Evaluation of antimicrobial susceptibility tests for Acinetobacter and Pseudomonas species using disks containing a high dose of meropenem.

The emergence and dissemination of carbapenem-resistant species of Acinetobacter and Pseudomonas have become a serious health concern. Routine antimicrobial disk susceptibility tests in clinical laboratories cannot distinguish between isolates that are highly carbapenem-resistant and those that are moderately carbapenem-resistant. The present study describes antimicrobial susceptibility tests using disks containing high doses (1000 µg) of meropenem. The diameters of inhibition zones were significantly negatively correlated with the MICs of Pseudomonas and Acinetobacter species for meropenem (R2: 0.93 and 0.91, respectively) and imipenem (R2: 0.75 and 0.84, respectively). Double disk synergy tests using clavulanic acid or sodium mercaptoacetate can detect ESBL or MBL producers. Susceptibility tests using disks containing high doses of meropenem can easily detect highly carbapenem-resistant isolates in a quantitative manner. These disks may be useful in bacteriological laboratories because of their technical ease, stability, and relatively low cost.

Investigation of in vitro antimicrobial and cytotoxic effects of gold nanoparticles capped with meropenem and imipenem.

Aim: This study aimed to investigate the in vitro antimicrobial effect of gold nanoparticles capped with meropenem and imipenem against various strains and to evaluate the cytotoxic effect of gold nanoparticles on healthy human colon epithelial cells. Materials & methods: Gold nanoparticles were synthesized via the Turkevich method and tested for antimicrobial effects using broth microdilution. Cell culture studies were performed using a cytotoxicity assay with alamarBlue™. Results & conclusion: Nanoparticles (10-20 nm) with antibiotic coating were more effective against Escherichia coli, Proteus spp. and Serratia marcescens than pure antibiotics. They had a cytotoxic effect on cells at high concentrations but were safe at low concentrations.

Pharmacokinetics and Therapeutic Target Attainment of Meropenem in Pediatric Post-Liver Transplant Patients: Extended vs Intermittent Infusion.

PURPOSE: The aim of this study is to characterize the concentration-time profile, pharmacokinetics parameters, and therapeutic target attainment of meropenem in pediatric post-liver transplant patients according to the duration of infusion. METHODS: This is a prospective cohort of pediatric transplant recipients with preserved renal function receiving meropenem 40 mg/kg every 8 hours. The patients were stratified into 2 groups based on infusion duration: G1 (15 minutes of intermittent infusion) and G1 (3 hours of extended infusion). Two blood samples per child were collected during the same interval within 48 hours of starting the antimicrobial. Meropenem concentrations were determined by high-performance liquid chromatography with tandem mass spectrometry. Pharmacokinetic parameters were assessed using a noncompartmental analysis. The therapeutic target was defined as 100% of the time above the minimum inhibitory concentration. FINDINGS: Fourteen patients with 28 measured meropenem concentrations were included. Lower values of volume of distribution and meropenem clearance compared with other critically ill pediatric populations were found. All patients achieved the therapeutic target against gram-negative pathogens with a minimum inhibitory concentration of ≤8 mg/L. Patients receiving a 15-minute infusion had higher values of peak and trough concentrations, resulting in unnecessary increased total drug exposure when compared to patients receiving a 3-hour infusion (P < .05). CONCLUSIONS: Meropenem at 120 mg/kg/d attained the therapeutic target against sensitive microorganisms in pediatric liver transplant recipients. The extended infusion should be preferred for patient safety. Because of the pharmacokinetic changes resulting from liver transplantation, individualized meropenem dosing regimens may be necessary.

Evaluation of the meropenem dosage and administration schedule in patients with bacteremia initial therapy.

