Optimization of meropenem dosage in the critically ill population based on renal function

Stability of meropenem in portable elastomeric infusion devices: which protocol should be implemented in clinical practice?

Meropenem has an excellent activity against gram-positive and gram-negative bacteria, including multi-resistant microorganisms. Even though meropenem is a great candidate for outpatient parenteral antimicrobial therapy (OPAT), its physicochemical stability is a major challenge. This work aimed to demonstrate the suitability of including meropenem in OPAT by elucidating its physicochemical stability in a range of commonly prescribed concentrations within portable elastomeric infusion devices. Physical and chemical stability were evaluated at two concentrations commonly used in clinical practice (2 and 25 mg/mL), and three temperatures (2°C-8°C, 25°C, and 32°C) using Accufuser portable elastomeric infusion devices. Drug adsorption onto portable elastomeric infusion devices was also determined at the end of the experiment. Meropenem stability significantly decreased at higher temperatures and when higher drug solution concentrations were used. Meropenem solutions at 2 mg/mL kept the drug content above 95% over 24 h at 2°C-8°C but just for 8 h at 25°C. Nevertheless, solutions containing 25 mg/mL of meropenem showed a dramatic decrease in chemical stability after 8 h 2°C-8°C and just after 4 h at 25°C or 32°C. However, physical stability was kept favorable during this period. The drug adsorption on the material of the elastomeric infusion device was below 1%, indicating the suitability of the chosen device. We propose several administration protocols for meropenem in portable elastomeric infusion devices in clinical practice, according to the results obtained in our study. The results obtained in this study open up the possibility of administering meropenem in an OPAT setting despite its short stability.IMPORTANCEAlthough outpatient parenteral antibiotic therapy can be a good approach to treating infections, a lack of data regarding antibiotic stability in portable elastomeric infusion devices restricts its safe and effective use. Actually, meropenem is used for prolonged periods above 24 h, and it is not physicochemically stable, which can compromise efficacy and toxicity. This work is of high importance to show the clinicians the real shelf life of meropenem when administered in portable elastomeric infusion devices. We propose several administration protocols for meropenem in portable elastomeric infusion devices in clinical practice, according to the stability drug results obtained in our study.

Stability of meropenem in portable elastomeric infusion devices: which protocol should be implemented in clinical practice?

IMPORTANCE

Although outpatient parenteral antibiotic therapy can be a good approach to treating infections, a lack of data regarding antibiotic stability in portable elastomeric infusion devices restricts its safe and effective use. Actually, meropenem is used for prolonged periods above 24 h, and it is not physicochemically stable, which can compromise efficacy and toxicity. This work is of high importance to show the clinicians the real shelf life of meropenem when administered in portable elastomeric infusion devices. We propose several administration protocols for meropenem in portable elastomeric infusion devices in clinical practice, according to the stability drug results obtained in our study.

First-in-human study to evaluate the safety, tolerability, and population pharmacokinetic/pharmacodynamic target attainment analysis of FL058 alone and in combination with meropenem in healthy subjects

FL058 is a novel diazabicyclooctane β-lactamase inhibitor. This first-in-human study evaluated the safety, tolerability, and population pharmacokinetic (PK)/pharmacodynamic target attainment analysis of FL058 alone and in combination with meropenem in healthy subjects. The results showed that the maximum tolerated dose of FL058 was 3,000 mg after single-dose infusion. FL058 in combination with meropenem did not cause any grade 3 or higher adverse event when the dose was escalated up to 1,000 mg/2,000 mg. FL058 exposure PK parameters showed dose proportionality. FL058 was excreted primarily in urine. No significant PK interaction was found between FL058 and meropenem. Population PK model analysis indicated that the PK profiles of FL058 and meropenem were consistent with the two-compartment model. The impact of covariates, creatinine clearance, concomitant use of meropenem, body weight, sex, and FL058 dose, on FL058 exposure was less than 10%. FL058/meropenem combination was safe and well tolerated up to a 1,000-mg/2,000-mg dose in healthy adults. The recommended minimum dose of FL058/meropenem combination was 500 mg/1,000 mg by intravenous infusion over 2 h every 8 h based on target attainment analysis. The good safety, tolerability, and satisfactory PK profiles of FL058 alone and in combination with meropenem in this first-in-human study will support further clinical development of FL058 in combination with meropenem in patients with target infections (ClinicalTrials.gov identifiers: NCT05055687, NCT05058118, and NCT05058105).

In vivo dose response and efficacy of the β-lactamase inhibitor, durlobactam, in combination with sulbactam against the Acinetobacter baumannii-calcoaceticus complex

Multi-drug resistant (MDR) Acinetobacter baumannii is emerging as a pathogen of increasing prevalence and concern. Infections associated with this Gram-negative pathogen are often associated with increased morbidity and mortality and few therapeutic options. The β-lactamase inhibitor sulbactam used commonly in combination with ampicillin demonstrates intrinsic antibacterial activity against A. baumannii acting as an inhibitor of PBP1 and PBP3, which participate in cell wall biosynthesis. The production of β-lactamases, particularly class D oxacillinases, however, has limited the utility of sulbactam resorting to increased doses and the need for alternate therapies. Durlobactam is a non-β-lactam β-lactamase inhibitor that demonstrates broad β-lactamase inhibition including class D enzymes produced by A. baumannii and has shown potent in vitro activity against MDR A. baumannii, particularly carbapenem-resistant isolates in susceptibility and pharmacodynamic model systems. The objective of this study is to evaluate the exposure-response relationship of sulbactam and durlobactam in combination using in vivo neutropenic thigh and lung models to establish PK/PD exposure magnitudes to project clinically effective doses. Utilizing established PK/PD determinants of %T>MIC and AUC/MIC for sulbactam and durlobactam, respectively, non-linear regressional analysis of drug exposure was evaluated relative to the 24-hour change in bacterial burden (log10 CFU/g). Co-modeling of the data across multiple strains exhibiting a broad range of MIC susceptibility suggested net 1-log10 CFU/g0 reduction can be achieved when sulbactam T>MIC exceeds 50% of the dosing interval and durlobactam AUC/MIC is 10. These data were ultimately used to support sulbactam-durlobactam dose selection for Phase 3 clinical trials.

Population pharmacokinetics of antibacterial agents in the older population: a literature review

INTRODUCTION

Older individuals face an elevated risk of developing bacterial infections. The optimal use of antibacterial agents in this population is challenging because of age-related physiological alterations, changes in pharmacokinetics (PK) and pharmacodynamics (PD), and the presence of multiple underlying diseases. Therefore, population pharmacokinetics (PPK) studies are of great importance for optimizing individual treatments and prompt identification of potential risk factors.

AREA COVERED

Our search involved keywords such as 'elderly,' 'old people,' and 'geriatric,' combined with 'population pharmacokinetics' and 'antibacterial agents.' This comprehensive search yielded 11 categories encompassing 28 antibacterial drugs, including vancomycin, ceftriaxone, meropenem, and linezolid. Out of 127 studies identified, 26 (20.5%) were associated with vancomycin, 14 (11%) with meropenem, and 14 (11%) with piperacillin. Other antibacterial agents were administered less frequently.

EXPERT OPINION

PPK studies are invaluable for elucidating the characteristics and relevant factors affecting the PK of antibacterial agents in the older population. Further research is warranted to develop and validate PPK models for antibacterial agents in this vulnerable population.

Efficiency of dosing software using Bayesian forecasting in achieving target antibiotic exposures in critically ill patients, a prospective cohort study

INTRODUCTION

Broad-spectrum antibiotics such as beta-lactams and vancomycin are frequently used to treat critically ill patients, however, a significant number do not achieve target exposures. Therapeutic drug monitoring (TDM) combined with Bayesian forecasting dosing software may improve target attainment in these patients. This study aims to describe the efficiency of dosing software for achieving target exposures of selected beta-lactam antibiotics and vancomycin in critically ill patients.

METHODS

A prospective cohort study was undertaken in an adult intensive care unit (ICU). Patients prescribed vancomycin, piperacillin-tazobactam and meropenem were included if they exhibited a subtherapeutic or supratherapeutic exposure informed by TDM. The dosing software, ID-ODS™, was used to generate dosing recommendations which could be either accepted or rejected by the treating team. Repeat antibiotic TDM were requested to determine if target exposures were achieved.

RESULTS

Between March 2020 and December 2021, 70 were included in the analysis. Software recommendations were accepted for 56 patients (80%) with 50 having repeated antibiotic measurements. Forty-three of the 50 patients (86%) achieved target exposures after one software recommendation, with 3 of the remaining 7 patients achieving target exposures after 2. Forty-seven patients out of the 50 patients (94%) achieved the secondary outcome of clinical cure. There were no antibiotic exposure-related adverse events reported.

CONCLUSION

The use of TDM combined with Bayesian forecasting dosing software increases the efficiency for achieving target antibiotic exposures in the ICU. Clinical trials comparing this approach with other dosing strategies are required to further validate these findings.

In silico evaluation of a beta-lactam dosing guideline among adults with serious infections

STUDY OBJECTIVE

The aim of this study was to compare the achievement of therapeutic pharmacokinetic-pharmacodynamic (PK-PD) exposure targets for beta-lactam antibiotics using product information dosing or guideline-based dosing for the treatment of serious infections.

DESIGN

In silico study.

DATA SOURCE

ID-ODSTM (Individually Designed Optimum Dosing Strategies).

PATIENTS AND INTERVENTION

None.

