Determination of alternative ceftolozane/tazobactam dosing regimens for patients with infections due to Pseudomonas aeruginosa with MIC values between 4 and 32 mg/L

Individualized antibiotic dosage regimens for patients with augmented renal clearance

Objectives: Augmented renal clearance (ARC) is a state of enhanced renal function commonly observed in 30%-65% of critically ill patients despite normal serum creatinine levels. Using unadjusted standard dosing regimens of renally eliminated drugs in ARC patients often leads to subtherapeutic concentrations, poor clinical outcomes, and the emergence of multidrug-resistant bacteria. We summarized pharmaceutical, pharmacokinetic, and pharmacodynamic research on the definition, underlying mechanisms, and risk factors of ARC to guide individualized dosing of antibiotics and various strategies for optimizing outcomes. Methods: We searched for articles between 2010 and 2022 in the MEDLINE database about ARC patients and antibiotics and further provided individualized antibiotic dosage regimens for patients with ARC. Results: 25 antibiotic dosage regimens for patients with ARC and various strategies for optimization of outcomes, such as extended infusion time, continuous infusion, increased dosage, and combination regimens, were summarized according to previous research. Conclusion: ARC patients, especially critically ill patients, need to make individualized adjustments to antibiotics, including dose, frequency, and method of administration. Further comprehensive research is required to determine ARC staging, expand the range of recommended antibiotics, and establish individualized dosing guidelines for ARC patients.

Rationale and evidence for the use of new beta-lactam/beta-lactamase inhibitor combinations and cefiderocol in critically ill patients

BACKGROUND

Healthcare-associated infections involving Gram-negative bacteria (GNB) with difficult-to-treat resistance (DTR) phenotype are associated with impaired patient-centered outcomes and poses daily therapeutic challenges in most of intensive care units worldwide. Over the recent years, four innovative β-lactam/β-lactamase inhibitor (BL/BLI) combinations (ceftolozane-tazobactam, ceftazidime-avibactam, imipenem-relebactam and meropenem-vaborbactam) and a new siderophore cephalosporin (cefiderocol) have been approved for the treatment of certain DTR-GNB infections. The literature addressing their microbiological spectrum, pharmacokinetics, clinical efficacy and safety was exhaustively audited by our group to support the recent guidelines of the French Intensive Care Society on their utilization in critically ill patients. This narrative review summarizes the available evidence and unanswered questions on these issues.

METHODS

A systematic search for English-language publications in PUBMED and the Cochrane Library database from inception to November 15, 2022.

RESULTS

These drugs have demonstrated relevant clinical success rates and a reduced renal risk in most of severe infections for whom polymyxin- and/or aminoglycoside-based regimen were historically used as last-resort strategies-namely, ceftazidime-avibactam for infections due to Klebsiella pneumoniae carbapenemase (KPC)- or OXA-48-like-producing Enterobacterales, meropenem-vaborbactam for KPC-producing Enterobacterales, ceftazidime-avibactam/aztreonam combination or cefiderocol for metallo-β-lactamase (MBL)-producing Enterobacterales, and ceftolozane-tazobactam, ceftazidime-avibactam and imipenem-relebactam for non-MBL-producing DTR Pseudomonas aeruginosa. However, limited clinical evidence exists in critically ill patients. Extended-infusion scheme (except for imipenem-relebactam) may be indicated for DTR-GNB with high minimal inhibitory concentrations and/or in case of augmented renal clearance. The potential benefit of combining these agents with other antimicrobials remains under-investigated, notably for the most severe presentations. Other important knowledge gaps include pharmacokinetic information in particular situations (e.g., pneumonia, other deep-seated infections, and renal replacement therapy), the hazard of treatment-emergent resistance and possible preventive measures, the safety of high-dose regimen, the potential usefulness of rapid molecular diagnostic tools to rationalize their empirical utilization, and optimal treatment durations. Comparative clinical, ecological, and medico-economic data are needed for infections in whom two or more of these agents exhibit in vitro activity against the causative pathogen.

CONCLUSIONS

New BL/BLI combinations and cefiderocol represent long-awaited options for improving the management of DTR-GNB infections. Several research axes must be explored to better define the positioning and appropriate administration scheme of these drugs in critically ill patients.

