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Meropenem is a broad spectrum carbapenem used for the treatment of cerebral infections. There is a need for data describing meropenem pharmacokinetics (PK) in the brain tissue to optimize therapy in these infections. Here, we present a meropenem PK model in the central nervous system and simulate dosing regimens. This was a population PK analysis of a previously published prospective study of patients admitted to the neurointesive care unit between 2016 and 2019 who received 2 g of meropenem intravenously every 8 h. Meropenem concentration was determined in blood, cerebrospinal fluid (CSF), and brain microdialysate. Meropenem was described by a six-compartment model: two compartments in the blood, two in the CSF, and two in the brain tissue. Creatinine clearance and brain glucose were included as covariates. The median elimination rate constant was 1.26 h -1 , the central plasma volume was 5.38 L, and the transfer rate constants from the blood to the CSF and from the blood to the brain were 0.001 h -1 and 0.02 h -1 , respectively. In the first 24 h, meropenem 2 g, administered every 8 h via intermittent and extended infusions achieved good target attainment in the CSF and brain, but continuous infusion (CI) was better at steady-state. Administering a 3 g loading dose (LD) followed by 8 g CI was beneficial for early target attainment. In conclusion, a meropenem PK model was developed using blood, CSF, and brain microdialysate samples. An 8 g CI may be needed for good target attainment in the CSF and brain. Giving a LD prior to the CI improved the probability of early target attainment.

Purpose: The aim of this prospective cohort study was to evaluate the therapeutic target attainment of 3-hour extended infusion of meropenem in patients with septic burns in the early and late periods of septic shock., Methods: Meropenem serum levels were determined by liquid chromatography from blood samples collected within 48 hours (early period) of therapy and 10 to 14 days afterward (late period). Pharmacokinetic properties were investigated by noncompartmental analysis, and the therapeutic target was defined as 100% of the time above the MIC (100%fT> MIC)., Findings: Fifteen patients with 90 measured meropenem concentrations were included. Throughout the entire course of antimicrobial therapy, the therapeutic target was attained against gram-negative pathogens with an MIC ≤ 2 mg/L. Pathogens with intermediate susceptibility to meropenem were only covered in the early phase of therapy., Implications: Higher-dose regimens or continuous infusions may be necessary to guarantee antimicrobial coverage of meropenem against less sensitive pathogens in patients with septic burns., Competing Interests: Declaration of Interest The authors have indicated that they have no conflicts of interest regarding the content of this article., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Introduction: Meropenem/vaborbactam (M/V) represents the first carbapenem and β-lactamase inhibitor combination approved for treatment of complicated urinary tract infections (cUTIs), including pyelonephritis. Vaborbactam is a novel boronic acid, β-lactamase inhibitor with a high affinity for serine β-lactamases, including Klebsiella pneumoniae carbapenemase (KPC). This combination, Vabomere™, was approved in August 2017 by the United States Food and Drug Administration for the treatment of cUTIs in patients 18 years or older, including pyelonephritis, caused by the following susceptible microorganisms: Escherichia coli, K. pneumoniae, and Enterobacter cloacae species complex. Areas covered: Relevant literature regarding microbiology, pharmacokinetics, pharmacodynamics, and clinical trials evaluating efficacy, safety, and tolerability will be discussed. Expert opinion: Current treatment options for KPC-producing infections such as aminoglycosides, polymyxins, fosfomycin, and tigecycline are associated with concerns regarding efficacy, toxicities, optimal dosing, and/or development of resistance. Additionally, resistance to the new combination product of ceftazidime/avibactam has also emerged. Current clinical evidence supporting the use of M/V for KPC-producing infections is limited to an open-label, randomized, phase III study in a small number of patients with serious infections due to carbapenem-resistant Enterobacteriaceae. Although M/V is not approved for KPC-producing infections, we believe that M/V will become a preferred agent for KPC-producing Enterobacteriaceae infections.

Meropenem exposures from 15 children (8-17 years old) with cystic fibrosis (CF) acute pulmonary exacerbation were analyzed to define the pharmacodynamic threshold required for a positive response. The primary endpoint was the relative increase in forced expiratory volume in 1 s (↑FEV 1 ) between pre- and posttreatment. Meropenem pharmacodynamic indices (fT > MIC, fAUC/MIC, fC min /MIC) over the first 24 h were estimated for each participant based on their individual parameter estimates and the isolated pathogen with the highest meropenem MIC. Pseudomonas aeruginosa was the most common pathogen (n = 11/15). The mean ± SD ↑FEV 1 was 18.8% ± 11.3% posttreatment. The mean (range) fT > MIC exposure was 63% (0-100%). An E max model determined a significant relationship between fT > MIC and ↑FEV 1 (r 2 = 0.8, P < 0.0004). 65% fT > MIC was a significant predictor of response; the median (25th, 75th %) ↑FEV 1 was 28.5% (22.2%, 31.7%) in those patients who achieved above 65% fT > MIC and 7.8% (1.1%, 12.6%) in those at or below 65% fT > MIC (P = 0.001). This is the first study in CF children to link meropenem exposure with a positive response as measured by ↑FEV 1 . Larger studies are required to confirm this exposure threshold., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Introduction: The use of antibiotics is mandatory in patients during extracorporeal membrane oxygenation (ECMO) support. Clinical studies have shown high variability in the antibiotic concentrations, as well as sequestration of them by the ECMO circuit, suggesting that the doses and/or interval administration used during ECMO may not be adequate. Thus, a fast response sensor to estimate antibiotic concentrations in this setting would contribute to improve dose adjustments. The biosensor PenP has been shown to have a dynamic range, sensitivity and specificity useful for pharmacokinetic (PK) tests in healthy subjects. However, the use of this biosensor in the context of a complex critical condition, such as ECMO during acute respiratory distress syndrome (ARDS), has not been tested., Objectives: To describe, by using PenP Biosensor, the pharmacokinetic of meropenem in a 24-h animal ARDS/ECMO model., Methods: The PK of meropenem was evaluated in a swine model before and during ECMO., Results: The PK parameters such as maximum concentration (Cmax), elimination rate constant (Ke), and cleareance (Cl), were not significantly altered during ECMO support., Conclusions: (a) ECMO does not affect the PK of meropenem, at least during the first 24 h; and (b) PenP has the potential to become an effective tool for making medical decisions associated with the dose model of antibiotics in a critical patient context.

In older adults, few studies confirm that adequate concentrations of antibiotics are achieved using current dosage regimens of intravenous β-lactam antibiotics. Our objective was to investigate trough concentrations of cefotaxime, meropenem, and piperacillin in older adults hospitalized with infection. We included 102 patients above 70 years of age. Total trough antibiotic concentrations were measured and related to suggested target intervals. Information on antibiotic dose, patient characteristics, and 28-day outcomes were collected from medical records and regression models were fitted. Trough concentrations for all three antibiotics exhibited considerable variation. Mean total trough concentrations for cefotaxime, meropenem, and piperacillin were 6.5 mg/L (range 0-44), 3.4 mg/L (range 0-11), and 30.2 mg/L (range 1.2-131), respectively. When a target range of non-species-related breakpoint - 5× non-species-related breakpoint was applied, only 36% of patients had both values within the target range. Regression models revealed that severe sepsis was associated with varying concentration levels and increasing age and diminishing kidney function with high concentration levels. The study was not powered to demonstrate consequences in clinical outcomes. Conclusively, in older adults treated with cefotaxime, meropenem, or piperacillin-tazobactam, trough antibiotic concentrations varied considerably. Better predictors to guide dosing regimens of β-lactam antibiotics or increased use of therapeutic drug monitoring are potential ways to address such variations.

This study was conducted to identify optimal dosage regimens and estimate pharmacokinetic/pharmacodynamic (PK/PD) characteristics of short-infusion (SI) versus extended-infusion (EI) biapenem against Pseudomonas aeruginosa infections in Chinese intensive care unit (ICU) patients. A total of 85 strains of P. aeruginosa were collected, and the minimum inhibitory concentration (MIC) of biapenem was measured by the serial two-fold agar dilution method. We designed four frequently used clinical regimens: biapenem 300 mg I.V. q12h, q8h, and q6h, and 600 mg q12h. The Monte Carlo Simulation (MCS) was performed using previously published pharmacokinetic data to calculate the probability of target attainment (PTA) and the cumulative fraction of response (CFR) of these regimens as an SI (0.5 h) and an EI (1 h, 2 h, 3 h, and 4 h). For a target of 40%fT >MIC (serum drug concentration remains above the MIC for a dosing period), none of the regimens achieved any CFRs>90% for P. aeruginosa, multidrug-resistant P. aeruginosa (MDR-PA) and even non-MDR-PA. The traditional biapenem SI regimens most commonly seen in clinical practice were insufficient in treating both MDR and non-MDR P. aeruginosa in ICU patients. However, biapenem 600 mg q12h over 2-4 h EI regimens could achieve CFR>90% with 20%fT >MIC . Clinical trials should aim to validate the potentially greater PK/PD index with higher, more frequent doses and longer extended infusions., (Copyright © 2017. Published by Elsevier B.V.)

