Pharmacokinetics of meropenem compared to imipenem-cilastatin in young, healthy males

Population Pharmacokinetic Modeling of Unbound Meropenem in Patients Undergoing Continuous Renal Replacement Therapy: An Observational Cohort Study

BACKGROUND

The most effective dosing strategy of meropenem for patients undergoing continuous renal replacement therapy (CRRT) remains uncertain. This study aimed to analyze the population pharmacokinetics (popPKs) of unbound meropenem and establish an appropriate dosing approach.

METHODS

This prospective study involved 19 patients for the development of a popPK model and an additional 10 for its validation. Ethical approval was obtained.

RESULTS

The clearance of unbound meropenem was influenced by the sequential organ failure assessment (SOFA) score [=2.22 × (SOFA score/12)^1.88] and the effluent flow rate from the CRRT device, with an interindividual variability of 44.5%. The volume of distribution was affected by the simplified acute physiology score II [=23.1 × (simplified acute physiology score II/52)^1.54]. Monte Carlo simulations suggested meropenem doses ranging from 1.0 to 3.0 g/d using continuous infusion to achieve a target time above the 4 times of minimum inhibitory concentration of the unbound form (%fT>4×MIC) of 100% for definitive therapy. For empirical therapy, a dose of 1.0 g/d using continuous infusion was recommended to target %fT>MIC of 100%.

CONCLUSIONS

This study developed a popPK model for unbound meropenem in patients undergoing CRRT and formulated dosing guidelines.

CLINICAL TRIAL REGISTRATION

UMIN000024321.

Plasma and Cerebrospinal Fluid Population Pharmacokinetics of Meropenem in Neurocritical Care Patients: a Prospective Two-Center Study

Morbidity and mortality related to ventriculitis in neurocritical care patients remain high. Antibiotic dose optimization may improve therapeutic outcomes. In this study, a population pharmacokinetic model of meropenem in infected critically ill patients was developed. We applied the final model to determine optimal meropenem dosing regimens required to achieve targeted cerebrospinal fluid exposures. Neurocritical care patients receiving meropenem and with a diagnosis of ventriculitis or extracranial infection were recruited from two centers to this study. Serial plasma and cerebrospinal fluid samples were collected and assayed. Population pharmacokinetic modeling and Monte Carlo dosing simulations were performed using Pmetrics. We sought to determine optimized dosing regimens that achieved meropenem cerebrospinal fluid concentrations above pathogen MICs for 40% of the dosing interval, or a higher target ratio of meropenem cerebrospinal fluid trough concentrations to pathogen MIC of ≥1. In total, 53 plasma and 34 cerebrospinal fluid samples were obtained from eight patients. Meropenem pharmacokinetics were appropriately described using a three-compartment model with linear plasma clearance scaled for creatinine clearance and cerebrospinal fluid penetration scaled for patient age. Considerable interindividual pharmacokinetic variability was apparent, particularly in the cerebrospinal fluid. Percent coefficients of variation for meropenem clearance from plasma and cerebrospinal fluid were 41.7% and 89.6%, respectively; for meropenem, the volume of distribution in plasma and cerebrospinal fluid values were 63.4% and 58.3%, respectively. High doses (up to 8 to 10 g/day) improved attainment of meropenem cerebrospinal fluid target exposures, particularly for less susceptible organisms (MICs, ≥0.25 mg/L). Standard meropenem doses of 2 g every 8 h may not achieve effective concentrations in cerebrospinal fluid in all critically ill patients. Higher doses, or alternative dosing methods (e.g., loading dose followed by continuous infusion) may be required to optimize cerebrospinal fluid exposures. Doses of up to 8 to 10 g/day either as intermittent boluses or continuous infusion would be suitable for patients with augmented renal clearance; lower doses may be considered for patients with impaired renal function as empirical suggestions. Ongoing dosing should be tailored to the individual patient circumstances. Notably, the study population was small and dosing recommendations may not be generalizable to all critically ill patients.

Methods for Determination of Meropenem Concentration in Biological Samples

Measuring the concentration of antibiotics in biological samples allow implementation of therapeutic monitoring of these drugs and contribute to the adjustment of the dosing regimen in patients. This increases the effectiveness of antimicrobial therapy, reduces the toxicity of these drugs and prevents the development of bacterial resistance. This review article summarizes current knowledge on methods for determining concentration of meropenem, an antibiotic drug from the group of carbapenems, in different biological samples. It provides a brief discussion of the chemical structure, physicochemical and pharmacokinetic properties of meropenem, different sample preparation techniques, use of apparatus and equipment, knowledge of the advantages and limitations of available methods, as well as directions in which new methods should be developed. This review should facilitate clinical laboratories to select and apply one of the established methods for measuring of meropenem, as well as to provide them with the necessary knowledge to develop new methods for quantification of meropenem in biological samples according to their needs.

Physiologically Based Pharmacokinetic Modeling of Meropenem in Preterm and Term Infants

BACKGROUND

Meropenem is a broad-spectrum carbapenem antibiotic approved by the US Food and Drug Administration for use in pediatric patients, including treating complicated intra-abdominal infections in infants < 3 months of age. The impact of maturation in glomerular filtration rate and tubular secretion by renal transporters on meropenem pharmacokinetics, and the effect on meropenem dosing, remains unknown. We applied physiologically based pharmacokinetic (PBPK) modeling to characterize the disposition of meropenem in preterm and term infants.

METHODS

An adult meropenem PBPK model was developed in PK-Sim® (Version 8) and scaled to infants accounting for renal transporter ontogeny and glomerular filtration rate maturation. The PBPK model was evaluated using 645 plasma concentrations from 181 infants (gestational age 23-40 weeks; postnatal age 1-95 days). The PBPK model-based simulations were performed to evaluate meropenem dosing in the product label for infants < 3 months of age treated for complicated intra-abdominal infections.

RESULTS

Our model predicted plasma concentrations in infants in agreement with the observed data (average fold error of 0.90). The PBPK model-predicted clearance in a virtual infant population was successfully able to capture the post hoc estimated clearance of meropenem in this population, estimated by a previously published model. For 90% of virtual infants, a 4-mg/L target plasma concentration was achieved for > 50% of the dosing interval following product label-recommended dosing.

CONCLUSIONS

Our PBPK model supports the meropenem dosing regimens recommended in the product label for infants <3 months of age.

