Antimicrobial spectrum of activity for meropenem and nine broad spectrum antimicrobials: report from the MYSTIC Program (2002) in North America

Therapeutic effect of vitamin K1 combined with meropenem on the treatment of pertussis syndrome

Clinical efficacy of vitamin K1 combined with meropenem on the treatment of pertussis syndrome was evaluated. Clinical data of 170 children with pertussis syndrome treated in the Second People's Hospital of Liaocheng from March 2015 to March 2017 were collected. Of these, 87 patients who were treated with vitamin K1 combined with meropenem were regarded as the experiment group. A total of 83 patients who were treated with meropenem alone were regarded as the control group. Both groups were treated with anti-infective, respiratory support, antispasmodic, expectorant and other basic treatments. The therapeutic effects, duration of spasmodic cough, length of hospitalization, antipyretic time, duration of voice disappearance and healing time were observed between the two groups. The duration of spasmodic cough and length of hospitalization in the experiment were lower than the control group, and the difference was statistically significant between the groups (P<0.05). The explicit efficiency (51.72%) and total effective efficiency (99.55%) in the experiment group were significantly higher than the explicit efficiency (36.14%) and total effective efficiency (78.31%) in the control group. There was a statistically significant difference between the groups (P<0.05). The voice disappearance time and healing time in the experiment group were significantly shorter than the control group, and there was a statistically significant difference between the groups (P<0.05). The antipyretic time in the experiment group was lower than that of the control group, the difference between the groups was not statistically significant (P>0.05). The treatment with vitamin K1 and meropenem has a significant effect in relieving pediatric pertussis syndrome, it can shorten the duration of spasmodic cough, antipyretic time, duration of voice disappearance and length of hospitalization in children with pertussis syndrome, and improve the efficacy clinically.

A comparison of adeB gene expression levels under conditions of induced resistance by different drugs in vitro in Acinetobacter baumannii

The present study was designed to analyze the difference of the adeB gene expression levels under conditions of induced resistance and to verify the significance of the AdeABC efflux pump in the in vitro induction of Acinetobacter baumannii (A. baumannii). Strains were isolated from blood or drainage samples in the First Hospital of China Medical University. The minimum inhibitory concentration (MIC) was determined by a broth microdilution method. In addition, an in vitro induction of drug-resistance tests was confirmed with the three drugs. The expression level of the adeB was determined by quantitative polymerase chain reaction (qPCR), and there were 19, 17 and 25 strains isolated from this test that were susceptible to amikacin, netilmicin and imipenem, respectively. Furthermore, 11, 15 and 8 stably resistant strains generated against amikacin, netilmicin and imipenem, respectively, by in vitro induction. The MIC values of all the imipenem-sensitive and imipenem-resistant strains decreased by no more than 2-fold under carbonyl cyanide 3-chlorophenylhydrazone (CCCP)-containing conditions. The MIC values of 10 amikacin-resistant and 14 netilmicin-resistant strains decreased 4-fold or more under CCCP-containing conditions. Furthermore, qPCR revealed that none of the imipenem-sensitive or the imipenem-resistant strains expressed the adeB gene, but there were 10 amikacin-resistant and 5 netilmicin-resistant strains that expressed the adeB gene. In conclusion, the present study confirmed that in vitro induction of drug-resistance tests in sensitive A. baumannii strains could produce drug-resistance following long-term exposure to low doses of antibacterial drugs. In addition, amikacin and netilmicin are more prone to producing drug-resistance compared to imipenem in vitro. The results of the efflux phenotype indicate the possible application of CCCP in the inhibition of the efflux system in some drugs. The inconsistency between efflux phenotype and qPCR of adeB indicates that other mechanisms may also be included in the induction of drug-resistance that work with the active mechanism in order to increase drug resistance to common clinically-used antimicrobial drugs.

Meropenem by Continuous Versus Intermittent Infusion in Ventilator-Associated Pneumonia due to Gram-Negative Bacilli

Background:

It is known that β-lactam antibiotics exhibit time-dependent bactericidal activity. Several studies have found continuous infusion of meropenem more effective than intermittent infusion in maintaining constant serum concentrations in excess of the minimum inhibitory concentration. However, limited data exist on the clinical efficacy of meropenem administered by continuous infusion.

Objective:

To evaluate the clinical efficacy of continuous versus intermittent infusion of meropenem for the treatment of ventilator-associated pneumonia (VAP) due to gram-negative bacilli.

Methods:

A retrospective cohort study was conducted of patients with VAP caused by gram-negative bacilli who received initial empiric antibiotic therapy with meropenem. We analyzed 2 contemporary cohorts: one group received meropenem by continuous infusion (1 g over 360 min every 6 h), the other by intermittent infusion (1 g over 30 min every 6 h). The administration method was prescribed according to the physician's discretion. Patients received meropenem plus tobramycin for 14 days.

Results:

There were no significant differences between patient groups with regard to gender, age, APACHE-II at intensive care unit admission, diagnosis, microorganism responsible for VAP, or organ dysfunction severity at the time VAP was suspected. The group receiving medication by continuous infusion showed a greater clinical cure rate than the group treated with intermittent infusion (38 of 42, 90.47%, vs 28 of 47, 59.57%, respectively, with OR 6.44 [95% Cl 1.97 to 21.05; p < 0.001]).

Conclusions:

Meropenem administered by continuous infusion may have more clinical efficacy than intermittent infusion.

An evolved oxazolidinone with selective potency against Mycobacterium tuberculosis and gram positive bacteria

Innovation of new antibacterials that are effective against strains that have developed resistance to existing drugs would strengthen our ability to treat and subsequently control spread of pathogenic bacteria. Increasing incidence of infections with drug resistant bacteria has become a common occurrence in recent times. We have developed an evolved oxazolidinone, T145, which inhibits growth of Enterococcus faecalis, Staphylococcus aureus and Mycobacterium tuberculosis (Mtb) with sub μg/ml potencies that are potentially therapeutically valuable. The oxazolidinone is bactericidal against Mtb but bacteriostatic against E. faecalis and S. aureus. In addition to therapeutically valuable potency and bactericidal activity against Mtb, T145 minimizes selection of spontaneous resistant mutants, a trait that prolongs longevity of a drug in clinical use.

Pharmacokinetics of meropenem in children receiving continuous renal replacement therapy: Validation of clinical trial simulations

Meropenem is frequently prescribed in critically ill children receiving continuous renal replacement therapy (CRRT). We previously used clinical trial simulations to evaluate dosing regimens of meropenem in this population and reported that a dose of 20 mg/kg every 12 hours optimizes target attainment. Meropenem pharmacokinetics were investigated in this prospective, open-label study to validate our previous in silico predictions. Seven patients received meropenem (13.8-22 mg/kg) administered intravenously every 12 hours as part of standard care. A mean dose of 18.6 mg/kg of meropenem was administered, resulting in a mean peak concentration of 80.1 μg/mL. Meropenem volume of distribution was 0.35 ± 0.085 L/kg. CRRT clearance was 40.2 ± 6.6 mL/(min · 1.73 m(2) ) and accounted for 63.4% of the total clearance of 74.8 ± 36.9 mL/(min · 1.73 m(2) ). Simulations demonstrated that a dose of 20 mg/kg every 12 hours resulted in a time above the minimum inhibitory concentration (%fT > MIC) of 100% in 5 out of 7 subjects, with a %fT > MIC of 93% and 43% in the remaining 2 subjects. We conclude that CRRT contributed significantly to the total clearance of meropenem. A dosing regimen of 20 mg/kg achieved good target attainment in critically ill children receiving CRRT, which is consistent with our previously published in silico predictions.