MEASUREMENTS AND MAIN RESULTS

In silico product information and guideline-based dosing simulations for cefepime, ceftazidime, flucloxacillin, meropenem, and piperacillin/tazobactam were performed using pharmacokinetic models from seriously ill patient populations. The median simulated concentration at 48 and 96 h was used to measure the probability of target attainment (PTA) to achieve predefined therapeutic and toxicity PK-PD targets. A multiple linear regression model was constructed to identify the effect of guideline-based dosing covariates on achieving pre-defined therapeutic targets. In total, 480 dosing simulations were performed. The PTA percentage with guideline-based dosing at 48 and 96 h was 80% and 68%, respectively, yielding significantly higher results when compared to product information dosing (48.45% and 49%, respectively), p < 0.001 at both time points. At 48 h, predefined toxicity thresholds were exceeded in 4.7% and 0% of simulations for guideline-based and product information-based dosing, respectively (p = 0.002). eGFR was significantly associated with the % PTA by guideline-based dosing, with eGFR values of 20 and 50 ml/min both statistically significant in leading to an increase in PTA.

CONCLUSIONS

Our study demonstrated that achievement of PK-PD exposures associated with an increased likelihood of effectiveness was more likely to occur with guideline-based dosing; especially at 48 h.

Meropenem Pharmacokinetics and Target Attainment in Critically Ill Patients

Purpose

This study aimed to investigate the pharmacokinetics and target attainment of meropenem and compare the effect of meropenem dosing regimens in critically ill patients.

Patients and Methods

Thirty-seven critically ill patients who were administered meropenem in intensive care units were analyzed. Patients were classified according to their renal function. Pharmacokinetic parameters were assessed based on Bayesian estimation. The target attainment of 40%fT > MIC (fraction time that the free concentration exceeds the minimum inhibitory concentration) and 100%fT > MIC with the pathogen MIC of 2 mg/L and 8 mg/L were specially focused. Furthermore, the effects of standard dosing (1g meropenem, 30 min intravenous infusion every 8h) and non-standard dosing (dosage regimens except standard dosing) were compared.

Results

The results showed that the values of meropenem clearance (CL), central volume of distribution (V1), intercompartmental clearance (Q), and peripheral volume of distribution (V2) were 3.3 L/h, 9.2 L, 20.1 L/h and 12.8 L, respectively. The CL of the patients among renal function groups was significantly different (p < 0.001). The tow targets attainment for the pathogen MIC of 2 mg/L and 8 mg/L were 89%, 73%, 49% and 27%, respectively. The severe renal impairment group has higher fraction of target attainment than the other group. The standard dosing achieved the target of 40%fT > 2/8 mg/L (85.7% and 81%, respectively) and patients with severe renal impairment achieved the target fraction of 100% for 40%fT > MIC. Additionally, there was no significant difference between standard and non-standard dosing group in target attainment.

Conclusion

Our findings indicate that renal function is an important covariate for both meropenem pharmacokinetics parameters and target attainment. The target attainment between standard and non-standard dosing group was not comparable. Therefore, therapeutic drug monitoring is indispensable in the dosing adjustment for critically ill patients if it is available.

Accuracy of a precision dosing software program for predicting antibiotic concentrations in critically ill patients

BACKGROUND

Critically ill patients with sepsis are predisposed to physiological changes that can reduce the probability of achieving target antibiotic exposures. Precision dosing software programs may be used to improve probability of obtaining these target exposures.

OBJECTIVE

To quantify the accuracy of a precision dosing software program for predicting antibiotic concentrations as well as to assess the impact of using software predictions on actual dosing adjustments.

PATIENTS AND METHODS

The software program ID-ODS was used to predict concentrations for piperacillin, meropenem and vancomycin using patient covariate data with and without the use of therapeutic drug monitoring (TDM) data. The impact of these predictions on actual dosage adjustments was determined by using software predicted concentrations versus measured concentrations.

RESULTS

Software predictions for piperacillin and meropenem exhibited large bias that improved with the addition of TDM data (bias improved from -28.8 to -2.0 mg/L for piperacillin and -3.0 to -0.1 mg/L for meropenem). Dosing changes using predicted concentrations of piperacillin and meropenem with TDM data versus measured concentrations were matched on 89.2% (107/120) and 71% (9/69) occasions, respectively. Although vancomycin predictions demonstrated good accuracy with and without TDM, these findings were limited by our small sample size.

CONCLUSION

These data demonstrate that precision dosing software programs may have scope to reasonably predict antibiotic concentrations in critically ill patients with sepsis. The addition of TDM data improves the predictive performance of the software for all three antibiotics and the ability to anticipate the correct dose change required.

Evaluation of Empirical Dosing Regimens for Meropenem in Intensive Care Unit Patients Using Population Pharmacokinetic Modeling and Target Attainment Analysis

In the present study, population pharmacokinetic (PK) analysis was performed based on meropenem data from a prospective study conducted in 114 critically ill patients with a wide range of renal functions and various disease conditions. The final model was a one-compartment model with linear elimination, with creatinine clearance and continuous renal replacement therapy affecting clearance, and total bodyweight impacting the volume of distribution. Our model is a valuable addition to the existing meropenem population PK models, and it could be particularly useful during implementation of a therapeutic drug monitoring program combined with Bayesian forecasting. Based on the final model developed, comprehensive Monte Carlo simulations were performed to evaluate the probability of target attainment (PTA) of 16 different dosing regimens. Simulation results showed that 2 g administered every 8 h with 3-h prolonged infusion (PI) and 4 g/day by continuous infusion (CI) appear to be two empirical dosing regimens that are superior to many other regimens when both target attainment and potential toxicity are considered and renal function information is not available. Following a daily CI dose of 6 g or higher, more than 30% of the population with a creatinine clearance of <60 mL/min is predicted to have neurotoxicity. With the availability of institution- and/or unit-specific meropenem susceptibility patterns, as well as an individual patient's renal function, our PTA results may represent useful references for physicians to make dosing decisions.

Population Pharmacokinetics/Pharmacodynamics and Clinical Outcomes of Meropenem in Critically Ill Patients

Several pathophysiological changes can alter meropenem pharmacokinetics in critically ill patients, thereby increasing the risk of subtherapeutic concentrations and affecting therapeutic outcomes. This study aimed to characterize the population pharmacokinetic (PPK) parameters of meropenem, evaluate the relationship between the pharmacokinetic/pharmacodynamic index of meropenem and treatment outcomes, and evaluate the different dosage regimens that can achieve 40%, 75%, and 100% of the dosing interval for which the free plasma concentrations remain above the MIC of the pathogens (fT_>MIC) targets. Critically ill adult patients treated with meropenem were recruited for this study. Five blood samples were collected from each patient. PPK models were developed using a nonlinear mixed-effects modeling approach, and the final model was subsequently used for Monte Carlo simulations to determine the optimal dosage regimens. A total of 247 concentrations from 52 patients were available for analysis. The two-compartment model with linear elimination adequately described the data. The mean PPK parameters were clearance (CL) of 4.8 L/h, central volume of distribution (V_C) of 11.4 L, peripheral volume of distribution (V_P) of 14.6 L, and intercompartment clearance of 10.5 L/h. Creatinine clearance was a significant covariate affecting CL, while serum albumin level and shock status were factors influencing V_C and V_P, respectively. Although 75% of the drug-resistant infection patients had fT_>MIC values of >40%, approximately 83% of them did not survive the infection. Therefore, 40% fT_>MIC might not be sufficient for critically ill patients, and a higher target, such as 75 to 100% fT_>MIC, should be considered for optimizing therapy. A 75% fT_>MIC could be reached using approved doses administered via a 3-h infusion.

Optimizing Meropenem in Highly Resistant Klebsiella pneumoniae Environments: Population Pharmacokinetics and Dosing Simulations in Critically Ill Patients

Critically ill patients are characterized by substantial pathophysiological changes that alter the pharmacokinetics (PK) of hydrophilic antibiotics, including carbapenems. Meropenem is a key antibiotic for multidrug-resistant Gram-negative bacilli, and such pathophysiological alterations can worsen treatment outcomes. This study aimed to determine the population PK of meropenem and to propose optimized dosing regimens for the treatment of multidrug-resistant Klebsiella pneumoniae in critically ill patients. Two plasma samples were collected from eligible patients over a dosing interval. Nonparametric population PK modeling was performed using Pmetrics. Monte Carlo simulations were applied to different dosing regimens to determine the probability of target attainment and the cumulative fraction of response, taking into account the local MIC distribution for K. pneumoniae. The targets of 40% and 100% for the fraction of time that free drug concentrations remained above the MIC (ƒT>MIC) were tested, as suggested for critically ill patients. A one-compartment PK model using data from 27 patients showed high interindividual variability. Significant PK covariates were the 8-h creatinine clearance for meropenem and the presence of an indwelling catheter for pleural, abdominal, or cerebrospinal fluid drainage for the meropenem volume of distribution. The target 100% ƒT>MIC for K. pneumoniae, with a MIC of ≤2 mg/liter, could be attained by the use of a continuous infusion of 2.0 g/day. Meropenem therapy in critically ill patients could be optimized for K. pneumoniae isolates with an MIC of ≤2 mg/liter by using a continuous infusion in settings with more than 50% isolates have a MIC of ≥32mg/L.

Dose optimization of β-lactams antibiotics in pediatrics and adults: A systematic review

Background: β-lactams remain the cornerstone of the empirical therapy to treat various bacterial infections. This systematic review aimed to analyze the data describing the dosing regimen of β-lactams.