Population Pharmacokinetics of Meropenem and Vaborbactam Based on Data from Noninfected Subjects and Infected Patients

Meropenem-vaborbactam is a broad-spectrum carbapenem–beta-lactamase inhibitor combination approved in the United States and Europe to treat patients with complicated urinary tract infections and in Europe for other serious bacterial infections, including hospital-acquired and ventilator-associated pneumonia. Population pharmacokinetic (PK) models were developed to characterize the time course of meropenem and vaborbactam using pooled data from two phase 1 and two phase 3 studies. Multicompartment disposition model structures with linear elimination processes were fit to the data using NONMEM 7.2. Since both drugs are cleared primarily by the kidneys, estimated glomerular filtration rate (eGFR) was evaluated as part of the base structural models. For both agents, a two-compartment model with zero-order input and first-order elimination best described the pharmacokinetic PK data, and a sigmoidal Hill-type equation best described the relationship between renal clearance and eGFR. For meropenem, the following significant covariate relationships were identified: clearance (CL) decreased with increasing age, CL was systematically different in subjects with end-stage renal disease, and all PK parameters increased with increasing weight. For vaborbactam, the following significant covariate relationships were identified: CL increased with increasing height, volume of the central compartment (V_c) increased with increasing body surface area, and CL, V_c, and volume of the peripheral compartment were systematically different between phase 1 noninfected subjects and phase 3 infected patients. Visual predictive checks demonstrated minimal bias, supporting the robustness of the final models. These models were useful for generating individual PK exposures for pharmacokinetic-pharmacodynamic (PK-PD) analyses for efficacy and Monte Carlo simulations to evaluate PK-PD target attainment.

Pharmacokinetics of meropenem during advanced organ support (ADVOS®) and continuous renal replacement therapy

The advanced organ support (ADVOS) system allows to eliminate water-soluble as well as protein-bound molecules. Despite its clinical features, to date nothing is known about the elimination of clinically relevant drugs such as antiinfectives. Therefore, we report a case treated with ADVOS, continuous renal replacement therapy (CRRT), and meropenem (1 g 8-hourly) for empiric sepsis therapy monitored by meropenem drug levels. ADVOS showed more efficient elimination of meropenem compared to CRRT which has to be considered when evaluating dosing regimens.

Physiologically based pharmacokinetic-pharmacodynamic evaluation of meropenem plus fosfomycin in paediatrics

AIMS

The objective of the current study was to evaluate paediatric dosing regimens for meropenem plus fosfomycin that generate sufficient coverage against multidrug-resistant bacteria.

METHODS

The physiologically based pharmacokinetic (PBPK) models of meropenem and fosfomycin were developed from previously published pharmacokinetic studies in five populations: healthy subjects of Japanese origin, and healthy adults, geriatric, paediatric and renally impaired of primarily Caucasian origins. Pharmacodynamic (PD) analyses were carried out by evaluating dosing regimens that achieved a ≥90% joint probability of target attainment (PTA), which was defined as the minimum of the marginal probabilities to achieve the target PD index of each antibiotic. For meropenem, the percentage of time over a 24-hour period wherein the free drug concentration was above the minimum inhibitory concentration (fT > MIC) of at least 40% was its PD target. The fosfomycin PD index was described by fAUC/MIC of at least 40.8.

RESULTS

For coadministration consisting of 20 mg/kg meropenem q8h as a 3-hour infusion and 35 mg/kg fosfomycin q8h also as a 3-hour infusion in a virtual paediatric population between 1 month and 12 years of age with normal renal function and a corresponding body weight between 3 and 50 kg, a joint PTA ≥ 90% is achieved at MICs of 16 and 64 mg/L for meropenem and fosfomycin coadministration, respectively, against Klebsiella pneumoniae and Pseudomonas aeruginosa.

CONCLUSION

The current study identified potentially effective paediatric dosing regimens for meropenem plus fosfomycin coadministration against multidrug-resistant bacteria.

Preliminary physiologically based pharmacokinetic modeling of renally cleared drugs in Chinese pregnant women

AIM

The aim of this study was to build and verify a preliminary physiologically based pharmacokinetic (PBPK) model of Chinese pregnant women. The model was used to predict maternal pharmacokinetics (PK) of 6 predominantly renally cleared drugs.

METHOD

Based on SimCYP Caucasian pregnancy population dataset, the preliminary Chinese pregnant population was built by updating several key parameters and equations according to physiological parameters of Chinese (or Japanese) pregnant women. Drug-specific parameters of 6 renally cleared drugs were validated through PBPK modeling of Caucasian non-pregnant, Caucasian pregnant and Chinese non-pregnant population. The preliminary PBPK model of Chinese pregnant population was then developed by integrating the preliminary Chinese pregnant population and the drug-specific parameters. This model was verified by comparing the predicted maternal PK of these 6 drugs with the observed in vivo data from the literature.

RESULTS

The preliminary Chinese pregnant population PBPK model successfully predicted the PK of 6 target drugs for different pregnancy stages. The predicted plasma concentrations time profiles fitted the observed data well, and most predicted PK parameters were within 2-fold of observed data.

CONCLUSIONS

The preliminary Chinese pregnant population PBPK model provided a useful tool to predict the maternal PK of 6 predominantly renally cleared drugs in Chinese pregnant women.

Drug Dosing Considerations in Critically Ill Patients Receiving Continuous Renal Replacement Therapy

Acute kidney injury is very common in critically ill patients requiring renal replacement therapy. Despite the advancement in medicine, the mortality rate from septic shock can be as high as 60%. This manuscript describes drug-dosing considerations and challenges for clinicians. For instance, drugs’ pharmacokinetic changes (e.g., decreased protein binding and increased volume of distribution) and drug property changes in critical illness affecting solute or drug clearance during renal replacement therapy. Moreover, different types of renal replacement therapy (intermittent hemodialysis, prolonged intermittent renal replacement therapy or sustained low-efficiency dialysis, and continuous renal replacement therapy) are discussed to describe how to optimize the drug administration strategies. With updated literature, pharmacodynamic targets and empirical dosing recommendations for commonly used antibiotics in critically ill patients receiving continuous renal replacement therapy are outlined. It is vital to utilize local epidemiology and resistance patterns to select appropriate antibiotics to optimize clinical outcomes. Therapeutic drug monitoring should be used, when possible. This review should be used as a guide to develop a patient-specific antibiotic therapy plan.

Ceftazidime/avibactam versus standard-of-care agents against carbapenem-resistant Enterobacteriaceae harbouring blaKPC in a one-compartment pharmacokinetic/pharmacodynamic model

Background

'Last-line' antimicrobial usage has promoted the emergence of MDR bacteria. Production of Klebsiella pneumoniae carbapenemases (KPCs) is increasingly common and leads to resistance to most antimicrobials. However, ceftazidime/avibactam demonstrates activity against KPC-producing strains. Ceftazidime/avibactam in the empirical setting remains unknown.

Methods

Strains underwent genetic analysis evaluating blaKPC presence/production and MICs were determined. Four strains were assessed in an in vitro, one-compartment pharmacokinetic (PK)/pharmacodynamic (PD) model for 96 h. The following bolus dosing exposures were tested: 2.5 g of ceftazidime/avibactam every 8 h, 2 g of meropenem every 8 h, 1.25 mg/kg polymyxin B every 12 h, amikacin 'once-daily dosing' (peak of 70-80 mg/L), tigecycline at 200 mg ×1 dose followed by 100 mg every 12 h, and a drug-free growth control.

