Pharmacokinetics and Pharmacodynamics of β-Lactamase Inhibitors

Impact of Hypothermic Temperature Control on Plasma and Soft Tissue Pharmacokinetics of Penicillin/Beta-Lactamase Inhibitor Combinations in Patients Resuscitated After Cardiac Arrest

BACKGROUND AND OBJECTIVES

Penicillin/beta-lactamase inhibitors are often used to treat aspiration pneumonia in patients resuscitated after cardiac arrest (CA). The impact of hypothermic temperature control on the pharmacokinetics of amoxicillin/clavulanate (AMO/CLAV) and ampicillin/sulbactam (AMP/SULB) has not been studied. Our objective was to evaluate the effects of hypothermic temperature control on the plasma and soft tissue pharmacokinetics of AMO/CLAV and AMP/SULB, including pulmonary concentrations of AMP/SULB, in patients resuscitated after CA.

METHODS

This prospective clinical study involved ten adult patients after CA receiving either AMO/CLAV 2 g/0.2 g or AMP/SULB 2 g/1 g intravenously every 8 h. Patients underwent hypothermic temperature control (33 ± 1 °C) for 24 h, followed by normothermia. Plasma, urine, muscle, and subcutaneous pharmacokinetics were measured and plasma protein-binding assessed for each subject. Microdialysis determined unbound drug concentrations in soft tissues. The pulmonary concentration of AMP/SULB was analyzed in the epithelial lining fluid.

RESULTS

No significant differences in plasma pharmacokinetics or renal excretion of AMO/CLAV and AMP/SULB were observed between the two temperature conditions. Soft tissue concentrations showed no consistent trend. Pharmacokinetic/pharmacodynamic targets (time that the unbound plasma concentrations were above the minimal inhibitory concentration [MIC] for MIC up to 8 mg/L) were met but not for 16 mg/L. Pulmonary concentrations of AMP/SULB in the epithelial lining fluid showed no clear trend.

CONCLUSION

This study indicates that hypothermic temperature control does not significantly affect plasma concentrations, soft tissue concentrations, or renal excretion of AMO/CLAV and AMP/SULB in patients resuscitated after CA. However, pulmonary concentrations of AMP/SULB exhibited interindividual variability.

Critical reappraisal of current issues for improving the proper clinical use of the incoming beta-lactam/beta-lactamase inhibitor combinations of tomorrow

INTRODUCTION

Although different novel beta-lactam/beta-lactamase inhibitor combinations (BL/BLIc) were recently licensed, resistance occurrence have been reported up to 15% of Gram-negative pathogens. For this reason, novel BL/BLIc of tomorrow will be released for managing difficult-to-treat resistance (DTR) Gram-negative infections.

AREAS COVERED

This review provides a critical reappraisal of current issues for improving the proper clinical use of the novel BL/BLIc of tomorrow. A literature search was performed on PubMed-MEDLINE (until December 2024) for retrieving available studies on cefepime-enmetazobactam, sulbactam-durlobactam, and cefepime-taniborbactam. Four different main areas were discussed according to available evidence: 1) translating findings coming from the randomized clinical trials into the real-world clinical practice; 2) defining the optimal joint pharmacokinetic/pharmacodynamic (PK/PD) target; 3) identifying proper dosing schedules in patients with renal dysfunction; 4) attributing proper relevance to the epithelial lining fluid (ELF) penetration rate in defining optimal dosing schedule for treating pneumonia.

EXPERT OPINION

Overall, old habits die hard and issues retrieved with licensed beta-lactams emerged also with novel BL/BLIc of tomorrow, potentially affecting their efficacy when used in real-world practice. Adopting appropriate corrective measures for overcoming these issues might increase the likelihood of preserving their efficacy in the future by minimizing the propensity risk of resistance development.

Pharmacokinetics of continuous infusion ceftolozane/tazobactam in two patients with extensive total body surface area burns

INTRODUCTION

Treatment of infections in patients with burn injuries is challenging due to altered antimicrobial pharmacokinetics. Continuous infusion β-lactam therapy may be a useful antimicrobial stewardship strategy to improve pharmacodynamic target attainment in this population.

CASE SUMMARIES

This report highlights the use of continuous infusion ceftolozane/tazobactam (C/T) in two patients with extensive total body surface area (TBSA) burns, suspected augmented renal clearance (ARC), and bloodstream infections caused by Pseudomonas aeruginosa with difficult-to-treat resistance (DTR P. aeruginosa). Both patients received C/T 9 g/day via continuous infusion. Minimum inhibitory concentrations (MIC) of C/T were 8/4 and 4/4 μg/mL in Cases 1 and 2, respectively.

DISCUSSION

Despite similar patient characteristics, average free plasma ceftolozane concentrations were 41.6 mg/L in Case 1 and 22.8 mg/L in Case 2. Measured free concentrations exceeded 4 times the MIC for 100% of each 24-h infusion (fT > 4xMIC), and bacteremia was successfully cleared in each case.

CONCLUSION

These cases highlight the variability of drug exposure in patients with extensive TBSA burn injuries and support continuous infusion β-lactam therapy as a proactive strategy to optimize pharmacodynamic target attainment when pharmacokinetics are unpredictable.

Utilizing an Opportunistic Clinical Study and Population-Based Pharmacokinetic Models to Identify Rational Empiric Dosing Regimens for Piperacillin-Tazobactam in Critically Ill Patients

Determining an effective dosing regimen for piperacillin-tazobactam in critically ill patients is challenging due to substantial pharmacokinetic variability caused by complex pathophysiological changes. To address this need, a prospective clinical study was conducted, which enrolled 112 critically ill patients and employed an opportunistic sampling strategy. Population modeling and simulation were performed to characterize the pharmacokinetics (PK) and probability of target attainment (PTA) of piperacillin-tazobactam under various dosing regimens. Both piperacillin and tazobactam final models were one-compartment models with zero-order input and first-order elimination. Significant covariates included lean body weight for piperacillin and creatinine clearance along with continuous renal replacement therapy (CRRT) for both drugs. Monte Carlo simulations demonstrated that continuous infusion can achieve higher PTA than intermittent and extended infusions. When considering the minimum inhibitory concentration (MIC) of 16 mg/L for Pseudomonas aeruginosa (a frequently encountered bacterial pathogen among critically ill patients) and a PK/PD target of 100% fT >MIC, continuous infusion of 6 g/day is recommended for critically ill patients with a CLcr <60 mL/min, 9 g/day for patients with CLcr in the range of 60 to 129 mL/min, and 12 g/day for patients with a CLcr ≥130 mL/min. In addition, extended infusion represents a good alternative, especially the 3 g q6h or 4 g q6h regimens which can achieve the designated European Committee on Antimicrobial Susceptibility Testing (EUCAST) non-species-related PK/PD breakpoint of 8 mg/L. Our study provided valuable insight into PTA outcomes, which, together with individual renal function of future patients and institution-specific piperacillin susceptibility patterns, may assist physicians when making dosing decisions.

Population pharmacokinetics of piperacillin-tazobactam in the plasma and cerebrospinal fluid of critically ill patients

Ventriculitis in neurocritical care patients leads to significant morbidity and mortality. Antibiotic dose optimization targeting pharmacokinetic/pharmacodynamic (PK/PD) exposures associated with improved bacterial killing may improve therapeutic outcomes. We sought to develop and apply a population PK model in infected critically ill patients to determine optimal piperacillin-tazobactam (PTZ) dosing regimens to achieve target cerebrospinal fluid (CSF) exposures. Neurosurgical patients with external ventricular drains and receiving PTZ treatment were recruited and had plasma and CSF samples collected and assayed. A population PK model was developed using plasma and CSF piperacillin and tazobactam concentrations. Eight patients were recruited. Median age was 59 years, median weight was 70 kg, and five patients were female. The median creatinine clearance was 84 mL/min/1.73 m2 (range 52-163). Substantial inter-individual PK variability was apparent, particularly in CSF. Piperacillin penetration into CSF had a median of 3.73% (range 0.73%-7.66%), and tazobactam CSF penetration was not predictable. Dosing recommendations to optimize CSF exposures for the treatment of ventriculitis were not possible due to substantial PK variability and very low drug penetration. High plasma PTZ exposures may not translate to effective exposures in CSF.

