Selecting the dosage of ceftazidime-avibactam in the perfect storm of nosocomial pneumonia

Ceftazidime-avibactam plus aztreonam cocktail for the treatment of VIM-producing Pseudomonas aeruginosa infections: good enough to have another?

BACKGROUND

Few active antibiotic options are available to treat MBL-producing Pseudomonas aeruginosa infections, and some of these options are either poorly tolerated or have pharmacokinetic limitations. The use of aztreonam monotherapy for treating MBL-producing P. aeruginosa remains controversial due to the risk of selecting resistant mutants during treatment.

OBJECTIVES

To describe the clinical outcomes of patients treated with ceftazidime-avibactam plus aztreonam for VIM-producing P. aeruginosa infections. The assessed outcomes include clinical success, clinical cure, all-cause mortality at day 28, combination therapy-associated adverse events, infection relapse and microbiological recurrence.

METHODS

This retrospective observational single-centre study was conducted at Clínica Universidad de Navarra, Pamplona, Spain. Eight patients with VIM-producing P. aeruginosa infections were included. Whole-genome sequencing of isolates was performed at Hospital Universitario Son Espases, Palma, Spain.

RESULTS

All isolates were susceptible to aztreonam and aztreonam-avibactam. No resistance mechanisms against these antibiotics were identified through whole-genome sequencing, except in one isolate that overexpressed the MexAB-OprM efflux pump. Clinical success and clinical cure were achieved in seven of eight patients, while all-cause mortality at day 28 was two of eight. Clinical cure was documented for five different infections and three distinct P. aeruginosa clones. No adverse events related to antibiotic therapy were reported, and no infection relapses occurred after treatment. Microbiological recurrence was observed in two cases.

CONCLUSIONS

In our experience, patients with VIM-producing P. aeruginosa infections treated with ceftazidime-avibactam plus aztreonam mostly achieved clinical success. However, given the limited sample size, further research is required to validate these findings.

Addressing carbapenemase-producing extensively drug-resistant Pseudomonas aeruginosa: the potential of cefiderocol and ceftazidime/avibactam plus aztreonam therapy

This study evaluated the activity of cefiderocol and the combination of ceftazidime/avibactam (CZA) plus aztreonam against carbapenemase-producing extensively drug-resistant (XDR) Pseudomonas aeruginosa isolates. Nine clinical XDR P. aeruginosa isolates with different sequence types and class A (GES) or B (VIM, IMP or NDM) carbapenemases were analysed. Time-kill assays assessed bacterial load reduction for each treatment, while chemostat experiments on four isolates validated these findings. All isolates showed resistance to CZA, with four also resistant to aztreonam. Seven isolates were susceptible to cefiderocol, but two displayed borderline susceptibility (MIC 2-4 mg/L). Time-kill assays demonstrated bactericidal activity by cefiderocol in six isolates at 24 h, while CZA plus aztreonam showed bactericidal effects in three isolates and synergistic/additive effects in four isolates. In the chemostat model, cefiderocol and CZA plus aztreonam were bactericidal in all four tested isolates, with cefiderocol showing greater bacterial reduction in three of these isolates. Both cefiderocol and CZA plus aztreonam achieved significant reductions in bacterial counts compared to controls, but there was no significant difference between cefiderocol monotherapy and the combination. Both cefiderocol and CZA plus aztreonam demonstrated activity against XDR P. aeruginosa carrying metallo-β-lactamase (MBL) and/or serine-β-lactamase (SBL) carbapenemases. Cefiderocol was the only consistently effective monotherapy with a bactericidal effect across all tested isolates in the chemostat model.

Synergistic efficacy of ceftazidime/avibactam and aztreonam against carbapenemase-producing Pseudomonas aeruginosa: insights from the hollow-fiber infection model

BACKGROUND

Combination therapy is an attractive therapeutic option for extensively drug-resistant (XDR) Pseudomonas aeruginosa infections. Existing data support the combination of aztreonam and ceftazidime/avibactam (CZA) against class serine-β-lactamase (SBL)- and metallo-β-lactamase (MBL) - producing Enterobacterales. However, data about that combination against SBL- and MBL-producing P. aeruginosa are scarce. The objective of the study was to assess the in vitro activity of CZA and aztreonam alone and in combination against SBL- and MBL-producing XDR P. aeruginosa isolates.