Methods: Systematic scientific and grey literature was performed in accordance with Preferred Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. The studies were retrieved and screened on the basis of pre-defined exclusion and inclusion criteria. The cohort studies, randomized controlled trials (RCT) and case reports that reported the dosing schedule of β-lactams are included in this study.

Results: A total of 52 studies met the inclusion criteria, of which 40 were cohort studies, 2 were case reports and 10 were RCTs. The majority of the studies (34/52) studied the pharmacokinetic (PK) parameters of a drug. A total of 20 studies proposed dosing schedule in pediatrics while 32 studies proposed dosing regimen among adults. Piperacillin (12/52) and Meropenem (11/52) were the most commonly used β-lactams used in hospitalized patients. As per available evidence, continuous infusion is considered as the most appropriate mode of administration to optimize the safety and efficacy of the treatment and improve the clinical outcomes.

Conclusion: Appropriate antibiotic therapy is challenging due to pathophysiological changes among different age groups. The optimization of pharmacokinetic/pharmacodynamic parameters is useful to support alternative dosing regimens such as an increase in dosing interval, continuous infusion, and increased bolus doses.

External Evaluation of Population Pharmacokinetic Models to Inform Precision Dosing of Meropenem in Critically Ill Patients

Routine clinical meropenem therapeutic drug monitoring data can be applied to model-informed precision dosing. The current study aimed to evaluate the adequacy and predictive capabilities of the published models with routine meropenem data and identify the dosing adaptations using a priori and Bayesian estimation. For this, 14 meropenem models for the external evaluation carried out on an independent cohort of 134 patients with 205 meropenem concentrations were encoded in NONMEM 7.3. The performance was determined using: 1) prediction-based and simulation-based diagnostics; and 2) predicted meropenem concentrations by a priori prediction using patient covariates only; and Bayesian forecasting using previous observations. The clinical implications were assessed according to the required dose adaptations using the meropenem concentrations. All assessments were stratified based on the patients with or without continuous renal replacement therapy. Although none of the models passed all tests, the model by Muro et al. showed the least bias. Bayesian forecasting could improve the predictability over an a priori approach, with a relative bias of −11.63–68.89% and −302.96%–130.37%, and a relative root mean squared error of 34.99–110.11% and 14.78–241.81%, respectively. A dosing change was required in 40.00–68.97% of the meropenem observation results after Bayesian forecasting. In summary, the published models couldn’t adequately describe the meropenem pharmacokinetics of our center. Although the selection of an initial meropenem dose with a priori prediction is challenging, the further model-based analysis combining therapeutic drug monitoring could be utilized in the clinical practice of meropenem therapy.

C/MIC > 4: A Potential Instrument to Predict the Efficacy of Meropenem

This prospective study aimed to explore the determinants of meropenem trough concentration (Ctrough) in patients with bacterial pneumonia and to investigate the association between its concentration and efficacy. From January 2019 to December 2019, patients with pulmonary infections were prospectively enrolled from the intensive care unit. Factors affecting the meropenem trough concentration were analyzed, and a multiple linear regression model was constructed. Logistic regression analyses were used to investigate the relationship between Ctrough and clinical efficacy. A total of 64 patients were enrolled, in whom 210 meropenem concentrations were measured. Of the total, 60.9% (39/64) were considered clinically successful after treatment. Ctrough may increase with increased blood urea nitrogen, albumin, and concomitant antifungal use. By contrast, concentration may decrease with increased endogenous creatinine clearance rate. Six variables, including Ctrough/minimum inhibitory concentration (MIC) > 4, were associated with the efficacy of meropenem. There was an independent correlation between Ctrough/MIC > 4 and efficacy after fully adjusting for confounding factors. Based upon renal function indexes, it is possible to predict changes in meropenem concentration and adjust the dosage precisely and individually. Ctrough/MIC > 4 is a potential instrument to predict successful treatment with meropenem.

The Evaluation of Meropenem Dosing Regimens Against ESBL-Producing Escherichia coli in ICU Patients Using Monte Carlo Simulation

Purpose

Methods

Results

Conclusion

Meropenem Target Attainment and Population Pharmacokinetics in Critically Ill Septic Patients with Preserved or Increased Renal Function

Purpose

Critically ill patients with preserved or increased renal function have been shown to be at risk of underexposure to meropenem. Although many meropenem population pharmacokinetic (PK) models have been published, there is no large prospective population PK study with rich sampling focusing on patients most at risk of suboptimal pharmacokinetic/pharmacodynamic (PK/PD) target attainment. Therefore, the aim of the present study was to evaluate PK/PD target attainment and to perform a thorough covariate screening using population PK modelling of meropenem in septic patients with preserved or increased renal function.

Patients and Methods

A single-centre prospective observational PK study was performed in the intensive care unit (ICU) of the University Hospitals Leuven. Patients with severe sepsis or septic shock and treated with meropenem in the ICU were screened for inclusion. Patients were excluded if they received renal replacement therapy or had an estimated glomerular filtration rate according to the Chronic Kidney Disease Epidemiology collaboration equation <70 mL/min/1.73m² on the day of PK sampling. Successful PK/PD target attainment was defined as an unbound meropenem trough concentration above 2 mg/L or 8 mg/L. Population PK modelling was performed with NONMEM7.4.

Results

In total, 58 patients were included, contributing 345 plasma samples over 70 dosing intervals. The 2 mg/L and 8 mg/L targets were successfully attained in 46% and 11% of all dosing intervals, respectively. A two-compartment population PK model with linear elimination and interindividual variability on clearance best described meropenem PK. The estimated creatinine clearance according to the Cockcroft-Gault equation was the only covariate retained during population PK analysis.

Conclusion

This study provided detailed insight into meropenem PK in critically ill patients with preserved or increased renal function. We observed poor PK/PD target attainment, for which renal function was the only significant covariate.

Trial Registration

This study is registered at ClinicalTrials.gov (NCT03560557).

Identification of factors affecting meropenem pharmacokinetics in critically ill patients: Impact of inflammation on clearance

INTRODUCTION

The purpose of this study was to explore factors influencing meropenem pharmacokinetics (PKs) in critically ill patients by developing a population PK model and to determine the optimal dosing strategy.

METHODS

This prospective observational study involved 12 critically ill patients admitted to the intensive care unit and treated with meropenem 1 g infused over 1 h every 8 h. Blood samples were collected on days 1, 2, and 5 immediately prior to dosing, and at 1, 2, 4, and 6 h after the start of infusion. Population PK parameters were estimated using nonlinear mixed-effects model software.

RESULTS

Meropenem PK was adequately described using a two-compartment model. Typical values of total and inter-compartmental clearance were 9.30 L/h and 9.70 L/h, respectively, and the central and peripheral compartment volumes of distribution were 12.61 L and 7.80 L, respectively. C-reactive protein (CRP) was identified as significant covariate affecting total meropenem clearance. The probability of target attainment (PTA) predicted by Monte Carlo simulations varied according to the patients' CRP. The PTA of 100% time above the minimum inhibitory concentration ≤2 mg/L for bacteria was achieved after a dose of 1 and 2 g infused over 4 h every 8 h in patients with CRP of 30 and 5 mg/dL, respectively.

CONCLUSION

The findings of this study suggest that CRP might be helpful in managing meropenem dosing in critically ill patients. Higher doses and extended infusion may be required to achieve optimal pharmacodynamic targets.

Pharmacokinetics of meropenem in critically ill patients in Saudi Arabia

Background

Meropenem is commonly used in the ICU to treat gram-negative infections. Due to various pathophysiological changes, critically ill patients are at higher risk of having subtherapeutic concentrations and hence have a higher risk of treatment failure—especially in regions where gram-negative drug resistance is increasing, such as Saudi Arabia. No studies have evaluated the pharmacokinetics of meropenem in critically ill patients in Saudi Arabia. Our primary objective is to assess the percentage of patients achieving the therapeutic target for meropenem.

Methods

This prospective observational study was conducted in the ICUs of King Khalid University Hospital. Patient were included if >18 years-of-age and received meropenem for a clinically suspected or proven bacterial infection. The primary outcome was to assess the percentage of patients who achieved the pharmacokinetic/pharmacodynamic (PKPD) therapeutic target of a free trough concentration four times the MIC. The secondary outcome was to estimate the pharmacokinetics of meropenem. Pharmacokinetic analysis was performed using Monolix Suite 2020R1 (Lixoft, France).

Results

Trough concentrations were highly variable and ranged from <0.5 µg/mL to 39 µg/mL, with a mean ± SD trough concentration of 8.5 ± 8 µg/mL. Only 46% of patients achieved the therapeutic target. The only significant predictor of failing to achieve the PKPD target was augmented renal clearance.

Conclusion

In conclusion, more than half of our patients did not achieve the PKPD target. Thus, there is a need for better dosing strategies of meropenem in critically ill patients in Saudi Arabia such as extended and continuous infusion.