BACKGROUND: The standard meropenem (MEPM) regimen allowed by insurance in Japan is 0.5 g two or three times a day. Differences in dosages and administration schedules in Japan were evaluated. METHODS: Patients with bacteremia for whom MEPM was used as the initial treatment at our institution between 2016 and 2021 were included. We retrospectively investigated patients classified into two groups: those treated according to severe infections (high-dose groupand others (low-dose group). After propensity score matching, we compared the probability of achieving free drug blood levels above the minimum inhibitory concentration (MIC) in 24 h (%fT > MIC) and outcomes. RESULTS: The probability of 100% fT > MIC was significantly higher in the high-dose group (96.4% vs 74.5%, odds ratio [OR] = 0.3, 95% confidence interval [CI] = 0.2-0.4, P = < 0.001). Regarding outcomes, the 30-day mortality rate was significantly lower in the high-dose group (1.4% vs. 11.4%, OR = 8.0, 95% CI = 1.5-43.7, P = 0.019). CONCLUSIONS: To improve outcomes in patients with bacteremia treated with MEPM, support for appropriate antimicrobial use is necessary for compliance with the dosage and administration schedule according to severe infections in initial treatment.

Population Pharmacokinetic Model and Dosing Simulation of Meropenem Using Measured Creatinine Clearance for Patients with Sepsis.

PURPOSE: Creatinine clearance (CCr) and pharmacokinetic parameters are markedly affected by pathophysiological changes in patients with sepsis. However, only a few reports have assessed renal function in patients with sepsis using the measured CCr. Furthermore, the administration regimen has not been sufficiently evaluated using a population PK (PPK) model across renal function broad ranges. Therefore, this study was performed to construct a meropenem PPK model for patients with sepsis using the measured CCr and evaluate the optimized meropenem dosing regimen based on the CCr. METHODS: Patients with sepsis who received intravenous meropenem at the Showa University Hospital were enrolled in this prospective observational study. The PPK model was constructed using blood samples and clinical information of patients. The probability of target attainment (PTA) indicates the likelihood of achieving 50% time above the minimum inhibitory concentration (% T > MIC) based on 10,000 virtual patients using Monte Carlo simulations. The PTA for each meropenem regimen was 50% T > MIC based on different renal functions using the Monte Carlo simulation. RESULTS: One hundred samples were collected from 31 patients. The final PPK model incorporating the measured CCr as a covariate in CL displayed the best fit. The recommended dosing regimen to achieve a PTA of 50% T > MIC of 4 mcg/mL was 1 g every 8 hours as a 3-hour prolonged infusion for patients with CCr 85-130 mL/min and 1 g every 8 hours as an 8-hour continuous infusion for patients with CCr ≥ 130 mL/min. CONCLUSIONS: This model precisely predicted meropenem concentrations in patients with sepsis by accurately evaluating renal function using the measured CCr. Extended dosing was demonstrated to be necessary to achieve a PTA of 50% T > MIC for patients with CCr ≥ 85 mL/min. Meropenem effectiveness can be maximized in patients with sepsis by selecting the appropriate dosing regimen based on renal function and the MIC.

Meropenem Population Pharmacokinetics and Simulations in Plasma, Cerebrospinal Fluid, and Brain Tissue.

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

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.

Impact of therapeutic plasma exchange on meropenem pharmacokinetics.

STUDY OBJECTIVE: The aim of this study was to investigate the impact of therapeutic plasma exchange (TPE) on the plasma concentrations and pharmacokinetic (PK) patterns of meropenem. DESIGN: Prospective, open-label, PK study. SETTING: Academic tertiary care medical center. PATIENTS: Eleven patients who underwent TPE. MEASUREMENTS: A single-center PK study was conducted on adult patients who underwent TPE. All patients received two phases of meropenem administration for research purposes. Meropenem PK studies were carried out after the administration of a single dose of 1 g of meropenem in the patients during TPE (phase 1) and compared with meropenem 1 g administration in the same patients without TPE (phase 2), which served as the control phase with an at least 72-h wash-out period separating the phases. MAIN RESULTS: The total clearance (CL) of meropenem during TPE was greater than the values obtained from the same patients without TPE (13.37 ± 6.23 L/h during TPE vs. 8.42 ± 2.84 L/h without TPE). The mean drug fraction eliminated during TPE was 14.22 ± 11.03%, and the mean amount of drug removed by the TPE was 142.23 ± 110.31 mg. CONCLUSIONS: These results indicate that the TPE had an impact on the elimination of meropenem in patients during the exchange procedure. The CL of meropenem during TPE was greater than the values obtained from the control phase without TPE.

