kill) were observed for both ertapenem (fT>MIC>or=23%) and meropenem (fT>MIC>or=75%). Ertapenem showed bacterial regrowth for seven of eight isolates, with MICs of>or=2 microg/ml (fT>MIC<or=20%), while meropenem displayed antibacterial potency that varied from a static effect to a 1-log bacterial reduction in these isolates (fT>MIC=30 to 65%). At a 10(7) inoculum, both agents eradicated bacteria due to adequate exposures (fT>MIC=20 to 45%). Due to low MICs, no difference in bacterial kill was noted for the majority of ESBL isolates tested. However, for isolates with raised ertapenem MICs of>or=2 microg/ml, meropenem displayed sustained efficacy due to its greater in vitro potency and higher resultant fT>MIC.

Influence of culture site-specific MIC distributions on the pharmacokinetic and pharmacodynamic properties of piperacillin/tazobactam and piperacillin: a data analysis

BACKGROUND

Investigators who perform pharmacokinetic/pharmacodynamic (PK-PD) modeling with Monte Carlo simulation have historically not stratified microbiological data by culture site. This lack of stratification might be problematic if susceptibility patterns differ among sites and might lead to differences in PK-PD.

OBJECTIVE

This study compared the PK-PD of 2 antimicrobial regimens against 5 gram-negative bacterial species form 3 culture sites.

METHODS

This data analysis was performed at the Department of Pharmacology, The University of Texas Health Science Center, San Antonio, Texas. Blood, pulmonary (ie, bronchial, endotracheal, lung, respiratory, sputum, and tracheal secretions), and wound distributions of MICs were extracted from the 2002 Intensive Care Unit Surveillance System database. Bacteria included Acinetobacter baumannii, Enterobacter cloacae, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. The PK properties of piperacillin/tazobactam (3.375 g every 4 hours) and piperacillin (3 g every 4 hours) were obtained from studies in healthy volunteers. Monte Carlo simulation was used in 10,000 patients for each antimicrobial-bacteria-culture site combination. The cumulative fraction of response (CFR) for a free percentage time above the MIC of > or =50% was determined for each combination, and a clinically significant difference was defined a priori as > or =10%.

RESULTS

Data from 2408 pulmonary, 490 blood, and 242 wound isolates were included. For piperacillin/tazobactam, the CFR varied <10% by culture site in all 5 bacterial species. Site-specific differences were noted in MIC50 for piperacillin versus E cloacae and E coli and MIC90 for piperacillin/tazobactam versus K pneumoniae and P aeruginosa. Likewise, for piperacillin, the CFR was similar among the 3 culture sites for P aeruginosa. However, the CFR for piperacillin varied by > or =10% for A baumannii (blood > wound), E cloacae (pulmonary > blood), E coli (pulmonary and blood > wound), and K pneumoniae (wound > blood).

CONCLUSIONS

The PK-PD models based on PK properties found in healthy humans and site-specific MIC distributions in this study suggest that for piperacillin, culture-site differences subsequently resulted in CFR differences that exceeded a predetermined level of clinical significance. Furthermore, these data suggest that traditional reporting strategies for microbiological data (ie, MIC50 and MIC90) might fail to adequately characterize the MIC population.

Comparative performance of different stochastic methods to simulate drug exposure and variability in a population

Monte Carlo simulations (MCSs) are increasingly being used to predict the pharmacokinetic variability of antimicrobials in a population. However, various MCS approaches may differ in the accuracy of the predictions. We compared the performance of 3 different MCS approaches using a data set with known parameter values and dispersion. Ten concentration-time profiles were randomly generated and used to determine the best-fit parameter estimates. Three MCS methods were subsequently used to simulate the AUC(0-infinity) of the population, using the central tendency and dispersion of the following in the subject sample: 1) K and V; 2) clearance and V; 3) AUC(0-infinity). In each scenario, 10000 subject simulations were performed. Compared to true AUC(0-infinity) of the population, mean biases by various methods were 1) 58.4, 2) 380.7, and 3) 12.5 mg h L(-1), respectively. Our results suggest that the most realistic MCS approach appeared to be based on the variability of AUC(0-infinity) in the subject sample.