Antibiotics in Necrotizing Soft Tissue Infections

Necrotizing soft tissue infections (NSTIs) are rare life-threatening bacterial infections characterized by an extensive necrosis of skin and subcutaneous tissues. Initial urgent management of NSTIs relies on broad-spectrum antibiotic therapy, rapid surgical debridement of all infected tissues and, when present, treatment of associated organ failures in the intensive care unit. Antibiotic therapy for NSTI patients faces several challenges and should (1) carry broad-spectrum activity against gram-positive and gram-negative pathogens because of frequent polymicrobial infections, considering extended coverage for multidrug resistance in selected cases. In practice, a broad-spectrum beta-lactam antibiotic (e.g., piperacillin-tazobactam) is the mainstay of empirical therapy; (2) decrease toxin production, typically using a clindamycin combination, mainly in proven or suspected group A streptococcus infections; and (3) achieve the best possible tissue diffusion with regards to impaired regional perfusion, tissue necrosis, and pharmacokinetic and pharmacodynamic alterations. The best duration of antibiotic treatment has not been well established and is generally comprised between 7 and 15 days. This article reviews the currently available knowledge regarding antibiotic use in NSTIs.

Population pharmacokinetics of meropenem in critically ill infant patients

BACKGROUND

Population pharmacokinetic analysis in critically ill infants remains a challenge for lack of information.

OBJECTIVES

To determine the population pharmacokinetic parameters of meropenem and evaluate the covariates affecting population pharmacokinetic parameters.

METHODS

A prospective study was conducted on 35 patients. A total of 160 blood samples were collected and determined free of drug concentrations of meropenem. Population pharmacokinetic data were analyzed using NONMEM software. Internal validation methods, including bootstrapping and prediction-corrected visual predictive checks, were applied to evaluate the robustness and predictive power of the final model.

RESULTS

A one-compartment model with first-order elimination showed the best fit to the data. The typical clearance (CL) values and volume of distribution (V_d) were 1.33 L/h and 2.27 L, respectively. Weight and creatinine clearance were influential covariates for CL, while weight was a significant covariate for V_d of meropenem. The model evaluation results suggested robustness and good predictability of the final model. The standard dosage regimens of meropenem achieved 40% f T_>MIC but not enough if a more aggressive target of 80% f T_>MIC at MIC value of ≥ 16 µg/mL is desired.

CONCLUSIONS

This population pharmacokinetic model could be used for suggesting individualized meropenem dosage regimens in critically ill infants.

Population Pharmacokinetics and Pharmacodynamics of Meropenem in Critically Ill Patients: How to Achieve Best Dosage Regimen According to the Clinical Situation

BACKGROUND AND OBJECTIVES

Meropenem is frequently used for the treatment of severe bacterial infections in critically ill patients. Because critically ill patients are more prone to pharmacokinetic variability than other patients, ensuring an effective blood concentration can be complex. Therefore, describing this variability to ensure a proper use of this antibiotic drug limits the rise and dissemination of antimicrobial resistance, and helps preserve the current antibiotic arsenal. The aims of this study were to describe the pharmacokinetics of meropenem in critically ill patients, to identify and quantify the patients' characteristics responsible for the observed pharmacokinetic variability, and to perform different dosing simulations in order to determine optimal individually adapted dosing regimens.

METHODS

A total of 58 patients hospitalized in the medical intensive care unit and receiving meropenem were enrolled, including 26 patients with renal replacement therapy. A population pharmacokinetic model was developed (using NONMEM software) and Monte Carlo simulations were performed with different dosing scenarios (bolus-like, extended, and continuous infusion) exploring the impact of clinical categories of residual diuresis (anuria, oliguria, and preserved diuresis) on the probability of target attainment (MIC: 1-45 mg/L).

RESULTS

The population pharmacokinetic model included five covariates with a significant impact on clearance: glomerular filtration rate, dialysis (continuous and semi-continuous), renal function status, and volume of residual diuresis. The clearance for a typical patient in our population is 4.20 L/h and volume of distribution approximately 44 L. Performed dosing regimen simulations suggested that, for equivalent doses, the continuous infusion mode (with loading dose) allowed the obtaining of the pharmacokinetic/pharmacodynamic target for a larger number of patients (100% for MIC ≤ 20 mg/L). Nevertheless, for the treatment of susceptible bacteria (MIC ≤ 2 mg/L), differences in the probability of target attainment between bolus-like, extended, and continuous infusions were negligible.

CONCLUSIONS

Identified covariates in the model are easily accessible information in patient health records. The model highlighted the importance of considering the patient's overall condition (renal function and dialysis) and the pathogen's characteristics (MIC target) during the establishment of a patient's dosing regimen.

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 (Vc) increased with increasing body surface area, and CL, Vc, 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.

Optimizing Antimicrobial Drug Dosing in Critically Ill Patients

A fundamental step in the successful management of sepsis and septic shock is early empiric antimicrobial therapy. However, for this to be effective, several decisions must be addressed simultaneously: (1) antimicrobial choices should be adequate, covering the most probable pathogens; (2) they should be administered in the appropriate dose, (3) by the correct route, and (4) using the correct mode of administration to achieve successful concentration at the infection site. In critically ill patients, antimicrobial dosing is a common challenge and a frequent source of errors, since these patients present deranged pharmacokinetics, namely increased volume of distribution and altered drug clearance, which either increased or decreased. Moreover, the clinical condition of these patients changes markedly over time, either improving or deteriorating. The consequent impact on drug pharmacokinetics further complicates the selection of correct drug schedules and dosing during the course of therapy. In recent years, the knowledge of pharmacokinetics and pharmacodynamics, drug dosing, therapeutic drug monitoring, and antimicrobial resistance in the critically ill patients has greatly improved, fostering strategies to optimize therapeutic efficacy and to reduce toxicity and adverse events. Nonetheless, delivering adequate and appropriate antimicrobial therapy is still a challenge, since pathogen resistance continues to rise, and new therapeutic agents remain scarce. We aim to review the available literature to assess the challenges, impact, and tools to optimize individualization of antimicrobial dosing to maximize exposure and effectiveness in critically ill patients.

A guide to therapeutic drug monitoring of β-lactam antibiotics

Therapeutic drug monitoring (TDM) opens the door to personalized medicine, yet it is infrequently applied to β-lactam antibiotics, one of the most commonly prescribed drug classes in the hospital setting. As we continue to understand more about β-lactam pharmacodynamics (PD) and wide inter- and intra-patient variability in pharmacokinetics (PK), the utility of TDM has become increasingly apparent. For β-lactams, the time that free concentrations remain above the minimum inhibitory concentration (MIC) as a function of the dosing interval (%fT>MIC) has been shown to best predict antibacterial effect. Many studies have shown that β-lactam %fT>MIC exposures are often suboptimal across a wide variety of disease states and clinical settings. A limitation to implementing this practice is the general lack of understanding on how to best operationalize this intervention and interpret the results. The instrumentation and expertise needed to quantify β-lactams for TDM is rarely available locally, but certain laboratories advertise these services and perform them regularly. Familiarity with the modalities and nuances of antimicrobial susceptibility testing is crucial to establishing β-lactam concentration targets that meet the relevant exposure thresholds. Evaluation of these concentrations is best accomplished using population PK software and Bayesian modeling, for which a multitude of programs are available. While TDM of β-lactams has shown an ability to increase the rate of target attainment, there is currently limited evidence to suggest that it leads to improved clinical outcomes. Although consensus guidelines for β-lactam TDM do not exist in the United States, guidance would help to promote this important practice and better standardize the approach across institutions. Herein, we discuss the basis for β-lactam TDM, review supporting evidence, and provide guidance for implementation in specific patient populations.

A narrative review of predictors for β-lactam antibiotic exposure during empirical treatment in critically ill patients

INTRODUCTION

: Emerging studies suggest that antibiotic pharmacokinetics (PK) are difficult to predict in critically ill patients. The high intra- and inter-patient PK variability makes it challenging to accurately predict the appropriate dosage required for a given patient. Identifying patients at risk could help clinicians to consider more individualized dosing regimens and perform therapeutic drug monitoring. We provide an overview of relevant predictors associated with target (non-)attainment of β-lactam antibiotics in critically ill patients.

AREAS COVERED

: This narrative review summarizes patient and clinical characteristics that can help to predict the attainment of target serum concentrations and to provide guidance on antimicrobial dose optimization. Literature was searched using Embase and Medline database, focusing on β-lactam antibiotics in critically ill patients.

EXPERT OPINION

: Adequate concentration attainment can be anticipated in critically ill patients prior to initiating empiric β-lactam antibiotic therapy based on readily available demographic and clinical factors. Male gender, younger age, and augmented renal clearance were the most significant predictors for target non-attainment and should be considered in further investigations to develop dosing algorithms for optimal β-lactam therapy.

Evaluation of pharmacokinetic and pharmacodynamic parameters of meropenem in critically ill patients with acute kidney disease

Purpose

No study has been evaluated pharmacokinetic (PK) and pharmacodynamic (PD) properties of β-lactam antibiotics in patients with acute kidney injury (AKI), not requiring renal replacement therapy (RRT). We evaluated the time that plasma concentrations remain above four times the MIC (ft > 4MIC) and PK parameters of meropenem in this population.

Methods

In this prospective, randomized clinical trial (RCT), all patients received standard dose (3 g daily) of meropenem for 48 h, then randomly allocated in standard or adjusted groups. The standard group received meropenem without dose adjustment. In the adjusted group, the meropenem dose was adjusted based on the Cockcroft-Gault(C-G) equation. Meropenem concentrations were measured at the peak and trough times on the 2nd and 5th days of the study.

Results

On the 2nd day of the study, 3 out of 10 (30%) of patients attained the PD target (≥ 80%ft > 4MIC). In the 5th day of the study, the PD target was attained in 2 out of 10 (20%) and 1 out of 5 (20%) of patients who received standard and adjusted doses of meropenem, respectively (p = 1). In all samples, increased volume of distribution (Vd) (median; IQR) (46.04; 23.06–103.18 L), terminal half-life (T1/2) (4.51; 2.67–8.88 h) and decreased clearance (6.52; 4.43–10.16 L/h) have been shown.