Rationale and Logistics of Continuous Infusion Cephalosporin Antibiotics

Cephalosporins have traditionally been administered as an intermittent infusion. With the knowledge that cephalosporins demonstrate a time-dependent pharmacodynamic profile, administration via continuous infusion may provide more effective antibiotic exposure for successful therapy. Proposed benefits of administration via continuous infusion include less IV manipulation, decreased potential for antibiotic resistance, and potential cost savings. The objective of this review was to provide a detailed assessment of available evidence for the use of continuous infusion cephalosporins and practical dosing and administration recommendations. Studies were gathered and assessed for inclusion via a literature search of PubMed and Ovid MEDLINE using mesh terms ["continuous infusion" and "cephalosporin"], "intermittent infusion", ["intermittent versus continuous" and "cephalosporin"], "continuous infusion cephalosporin", as well as specific drug names. References from included studies were also evaluated for inclusion. Data which compared the two administration methods (continuous infusion vs. intermittent infusion) were evaluated. Thirty-five studies were analyzed among several cephalosporins with variable delivery. Dosing regimens utilized in the selected studies were assessed with known compatibility and stability data and further summarized.

Aztreonam-avibactam: The dynamic duo against multidrug-resistant gram-negative pathogens

Antimicrobial resistance poses a significant public health challenge, particularly with the rise of gram-negative hospital-acquired infections resistant to carbapenems. Aztreonam-avibactam (ATM-AVI) is a promising new combination therapy designed to combat multidrug-resistant (MDR) gram-negative bacteria, including those producing metallo-β-lactamases (MBLs). Aztreonam, a monobactam antibiotic, is resistant to hydrolysis by MBLs but can be degraded by other β-lactamases. Avibactam, a novel non-β-lactam β-lactamase inhibitor, effectively neutralizes extended-spectrum β-lactamases (ESBLs) and AmpC β-lactamases, restoring aztreonam's efficacy against resistant pathogens. This review covers the chemistry, mechanisms of action, spectrum of activity, pharmacokinetics, pharmacodynamics, and clinical efficacy of ATM-AVI. ATM-AVI combination has shown efficacy against a wide range of resistant Enterobacterales and other gram-negative bacteria in both in vitro and clinical studies. Pharmacokinetic and pharmacodynamic analyses demonstrate that ATM-AVI maintains effective drug concentrations in the body, with dose adjustments recommended for patients with renal impairment. Clinical trials, including the REVISIT and ASSEMBLE studies, have demonstrated the safety and efficacy of ATM-AVI in treating complicated intra-abdominal infections (cIAI), urinary tract infections (UTIs), and hospital-acquired pneumonia (HAP) caused by MDR gram-negative pathogens. The European Medicines Agency (EMA) has approved ATM-AVI for these indications, and further research is ongoing to optimize dosing regimens and expand its clinical use. This combination represents a critical advancement in the fight against antimicrobial resistance, offering a new therapeutic option for treating severe infections caused by MDR gram-negative, including MBL-producing, bacteria.

Sulbactam-durlobactam for the treatment of Acinetobacter baumannii-calcoaceticus complex

INTRODUCTION

Infections with Acinetobacter baumannii-calcoaceticus complex (ABC) pose difficulty for clinicians given a limited arsenal of effective antimicrobials. Sulbactam/durlobactam provides a novel treatment option for patients experiencing hospital- or ventilator-acquired pneumonia with susceptible strains.

AREAS COVERED

This review provides a comprehensive discussion of sulbactam/durlobactam, including basic characteristics, in vitro activity, and clinical trial data supporting its use for the treatment of ABC. Manufacturer's data, published literature to date, and conference data are utilized in this review.

EXPERT OPINION

Sulbactam/durlobactam offers clinicians a new and effective treatment option for resistant ABC infection. Sulbactam, when combined with durlobactam, displays enhanced potency against ABC isolates, which has translated into positive clinical outcomes observed in clinical trials and post-marketing case studies. Although overall treatment indications and clinical experience are limited to date, sulbactam/durlobactam offers a familiar and favorable safety profile in comparison with alternative agents. Factors associated with use of combination antibiotic therapy, availability of commercial drug susceptibility testing, and cost-effectiveness are all currently key considerations for sulbactam/durlobactam use.

In vivo efficacy of enmetazobactam combined with cefepime in a murine pneumonia model induced by OXA-48-producing Klebsiella pneumoniae

Cefepime/enmetazobactam is a new β-lactam/β-lactamase inhibitor combination with broad-spectrum activity against multidrug-resistant Enterobacterales, including OXA-48-producing isolates. Furthermore, cefepime and enmetazobactam have demonstrated similar and excellent intrapulmonary penetration, supporting the use of this new antibiotic combination in the treatment of hospital-acquired pneumonia. This study evaluated the in vivo efficacy of cefepime/enmetazobactam in a murine neutropenic pneumonia model infected with various OXA-48-producing K. pneumoniae strains. Mice were subcutaneously administered with cefepime (100 mg/kg/q2h), alone or combined with enmetazobactam (30 mg/kg/q2h), or intraperitoneally with meropenem (100 mg/kg/q2h) at 2 h post-infection. Mice were euthanized at 26 h post-infection for bacterial enumeration in lungs and spleen. A robust growth was achieved in untreated control mice. Cefepime alone or meropenem had no effect on reducing the bacterial burden in lungs after a 24-h period of treatment. The addition of enmetazobactam to cefepime resulted in a 2-log10 CFU/g bioburden reduction in lungs compared to 26-h controls for all strains, including the strain harboring the highest MIC (= 8 µg/mL) to cefepime/enmetazobactam. When changes of bacterial burden were assessed relative to 2-h controls, bacterial stasis was observed. These data highlight the limited in vivo activity of meropenem against OXA-48-producing Enterobacterales despite in vitro susceptibility. Conversely, cefepime/enmetazobactam with a human-mimicking regimen demonstrated a significant antibacterial effect in the pneumonia model induced by three OXA-48-producing K. pneumoniae strains, compared with cefepime or meropenem at 24 h post-infection. Therefore, cefepime/enmetazobactam may be a new alternative for lung infections due to Enterobacterales producing OXA-48.

IMPORTANCE

Third-generation cephalosporin-resistant Klebsiella pneumoniae with extended-spectrum β-lactamases as principal resistance determinants are classified as critical priority pathogens. Their increasing occurrence has led clinicians to widely use carbapenems. Accordingly, carbapenem resistance in Klebsiella pneumoniae has spread in recent decades across several countries, and OXA-48-like carbapenemases are one of the main determinants of carbapenem resistance in Enterobacterales. Cefepime/enmetazobactam is a novel β-lactam/β-lactamase inhibitor combination that demonstrated excellent intrapulmonary penetration, supporting its use in the treatment of pneumonia. This study examined the efficacy of enmetazobactam, in combination with cefepime, compared to carbapenems for OXA-48-producing Klebsiella pneumoniae in a 24-h murine neutropenic pneumonia model. The combination showed a bacteriostatic effect using the 2-h controls as reference. Compared to 24-h controls, and to cefepime or meropenem monotherapies, the co-administration of enmetazobactam with cefepime demonstrated a pronounced in vivo bactericidal activity against cefepime-non-susceptible K. pneumoniae isolates with cefepime/enmetazobactam MICs up to 8 µg/mL in this model.

A Difficult Case of Ventriculitis in a 40-Year-Old Woman with Acute Myeloid Leukemia

Ventriculitis and nosocomial meningitis caused by carbapenem-resistant Gram-negative and vancomycin-resistant Gram-positive bacteria represent a growing treatment challenge. A case of ventriculitis and bacteremia caused by carbapenem-resistant, KPC-producing Klebsiella pneumoniae and vancomycin-resistant Enterococcus faecium in a young woman with acute leukemia who was successfully treated with meropenem/vaborbactam (MVB), rifampicin, and linezolid is described in this paper. This case report emphasizes the importance of a multidisciplinary strategy, including infectious focus control, for the treatment of device-associated central nervous system (CNS) infections from multidrug-resistant bacteria. Considering the novel resistance patterns, more research on drug penetration into the central nervous system, as well as on the necessity of association therapies, is needed.