METHODS

The combination was analyzed by means of the hollow-fiber infection model in three selected carbapenemase-producing P. aeruginosa isolates that were representative of the three most common XDRP. aeruginosa high-risk clones (ST175, ST111, ST235) responsible for global nosocomial infection outbreaks.

RESULTS

The three isolates were nonsusceptible to CZA and nonsusceptible to aztreonam. In the dynamic hollow-fiber infection model, the combination of CZA plus aztreonam exerts a bactericidal effect on the isolates, regardless of their resistance mechanism and demonstrates synergistic interactions against three isolates, achieving a bacterial reduction of 5.07 log10 CFU/ml, 5.2 log10 CFU/ml and 4 log10 CFU/ml, respectively.

CONCLUSION

The combination of CZA and aztreonam significantly enhanced the in vitro efficacy against XDR P. aeruginosa isolates compared to each monotherapy. This improvement suggests that the combination could serve as a feasible treatment alternative for infections caused by carbapenemase-producing XDR P. aeruginosa, especially in scenarios where no other treatment options are available.

Dosing Evaluation of Ceftazidime-Avibactam in Intensive Care Unit Patients Based on Pharmacokinetic/Pharmacodynamic (PK/PD) Modeling and Simulation

P. aeruginosa is the most common microorganism involved in many ICU-acquired infections. A correct dosage regimen is pivotal to avoiding resistance development, worse outcomes and higher mortality rates. The aim of this study was to perform a pharmacokinetic-pharmacodynamic (PK/PD) evaluation of recommended dosing regimens of ceftazidime-avibactam (CAZ-AVI) in ICU patients with different degrees of renal function for a specific strain of Pseudomonas aeruginosa. A semi-mechanistic PK/PD model has been developed. It allows for the simulation of CAZ-AVI steady-state plasma level curves and the evolution of bacterial growth curves. The percentage of bacterial load reduction and the value of the recommended PK/PD indices have been taken into account to define the success or failure of the regimens. Probabilistic analysis was performed using Monte Carlo simulations of two populations: control and ICU. In both populations, dosing regimens endorsed for patients with CLcr higher than 10 mL/min reach the PK/PD indices recommended, T > MIC > 90% and Cmin/MIC > 1.3. While dosage regimens endorsed for patients with CLcr of 10 mL/min or lower fail (T > MIC < 60% and Cmin/MIC < 0.35). However, proposed dosing regimens based on shortening dosing intervals for these patients would be successful, increasing bacterial load reduction by almost 50% and reaching the proposed PK/PD indices. Therefore, CAZ-AVI dosing strategies based on model-informed precision dosing (MIPD) could directly influence the efficacy of results in ICU patients with renal insufficiency.

Activities of aztreonam in combination with several novel β-lactam-β-lactamase inhibitor combinations against carbapenem-resistant Klebsiella pneumoniae strains coproducing KPC and NDM

Isolates coproducing serine/metallo-carbapenems are a serious emerging public health threat, given their rapid dissemination and the limited number of treatment options. The purposes of this study were to evaluate the in vitro antibacterial activity of novel β-lactam-β-lactamase inhibitor combinations (BLBLIs) against carbapenem-resistant Klebsiella pneumoniae (CRKP) coproducing metallo-β-lactamase and serine-β-lactamase, and to explore their effects in combination with aztreonam, meropenem, or polymyxin in order to identify the best therapeutic options. Four CRKP isolates coproducing K. pneumoniae carbapenemase (KPC) and New Delhi metallo-β-lactamase (NDM) were selected, and a microdilution broth method was used to determine their susceptibility to antibiotics. Time-kill assay was used to detect the bactericidal effects of the combinations of antibiotics. The minimum inhibitory concentration (MIC) values for imipenem and meropenem in three isolates did not decrease after the addition of relebactam or varbobactam, but the addition of avibactam to aztreonam reduced the MIC by more than 64-fold. Time-kill assay demonstrated that imipenem-cilastatin/relebactam (ICR) alone exerted a bacteriostatic effect against three isolates (average reduction: 1.88 log10 CFU/mL) and ICR combined with aztreonam exerted an additive effect. Aztreonam combined with meropenem/varbobactam (MEV) or ceftazidime/avibactam (CZA) showed synergistic effects, while the effect of aztreonam combined with CZA was inferior to that of MEV. Compared with the same concentration of aztreonam plus CZA combination, aztreonam/avibactam had a better bactericidal effect (24 h bacterial count reduction >3 log10CFU/mL). These data indicate that the combination of ATM with several new BLBLIs exerts powerful bactericidal activity, which suggests that these double β-lactam combinations might provide potential alternative treatments for infections caused by pathogens coproducing-serine/metallo-carbapenems.