Results

Thirty blaKPC-producing strains were evaluated; 97% of strains were ceftazidime/avibactam susceptible with MIC50/MIC90 values of 0.38/1.5 mg/L (range 0.032-16 mg/L). Two K. pneumoniae strains, one Klebsiella oxytoca strain and one Citrobacter freundii strain underwent further analysis in PK/PD models. Ceftazidime/avibactam displayed potent activity with a reduction of 4.23 ± 0.42 cfu/mL from the initial inoculum at 96 h. Against susceptible isolates, amikacin displayed similar activity compared with ceftazidime/avibactam at 96 h, although this was not demonstrated against all strains. Polymyxin B produced comparable activity to ceftazidime/avibactam against two strains. Neither meropenem nor tigecycline produced effective killing and were comparable to the drug-free growth control at 96 h.

Conclusions

blaKPC-producing organisms demonstrated susceptibility to ceftazidime/avibactam and bactericidal activity was observed in the PK/PD model. Based on these data, ceftazidime/avibactam is a valuable agent for treating KPC-producing organisms and should be considered for treatment of infections caused by these pathogens.

Pharmacokinetic variability of beta-lactams in critically ill patients: A narrative review

The use of antibacterial drugs is very common in critically ill patients and beta-lactam agents are widely used in this context. Critically ill patients show several characteristics (e.g., sepsis, renal impairment or conversely augmented renal clearance, renal replacement therapy) that may alter beta-lactam pharmacokinetics (PK) in comparison with non-critically ill patients. This narrative literature review aims to identify recent studies quantifying the variability of beta-lactams volume of distribution and clearance and to determine its main determinants. Seventy studies published between 2000 and 2018 were retained. Data on volume of distribution and clearance variability were reported for 5 penicillins, 3 beta-lactamase inhibitors, 6 cephalosporins and 4 carbapenems. Data confirm specific changes in PK parameters and important variability of beta-lactam PK in critically ill patients. Renal function, body weight and use of renal replacement therapy are the principal factors influencing PK parameters described in this population. Few studies have directly compared beta-lactam PK in critically ill versus non-critically ill patients. Conclusions are also limited by small study size and sparse PK data in several studies. These results suggest approaches to assess this PK variability in clinical practice. Beta-lactam therapeutic drug monitoring seems to be the best way to deal with this issue.

A Nonparametric Pharmacokinetic Approach to Determine the Optimal Dosing Regimen for 30-Minute and 3-Hour Meropenem Infusions in Critically Ill Patients

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.

Utilizing Monte Carlo Simulations to Optimize Institutional Empiric Antipseudomonal Therapy

Pseudomonas aeruginosa is a common pathogen implicated in nosocomial infections with increasing resistance to a limited arsenal of antibiotics. Monte Carlo simulation provides antimicrobial stewardship teams with an additional tool to guide empiric therapy. We modeled empiric therapies with antipseudomonal β-lactam antibiotic regimens to determine which were most likely to achieve probability of target attainment (PTA) of ≥90%. Microbiological data for P. aeruginosa was reviewed for 2012. Antibiotics modeled for intermittent and prolonged infusion were aztreonam, cefepime, meropenem, and piperacillin/tazobactam. Using minimum inhibitory concentrations (MICs) from institution-specific isolates, and pharmacokinetic and pharmacodynamic parameters from previously published studies, a 10,000-subject Monte Carlo simulation was performed for each regimen to determine PTA. MICs from 272 isolates were included in this analysis. No intermittent infusion regimens achieved PTA ≥90%. Prolonged infusions of cefepime 2000 mg Q8 h, meropenem 1000 mg Q8 h, and meropenem 2000 mg Q8 h demonstrated PTA of 93%, 92%, and 100%, respectively. Prolonged infusions of piperacillin/tazobactam 4.5 g Q6 h and aztreonam 2 g Q8 h failed to achieved PTA ≥90% but demonstrated PTA of 81% and 73%, respectively. Standard doses of β-lactam antibiotics as intermittent infusion did not achieve 90% PTA against P. aeruginosa isolated at our institution; however, some prolonged infusions were able to achieve these targets.

Broad-spectrum β-lactams in obese non-critically ill patients

Objectives:

Obesity may alter the pharmacokinetics of β-lactams. The goal of this study was to evaluate if and why serum concentrations are inadequate when standard β-lactam regimens are administered to obese, non-critically ill patients.

Subjects and methods:

During first year, we consecutively included infected, obese patients (body mass index (BMI) ⩾30 kg m⁻²) who received meropenem (MEM), piperacillin-tazobactam (TZP) or cefepime/ceftazidime (CEF). Patients with severe sepsis or septic shock, or those hospitalized in the intensive care unit were excluded. Serum drug concentrations were measured twice during the elimination phase by high-performance liquid chromatography. We evaluated whether free or total drug concentrations were >1 time (fT>minimal inhibition concentration (MIC)) or >4 times (T>4MIC) the clinical breakpoints for Pseudomonas aeruginosa during optimal periods of time: ⩾40% for MEM, ⩾50% for TZP and ⩾70% for CEF.

Results:

We included 56 patients (median BMI: 36 kg m⁻²): 14 received MEM, 31 TZP and 11 CEF. The percentage of patients who attained target fT>MIC and T>4MIC were 93% and 21% for MEM, 68% and 19% for TZP, and 73% and 18% for CEF, respectively. High creatinine clearance (107 (range: 6–398) ml min⁻¹) was the only risk factor in univariate and multivariate analyses to predict insufficient serum concentrations.

Conclusions:

In obese, non-critically ill patients, standard drug regimens of TZP and CEF resulted in insufficient drug concentrations to treat infections due to less susceptible bacteria. Augmented renal clearance was responsible for these low serum concentrations. New dosage regimens need to be explored in this patient population (EUDRA-CT: 2011-004239-29).

Pharmacokinetics of meropenem and piperacillin in critically ill patients with indwelling surgical drains

Meropenem and piperacillin are two commonly prescribed antibiotics in critically ill surgical patients. To date, the pharmacokinetics of these antibiotics in the presence of indwelling abdominal surgical drains is poorly defined. This was a prospective pharmacokinetic study of meropenem and piperacillin. Serial plasma, urine and surgical drain fluid samples were collected over one dosing interval of antibiotic treatment in ten patients (meropenem, n = 5; piperacillin n = 5). Drug concentrations were measured using a validated high-performance liquid chromatography assay. Median (interquartile range) pharmacokinetic parameter estimates for meropenem were as follows: area under concentration-time curve (AUC), 128.7 mgh/L (95.3-176.7 mgh/L); clearance (CL), 5.7 L/h (5.1-10.5 L/h); volume of distribution (Vd), 0.41 L/kg (0.35-0.56 L/kg); AUC ratio (drain:plasma), 0.2 (0.1-0.2); and calculated antibiotic clearance via surgical drain, 3.8% (2.8-5.4%). For piperacillin, unbound pharmacokinetic results were as follows; AUC, 344.3 mgh/L (341.1-348.4 mgh/L); CL, 13.1 L/h (12.9-13.2 L/h); Vd, 0.63 L/kg (0.38-1.28 L/kg); AUC ratio (drain:plasma), 0.2 (0.2-0.3); and calculated antibiotic clearance via surgical drain 8.2% (3.3-14.0%). A linear correlation was present between the percentage of antibiotic cleared through the drain and the volume of surgical drain fluid output for meropenem (r(2) = 0.89; P = 0.05) and piperacillin (r(2) = 0.63; P = 0.20). Meropenem and piperacillin have altered pharmacokinetics in critically ill patients with indwelling surgical drains. We propose that only when very high drain fluid output is present (>1000 mL/day) would an additional dose of antibiotic be necessary.