Conclusion

In critically ill patients with AKI, who not receive RRT, standard doses, and adjusted according to renal function of meropenem failed to achieve PD target of ≥ 80%ft > 4MIC. Higher doses are required for this target.

Retrospectively registered

The study protocol with registered retrospectively and approved on January 19, 2019, with the number of IRCT20160412027346N5.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00228-020-03062-0.

Carbapenem-sparing strategy: carbapenemase, treatment, and stewardship

PURPOSE OF REVIEW

describing the current role of carbapenems and carbapenem-sparing strategies in the setting of antimicrobial stewardship programs.

RECENT FINDINGS

sparing carbapenems with other drugs appears to be an interesting perspective for a variety of reasons in the current context of the multidrug-resistant (MDR) pandemic. Specific algorithms should also be precisely investigated to define better how to spare carbapenems within empiric and targeted regimens, with combination treatment or monotherapies, aiming at the best use of the new drugs and improving de-escalation as soon as possible for most of the patients.

SUMMARY

stewardship programs may be useful in reducing probable misuse and overuse of antibiotics, which has probably contributed to the emergence of carbapenem-resistant bacteria worldwide. The proposal of carbapenem-sparing strategies has then generated substantial scientific debate and, overall, the concept of sparing these drugs is well advocated together with judicious use of novel drugs, appropriate measures of infection control and prevention as well as in stewardship programs to curb the spread of MDR and XDR-strains in healthcare facilities.

What Are the Current Approaches to Optimising Antimicrobial Dosing in the Intensive Care Unit?

Antimicrobial dosing in the intensive care unit (ICU) can be problematic due to various challenges including unique physiological changes observed in critically ill patients and the presence of pathogens with reduced susceptibility. These challenges result in reduced likelihood of standard antimicrobial dosing regimens achieving target exposures associated with optimal patient outcomes. Therefore, the aim of this review is to explore the various methods for optimisation of antimicrobial dosing in ICU patients. Dosing nomograms developed from pharmacokinetic/statistical models and therapeutic drug monitoring are commonly used. However, recent advances in mathematical and statistical modelling have resulted in the development of novel dosing software that utilise Bayesian forecasting and/or artificial intelligence. These programs utilise therapeutic drug monitoring results to further personalise antimicrobial therapy based on each patient’s clinical characteristics. Studies quantifying the clinical and cost benefits associated with dosing software are required before widespread use as a point-of-care system can be justified.

External evaluation of population pharmacokinetic models for continuous administration of meropenem in critically ill adult patients

PURPOSE

Beta-lactams (BL), the most commonly prescribed class of antibiotics, are recommended as the first-line therapy for multiple indications in infectious disease guidelines. Meropenem (MERO) is frequently used in intensive care units (ICU) to treat bacterial infections with or without sepsis. The pharmacokinetics of MERO display a large variability in patients admitted to ICUs due to altered pathophysiology. The aim of this study was to perform an external evaluation of published population pharmacokinetic models of MERO in order to test their predictive performance in a cohort of ICU adult patients.

METHODS

A literature search in PubMed/Medline database was made following the PRISMA statement. External evaluation was performed using NONMEM software, and the bias and inaccuracy values were calculated.

RESULTS

An external validation dataset from the Timone Hospital in Marseille, France, included 84 concentration samples from 27 patients. Four models of MERO were identified according to the inclusion criteria of the study. None of the models presented acceptable values of bias and inaccuracy.

CONCLUSION

While performing external evaluations on some populations may confirm a model's suitability to diverse groups of patients, there is still some variability that cannot be explained nor solved by the procedure. This brings to light the difficulty to develop only one model for ICU patients and the need to develop one specific model to each population of critically ill patients.

Population pharmacokinetics and evaluation of the predictive performance of pharmacokinetic models in critically ill patients receiving continuous infusion meropenem: a comparison of eight pharmacokinetic models

Background

Several population pharmacokinetic (PopPK) models for meropenem dosing in ICU patients are available. It is not known to what extent these models can predict meropenem concentrations in an independent validation dataset when meropenem is infused continuously.

Patients and methods

A PopPK model was developed with concentration-time data collected from routine care of 21 ICU patients (38 samples) receiving continuous infusion meropenem. The predictability of this model and seven other published PopPK models was studied using an independent dataset that consisted of 47 ICU patients (161 samples) receiving continuous infusion meropenem. A statistical comparison of imprecision (mean square prediction error) and bias (mean prediction error) was conducted.

Results

A one-compartment model with linear elimination and creatinine clearance as a covariate of clearance best described our data. The mean ± SD parameter estimate for CL was 9.89 ± 3.71 L/h. The estimated volume of distribution was 48.1 L. The different PopPK models showed a bias in predicting serum concentrations from the validation dataset that ranged from -8.76 to 7.06 mg/L. Imprecision ranged from 9.90 to 42.1 mg/L.

Conclusions

Published PopPK models for meropenem vary considerably in their predictive performance when validated in an external dataset of ICU patients receiving continuous infusion meropenem. It is necessary to validate PopPK models in a target population before implementing them in a therapeutic drug monitoring program aimed at optimizing meropenem dosing.

Effect of Clinically Meaningful Antibiotic Concentrations on Recovery of Escherichia coli and Klebsiella pneumoniae Isolates from Anaerobic Blood Culture Bottles with and without Antibiotic Binding Resins

Blood cultures are routinely collected in pairs of aerobic and anaerobic bottles. Artificial sterilization of Gram-negative bacteria in aerobic bottles containing clinically meaningful antibiotic concentrations has previously been observed. This study assessed recovery from anaerobic bottles with and without antibiotic binding resins. We studied the recovery of Escherichia coli and Klebsiella pneumoniae when exposed to meropenem, imipenem, cefepime, cefazolin, levofloxacin, and piperacillin-tazobactam in resin-containing BacT/Alert FN Plus and BD Bactec Plus anaerobic/F bottles as well as resin-free BacT/Alert SN and BD Bactec standard anaerobic bottles. Bottles were inoculated with bacteria and whole blood containing peak, midpoint, or trough concentrations and incubated for up to 120 hours in their respective detection systems. In E. coli resin-containing bottles, recovery was observed in 10/24 (42%), 17/24 (71%), and 18/24 (75%) (P = 0.034) of those exposed to peak, midpoint, and trough concentrations, respectively. In K. pneumoniae resin-containing bottles, recovery was observed in 8/16 (50%), 10/16 (63%), and 10/16 (63%) (P = 0.710), respectively. No growth was detected in bottles containing cefepime regardless of concentration, while recovery was observed in the presence of all concentrations of cefazolin and piperacillin-tazobactam. Recovery in bottles with meropenem and imipenem was more frequently observed in BacT/Alert FN Plus bottles compared with Bactec Plus bottles. Resin-free bottles demonstrated significantly lower recovery than bottles containing binding resin. Clinical concentrations of certain antibiotics can adversely affect detection of E. coli and K. pneumoniae in anaerobic blood culture bottles. Obtaining blood cultures immediately before a dose and utilizing resin-containing anaerobic bottles will maximize the likelihood of recovery.

Meropenem-nacubactam activity against AmpC-overproducing and KPC-expressing Pseudomonas aeruginosa in a neutropenic murine lung infection model

Nacubactam is a novel non-β-lactam diazabicyclooctane β-lactamase inhibitor under development for the treatment of serious Gram-negative infections. This study assessed the efficacy of human-simulated epithelial lining fluid (ELF) exposure of nacubactam in combination with meropenem against AmpC-overproducing (n=4) and Klebsiella pneumoniae carbapenemase (KPC)-expressing (n=3) Pseudomonas aeruginosa isolates in the neutropenic murine lung infection model. Meropenem, nacubactam and meropenem-nacubactam (1:1 concentration ratio) minimum inhibitory concentrations (MICs) were determined in triplicate using broth microdilution. Regimens that provided ELF profiles mimicking those observed in humans given nacubactam 2 g q8h (1.5-h infusion) alone and in combination with a subtherapeutic ELF exposure of meropenem were administered 2 h after inoculation. Efficacy was assessed as the change in log₁₀ colony-forming units (CFU)/lung at 24 h compared with 24-h meropenem monotherapy. Meropenem, nacubactam and meropenem-nacubactam MICs were 8->64, 128->256 and 2-16 mg/L, respectively. Meropenem and nacubactam monotherapy groups demonstrated bacterial growth over 24 h for each isolate. Against AmpC-overproducing and KPC-expressing P. aeruginosa isolates, meropenem-nacubactam resulted in -2.73±0.93 and -4.35±1.90 log₁₀CFU/lung reduction, respectively, relative to meropenem monotherapy. Meropenem-nacubactam showed promising in-vivo activity against meropenem-resistant P. aeruginosa, indicative of a potential role for the treatment of infections caused by these challenging pathogens.