Background and Objective: For patients with intracranial infection, local intrathecal administration of meropenem may be a useful method to obtain a sufficient drug concentration in the cerebral spinal fluid (CSF). However, a large inter-individual variability may pose treatment efficacy at risk. This study aimed to identify factors affecting drug concentration in the CSF using population pharmacokinetics method., Methods: After craniotomy, aneurysm patients with an indwelling lumbar cistern drainage tube who received a combined intravenous and intrathecal administration of meropenem for the treatment of suspected intracranial infection were enrolled. Venous blood and CSF specimens were collected for determining meropenem concentrations. Nonlinear mixed-effects modeling method was used to fit blood and CSF concentrations simultaneously and to develop the population pharmacokinetic model. The proposed model was applied to simulate dosage regimens., Results: A three-compartmental model was established to describe meropenem in vivo behavior. Lumbar CSF drainage resulted in a drug loss, and drug clearance in CSF (CL CSF ) was employed to describe this. The covariate analysis found that the drainage volume (mL/day) was strongly associated with CL CSF , and the effect of creatinine clearance was significant on the clearance of meropenem in blood (CL). Visual predictive check suggested that the proposed pharmacokinetic model agreed well with the observations. Simulation showed that both intravenous and intrathecal doses should be increased with the increases of minimum inhibitory concentration and daily CSF drainage volume., Conclusion: This model incorporates covariates of the creatinine clearance and the drainage volume, and a simple to use dosage regimen table was created to guide clinicians with meropenem dosing.

The purpose of this study was to estimate the in vivo pharmacokinetics of meropenem during intermittent-infusion hemodiafiltration (I-HDF) and clarify its optimal dosage and dosing interval in patients receiving I-HDF. The clearance of meropenem by online hemodiafiltration (OL-HDF) and I-HDF was predicted using an in vitro system and assessed to establish whether the results obtained are applicable to clinical cases. In the in vivo study, the mean volume of distribution (Vd), non-I-HDF clearance (CL non-I-HDF ), and I-HDF clearance (CL I-HDF ) were 15.80 ± 3.59 l, 1.05 ± 0.27 l/h, and 5.78 ± 1.03 l/h. Dosing regimens of 0.25 g once daily for a MIC of 8 μg/ml and of 0.5 g once daily for a MIC of 16 μg/ml achieved 40% T > MIC. In the in vitro and in vivo studies, observed CL HDF was similar to predictive CL HDF (= C f /C p  × (Q D  + Q SUB )). In conclusion, adjustments to the dose and interval of meropenem were developed based on the presumed susceptibility of pathogens to meropenem in patients receiving I-HDF. We suggest 0.5 g once daily as an appropriate regimen for empirical treatment., (Copyright © 2017 Japanese Society of Chemotherapy and The Japanese Association for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.)

Background: The aim of the study was to describe the population pharmacokinetics (PK) of meropenem in critically ill patients receiving sustained low-efficiency dialysis (SLED)., Methods: Prospective population PK study on 19 septic patients treated with meropenem and receiving SLED for acute kidney injury. Serial blood samples for determination of meropenem concentrations were taken before, during and after SLED in up to three sessions per patient. Nonparametric population PK analysis with Monte Carlo simulations were used. Pharmacodynamic (PD) targets of 40% and 100% time above the minimal inhibitory concentration (f T > MIC ) were used for probability of target attainment (PTA) and fractional target attainment (FTA) against Pseudomonas aeruginosa., Results: A two-compartment linear population PK model was most appropriate with residual diuresis supported as significant covariate affecting meropenem clearance. In patients without residual diuresis the PTA for both targets (40% and 100% f T > MIC ) and susceptible P. aeruginosa (MIC ≤ 2 mg/L) was > 95% for a dose of 0.5 g 8-hourly. In patients with a residual diuresis of 300 mL/d 1 g 12-hourly and 2 g 8-hourly would be required to achieve a PTA of > 95% and 93% for targets of 40% f T > MIC and 100% f T > MIC , respectively. A dose of 2 g 8-hourly would be able to achieve a FTA of 97% for 100% f T > MIC in patients with residual diuresis., Conclusions: We found a relevant PK variability for meropenem in patients on SLED, which was significantly influenced by the degree of residual diuresis. As a result dosing recommendations for meropenem in patients on SLED to achieve adequate PD targets greatly vary. Therapeutic drug monitoring may help to further optimise individual dosing., Trial Registration: Clincialtrials.gov, NCT02287493 .

This case series explored the pharmacokinetic/pharmacodynamic (PK/PD) characteristics of meropenem (MEM) in adult cystic fibrosis (CF) patients hospitalized for a pulmonary exacerbation. From January 2015 to June 2016, all adult patients with cystic fibrosis (CF) and chronic pulmonary infection due to meropenem (MEM)-susceptible/intermediate Pseudomonas aeruginosa who received at least 48 h of MEM as an extended 3-hour infusion for treating a pulmonary exacerbation were enrolled. MEM plasma concentrations were determined by high-performance liquid chromatography. Six adult CF patients with a median age of 47 years were included in the study. MEM showed a high Vd (mean 45.98 L, standard deviation [SD] ±34.45). A minimal PK/PD target of 40% T > minimum inhibitory concentration (MIC) with respect to the MEM MIC of P. aeruginosa strains isolated from sputum during exacerbation was achieved in 5/6 patients (83%). MEM failed to achieve this target only in one patient, whose strain showed the highest MEM MIC in our cohort (8 mg/L). In all patients, MEM was well tolerated, and no adverse events were reported. In conclusion, high-dose, extended-infusion MEM during pulmonary exacerbation showed a high Vd in six adult CF patients with high median age, and was well tolerated.

Objectives: To use a population pharmacokinetic approach to define maximally effective meropenem dosing recommendations for treatment of Acinetobacter baumannii and Pseudomonas aeruginosa infections in a large cohort of patients with septic shock., Methods: Adult patients with septic shock and conserved renal function, treated with meropenem, were eligible for inclusion. Seven blood samples were collected during a single dosing interval and meropenem concentrations were measured by a validated HPLC-MS/MS method. Monte Carlo simulations were employed to define optimum dosing regimens for treatment of empirical or targeted therapy of A. baumannii and P. aeruginosa. EudraCT-no. 2014-002555-26 and NCT02240277., Results: Fifty patients were included, 26 male and 24 female, with a median age of 64 years with an all-cause 90 day mortality of 34%. A two-compartment linear model including creatinine clearance (CLCR) as a covariate best described meropenem pharmacokinetics. For empirical treatment of A. baumannii, 2000 mg/6 h was required by intermittent (30 min) or prolonged (3 h) infusion, whereas 6000 mg/day was required with continuous infusion. For P. aeruginosa, 2000 mg/8 h or 1000 mg/6 h was required for both empirical and targeted treatment. In patients with a CLCR of ≤ 100 mL/min, successful concentration targets could be reached with intermittent dosing of 1000 mg/8 h., Conclusions: In patients with septic shock and possible augmented renal clearance, doses should be increased and/or administration should be performed by prolonged or continuous infusion to increase the likelihood of achieving therapeutic drug concentrations. In patients with normal renal function, however, standard dosing seems to be sufficient., (© The Author 2017. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Background: Acinetobacter baumannii(ACBN) is a MDR organism causing pneumonia in ventilated patients. High MICs often result in insufficient lung exposures, thus poor outcomes have been observed with parenteral antimicrobials. Amikacin Inhale(AMK-I), is a drug-device combination of amikacin and a Pulmonary Drug Delivery System device. We aimed to describe the pharmacodynamic profile of human simulated epithelial lining fluid(ELF) exposures of AMK-I and intravenous meropenem alone and in combination against ACBN with variable susceptibility profiles., Methods: AMK-I ELF exposures and the ELF profile of meropenem achieved after intravenous administration were evaluated in an in vitro pharmacodynamic model. Nine ACBN with amikacin/meropenem MICs of 2-512/2 to >64 mg/L were utilized. MICs were repeated post exposure to assess the development of resistance., Results: AMK-I monotherapy rapidly achieved and sustained bactericidal activity for isolates with amikacin MIC ≤128 mg/L. For isolates with MICs of 256 and 512 mg/L initial reductions in bacterial density were observed followed by regrowth. The combination produced similar bactericidal activity against ACBN with amikacin MICs of ≤128. While the combination regimen produced initial reductions and prolonged the duration of activity against organisms with MICs of 256 and 512 mg/L, regrowth and MIC elevations were noted during the 72-h exposure period., Conclusion: The combination achieved rapid and sustained efficacy when amikacin MICs were ≤128 mg/L and prolonged the duration of activity compared to monotherapy for organisms with MICs 256 mg/L and 512 mg/L. These data support the utility of AMK-I as an adjunct for the treatment of pneumonia caused by A. baumannii with MICs above current susceptibility break-points.