What are the optimal pharmacokinetic/pharmacodynamic targets for β-lactamase inhibitors? A systematic review

BACKGROUND

Pharmacokinetic/pharmacodynamic (PK/PD) indices are widely used for the selection of optimum antibiotic doses. For β-lactam antibiotics, fT>MIC, best relates antibiotic exposure to efficacy and is widely used to guide the dosing of β-lactam/β-lactamase inhibitor (BLI) combinations, often without considering any PK/PD exposure requirements for BLIs.

OBJECTIVES

This systematic review aimed to describe the PK/PD exposure requirements of BLIs for optimal microbiological efficacy when used in combination with β-lactam antibiotics.

METHODS

Literature was searched online through PubMed, Embase, Web of Science, Scopus and Cochrane Library databases up to 5 June 2023. Studies that report the PK/PD index and threshold concentration of BLIs approved for clinical use were included. Narrative data synthesis was carried out to assimilate the available evidence.

RESULTS

Twenty-three studies were included. The PK/PD index that described the efficacy of BLIs was fT>CT for tazobactam, avibactam and clavulanic acid and fAUC0-24/MIC for relebactam and vaborbactam. The optimal magnitude of the PK/PD index is variable for each BLI based on the companion β-lactam antibiotics, type of bacteria and β-lactamase enzyme gene transcription levels.

CONCLUSIONS

The PK/PD index that describes the efficacy of BLIs and the exposure measure required for their efficacy is variable among inhibitors; as a result, it is difficult to make clear inference on what the optimum index is. Further PK/PD profiling of BLI, using preclinical infection models that simulate the anticipated mode(s) of clinical use, is warranted to streamline the exposure targets for use in the optimization of dosing regimens.

In vitro pharmacokinetics/pharmacodynamics of FL058 (a novel beta-lactamase inhibitor) combined with meropenem against carbapenemase-producing Enterobacterales

Objective: FL058 is a novel beta-lactamase inhibitor with a broad spectrum of activity and a favorable safety profile. The objective of this study was to evaluate pharmacokinetic/pharmacodynamic (PK/PD) relationships for the combination of FL058 and meropenem in an in vitro infection model. Methods: By simulating human concentration-time profiles in the in vitro model, meropenem combined with FL058 when administered 1 g/0.5 g, 1 g/1 g, 2 g/1 g, and 2 g/2 g q8h by 3-h infusion achieved approximately 2- and 4-log10 kill to KPC/OXA-producing Klebsiella pneumoniae and Escherichia coli; the combination therapy could not inhibit NDM-producing K. pneumoniae but could maintain NDM-producing E. coli around a baseline. Results: The PK/PD indexes that best described the bacterial killing from baseline in log10 CFU/mL at 24 h were the percent time of free drug above the minimal inhibitory concentration (MIC) (%fT > MIC, MIC with FL058 at 4 mg/L) for meropenem and the percent time of free drug above 1 mg/L (%fT > 1 mg/L) for FL058. The targets for achieving a static effect and the 1- and 2-log10 kill were 74, 83, and 99 for %fT > MIC of meropenem and 40, 48, and 64 for %fT > 1 mg/L of FL058, respectively. The PK/PD index of %fT > 1 mg/L can provide a basis for evaluating clinical dosing regimens for FL058 combined with meropenem. Conclusion: FL058 combined with meropenem might be a potential treatment for KPC- and/or OXA-48-producing Enterobacterales infection.

Balancing the scales: achieving the optimal beta-lactam to beta-lactamase inhibitor ratio with continuous infusion piperacillin/tazobactam against extended spectrum beta-lactamase producing Enterobacterales

Piperacillin/tazobactam (TZP) is administered intravenously in a fixed ratio (8:1) with the potential for inadequate tazobactam exposure to ensure piperacillin activity against Enterobacterales. Adult patients receiving continuous infusion (CI) of TZP and therapeutic drug monitoring (TDM) of both agents were evaluated. Demographic variables and other pertinent laboratory data were collected retrospectively. A population pharmacokinetic approach was used to select the best kidney function model predictive of TZP clearance (CL). The probability of target attainment (PTA), cumulative fraction of response (CFR) and the ratio between piperacillin and tazobactam were computed to identify optimal dosage regimens by continuous infusion across kidney function. This study included 257 critically ill patients (79.3% male) with intra-abdominal, bloodstream, and hospital-acquired pneumonia infections in 89.5% as the primary indication. The median (min-max range) age, body weight, and estimated glomerular filtration rate (eGFR) were 66 (23-93) years, 75 (39-310) kg, and 79.2 (6.4-234) mL/min, respectively. Doses of up to 22.5 g/day were used to optimize TZP based on TDM. The 2021 chronic kidney disease epidemiology equation in mL/min best modeled TZP CL. The ratio of piperacillin:tazobactam increased from 6:1 to 10:1 between an eGFR of <20 mL/min and >120 mL/min. At conventional doses, the PTA is below 90% when eGFR is ≥100 mL/min. Daily doses of 18 g/day and 22.5 g/day by CI are expected to achieve a >80% CFR when eGFR is 100-120 mL/min and >120-160 mL/min, respectively. Inadequate piperacillin and tazobactam exposure is likely in patients with eGFR ≥ 100 mL/min. Dose regimen adjustments informed by TDM should be evaluated in this specific population.

Breaking Down the Breakpoints: Rationale for the 2022 Clinical and Laboratory Standards Institute Revised Piperacillin-Tazobactam Breakpoints Against Enterobacterales

Piperacillin-tazobactam (PTZ) is one of the most common antibiotics administered to hospitalized patients. Its broad activity against gram-negative, gram-positive, and anaerobic pathogens; efficacy in clinical trials across diverse infection types and patient populations; and generally favorable toxicity profile make it a particularly appealing antibiotic agent. PTZ susceptibility interpretive criteria (ie, breakpoints) for the Enterobacterales were initially established in 1992, as the drug was undergoing approval by the US Food and Drug Administration. In the ensuing 30 years, changes in the molecular epidemiology of the Enterobacterales and its impact on PTZ susceptibility testing, mounting pharmacokinetic/pharmacodynamic data generated from sophisticated techniques such as population pharmacokinetic modeling and Monte Carlo simulation, and disturbing safety signals in a large clinical trial prompted the Clinical Laboratory and Standards Institute (CLSI) to review available evidence to determine the need for revision of the PTZ breakpoints for Enterobacterales. After an extensive literature review and formal voting process, the susceptibility criteria were revised in the 2022 CLSI M100 document to the following: ≤8/4 µg/mL (susceptible), 16/4 µg/mL (susceptible dose-dependent), and ≥32/4 µg/mL (resistant). Herein, we provide a brief overview of the CLSI process of antibiotic breakpoint revisions and elaborate on the available data that ultimately led to the decision to revise the PTZ breakpoints.

Utilizing Ceftazidime/Avibactam Therapeutic Drug Monitoring in the Treatment of Neurosurgical Meningitis Caused by Difficult-to-Treat Resistant Pseudomonas aeruginosa and KPC-Producing Enterobacterales

Background

Central nervous system (CNS) infections caused by Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacterales and difficult-to-treat resistant (DTR) Pseudomonas aeruginosa represent a formidable clinical challenge. Antimicrobial regimens that efficiently penetrate the cerebrospinal fluid (CSF) and achieve sufficient concentrations associated with microbiologic and clinical cure are limited. We evaluated therapy with ceftazidime-avibactam (CAZ-AVI) in order to guide precise dosing in the treatment of CNS infections.

Methods

Therapeutic drug monitoring (TDM) was performed in 3 patients with health care-associated ventriculitis and meningitis (HAVM) using CAZ-AVI 2.5 g infused intravenously every 8 hours as standard and extended infusion. Simultaneous CSF and plasma samples were obtained throughout the dosing interval in each patient. Concentrations of CAZ and AVI were determined by liquid chromatography/mass spectrometry.