Pharmacodynamic profiling of intravenous antibiotics against prevalent Gram-negative organisms across the globe: the PASSPORT Program-Asia-Pacific Region

Due to escalating antimicrobial resistance amongst Gram-negative organisms, the choice of effective empirical antimicrobial regimens has become challenging. Monte Carlo simulations were conducted for conventional and prolonged infusion regimens of doripenem, imipenem and meropenem using pharmacokinetic data from adult patients with conserved renal function. Minimum inhibitory concentration data against Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii were incorporated from the COMPACT surveillance programme in the Asia-Pacific region of the world. The cumulative fraction of response (CFR) was determined for each regimen against each bacterial population. All simulated carbapenem regimens achieved an optimal CFR against E. coli and K. pneumoniae (94.5-100% CFR). Against P. aeruginosa, doripenem achieved 78.7-92.6% CFR, imipenem achieved 60.4-79.0% CFR and meropenem achieved 73.0-85.1% CFR. The only dosing regimen to achieve ≥ 90% CFR against P. aeruginosa was doripenem 1000 mg and 2000 mg every 8 h (4-h infusion). Carbapenem CFRs against A. baumannii were much lower (29.2-54.4% CFR). CFRs for non-fermenting isolates were ca. 10% lower for isolates collected in the Intensive Care Unit. Carbapenem resistance amongst Enterobacteriaceae remains low in the Asia-Pacific region and thus standard carbapenem dosing regimens had a high likelihood of achieving pharmacodynamic exposures. However, larger doses combined with prolonged infusion will be required to increase the CFR for these carbapenems against resistant non-fermenting Gram-negatives that are common in these countries. The safety and efficacy of these high dosing regimens will need to be confirmed in the clinical setting.

Comparison of 2002–2006 OPTAMA Programs for US Hospitals: Focus on Gram-Negative Resistance

Background:

Resistance among gram-negative bacteria is increasing within the US.

Objective:

To determine pharmacodynamic target attainment rates for 10 antimicrobials against selected gram-negative bacilli and compare these results with previous Optimizing Pharmacodynamic Target Attainment Using the MYSTIC Antibiogram (OPTAMA) assessments.

Methods:

A 5000-patient Monte Carlo simulation using data from population pharmacokinetic studies was employed to estimate the pharmacokinetic profiles for standard and/or prolonged infusion (PI) regimens of cefepime, ceftazidime, ceftriaxone, ciprofloxacin, ertapenem, imipenem, levofloxacin, meropenem, piperacillin–tazobactam, and tigecycline. Minimum inhibitory concentration data were obtained from intensive care units of 15 US hospitals participating in the 2006 MYSTIC (Meropenem Yearly Susceptibility Test Information Collection) study for 640 Escherichia coli, 618 Klebsiella spp., and 606 Pseudomonas aeruginosa isolates. Cumulative fraction of response (CFR) was calculated using pharmacodynamic targets for each antibiotic and compared with results from the 2002 and 2004 OPTAMA studies.

Results:

Against E. coli, CFRs greater than 92% were maintained for all regimens except the fluoroquinolones (CFR range 69.4–72%), which showed a 7% decrease compared with 2004. The presence of Klebsiella spp. producing KPC-type carbapenemases with associated multidrug resistance resulted in a 7% or greater drop in CFR of standard regimens relative to 2004. Despite these resistant phenotypes, high-dose PI regimens (2 g every 8 hours as 3-hour PI) of cefepime and meropenem achieved CFRs of 97% and 95.8%, respectively. Excluding 3 KPC-harboring hospitals resulted in CFR increases to greater than 98% for carbapenems and cefepime and greater than 88% for all other agents tested, except tigecycline. Against P. aeruginosa, the fluoroquinolones had the lowest CFR (55.8–63.9%), followed by imipenem (74.6-80.4%). The most predictable activity was seen with cefepime 2 g every 12 hours or higher (>90%), ceftazidime 2 g every 8 hours (97.9%), and meropenem 1-2 g every 8 hours (86.7–92.6%). Use of PI for piperacillin-tazobactam and meropenem increased CFRs by 6% and 4%, respectively, over standard infusions.

Conclusions:

Relative to previous years, an increase in resistance was noted among gram-negative bacilli to common antibiotics, resulting in disproportionate decreases in pharmacodynamic target attainment. The use of PI for β-lactams may help to overcome these decreases.

Antibiotic resistance surveillance over a 4-year period (2000–2003) in Turkey: results of the MYSTIC Program

The Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program is a global study that provides antimicrobial susceptibility data in centers prescribing meropenem. The activity of meropenem and 7 broad-spectrum antimicrobials have been examined against 5208 bacterial isolates from 9 Turkish centers between 2000 and 2003. Cumulative susceptibility rates against all species of Enterobacteriaceae combined were ranked as follows: meropenem (99.3%), imipenem (97.6%), cefepime (80.0%), piperacillin-tazobactam (73.6%), ceftazidime (70.3%), ciprofloxacin (70.1%), cefotaxime (66.9%), and tobramycin (67.2%). The production of extended-spectrum beta-lactamases (ESBLs) was detected in 48.7% of Klebsiella pneumoniae and in 19.5% of Escherichia coli isolates. Of ESBL producing K. pneumoniae isolates, 75.7% were resistant to tobramycin, 40.3% to ciprofloxacin, and 48.3% to piperacillin-tazobactam. Only piperacillin/tazobactam and carbapenems were active against more than 50% of Pseudomonas aeruginosa at the National Committee for Clinical Laboratory Standards-susceptible breakpoint, and the carbapenems were the most active compounds against Acinetobacter spp. These data confirm the continued potency of meropenem against Enterobacteriaceae in units where it is actively being prescribed.

Piperacillin-tazobactam: a beta-lactam/beta-lactamase inhibitor combination

Piperacillin-tazobactam is a beta-lactam/beta-lactamase inhibitor combination with a broad spectrum of antibacterial activity that includes Gram-positive and -negative aerobic and anaerobic bacteria. Piperacillin-tazobactam retains its in vitro activity against broad-spectrum beta-lactamase-producing and some extended-spectrum beta-lactamase-producing Enterobacteriaceae, but not against isolates of Gram-negative bacilli harboring AmpC beta-lactamases. Piperacillin-tazobactam has recently been reformulated to include ethylenediaminetetraacetic acid and sodium citrate; this new formulation has been shown to be compatible in vitro with the two aminoglycosides, gentamicin and amikacin, allowing for simultaneous Y-site infusion, but not with tobramycin. Multicenter, randomized, double-blinded clinical trials have demonstrated piperacillin-tazobactam to be as clinically effective as relevant comparator antibiotics. Clinical trials have demonstrated piperacillin-tazobactam to be effective for the treatment of patients with intra-abdominal infections, skin and soft tissue infections, lower respiratory tract infections, complicated urinary tract infections, gynecological infections and more recently, febrile neutropenia. Piperacillin-tazobactam has an excellent safety and tolerability profile and continues to be a reliable option for the empiric treatment of moderate-to-severe infections in hospitalized patients.