Background: Nosocomial pneumonia (NP) is a frequent complication among patients with intracerebral hemorrhage (ICH). However, there are currently no pharmacokinetic (PK) and pharmacodynamic (PD) data to guide meropenem dosing in these patients., Objective: To investigate the PK/PD properties of meropenem in these patients and whether the usual dosing regimens of meropenem (2-hour infusion, 1 g, every 8 hours) was suitable., Methods: A total of 11 patients with a diagnosis of ICH complicated with NP were selected in the emergency internal medicine and treated with a 1-g/2-hours extended infusion model. The plasma concentrations of meropenem were determined by high-performance liquid chromatography. PK parameters were estimated by plasma concentration versus time profile using WinNonlin software. The probability of target attainments (PTAs) of meropenem at different minimum inhibitory concentrations (MICs) based on percentage time that concentrations were above the minimum inhibitory concentration (%T>MIC) value were performed by Monte Carlo simulation., Results: The volume of distribution and total body clearance of meropenem were 55.55 L/kg and 22.89 L/h, respectively. Using 40%T>MIC, PTA was >90% at MICs ≤4 µg/mL. Using 80% or 100%T>MIC, PTA was >90% only at MICs ≤1 µg/mL., Conclusions: The PK/PD profile of dosing regimens tested will assist in selecting the appropriate meropenem regimens for these patients. At a target of 40%T>MIC, the usual dosing regimens can provide good coverage for pathogens with MICs of ≤4 µg/mL. However, when a higher target (80% or 100%) is desired for difficult-to-treat infections, larger doses, prolonged infusions, shorter intervals, and/or combination therapy may be required.

Cefiderocol (S-649266) is a novel siderophore cephalosporin with potent in vitro activity against clinically encountered multidrug-resistant (MDR) Gram-negative isolates; however, its spectrum of antibacterial activity against these difficult-to-treat isolates remains to be fully explored in vivo Here, we evaluated the efficacy of cefiderocol humanized exposures in a neutropenic murine thigh model to support a suitable MIC breakpoint. Furthermore, we compared cefiderocol's efficacy with humanized exposures of meropenem and cefepime against a subset of these phenotypically diverse isolates. Ninety-five Gram-negative isolates were studied. Efficacy was determined as the change in log 10 CFU at 24 h compared with 0-h controls. Bacterial stasis or ≥1 log reduction in 67 isolates with MICs of ≤4 μg/ml was noted in 77, 88, and 85% of Enterobacteriaceae , Acinetobacter baumannii , and Pseudomonas aeruginosa , respectively. For isolates with MICs of ≥8 μg/ml, bacterial stasis or ≥1 log 10 reduction was observed in only 2 of 28 (8 Enterobacteriaceae , 19 A. baumannii , and 1 P. aeruginosa ) strains. Against highly resistant meropenem and cefepime organisms, cefiderocol maintained its in vivo efficacy. Overall, humanized exposures of cefiderocol produced similar reductions in bacterial density for organisms with MICs of ≤4 μg/ml, whereas isolates with MICs of ≥8 μg/ml generally displayed bacterial growth in the presence of the compound. Data derived in the current study will assist with the delineation of MIC susceptibility breakpoints for cefiderocol against these important nosocomial Gram-negative pathogens; however, additional clinical data are required to substantiate these observations., (Copyright © 2017 American Society for Microbiology.)

On August 29, 2017, the United States Food and Drug Administration (FDA) approved meropenem/ vaborbactam fixed combination for the treatment of adults with complicated urinary tract infections (cUTI). The decision was based on substantial preclinical and clinical data, including two recent trials involving hundreds of adults with cUTI. Meropenem/ vaborbactam represents a powerful new treatment option to address antibiotic-resistant pathogens, including Klebsiella pneumoniae carbapenemase-producing bacteria. In this paper, we examine the work that led to FDA approval, with special emphasis on molecular pharmacology, pharmacokinetics, metabolism, efficacy and drug safety. We also look ahead, to explore how this promising new antimicrobial agent might be used in the near future to confront other drug-resistant infections.., (Copyright 2017 Clarivate Analytics.)

We assessed the population pharmacokinetics of high-dose continuous-infusion (HDCI) meropenem in a cohort of patients with Klebsiella pneumoniae carbapenemase (KPC)-producing Klebsiella pneumoniae (KPC-Kp) infections. Monte Carlo simulations were used to define the permissible HDCI meropenem regimens that could be safely considered for the treatment of KPC-Kp infections due to meropenem-resistant strains. Permissible doses were arbitrarily defined as those associated with a ≤10% to 15% likelihood of meropenem steady-state concentrations ( C ss ) of >100 mg/liter. Probabilities of target attainment (PTA) of four incremental pharmacodynamic determinants for meropenem efficacy (100% T >1×MIC , 100% T >2×MIC , 100% T >3×MIC , and 100% T >4×MIC , where "T >MIC " represents the time during which the plasma concentration of this time-dependent antibacterial agent is maintained above the MIC for the pathogen) in relation to different classes of renal function were calculated. The cumulative fractions of response (CFR) for the permissible HDCI meropenem regimens were calculated against the MIC distribution of the KPC-Kp clinical isolates that were collected routinely at our University Hospital between 2013 and 2016 ( n = 169). Ninety-seven meropenem C ss were included in the analysis. The final model included creatinine clearance (CrCL) as a covariate and explained 94% of the population variability. Monte Carlo simulations based on licensed dosages of up to 6 g/day predicted an acceptable PTA (>80%) of 100% T >1×MIC against KPC-Kp with a meropenem MIC of ≤32 mg/liter in patients with a CrCL level of <130 ml/min. Dosages of 8 g/day were needed for achieving the same target in patients with CrCL at levels of 130 to 200 ml/min. In dealing with pathogens with a meropenem MIC of 64 mg/liter, HDCI regimens using meropenem at higher than licensed levels should be considered. In these cases, real-time therapeutic drug monitoring could be a useful adjunct for optimized care. The predicted CFR were >75% in all of the classes of renal function., (Copyright © 2017 American Society for Microbiology.)

Antibiotics are often used in neonates despite the absence of relevant dosing information in drug labels. For neonatal dosing, clinicians must extrapolate data from studies for adults and older children, who have strikingly different physiologies. As a result, dosing extrapolation can lead to increased toxicity or efficacy failures in neonates. Driven by these differences and recent legislation mandating the study of drugs in children and neonates, an increasing number of pharmacokinetic studies of antibiotics are being performed in neonates. These studies have led to new dosing recommendations with particular consideration for neonate body size and maturation. Herein, we highlight the available pharmacokinetic data for commonly used systemic antibiotics in neonates.

Purpose: In critical burn patients, the pharmacokinetic parameters (absorption, distribution, metabolism, and excretion) of many classes of drugs, including antibiotics, are altered. The aim of this study was to compare 2 groups of burn patients undergoing treatment for health care-associated infections with and without therapeutic drug monitoring., Methods: A retrospective analysis of a clinical intervention (ie, a before/after study) was conducted with patients with health care-associated pneumonia, burn infection, bloodstream infection, and urinary tract infection in the burn intensive care unit of a tertiary care hospital. The patients were divided into 2 groups: (1) those admitted from May 2005 to October 2008 who received conventional antimicrobial dose regimens; and (2) those admitted from November 2008 to June 2011 who received antibiotics (imipenem, meropenem, piperacillin, and vancomycin) with doses adjusted according to plasma monitoring and pharmacokinetic modeling. General characteristics of the groups were analyzed, as were clinical outcomes and 14-day and in-hospital mortality., Findings: Sixty-three patients formed the conventional treatment group, and 77 comprised the monitored treatment group. The groups were homogeneous, median age was 31 years (range: 1-90) and 66% were male. Improvement occurred in 60% of the patients under monitored treatment (vs 52% with conventional treatment); 14-day mortality was 16% vs 14%; and the in-hospital mortality was similar between groups (39% vs 36%). In the final multivariate models, variables significantly associated with in-hospital mortality were total burn surface area ≥30%, older age, and male sex. Treatment group did not affect the prognosis., Implications: Therapeutic drug monitoring of antimicrobial treatment did not alter the prognosis of these burn patients. More trials are needed to support the use of therapeutic drug monitoring to optimize treatment in burn patients., (Copyright © 2017 Elsevier HS Journals, Inc. All rights reserved.)