Antimicrobial susceptibility of ceftolozane-tazobactam against multidrug-resistant Pseudomonas aeruginosa isolates from Melbourne, Australia

We collected 163 clinical Pseudomonas aeruginosa isolates at a tertiary hospital specialising in adult cystic fibrosis (CF) and lung transplantation (LTx) in Melbourne, Australia, to explore the activity of ceftolozane-tazobactam (C/T) in populations at high-risk for antimicrobial resistance. Of these, 144 (88.3%) were collected from sputum, and 19 (11.7%) from bronchoalveolar lavage. Most (85.3%) were derived from patients with cystic fibrosis and included a subset of patients that had undergone LTx. These isolates were tested against 11 antibiotics, including C/T, using Sensititre plates for broth microdilution (BMD) testing. Sixty (36.8%) isolates were classified as multidrug resistant (MDR) and 32 (19.6%) were extensively drug resistant (XDR). Overall, 133/163 (81.6%) isolates were susceptible to C/T. For MDR and XDR isolates, 88.3% and 28.1% were C/T susceptible, respectively. Among the non-MDR/XDR isolates, 100% remained susceptible to C/T. Comparisons of C/T susceptibility were made using BioMérieux Etests and Liofilchem MIC test strips (MTS). Categorical agreement to BMD was >93% for both test strips, but essential agreement to BMD was slightly higher with Etest (89.0%) compared to Liofilchem (74.8%). In conclusion, C/T retained activity against most MDR and over a quarter of XDR P. aeruginosa isolates from complex patients with CF and post-LTx.

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.

Comparison of Ceftolozane/Tazobactam Infusion Regimens in a Hollow-Fiber Infection Model against Extensively Drug-Resistant Pseudomonas aeruginosa Isolates

The aim of this study was to compare the efficacy of intermittent (1-h), extended (4-h), and continuous ceftolozane-tazobactam (C/T) infusion against three extensively drug-resistant (XDR) sequence type (ST) 175 P. aeruginosa isolates with different susceptibilities to C/T (MIC = 2 to 16 mg/L) in a 7-day hollow-fiber infection model (HFIM). C/T in continuous infusion achieved the largest reduction in total number of bacterial colonies in the overall treatment arms for both C/T-susceptible and -resistant isolates. It was also the only regimen with bactericidal activity against all three isolates. These data suggest that continuous C/T infusion should be considered a potential treatment for infections caused by XDR P. aeruginosa isolates, including nonsusceptible ones. Proper use of C/T dosing regimens may lead to better clinical management of XDR P. aeruginosa infections.

IMPORTANCE Ceftolozane-tazobactam (C/T) is an antipseudomonal antibiotic with a high clinical impact in treating infection caused by extensively drug-resistant (XDR) Pseudomonas aeruginosa isolates, but resistance is emerging. Given its time-dependent behavior, C/T continuous infusion can improve exposure and therefore the pharmacokinetic/pharmacodynamic target attainment. We compared the efficacy of intermittent, extended, and continuous C/T infusion against three XDR ST175 P. aeruginosa isolates with different C/T MICs by means of an in vitro dynamic hollow-fiber model. We demonstrated that C/T in continuous infusion achieved the largest reduction in bacterial density in the overall treatment arms for both susceptible and resistant isolates. It was also the only regimen with bactericidal activity against all three isolates. Through this study, we want to demonstrate that developing individually tailored antimicrobial treatments is becoming essential. Our results support the role of C/T level monitoring and of dose adjustments for better clinical management and outcomes.

Therapeutic Drug Monitoring and Prolonged Infusions of Ceftolozane/Tazobactam for MDR/XDR Pseudomonas aeruginosa Infections: An Observational Study

BACKGROUND AND OBJECTIVE

Prolonged infusion of ceftolozane/tazobactam (C/T) is a strategy used to increase achievement of pharmacokinetic/pharmacodynamic targets for the treatment of multi- or extensively drug-resistant MDR/XDR Gram-negative microorganisms. The objective of this study was to describe our therapeutic drug monitoring (TDM) experience of C/T administered by prolonged infusion or intermittent infusion to patients with MDR/XDR Pseudomonas aeruginosa infections. Our outcomes of interest were pharmacokinetic/pharmacodynamic target achievement and clinical cure.

METHODS

Patients with MDR/XDR P. aeruginosa infections treated with C/T were enrolled between February 2018 and February 2020. Blood samples were obtained as part of a TDM program. The pharmacokinetic/pharmacodynamic therapeutic target of C/T was defined as 100% of the duration of the dosing interval that free concentrations are above the minimum inhibitory concentration (MIC) (100 %ƒT ≥ MIC) of the causative pathogen. Dose changes were performed according to TDM results.