The primary pharmacology of ceftazidime/avibactam: in vivo translational biology and pharmacokinetics/pharmacodynamics (PK/PD)

This review describes the translational in vivo and non-clinical pharmacokinetics/pharmacodynamics (PK/PD) research that supported clinical trialling and subsequently licensing approval of ceftazidime/avibactam, a new β-lactam/β-lactamase inhibitor combination aimed at the treatment of infections by Enterobacterales and Pseudomonas aeruginosa. The review thematically follows on from the co-published article, Nichols et al. (J Antimicrob Chemother 2022; dkac171). Avibactam protected ceftazidime in animal models of infection with ceftazidime-resistant, β-lactamase-producing bacteria. For example, a single subcutaneous dose of ceftazidime at 1024 mg/kg yielded little effect on the growth of ceftazidime-resistant, blaKPC-2-carrying Klebsiella pneumoniae in the thighs of neutropenic mice (final counts of 4 × 108 to 8 × 108 cfu/thigh). In contrast, co-administration of avibactam in a 4:1 ratio (ceftazidime:avibactam) was bactericidal in the same model (final counts of 2 × 104 to 3 × 104 cfu/thigh). In a rat abdominal abscess model, therapy with ceftazidime or ceftazidime/avibactam (4:1 w/w) against blaKPC-2-positive K. pneumoniae resulted in 9.3 versus 3.3 log cfu/abscess, respectively, after 52 h. With respect to PK/PD, in Monte Carlo simulations, attainment of unbound drug exposure targets (ceftazidime fT>8 mg/L and avibactam fT>1 mg/L, each for 50% of the dosing interval) for the labelled dose of ceftazidime/avibactam (2 and 0.5 g, respectively, q8h by 2 h IV infusion), including dose adjustments for patients with impaired renal function, ranged between 94.8% and 99.6% of patients, depending on the infection modelled.

Pharmacodynamic Thresholds for Beta-Lactam Antibiotics: A Story of Mouse Versus Man

Beta-lactams remain a critical member of our antibiotic armamentarium and are among the most commonly prescribed antibiotic classes in the inpatient setting. For these agents, the percentage of time that the free concentration remains above the minimum inhibitory concentration (%fT > MIC) of the pathogen has been shown to be the best predictor of antibacterial killing effects. However, debate remains about the quantity of fT > MIC exposure needed for successful clinical response. While pre-clinical animal based studies, such as the neutropenic thigh infection model, have been widely used to support dosing regimen selection for clinical development and susceptibility breakpoint evaluation, pharmacodynamic based studies in human patients are used validate exposures needed in the clinic and for guidance during therapeutic drug monitoring (TDM). For the majority of studied beta-lactams, pre-clinical animal studies routinely demonstrated the fT > MIC should exceed approximately 40–70% fT > MIC to achieve 1 log reductions in colony forming units. In contrast, clinical studies tend to suggest higher exposures may be needed, but tremendous variability exists study to study. Herein, we will review and critique pre-clinical versus human-based pharmacodynamic studies aimed at determining beta-lactam exposure thresholds, so as to determine which targets may be best suited for optimal dosage selection, TDM, and for susceptibility breakpoint determination. Based on our review of murine and clinical literature on beta-lactam pharmacodynamic thresholds, murine based targets specific to each antibiotic are most useful during dosage regimen development and susceptibility breakpoint assessment, while a range of exposures between 50 and 100% fT > MIC are reasonable to define the beta-lactam TDM therapeutic window for most infections.