Appropriate antibiotic dosing is critical to improve outcomes in critically ill patients with sepsis. The addition of continuous renal replacement therapy makes achieving appropriate antibiotic dosing more difficult. The lack of continuous renal replacement therapy standardization results in treatment variability between patients and may influence whether appropriate antibiotic exposure is achieved. The aim of this study was to determine if continuous renal replacement therapy effluent flow rate impacts attaining appropriate antibiotic concentrations when conventional continuous renal replacement therapy antibiotic doses were used. This study used Monte Carlo simulations to evaluate the effect of effluent flow rate variance on pharmacodynamic target attainment for cefepime, ceftazidime, levofloxacin, meropenem, piperacillin, and tazobactam. Published demographic and pharmacokinetic parameters for each antibiotic were used to develop a pharmacokinetic model. Monte Carlo simulations of 5000 patients were evaluated for each antibiotic dosing regimen at the extremes of Kidney Disease: Improving Global Outcomes guidelines recommended effluent flow rates (20 and 35 mL/kg/h). The probability of target attainment was calculated using antibiotic-specific pharmacodynamic targets assessed over the first 72 hours of therapy. Most conventional published antibiotic dosing recommendations, except for levofloxacin, reach acceptable probability of target attainment rates when effluent rates of 20 or 35 mL/kg/h are used., (Copyright © 2017 National Kidney Foundation, Inc. Published by Elsevier Inc. All rights reserved.)

Pseudomonas aeruginosa utilizes a plethora of substrate specific channels for the uptake of small nutrients. OccD3 (OpdP or PA4501) is an OprD-like arginine uptake channel of P. aeruginosa whose role has been implicated in carbapenem uptake. To understand the mechanism of selective permeation, we reconstituted single OccD3 channels in a planar lipid bilayer and characterized the interaction with Imipenem and Meropenem, analyzing the ion current fluctuation in the presence of substrates. We performed point mutations in the constriction region of OccD3 to understand the binding and translocation of antibiotic in OccD3. By mutating two key residues in the substrate binding sites of OccD3 (located in the internal loop L7 and basic ladder), we emphasize the importance of these residues. We show that carbapenem antibiotics follow a similar path as arginine through the constriction zone and the basic ladder to translocate across OccD3.

Background: The second-line drugs recommended to treat drug-resistant TB are toxic, expensive and difficult to procure. Given increasing resistance, the need for additional anti-TB drugs has become more urgent. But new drugs take time to develop and are expensive. Some commercially available drugs have reported anti-mycobacterial activity but are not routinely used because supporting laboratory and clinical evidence is sparse., Methods: We analysed 217 MDR M. tuberculosis isolates including 153 initial isolates from unique patients and 64 isolates from follow-up specimens during the course of treatment. The resazurin microdilution assay was performed to determine MICs of trimethoprim/sulfamethoxazole, mefloquine, thioridazine, clofazimine, amoxicillin/clavulanate, meropenem/clavulanate, nitazoxanide, linezolid and oxyphenbutazone. Isoniazid was used for validation. We calculated the MIC 50 and MIC 90 as the MICs at which growth of 50% and 90% of isolates was inhibited, respectively., Results: The MIC 50 s, in mg/L, for initial isolates were as follows: trimethoprim/sulfamethoxazole, 0.2/4; mefloquine, 8; thioridazine, 4; clofazimine, 0.25; amoxicillin/clavulanate, 16/8; meropenem/clavulanate, 1/2.5; nitazoxanide, 16; linezolid, 0.25; and oxyphenbutazone, 40. The MIC 90 s, in mg/L, for initial isolates were as follows: trimethoprim/sulfamethoxazole, 0.4/8; mefloquine, 8; thioridazine, 8; clofazimine, 0.5; amoxicillin/clavulanate, 32/16; meropenem/clavulanate, 8/2.5; nitazoxanide, 16; linezolid, 0.25; and oxyphenbutazone, 60. By comparison, the MIC 90 of isoniazid was >4 mg/L, as expected. There was no evidence that previous treatment affected susceptibility to any drug., Conclusions: Most drugs demonstrated efficacy against M. tuberculosis . When these MICs are compared with the published pharmacokinetic/pharmacodynamic profiles of the respective drugs in humans, trimethoprim/sulfamethoxazole, meropenem/clavulanate, linezolid, clofazimine and nitazoxanide appear promising and warrant further clinical investigation., (© The Author 2017. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

A comparison of carbapenem molecules for the detection of carbapenemase-producing bacteria by MALDI-TOF MS showed that imipenem exhibited higher sensitivity (97%) and specificity (100%) scores for Pseudomonas aeruginosa than meropenem. However, meropenem was more efficient (98% sensitivity and 100% specificity) against Enterobacteriaceae., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Background: The antibiotic meropenem is commonly administered in patients with severe sepsis and septic shock. We compared the pharmacokinetic, clinical, and bacteriological efficacies of continuous infusion of meropenem versus intermittent administration in such patients., Methods: Patients admitted to the Intensive Care Unit (ICU) with severe sepsis or septic shock who received meropenem were randomly assigned to either the continuous (n = 25) or intermittent groups (n = 25). The continuous group received a loading dose of 0.5 g of meropenem followed by a continuous infusion of 3 g/day; the intermittent group received an initial dose of 1.5 g followed by 1 g for every 8 h. Clinical success, microbiological eradication, superinfection, ICU mortality, length of ICU stay, and duration of meropenem treatment were assessed. Serial plasma meropenem concentrations for the first and third dosing periods (steady state) were also measured., Results: Clinical success was similar in both the continuous (64%) and intermittent (56%) groups (P = 0.564); the rates of microbiological eradication and superinfection (81.8% vs. 66.7% [ P = 0.255] and 4% vs. 16% [ P = 0.157], respectively) showed improvement in the continuous group. The duration of meropenem treatment was significantly shorter in the continuous group (7.6 vs. 9.4 days; P= 0.035), where a better steady-state concentration was also achieved. Peak and trough concentrations were significantly different between the continuous and intermittent groups both in the first (Cmax: 19.8 mg/L vs. 51.8 mg/L, P= 0.000; Cmin: 11.2 mg/L vs. 0.5 mg/L, P= 0.000) and third dosing periods (Cmax: 12.5 mg/L vs. 46.4 mg/L, P= 0.000; Cmin: 11.4 mg/L vs. 0.6 mg/L, P= 0.000). For medium-susceptibility pathogens, continuous infusion concentrations above the minimal inhibitory concentration were 100%, which was better than that in the intermittent group., Conclusions: Continuous infusion of meropenem provides significantly shorter treatment duration and a tendency for superior bacteriological efficacy than intermittent administration. Continuous infusion may be more optimal against intermediate-susceptibility pathogens.

Critically ill patients frequently have substantially altered pharmacokinetics compared to non-critically ill patients. We investigated the impact of pharmacokinetic alterations on bacterial killing and resistance for commonly used meropenem dosing regimens. A Pseudomonas aeruginosa isolate (MIC meropenem 0.25 mg/liter) was studied in the hollow-fiber infection model (inoculum ∼10 7.5 CFU/ml; 10 days). Pharmacokinetic profiles representing critically ill patients with augmented renal clearance (ARC), normal, or impaired renal function (creatinine clearances of 285, 120, or ∼10 ml/min, respectively) were generated for three meropenem regimens (2, 1, and 0.5 g administered as 8-hourly 30-min infusions), plus 1 g given 12 hourly with impaired renal function. The time course of total and less-susceptible populations and MICs were determined. Mechanism-based modeling (MBM) was performed using S-ADAPT. All dosing regimens across all renal functions produced similar initial bacterial killing (≤∼2.5 log 10 ). For all regimens subjected to ARC, regrowth occurred after 7 h. For normal and impaired renal function, bacterial killing continued until 23 to 47 h; regrowth then occurred with 0.5- and 1-g regimens with normal renal function ( fT >5×MIC = 56 and 69%, fC min /MIC < 2); the emergence of less-susceptible populations (≥32-fold increases in MIC) accompanied all regrowth. Bacterial counts remained suppressed across 10 days with normal (2-g 8-hourly regimen) and impaired (all regimens) renal function ( fT >5×MIC ≥ 82%, fC min /MIC ≥ 2). The MBM successfully described bacterial killing and regrowth for all renal functions and regimens simultaneously. Optimized dosing regimens, including extended infusions and/or combinations, supported by MBM and Monte Carlo simulations, should be evaluated in the context of ARC to maximize bacterial killing and suppress resistance emergence., (Copyright © 2017 American Society for Microbiology.)

Pharmacodynamics of a polymyxin B, meropenem, and rifampin triple combination were examined against Klebsiella pneumoniae carbapenemase-producing Klebsiella pneumoniae (KPC-Kp) ST258. In time-kill experiments against three KPC-Kp isolates, triple combination generated 8.14, 8.19, and 8.29 log 10 CFU/ml reductions within 24 h. In the hollow-fiber infection model, the triple combination caused maximal killing of 5.16 log 10 CFU/ml at 78 h and the time required for regrowth was more than doubled versus the 2-drug combinations. Remarkably, combinations with a high single-dose polymyxin B burst plus rifampin preserved KPC-Kp polymyxin susceptibility (MIC 240 h = 0.5 mg/liter) versus the same combination with traditionally dosed polymyxin B, where resistance was amplified (MIC 240 h = 32 mg/liter)., (Copyright © 2017 American Society for Microbiology.)