Imipenem and meropenem: Comparison of in vitro activity, pharmacokinetics, clinical trials and adverse effects

OBJECTIVE

To compare and contrast imipenem and meropenem in terms of in vitro activity, pharmacokinetics, clinical efficacy and adverse effects.

DATA SELECTION

MEDLINE search from 1975 to 1997 and follow-up of references.

DATA EXTRACTION

Clinical trials comparing imipenem with meropenem, or either imipenem or meropenem with standard therapy in the treatment of serious infections were selected.

DATA SYNTHESIS

Imipenem, the first carbapenem, was first marketed in 1987; meropenem was introduced to the market in 1996. In general, imipenem is more active against Gram-positive cocci while meropenem is more active against Gram-negative bacilli. The agents display similar pharmacokinetics. Clinical studies in patients with serious infections (intra-abdominal infection, respiratory infection, septicemia, febrile neutropenia) report similar bacteriological and clinical cure rates with imipenem and meropenem. Meropenem is approved for the treatment of bacterial meningitis, whereas imipenem is not. Adverse effects are similar.

CONCLUSIONS

Current literature supports the use of imipenem at a dose of 500 mg every 6 h and meropenem at 1 g every 8 h for the treatment of severe infections. For the treatment of serious infections, imipenem (500 mg every 6 h or 2 g/day [$98/day]) is more economical than meropenem (1 g every 8 h or 3 g/day [$142/day]) based on acquisition cost.

Antibiotic dosing in critically ill patients with acute kidney injury

A common cause of acute kidney injury (AKI) is sepsis, which makes appropriate dosing of antibiotics in these patients essential. Drug dosing in critically ill patients with AKI, however, can be complicated. Critical illness and AKI can both substantially alter pharmacokinetic parameters as compared with healthy individuals or patients with end-stage renal disease. Furthermore, drug pharmacokinetic parameters are highly variable within the critically ill population. The volume of distribution of hydrophilic agents can increase as a result of fluid overload and decreased binding of the drug to serum proteins, and antibiotic loading doses must be adjusted upwards to account for these changes. Although renal elimination of drugs is decreased in patients with AKI, residual renal function in conjunction with renal replacement therapies (RRTs) result in enhanced drug clearance, and maintenance doses must reflect this situation. Antibiotic dosing decisions should be individualized to take into account patient-related, RRT-related, and drug-related factors. Efforts must also be made to optimize the attainment of antibiotic pharmacodynamic goals in this population.

Clinical review: Drug metabolism and nonrenal clearance in acute kidney injury

Decreased renal drug clearance is an obvious consequence of acute kidney injury (AKI). However, there is growing evidence to suggest that nonrenal drug clearance is also affected. Data derived from human and animal studies suggest that hepatic drug metabolism and transporter function are components of nonrenal clearance affected by AKI. Acute kidney injury may also impair the clearance of formed metabolites. The fact that AKI does not solely influence kidney function may have important implications for drug dosing, not only of renally eliminated drugs but also of those that are hepatically cleared. A review of the literature addressing the topic of drug metabolism and clearance alterations in AKI reveals that changes in nonrenal clearance are highly complicated and poorly studied, but they may be quite common. At present, our understanding of how AKI affects drug metabolism and nonrenal clearance is limited. However, based on the available evidence, clinicians should be cognizant that even hepatically eliminated drugs and formed drug metabolites may accumulate during AKI, and renal replacement therapy may affect nonrenal clearance as well as drug metabolite clearance.

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.

Efficacies of caspofungin and a combination of caspofungin and meropenem in the treatment of murine disseminated candidiasis

Disseminated candidiasis is relatively common in immunocompromised patients. The treatment protocol of these patients usually includes broad-spectrum antibiotics and also emprical antifungals initiated due to unresponsiveness to antibiotics. In this study the efficacies of caspofungin and meropenem - separately and together - in mice with disseminated candidiasis were studied. Immunocompetent mice were infected intravenously with 2x10(6) CFU of Candida albicans. At 24 h postinfection, intraperitoneal therapy was initiated and was continued for 7 days. Therapy groups included those given caspofungin (0.5, 1.25, 5 mg/kg/day), meropenem (20 mg/kg/day), and a combination of the two drugs. The outcome of therapy was evaluated by kidney tissue burden studies and histologic examination. In vitro, drug susceptibilities were tested by checkerboard analysis. Kidney CFU counts showed that mice that had received both drugs had lower residual burdens. Caspofungin was effective at doses of 0.5, 1.25, 5 mg/kg compared to infected untreated controls. In vitro, MICs of caspofungin and meropenem were <0.075 micro g/ml and >64 micro g/ml, respectively. Synergism was observed with the combination. Histopathology showed that the degree of inflammation was 25% less and tubular necrosis was more restricted in combined therapy than monotherapy. The results indicate that concurrent caspofungin and meropenem therapy may be beneficial.

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.

An evaluation of an optimal sampling strategy for meropenem in febrile neutropenics

Optimal sampling design with nonparametric population modeling offers the opportunity to determine pharmacokinetic parameters for patients in whom blood sampling is restricted. This approach was compared to a standard individualized modeling method for meropenem pharmacokinetics in febrile neutropenic patients. The population modeling program, nonparametric approach of expectation maximization (NPEM), with a full data set was compared to a sparse data set selected by D-optimal sampling design. The authors demonstrated that the D-optimal sampling strategy, when applied to this clinical population, provided good pharmacokinetic parameter estimates along with their variability. Four individualized and optimally selected sampling time points provided the same parameter estimates as more intensive sampling regimens using traditional and population modeling techniques. The different modeling methods were considerably consistent, except for the estimation of CL(d) with sparse sampling. The findings suggest that D-optimal sparse sampling is a reasonable approach to population pharmacokinetic/pharmacodynamic studies during drug development when limited sampling is necessary.

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.