Imipenem cilastatin sodium-associated thrombocytopenia in an older patient: A case report and literature review.

Imipenem cilastatin sodium, as a member of a new generation of ß-lactam antibiotics, has a broad spectrum of antibacterial activity and a very wide range of application. Thrombocytopenia has been reported as a rare adverse event in several studies of patients treated with imipenem cilastatin sodium. In this study, we present a case of thrombocytopenia associated with imipenem cilastatin sodium in an older patient. The 78-year-old male patient with pulmonary infection was initiated on anti-infection therapy with imipenem cilastatin sodium. On the 9th day after imipenem cilastatin sodium administration, the patient experienced a sudden and dramatic decrease in platelet count. Similarly, on the 4th day after the re-administration of imipenem cilastatin sodium for anti-infection therapy, the patient's platelet count showed a remarkable downward trend again. A time correlation between the drug therapy and the occurrence of platelet reaction was found. The patient's platelet count gradually returned to the normal level on the 6th day after the first drug withdrawal and the 13th day after the second drug withdrawal, respectively. Considering the widespread use of imipenem cilastatin sodium, healthcare providers should improve the notification of thrombocytopenia associated with imipenem cilastatin sodium.

Therapeutic Target Attainment of 3-Hour Extended Infusion of Meropenem in Patients With Septic Burns.

PURPOSE: The aim of this prospective cohort study was to evaluate the therapeutic target attainment of 3-hour extended infusion of meropenem in patients with septic burns in the early and late periods of septic shock. METHODS: Meropenem serum levels were determined by liquid chromatography from blood samples collected within 48 hours (early period) of therapy and 10 to 14 days afterward (late period). Pharmacokinetic properties were investigated by noncompartmental analysis, and the therapeutic target was defined as 100% of the time above the MIC (100%fT> MIC). FINDINGS: Fifteen patients with 90 measured meropenem concentrations were included. Throughout the entire course of antimicrobial therapy, the therapeutic target was attained against gram-negative pathogens with an MIC ≤ 2 mg/L. Pathogens with intermediate susceptibility to meropenem were only covered in the early phase of therapy. IMPLICATIONS: Higher-dose regimens or continuous infusions may be necessary to guarantee antimicrobial coverage of meropenem against less sensitive pathogens in patients with septic burns.

Mutation and evolution of metallo-beta-lactamase CphA under the selective pressure of biapenem continuous concentration gradient.

One of the resistance mechanisms of superbugs is to hydrolyze antibiotics by producing metallo-ß-lactamases (MßLs). To verify how MßLs evolved to increase in activity in response to various ß-lactam antibiotics, the mutation and evolution of CphA from Aeromonas hydrophila (Zn2+-dependent MßL) was investigated in a medium with a continuous biapenem (BIA) concentration gradient. The results showed that a single-base mutation M1 and two frameshift mutations M3 and M4 were observed. Furthermore, a nonsense mutation M2 was observed. Compared with wild-type (WT), the minimum inhibitory concentrations (MICs) of the M3 and M4 increased by more than 128 times, and the catalytic efficiency of BIA by the M3 and M4 increased by 752% and 376% respectively. In the mutants, the carbon skeleton migration caused by the outward motion of the loop3 near the entrance of the binding pocket increased the cavity volume of the binding pocket and was more conducive to the entry and expulsion of BIA and its hydrolytic product in the binding pocket. The conformational change effect originated from mutations is transmitted to the binding pocket through the interactions between the side chain amino acid residues of the C-terminal and those of the loop3, thus affecting the binding and hydrolysis capability of the mutants to BIA in the binding pocket. All these indicated that during the repeated drug-endurance and -resistance, the CphA completed its mutation and conformational change and evolved to the mutants with a more delicate structure and stronger hydrolysis ability by a genetic mutation.

Structure of a B12-dependent radical SAM enzyme in carbapenem biosynthesis.