Time-Kill Evaluation of Antibiotic Combinations Containing Ceftazidime-Avibactam against Extensively Drug-Resistant Pseudomonas aeruginosa and Their Potential Role against Ceftazidime-Avibactam-Resistant Isolates

Ceftazidime-avibactam (CZA) has emerged as a promising solution to the lack of new antibiotics against Pseudomonas aeruginosa infections. Data from in vitro assays of CZA combinations, however, are scarce. The objective of our study was to perform a time-kill analysis of the effectiveness of CZA alone and in combination with other antibiotics against a collection of extensively drug-resistant (XDR) P. aeruginosa isolates. Twenty-one previously characterized representative XDR P. aeruginosa isolates were selected. Antibiotic susceptibility was tested by broth microdilution, and results were interpreted using CLSI criteria. The time-kill experiments were performed in duplicate for each isolate. Antibiotics were tested at clinically achievable free-drug concentrations. Different treatment options, including CZA alone and combined with amikacin, aztreonam, meropenem, and colistin, were evaluated to identify the most effective combinations. Seven isolates were resistant to CZA (MIC ≥ 16/4 mg/liter), including four metallo-β-lactamase (MBL)-carrying isolates and two class A carbapenemases. Five of them were resistant or intermediate to aztreonam (MIC ≥ 16 mg/liter). Three isolates were resistant to amikacin (MIC ≥ 64 mg/liter) and one to colistin (MIC ≥ 4 mg/liter). CZA monotherapy had a bactericidal effect in 100% (14/14) of the CZA-susceptible isolates. Combination therapies achieved a greater overall reduction in bacterial load than monotherapy for the CZA-resistant isolates. CZA plus colistin was additive or synergistic in 100% (7/7) of the CZA-resistant isolates, while CZA plus amikacin and CZA plus aztreonam were additive or synergistic in 85%. CZA combined with colistin, amikacin, or aztreonam was more effective than monotherapy against XDR P. aeruginosa isolates. A CZA combination could be useful for treating XDR P. aeruginosa infections, including those caused by CZA-resistant isolates.

IMPORTANCE The emergence of resistance to antibiotics is a serious public health problem worldwide and can be a cause of mortality. For this reason, antibiotic treatment is compromised, and we have few therapeutic options to treat infections. The main goal of our study is to search for new treatment options for infections caused by difficult-to-treat resistant germs. Pseudomonas aeruginosa is a Gram-negative bacterium distributed throughout the world with the ability to become resistant to most available antibiotics. Ceftazidime-avibactam (CZA) emerged as a promising solution to the lack of new antibiotics against infections caused by P. aeruginosa strains. This study intended to analyze the effect of CZA alone or in combination with other available antibiotics against P. aeruginosa strains. The combination of CZA with other antibiotics could be more effective than monotherapy against extensively drug-resistant P. aeruginosa strains.

Sigmoid Emax Modeling To Define the Fixed Concentration of Enmetazobactam for MIC Testing in Combination with Cefepime

The use of carbapenem antibiotics to treat infections caused by Enterobacterales expressing increasingly aggressive extended-spectrum β-lactamases (ESBLs) has contributed to the emergence of carbapenem resistance. Enmetazobactam is a novel ESBL inhibitor being developed in combination with cefepime as a carbapenem-sparing option for infections caused by ESBL-producing Enterobacterales. Cefepime-enmetazobactam checkerboard MIC profiles were obtained for a challenge panel of cefepime-resistant ESBL-producing clinical isolates of Klebsiella pneumoniae. Sigmoid maximum effect (E_max) modeling described cefepime MICs as a function of enmetazobactam concentration with no bias. A concentration of 8 μg/ml enmetazobactam proved sufficient to restore >95% of cefepime antibacterial activity in vitro against >95% of isolates tested. These results support a fixed concentration of 8 μg/ml of enmetazobactam for MIC testing.

Evaluation of the post-antibiotic effect in vivo for the combination of a β-lactam antibiotic and a β-lactamase inhibitor: ceftazidime-avibactam in neutropenic mouse thigh and lung infections

The post-antibiotic effect (PAE) of ceftazidime-avibactam in vivo was evaluated using models of thigh- and lung-infection with Pseudomonas aeruginosa in neutropenic mice. In thigh-infected mice, the PAE was negative (-2.18 to -0.11 h) for three of four strains: caused by a 'burst' of rapid bacterial growth after the drug concentrations had fallen below their pre-specified target values. With lung infection, PAE was positive, and longer for target drug concentrations in ELF (>2 h) than plasma (1.69-1.88 h). The time to the start of regrowth was quantified as a new parameter, PAE_R, which was positive (0.35-1.00 h) in both thigh- and lung-infected mice. In the context that measurements of the PAE of β-lactam/β-lactamase inhibitor combinations in vivo have not previously been reported, it is noted that the negative values were consistent with previous measurements of the PAE of ceftazidime-avibactam in vitro and of ceftazidime alone in vivo.