Addressing resistance evolution in Pseudomonas aeruginosa using pharmacodynamic modelling: application to meropenem dosage and combination therapy

Isolates of Pseudomonas aeruginosa (n = 208) were collected from an 810-bed hospital in Connecticut, USA. A model employing the pharmacokinetic properties of meropenem, susceptibility results and Monte Carlo simulation was used to analyse four different dosing regimens of meropenem at pharmacodynamic endpoints. Cumulative fraction of response (CFR) was assessed at bacteriostatic and bactericidal endpoints for the entire population of isolates, as well as for isolates from principal anatomical sites. CFR was also evaluated at endpoints shown to suppress emergence of resistance in 'susceptible'P. aeruginosa with either monotherapy or combination therapy. The bacteriostatic/bactericidal CFR of meropenem 1 g every 8 h (q8h), 2 g q8h, 1 g q8h infused over 3 h (3-h INF), and 2 g q8h 3-h INF were 76%/73%, 80%/76%, 77%/75% and 79%/78%, respectively. At the monotherapeutic suppressive endpoint, CFRs against susceptible isolates were 21%, 35%, 32% and 50%, respectively. When combination therapy with an aminoglycoside was simulated, the CFRs for the same regimens were 50%, 64%, 65% and 79%, respectively. Bactericidal CFRs for all regimens against wound isolates were significantly higher (p <0.03 for each regimen) than CFRs for the entire population. Meropenem 2 g q8h with a 3-h infusion in combination with an aminoglycoside provides the greatest likelihood of P. aeruginosa coverage, and may help to prevent development of resistance, although local MIC data are essential to inform therapeutic decisions.

Evaluating Empiric Treatment Options for Secondary Peritonitis Using Pharmacodynamic Profiling

BACKGROUND

Selecting an appropriate agent for empiric antibiotic therapy for secondary peritonitis is challenging. The pathogens responsible, aerobic gram-negative bacilli in particular, are becoming more resistant to antibiotics. The purpose of this study was to predict the ability of common antimicrobial regimens to achieve optimal pharmacodynamic exposure against aerobic bacteria implicated in secondary peritonitis, while considering current national resistance trends.

METHODS

Monte Carlo simulation was used to model pharmacodynamic endpoints and compare the cumulative fraction of response (CFR) for imipenem-cilastatin, meropenem, ertapenem, piperacillin/tazobactam, ceftazidime, ceftriaxone, ciprofloxacin, and levofloxacin against isolates of species associated with secondary peritonitis. Minimum inhibitory concentration (MIC) distributions for isolates collected in North America were obtained from the 2004 MYSTIC database. Pharmacokinetic parameters were derived from the literature; the endpoints evaluated included free drug time above the MIC (fT(>MIC)) and the area under the concentration-time curve to MIC ratio (AUC:MIC).

RESULTS

The simulation predicted that several compounds would have a superior probability of providing appropriate coverage of aerobic bacteria: Imipenem-cilastatin (98.6% CFR at 1 g q8h), meropenem (98.2% CFR at 1 g q8h), ertapenem (91.7% CFR at 1 g q24h), piperacillin/ tazobactam (93.7% CFR at 3.375 g q6h), ceftazidime (91.1% CFR at 2 g q8h), and cefepime (92.9% CFR at 1 g q12h and 95.8% CFR at 2 g q12h). Ceftriaxone, ciprofloxacin, and levofloxacin exhibited CFRs < 82%.

CONCLUSIONS

Considering contemporary susceptibility data for aerobic bacteria, monotherapy with any of the three carbapenems or piperacillin/tazobactam 3.375 g q6h would provide optimal exposure for the pathogens commonly encountered in secondary peritonitis. Cefepime (in combination with metronidazole to provide anti-anaerobic coverage) also would be an acceptable choice, as would ceftazidime given at 2 g q8h (again in combination with metronidazole). Despite the popularity of combination therapy based on ciprofloxacin, levofloxacin, or ceftriaxone with metronidazole, these choices appear to be inferior to the other options because of emerging antibiotic resistance, particularly in E. coli.

Population pharmacokinetic analysis and dosing regimen optimization of meropenem in adult patients

The objectives of this study were to develop a meropenem population pharmacokinetic model using patient data and use it to explore alternative dosage regimens that could optimize the currently used dosing regimen to achieve higher likelihood of pharmacodynamic exposure against pathogenic bacteria. We gathered concentration data from 79 patients (ages 18-93 years) who received meropenem 0.5, 1, or 2 g over 0.5- or 3-hour infusion every 8 hours. Meropenem population pharmacokinetic analysis was performed using the NONMEM program. A 2-compartment model fit the data best. Creatinine clearance, age, and body weight were the most significant covariates to affect meropenem pharmacokinetics. Monte Carlo simulation was applied to mimic the concentration-time profiles while 1 g meropenem was administrated via infusion over 0.5, 1, 2, and 3 hours. The 3-hour prolonged infusion improved the likelihood of obtaining both bacteriostatic and bactericidal exposures most notably at the current susceptibility breakpoints.

Comparative Review of the Carbapenems

The carbapenems are beta-lactam antimicrobial agents with an exceptionally broad spectrum of activity. Older carbapenems, such as imipenem, were often susceptible to degradation by the enzyme dehydropeptidase-1 (DHP-1) located in renal tubules and required co-administration with a DHP-1 inhibitor such as cilastatin. Later additions to the class such as meropenem, ertapenem and doripenem demonstrated increased stability to DHP-1 and are administered without a DHP-1 inhibitor. Like all beta-lactam antimicrobial agents, carbapenems act by inhibiting bacterial cell wall synthesis by binding to and inactivating penicillin-binding proteins (PBPs). Carbapenems are stable to most beta-lactamases including AmpC beta-lactamases and extended-spectrum beta-lactamases. Resistance to carbapenems develops when bacteria acquire or develop structural changes within their PBPs, when they acquire metallo-beta-lactamases that are capable of rapidly degrading carbapenems, or when changes in membrane permeability arise as a result of loss of specific outer membrane porins. Carbapenems (imipenem, meropenem, doripenem) possess broad-spectrum in vitro activity, which includes activity against many Gram-positive, Gram-negative and anaerobic bacteria; carbapenems lack activity against Enterococcus faecium, methicillin-resistant Staphylococcus aureus and Stenotrophomonas maltophilia. Compared with imipenem, meropenem and doripenem, the spectrum of activity of ertapenem is more limited primarily because it lacks activity against Pseudomonas aeruginosa and Enterococcus spp. Imipenem, meropenem and doripenem have in vivo half lives of approximately 1 hour, while ertapenem has a half-life of approximately 4 hours making it suitable for once-daily administration. As with other beta-lactam antimicrobial agents, the most important pharmacodynamic parameter predicting in vivo efficacy is the time that the plasma drug concentration is maintained above the minimum inhibitory concentration (T>MIC). Imipenem/cilastatin and meropenem have been studied in comparative clinical trials establishing their efficacy in the treatment of a variety of infections including complicated intra-abdominal infections, skin and skin structure infections, community-acquired pneumonia, nosocomial pneumonia, complicated urinary tract infections, meningitis (meropenem only) and febrile neutropenia. The current role for imipenem/cilastatin and meropenem in therapy remains for use in moderate to severe nosocomial and polymicrobial infections. The unique antimicrobial spectrum and pharmacokinetic properties of ertapenem make it more suited to treatment of community-acquired infections and outpatient intravenous antimicrobial therapy than for the treatment of nosocomial infections. Doripenem is a promising new carbapenem with similar properties to those of meropenem, although it appears to have more potent in vitro activity against P. aeruginosa than meropenem. Clinical trials are required to establish the efficacy and safety of doripenem in moderate to severe infections, including nosocomial infections.