Carbapenems are antibiotics of last resort in the clinic. Owing to their potency and broad-spectrum activity, they are an important part of the antibiotic arsenal. The vital role of carbapenems is exemplified by the approval acquired by Merck from the US Food and Drug Administration (FDA) for the use of an imipenem combination therapy to treat the increased levels of hospital-acquired and ventilator-associated bacterial pneumonia that have occurred during the COVID-19 pandemic1. The C6 hydroxyethyl side chain distinguishes the clinically used carbapenems from the other classes of ß-lactam antibiotics and is responsible for their low susceptibility to inactivation by occluding water from the ß-lactamase active site2. The construction of the C6 hydroxyethyl side chain is mediated by cobalamin- or B12-dependent radical S-adenosylmethionine (SAM) enzymes3. These radical SAM methylases (RSMTs) assemble the alkyl backbone by sequential methylation reactions, and thereby underlie the therapeutic usefulness of clinically used carbapenems. Here we present X-ray crystal structures of TokK, a B12-dependent RSMT that catalyses three-sequential methylations during the biosynthesis of asparenomycin A. These structures, which contain the two metallocofactors of the enzyme and were determined in the presence and absence of a carbapenam substrate, provide a visualization of a B12-dependent RSMT that uses the radical mechanism that is shared by most of these enzymes. The structures provide insight into the stereochemistry of initial C6 methylation and suggest that substrate positioning governs the rate of each methylation event.

A dosing nomograph for cerebrospinal fluid penetration of meropenem applied by continuous infusion in patients with nosocomial ventriculitis.

OBJECTIVES: In difficult-to-treat infections such as nosocomial ventriculitis, meropenem exposure in the infected compartment is often uncertain but crucial for antibacterial effects. The aim of this study was to investigate the cerebrospinal fluid (CSF) penetration of meropenem in patients with nosocomial ventriculitis and to derive a nomograph to predict effective meropenem doses as a function of clinical parameters. METHODS: Retrospective patient data including meropenem serum and CSF levels as well as CSF inflammation markers were analyzed using NONMEM to assess the general pharmacokinetics and CSF penetration. Monte Carlo simulations were used to evaluate different meropenem dosing regimens. Probability of target attainment (PTA) in CSF was assessed, and a nomograph to achieve a target twice the minimal inhibitory concentration (MIC) during the dosing interval (100 %fT > 2x MIC) was developed. RESULTS: A one-compartment model with meropenem clearance dependent on the estimated glomerular filtration rate (CKD-EPI eGFR, p < 0.001) best described meropenem serum pharmacokinetics of 51 critically ill patients. CSF penetration ratio was correlated with the amount of protein in CSF (p < 0.001), with higher CSF protein levels accounting for higher penetration ratios. Preserved renal function (CKD-EPI eGFR >50 mL/min/1.73 m2) and low CSF protein levels (<500 mg/L) resulted in 80% PTA 100 %fT >2xMIC) for a meropenem dose of 6 g/24 h. DISCUSSION: High interindividual variability in meropenem CSF concentration was observed in patients with nosocomial ventriculitis. A nomograph to predict the daily meropenem dose required for target attainment for a given eGFR and CSF protein count was developed.

Biapenem.

Biapenem is a novel parenteral broad spectrum carbapenem primarily used for the treatment of complicated infections like sepsis, lower respiratory infections, urinary tract infections, intra-abdominal and genitourinary infections etc. in Japan, Thailand and China since two decades, has been recently approved in India. Biapenem shows good bactericidal activity against Gram-positive bacteria including streptococcus pneumoniae, pyogenes and methicillin-susceptible staphylococcus aureus (MSSA). It also shows antibacterial activities against Gram-negative bacteria including resistant Pseudomonas aeruginosa and Acinetobacter baumannii. Evidence from international studies confirmed that biapenem can be used as effectively and safely as meropenem or imipenem/ cilastatin in the treatment of various infectious diseases. This article summarizes the milestones, unique structure, mechanism of action, pharmacokinetics, special pharmacological properties and spectrum of in vitro activity of biapenem. The results of comparative clinical trials on Biapenem are also described, as is the patient safety and tolerability observed during these studies.

In vitro effectiveness of biapenem against IMP-producing Enterobacteriaceae.