The study objective was to evaluate meropenem population pharmacokinetics and pharmacodynamics in nonobese, obese, and morbidly obese patients. Forty adult patients-11 nonobese (body mass index [BMI] < 30 kg/m 2 ), 9 obese (30 kg/m 2 ≤ BMI < 40 kg/m 2 ), and 20 morbidly obese (BMI ≥ 40 kg/m 2 )-received meropenem 500 mg every 6 hours (q6h), q8h, or q12h or 1 g q6h or q8h, infused over 0.5 hour. Population pharmacokinetic modeling was performed using NONMEM, and 5000-patient Monte-Carlo simulations were performed to calculate probability of target attainment (PTA) for 5 dosing regimens, infused over 0.5 and 3 hours, using fT>MIC of 40%, 54%, and 100% of the dosing interval. A 2-compartment linear-elimination model best described the serum concentration-time data, and creatinine clearance was significantly associated with systemic clearance. Pharmacokinetic parameters were not significantly different among patient groups. In patients with creatinine clearances ≥50 mL/min, all simulated dosing regimens achieved >90% PTA at 40% fT>MIC in all patient groups at MICs ≤2 mg/L. Only 500 mg q8h, infused over 0.5 hour, did not achieve >90% PTA at 54% fT>MIC in nonobese and morbidly obese patients. At 100% fT>MIC, 1 g q6h and 2 g q8h, infused over 3 hours, reliably achieved >90% PTA in all patient groups. Meropenem pharmacokinetics are comparable among nonobese, obese, and morbidly obese patients. Standard dosing regimens provide adequate pharmacodynamic exposures for susceptible pathogens at 40% and 54% fT>MIC, but prolonged infusions of larger doses are needed for adequate exposures at 100% fT>MIC. Dosage adjustments based solely on body weight are unnecessary., (© 2016, The American College of Clinical Pharmacology.)

Objectives: The aim of this study was to evaluate different dosage regimens of meropenem in elderly patients in relation with renal function using a population pharmacokinetic (popPK) model., Methods: The data of 178 elderly patients treated with meropenem was collected from different sources. A popPK model was developed by using NONMEM® and the influence of different covariates on meropenem CL and V 1 was observed. Monte Carlo dosing simulations were performed at steady state to observe the % T > MIC for targets of 40, 60 and 80% of dosage intervals at different levels of creatinine clearance (CL CR )., Results: The data was described by a two-compartment model and the values of parameter estimates for CL, V 1 , Q and V 2 were 5.27 L/h, 17.2 L, 9.92 L/h and 10.6 L, respectively. The CL CR , body weight and centre had a significant influence on meropenem CL while no direct influence of age was observed. Extended infusions had pharmacokinetic and pharmacodynamic (PK/PD) breakpoint one dilution greater than corresponding short infusion regimens for each target of % T > MIC., Conclusion: Meropenem CL was significantly lower in the elderly compared to CL reported in younger patients due to the reduced renal function. An extended infusion of 1000 mg q8h can be considered for empirical treatment of infections in elderly patients when CL CR is ≤ 50 mL/min. A continuous infusion of 3000 mg daily dose is preferred if CL CR  > 50 mL/min. However, a higher daily dose of meropenem would be required for resistant strains (MIC >8 mg/L) of bacteria if CL CR is >100 mL/min.

Meropenem is a carbapenem antibiotic that exhibits time-dependent bactericidal activity, traditionally dosed intravenously at 1 g every 8 h. In order to maximize its pharmacodynamic activity and reduce costs, an alternative regimen employed by many institutions is 500 mg every 6 h. The objective of this review was to summarize and evaluate published literature comparing clinical outcomes associated with these two meropenem dosing regimens. The literature was searched up to October 2016 using the MEDLINE, EMBASE, and Google Scholar databases. Three retrospective cohort studies were identified that compared clinical outcomes in general infectious disease patients (two studies) and patients with febrile neutropenia (one study). All studies reported no difference in clinical outcomes (clinical success, time to defervescence, sign or symptom resolution, length of stay, mortality, need for other antibiotics, and seizure rates). One study reported reduced economic costs with the alternative dosing. Interpretation of findings was primarily limited by small sample sizes and generalizability. Based on the data reviewed, the alternative dosing regimen of meropenem 500 mg intravenously every 6 h could be considered a therapeutic option. Future studies are needed to confirm the findings of this review, especially in high-risk populations such as immunocompromised patients or those with severe infections.

Acinetobacter baumannii is emerging with resistance to polymyxins. In 24-h time-kill experiments, high-dose ampicillin-sulbactam in combination with meropenem and polymyxin B achieved additivity or synergy against 10 8 CFU/ml of two clinical A. baumannii isolates resistant to all three drugs (maximum reductions, 1.6 and 3.1 logs). In a 14-day hollow-fiber infection model, high-dose ampicillin-sulbactam (8/4 g every 8 h, respectively) in combination with meropenem (2 g every 8 h) and polymyxin B (1.43 mg/kg of body weight every 12 h with loading dose) resulted in rapid (96 h) eradication of A. baumannii ., (Copyright © 2017 American Society for Microbiology.)

The effect of real-time pharmacokinetic/pharmacodynamic (PK/PD) optimisation of high-dose continuous-infusion meropenem on the clinical outcome of patients receiving combination antimicrobial therapy for treatment of KPC-producing Klebsiella pneumoniae (KPC-Kp) infections was retrospectively assessed. Data for all patients with KPC-Kp-related infections who received antimicrobial combination therapy containing high-dose continuous-infusion meropenem optimised by means of therapeutic drug monitoring (TDM) were retrieved. Optimal PK/PD exposure was considered a steady-state concentration to minimum inhibitory concentration ratio (C ss /MIC) of 1-4. Univariate binary logistic regression analysis was performed to identify independent predictors of clinical outcome. Among the 30 eligible patients, 53.3% had infections caused by meropenem-resistant KPC-Kp (MIC ≥ 16 mg/L). Tigecycline and colistin were the two antimicrobials most frequently combined with meropenem. Mean doses of continuous-infusion meropenem ranged from 1.7 to 13.2 g/daily. The C ss /MIC ratio was ≥1 in 73.3% of cases and ≥4 in 50.0%. Clinical outcome was successful in 73.3% of cases after a median treatment length of 14.0 days. In univariate analysis, a significant correlation with successful clinical outcome was found for a C ss /MIC ratio ≥1 (OR = 10.556, 95% CI 1.612-69.122; P = 0.014), a C ss /MIC ratio ≥4 (OR = 12.250, 95% CI 1.268-118.361; P = 0.030) and a Charlson co-morbidity index of ≥4 (OR = 0.158, 95% CI 0.025-0.999; P = 0.05). High-dose continuous-infusion meropenem optimised by means of real-time TDM may represent a valuable tool in improving clinical outcome when dealing with the treatment of infections caused by KPC-Kp with a meropenem MIC ≤ 64 mg/L., (Copyright © 2016 Elsevier B.V. and International Society of Chemotherapy. All rights reserved.)

Objective: Meropenem is important for management of postneurosurgical meningitis, but the data about its penetration into cerebrospinal fluid (CSF) are inadequate. This prospective, open-label study investigated the pharmacokinetic profile of meropenem in patients with postneurosurgical meningitis, especially its CSF penetration., Methods: A total of 82 patients with postneurosurgical meningitis were included to receive meropenem intravenously according to a regimen of 2 g every 8 hours, 1 g every 8 hours, or 1 g every 6 hours. After infusion of 4 doses, blood and CSF samples were collected simultaneously at predefined time points. The high-performance liquid chromatography ultraviolet method was used to determine the concentration of meropenem., Results: The peak meropenem concentration in blood and CSF was 43.2 ± 5.3 and 2.4 ± 0.3 mg/L in the group who received 2 g every 8 hours; 28.9 ± 2.7 and 1.2 ± 0.2 mg/L in the group who received 1g every 8 hours; and31.5 ± 3.4 and 1.6 ± 0.2 mg/L in the group who received 1g every 6 hours. The maximal percent penetration into CSF was 17.6% ± 7.3%, 14.3% ± 1.7%, and 30.9% ± 24.2%, respectively., Conclusions: Dosing regimens of meropenem 1 g every 6 hours and 2 g every 8 hours provided higher CSF penetration than 1 g every 8 hours. A higher dose and shorter dosing interval of meropenem may be more useful for clearance of pathogens., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Background: Meropenem is used for the treatment of severe lower respiratory tract infections (LRTIs) caused by multidrug-resistant Gram-negative bacilli., Objective: We evaluated the clinical benefits of a strategy of meropenem dosing based on a population pharmacokinetics/pharmacodynamics (PK/PD) model in elderly patients with an LRTI., Methods: In this prospective single-center open-label randomized controlled trial, 79 elderly patients with an LRTI caused by Gram-negative bacilli were randomized to a study group (SG) or a control group (CG). The latter received meropenem according to a regimen decided by the attending physician. The SG received individualized meropenem therapy with a dosing strategy based on software developed from a meropenem population PK/PD model. The primary endpoint was clinical response to meropenem therapy. Secondary endpoints were the amount of antibiotics used and bacteriologic response., Results: Klebsiella pneumoniae was the most common pathogen (32.9%), followed by Pseudomonas aeruginosa (30.4%) and Escherichia coli (17.7%). A total of 63 (79.7%) patients achieved clinical success. Prevalence of clinical success was significantly higher in the SG than in the CG (89.7 vs. 70.0%; p = 0.029). The daily dose of meropenem was significantly lower in the SG than in the CG (1.5 vs. 2.0 g; p = 0.017). A total of 52 (65.8%) patients experienced bacteriologic success, the median duration of meropenem therapy was 9 days, and the median total dose of meropenem was 18.0 g. There were no significant differences between the groups in these parameters., Conclusions: A strategy for meropenem dosing based on a population PK/PD model can improve clinical response and avoid overtreatment in elderly patients with an LRTI. ClinicalTrials.gov registration number NCT01944319.