Population pharmacokinetics of meropenem in febrile neutropenic patients in Korea

Population pharmacokinetic parameters of meropenem in 57 febrile neutropenic patients and minimal inhibitory concentration (MIC) data for clinically isolated Pseudomonas aeruginosa and Escherichia coli were applied to estimate the time above the MIC (T>MIC) using the Monte Carlo simulation method. Mean population clearance (CL) and volume of distribution (V(d)) of meropenem were proportional to creatinine clearance (CL(Cr)) and body weight, respectively: CL (L/h)=9.7 x (CL(Cr)(mL/min)/120); V(d) (L)=14.6 x (body weight (kg)/61). In 1000 simulated patients treated with meropenem 0.5g or 1g every 8h, the proportions of patients who had a T>MIC less than 40% of the dosing interval were 46.3% and 39.5% for P. aeruginosa and 5.8% and 5.6% for E. coli, respectively. The overwhelming resistance of the pathogenic microorganisms, especially P. aeruginosa, in our data compared with that reported in North America suggests the importance of regions or countries as a critical factor for determining the dosage regimen of meropenem in addition to patient characteristics and pharmacokinetics.

An overview of the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program: 1997-2004

This overview provides a summary of the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program over an 8-year period from 1997 to 2004. The evolution of the MYSTIC Program is described, as well as its design compared with other surveillance programs. In addition, the global MYSTIC Program data, published to date, are summarized, and the empiric use of carbapenems, their current indications, and meropenem usage versus resistance was discussed. From 1997 to 2004, 120 medical centers that were actively prescribing meropenem in 32 countries worldwide participated in the program. The MYSTIC Program results demonstrate the sustained potency and continued effectiveness of meropenem globally against clinically relevant Gram-negative and Gram-positive pathogens including extended spectrum beta-lactamase- and AmpC beta-lactamase-producing organisms, which may also display resistance to the fluoroquinolones and/or aminoglycosides. Furthermore, in centers actively prescribing meropenem, resistance to meropenem is not increasing despite greater resistance among the comparator antimicrobial agents. Thus, antipseudomonal carbapenems such as meropenem and imipenem remain an effective treatment option.

Antimicrobial susceptibility pattern comparisons among intensive care unit and general ward Gram-negative isolates from the Meropenem Yearly Susceptibility Test Information Collection Program (USA)

The Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program is a global, longitudinal antimicrobial resistance surveillance network of greater than 100 medical centers worldwide monitoring the susceptibility of bacterial pathogens to carbapenems and other broad-spectrum agents. Between 1999 and 2002, 15 US medical centers referred up to 200 nonduplicate isolates from clinical infections to a central processing laboratory. During this 4-year period, the antimicrobial activity of 11 broad-spectrum agents was assessed against 5389 bacterial isolates using Clinical and Laboratory Standards Institute (formerly National Committee for Clinical Laboratory Standards)-recommended methods with interpretive criteria. Analysis of the MIC results for pathogens isolated from patients hospitalized in intensive care units (ICUs) were compared to results from pathogens isolated in non-ICU settings. Among Enterobacteriaceae (3884 strains), the carbapenems (imipenem and meropenem) demonstrated the highest susceptibility rates (> or =98.7%) and with only a 1% increase in resistance for ICU isolates compared to non-ICU organisms. Other antimicrobial agents tested demonstrated consistently higher susceptibility rates against Enterobacteriaceae isolates from ICU (89.7-98.7%) and non-ICU (93.2-99.9%) areas. For the nonfermentative Gram-negative bacilli, the rank order of the most active agents having lowest percentage resistance rates were tobramycin (15.5%) < cefepime < imipenem < piperacillin/tazobactam < ceftazidime < meropenem (21.9%) for ICU isolates, and meropenem (7.8%) < cefepime < imipenem < piperacillin/tazobactam < ceftazidime < tobramycin (12.9%) among non-ICU strains. All tested agents showed lower susceptibility rates (range, 1.0-15.3%) and higher resistance rates (range, 0.1-15.1%) for both Enterobacteriaceae and nonfermentative Gram-negative bacilli among the ICU isolates compared to the non-ICU isolates (except for ciprofloxacin against Enterobacteriaceae). Continued surveillance of these broad-spectrum antimicrobial agents in both ICU and general hospital wards appears warranted to monitor the occurrence and spread of antimicrobial resistance in pathogens causing serious infections in these care areas and the possible emergence of resistance mechanisms that could compromise empiric carbapenem therapy.

Comparison of censored regression and standard regression analyses for modeling relationships between antimicrobial susceptibility and patient- and institution-specific variables

In order to identify patients likely to be infected with resistant bacterial pathogens, analytic methods such as standard regression (SR) may be applied to surveillance data to determine patient- and institution-specific factors predictive of an increased MIC. However, the censored nature of MIC data (e.g., MIC < or = 0.5 mg/liter or MIC > 8 mg/liter) imposes certain limitations on the use of SR. In order to investigate the nature of these limitations, simulations were performed to compare a regression tailored for censored data (censored regression [CR]) and one tailored for an SR. By using a model relating piperacillin-tazobactam MICs against Enterobacter spp. to patient age and hospital bed capacity, 200 simulations of 500 isolates were performed. Various MIC censoring patterns were imposed by using 26 left- or right-censored (L,R) pairs (i.e., MICs < or = 2 mg/liter(L) [2L] or MICs > 2 mg/liter(R) [2R], respectively). Data were fit by CR and SR for which censored MICs were either (i) excluded, (ii) replaced by 2L or 2R, or (iii) replaced by 2(L - 1) or 2(R + 1). Total censoring for the 26 pairs ranged from 7 to 86%. By CR, deviations of average parameter estimates from the true parameter values were <0.10 log2 (mg/liter) for all parameters for each of the 26 pairs. By SR, these deviations were >0.10 log2 (mg/liter) for at least 18 of the 26 pairs for all but one parameter. Two-standard-error confidence intervals for individual parameters contained as little as 0% of cases for all SR approaches but > or = 91.5% of cases for the CR approach. When censored MIC data are modeled, CR may reduce or eliminate biased parameter estimates obtained by SR.

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.