RESULTS

Forty patients were included: 13 (32.5%) with a proven MDR and 27 (67.5%) with a XDR P. aeruginosa infection. C/T was administered by prolonged infusion in 32 (80%) patients and by intermittent infusion in 8 (20%) patients. Lower doses were administered in the prolonged infusion compared to the intermittent infusion group [3 (9.4%) vs. 5 (62.5%] patients received a dose of 9 g/day (ceftolozane 2 g + tazobactam 1 g, every 8 h; p = 0.004). All patients achieved the pharmacokinetic/pharmacodynamic target and C/T concentrations exceeded 10 × MIC in > 50% of patients in both groups. TDM-recommended dose reductions occurred in 19 (47.5%) patients, being 16 (84.2%) in the prolonged infusion group. A high proportion of patients achieved clinical cure (82.5%).

CONCLUSIONS

The administration of C/T by prolonged infusion with TDM-guided dosing allowed the achievement of a pharmacokinetic/pharmacodynamic target even at lower doses. C/T showed a high efficacy for treating MDR/XDR P. aeruginosa infections.

Drug Regimens of Novel Antibiotics in Critically Ill Patients with Varying Renal Functions: A Rapid Review

There is currently an increase in the emergence of multidrug-resistant bacteria (MDR) worldwide, requiring the development of novel antibiotics. However, it is not only the choice of antibiotic that is important in treating an infection; the drug regimen also deserves special attention to avoid underdosing and excessive concentrations. Critically ill patients often have marked variation in renal function, ranging from augmented renal clearance (ARC), defined as a measured creatinine clearance (CrCL) ≥ 130 mL/min*1.73 m², to acute kidney injury (AKI), eventually requiring renal replacement therapy (RRT), which can affect antibiotic exposure. All novel beta-lactam (BLs) and/or beta-lactam/beta-lactamases inhibitors (BL/BLIs) antibiotics have specific pharmacokinetic properties, such as hydrophilicity, low plasma–protein binding, small volume of distribution, low molecular weight, and predominant renal clearance, which require adaptation of dosage regimens in the presence of abnormal renal function or RRT. However, there are limited data on the topic. The aim of this review was therefore to summarize available PK studies on these novel antibiotics performed in patients with ARC or AKI, or requiring RRT, in order to provide a practical approach to guide clinicians in the choice of the best dosage regimens in critically ill patients.

Optimizing Doses of Ceftolozane/Tazobactam as Monotherapy or in Combination with Amikacin to Treat Carbapenem-Resistant Pseudomonas aeruginosa

Carbapenem-resistant Pseudomonas aeruginosa (CRPA) is a hospital-acquired pathogen with a high mortality rate and limited treatment options. We investigated the activity of ceftolozane/tazobactam (C/T) and its synergistic effects with amikacin to extend the range of optimal therapeutic choices with appropriate doses. The E-test method is used to determine in vitro activity. The optimal dosing regimens to achieve a probability of target attainment (PTA) and a cumulative fraction of response (CFR) of ≥90% were simulated using the Monte Carlo method. Of the 66 CRPA isolates, the rate of susceptibility to C/T was 86.36%, with an MIC50 and an MIC90 of 0.75 and 24 µg/mL, respectively. Synergistic and additive effects between C/T and amikacin were observed in 24 (40%) and 18 (30%) of 60 CRPA isolates, respectively. The extended infusion of C/T regimens achieved a ≥90% PTA of 75% and a 100% fT > MIC at C/T MICs of 4 and 2 µg/mL, respectively. Only the combination of either a short or prolonged C/T infusion with a loading dose of amikacin of 20−25 mg/kg, followed by 15−20 mg/kg/day amikacin dosage, achieved ≥90% CFR. The C/T infusion, combined with currently recommended amikacin dose regimens, should be considered to manage CRPA infections.

Impact of ceftolozane/tazobactam concentrations in continuous infusion against extensively drug-resistant Pseudomonas aeruginosa isolates in a hollow-fiber infection model

Ceftolozane/tazobactam (C/T) has emerged as a potential agent for the treatment of extensively drug-resistant (XDR) Pseudomonas aeruginosa infections. As it is a time-dependent antimicrobial, prolonged infusion may help achieve pharmacokinetic/pharmacodynamic (PK/PD) targets. To compare alternative steady-state concentrations (Css) of C/T in continuous infusion (CI) against three XDR P. aeruginosa ST175 isolates with C/T minimum inhibitory concentration (MIC) values of 2 to 16 mg/L in a hollow-fiber infection model (HFIM). Duplicate 10-day HFIM assays were performed to evaluate Css of C/T in CI: one compared 20 and 45 mg/L against the C/T-susceptible isolate while the other compared 45 and 80 mg/L against the two C/T-non-susceptible isolates. C/T resistance emerged when C/T-susceptible isolate was treated with C/T in CI at a Css of 20 mg/L; which showed a deletion in the gene encoding AmpC β-lactamase. The higher dosing regimen (80 mg/L) showed a slight advantage in effectiveness. The higher dosing regimen has the greatest bactericidal effect, regardless of C/T MIC. Exposure to the suboptimal Css of 20 mg/L led to the emergence of C/T resistance in the susceptible isolate. Antimicrobial regimens should be optimized through C/T levels monitoring and dose adjustments to improve clinical management.