Results

Bacterial identification revealed KPC-producing Klebsiella pneumoniae (KPC-Kp), DTR Pseudomonas aeruginosa, and KPC-producing Enterobacter cloacae (KPC-Ent.c). All isolates were resistant to carbapenems. The minimum inhibitory concentrations (MICs) of CAZ-AVI were 0.25/4, 4/4, and 0.25/4 μg/mL, respectively. CAZ and AVI concentrations were determined in CSF samples ranging from 29.0 to 15.0 µg/mL (CAZ component) and 4.20 to 0.92 µg/mL (AVI component), respectively. AVI achieved concentrations ≥1 µg/mL in 11 out of 12 CSF samples collected throughout the dosing interval. Clinical and microbiologic cure were attained in all patients.

Conclusions

Postinfusion concentrations of CAZ-AVI were measured in plasma and CSF samples obtained from 3 patients with complicated CNS infections caused by antimicrobial-resistant isolates. The measured concentrations revealed that standard CAZ and AVI exposures sufficiently attained values correlating to 50% fT > MIC, which are associated with efficient bacterial killing.

AcrAB-TolC, a major efflux pump in Gram negative bacteria: toward understanding its operation mechanism

Antibiotic resistance (AR) is a silent pandemic that kills millions worldwide. Although the development of new therapeutic agents against antibiotic resistance is in urgent demand, this has presented a great challenge, especially for Gram-negative bacteria that have inherent drug-resistance mediated by impermeable outer membranes and multidrug efflux pumps that actively extrude various drugs from the bacteria. For the last two decades, multidrug efflux pumps, including AcrAB-TolC, the most clinically important efflux pump in Gram-negative bacteria, have drawn great attention as strategic targets for re-sensitizing bacteria to the existing antibiotics. This article aims to provide a concise overview of the AcrAB-TolC operational mechanism, reviewing its architecture and substrate specificity, as well as the recent development of AcrAB-TolC inhibitors. [BMB Reports 2023; 56(6): 326-334].

AcrAB-TolC, a major efflux pump in Gram negative bacteria: toward understanding its operation mechanism

Antibiotic resistance (AR) is a silent pandemic that kills millions worldwide. Although the development of new therapeutic agents against antibiotic resistance is in urgent demand, this has presented a great challenge, especially for Gram-negative bacteria that have inherent drug-resistance mediated by impermeable outer membranes and multidrug efflux pumps that actively extrude various drugs from the bacteria. For the last two decades, multidrug efflux pumps, including AcrAB-TolC, the most clinically important efflux pump in Gram-negative bacteria, have drawn great attention as strategic targets for re-sensitizing bacteria to the existing antibiotics. This article aims to provide a concise overview of the AcrAB-TolC operational mechanism, reviewing its architecture and substrate specificity, as well as the recent development of AcrAB-TolC inhibitors. [BMB Reports 2023; 56(6): 326-334].

A novel method to evaluate ceftazidime/avibactam therapy in patients with carbapenemase-producing Enterobactericeae (CPE) bloodstream infections

INTRODUCTION

This study reports experience managing eight patients with bloodstream infections treated with a continuous infusion of ceftazidime-avibactam.

METHODS

Patients who were treated for documented CPE BSIs susceptible to CAZ-AVI and who underwent real-time therapeutic drug monitoring were retrospectively assessed. Ceftazidime MICs were assessed in presence of increasing concentrations of avibactam by the broth microdilution method. An inhibitory sigmoid Emax model was used to characterize ceftazidime MIC reduction as a function of avibactam concentration, and the MICi was derived by conditioning the best-fit model using steady-state avibactam concentrations (Css). Ceftazidime fCss/MICi ratio was calculated for each patient and correlated to microbiological outcome.

RESULTS

By adopting the innovative concept of effective MIC with an inhibitor (MICi), a trend towards higher microbiological failure and resistance development was found in patients with a lower ceftazidime fCss/MICi ratio (2/3 vs. 0/5).

CONCLUSION

Assessment of changes in the ceftazidime MIC in relation to increasing avibactam concentration could represent a more robust pharmacokinetic/pharmacodynamic method for predicting microbiological failure given beta-lactam/beta-lactamase inhibitor combinations.

Activity of Oral Tebipenem-Avibactam in a Mouse Model of Mycobacterium abscessus Lung Infection

The combination of the β-lactam tebipenem and the β-lactamase inhibitor avibactam shows potent bactericidal activity against Mycobacterium abscessus in vitro. Here, we report that the combination of the respective oral prodrugs tebipenem-pivoxil and avibactam ARX-1796 showed efficacy in a mouse model of M. abscessus lung infection. The results suggest that tebipenem-avibactam presents an attractive oral drug candidate pair for the treatment of M. abscessus pulmonary disease and could inform the design of clinical trials.

Development of an optimized and practical pharmacokinetics/pharmacodynamics analysis method for aztreonam/nacubactam against carbapenemase-producing K. pneumoniae

BACKGROUND

Nacubactam, a new β-lactamase inhibitor with antibacterial activity, is being developed as a single drug to be co-administered with cefepime or aztreonam. However, determining pharmacokinetics/pharmacodynamics (PK/PD) parameters in β-lactam/β-lactamase inhibitor combinations remains challenging. We aimed to establish a practical PK/PD analysis method for aztreonam/nacubactam that incorporates instantaneous MIC (MICi).

METHODS

Based on chequerboard MIC measurements, MICi of aztreonam against carbapenemase-producing Klebsiella pneumoniae in the presence of nacubactam was simulated.

RESULTS

The mean change in the bacterial count of thigh-infected mice in an in vivo PD study was plotted based on %fT>MICi and analysed using the inhibitory effect sigmoid Imax model. fT>MICi calculated from the PK experiments showed a high correlation with the in vivo bactericidal effect, suggesting that fT>MICi is the optimal PK/PD parameter for aztreonam/nacubactam. The target values of fT>MICi achieving growth inhibition, 1 log10 kill and 2 log10 kill, were 22, 38% and 75%, respectively.

CONCLUSIONS

The PK/PD analysis method proposed in this study is promising for determining practical PK/PD parameters in combination therapy. In addition, this is the first report of aztreonam/nacubactam showing a potent in vivo therapeutic effect against NDM-producing K. pneumoniae.

Evaluation of Piperacillin/Sulbactam, Piperacillin/Tazobactam and Cefoperazone/Sulbactam Dosages in Gram-Negative Bacterial Bloodstream Infections by Monte Carlo Simulation

The optimal regimens of piperacillin/sulbactam (PIS 2:1), piperacillin/tazobactam (PTZ 8:1), and cefoperazone/sulbactam (CSL 2:1) are not well defined in patients based on renal function. This study was conducted to identify optimal regimens of BLBLIs in these patients. The antimicrobial sensitivity test was performed by a two-fold agar dilution method. Monte Carlo simulation (MCS) was used to simulate the probability of target attainment (PTA) and the cumulative fraction of response (CFR) for various dosing regimens in patients with different renal functions. For strains with an MIC ≤ 8/4 mg/L, PIS 4.5 g q6h achieved 99.03%PTA in the subset of patients with creatinine clearance (CrCL) > 90 mL/min. For patients with CrCL 60-90 mL/min, PIS 4.5 g q6h achieved 81.2% CFR; for those with CrCL 40-59 mL/min, PIS 4.5 g q8h achieved 80.25% CFR. However, for patients infected by ESBL-producing Enterobacteriaceae, PIS 4.5 g q6h achieved a CFR lower than 80%. For patients infected by A. baumannii with a CrCL of 31-60 mL/min, PIS 6.0 g q8h and 4.5 g q6h achieved 81.24% and 82.42% CFR, respectively. For those infected by P. aeruginosa, PIS 4.5 g q6h reached 90% CFR. PIS and PTZ achieved a similar CFR when piperacillin was at the same dose. The CFRs of CSL were much lower than those of the other two agents in Enterobacteriaceae and P. aeruginosa infections. The antibacterial spectrum of PIS is superior to that of PTZ and CSL. Higher dosages and dosing adjustment according to renal function should be considered to treat Gram-negative bacterial BSIs.

Jumping into the future: overcoming pharmacokinetic/pharmacodynamic hurdles to optimize the treatment of severe difficult to treat-Gram-negative infections with novel beta-lactams

INTRODUCTION

The choice of best therapeutic strategy for difficult-to-treat resistance (DTR) Gram-negative infections currently represents an unmet clinical need.