The Pharmacodynamics of Prolonged Infusion β-Lactams for the Treatment of Pseudomonas aeruginosa Infections: A Systematic Review

PURPOSE

Pseudomonas aeruginosa is a commonly isolated nosocomial pathogen for which treatment options are often limited for multidrug-resistant isolates. In addition to newer available antimicrobial agents active against P. aeruginosa, strategies such as extended (eg, prolonged or continuous) infusion have been suggested to optimize the pharmacokinetic and pharmacodynamic profiles of β-lactams. Literature regarding clinical outcomes for extended infusion β-lactams has been controversial; however, this use seems most beneficial in patients with severe illness. Prolonged infusion of β-lactams (eg, 3- to 4-hour infusion) can enhance the pharmacodynamic target attainment via increasing the amount of time throughout the dosing interval to which the free drug concentration remains above the MIC (minimum inhibitory concentration) of the organism (fT > MIC). This systematic review summarizes current literature related to the probability of target attainment (PTA) of various antipseudomonal β-lactam regimens administered as prolonged infusions in an effort to provide guidance in selecting optimal dosing regimens and infusion times for the treatment of P. aeruginosa infections.

METHODS

A literature search for all pertinent studies was performed by using the PubMed database (with no year limit) through March 31, 2019.

FINDINGS

Thirty-nine studies were included. Although many standard antipseudomonal β-lactam intermittent infusion regimens can provide adequate PTA against most susceptible isolates, prolonged infusion may enhance percent fT > MIC for organisms with higher MICs (eg, nonsusceptible) or patients with altered pharmacokinetic profiles (eg, obese, critically ill, those with febrile neutropenia).

IMPLICATIONS

Prolonged infusion β-lactam regimens can enhance PTA against nonsusceptible P. aeruginosa isolates and may provide a potential therapeutic option for multidrug-resistant infections. Before implementing prolonged infusion antipseudomonal β-lactams, institutions should consider the half-life of the antibiotic, local incidence of P. aeruginosa infections, antibiotic MIC distributions or MICs isolated from individual patients, individual patient characteristics that may alter pharmacokinetic variables, and PTA (eg, critically ill), as well as implementation challenges.

Effect of renal clearance and continuous renal replacement therapy on appropriateness of recommended meropenem dosing regimens in critically ill patients with susceptible life-threatening infections

Background

Meropenem plasma concentration above a pathogen's MIC over the whole dosing interval (100% ƒT>MIC) is a determinant of outcome in severe infections. Significant variability of meropenem pharmacokinetics is reported in ICU patients.

Objectives

To characterize meropenem pharmacokinetics in variable CLCR or renal replacement therapy and assess the appropriateness of recommended regimens for MIC coverage.

Methods

A pharmacokinetic analysis (NONMEM) was conducted with external model validation. Patient characteristics were tested on meropenem clearance estimates, differentiated according to the presence/absence of continuous renal replacement therapy (CRRT, CLCRRT or CLno-CRRT). Simulations evaluated the appropriateness of recommended dosing for achieving 100% fT>MIC in 90% of patients.

Results

A total of 101 patients were studied: median 63 years (range 49-70), 56% male, SAPS II 38 (27-48). 32% had a CLCR >60 mL/min, 49% underwent CRRT and 32% presented severe sepsis or septic shock. A total of 127 pathogens were documented: 76% Gram-negatives, 24% Gram-positives (meropenem MIC90 2 mg/L, corresponding to EUCAST susceptibility breakpoint). Three hundred and eighty plasma and 129 filtrate-dialysate meropenem concentrations were analysed: two-compartment modelling best described the data. Predicted meropenem CLno-CRRT was 59% lower in impaired (CLCR 30 mL/min) compared to normal (CLCR 100 mL/min) renal function. Simulations showed that recommended regimens appropriately cover MIC90 in patients with CLCR <60 mL/min. Patients with CLCR of 60 to <90 mL/min need 6 g/day to achieve appropriate coverage. In patients with CLCR ≥90 mL/min, appropriate exposure is achieved with increased dose, frequency of administration and infusion duration, or continuous infusion.

Conclusions

Recommended meropenem regimens are suboptimal in ICU patients with normal or augmented renal clearance. Modified dosing or infusion modalities achieve appropriate MIC coverage for optimized antibacterial efficacy in meropenem-susceptible life-threatening infections.

Recovery of Gram-Negative Bacteria from Aerobic Blood Culture Bottles Containing Antibiotic Binding Resins after Exposure to β-Lactam and Fluoroquinolone Concentrations

Blood culture bottles containing antibiotic binding resins are routinely used to minimize artificial sterilization in the presence of antibiotics. However, the resin binding kinetics can differ between antibiotics and concentrations. This study assessed the impact of clinically meaningful peak, midpoint, and trough concentrations of meropenem, imipenem, cefepime, cefazolin, levofloxacin, and piperacillin-tazobactam on the recovery of Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumoniae from resin-containing BacT/Alert FA Plus and Bactec Aerobic/F blood culture bottles. P. aeruginosa-inoculated bottles alarmed positive in 4/20 (20%), 16/20 (80%), and 20/20 (100%) of those with peak, midpoint, and trough concentrations of antipseudomonal agents, respectively (P ≤ 0.001). E. coli was recovered from 8/24 (33%), 11/24 (46%), and 14/24 (58%) of bottles with peak, midpoint, and trough concentrations, respectively (P = 0.221). K. pneumoniae was recovered from 8/16 (50%) at all concentrations of the studied antibiotics (P = 1.0). BacT/Alert and Bactec bottles inoculated with antibiotics and P. aeruginosa had similar times to detection (TTD) (P = 0.352); however, antibiotic-containing BacT/Alert bottles had a shorter TTD compared with antibiotic-containing Bactec bottles for E. coli (P = 0.026) and K. pneumoniae (P ≤ 0.001). Pathogen recovery in BacT/Alert FA Plus and Bactec Aerobic/F blood culture bottles containing antibiotic binding resins was greatly reduced in the presence of antibiotics, especially at higher concentrations. These data support the practice of drawing blood cultures immediately before an antibiotic dose to maximize the chances of pathogen recovery.

Evaluation of Plazomicin, Tigecycline, and Meropenem Pharmacodynamic Exposure against Carbapenem-Resistant Enterobacteriaceae in Patients with Bloodstream Infection or Hospital-Acquired/Ventilator-Associated Pneumonia from the CARE Study (ACHN-490-007)

INTRODUCTION

CARE was a Phase 3, randomized study evaluating the efficacy and safety of plazomicin-based combination therapy compared with colistin-based combination therapy for the treatment of patients with bloodstream infections or hospital-acquired/ventilator-associated pneumonia due to carbapenem-resistant Enterobacteriaceae (CRE). Adjunctive therapies included either tigecycline or meropenem. We sought to understand the contribution of tigecycline and meropenem to plazomicin-treated-patient outcomes by determining their observed pharmacodynamic exposures against baseline pathogens.

METHODS

Blood samples collected for plazomicin therapeutic monitoring were assayed for tigecycline and meropenem concentrations. Population pharmacokinetic models were constructed for each antibiotic. Using the individual Bayesian posterior or a covariate-based model, concentration time profiles were simulated to estimate the pharmacodynamic exposures for each patient. Pharmacodynamic thresholds for plazomicin, tigecycline, and meropenem were a total area under the curve to minimum inhibitory concentration ratio (AUC/MIC) ≥ 85, free (f) AUC/MIC ≥ 0.9, and free time above the MIC (fT > MIC) of ≥ 40%, respectively.

RESULTS

Fifteen plazomicin-treated patients were included (12 received tigecycline, 4 received meropenem, 1 received both). Microbiological response was observed in 13 (86.7%) and clinical efficacy was achieved in 11 (73.3%). Plazomicin achieved its pharmacodynamic target in all 15 patients. Meropenem fT > MIC was 0% in all 4 patients, and tigecycline fAUC/MIC was ≥ 0.9 in 9 (75%) patients. Overall, 6 (40%) of 15 patients had a tigecycline or meropenem exposure below the requisite thresholds. Microbiological response and clinical efficacy were observed in 100% (6/6) and 83.3% (5/6) of patients with low threshold attainment by tigecycline and meropenem dosing regimens, respectively.

CONCLUSIONS

Plazomicin successfully achieved its requisite pharmacodynamic exposure, and these data suggest that optimization of tigecycline and meropenem therapy was not required for the combination to achieve microbiological response and clinical efficacy against serious CRE infections.

TRIAL REGISTRATION

ClinicalTrials.gov number, NCT01970371.

FUNDING

Achaogen, Inc.

Development of a dosing nomogram for continuous-infusion meropenem in critically ill patients based on a validated population pharmacokinetic model

Background

Optimal antibiotic exposure is a vital but challenging prerequisite for achieving clinical success in ICU patients.

Objectives

To develop and externally validate a population pharmacokinetic model for continuous-infusion meropenem in critically ill patients and to establish a nomogram based on a routinely available marker of renal function.

Methods

A population pharmacokinetic model was developed in NONMEM® 7.3 based on steady-state meropenem concentrations (CSS) collected during therapeutic drug monitoring. Different serum creatinine-based markers of renal function were compared for their influence on meropenem clearance (the Cockcroft-Gault creatinine clearance CLCRCG, the CLCR bedside estimate according to Jelliffe, the Chronic Kidney Disease Epidemiology Collaboration equation and the four-variable Modification of Diet in Renal Disease equation). After validation of the pharmacokinetic model with independent data, a dosing nomogram was developed, relating renal function to the daily doses required to achieve selected target concentrations (4/8/16 mg/L) in 90% of the patients. Probability of target attainment was determined for efficacy (CSS ≥8 mg/L) and potentially increased likelihood of adverse drug reactions (CSS >32 mg/L).