Ceftolozane/tazobactam exposure in critically ill patients undergoing continuous renal replacement therapy: a PK/PD approach to tailor dosing

OBJECTIVES

To investigate the influence of continuous renal replacement therapy (CRRT) intensity on the clearance of ceftolozane/tazobactam in critical care patients, and to evaluate if the reported doses would achieve an optimal pharmacokinetic/pharmacodynamic (PK/PD) target against Pseudomonas aeruginosa exhibiting different MICs.

METHODS

The MEDLINE-PubMed database was searched from inception to January 2020 to retrieve observational studies or case reports investigating the PK behaviour of ceftolozane/tazobactam during CRRT. Relevant CRRT settings and PK variables were extracted, and the influence of CRRT intensity on ceftolozane/tazobactam total clearance (CLtot) was determined by simple linear regression. The optimal PK/PD target for the reported doses was deemed to be achieved when ceftolozane trough concentrations (Cmin) were above the MIC (less intensive target) or four times the MIC (intensive target) for P. aeruginosa.

RESULTS

Data from six studies including 11 patients (mean age 56.6 years) were analysed. Mean blood flow rate and effluent flow rate were 161.8 mL/min and 2383.4 mL/h, respectively. Ceftolozane Cmin ranged from 25.8 to 79.4 mg/L. A significant correlation was found for ceftolozane CLtot and effluent flow rate (P = 0.027). The intensive PK/PD target was achieved by 100% and 50% of the reported doses for MIC, respectively, up to 4 and 8 mg/L.

CONCLUSIONS

A significant correlation between effluent flow rate and ceftolozane clearance during CRRT could be identified. Higher dosing regimens coupled with continuous/extended infusion may be required in the case of higher CRRT intensity, deep-seated infections or poorly susceptible isolates. Larger studies assessing ceftolozane PK in different CRRT settings are warranted.

Lung penetration, bronchopulmonary pharmacokinetic/pharmacodynamic profile and safety of 3 g of ceftolozane/tazobactam administered to ventilated, critically ill patients with pneumonia

Objectives

Ceftolozane/tazobactam is approved for hospital-acquired/ventilator-associated bacterial pneumonia at double the dose (i.e. 2 g/1 g) recommended for other indications. We evaluated the bronchopulmonary pharmacokinetic/pharmacodynamic profile of this 3 g ceftolozane/tazobactam regimen in ventilated pneumonia patients.

Methods

This was an open-label, multicentre, Phase 1 trial (clinicaltrials.gov: NCT02387372). Mechanically ventilated patients with proven/suspected pneumonia received four to six doses of 3 g of ceftolozane/tazobactam (adjusted for renal function) q8h. Serial plasma samples were collected after the first and last doses. One bronchoalveolar lavage sample per patient was collected at 1, 2, 4, 6 or 8 h after the last dose and epithelial lining fluid (ELF) drug concentrations were determined. Pharmacokinetic parameters were estimated by non-compartmental analysis and pharmacodynamic analyses were conducted to graphically evaluate achievement of target exposures (plasma and ELF ceftolozane concentrations >4 mg/L and tazobactam concentrations >1 mg/L; target in plasma: ≥30% and ≥20% of the dosing interval, respectively).

Results

Twenty-six patients received four to six doses of study drug; 22 were included in the ELF analyses. Ceftolozane and tazobactam T_max (6 and 2 h, respectively) were delayed in ELF compared with plasma (1 h). Lung penetration, expressed as the ratio of mean drug exposure (AUC) in ELF to plasma, was 50% (ceftolozane) and 62% (tazobactam). Mean ceftolozane and tazobactam ELF concentrations remained >4 mg/L and >1 mg/L, respectively, for 100% of the dosing interval. There were no deaths or adverse event-related study discontinuations.

Conclusions

In ventilated pneumonia patients, 3 g of ceftolozane/tazobactam q8h yielded ELF exposures considered adequate to cover ceftolozane/tazobactam-susceptible respiratory pathogens.