The objective of this study was to assess the achievement of pharmacokinetic/pharmacodynamic (PK/PD) targets of meropenem (MEM) in critically-ill patients with bloodstream infections (BSI) due to Klebsiella pneumoniae-carbapenemase-producing Klebsiella pneumoniae (KPC-Kp) with MEM minimum inhibitory concentrations (MICs) ≥16 mg/L. Nineteen critically-ill patients with KPC-Kp BSI were given combination therapy including MEM, tigecycline, plus colistin or gentamicin (according to susceptibility testing). MEM was administered as an extended 3-hour infusion of 2 g every 8 hours, or adjusted according to renal function. MEM plasma concentrations were determined by high-performance liquid chromatography. PK/PD targets for MEM were defined as T > 40% 1×MIC and T > 40% 4×MIC. Possible synergisms between MEM and coadministered agents were assessed by time-kill assays based on plasma levels for MEM and on fixed plasma concentrations for the other agents. In none of 19 patients MEM reached any PK/PD target. The actual MEM MICs were 256, 512, and 1024 mg/L in 1, 3, and 15 isolates, respectively. However, theoretically, the PK/PD target of T > 40% 1×MIC could have been achieved in 95%, 68%, 32% and 0% of the isolates for MIC equal to 8, 16, 32, and 64 mg/L, respectively. No synergisms were observed between MEM and coadministered agents. In conclusion, high-dose MEM failed to reach PK/PD targets in 19 patients with BSI due to KPC-Kp with very high MEM MICs. On a theoretical basis, our results suggest a possible usefulness of MEM against resistant blood isolates with MICs up to 32 mg/L.

High-dose meropenem (MEPM; 6 g/day) has been approved as a treatment for purulent meningitis; however, little is known regarding its in vivo efficacy in refractory lower respiratory tract infections. The purpose of this study was to evaluate the efficacy of MEPM at 6 g/day in a murine model of severe pneumonia caused by MEPM-resistant Pseudomonas aeruginosa Experimental pneumonia induced by MEPM-resistant P. aeruginosa was treated with normal-dose MEPM (150 mg/kg of body weight, simulating a 3-g/day regimen in humans) or high-dose MEPM (500 mg/kg, simulating a 6-g/day regimen in humans). Mice treated with high-dose MEPM showed significantly restored survival relative to that of untreated mice and tended to show a survival rate higher than that of mice treated with normal-dose MEPM. The viable bacterial counts (of two clinical isolates) in the lungs decreased significantly in mice treated with high-dose MEPM from those for untreated mice (P < 0.001) or mice treated with normal-dose MEPM (P, <0.01 and <0.05). The number of inflammatory cells in the bronchoalveolar lavage fluid (BALF) was also significantly lower in mice treated with high-dose MEPM than in untreated mice. The free MEPM concentration in the epithelial lining fluid (ELF) exceeded 16 μg/ml for 85 min in mice treated with high-dose MEPM, but not for mice treated with normal-dose MEPM. Our results demonstrate that high-dose MEPM (6 g/day) might provide better protection against pneumonia caused by MEPM-resistant strains of P. aeruginosa than the dose normally administered (less than 3 g/day)., (Copyright © 2016 American Society for Microbiology.)

Meropenem, a second carbapenem antimicrobial agent with a broad spectrum of activity, is used to treat sepsis and resistant-bacterial infections in veterinary medicine. The objective of this study was to identify the pharmacokinetics of meropenem in dogs receiving intermittent hemodialysis (IHD) and to determine the proper dosing in renal failure patients receiving IHD. Five healthy beagle dogs were given a single i.v. dose of 24 mg/kg of meropenem and received IHD. The blood flow rate, dialysate flow, and ultrafiltration rate were maintained at 40 mL/min, 300 mL/min, and 40 mL/h, respectively. Blood samples were collected for 24 h from the jugular vein and from the extracorporeal arterial and venous line. Urine samples and dialysate were also collected. The concentrations of meropenem were assayed using HPLC/MS/MS determination. The peak plasma concentration was 116 ± 37 μg/mL at 15 min. The systemic clearance was 347 ± 117 mL/h/kg, and the steady-state volume of distribution was 223 ± 67 mL/kg. Dialysis clearance was 71.1 ± 34.3 mL/h/kg, and the extraction ratio by hemodialysis was 0.455 ± 0.150. The half-life (T 1/2 ) in dogs with IHD decreased compared with those without IHD, and the reduction in T 1/2 was greater in renal failure patients than in normal patients. Sixty-nine percent and 21% of the administered drug were recovered by urine and dialysate in the unchanged form, respectively. In conclusion, additional dosing of 24 mg/kg of meropenem after dialysis could be necessary according to the residual renal function of the patient based on the simulated data., (© 2016 John Wiley & Sons Ltd.)

Objectives: The aim of the study was to describe the pharmacokinetics and predicted efficacy of meropenem after intravenous (IV), intramuscular (IM) and subcutaneous (SC) administration to cats at a single dose of 10 mg/kg., Methods: Five adult healthy cats were used. Blood samples were withdrawn at predetermined times over a 12 h period. Meropenem concentrations were determined by microbiological assay. Pharmacokinetic analyses were performed with computer software. Initial estimates were determined using the residual method and refitted by non-linear regression. The time that plasma concentrations were greater than the minimum inhibitory concentration (T >MIC) was estimated by applying bibliographic MIC values and meropenem MIC breakpoint., Results: Maximum plasma concentrations of meropenem were 101.02 µg/ml (C p(0) , IV), 27.21 µg/ml (C max , IM) and 15.57 µg/ml (C max , SC). Bioavailability was 99.69% (IM) and 96.52 % (SC). Elimination half-lives for the IV, IM and SC administration were 1.35, 2.10 and 2.26 h, respectively., Conclusions and Relevance: Meropenem, when administered to cats at a dose of 10 mg/kg q12h,, is effective against bacteria with MIC values of 6 μg/ml, 7 μg/ml and 10 μg/ml for IV, IM and SC administration, respectively. However, clinical trials are necessary to confirm clinical efficacy of the proposed dosage regimen., (© The Author(s) 2015.)

Currently there are no pharmacokinetic (PK) data to guide antibiotic dosing in critically ill Australian Indigenous patients with severe sepsis. This study aimed to determine whether the population pharmacokinetics of meropenem were different between critically ill Australian Indigenous and critically ill Caucasian patients. Serial plasma and urine samples as well as clinical and demographic data were collected over two dosing intervals from critically ill Australian Indigenous patients. Plasma meropenem concentrations were assayed by validated chromatography. Concentration-time data were analysed with data from a previous PK study in critically ill Caucasian patients using Pmetrics. The population PK model was subsequently used for Monte Carlo dosing simulations to describe optimal doses for these patients. Six Indigenous and five Caucasian subjects were included. A two-compartment model described the data adequately, with meropenem clearance and volume of distribution of the central compartment described by creatinine clearance (CL Cr ) and patient weight, respectively. Patient ethnicity was not supported as a covariate in the final model. Significant differences were observed for meropenem clearance between the Indigenous and Caucasian groups [median 11.0 (range 3.0-14.1) L/h vs. 17.4 (4.3-30.3) L/h, respectively; P <0.01]. Standard dosing regimens (1 g intravenous every 8 h as a 30-min infusion) consistently achieved target exposures at the minimum inhibitory concentration breakpoint in the absence of augmented renal clearance. No significant interethnic differences in meropenem pharmacokinetics between the Indigenous and Caucasian groups were detected and CL Cr was found to be the strongest determinant of appropriate dosing regimens., (Crown Copyright © 2016. Published by Elsevier B.V. All rights reserved.)