Results

In total, 433 plasma concentrations (3.20-48.0 mg/L) from 195 patients (median/P0.05 - P0.95 at baseline: weight 77.0/55.0-114 kg, CLCRCG 63.0/19.6-168 mL/min) were used for model building. We found that CLCRCG best described meropenem clearance (CL = 7.71 L/h, CLCRCG = 80 mL/min). The developed model was successfully validated with external data (n = 171, 73 patients). According to the nomogram, daily doses of 910/1480/2050/2800/3940 mg were required to reach a target CSS = 8 mg/L in 90% of patients with CLCRCG = 20/50/80/120/180 mL/min, respectively. A low probability of adverse drug reactions (<0.5%) was associated with these doses.

Conclusions

A dosing nomogram was developed for continuous-infusion meropenem based on renal function in a critically ill population.

Early target attainment of continuous infusion piperacillin/tazobactam and meropenem in critically ill patients: A prospective observational study

PURPOSE

To evaluate target attainment of empirically dosed continuous infusion piperacillin/tazobactam (TZP) and meropenem (MER) in critically ill patients.

PATIENTS AND METHODS

Patients were sampled on a daily basis. TZP or MER concentrations were evaluated during the first two days antibiotic therapy. The lower limit of the target range was defined as unbound concentrations equaling 4 times the epidemiological cutoff value of P. aeruginosa. The upper limit of the target range was based on the risk of toxicity, i.e. unbound concentrations >160 mg/L for TZP and > 45 mg/L for MER. Multivariable logistic regression was used to evaluate factors associated with target attainment.

RESULTS

Data from 253 patients were analyzed. Overall, 76/205 (37.1%) and 36/48 (75%) of the patients receiving TZP or MER respectively, attained target concentrations. In multivariable analysis, estimated creatinine clearance was identified as a risk factor for target non-attainment (OR 0.988, 95%CI [0.982;0.994]). Patients receiving MER were more likely to attain target concentrations compared with patients receiving TZP (OR 6.02, 95%CI [2.12;18.4]).

CONCLUSION

Target attainment of empiric antibiotic therapy in critically ill patients was low (37%) for TZP and moderate (75%) for MER, despite the use of a loading dose and despite optimization of the mode of infusion.

Where should antibiotic gradient diffusion strips be crossed to assess synergy? A comparison of the standard method with a novel method using steady-state antimicrobial concentrations

Multi-drug resistance among Pseudomonas aeruginosa in hospitals, and particularly intensive care units, has achieved alarming rates. Some combination antimicrobial therapies have demonstrated promising synergistic effects and an ability to overcome resistance without increasing drug-related toxicities. Nevertheless, rapid and feasible methods to identify synergy have not been routinely implemented in clinical microbiology laboratories. Synergistic activity of meropenem plus tobramycin or levofloxacin against clinical P. aeruginosa isolates (N=21) was assessed by two different methods using gradient diffusion strips (GDSs). A 90° angle was created at the intersection of the minimum inhibitory concentration (MIC) of each drug by the standard method, and by a novel method, the cross was placed at clinically relevant steady-state concentrations (C_ss) based on recommended dosing regimens. Fractional inhibitory concentration indexes were determined to describe antibiotic interactions. Time-kill analyses were performed over 24 h in duplicate for instances of discordance between the standard cross method and the novel method. Synergy between meropenem and tobramycin by the novel method was observed in one (4.8%) isolate and between meropenem and levofloxacin in two (9.5%) isolates. Agreement with the standard method was 86-100% for meropenem plus tobramycin and meropenem plus levofloxacin combinations, respectively. Time-kill studies resulted in agreement with GDSs crossed at C_ss in two of three instances of discordance between GDS methods. This novel method of synergy testing that involves crossing GDSs at steady-state concentrations may be a rapid and feasible tool for routine practice. Further comparisons of this novel procedure with time-kill methods are needed.

A novel reversed-phase high-performance liquid chromatographic assay for the simultaneous determination of imipenem and meropenem in human plasma and its application in TDM

A rapid and specific reversed-phase high-performance liquid chromatographic (RP-HPLC) assay with UV detection has been developed and validated for the simultaneous determination of imipenem and meropenem in human plasma. The extraction process was performed through protein precipitation method using acetonitrile and dichloromethane, and the recoveries of quality controls (QCs) were > 91.5%. Isocratic elution followed by gradient elution of acetonitrile and water was employed over a C18 analytical column for separation. The detection was performed at 298 nm. This method was accurate and reproducible (coefficient of variation, CV < 8%), allowing quantification of carbapenem at the plasma-level ranges from 0.1 to 100 μg/ml without interference of any of the 30 frequently prescribed drugs. Stabilities of imipenem and meropenem were determined with or without stabilizer solutions at -80°C, -20°C, +4 °C and room temperature 20°C. These two drugs showed higher stability at the low temperatures. Addition of 3-(N-morpholino) propanesulfonic acid (MOPS) might also increase their stability. The results of therapeutic drug monitoring (TDM) in neonates and adults showed high inter- and intra- individual variabilities in the trough concentrations of imipenem and meropenem, thus confirming the importance and necessity of TDM. For neonatal patients, imipenem 20 mg/kg, q12h (40mg/kg/day) failed to produce significant therapeutic effects, and either the dose or the frequency was adjusted to achieve 60mg/kg/day or above to maintain the trough concentration required for the curative effect. The low operational cost and good separation efficiency would help implement this assay for the routine therapeutic drug monitoring of imipenem and meropenem in hospitals.

Pharmacokinetics-pharmacodynamics issues relevant for the clinical use of beta-lactam antibiotics in critically ill patients

Antimicrobials are among the most important and commonly prescribed drugs in the management of critically ill patients and beta-lactams are the most common antibiotic class used. Critically ill patient's pathophysiological factors lead to altered pharmacokinetics and pharmacodynamics of beta-lactams.A comprehensive bibliographic search in PubMed database of all English language articles published from January 2000 to December 2017 was performed, allowing the selection of articles addressing the pharmacokinetics or pharmacodynamics of beta-lactam antibiotics in critically ill patients.In critically ill patients, several factors may increase volume of distribution and enhance renal clearance, inducing high intra- and inter-patient variability in beta-lactam concentration and promoting the risk of antibiotic underdosing. The duration of infusion of beta-lactams has been shown to influence the fT > minimal inhibitory concentration and an improved beta-lactam pharmacodynamics profile may be obtained by longer exposure with more frequent dosing, extended infusions, or continuous infusions.The use of extracorporeal support techniques in the critically ill may further contribute to this problem and we recommend not reducing standard antibiotic dosage since no drug accumulation was found in the available literature and to maintain continuous or prolonged infusion, especially for the treatment of infections caused by multidrug-resistant bacteria.Prediction of outcome based on concentrations in plasma results in overestimation of antimicrobial activity at the site of infection, namely in cerebrospinal fluid and the lung. Therefore, although no studies have assessed clinical outcome, we recommend using higher than standard dosing, preferably with continuous or prolonged infusions, especially when treating less susceptible bacterial strains at these sites, as the pharmacodynamics profile may improve with no apparent increase in toxicity.A therapeutic drug monitoring-guided approach could be particularly useful in critically ill patients in whom achieving target concentrations is more difficult, such as obese patients, immunocompromised patients, those infected by highly resistant bacterial strains, patients with augmented renal clearance, and those undergoing extracorporeal support techniques.

The exploration of population pharmacokinetic model for meropenem in augmented renal clearance and investigation of optimum setting of dose

In recent years, augmented renal clearance (ARC), in which renal function is excessively enhanced, has been reported, and its influence on β-lactam antibiotics has been investigated. In this study, we aimed to determine the optimum population pharmacokinetic model of meropenem in patients with sepsis with ARC, and evaluated dosing regimens based on renal function. Seventeen subjects (6 with ARC and 11 without) were enrolled in this study. Predicted meropenem concentrations were evaluated for bias and precision using the Bland-Altman method. To examine the dosing regimen, Monte Carlo simulation was performed to calculate the cumulative fraction of response (CFR). In patients with ARC, the bias (average of the predicted value and measured value residuals) of models constructed by Crandon et al. (2011), Roberts et al. (2009), and Jaruratanasirikul et al. (2015) were 5.96 μg/mL, 10.91 μg/mL, and 4.41 μg/mL, respectively. Following 2 g meropenem every 8 h (180 min infusion), CFR ≥ 90%, a criterion of success for empirical therapy, was achieved, even with creatinine clearance of 130-250 mL/min. For patients with sepsis and ARC, the model of Jaruratanasirikul et al. showed the highest degree of accuracy and precision and confirmed the efficacy of the meropenem dosing regimen in this patient population.