AREAS COVERED

This review provides a critical reappraisal of real-world evidence supporting the role of pharmacokinetic/pharmacodynamic (PK/PD) optimization of novel beta-lactams in the management of DTR Gram-negative infections. The aim was to focus on prolonged and/or continuous infusion administration, penetration rates into deep-seated infections, and maximization of PK/PD targets in special renal patient populations. Retrieved findings were applied to the three most critical clinical scenarios of Gram-negative resistance phenotypes (i.e. carbapenem-resistant Enterobacterales; difficult-to-treat resistant Pseudomonas aeruginosa, and carbapenem-resistant Acinetobacter baumannii).

EXPERT OPINION

Several studies supported the role of PK/PD optimization of beta-lactams in the management of DTR Gram-negative infections for both maximizing clinical efficacy and preventing resistance emergence. Optimizing antimicrobial therapy with novel beta-lactams based on the so called 'antimicrobial therapy puzzle' PK/PD concepts may represent a definitive jump into the future toward a personalized patient management of DTR Gram negative infections. Establishing a dedicated and coordinated multidisciplinary team and implementing a real-time TDM-guided personalized antimicrobial exposure optimization of novel beta-lactams based on expert clinical pharmacological interpretation, could represent crucial cornerstones for the proper management of DTR Gram-negative infections.

Ceftazidime-Avibactam Treatment for Severe Post-Neurosurgical Meningitis and Abscess Caused by Extended-Spectrum β-Lactamase Escherichia coli in a Pediatric Patient: A Case Report

Post-neurosurgical infections caused by multidrug-resistant Enterobacterales are difficult to treat due to limited therapeutic options. Ceftazidime-avibactam (CAZ-AVI), a combination of cephalosporin and a novel β-lactamase inhibitor, has exhibited potential activity against multi/extensive drug-resistant (MDR/XDR) gram-negative bacilli. Several reports have described the successful treatment of central infections caused by MDR/XDR Pseudomonas aeruginosa or Enterobacterales. However, data on the efficacy and effective drug distribution of CAZ-AVI in the central nervous system (CNS), particularly in children, are lacking. We report a case of a 4-year-old girl with post-neurosurgical meningitis and abscess caused by extended-spectrum β-lactamase-producing Escherichia coli successfully treated with CAZ-AVI. CAZ-AVI therapeutic drug monitoring was performed to evaluate its efficacy and effective drug distribution in the CNS. We measured CAZ (15.6, 7.1, and 3.5 μg/mL) and AVI (4.0, 2.1, and 1.2 μg/mL) in cerebrospinal fluid (CSF) samples obtained 3, 5, and 7 h after the administration of the 15th CAZ-AVI dose (2.5 g, q8h, iv), respectively. We also measured CAZ (57.0 and 25.8 μg/mL) and AVI (11.3 and 4.5 μg/mL) in serum samples obtained 3 and 5 h after the administration, respectively. CAZ-AVI achieved an adequate CSF concentration throughout the drug interval. Our case provides evidence for using CAZ-AVI to treat CNS infections.

A descriptive pharmacokinetic/pharmacodynamic analysis of continuous infusion ceftazidime-avibactam in a case series of critically ill renal patients treated for documented carbapenem-resistant Gram-negative bloodstream infections and/or ventilator-associated pneumonia

OBJECTIVES

To describe the pharmacokinetic/pharmacodynamic (PK/PD) behaviour of continuous infusion (CI) ceftazidime-avibactam and the microbiological outcome in a case series of critically ill renal patients treated for documented carbapenem-resistant Gram-negative (CR-GN) bloodstream infections (BSI) and/or ventilator-associated pneumonia (VAP).

METHODS

Critically ill patients with different degrees of renal function who were treated with CI ceftazidime-avibactam for documented CR-GN infections, and who underwent therapeutic drug monitoring from April 2021 to March 2022, were retrospectively assessed. Ceftazidime and avibactam concentrations were determined at steady-state, and the free fraction (fC_ss) was calculated. The joint PK/PD target of ceftazidime-avibactam was considered as optimal when both C_ss/MIC ratio for ceftazidime ≥4 (equivalent to 100%fT>_4xMIC) and C_ss/C_T ratio for avibactam >1 (equivalent to 100% fT>C_T of 4.0 mg/L) were simultaneously achieved (quasi-optimal if only one of the two was achieved, and suboptimal if neither of the two was achieved). The relationship between ceftazidime-avibactam PK/PD targets and microbiological outcome was assessed.

RESULTS

Ten patients with documented CR-GN infections (5 BSIs, 4 VAP, 1 BSI+VAP) were retrieved. The joint PK/PD targets of ceftazidime-avibactam were optimal and quasi-optimal in eight and two cases, respectively. Microbiological failure occurred in two patients (one with VAP, one with BSI+VAP), one of whom developed ceftazidime-avibactam resistance. Both underwent renal replacement therapy, and failed despite attaining optimal joint PK/PD target and receiving fosfomycin co-treatment.

CONCLUSION

CI administration may enable optimal joint PK/PD targets of ceftazidime-avibactam to be achieved in most critical renal patients with CR-GN infections, and may help to minimize the risk of microbiological failure.

Shedding Light on Amoxicillin, Amoxicillin-clavulanate, and Cephalexin Dosing in Children from a Pharmacist's Perspective

Selection of an antibiotic and dosing regimen requires consideration of multiple factors including microbiological data, site of infection, pharmacokinetics, and how it relates to the pharmacodynamic target. Given the multiple dosage regimens of amoxicillin with/without clavulanate and cephalexin, we review the principles of dose selection from a pharmacist's perspective.

Pharmacokinetics, Pharmacodynamics, and Dosing Considerations of Novel β-Lactams and β-Lactam/β-Lactamase Inhibitors in Critically Ill Adult Patients: Focus on Obesity, Augmented Renal Clearance, Renal Replacement Therapies, and Extracorporeal Membrane Oxygenation

OBJECTIVE

Dose optimization of novel β-lactam antibiotics (NBLA) has become necessary given the increased prevalence of multidrug-resistant infections in intensive care units coupled with the limited number of available treatment options. Unfortunately, recommended dose regimens of NBLA based on PK/PD indices are not well-defined for critically ill patients presenting with special situations (i.e., obesity, extracorporeal membrane oxygenation (ECMO), augmented renal clearance (ARC), and renal replacement therapies (RRT)). This review aimed to discuss and summarize the available literature on the PK/PD attained indices of NBLA among critically ill patients with special circumstances.

DATA SOURCES

PubMed, MEDLINE, Scopus, Google Scholar, and Embase databases were searched for studies published between January 2011 and May 2022.

STUDY SELECTION AND DATA EXTRACTION

Articles relevant to NBLA (i.e., ceftolozane/tazobactam, ceftazidime/avibactam, cefiderocol, ceftobiprole, imipenem/relebactam, and meropenem/vaborbactam) were selected. The MeSH terms of "obesity", "augmented renal clearance", "renal replacement therapy", "extracorporeal membrane oxygenation", "pharmacokinetic", "pharmacodynamic" "critically ill", and "intensive care" were used for identification of articles. The search was limited to adult humans' studies that were published in English. A narrative synthesis of included studies was then conducted accordingly.

DATA SYNTHESIS

Available evidence surrounding the use of NBLA among critically ill patients presenting with special situations was limited by the small sample size of the included studies coupled with high heterogeneity. The PK/PD target attainments of NBLA were reported to be minimally affected by obesity and/or ECMO, whereas the effect of renal functionality (in the form of either ARC or RRT) was more substantial.

CONCLUSION

Critically ill patients presenting with special circumstances might be at risk of altered NBLA pharmacokinetics, particularly in the settings of ARC and RRT. More robust, well-designed trials are still required to define effective dose regimens able to attain therapeutic PK/PD indices of NBLA when utilized in those special scenarios, and thus aid in improving the patients' outcomes.