Pharmacokinetics and pharmacodynamics of imipenem during continuous renal replacement therapy in critically ill patients

The pharmacokinetics of imipenem were studied in adult intensive care unit (ICU) patients during continuous venovenous hemofiltration (CVVH; n=6 patients) or hemodiafiltration (CVVHDF; n=6 patients). Patients (mean+/-standard deviation age, 50.9+/-15.9 years; weight, 98.5+/-15.9 kg) received imipenem at 0.5 g every 8 to 12 h (total daily doses of 1 to 1.5 g/day) by intravenous infusion over 30 min. Pre- and postmembrane blood (plasma) and corresponding ultrafiltrate or dialysate samples were collected 1, 2, 4, and 8 or 12 h (depending on dosing interval) after completion of the drug infusion. Drug concentrations were measured using validated high-performance liquid chromatography methods. Mean systemic clearance (CL(S)) and elimination half-life (t1/2) of imipenem were 145+/-18 ml/min and 2.7+/-1.3 h during CVVH versus 178+/-18 ml/min and 2.6+/-1.6 h during CVVHDF, respectively. Imipenem clearance was substantially increased during both CVVH and CVVHDF, with membrane clearance representing 25% and 32% of CL(S), respectively. The results of this study indicate that CVVH and CVVHDF contribute to imipenem clearance to a greater degree than previously reported. Imipenem doses of 1.0 g/day appear to achieve concentrations adequate to treat most common gram-negative pathogens (MIC up to 2 microg/ml) during CVVH or CVVHDF, but doses of 2.0 g/day or more may be required to adequately treat and prevent resistance in pathogens with higher MICs (MIC=4 to 8 microg/ml). Higher doses should only be used after consideration of potential central nervous system toxicities or other risks of therapy in these severely ill patients.

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.

Pharmacokinetics and Pharmacodynamics of Meropenem in Febrile Neutropenic Patients with Bacteremia

BACKGROUND:

Pharmacodynamic investigations with antimicrobials define the relationship between the infecting organism and achievable drug concentrations with clinical outcome.

OBJECTIVE:

To examine this relationship for meropenem in a population of patients who are at high risk of infection-related morbidity and mortality.

METHODS:

The study was a retrospective analysis of a multicenter, randomized, blinded clinical trial. A population-based predictive model was created using data from adults with febrile neutropenia and the nonparametric modeling program, NPEM. Patient age, body weight, and serum creatinine level were covariates in the model used to predict unbound concentrations for each patient. Pathogen susceptibility was estimated using product literature minimum inhibitory concentrations for effectiveness against 50% of microorganisms (MIC50) for specific organisms. The pharmacodynamic index of percent time above MIC (% T>MIC) was analyzed for its association with clinical outcome.

RESULTS:

A 2-compartment pharmacokinetic model using patient covariates of body weight and renal function best described the pharmacokinetics of meropenem in febrile neutropenic patients. Sixty patients with confirmed gram-positive or -negative bacteremia were studied. An average of 83% T>MIC was identified for the 42 clinical responders compared with 59% T>MIC for the 18 nonresponders (p = 0.04). An 80% clinical response rate was evident when the % T>MIC for meropenem exceeded 75% of the dosing interval (p = 0.01).

CONCLUSIONS:

To our knowledge, this is the first published report of a relationship between a pharmacodynamic index and clinical outcome in a febrile neutropenic population. Based on this relationship, dosing with intravenous meropenem 500 mg every 6 hours is predicted to be comparable to the currently recommended 1 g every 8 hours for serious infections. Our model provides further justification for a prospective clinical trial to evaluate a pharmacodynamically targeted meropenem dosing schedule as to its ability to improve clinical outcome in these patients.

Determination and pharmacokinetic study of meropenem in rat bile using on-line microdialysis and liquid chromatography

Meropenem is a carbapenem antibiotic with a wide spectrum of activity against both Gram-positive and Gram-negative bacteria. Because of its clinical efficacy, meropenem is an excellent choice for the treatment of serious infections in both adults and children. The knowledge of tissue concentrations of antibiotic in an infection site is valuable for the prediction of treatment outcome. To investigate the biliary disposition of meropenem, we utilized a minimally invasive sampling technique with a shunt linear microdialysis probe for continuous sampling in the biliary excretion studies. Analysis of meropenem in the dialysates was achieved using a LiChrosorb RP-18 column (Merck, 250 x 4.6 mm I.D.; particle size 5 microm) maintained at ambient temperature. The mobile phase was 50 mM monosodium phosphoric acid-methanol (80:20, v/v, pH 3.0). The UV detector wavelength was set at 298 nm. The area under the concentration-time curve and elimination half-lives of meropenem were about 6144 +/- 1494 min microg/ml and 61 +/- 17 min, respectively. This study represents a successful application of the microdialysis technique, which is an effective method for pharmacokinetic and biliary drug excretion studies.

Evaluation of panipenem/betamipron (PAPM/BP) in pneumonia in elderly patients

The present multicenter study evaluated the clinical and bacteriological efficacy and safety of panipenem/betamipron (PAPM/BP) for treating pneumonia in elderly patients. Forty-three episodes of pneumonia in 43 patients were treated with PAPM/BP as the sole antibiotic agent. All patients were 65 years of age or older, and were given PAPM/BP at a total daily dosage range of 0.5-2.0 g. The clinical efficacy rate, expressed as a percentage of the total number of excellent and good responses, was 56.4%. Of the 43 patients, 13 were evaluated bacteriologically. In these 13 patients, the eradication rate, expressed as a percentage of the total number of "eradicated" and "replaced" efficacies, was 30.8%. Adverse effects and abnormal laboratory findings occurred in 2 patients, which was 4.6% of the total number of patients evaluated. No serious adverse effects were observed. We concluded that PAPM/BP was well tolerated overall, and was effective and safe for most of the elderly patients.

Meropenem versus ceftazidime in the treatment of cancer patients with febrile neutropenia: a randomized, double-blind trial

PURPOSE

To compare meropenem, a carbapenem antibiotic, with ceftazidime for the empirical treatment of patients with febrile neutropenia.

PATIENTS AND METHODS

A prospective, double-blind, randomized clinical trial was conducted at medical centers in North America and the Netherlands. A total of 411 cancer patients (196 treated with meropenem and 215 treated with ceftazidime), who had 471 episodes of fever, participated in the trial. For each neutropenic episode, patients were allocated at random to receive intravenous administration of meropenem (1 g every 8 hours) or ceftazidime (2 g every 8 hours). Treatment could be modified at any time. Key end points were clinical and bacteriologic outcomes, eradication of infecting organism, and adverse events.

RESULTS

The rate of successful clinical response at the end of therapy was significantly higher for patients treated with meropenem than for those on ceftazidime for all episodes (54% v 44%, respectively) and for episodes of fever of unknown origin (62% v 46%, respectively), but differences between groups were not statistically significant for clinically defined or microbiologically defined infections. Meropenem was significantly more effective than ceftazidime in severely neutropenic (</= 100 cells/microliter) patients (55% v 43%, respectively), bone marrow transplant patients (73% v 27%, respectively), and patients given antibiotic prophylaxis before study entry (71% v 52%, respectively). Common adverse effects of meropenem and ceftazidime therapy were rash, diarrhea, and nausea and vomiting.

CONCLUSION

Monotherapy with meropenem represents a suitable choice for initial empirical antibiotic therapy for febrile episodes in neutropenic cancer patients.