In Vivo Efficacy of Plazomicin Alone or in Combination with Meropenem or Tigecycline against Enterobacteriaceae Isolates Exhibiting Various Resistance Mechanisms in an Immunocompetent Murine Septicemia Model

Plazomicin is a novel aminoglycoside with potent in vitro activity against multidrug- and carbapenem-resistant Enterobacteriaceae The objective of this study was to assess the efficacy of plazomicin exposure, alone and in combination with meropenem or tigecycline, against Enterobacteriaceae in the immunocompetent murine septicemia model. ICR mice were inoculated intraperitoneally with bacterial suspensions. Eight Enterobacteriaceae isolates with wide ranges of plazomicin, meropenem, and tigecycline MICs were utilized. Treatment mice were administered plazomicin, meropenem, or tigecycline human-equivalent doses alone or in combinations of plazomicin-meropenem and plazomicin-tigecycline. Treatments were initiated at 1 h postinfection and continued for 24 h. Efficacy was assessed by determination of mouse survival through 96 h. Compared with the survival of the controls, plazomicin monotherapy produced a significant improvement in survival for all mice infected with the isolates (P < 0.05) and resulted in overall survival rates of 86% (n = 50) and 53.3% (n = 30) for mice infected with isolates with plazomicin MICs of ≤4 and ≥8 mg/liter, respectively (P < 0.05). The survival of the meropenem and tigecycline groups correlated well with susceptibilities of their respective isolates, with incremental increases in survival being observed at lower MIC values. For mice infected with isolate Klebsiella pneumoniae 561 (plazomicin, meropenem, and tigecycline MICs, 8, >32, and 2 mg/liter, respectively), combination therapies showed a significant reduction in mortality compared with that achieved with any monotherapy (P < 0.05). Plazomicin monotherapy resulted in improved survival in the immunocompetent murine septicemia model, notably, for mice infected with isolates with plazomicin MICs of ≤4 mg/liter. As evidenced by our current data, coadministration of meropenem or tigecycline could potentially lead to a further improvement in survival. These data support a role for plazomicin in the management of septicemia due to Enterobacteriaceae with plazomicin MICs of ≤4 mg/liter, including carbapenem-resistant isolates.

Role of renal function in risk assessment of target non-attainment after standard dosing of meropenem in critically ill patients: a prospective observational study

Background

Severe bacterial infections remain a major challenge in intensive care units because of their high prevalence and mortality. Adequate antibiotic exposure has been associated with clinical success in critically ill patients. The objective of this study was to investigate the target attainment of standard meropenem dosing in a heterogeneous critically ill population, to quantify the impact of the full renal function spectrum on meropenem exposure and target attainment, and ultimately to translate the findings into a tool for practical application.

Methods

A prospective observational single-centre study was performed with critically ill patients with severe infections receiving standard dosing of meropenem. Serial blood samples were drawn over 4 study days to determine meropenem serum concentrations. Renal function was assessed by creatinine clearance according to the Cockcroft and Gault equation (CLCR_CG). Variability in meropenem serum concentrations was quantified at the middle and end of each monitored dosing interval. The attainment of two pharmacokinetic/pharmacodynamic targets (100%T_>MIC, 50%T_>4×MIC) was evaluated for minimum inhibitory concentration (MIC) values of 2 mg/L and 8 mg/L and standard meropenem dosing (1000 mg, 30-minute infusion, every 8 h). Furthermore, we assessed the impact of CLCR_CG on meropenem concentrations and target attainment and developed a tool for risk assessment of target non-attainment.

Results

Large inter- and intra-patient variability in meropenem concentrations was observed in the critically ill population (n = 48). Attainment of the target 100%T_>MIC was merely 48.4% and 20.6%, given MIC values of 2 mg/L and 8 mg/L, respectively, and similar for the target 50%T_>4×MIC. A hyperbolic relationship between CLCR_CG (25–255 ml/minute) and meropenem serum concentrations at the end of the dosing interval (C_8h) was derived. For infections with pathogens of MIC 2 mg/L, mild renal impairment up to augmented renal function was identified as a risk factor for target non-attainment (for MIC 8 mg/L, additionally, moderate renal impairment).

Conclusions

The investigated standard meropenem dosing regimen appeared to result in insufficient meropenem exposure in a considerable fraction of critically ill patients. An easy- and free-to-use tool (the MeroRisk Calculator) for assessing the risk of target non-attainment for a given renal function and MIC value was developed.

Trial registration

Clinicaltrials.gov, NCT01793012. Registered on 24 January 2013.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-017-1829-4) contains supplementary material, which is available to authorized users.

Effects of Clinically Meaningful Concentrations of Antipseudomonal β-Lactams on Time to Detection and Organism Growth in Blood Culture Bottles

The effectiveness of antimicrobial binding resins present in blood culture (BC) bottles in removing meropenem, ceftolozane-tazobactam, and ceftazidime-avibactam is unknown. We assessed the time to detection (TTD) and growth of 2 Pseudomonas aeruginosa isolates in the presence of clinically meaningful concentrations of these antibiotics. Bactec Plus Aerobic/F and BacT/Alert FA Plus BC bottles were inoculated with one of two isolates (1 meropenem susceptible and 1 resistant), followed by fresh whole blood containing the peak, midpoint, or trough plasma concentrations for meropenem, ceftolozane-tazobactam, and ceftazidime-avibactam. Matching bottles were loaded into their respective detection instruments and a standard incubator at 37°C, with TTD and CFU being monitored for up to 72 h. Bacterial growth was observed for 11/48 (22.9%), 22/48 (45.8%), and 47/48 (97.9%) of all BC bottles inoculated with the peak, midpoint, and trough concentrations, respectively (P ≤ 0.001). When P. aeruginosa was isolated, the TTD was typically <26 h, and no differences between Bactec and BacT/Alert bottles were observed. In both systems, meropenem was removed to a greater degree than were ceftolozane and ceftazidime; however, concentrations for all antibiotics remained above the MIC for the susceptible organisms at 12 h. BC bottles containing antibiotic binding resins may not sufficiently inactivate achievable concentrations of meropenem, ceftolozane-tazobactam, and ceftazidime-avibactam. The consistent identification of both P. aeruginosa isolates was observed only in the presence of antibiotic trough concentrations. To minimize false-negative BC results for patients already receiving these antibiotics, cultures should be collected just prior to the next dose, when antibiotic concentrations are lowest.

Optimizing β-lactams treatment in critically-ill patients using pharmacokinetics/pharmacodynamics targets: are first conventional doses effective?

INTRODUCTION

The pharmacokinetic/pharmacodynamic index determining β-lactam activity is the percentage of the dosing interval (%T) during which their free serum concentration remains above a critical threshold over the minimum inhibitory concentration (MIC). Regrettably, neither the value of %T nor that of the threshold are clearly defined for critically-ill patients. Areas covered: We review and assess the targets proposed for β-lactams in critical illness by screening the literature since 1997. Depending on the study intention (clinical cure vs. suppression of resistance), targets proposed range from 20%T > 1xMIC to 100%T > 5xMIC. Assessment and comparative analysis of their respective clinical efficacy suggest that a value of 100%T > 4xMIC may be needed. Simulation studies, however, show that this target will not be reached at first dose for the majority of critically-ill patients if using the most commonly recommended doses. Expert commentary: Considering that critically-ill patients are highly vulnerable and likely to experience antibiotic underexposure, and because effective initial treatment is a key determinant of clinical outcome, we support the use of a target of 100%T > 4xMIC, which could not only maximize efficacy but also minimize emergence of resistance. Clinical and microbiological studies are needed to test for the feasibility and effectiveness of reaching such a demanding target.

Population pharmacokinetics of levofloxacin in Korean patients

Levofloxacin (LVFX) has different effects depending on the area under the concentration-time curve (AUC)/minimum inhibitory concentration (MIC) ratio. While AUC can be expressed as dose/clearance (CL), we measured serial concentrations of LVFX in Koreans and tried to set a Korean-specific equation, estimating the CL of the antibiotic. In total, 38 patients, aged 18-87 years, received once daily intravenous LVFX doses of 500 mg or 250 mg, depending on their renal function. Four plasma samples were obtained according to a D optimal sampling design. The population pharmacokinetic (PK) parameters of LVFX were estimated using non-linear mixed-effect modeling (NONMEM, ver. 7.2). The CL of LVFX was dependent on creatinine clearance (CLCR) as a covariate. The mean population PK parameters of LVFX in Koreans were as follows: CL (l/hour) = 6.19 ×  (CLCR/75)(1.32). The CL of LVFX in Koreans is expected to be lower than that in Western people.

Comparison of Short Versus Prolonged Infusion of Standard Dose of Meropenem Against Carbapenemase-Producing Klebsiella pneumoniae Isolates in Different Patient Groups: A Pharmacokinetic-Pharmacodynamic Approach

Dose optimization is required to increase carbapenem's efficacy against carbapenemase-producing isolates. Four clinical Klebsiella pneumoniae isolates were used: one susceptible to meropenem with minimum inhibitory concentration (MIC) 0.031 mg/L and 3 verona integron-borne metallo bete-lactamase-1-producing isolates with MICs 8, 16, and 128 mg/L. The human pharmacokinetics of short (0.5-h) and prolonged (3-h) infusion regimens of 1 g meropenem every 8 h were simulated in an in vitro pharmacokinetic-pharmacodynamic model. Time-kill curves were constructed for each isolate and dosing regimen, and the %T > MIC associated with maximal bactericidal activity was estimated. The percentage of pharmacodynamic target attainment for isolates with different MICs was calculated for 350 ICU, surgical, and internal medicine patients. The isolates with MIC ≤8 mg/L were killed with both dosing regimens. The %T > MIC corresponding to maximal bactericidal activity was ∼40%. The percentages of target attainment were >90%, 61%-83%, 23%-33%, and <3% with the short infusion regimen and >90%, 98%-99%, 55%-79%, and <5% with the prolonged infusion regimen for isolates with MIC ≤2, 4, 8, and ≥16 mg/L, respectively. The lowest target attainment rates were observed for the ICU patients and the highest for internal medicine patients. The prolonged infusion regimen was more effective than the short infusion regimen against isolates with MIC 4-8 mg/L.

Population Pharmacokinetics and Pharmacodynamics of Meropenem in Nonobese, Obese, and Morbidly Obese Patients

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/m² ), 9 obese (30 kg/m² ≤ BMI < 40 kg/m² ), and 20 morbidly obese (BMI ≥ 40 kg/m² )-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.