Susceptibility of clinical isolates of multiresistant Pseudomonas aeruginosa to a hospital disinfectant and molecular typing

The aim of this study was to evaluate the susceptibility of 35 resistant Pseudomonas aeruginosa clinical isolates to a quaternary ammonium hospital disinfectant. The methodology was the AOAC Use-Dilution Test, with disinfectant at its use-concentration. In addition, the chromosomal DNA profile of the isolates were determined by macro-restriction pulsed field gel electrophoresis (PFGE) method aiming to verify the relatedness among them and the behavior of isolates from the same group regarding the susceptibility to the disinfectant. Seventy one percent of the isolates were multiresistant to antibiotics and 43% showed a reduced susceptibility to the disinfectant. The PFGE methodology detected 18 major clonal groups. We found isolates with reduced susceptibility to the disinfectant and we think that these are worrying data that should be further investigated including different organisms and chemical agents in order to demonstrate that microorganisms can be destroyed by biocide as necessary. We also found strains of the same clonal groups showing different susceptibility to the disinfectant. This is an interesting observation considering that only few works are available about this subject. PFGE profile seems not to be a reliable marker for resistance to disinfectants.

Derivation of Meropenem Dosage in Patients Receiving Continuous Veno-Venous Hemofiltration Based on Pharmacodynamic Target Attainment

BACKGROUND

Dosage recommendations for antibiotics in patients receiving continuous veno-venous hemofiltration (CVVH) should be based on pharmacodynamic requirements. For meropenem, this would be achieving appropriate time above the minimum inhibitory concentration (T > MIC). We employed Monte Carlo simulation to calculate the bactericidal target attainment for various dosing regimens of meropenem against Pseudomonas aeruginosa and Acinetobacter species.

METHODS

Target attainment at 40% T > MIC was calculated for 5,000 simulated subjects receiving meropenem 1,000 mg every 12 and 8 h, and 500 mg every 12, 8 and 6 h. Pharmacokinetics were extrapolated from primary literature sources utilizing similar methods of CVVH. MIC data for P. aeruginosa and Acinetobacter species were derived from the US 2003 MYSTIC study. Target attainment at the breakpoint of 4 microg/ml was also calculated.

RESULTS

Only regimens of 1,000 mg every 8 h and 500 mg every 6 h essentially achieve 100% target attainment at the breakpoint. However, due to higher peak concentrations, 1,000 mg every 8 h is able to attain improved target attainment against more resistant populations of P. aeruginosa and Acinetobacter species, thus providing the greatest probability of bactericidal exposure.

CONCLUSION

Meropenem 1,000 mg every 8 h optimizes the pharmacodynamic profile in patients undergoing CVVH. Lower doses or increased dosing intervals should not be advocated for inpatients receiving this renal replacement technique. .

Evaluation by monte carlo simulation of the pharmacokinetics of two doses of meropenem administered intermittently or as a continuous infusion in healthy volunteers

Meropenem is a broad-spectrum carbapenem antibacterial agent. In order to optimize levels in plasma relative to the MICs, the ideal dose level and dosage regimen need to be determined. The pharmacokinetics of meropenem were studied in two groups, each comprising eight healthy volunteers who received the following doses: 500 mg as an intravenous infusion over 30 min three times a day (t.i.d.) versus a 250-mg loading dose followed by a 1,500 mg continuous infusion over 24 h for group A and 1,000 mg as an intravenous infusion over 30 min t.i.d. versus a 500-mg loading dose followed by a 3,000-mg continuous infusion over 24 h for group B. Meropenem concentrations in plasma and urine were determined by liquid chromatography-mass spectrometry/mass spectrometry and high-performance liquid chromatography with UV detection, respectively. Pharmacokinetic calculations were done by use of a two-compartment open model, and the data were extrapolated by Monte Carlo simulations for 10,000 simulated subjects for pharmacodynamic evaluation. There were no significant differences in total clearance and renal clearance between group A and group B or between the intermittent treatment and the continuous infusion. The analyses of the probability of target attainment by MIC for the high- and low-dose continuous infusions were robust up to MICs of 4 mg/liter and 2 mg/liter, respectively. The corresponding values for intermittent infusions were only 0.5 mg/liter and 0.25 mg/liter. When these observations were correlated with MICs obtained from the MYSTIC database, intermittent infusion results in adequate activity against two of the most common nosocomially acquired pathogens, Klebsiella pneumoniae and Enterobacter cloacae. However, against Pseudomonas aeruginosa, the evaluation shows a clear advantage of high-dose therapy administered as a continuous infusion. We believe that in the empirical therapy situation, the continuous-infusion mode of administration is most worth the extra efforts. We conclude that clinical trials for evaluation of the continuous infusions of meropenem in critically ill patients are warranted.

Population pharmacokinetics and pharmacodynamics of piperacillin/tazobactam in patients with complicated intra-abdominal infection

OBJECTIVES

We investigated the population pharmacokinetics and pharmacodynamics of piperacillin and tazobactam in hospitalized patients.

PATIENTS AND METHODS

A multicentre, randomized clinical trial was conducted in hospitalized patients with complicated intra-abdominal infection. Patients received piperacillin/tazobactam administered by either continuous infusion (13.5 g over 24 h, n = 130) or intermittent infusion (3.375 g every 6 h, n = 132). NONMEM was used to perform population pharmacokinetic analysis in a subset of patients (n = 56) who had serum samples obtained at steady-state for drug concentration analyses. Classification and regression tree analysis was used to identify the breakpoints of piperacillin PK-PD indexes in 94 patients with causative pathogen's MIC.

RESULTS

A one-compartment model was applied to fit the data. Creatinine clearance and body weight were the most significant variables to explain patient variability in piperacillin and tazobactam clearance and volume of distribution. The infusion method had no influence on PK parameters. For patients (n = 30) receiving intermittent infusion in the pharmacokinetic study, mean Cmax and half-life were 122.22 mg/L and 1.17 h for piperacillin, and 15.74 mg/L and 1.81 h for tazobactam. For patients (n = 26) receiving continuous infusion in the pharmacokinetic study, mean steady-state concentration was 35.31 +/- 12.15 mg/L for piperacillin and 7.29 +/- 3.28 mg/L for tazobactam. As a result of a low rate of failures (<11%) observed in the trial and the low MICs for infecting pathogens, no association could be established between clinical/microbiological outcome and drug exposure.

CONCLUSIONS

Intermittent infusion and continuous infusion of piperacillin and tazobactam provided sufficient drug exposure to treat those pathogens commonly implicated in intra-abdominal infections.

Trends in antimicrobial susceptibilities among bacterial pathogens isolated from patients hospitalized in European medical centers: 6-year report of the MYSTIC Surveillance Study (1997-2002)

The Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program provides antimicrobial susceptibility data. The activity of meropenem and 7 broad-spectrum antimicrobials have been examined against 12645 bacterial isolates from 14 European centers between 1997 and 2002. Cumulative susceptibility rates against all species of Enterobacteriaceae combined were ranked as follows: meropenem (99.9%) > imipenem (97.7%) > ciprofloxacin (86.0%) > piperacillin-tazobactam (85.6%) > ceftazidime (85.4%) > gentamicin (85.4%) > tobramycin (85.0%) > cefotaxime (83.8%). The carbapenems were also found to be the most active of the classes tested against nonfermentative Gram-negative bacilli. Against methicillin-susceptible Staphylococcus aureus and coagulase-negative staphylococci, all beta-lactams tested (except ceftazidime) had susceptibility rates of > or = 99.0% and > or = 94.3%, respectively. Over the 6-year period, there was no loss of activity or increase in resistance rate for either carbapenem against any of the species tested. These data confirm the continued potency and broad-spectrum activity of meropenem in units where it is actively being prescribed.