Postantibiotic leukocyte enhancement of meropenem against gram-positive and gram-negative strains

The postantibiotic leukocyte enhancement (PALE) of meropenem in vitro in comparison with that of imipenem was evaluated with 24 recently isolated gram-positive and gram-negative strains. In general, pre-exposure to carbapenems (at four times the MIC for 2 h) led to increased polymorphonuclear cell phagocytic killing. The PALE of imipenem was generally significantly less than that observed with meropenem.

Comparative pharmacokinetics of the carbapenems: clinical implications

During the last few decades, several carbapenems have been developed. The major characteristic of the newer drugs, such as MK-826, is a prolonged half-life. Alternatively, some carbapenems have been developed that can be given orally, such as CS-834 and L-084. Although imipenem and panipenem have to be administered with a co-drug to prevent degradation by the enzyme dehydropeptidase-1 and reduce nephrotoxicity, the newer drugs such as meropenem, biapenem and lenapenem are relatively stable towards that enzyme. Structural modifications have, besides changes in pharmacology, also led to varying antimicrobial properties. For instance, meropenem is relatively more active against Gram-negative organisms than most other carbapenems, but is slightly less active against Gram-positive organisms. Except for half-life and bioavailability, the pharmacokinetic properties of the carbapenems are relatively similar. Distribution is mainly in extracellular body-water, as observed both from the volumes of distribution and from blister studies. Some carbapenems have a better penetration in cerebrospinal fluid than others. In patients with renal dysfunction, doses have to be adjusted, and special care must be taken with imipenem/cilastatin and panipenem/betamipron to prevent accumulation of the co-drugs, as the pharmacokinetic properties of the co-drugs differ from those of the drugs themselves. However, toxicity of the co-drugs has not been shown. The carbapenems differ in proconvulsive activity. Imipenem shows relatively the highest proconvulsive activity, especially at higher concentrations. Pharmacodynamic studies have shown that the major surrogate parameter for antimicrobial efficacy is the percentage of time of the dosage interval above the minimum inhibitory concentration (MIC). The minimum percentage percentage of time above the MIC (TaM) needed for optimal effect is known in animals (30 to 50%), but not in humans. It is probably less than 100%, but may be higher than 50%. Dosage regimens currently in use result in a TaM of about 50% at 4 mg/L, which is the current 'susceptible' breakpoint determined by the National Committee for Clinical Laboratory Standards (NCCLS) for most micro-organisms. Dosage regimens in patients with reduced renal clearance should be based on the TaM. The increased half-life of the newer carbapenems will probably lead to less frequent administration, although continuous infusion may still be the optimal mode of administration for these drugs. The availability of oral carbapenems will have a profound effect on the use of carbapenems in the community.

Comparative cerebrospinal fluid diffusion of imipenem and meropenem in rats

The main objective of this study was to compare the cerebrospinal fluid (CSF) diffusion of imipenem and meropenem at steady state, following intravenous infusions at various rates in rats. A preliminary experiment was conducted to estimate the elimination half-lives of these two carbapenem antibiotics, and then to evaluate the infusion duration necessary to reach steady state. CSF diffusion of imipenem was essentially linear over the wide range of infusion rates (66-1,320microg min(-1)) and corresponding steady-state plasma concentrations (11.7-443.0 microg mL(-1)). Conversely the CSF diffusion of meropenem was saturable, with a predicted maximum CSF concentration equal to 1.3 microg mL(-1). Extrapolation of these data to the clinical situation may not be possible since the rats had normal blood-brain and blood-CSF barriers whereas patients with diseases such as meningitis may not. However, it is suggested that the observed differences in the diffusion characteristics of imipenem and meropenem may be partly responsible for their differences in toxicity and efficacy at the central level.

Prospective, randomized, investigator-blinded study of the efficacy and safety of meropenem vs. cefotaxime therapy in bacterial meningitis in children. Meropenem Meningitis Study Group

OBJECTIVES

To compare the efficacy and safety of meropenem with cefotaxime for the treatment of infants and children with bacterial meningitis.

METHODS

Infants and children with strongly suspected or documented bacterial meningitis were randomly assigned in a prospective multicenter study to receive either meropenem or cefotaxime. Patients were assessed at the end of therapy and at 5 to 7 weeks and 5 to 7 months after the end of treatment for the presence of neurologic and sensory neural sequelae.

RESULTS

A total of 258 children were randomized to either treatment group. A further 8 patients with suspected pneumococcal meningitis were treated with meropenem without randomization. Of the randomized patients 154 were fully evaluable, 79 in the meropenem group and 75 in the cefotaxime group. At the end of treatment there were no significant differences in clinical outcome between the two treatment groups. Clinical cure with or without sequelae was achieved in 97 and 96% of the meropenem- and cefotaxime-treated patients, respectively. At the end of treatment and at 5 to 7 weeks, 46 and 54% of meropenem patients were cured with no sequelae, respectively. Corresponding results for cefotaxime patients were 56 and 58%. All pathogens were eradicated. In total 37 patients had seizures during treatment, 15 (12%) in the meropenem and 22 (17%) in the cefotaxime group. None of the seizures was considered to be drug-related.

CONCLUSIONS

This trial shows that meropenem is suitable therapy for bacterial meningitis in infants and children and that it offers an efficacy and safety profile similar to that of cefotaxime.

Pharmacokinetics of meropenem in critically ill patients with acute renal failure undergoing continuous venovenous hemofiltration

OBJECTIVE

Meropenem is a broad-spectrum antibiotic used for severe infections. In patients with chronic end-stage renal failure, meropenem clearance is reduced and doses must be adjusted according to the creatinine clearance. The aim of this study was to assess pharmacokinetic data of meropenem in patients with acute renal failure and to determine the amount of drug removed by continuous venovenous hemofiltration, an often-used renal replacement therapy in patients with acute renal failure.

METHODS

Nine critically ill anuric patients with acute renal failure undergoing continuous venovenous hemofiltration received 500 mg meropenem 2 or 3 times daily. Plasma and hemofiltrate concentrations were determined during 1 dosing interval at steady state. Pharmacokinetic parameters were calculated for a 2-compartment open model and dose requirements were calculated.

RESULTS

The total meropenem clearance was 52.0 +/- 8.4 mL/min, with a hemofiltration clearance of 22.0 +/- 4.7 mL/min and a nonrenal-nonhemofiltration clearance of 29.9 +/- 5.4 mL/min; 235.9 +/- 88.6 mg, or 47.2% +/- 17.7%, of the dose were removed through continuous venovenous hemofiltration. The terminal elimination half-life was 8.7 +/- 3.5 hours and the volume of distribution at steady state was 12.4 +/- 1.8 L. Peak and trough concentrations for a dosing interval of 12 hours were 38.9 +/- 9.7 mg/L and 7.3 +/- 1.3 mg/L, respectively. The corresponding concentrations for a dosing interval of 8 hours were 44.7 +/- 10.4 mg/L and 11.9 +/- 0.7 mg/L, respectively.