The options available for treating infections with carbapenemase-producing Enterobacteriaceae (CPE) are limited; with the increasing threat of these infections, new treatments are urgently needed. Biapenem (BIPM) is a carbapenem, and limited data confirming its in vitro killing effect against CPE are available. In this study, we examined the minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of BIPM for 14 IMP-1-producing Enterobacteriaceae strains isolated from the Okayama region in Japan. The MICs against almost all the isolates were lower than 0.5 µg ml-1, indicating susceptibility to BIPM, while approximately half of the isolates were confirmed to be bacteriostatic to BIPM. However, initial killing to a 99.9 % reduction was observed in seven out of eight strains in a time-kill assay. Despite the small data set, we concluded that the in vitro efficacy of BIPM suggests that the drug could be a new therapeutic option against infection with IMP-producing CPE.

Meropenem-induced thrombocytopenia: a paediatric case.

Meropenem is a broad-spectrum carbapenem widely used to treat both Gram-positive and negative bacterial infections, including extended-spectrum beta-lactamase-producing microbes. We describe the occurrence of thrombocytopenia and hypersensitivity in a boy receiving intravenous meropenem for intra-abdominal sepsis secondary to perforated appendicitis. The patient developed a pruritic maculopapular rash with occasional petechiae, associated with severe thrombocytopenia, after 7 days of meropenem administration. Investigations for other causes of thrombocytopenia, including possible line sepsis, were unfruitful, and the thrombocytopenia did not resolve until cessation of meropenem. Drug-induced reactions should be considered in children receiving meropenem who present with a rash and thrombocytopenia.

Inhibitory effects of indoxyl sulfate and creatinine on the renal transport of meropenem and biapenem in rats.

Carbapenem antibiotics are excreted preferentially in the urine after intravenous administration, with organic anion transporters (OATs) known to be involved in the renal tubular secretion of carbapenem antibiotics. Various uremic toxins (UTs) accumulate in the blood of patients with end-stage renal failure, and some UTs such as indoxyl sulfate (IS) and creatinine (Cr) are excreted in the urine via OATs. However, information about the possible interactions between these UTs and carbapenems in the renal secretion remains limited. In this study, we investigated the effects of IS and Cr on the renal transport of anionic meropenem and zwitterionic biapenem by using rat renal cortical slices. The uptake of meropenem and biapenem in the renal cortical slices was significantly decreased in the presence of 0.1 mM IS or 1 mM Cr. When biapenem and Cr were co-administered to rats intravenously, biapenem clearance from the plasma was clearly retarded, reflecting the current in vitro results. However, IS and Cr exerted no inhibitory effect on the uptake of metformin, a substrate of renal organic cation transporter (OCT) 2, in the renal cortical slices. Thus, our findings indicate that IS and Cr interfere with the renal secretion of carbapenem antibiotics by preferentially inhibiting OATs.

A metallo-ß-lactamase enzyme for internal detoxification of the antibiotic thienamycin.

Thienamycin, the first representative of carbapenem antibiotics was discovered in the mid-1970s from soil microorganism, Streptomyces cattleya, during the race to discover inhibitors of bacterial peptidoglycan synthesis. Chemically modified into imipenem (N-formimidoyl thienamycin), now one of the most clinically important antibiotics, thienamycin is encoded by a thienamycin gene cluster composed of 22 genes (thnA to thnV) from S. cattleya NRRL 8057 genome. Interestingly, the role of all thn-genes has been experimentally demonstrated in the thienamycin biosynthesis, except thnS, despite its annotation as putative ß-lactamase. Here, we expressed thnS gene and investigated its activities against various substrates. Our analyses revealed that ThnS belonged to the superfamily of metallo-ß-lactamase fold proteins. Compared to known ß-lactamases such as OXA-48 and NDM-1, ThnS exhibited a lower affinity and less efficiency toward penicillin G and cefotaxime, while imipenem is more actively hydrolysed. Moreover, like most MBL fold enzymes, additional enzymatic activities of ThnS were detected such as hydrolysis of ascorbic acid, single strand DNA, and ribosomal RNA. ThnS appears as a MBL enzyme with multiple activities including a specialised ß-lactamase activity toward imipenem. Thus, like toxin/antitoxin systems, the role of thnS gene within the thienamycin gene cluster appears as an antidote against the produced thienamycin.