A Post-Neurosurgical Infection due to KPC-Producing Klebsiella pneumoniae Treated with Meropenem-Vaborbactam: A Case Report

This case report describes a patient with a KPC-producing K. pneumoniae post-neurosurgical infection with bacteremia. There is limited evidence to guide antibiotic treatment decisions for such infections. The patient was treated with meropenem-vaborbactam. Meropenem-vaborbactam monotherapy was associated with bacteremia clearance.

Trends of Fixed-Dose Combination Antibiotic Consumption in Hospitals in China: Analysis of Data from the Center for Antibacterial Surveillance, 2013-2019

Background: Fixed-dose combination (FDC) antibiotics can be clinically inappropriate and are concerning with regards to antimicrobial resistance, with little usage data available in low- and middle-income countries. Methods: Based on retrospective data from the Center for Antibacterial Surveillance, we investigated the consumption of FDC antibiotics in hospital inpatient settings in China from 1 January 2013 to 31 December 2019. The metric for assessing antibiotic consumption was the number of daily defined doses per 100 bed days (DDD/100BDs). FDC antibiotics were classified according to their composition and the Access, Watch, Reserve (AWaRe) classification of the World Health Organization. Results: A total of 24 FDC antibiotics were identified, the consumption of which increased sharply from 8.5 DDD/100BDs in 2013 to 10.2 DDD/100BDs in 2019 (p < 0.05) despite the reduction in the total antibiotic consumption in these hospitals. The increase was mainly driven by FDC antibiotics in the Not Recommended group of the AWaRe classification, whose consumption accounted for 63.0% (6.4 DDD/100BDs) of the overall FDC antibiotic consumption in 2019, while the consumption of FDC antibiotics in the Access group only accounted for 13.5% (1.4 DDD/100BDs). Conclusion: FDC antibiotic consumption significantly increased during the study period and accounted for a substantial proportion of all systemic antibiotic usage in hospitals in China. FDC antibiotics in the Not Recommended group were most frequently consumed, which raises concerns about the appropriateness of FDC antibiotic use.

New Perspectives on Antimicrobial Agents: Imipenem-Relebactam

Imipenem (IMI)/cilastatin/relebactam (REL) (I/R) is a novel β-lactam/β-lactamase inhibitor combination with expanded microbiologic activity against carbapenem-resistant non-Morganellaceae Enterobacterales (CR-NME) and difficult-to-treat (DTR) Pseudomonas aeruginosa. Relebactam, a bicyclic diazabicyclooctane, has no direct antimicrobial activity but provides reliable inhibition of many Ambler class A and class C enzymes. It is currently approved for the treatment of adult patients with hospital-acquired bacterial pneumonia and ventilator-associated bacterial pneumonia (HABP/VABP) and those with complicated urinary tract infections (cUTIs) and complicated intra-abdominal infections (cIAIs) when limited or no alternative treatments are available. Given the number of recently approved β-lactams with expanded activity against highly resistant Gram-negative pathogens, this review summarizes the published literature on I/R, with a focus on its similar and distinguishing characteristics relative to those of other recently approved agents. Overall, available data support its use for the treatment of patients with HABP/VABP, cUTI, and cIAI due to CR-NME and DTR P. aeruginosa. Data indicate that I/R retains some activity against CR-NME and DTR P. aeruginosa isolates that are resistant to the newer β-lactams and vice versa, suggesting that susceptibility testing be performed for all the newer agents to determine optimal treatment options for patients with CR-NME and DTR P. aeruginosa infections. Further comparative PK/PD and clinical studies are warranted to determine the optimal role of I/R, alone and in combination, for the treatment of patients with highly resistant Gram-negative infections. Until further data are available, I/R is a potential treatment for patients with CR-NME and DTR P. aeruginosa infections when the benefits outweigh the risks.

The primary pharmacology of ceftazidime/avibactam: in vitro translational biology

Previous reviews of ceftazidime/avibactam have focused on in vitro molecular enzymology and microbiology or the clinically associated properties of the combination. Here we take a different approach. We initiate a series of linked reviews that analyse research on the combination that built the primary pharmacology data required to support the clinical and business risk decisions to perform randomized controlled Phase 3 clinical trials, and the additional microbiological research that was added to the above, and the safety and chemical manufacturing and controls data, that constituted successful regulatory licensing applications for ceftazidime/avibactam in multiple countries, including the USA and the EU. The aim of the series is to provide both a source of reference for clinicians and microbiologists to be able to use ceftazidime/avibactam to its best advantage for patients, but also a case study of bringing a novel β-lactamase inhibitor (in combination with an established β-lactam) through the microbiological aspects of clinical development and regulatory applications, updated finally with a review of resistance occurring in patients under treatment. This first article reviews the biochemistry, structural biology and basic microbiology of the combination, showing that avibactam inhibits the great majority of serine-dependent β-lactamases in Enterobacterales and Pseudomonas aeruginosa to restore the in vitro antibacterial activity of ceftazidime. Translation to efficacy against infections in vivo is reviewed in the second co-published article, Nichols et al. (J Antimicrob Chemother 2022; dkac172).

Assessment of rationality of available fixed dose combinations of antibiotics in India

OBJECTIVE

India is among the largest consumers of antibiotics. Easy availability and growing sales of Fixed Dose Combinations (FDCs) of antibiotics can worsen Antimicrobial Resistance (AMR). There is lack of comprehensive data on available antibiotic FDC formulations, their dose strengths and adequacy of scientific evidence regarding their efficacy, safety and suitability for human use. In the present work, we aimed at addressing this knowledge gap.

METHODS

Availability of FDCs was ascertained from the Current Index of Medical Specialties (CIMS) [Issue Jan-April 2020]. Customized data abstraction form was used to capture pertinent information for these FDCs. Assessment of rationality was done based on standard parameters.

RESULTS

More than 90% of the existing FDCs were found to be irrational; with two third of them being unapproved and or banned from use in the country.

CONCLUSIONS

Although the regulatory agency has already taken cognizance of the seriousness of the matter; there is an urgent need to revisit these FDCs to promote prudent antibiotic use.

EXPERT OPINION

High antibiotic use is associated with antimicrobial resistance; it is imperative that all factors which lead to high antibiotic use are adequately addressed. Easy availability of fixed dose combinations (FDCs) has begun to catch the attention of regulators in developing economies like India leading to a ban of 330 FDCs of which 19% were antibiotic combinations. The continuing presence and increasing sales of these irrational FDCs is a concern for effective antimicrobial stewardship.

The role of tazobactam-based combinations for the management of infections due to extended-spectrum β-lactamase-producing Enterobacterales: Insights from the Society of Infectious Diseases Pharmacists

Extended-spectrum β-lactamase (ESBL)-producing Enterobacterales are a global threat to public health due to their antimicrobial resistance profile and, consequently, their limited available treatment options. Tazobactam is a sulfone β-lactamase inhibitor with in vitro inhibitory activity against common ESBLs in Enterobacterales, including CTX-M. However, the role of tazobactam-based combinations in treating infections caused by ESBL-producing Enterobacterales remains unclear. In the United States, two tazobactam-based combinations are available, piperacillin-tazobactam and ceftolozane-tazobactam. We evaluated and compared the roles of tazobactam-based combinations against ESBL-producing organisms with emphasis on pharmacokinetic/pharmacodynamic exposures in relation to MIC distributions and established breakpoints, clinical outcomes data specific to infection site, and considerations for downstream effects with these agents regarding antimicrobial resistance development. While limited data with ceftolozane-tazobactam are encouraging for its potential role in infections due to ESBL-producing Enterobacterales, further evidence is needed to determine its place in therapy. Conversely, currently available microbiologic, pharmacokinetic, pharmacodynamic, and clinical data do not suggest a role for piperacillin-tazobactam, and we caution clinicians against its usage for these infections.