CONCLUSION

Pharmacokinetic data of anuric patients with acute renal failure were similar to those of patients with end-stage renal failure. Because hemofiltration contributes significantly to meropenem elimination, the recommended dose for critically ill anuric patients receiving continuous venovenous hemofiltration should be increased by 100% to avoid potential underdosing.

Pharmacokinetics of meropenem in critically ill patients with acute renal failure treated by continuous hemodiafiltration

The pharmacokinetics of meropenem were studied in nine anuric critically ill patients treated by continuous venovenous hemodiafiltration. Peak levels after infusion of 1,000 mg over 30 min amounted to 103.2 +/- 45.9 microgram/ml, and trough levels at 12 h were 9.6 +/- 3.8 microgram/ml. A dosage of 1,000 mg of meropenem twice a day provides plasma drug levels covering intermediately susceptible microorganisms. Further reductions of the dosage might be appropriate for highly susceptible bacteria or when renal replacement therapies with lower clearances are applied.

Analysis of recent antimicrobial agents in human biological fluids by high-performance liquid chromatography

Our previous review on the liquid chromatographic (LC) analysis of anti-bacterial agents was published in 1990 in a special issue of the Journal of Chromatography. Eight years later, some new agents have been registered and numerous other are under clinical experiment. In spite of therapeutic problems encountered with certain bacterial pathogens, the development of novel drug candidates has slowed partially due to the need for identification of new bacterial targets and the cost of the research. The present overview updates the LC methods for the quantitations of recent antimicrobial agents (marketed and in clinical development) in human biological fluids. Consideration has been given to procedures permitting the determination of isomers and metabolites as well as methods regarding tissue extracts or liquid sampled from physiological sanctuaries. LC methods are available for the quantitation of almost all registered or investigated recent anti-infective drugs and some are applicable in routine practice. Nevertheless, few techniques have been validated for the determination in tissue extracts limiting the development of penetration studies.

Determination of meropenem in serum by high-performance liquid chromatography with column switching

A rapid, accurate and sensitive liquid chromatographic assay with on-line solid-phase extraction for determination of meropenem in serum is described. Sample was directly injected onto the extraction column for sample clean-up and extraction. Thereafter, using an on-line column-switching system the drug was quantitatively transferred and separated on a C18 analytical column. Ultraviolet absorption at 298 nm was used for detection. The assay was linear from 1 to 100 micrograms/ml. Recovery was 98.5%. Based on a 20-microliters sample volume (serum- water, 1:1, v/v), detection limit was 0.1 microgram/ml. An application of the method to study the pharmacokinetics of meropenem is given.

Meropenem versus cefuroxime plus gentamicin for treatment of serious infections in elderly patients

In this multicenter study, the efficacy of and tolerability for meropenem were compared with those for the combination of cefuroxime-gentamicin (+/- metronidazole) for the treatment of serious bacterial infections in patients > or = 65 years of age. A total of 79 patients were randomized; thirty-nine received meropenem (1 g/8 h), and 40 received cefuroxime (1.5 g/8 h) plus gentamicin (4 mg/kg of body weight daily) for 5 to 10 days. Metronidazole (500 mg/6 h) could be added to the cefuroxime-gentamicin regimen for the treatment of intra-abdominal infections (n = 10). Seventy patients were evaluable for clinical efficacy; the primary diagnoses were as follows: pneumonia in 41 patients (20 treated with meropenem, 21 treated with cefuroxime-gentamicin), intra-abdominal infection in 10 patients (7 meropenem, 3 cefuroxime-gentamicin-metronidazole), urinary tract infection (UTI) in 11 patients (6 meropenem, 5 cefuroxime-gentamicin), sepsis syndrome in 7 patients (4 meropenem, 3 cefuroxime-gentamicin), and "other" in 1 patient (cefuroxime-gentamicin). The pathogens isolated from 18 patients with bacteremia were as follows: Staphylococcus spp. (n = 2), Streptococcus spp. (n = 2), members of the family Enterobacteriaceae (n = 11), and Bacteroides spp. (n = 3). A satisfactory clinical response at the end of therapy was achieved in 26 of 37 (70%) and 24 of 33 (73%) evaluable patients treated with meropenem and combination therapy, respectively. Clinical success was achieved in 23 of 31 (74%) and 21 of 28 (75%) evaluable patients with infections other than UTIs, respectively. A satisfactory microbiological response occurred in 15 of 22 (68%) patients in the meropenem group compared with 12 of 19 (63%) treated with combination therapy. Renal failure occurred during therapy in 2 of 39 (5%) meropenem recipients compared with 5 of 40 (13%) of those treated with combination therapy. The findings in this small study indicate that meropenem is as efficacious for and as well tolerated by elderly patients as the combination of cefuroxime-gentamicin (+/- metronidazole).

Pharmacokinetics of meropenem in febrile neutropenic patients. Swedish study group

To determine the impact of neutropenia on the pharmacokinetics of meropenem, 14 patients with fever and neutropenia were given 1 g of meropenem i.v. every 8 h as an infusion over 30 min. The volume of distribution (16.2 l/1.73 m2) and the nonrenal clearance [75 ml/(min x 1.73 m2)] in this group were significantly increased compared to healthy subjects studied previously with identical techniques. The kinetic study was repeated when the patients had a normal temperature and a raised neutrophil count; most kinetic variables did not differ from the findings on the first day of treatment. The pharmacokinetic profile of meropenem in febrile neutropenic patients differs from earlier findings in healthy subjects. Considering these data and known minimum inhibitory concentration values for common pathogens, meropenem administered every 6 to 8 h seems an appropriate regimen in patients with febrile neutropenia. The shorter time interval may be used for treatment of Pseudomonas infection.

Prospective, randomised, multicentre study of meropenem versus imipenem/cilastatin as empiric monotherapy in severe nosocomial infections

The clinical and bacteriological efficacy and the tolerability of meropenem versus imipenem/cilastatin (both 1 g t.i.d.) in severe nosocomial infections were compared in a multicentre, randomised, nonblinded study. A total of 151 patients were recruited; 133 (66 meropenem, 67 imipenem/cilastatin) were clinically evaluable and 84 (42 meropenem, 42 imipenem/cilastatin) bacteriologically evaluable. Most clinically evaluable patients (90%) were in intensive care units, required mechanical ventilation (72%), and had received previous antibiotic therapy (62%). The mean (+/- SD) APACHE II score was 15.2 (+/- 6.6) in the meropenem group and 17.8 (+/- 6.8) in the imipenem/cilastatin group. The primary infections were nosocomial lower respiratory tract infections (56% of patients), intra-abdominal infections (15%), septicaemia (21%), skin/skin structure infections (5%), and complicated urinary tract infections (3%); 35% of the patients had two or more infections. There was no significant difference between the meropenem and imipenem/cilastatin groups in the rates of satisfactory clinical (weighted percentage 87% vs. 74%) or bacteriological (weighted percentage 79% vs. 71%) response. There was a slightly higher rate of clinical success with meropenem against primary or secondary lower respiratory tract infection (89% vs. 76%). Drug-related adverse events occurred in 17% and 15% of meropenem and imipenem/cilastatin patients, respectively. Meropenem (1 g t.i.d.) was as efficacious as the same dose of imipenem/cilastatin in this setting, and both drugs were well tolerated.