Intrapulmonary Pharmacokinetics of Cefepime and Enmetazobactam in Healthy Volunteers: Towards New Treatments for Nosocomial Pneumonia

Cefepime-enmetazobactam is a novel β-lactam-β-lactamase inhibitor combination with broad-spectrum antimicrobial activity against a range of multidrug-resistant Enterobacteriaceae This agent is being developed for a range of serious hospital infections. An understanding of the extent of partitioning of β-lactam-β-lactamase inhibitor combinations into the human lung is required to better understand the potential role of cefepime-enmetazobactam for the treatment of nosocomial pneumonia. A total of 20 healthy volunteers were used to study the intrapulmonary pharmacokinetics of a regimen of 2 g cefepime-1 g enmetazobactam every 8 h intravenously (2 g/1 g q8h i.v.). Each volunteer contributed multiple plasma samples and a single epithelial lining fluid (ELF) sample, obtained by bronchoalveolar lavage. Concentrations of cefepime and enmetazobactam were quantified using liquid chromatography-tandem mass spectrometry. The pharmacokinetic data were modeled using a population methodology, and Monte Carlo simulations were performed to assess the attainment of pharmacodynamic targets defined in preclinical models. The concentration-time profiles of both agents in plasma and ELF were similar. The mean ± standard deviation percentage of partitioning of total drug concentrations of cefepime and enmetazobactam between plasma and ELF was 60.59% ± 28.62% and 53.03% ± 21.05%, respectively. Using pharmacodynamic targets for cefepime of greater than the MIC and free enmetazobactam concentrations of >2 mg/liter in ELF of 20% of the dosing interval, a regimen of cefepime-enmetazobactam of 2 g/0.5 g q8h i.v. infused over 2 h resulted in a probability of target attainment of ≥90% for Enterobacteriaceae with cefepime-enmetazobactam MICs of ≤8 mg/liter. This result provides a rationale to further consider cefepime-enmetazobactam for the treatment of nosocomial pneumonia caused by multidrug-resistant Enterobacteriaceae.

Treatment options for K. pneumoniae, P. aeruginosa and A. baumannii co-resistant to carbapenems, aminoglycosides, polymyxins and tigecycline: an approach based on the mechanisms of resistance to carbapenems

The management of carbapenem-resistant infections is often based on polymyxins, tigecycline, aminoglycosides and their combinations. However, in a recent systematic review, we found that Gram-negative bacteria (GNB) co-resistant to carbapanems, aminoglycosides, polymyxins and tigecycline (CAPT-resistant) are increasingly being reported worldwide. Clinical data to guide the treatment of CAPT-resistant GNB are scarce and based exclusively on few case reports and small case series, but seem to indicate that appropriate (in vitro active) antimicrobial regimens, including newer antibiotics and synergistic combinations, may be associated with lower mortality. In this review, we consolidate the available literature to inform clinicians dealing with CAPT-resistant GNB about treatment options by considering the mechanisms of resistance to carbapenems. In combination with rapid diagnostic methods that allow fast detection of carbapenemase production, the approach proposed in this review may guide a timely and targeted treatment of patients with infections by CAPT-resistant GNB. Specifically, we focus on the three most problematic species, namely Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii. Several treatment options are currently available for CAPT-resistant K. pneumonia. Newer β-lactam-β-lactamase combinations, including the combination of ceftazidime/avibactam with aztreonam against metallo-β-lactamase-producing isolates, appear to be more effective compared to combinations of older agents. Options for P. aeruginosa (especially metallo-β-lactamase-producing strains) and A. baumannii remain limited. Synergistic combination of older agents (e.g., polymyxin- or fosfomycin-based synergistic combinations) may represent a last resort option, but their use against CAPT-resistant GNB requires further study.