Carbapenem-resistant Acinetobacter baumannii (CRAB) is an important clinical threat. Combination therapy that exerts a synergistic effect has become a potential solution to combat CRAB. However, choosing an optimal combination regimen is challenging. A dynamic in vitro pharmacokinetic/pharmacodynamic (PK/PD) model that can simulate the pharmacokinetic profiles of antibiotics provides a powerful tool to compare antibacterial responses to different clinical dosage regimens. In this study, the synergistic effect of the combination of meropenem and colistin was tested in 12 clinical CRAB isolates from Chinese patients using the chequerboard technique. The antibacterial effect was investigated in an in vitro PK/PD diffusion model by simulating different dosage regimens: meropenem monotherapy (0.5 g with 0.5-h infusion or 1 g with 3-h infusion); colistin monotherapy (fixed unbound concentration maintained at 0.25, 0.5 or 1 mg/L); and combination of meropenem and colistin. The chequerboard method showed that the combination of meropenem and colistin had synergistic effects against all 12 isolates, with fractional inhibitory concentration indices (FICIs) of ≤0.5. Moreover, the dynamic in vitro PK/PD model demonstrated that for clinical CRAB isolates with a meropenem MIC of 128 mg/L, the combination (meropenem 1 g with 3-h infusion combined with colistin maintained at 1 mg/L) could achieve 3.8 log 10 killing after 24 h, whereas monotherapy was unable to provide such an antibacterial effect. Taken together, these results suggest that the combination of meropenem and colistin might be a promising therapy against CRAB., (Copyright © 2016 Elsevier B.V. and International Society of Chemotherapy. All rights reserved.)

Meropenem is used to manage postneurosurgical meningitis, but its population pharmacokinetics (PPK) in plasma and cerebrospinal fluid (CSF) in this patient group are not well-known. Our aims were to (i) characterize meropenem PPK in plasma and CSF and (ii) recommend favorable dosing regimens in postneurosurgical meningitis patients. Eighty-two patients were enrolled to receive meropenem infusions of 2 g every 8 h (q8h), 1 g q8h, or 1 g q6h for at least 3 days. Serial blood and CSF samples were collected, and concentrations were determined and analyzed via population modeling. Probabilities of target attainment (PTA) were predicted via Monte Carlo simulations, using the target of unbound meropenem concentrations above the MICs for at least 40% of dosing intervals in plasma and at least of 50% or 100% of dosing intervals in CSF. A two-compartment model plus another CSF compartment best described the data. The central, intercentral/peripheral, and intercentral/CSF compartment clearances were 22.2 liters/h, 1.79 liters/h, and 0.01 liter/h, respectively. Distribution volumes of the central and peripheral compartments were 17.9 liters and 3.84 liters, respectively. The CSF compartment volume was fixed at 0.13 liter, with its clearance calculated by the observed drainage amount. The multiplier for the transfer from the central to the CSF compartment was 0.172. Simulation results show that the PTAs increase as infusion is prolonged and as the daily CSF drainage volume decreases. A 4-hour infusion of 2 g q8h with CSF drainage of less than 150 ml/day, which provides a PTA of >90% for MICs of ≤8 mg/liter in blood and of ≤0.5 mg/liter or 0.25 mg/liter in CSF, is recommended. (This study has been registered at ClinicalTrials.gov under identifier NCT02506686.)., (Copyright © 2016 Lu et al.)

The present study evaluated the efficacy and safety of biapenem in elderly Chinese patients with lower respiratory tract infections (LRTIs) and proposed optimal dosage regimen on the basis of pharmacokinetic/pharmacodynamic (PK/PD) analysis. The clinical efficacy, bacterial eradication and comprehensive therapeutic effect rates of biapenem were 70.3 (78/111), 68.5 (37/54) and 61.1% (33/54), respectively. Drug-related adverse reactions were seen in 12.6% of patients (14/111). The total protein level, Acute Physiology and Chronic Health Evaluation (APACHE) II score, %fT>MIC, fAUC24/MIC and fCmax/MIC values of patients had significant impacts (P < 0.05) on clinical and bacteriological efficacy. However, logistic regression analysis showed that only %fT>MIC independently influenced comprehensive therapeutic effect (P < 0.01, odds ratio = 1.064). The cut-off value for predicting comprehensive therapeutic effect using %fT>MIC was 75.0%; the sensitivity and specificity were 87.9 and 85.7%, respectively. Monte Carlo simulations revealed that the usual dosage regimen (300 mg every 12 hours, 0.5 hour infusion) was considered to be insufficient to obtain satisfactory therapeutic outcomes against low susceptible pathogens for elderly Chinese patients with LRTIs (CLcr = 70 ml/min).

Background: Pharmacokinetics of meropenem differ widely in the critically ill population. It is imperative to maintain meropenem concentrations above the inhibitory concentrations for most of the interdose interval. A population pharmacokinetic/pharmacodynamic model was developed to determine the probability of target attainment for 3-hour and 30-minute infusion regimens in this population., Methods: This study was performed in an intensive care setting among adult patients who were initiated on meropenem at a dose of 1000 mg. Multiple blood specimens were collected at predetermined time points during the interdose period, and meropenem concentrations were measured using high performance liquid chromatography. Using Pmetrics, a pharmacokinetic/pharmacodynamic model was developed and validated. Monte Carlo simulation was performed, and probability of target attainment (100% T > minimum inhibitory concentration (MIC), with a probability >0.9) for doubling MICs was determined for different regimens of meropenem., Results: A 2-compartment multiplicative gamma error model best described the population parameters from 34 patients. The pharmacokinetic parameters used in the final model were Ke (elimination rate constant from the central compartment), Vc (volume of distribution of central compartment), KCP and KPC (intercompartmental rate constants), and IC2 (the fitted amount of meropenem in the peripheral compartment). Inclusion of creatinine clearance (CLcreat) and body weight as covariates improved the model prediction (Ke = Ke0 × (Equation is included in full-text article.), Vc = Vc0 × Weight). The Ke and Vc [geometric mean (range)] of the individuals were 0.54 (0.01-2.61)/h and 9.36 (4.35-21.62) L, respectively. The probability of attaining the target, T > MIC of 100%, was higher for 3-hour infusion regimens compared with 30-minute infusion regimens for all ranges of CLcreat., Conclusions: This study emphasizes that extended regimens of meropenem are preferable for treating infections caused by bacteria with higher MICs. The nonparametric analysis using body weight and CLcreat as covariate adequately predicted the pharmacokinetics of meropenem in critically ill patients with a wide range of renal function.

Introduction: The aim of the study was to assess whether the penetration of antibiotics is affected by decreased tissue perfusion in patients with limb ischaemia, thus reducing its concentration in tissues below the minimum inhibitory concentration (MIC) breakpoints of antibiotics for different microorganisms., Methods: Prospective study. Candidates for major amputation with critical lower limb ischaemia and an infection on antibiotic treatment, were included. Three levels of perfusion in the lower limb were determined by measuring the transcutaneous oxygen pressure (TcPO2). A central line blood specimen, as well as biopsies of the skin, muscle, and bone, were taken at each perfusion level. The antibiotic concentration was determined using HPLC., Results: The total number of cases was 61 (46 patients): 6 clindamycin, 9 vancomycin, 8 linezolid, 18 levofloxacin, 9 ceftazidime, and 11 meropenem. Statistically significant differences were found in TcPO2 at all levels (ANOVA, P=.000). The vancomycin, levofloxacin and ceftazidime skin concentration depends on perfusion. Vancomycin and levofloxacin diffusion in bone is worse than in other tissues. Ceftazidime concentration does not exceed the MIC breakpoint of Pseudomonas aeruginosa in ischaemic tissues., Conclusions: Meropenem and linezolid diffuse in all tissues, regardless of perfusion, reaching concentrations above the MIC of the target microorganisms, ensuring its effectiveness in ischaemic tissues., (Copyright © 2015 Elsevier España, S.L.U. and Sociedad Española de Enfermedades Infecciosas y Microbiología Clínica. All rights reserved.)