Population Pharmacokinetics of Piperacillin and Tazobactam in Critically Ill Patients Receiving Extracorporeal Membrane Oxygenation: an ASAP ECMO Study

Our study aimed to describe the population pharmacokinetics (PK) of piperacillin and tazobactam in patients on extracorporeal membrane oxygenation (ECMO), with and without renal replacement therapy (RRT). We also aimed to use dosing simulations to identify the optimal dosing strategy for these patient groups. Serial piperacillin and tazobactam plasma concentrations were measured with data analyzed using a population PK approach that included staged testing of patient and treatment covariates. Dosing simulations were conducted to identify the optimal dosing strategy that achieved piperacillin target exposures of 50% and 100% fraction of time free drug concentration is above MIC (%fT_>MIC) and toxic exposures of greater than 360 mg/liter. The tazobactam target of percentage of time free concentrations of >2 mg/liter was also assessed. Twenty-seven patients were enrolled, of which 14 patients were receiving concurrent RRT. Piperacillin and tazobactam were both adequately described by two-compartment models, with body mass index, creatinine clearance, and RRT as significant predictors of PK. There were no substantial differences between observed PK parameters and published parameters from non-ECMO patients. Based on dosing simulations, a 4.5-g every 6 hours regimen administered over 4 hours achieves high probabilities of efficacy at a piperacillin MIC of 16 mg/liter while exposing patients to a <3% probability of toxic concentrations. In patients receiving ECMO and RRT, a frequency reduction to every 12 hours dosing lowers the probability of toxic concentrations, although this remains at 7 to 9%. In ECMO patients, piperacillin and tazobactam should be dosed in line with standard recommendations for the critically ill.

Clinical Pharmacokinetics and Pharmacodynamics of Imipenem-Cilastatin/Relebactam Combination Therapy

On 16 July, 2019, the US Food and Drug Administration approved imipenem-cilastatin/relebactam (Recarbrio™) for the treatment of adults with complicated urinary tract infections and complicated intra-abdominal infections. This decision was based on substantial clinical and pre-clinical data, including rigorous pharmacokinetic and pharmacodynamic work, and is an important step forward in the management of these debilitating conditions. This article provides an overview of the body of research associated with imipenem-cilastatin/relebactam, beginning with an examination of the fundamental underpinnings of the pharmacokinetic/pharmacodynamic index. This is followed by the pharmacokinetic/pharmacodynamic work that led to the approval of this novel drug combination, including data derived from checkerboard and hollow fiber infection studies, as well as large, multi-center, phase III clinical trials known as RESTORE-IMI 1 and RESTORE-IMI 2. The article also explores how this important new antibiotic may be used to treat other infections in the years to come, including hospital-acquired bacterial pneumonia and ventilator-associated pneumonia attributed to imipenem-non-susceptible pathogens and certain atypical mycobacterial infections.

Old and New Beta-Lactamase Inhibitors: Molecular Structure, Mechanism of Action, and Clinical Use

The β-lactams have a central place in the antibacterial armamentarium, but the increasing resistance to these drugs, especially among Gram-negative bacteria, is becoming one of the major threats to public health worldwide. Treatment options are limited, and only a small number of novel antibiotics are in development. However, one of the responses to this threat is the combination of β-lactam antibiotics with β-lactamase inhibitors, which are successfully used in the clinic for overcoming resistance by inhibiting β-lactamases. The existing inhibitors inactivate most of class A and C serine β-lactamases, but several of class D and B (metallo-β-lactamase) are resistant. The present review provides the status and knowledge concerning current β-lactamase inhibitors and an update on research efforts to identify and develop new and more efficient β-lactamase inhibitors.

Pharmacokinetics of Non-β-Lactam β-Lactamase Inhibitors

The growing emergence of drug-resistant bacterial strains is an issue to treat severe infections, and many efforts have identified new pharmacological agents. The inhibitors of β-lactamases (BLI) have gained a prominent role in the safeguard of beta-lactams. In the last years, new β-lactam-BLI combinations have been registered or are still under clinical evaluation, demonstrating their effectiveness to treat complicated infections. It is also noteworthy that the pharmacokinetics of BLIs partly matches that of β-lactams companions, meaning that some clinical situations, as well as renal impairment and renal replacement therapies, may alter the disposition of both drugs. Common pharmacokinetic characteristics, linear pharmacokinetics across a wide range of doses, and known pharmacokinetic/pharmacodynamic parameters may guide modifications of dosing regimens for both β-lactams and BLIs. However, comorbidities (i.e., burns, diabetes, cancer) and severe changes in individual pathological conditions (i.e., acute renal impairment, sepsis) could make dose adaptation difficult, because the impact of those factors on BLI pharmacokinetics is partly known. Therapeutic drug monitoring protocols may overcome those issues and offer strategies to personalize drug doses in the intensive care setting. Further prospective clinical trials are warranted to improve the use of BLIs and their β-lactam companions in severe and complicated infections.

Current evidence for therapy of ceftriaxone-resistant Gram-negative bacteremia

PURPOSE OF REVIEW

This article aims to give a state-of-the-art assessment of treatment options for bloodstream infection because of ceftriaxone-resistant Gram-negative bacilli, especially those caused by extended-spectrum beta-lactamase (ESBL) or AmpC-producing Enterobacteriaceae. In particular, this review assesses whether current data support 'carbapenem-sparing options' for treatment of these serious infections.

RECENT FINDINGS

The MERINO trial refuted earlier observational studies some of which showed equivalence in outcomes between beta-lactam/beta-lactamase inhibitor combinations and carbapenems for treatment of bloodstream infection because of ceftriaxone-resistant Escherichia coli or Klebsiella spp. Although numerous factors influence mortality following bloodstream infection, the variability in piperacillin/tazobactam MICs observed in the MERINO trial make this a less secure option than meropenem. However, the search for carbapenem-sparing options continues with four randomized controlled trials (RCTs) in progress and a number of other options in clinical development.

SUMMARY

Hard outcomes from RCTs are still needed before intravenous carbapenems can be displaced as the treatment of choice for ceftriaxone-resistant Gram-negative bacilli.

Mono vs. combo regimens with novel beta-lactam/beta-lactamase inhibitor combinations for the treatment of infections due to carbapenemase-producing Enterobacterales: insights from the literature

Ceftazidime-avibactam (CZA), meropenem-vaborbactam (MVB) and imipenem-relebactam (I-R) are combinations of old ß-lactams with novel non-ß-lactam ß-lactamase inhibitors (BLBLIs) able to inhibit some carbapenemases, such as the KPC-type, thus are becoming the standard for difficult-to-treat carbapenemase-producing Enterobacterales (CPE); a practical question is whether these novel BLBLIs should be used as monotherapy or as part of a combination regimen with other antibiotics, and if so, with which ones, to reduce the emergence of resistant strains and to optimize their efficacy. In this short review, we assessed clinical outcomes in patients with CPE-infections treated with the novel BLBLIs as mono- or combo-regimens, and laboratory studies on the synergistic effects with other antimicrobials. Available evidence on combination therapy is scarce and mainly limited to retrospective studies involving 630 patients treated with CZA: aminoglycosides were used in 39.6% of 336 patients treated with combo-regimens, followed by polymyxin B/colistin (24.4%), tigecycline (24.1%), carbapenems (13.4%) and fosfomycin (5.4%). Aminoglycosides could be useful in case of bloodstream and severe urinary infections. Pneumonia is a risk factor for CZA-resistance emergence: fosfomycin, due to favorable lung pharmacokinetics/pharmacodynamics, could represent an interesting partner; fosfomycin could be added also for osteomyelitis. Tigecycline could be preferred for intrabdominal and skin-soft tissue infections. Due to nephrotoxicity and lack of in vitro synergy, the association CZA/colistin seems not optimal. MVB and I-R were mostly used as monotherapies. Currently, there is no definitive evidence whether combinations are more effective than monotherapies; further studies are warranted, and to date only personal opinions can be provided.

Clinical and Microbiologic Efficacy and Safety of Imipenem/Cilastatin/Relebactam in Complicated Infections: A Meta-analysis

BACKGROUND

Antimicrobial resistance is on the rise. The use of redundant and inappropriate antibiotics is contributing to recurrent infections and resistance. Newer antibiotics with more robust coverage for Gram-negative bacteria are in great demand for complicated urinary tract infections (cUTIs), complicated intra-abdominal infections (cIAIs), hospital-acquired bacterial pneumonia (HABP), and ventilator-associated bacterial pneumonia (VABP).