Pharmacodynamic profiling of imipenem, meropenem and ertapenem against clinical isolates of extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella spp. from Brazil

The pharmacodynamic potency of imipenem, meropenem and ertapenem against extended-spectrum beta-lactamase (ESBL)-producing isolates was investigated. Minimal inhibitory concentration (MIC) determination, confirmation of ESBLs by Etest and the disk approximation test were performed for 133 ESBL-producing isolates of Escherichia coli and Klebsiella spp. Pharmacodynamic exposure, measured as percent of the dosing interval during which free drug was above the MIC (% fT>MIC), was modelled via a 5000-subject Monte Carlo simulation. Bactericidal cumulative fraction of response (CFR), defined as 40% fT>MIC, was calculated against each bacterial population. All agents achieved high bactericidal CFR against all ESBL isolates as a group, but ertapenem (96.26%) was slightly less effective than imipenem (99.96%) and meropenem (99.90%) (P<0.05). Similar results were observed against Klebsiella spp. only (P<0.05). Against E. coli, CFRs were close to 100%. Ertapenem is probably an effective agent against ESBL-producing bacteria, although its ability to achieve bactericidal pharmacodynamic exposures will depend on the bacterial susceptibility.

Ertapenem: a review of its use in the treatment of bacterial infections

The Group 1, 1 beta-methyl carbapenem ertapenem (Invanz) is approved for parenteral use in patients with complicated intra-abdominal infection (cIAI), community-acquired pneumonia (CAP) and acute pelvic infection caused by susceptible strains of certain designated organisms in both the US and the EU. Additional approved indications in the US include complicated skin and skin structure infection (cSSSI) and complicated urinary tract infection (cUTI). Ertapenem is approved for use in adults in both the US and the EU and in paediatric patients aged >or=3 months in the US. Ertapenem has a broad spectrum of in vitro activity against Gram-negative pathogens, including extended-spectrum beta-lactamase (ESBL)- and AmpC-producing Enterobacteriaceae, Gram-positive pathogens and anaerobic pathogens. It has similar efficacy to comparator antibacterials such as piperacillin/tazobactam in cSSSI (including diabetic foot infection), cIAI and acute pelvic infection and ceftriaxone with or without metronidazole in cIAI, cUTI and CAP. The drug has also shown efficacy in the treatment of paediatric patients with complicated community-acquired bacterial infections. Ertapenem has a convenient once-daily administration schedule and is generally well tolerated. Thus, ertapenem is an important option for the empirical treatment of complicated community-acquired bacterial infections in hospitalised patients.

Assay of ertapenem in human serum by high-performance liquid chromatography

Ertapenem is a new carbapenem with a broad spectrum of activity and an extended half-life, permitting once daily administration. Although high-performance liquid chromatography (HPLC) methods have been described for ertapenem, these are complex and involve column switching and thus this type of assay may not suitable for use in routine clinical microbiology laboratories. In this study we report a rapid, straightforward HPLC method for the detection of ertapenem in human serum.

Comparison of pharmacodynamic target attainment between healthy subjects and patients for ceftazidime and meropenem

STUDY OBJECTIVE

To compare the pharmacodynamics of two beta-lactams--ceftazidime and meropenem--in healthy subjects versus patients.

DESIGN

Monte Carlo simulation based on published pharmacokinetic studies.

SUBJECTS

One hundred and ninety-seven participants (75 healthy volunteers and 122 patients) from published pharmacokinetic studies of ceftazidime or meropenem.

MEASUREMENTS AND MAIN RESULTS

Data on total body clearance and volume of distribution for ceftazidime and meropenem in healthy subjects and patients were obtained from published studies. Monte Carlo simulations were performed based on the pharmacokinetics from each study for ceftazidime 1000 mg every 8 hours and meropenem 1000 mg every 8 hours against isolates of Escherichia coli , Klebsiella pneumoniae , Acinetobacter baumannii , and Pseudomonas aeruginosa collected from North and South America. We calculated the likelihood of obtaining bactericidal exposures (50% time above the minimum inhibitory concentration [MIC] for ceftazidime and 40% time above the MIC for meropenem) for each combination of pharmacokinetic study data and MIC distribution. Linear regression was used to compare target attainments for healthy subjects versus patients. Only three drug-pathogen combinations differed in target attainment between healthy subjects and patients: ceftazidime against P. aeruginosa in North America and meropenem against E. coli and P. aeruginosa in South America. The regression line of target attainment for patients versus healthy subjects had a slope of 1.04 (95% confidence interval [CI] 0.983-1.093) and a y intercept of -3.73 (95% CI -8.265-0.827, r2 = 0.992). The beta values for slope and intercept did not differ to a statistically significant extent between the regression line and the line of identity (p=0.264).

CONCLUSION

The pharmacodynamic target attainment calculated with healthy subject pharmacokinetic data was predictive of patient target target attainment for ceftazidime and meropenem.