Simulation of Antibiotic Pharmacodynamic Exposure for the Empiric Treatment of Nosocomial Bloodstream Infections: A Report from the OPTAMA Program

OBJECTIVE

We developed a model to predict the pharmacodynamic exposure of antibiotics against bacteria commonly implicated in nosocomial bloodstream infections to determine which dosage regimens would provide the greatest likelihood of obtaining a bactericidal effect.

METHODS

Pharmacodynamic exposures were simulated for 5000 subjects receiving standard doses of ceftazidime, cefepime, piperacillin/tazobactam, meropenem, imipenem, or ciprofloxacin. Exposures were indexed to the MICs of bacteria weighted by their prevalence in causing nosocomial bloodstream infections, derived from 2002 SENTRY data. Enterococci were excluded. MIC data were derived from the 2003 Meropenem Yearly Surveillance Test Information Collection resistance study. The probabilities of achieving bactericidal exposures (ie, target attainment) for each antibiotic regimen were compared. The effect of increasing prevalence of methicillin-resistant Staphylococcus aureus (MRSA) on attainment of bactericidal targets was tested.

RESULTS

All dosage regimens except ciprofloxacin and ceftazidime 1 g q8h achieved >90% likelihood of bactericidal exposure. The rank order of target attainment was as follows: imipenem 500 mg q6h, 100.0%; imipenem 1 g q8h, 99.9%; cefepime 2 g q12h, 99.4%; meropenem 1 g q8h, 98.4%; cefepime 1 g q12h, 98.2%; piperacillin/tazobactam 3.375 g q6h, 97.9%; piperacillin/tazobactam 4.5 gq8h, 95.0%; ceftazidime 2 g q8h, 94.2%; ceftazidime 1 g q8h, 71.7%; ciprofloxacin 400 mg q8h, 63.3%; and ciprofloxacin 400 mg q12h,63.0%. Target attainments dropped to <90% for all agents when MRSA was modeled at > or =10% prevalence.

CONCLUSIONS

The results of this model analysis suggest that standard doses of the carbapenems, piperacillin/tazobactam, and cefepime, and higher doses of ceftazidime, may provide optimal likelihood of achieving bactericidal exposure against pathogens implicated in nosocomial bloodstream infections, excluding MRSA and enterococci. When MRSA rates are > or =10%, therapy with an antibiotic that has activity against this phenotype should be empirically initiated.

Ertapenem: review of a new carbapenem

The carbapenems are beta-lactam-type antibiotics with an exceptionally broad spectrum of activity. Ertapenem is a new carbapenem developed to address the pharmacokinetic shortcomings (short half-life) of imipenem and meropenem. Ertapenem shares similar structural features with meropenem, including its stability to dehydropeptidase-1, allowing it to be administered without a dehydropeptidase-1 inhibitor. Ertapenem, like imipenem and meropenem, demonstrates broad-spectrum antimicrobial activity against many Gram-positive and -negative aerobes and anaerobes and is resistant to nearly all beta-lactamases, including extended-spectrum beta-lactamases and AmpCs. However, it differs from both imipenem and meropenem in demonstrating limited activity against Enterococcusspp., Pseudomonasaeruginosa and other nonfermentative Gram-negative bacteria commonly associated with nosocomial infections. The extensive protein binding of ertapenem extends the half-life and allows for once-daily dosing. Prospective, multicenter, randomized, double-blind, comparative clinical studies demonstrate similar clinical efficacy of ertapenem compared with other agents. Clinical trials of complicated intra-abdominal infection, acute pelvic infection, complicated skin and soft-structure infection, community-acquired pneumonia and complicated urinary tract infections demonstrated that ertapenem has equivalent efficacy and safety compared with ceftriaxone and piperacillin/tazobactam. Ertapenem is a promising new carbapenem with excellent efficacy and safety for the treatment of a variety of community-acquired infections. It also appears to be of great value as an outpatient parenteral antimicrobial therapy.

In vitro and in vivo activities of novel 6-methylidene penems as beta-lactamase inhibitors

Novel penem molecules with heterocycle substitutions at the 6 position via a methylidene linkage were investigated for their activities and efficacy as beta-lactamase inhibitors. The concentrations of these molecules that resulted in 50% inhibition of enzyme activity were 0.4 to 3.1 nM for the TEM-1 enzyme, 7.8 to 72 nM for Imi-1, 1.5 to 4.8 nM for AmpC, and 14 to 260 nM for a CcrA metalloenzyme. All the inhibitors were more stable than imipenem against hydrolysis by hog and human dehydropeptidases. Piperacillin was combined with a constant 4-microg/ml concentration of each inhibitor for MIC determinations. The combinations reduced piperacillin MICs by 2- to 32-fold for extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae strains. The MICs for piperacillin-resistant (MIC of piperacillin, >64 microg/ml) strains of Enterobacter spp., Citrobacter spp., and Serratia spp. were reduced to the level of susceptibility (MIC of piperacillin, < or =16 microg/ml) when the drug was combined with 4, 2, or 1 microg of these penem inhibitors/ml. Protection against acute lethal bacterial infections with class A and C beta-lactamase- and ESBL-producing organisms in mice was also demonstrated with piperacillin plus inhibitor. Median effective doses were reduced by approximately two- to eightfold compared to those of piperacillin alone when the drug was combined with the various inhibitors at a 4:1 ratio. Pharmacokinetic analysis after intravenous administration of the various inhibitors showed mean residence times of 0.1 to 0.5 h, clearance rates of 15 to 81 ml/min/kg, and volumes of distribution between 0.4 and 2.5 liters/kg. The novel methylidene penem molecules inhibit both class A and class C enzymes and warrant further investigation for potential as therapeutic agents when used in combination with a beta-lactam antibiotic.

Pharmacokinetic Evaluation of Meropenem and Imipenem in Critically Ill Patients with Sepsis

OBJECTIVE

To evaluate and compare the pharmacokinetic profiles of imipenem and meropenem in a population of critically ill patients with sepsis to find possible differences that may help in selecting the most appropriate drug and/or dosage in order to optimise empiric antimicrobial therapy.

PATIENTS AND METHODS

This was a single-centre, randomised, nonblind study of the pharmacokinetics of both intravenous imipenem 1g and meropenem 1g in 20 patients admitted to an intensive care unit with sepsis in whom antimicrobial therapy was indicated on clinical grounds. Patients were divided into two groups: group I received intravenous imipenem 1g plus cilastatin 1g, and group II received intravenous meropenem 1g over 30 minutes. Peripheral blood samples were collected at 0, 0.5 (end of infusion), 0.75, 1, 1.5, 2, 3, 4, 6 and 8 hours after the first dose and were centrifuged for 10 minutes at 4 masculineC. Urine samples were collected during the 8 hours after antimicrobial administration at 2-hour intervals: 0-2, 2-4, 4-6 and 6-8 hours. The total volume of urine was recorded; the serum and urine samples were immediately frozen and stored at -80 masculineC until assayed. Pharmacokinetic analysis was carried out through computerised programs using the least-square regression method and a two-compartment open model. Statistical differences were evaluated by means of one-way ANOVA.