MATERIALS AND METHODS

We performed this meta-analysis to evaluate the efficacy and safety profile of a new antibiotic, Imipenem/cilastatin/relebactam, compared to other broad-spectrum antibiotics for complicated infections. We conducted a systemic review search on PubMed, Embase, and Central Cochrane Registry. We included randomized clinical trials-with the standard of care as comparator arm with Imipenem/cilastatin/relebactam as intervention arm. For continuous variables, the mean difference was used. For discrete variables, we used the odds ratio. For effect sizes, we used a confidence interval of 95%. A P-value of less than 0.05 was used for statistical significance. Analysis was done using a random-effects model irrespective of heterogeneity. Heterogeneity was evaluated using the I² statistic.

RESULTS

The authors observed similar efficacy at clinical and microbiologic response levels on early follow-up and late follow-up compared to the established standard of care. The incidence of drug-related adverse events, serious adverse events, and drug discontinuation due to adverse events were comparable across both groups.

CONCLUSION

Imipenem/cilastatin/relebactam has a non-inferior safety and efficacy profile compared to peer antibiotics to treat severe bacterial infections (cUTIs, cIAIs, HABP, VABP).

A new pharmacodynamic approach to study antibiotic combinations against enterococci in vivo: Application to ampicillin plus ceftriaxone

The combination of ampicillin (AMP) and ceftriaxone (CRO) is considered synergistic against Enterococcus faecalis based on in vitro tests and the rabbit endocarditis model, however, in vitro assays are limited by the use of fixed antibiotic concentrations and the rabbit model by poor bacterial growth, high variability, and the use of point dose-effect estimations, that may lead to inaccurate assessment of antibiotic combinations and hinder optimal translation. Here, we tested AMP+CRO against two strains of E. faecalis and one of E. faecium in an optimized mouse thigh infection model that yields high bacterial growth and allows to define the complete dose-response relationship. By fitting Hill’s sigmoid model and estimating the parameters maximal effect (E_max) and effective dose 50 (ED₅₀), the following interactions were defined: synergism (E_max increase ≥2 log₁₀ CFU/g), antagonism (E_max reduction ≥1 log₁₀ CFU/g) and potentiation (ED₅₀ reduction ≥50% without changes in E_max). AMP monotherapy was effective against the three strains, yielding valid dose-response curves in terms of dose and the index fT_>MIC. CRO monotherapy showed no effect. The combination AMP+CRO against E. faecalis led to potentiation (59–81% ED₅₀ reduction) and not synergism (no changes in E_max). Against E. faecium, the combination was indifferent. The optimized mouse infection model allowed to obtain the complete dose-response curve of AMP+CRO and to define its interaction based on pharmacodynamic parameter changes. Integrating these results with the pharmacokinetics will allow to derive the PK/PD index bound to the activity of the combination, essential for proper translation to the clinic.

A Clinical Review and Critical Evaluation of Imipenem-Relebactam: Evidence to Date

Imipenem-relebactam (I-R) is a novel beta-lactam/beta-lactamase inhibitor combination given with cilastatin. It is indicated for the treatment of complicated urinary tract infections, complicated intra-abdominal infections, and hospital-acquired or ventilator-associated bacterial pneumonia. A literature search was completed to evaluate the evidence to date of I-R. I-R has in vitro activity against multidrug-resistant organisms including carbapenem-resistant Pseudomonas aeruginosa and extended-spectrum beta-lactamase and carbapenem-resistant Enterobacterales. It was granted FDA approval following the promising results of two phase II clinical trials in patients with complicated urinary tract infections and complicated intra-abdominal infections. The most common adverse drug events associated with I-R were nausea (6%), diarrhea (6%), and headache (4%). I-R is a new beta-lactam/beta-lactamase inhibitor combination that will be most likely used for patients with multidrug-resistant gram-negative infections in which there are limited or no available alternative treatment options.

Association between minimum inhibitory concentration, beta-lactamase genes and mortality for patients treated with piperacillin/tazobactam or meropenem from the MERINO study

INTRODUCTION

This study aims to assess the association of piperacillin/tazobactam and meropenem minimum inhibitory concentration (MIC) and beta-lactam resistance genes with mortality in the MERINO trial.

METHODS

Blood culture isolates from enrolled patients were tested by broth microdilution and whole genome sequencing at a central laboratory. Multivariate logistic regression was performed to account for confounders. Absolute risk increase for 30-day mortality between treatment groups was calculated for the primary analysis (PA) and the microbiologic assessable (MA) populations.

RESULTS

320 isolates from 379 enrolled patients were available with susceptibility to piperacillin/tazobactam 94% and meropenem 100%. The piperacillin/tazobactam non-susceptible breakpoint (MIC > 16 mg/L) best predicted 30-day mortality after accounting for confounders (odds ratio 14.9, 95% CI 2.8 - 87.2). The absolute risk increase for 30-day mortality for patients treated with piperacillin/tazobactam compared with meropenem was 9% (95% CI 3% - 15%) and 8% (95% CI 2% - 15%) for the original PA population and the post-hoc MA populations, which reduced to 5% (95% CI -1% - 10%) after excluding strains with piperacillin/tazobactam MIC values > 16 mg/L. Isolates co-harboring ESBL and OXA-1 genes were associated with elevated piperacillin/tazobactam MICs and the highest risk increase in 30-mortality of 14% (95% CI 2% - 28%).

CONCLUSION

After excluding non-susceptible strains, the 30-day mortality difference was from the MERINO trial was less pronounced for piperacillin/tazobactam. Poor reliability in susceptibility testing performance for piperacillin/tazobactam and the high prevalence of OXA co-harboring ESBLs suggests meropenem remains the preferred choice for definitive treatment of ceftriaxone non-susceptible E. coli and Klebsiella.

Using Therapeutic Drug Monitoring to Treat KPC-Producing Klebsiella pneumoniae Central Nervous System Infection With Ceftazidime/Avibactam

This report describes the treatment of Klebsiella pneumoniae carbapenemase (KPC)–3–producing multidrug-resistant K. pneumoniae with ceftazidime/avibactam (CAZ-AVI) in a patient who developed postneurosurgical meningitis and bacteremia. Therapeutic drug monitoring of cerebrospinal fluid and blood samples demonstrated CAZ-AVI concentration levels 20-fold greater than the minimum inhibitory concentration in the first 60 minutes postinfusion, providing evidence for the utility of CAZ-AVI in treating KPC–Klebsiella pneumoniae central nervous system infections.

Pharmacokinetics-Pharmacodynamics of Enmetazobactam Combined with Cefepime in a Neutropenic Murine Thigh Infection Model

Third-generation cephalosporin (3GC)-resistant Enterobacteriaceae are classified as critical priority pathogens, with extended-spectrum β-lactamases (ESBLs) as principal resistance determinants. Enmetazobactam (formerly AAI101) is a novel ESBL inhibitor developed in combination with cefepime for empirical treatment of serious Gram-negative infections in settings where ESBLs are prevalent. Cefepime-enmetazobactam has been investigated in a phase 3 trial in patients with complicated urinary tract infections or acute pyelonephritis. This study examined pharmacokinetic-pharmacodynamic (PK-PD) relationships of enmetazobactam, in combination with cefepime, for ESBL-producing isolates of Klebsiella pneumoniae in 26-h murine neutropenic thigh infection models. Enmetazobactam dose fractionation identified the time above a free threshold concentration (fT > C_T ) as the PK-PD index predictive of efficacy. Nine ESBL-producing isolates of K. pneumoniae, resistant to cefepime and piperacillin-tazobactam, were included in enmetazobactam dose-ranging studies. The isolates encoded CTX-M-type, SHV-12, DHA-1, and OXA-48 β-lactamases and covered a cefepime-enmetazobactam MIC range from 0.06 to 2 μg/ml. Enmetazobactam restored the efficacy of cefepime against all isolates tested. Sigmoid curve fitting across the combined set of isolates identified enmetazobactam PK-PD targets for stasis and for a 1-log₁₀ bioburden reduction of 8% and 44% fT > 2 μg/ml, respectively, with a concomitant cefepime PK-PD target of 40 to 60% fT > cefepime-enmetazobactam MIC. These findings support clinical dose selection and breakpoint setting for cefepime-enmetazobactam.