Objectives: This study was designed to evaluate the pharmacodynamics of doripenem, imipenem and meropenem as a predictor of clinical success, mortality, 28 day recurrence and development of resistance in patients treated for Pseudomonas aeruginosa ventilator-associated pneumonia (VAP)., Patients and Methods: Previously published demographic and outcome data derived from patients treated for P. aeruginosa VAP with doripenem, imipenem or meropenem were utilized. Patient-specific data were used in conjunction with published population pharmacokinetic models to construct concentration-time profiles for each patient. Etest MICs were used to determine pharmacodynamic profiles. Classification and regression tree (CART) analysis was utilized to partition pharmacodynamics based on outcomes with P values of 0.05., Results: Eighty-six patients were included in the analysis. Initial carbapenem MICs ranged from 0.03 to 32 mg/L. VAP recurred in 28 patients; of these, 17 patients were initially infected with susceptible organisms, and 14 of them developed resistance. CART fT>MIC partitions identified for clinical success and survival were 19.2% (P = 0.016) and 47.9% (P < 0.001), respectively. No statistically significant partitions for fT>MIC were identified for recurrence or resistance development., Conclusions: We identified fT>MIC cut-offs for positive clinical outcomes in patients with P. aeruginosa VAP that were similar to those observed in animal models of infection for stasis (∼20%) and 1 log decreases in cfu (∼40%). Although in vitro studies have suggested a link between drug exposure and development of resistance, we were unable to identify such a relationship clinically., (© The Author 2016. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)

This study aimed to describe the pharmacokinetic (PK) characteristics of meropenem in children with severe infections and to assess the pharmacokinetic/pharmacodynamic (PK/PD) profiles of various meropenem dosage regimens in these patients. Fourteen children with severe infections received intravenous (i.v.) bolus doses of meropenem (20 mg/kg/dose) every 8 h (q8h). Serum samples were obtained before and serially after the second dose of meropenem, and a population PK analysis was performed. The final model was used to simulate serum concentration-time profiles with various dosage regimens. The PK/PD target was to achieve a serum meropenem concentration higher than the minimum inhibitory concentration (MIC) of the causative organism (i.e. Pseudomonas aeruginosa and Enterobacteriaceae) for ≥40% of the dosing interval (40%T>MIC). The median age and weight of the children were 6.0 years and 20.0 kg, respectively. Meropenem serum concentration-time profiles were best described by a two-compartmental model with first-order elimination. The simulations showed that the probabilities of target attainment (PTAs) for organisms with an MIC of 1 mg/L were 0.678 and 1.000 following i.v. bolus and 3-h infusion of meropenem (20 mg/kg/dose), respectively. Using a 3-h infusion of a 20 mg/kg/dose, the PTA was 0.999 and 0.765 for organisms with MICs of 4 mg/L and 8 mg/L, respectively. Meropenem given as i.v. bolus doses of 20 mg/kg/dose q8h appeared to be inadequate for PK/PD target attainment for organisms with an MIC of 1 mg/L. The simulations showed that meropenem administration via a 3-h infusion using the same dose improved the PTA., (Copyright © 2016 Elsevier B.V. and International Society of Chemotherapy. All rights reserved.)

Severe pathophysiological changes in critical illness can lead to dramatically altered antimicrobial pharmacokinetics (PK). The additional effect of obesity on PK potentially increases the challenge for effective dosing. The aim of this prospective study was to describe the population PK of meropenem for a cohort of critically ill patients, including obese and morbidly obese patients. Critically ill patients prescribed meropenem were recruited into the following three body mass index (BMI) groups: nonobese (18.5 to 29.9 kg/m(2)), obese (30.0 to 39.9 kg/m(2)), and morbidly obese (≥40 kg/m(2)). Serial plasma samples were taken, and meropenem concentrations were determined using a validated chromatographic method. Population PK analysis and Monte Carlo dosing simulations were undertaken with Pmetrics. Nineteen critically ill patients with different BMI categories were enrolled. The patients' mean ± standard deviation (SD) age, weight, and BMI were 49 ± 15.9 years, 95 ± 22.0 kg, and 33 ± 7.0 kg/m(2), respectively. A two-compartment model described the data adequately. The mean ± SD parameter estimates for the final covariate model were as follows: clearance (CL), 15.5 ± 6.0 liters/h; volume of distribution in the central compartment (V1), 11.7 ± 5.8 liters; intercompartmental clearance from the central compartment to the peripheral compartment, 25.6 ± 35.1 liters h(-1); and intercompartmental clearance from the peripheral compartment to the central compartment, 8.32 ± 12.24 liters h(-1) Higher creatinine clearance (CLCR) was associated with a lower probability of target attainment, with BMI having little effect. Although obesity was found to be associated with an increased V1, dose adjustment based on CLCR appears to be more important than patient BMI., (Copyright © 2016, American Society for Microbiology. All Rights Reserved.)

Background & Aims: The pharmacokinetics of β-lactam antibiotics have not been well defined in critically ill patients with cirrhosis., Methods: We reviewed data from critically ill patients with cirrhosis and matched controls in whom routine therapeutic drug monitoring of two broad-spectrum β-lactam antibiotics (piperacillin/tazobactam and meropenem) had been performed. Serum drug concentrations were measured twice by high-performance liquid chromatography. Antibiotic pharmacokinetics were calculated using a one-compartment model. We considered that therapy was adequate when serum drug concentrations were between 4 and 8 times the minimal inhibitory concentration of Pseudomonas aeruginosa during optimal periods of time for each drug (≥ 50% for piperacillin/tazobactam; ≥ 40% for meropenem)., Results: We studied 38 patients with cirrhosis (16 for piperacillin/tazobactam and 22 for meropenem) and 38 matched controls. Drug dosing was similar in the two groups. The pharmacokinetics analysis showed a lower volume of distribution of meropenem (P = 0.05) and a lower antibiotic clearance of piperacillin/tazobactam (P = 0.009) in patients with cirrhosis than in the matched controls. Patients with cirrhosis were more likely than those without cirrhosis to have excessive serum β-lactam concentrations (P = 0.015), in particular for piperacillin/tazobactam., Conclusions: Standard β-lactam antibiotics regimens resulted in excessive serum concentrations in two thirds of the patients with cirrhosis. This was particularly true for piperacillin/tazobactam, probably because of reduced drug clearance., (© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Purpose: Patients admitted to intensive care unit (ICU) with Klebsiella pneumoniae infections are characterized by high mortality. The aims of the present study were to investigate the population pharmacokinetics parameters and to assess the probability of target attainment of meropenem in critically ill patients to provide information for more effective regimens., Methods: Twenty-seven consecutive patients were included in the study. Meropenem was administered as 3-h intravenous (i.v.) infusions at doses of 1-2 g every 8 or 12 h. Meropenem plasma concentrations were measured by a high-performance liquid chromatography (HPLC) method, and a population pharmacokinetics analysis was performed using NONMEM software. Meropenem plasma disposition was simulated for extended (3 h; 5 h) or continuous i.v. infusions, and the following parameters were calculated: time during which free drug concentrations were above minimum inhibitory concentration (MIC) (fT > MIC), free minimum plasma concentrations above 4× MIC (fCmin > 4× MIC), probability of target attainment (PTA), and cumulative fraction of response (CFR)., Results: Gender and severity of sepsis affected meropenem clearance, whose typical population values ranged from 6.22 up to 12.04 L/h (mean ± standard deviation (SD) value, 9.38 ± 4.47 L/h). Mean C min value was 7.90 ± 7.91 mg/L, suggesting a high interindividual variability. The simulation confirmed that 88 and 97.5 % of patients achieved effective C min > 4× MIC values after 3- and 5-h i.v. infusions of meropenem 2 g × 3/day, respectively. On the contrary, the same total daily doses reached the target C min > 4× MIC values in 100 % of patients when administered as continuous i.v. infusions., Conclusions: Several factors may influence meropenem pharmacokinetics in ICU patients. Continuous i.v. infusions of meropenem seem to be more effective than standard regimens to achieve optimal therapeutic targets.

The usefulness of β-lactam antimicrobial agents is threatened as never before by β-lactamase-producing bacteria. For this reason, there has been renewed interest in the development of broad-spectrum β-lactamase inhibitors. Herein we describe the results of dose fractionation and dose-ranging studies carried out using a one-compartment in vitro infection model to determine the exposure measure for CB-618, a novel β-lactamase inhibitor, most predictive of the efficacy when given in combination with meropenem. The challenge panel included Enterobacteriaceae clinical isolates, which collectively produced a wide range of β-lactamase enzymes (KPC-2, KPC-3, FOX-5, OXA-48, SHV-11, SHV-27, and TEM-1). Human concentration-time profiles were simulated for each drug, and samples were collected for drug concentration and bacterial density determinations. Using data from dose fractionation studies and a challenge Klebsiella pneumoniae isolate (CB-618-potentiated meropenem MIC = 1 mg/liter), relationships between change from baseline in log10 CFU/ml at 24 h and each of CB-618 area under the concentration-time curve over 24 h (AUC0-24), maximum concentration (Cmax), and percentage of the dosing interval that CB-618 concentrations remained above a given threshold were evaluated in combination with meropenem at 2 g every 8 h (q8h). The exposure measures most closely associated with CB-618 efficacy in combination with meropenem were the CB-618 AUC0-24 (r(2) = 0.835) and Cmax (r(2) = 0.826). Using the CB-618 AUC0-24 indexed to the CB-618-potentiated meropenem MIC value, the relationship between change from baseline in log10 CFU/ml at 24 h and CB-618 AUC0-24/MIC ratio in combination with meropenem was evaluated using the pooled data from five challenge isolates; the CB-618 AUC0-24/MIC ratio associated with net bacterial stasis and the 1- and 2-log10 CFU/ml reductions from baseline at 24 h were 27.3, 86.1, and 444.8, respectively. These data provide a pharmacokinetics-pharmacodynamics (PK-PD) basis for evaluating potential CB-618 dosing regimens in combination with meropenem in future studies., (Copyright © 2016, American Society for Microbiology. All Rights Reserved.)