RESULTS

The following pharmacokinetic differences between the two drugs were observed: the imipenem mean peak serum concentration was significantly higher than for meropenem (90.1 +/- 50.9 vs 46.6 +/- 14.6 mg/L, p < 0.01); the area under the serum concentration-time curve was significantly higher for imipenem than for meropenem (216.5 +/- 86.3 vs 99.5 +/- 23.9 mg . h/L, p < 0.01), while the mean volume of distribution and mean total clearance were significantly higher for meropenem than for imipenem (25 +/- 4.1 vs 17.4 +/- 4.5L, p < 0.01 and 191 +/- 52.2 vs 116.4 +/- 42.3 mL/min, p < 0.01, respectively).

CONCLUSION

The more favourable pharmacokinetic profile of imipenem compared with meropenem in critically ill patients with sepsis might balance the possibly greater potency demonstrated in vitro for meropenem against Gram-negative strains. Hence, the clinical efficacy of the two carbapenems depends mostly on their correct dosage.

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

BACKGROUND

Bacteria that produce extended-spectrum beta-lactamases (ESBLs) are resistant to penicillins,cephalosporins, and monobactams. The results of clinical studies suggest that the carbapenems imipenem and meropenem may be effective against bacteria that produce ESBLs, although it is not known whether the new once-daily carbapenem ertapenem or the fluoroquinolones are useful against infections caused by ESBL-producing bacteria.

OBJECTIVE

The present study compared the simulated pharmacodynamics of the carbapenems imipenem,meropenem, and ertapenem; the simulated pharmacodynamics of the fluoroquinolones levofloxacin, gatifloxacin, and ciprofloxacin with those of the carbapenems; and the simulated pharmacodynamics of levofloxacin 750 mg with those of levofloxacin 500 mg, all against gram-negative isolates that did and did not produce ESBLs

METHODS

Pharmacokinetic data were obtained from studies in healthy humans. Minimum inhibitory concentrationsMICs) for bacteria that did and did not produce ESBLs were determined in triplicate using broth-microdilution techniques as recommended by National Committee for Clinical Laboratory Standards guidelines. Monte Carlo simulation was used to construct pharmacodynamic models for imipenem, meropenem, ertapenem, levofloxacin, gatifloxacin, and ciprofloxacin. Pharmacodynamic measures of interest were the probability of the free concentration remaining above the MIC >-40% of the time (T>MIC > or =40%) for carbapenems and the likelihood of achieving a free AUC:MIC ratio > or =125 for fluoroquinolones.

RESULTS

MICs were determined for 39 isolates that produced ESBLs and 45 isolates that did not Bacteria that did not produce ESBLs were > or =93% susceptible to all carbapenems and fluoroquinolones tested. Among bacteria that produced ESBLs, rates of susceptibility to the specific agents were as follows: imipenem, 100%; meropenem, 97%; ertapenem, 87%; levofloxacin, 54%; gatifloxacin, 44%; and ciprofloxacin, 36%. In the pharmacodynamic models, imipenem and meropenem had an equal likelihood of achieving a free T>MIC > or =40% against bacteria that produced ESBLs (> or =97%) and bacteria that did not produce ESBLs (> or =98%). In contrast, the likelihood of ertapenem achieving a free T>MIC > or =40% was lower against bacteria that produced ESBLs (78%) than against bacteria that did not produce ESBLs (94%). Similarly, the fluoroquinolones were less likely to achieve a free AUC:MIC ratio > or =125 against bacteria that produced ESBLs (2%-13%) than against bacteria that did not produce ESBLs (85%-91%).

CONCLUSIONS

Carbapenems had superior in vitro activity against bacteria that produced ESBLs compared with fluoroquinolones. Pharmacodynamic modeling based on local ESBL-producing isolates and pharmacokinetic data from healthy humans indicated that imipenem and meropenem may have a greater likelihood of achieving pharmacodynamic targets against bacteria that produce ESBLs than ertapenem or fluoroquinolones.

Antimicrobial resistance rates and clonality results from the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) programme: report of year five (2003)

The U.S. Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Programme in the fifth year continues to monitor the spectrum of activity and potency of meropenem within medical centers where carbapenems are used for the treatment of serious infections. The antimicrobial activity of 11 broad-spectrum agents (including initial comparisons for levofloxacin) was assessed against 2,848 isolates in 2003. The minimum inhibitory concentration (MIC) results demonstrate the continued high potency of meropenem against all monitored pathogens. Against all Gram-negative bacilli tested, the overall rank order of susceptibility was meropenem (96.3%) > imipenem (95.6%) > cefepime (93.7%) > tobramycin (91.9%) > piperacillin/tazobactam (90.2%) > ceftazidime (90.1%) > gentamicin (89.6%) > levofloxacin (82.8%) > ciprofloxacin (82.5%) > aztreonam (81.8%) > ceftriaxone (72.3%). Clonal-based resistances were observed that adversely influenced carbapenem resistance rates, particularly among Klebsiella spp. and Acinetobacter baumannii isolates. Continued surveillance of the carbapenem class and other broad-spectrum agents is warranted to monitor activity against pathogens causing serious infections in hospitalized patients.

Optimizing pharmacodynamic target attainment using the MYSTIC antibiogram: data collected in North America in 2002

The OPTAMA Program is intended to examine typical antimicrobial regimens used in the treatment of common nosocomial pathogens and the likelihood of these regimens attaining appropriate pharmacodynamic exposure in different parts of the world. A 5,000-subject Monte Carlo simulation was used to estimate pharmacodynamic target attainment for meropenem, imipenem, ceftazidime, cefepime, piperacillin-tazobactam, and ciprofloxacin against Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa. Standard dosing regimens from North America were used. Pharmacokinetic parameter variability was derived from existing healthy volunteer data, and MIC data came from the 2002 MYSTIC Program. Ciprofloxacin displayed the lowest target attainment against all bacterial species (41 to 46% for A. baumannii, 53 to 59% for P. aeruginosa, and 80 to 85% for the Enterobacteriaceae). Increasing the dose to 400 mg every 8 h did not significantly increase target attainment against nonfermenters. Piperacillin-tazobactam target attainments were similar to that of ceftazidime against all pathogens. Higher doses of both compounds were needed to achieve better target attainments against P. aeruginosa. Overall, meropenem, imipenem, and cefepime attained the highest probabilities of attainment against the Enterobacteriaceae (99 to 100%). The carbapenems appear to be the most useful agents against A. baumannii (88 to 92%), and these agents, along with higher doses of any of the beta-lactams, would be the most appropriate choices for empirical therapy for P. aeruginosa infection. Given the lack of agreement between percent susceptibility and probability of target attainment for certain antimicrobial regimens, a methodology employing stochastic pharmacodynamic analyses may be a more useful tool for differentiating the most-optimal compounds and dosing regimens in the clinical setting of initial empirical therapy.

Antibacterial agents in pediatrics

Antibiotics are among the most widely prescribed therapeutic agents in children. Several new trends in antibiotic usage for pediatric care have emerged. New mechanisms of antibacterial resistance have required a broader repertoire of antibiotic usage, including new agents directed at multidrug resistance. After promotion of judicious antibiotic use, there has been a decline in the number of pediatric prescriptions for antibiotics. Recent legislation addresses the necessity for pediatric clinical drug trials, ensuring development of further antibacterial agents for use in pediatric patients.