High-performance liquid chromatographic assay for meropenem in serum

High-performance liquid chromatographic procedures have been developed for the measurement of meropenem in serum. The separation was performed on an Ultrasphere XL-ODS analytical column (75 x 4.6 min I.D.). The mobile phase consisted of 10.53 mmol/l ammonium acetate-acetonitrile (95:5, v/v) (pH 4). The UV detection was at 298 nm. The quantitation limit both in serum and water was 0.25 micrograms/ml. The method was validated in serum and aqueous solution over the concentration range 0.25-50 micrograms/ml. The extraction recovery from serum spiked with meropenem was 99.7 +/- 3.4%. The intra- and inter-assay coefficients of variation were below 6%. Stored at -80 degrees C for three months at various concentrations in serum and in aqueous solution, meropenem did not reveal any appreciable degradation. After 24 h, it was also stable at 4 degrees C in serum, aqueous solution and supernatant of extraction but not at room temperature. The stability of the drug was also confirmed in serum after repeated freezing-thawing cycles at -80 degrees C on four consecutive days.

Serum bactericidal activities and comparative pharmacokinetics of meropenem and imipenem-cilastatin

The pharmacokinetics and serum bactericidal activities (SBAs) of imipenem and meropenem were investigated in a randomized crossover study. Twelve healthy male volunteers received a constant 30-min infusion of either 1 g of imipenem plus 1 g of cilastatin or 1 g of meropenem. The concentrations of the drugs in serum and urine were determined by bioassay and high-pressure liquid chromatography. Pharmacokinetic parameters were based on an open two-compartment model and a noncompartmental technique. At the end of infusion, the mean concentrations of imipenem and meropenem measured in serum were 61.2 +/- 9.8 and 51.6 +/- 6.5 mg/liter, respectively; urinary recoveries were 48.6% +/- 8.2% and 60.0% +/- 6.5% of the dose in 12 h, respectively; and the areas under the concentration-time curve from time zero to infinity were 96.1 +/- 14.4 and 70.5 +/- 10.3 mg.h/liter, respectively (P < or = 0.02). Imipenem had a mean half-life of 66.7 +/- 10.4 min; that of meropenem was 64.4 +/- 6.9 min. The volumes of distribution at steady state of imipenem and meropenem were 15.3 +/- 3.3 and 18.6 +/- 3.0 liters/70 kg, respectively, and the mean renal clearances per 1.73 m2 were 85.6 +/- 17.6 and 144.6 +/- 26.0 ml/min, respectively. Both antibiotics were well tolerated in this single-dose administration study. The SBAs were measured by the microdilution method of Reller and Stratton (L. B. Reller and C. W. Stratton, J. Infect. Dis. 136:196-204, 1977) against 40 clinically isolated strains. Mean reciprocal bactericidal titers were measured 1 and 6 h after administration. After 1 and 6 h the median SBAs for imipenem and meropenem, were 409 and 34.9 and 97.9 and 5.8, respectively, against Staphylococcus aureus, 19.9 and 4.4 and 19.4 and 4.8, respectively, against Pseudomonas aeruginosa, 34.3 and 2.2 and 232 and 15.5, respectively, against Enterobacter cloacae, and 13.4 and 2.25 and 90.7 and 7.9, respectively, against Proteus mirabilis. Both drugs had rather short biological elimination half-lives and a predominantly renal route of elimination. Both carbapenems revealed high SBAs against clinically important pathogens at 1 h; meropenem had a higher SBA against E. cloacae and P. mirabilis, and the SBA of imipenem against S. aureus was greater than the SBA of meropenem.

Imipenem/cilastatin: an update of its antibacterial activity, pharmacokinetics and therapeutic efficacy in the treatment of serious infections

The prototype carbapenem antibacterial agent imipenem has a very broad spectrum of antibacterial activity, encompassing most Gram-negative and Gram-positive aerobes and anaerobes, including most beta-lactamase-producing species. It is coadministered with a renal dehydropeptidase inhibitor, cilastatin, in order to prevent its renal metabolism in clinical use. Extensive clinical experience gained with imipenem/cilastatin has shown it to provide effective monotherapy for septicaemia, neutropenic fever, and intra-abdominal, lower respiratory tract, genitourinary, gynaecological, skin and soft tissues, and bone and joint infections. In these indications, imipenem/cilastatin generally exhibits similar efficacy to broad-spectrum cephalosporins and other carbapenems and is at least equivalent to standard aminoglycoside-based and other combination regimens. Imipenem/cilastatin is generally well tolerated by adults and children, with local injection site events, gastrointestinal disturbances and dermatological reactions being the most common adverse events. Seizures have also been reported, occurring mostly in patients with impaired renal function or CNS pathology, or with excessive dosage. Although it is no longer a unique compound, as newer carbapenems such as meropenem are becoming available, imipenem/cilastatin nevertheless remains an important agent with established efficacy as monotherapy for moderate to severe bacterial infections. Its particular niche is in treating infections known or suspected to be caused by multiresistant pathogens.

Randomized comparison of meropenem with cefotaxime for treatment of bacterial meningitis. Meropenem Meningitis Study Group

Broad-spectrum cephalosporins are drugs of choice for the treatment of meningitis in communities which can afford them. The emergence of cephalosporin-resistant pneumococci demands the clinical trial of alternate agents. Carbapenems are active against the bacteria causing meningitis, but the use of imipenem-cilastatin was frustrated by drug-associated seizures. The safety and efficacy of meropenem, a new carbapenem, were compared to those of cefotaxime in a prospective randomized trial of 190 children with bacterial meningitis. Seizures occurred within 24 h before antibiotic therapy in 16 of 98 patients (16%) randomized to receive meropenem and in 6 of 92 patients (7%) randomized to receive cefotaxime. In patients without seizures before therapy, seizures occurred during therapy in 5 of 82 patients (6%) receiving meropenem and in 1 of 86 patients (1%) receiving cefotaxime (95% confidence interval: -0.7%, 10.6%). None were thought to be drug related. Twenty-four meropenem-treated patients (24%) and 11 cefotaxime-treated patients (12%) had neurological abnormalities before therapy. In patients without pretherapy neurological abnormalities, these abnormalities were present after treatment in 4 of 74 meropenem-treated patients (5%) and in 2 of 81 cefotaxime-treated patients (2%) (95% confidence interval: -3.2%, 9.1%). Of 75 meropenem-treated and 64 cefotaxime-treated patients with pretherapy positive cerebrospinal-fluid cultures, 68 and 59, respectively, had repeat lumbar punctures. Bacterial eradication was found to be 100% in both groups. Our data suggest that meropenem may be a carbapenem agent that is well tolerated and effective in the treatment of bacterial meningitis.