Pharmacodynamic comparisons of antimicrobials against nosocomial isolates of escherichia coli, klebsiella pneumoniae, acinetobacter baumannii and pseudomonas aeruginosa from the MYSTIC surveillance program: the OPTAMA Program, South America 2002

The OPTAMA (Optimizing Pharmacodynamic Target Attainment using the MYSTIC [Meropenem Yearly Susceptibility Test Information Collection] Antibiogram) Program provides insight into the appropriate antibiotic options for empiric therapy for common nosocomial pathogens. In this report, South America is represented by Brazil, Colombia, Peru, and Venezuela. A 5000-subject Monte Carlo Simulation estimated pharmacodynamic target attainment for meropenem, imipenem, ceftazidime, cefepime, piperacillin/tazobactam, and ciprofloxacin against Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa. Pharmacokinetic parameter variability was derived from existing healthy volunteer data, and minimum inhibitory concentration (MIC) data came from the 2002 MYSTIC program. Piperacillin/tazobactam and ciprofloxacin displayed the lowest target attainment against all bacterial species (14% to 24% for A. baumannii, 26% to 37% for P. aeruginosa, and 48% to 66% for the Enterobacteriaceae). Overall, the carbapenems had the highest probabilities of attainment against the Enterobacteriaceae (98% to 100%) and A. baumannii (73% to 74%), whereas cefepime obtained the greatest target attainment against P. aeruginosa (65%). Because no single regimen had high target attainment against A. baumannii and P. aeruginosa, the use of combination therapy to treat these pathogens in South America may be justified. Because of the lack of agreement with percent susceptibility for certain antimicrobial regimens, the use of pharmacodynamic target attainment may be a more accurate predictor of microbiologic success.

Optimizing antimicrobial pharmacodynamics: dosage strategies for meropenem

INTRODUCTION

Carbapenems are broad-spectrum antibiotics that are often employed as the last line of therapy for patients with nonresponsive nosocomial infections. Consideration of pharmacodynamic principles in dosage regimens for these agents can maximize their antibacterial effectiveness and reduce the number of bacterial strains that survive to mutate or continue infection.

OBJECTIVE

The objectives of this review were to highlight examples of the application of pharmacodynamics to the carbapenems (particularly meropenem) and to comment on clinical utility of these dosage regimens.

METHODS

Relevant information was identified through a MEDLINE search of the literature (1980-present) using the terms carbapenem, pharmacodynamic, pharmacokinetic, pharmacoeconomic, meropenem, imipenem, ertapenem, biapenem, and panipenem. Additionally, meeting posters were identified from the International Conference of Antimicrobial Agents and Chemotherapy (years 2001-2003) and the International Conference of the American Thoracic Society (years 2002-2003). All studies demonstrating the pharmacodynamics of the carbapenems by incorporating changes in dosage strategies were included.

RESULTS

Only relevant data for meropenem were identified in our literature search. The dosage scheme for meropenem may be modified to maximize the percentage of the dosage interval that drug concentrations remain above the minimum inhibitory concentration, an important parameter related to the bacterial kill rate. Only relevant data for meropenem were identified in our literature search. Human volunteer and Monte Carlo simulation studies suggested that in the treatment of susceptible pathogens, higher meropenem doses, increased frequency of administration, or prolonged duration of infusion resulted in improved pharmacodynamics.

CONCLUSION

When proper pharmacodynamic principles are applied to dosage strategies for meropenem, clinical and microbiological outcomes can be optimized.

Alternative and/or integrative therapies for pneumonia under development

PURPOSE OF REVIEW

Increasing antimicrobial resistance among common respiratory bacteria has created challenges in selecting appropriate therapy for pneumonia. Fortunately, the analysis of genome sequences has allowed us to find novel, nontraditional targets that are involved in disease pathogenesis or in adaptation and growth in infection sites. The advantage of the nonclassical targets is that targeting these sites could ablate infection without inducing resistance. Interfering with bacterial adhesion, inhibiting, neutralizing and clearing endotoxin, and administering cytokines as immunoadjuvants are the most promising alternative or integrative treatments for pneumonia that are under development.

RECENT FINDINGS

Interference with bacterial adhesion is possible using inhibitors of sortase or inactivators of the srtA gene against gram-positive bacteria, inhibitors of the periplasmic chaperone or those of usher function against gram-negative bacteria, novel polysaccharides that are present on echinoderm surfaces, antiadhesin vaccines, or the passive administration of antiadhesin antibodies. Inhibition, neutralization, and clearance of endotoxin possibly interferes in the lipid A biosynthetic pathway or using lipid A analogues with reduced or lack of ability to activate the major endotoxin receptors or proteins such as recombinant Limulus antilipopolysaccharide factor, bactericidal/permeability increasing protein, or lipopolysaccharide binding protein. Tumor necrosis factor 70-80, an adenoviral vector that encodes murine tumor necrosis factor alpha, and recombinant interferon gamma seem to be the most promising cytokines for use as immunoadjuvants for the treatment of pneumonia.

SUMMARY

Ideally, potential treatment of life-threatening bacterial pneumonia will combine immunoadjuvant and conventional antibiotic therapy. Compounds capable of stimulating early host defense and microbial clearance, but not the later phases of inflammatory tissue injury associated with sepsis, may be advantageous.

Pharmacodynamics of Meropenem and Imipenem Against Enterobacteriaceae,Acinetobacter baumannii, andPseudomonas aeruginosa

STUDY OBJECTIVE

To compare the pharmacodynamics of meropenem and imipenem, both administered as 500 mg every 6 hours, against populations of Enterobacteriaceae, Acinetobacter baumannii, and Pseudomonas aeruginosa.

DESIGN

Ten thousand-subject Monte Carlo simulation.

INTERVENTION

Variability in total body clearance (ClT), volume of distribution as calculated by the terminal elimination rate (Vdbeta), and minimum inhibitory concentration (MIC) distributions (Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Serratia marcescens, A. baumannii, P. aeruginosa) were derived from the literature for both meropenem and imipenem. For the free drug concentrations, the percentage of the dosing interval that the drug concentrations remain above the MIC (%T>MIC) for each carbapenem-bacteria combination was calculated for 10,000 iterations, substituting a different ClT, Vdbeta, fraction of unbound drug, and MIC into the equation each time based on the probability distribution for each parameter. Probabilities of attaining targets of 30%, 50%, and 100% T>MIC were calculated.

MEASUREMENTS AND MAIN RESULTS

Meropenem free drug %T>MIC exposure was significantly greater than that of imipenem against Enterobacteriaceae and P. aeruginosa, whereas imipenem exposure was greater for A. baumannii. For both agents, free drug %T>MIC exposure was greatest against Enterobacteriaceae and less for A. baumannii and P. aeruginosa. Probabilities of target attainment for 30% and 50% T>MIC were similar between drugs for most bacteria. At 100% T>MIC, meropenem target attainments were greater than those of imipenem against Enterobacteriaceae and P. aeruginosa, and imipenem attainment was higher for A. baumannii.

CONCLUSION

The probability of attaining lower pharmacodynamic targets for most gram-negative bacteria is similar for these carbapenems; however, differences become apparent as the pharmacodynamic requirement increases. Further study of the benefits of achieving this pharmacodynamic breakpoint with a higher probability of attaining targets is necessary.