New Perspectives on Antimicrobial Agents: Ceftolozane-Tazobactam

Ceftolozane-tazobactam (C/T) is a new fifth-generation cephalosporin/beta-lactamase inhibitor combination approved by the Food and Drug Administration and the European Medicines Agency for treatment of complicated intraabdominal infections, complicated urinary tract infections, and hospital-acquired pneumonia in adult patients. This review will briefly describe the pharmacology of C/T and focus on the emerging clinical trial and real-world data supporting its current utilization. Additionally, our synthesis of these data over time has set our current usage of C/T at Barnes-Jewish Hospital (BJH). C/T is primarily employed as directed monotherapy at BJH when Pseudomonas aeruginosa isolates are identified with resistance to other beta-lactams. C/T can also be used empirically in specific clinical situations at BJH prior to microbiological detection of an antibiotic-resistant P. aeruginosa isolate. These situations include critically ill patients in the intensive care unit (ICU) setting, where there is a high likelihood of infection with multidrug-resistant (MDR) P. aeruginosa; patients failing therapy with a carbapenem; specific patient populations known to be at high risk for infection with MDR P. aeruginosa (e.g., lung transplant and cystic fibrosis patients); and patients know to have previous infection or colonization with MDR P. aeruginosa.

Pharmacokinetic/pharmacodynamic target attainment in critically ill renal patients on antimicrobial usage: focus on novel beta-lactams and beta lactams/beta-lactamase inhibitors

INTRODUCTION

Several novel beta-lactams (BLs) and/or beta lactams/beta-lactamase inhibitors (BL/BLIs) have been recently developed for the management of multidrug-resistant bacterial infections. Data concerning dose optimization in critically ill patients with altered renal function are scanty.

AREAS COVERED

This article provides a critical reappraisal of pharmacokinetic and clinical issues emerged with novel BLs and/or BL/BLIs in renal critically ill patients. Clinical and pharmacokinetic studies published in English until December 2020 were searched on the PubMed-MEDLINE database.

EXPERT OPINION

Several issues emerged with the use of novel BLs and/or BL/BLIs in critically ill renal patients. Suboptimal clinical response rate with ceftazidime-avibactam and ceftolozane-tazobactam was reported in phase II-III trials in patients with moderate kidney injury; data on patients undergoing renal replacement therapy are limited to some case reports; dose adjustment in augmented renal clearance is provided only for cefiderocol. Implementation of altered dosing strategies (prolonged infusion and/or higher dosage) coupled with adaptive real-time therapeutic drug monitoring could represent the most effective approach in warranting optimal pharmacokinetic/pharmacodynamic targets with novel BLs and/or BL/BLIs in challenging scenarios, thus minimizing the risk of clinical failure and/or of resistance selection.

In vitro synergy of β-lactam combinations against KPC-producing Klebsiella pneumoniae strains

BACKGROUND

Double carbapenem therapy has been promoted as an alternative treatment for infections due to carbapenemase-producing Enterobacteriaceae where carbapenemase inhibitors are unavailable or when other agents have demonstrated toxicity with equally limited evidence. The capacity of other β-lactams and β-lactamase inhibitors to provide synergistic activity with carbapenems is unclear.

OBJECTIVES

This study sought to investigate the in vitro synergistic potential of other β-lactam/β-lactamase combinations with meropenem against KPC producers.

METHODS

Time-kill assays were performed on 24 unique strains of KPC-producing Klebsiella pneumoniae. Combinations evaluated included meropenem or imipenem with one of the following: ertapenem, piperacillin/tazobactam or ceftolozane/tazobactam. Concentrations used for each drug were those considered physiologically attainable in patients with a time above the concentration exceeding 40%-50% of the dose interval. Combinations were considered to be synergistic when they reduced bacterial cfu/mL by ≥2 log10 at 24 h as compared with the single most active agent.

RESULTS

The combination of piperacillin/tazobactam with meropenem was found to be synergistic against 70.8% of the isolates, followed by ertapenem with meropenem (58.3%) and ceftolozane/tazobactam with meropenem (41.7%). The piperacillin/tazobactam combination was found to be more bactericidal than the other combinations, with 58.3% of isolates demonstrating a ≥4 log10 cfu/mL reduction at 24 h, as compared with 37.5% for ertapenem and 20.8% for ceftolozane/tazobactam combinations.

CONCLUSIONS

The combination of piperacillin/tazobactam with meropenem may be a potential therapy against KPC-producing K. pneumoniae when other therapies are unavailable or prohibitively toxic.

Modifiable Risk Factors for the Emergence of Ceftolozane-Tazobactam Resistance

BACKGROUND

Ceftolozane-tazobactam (TOL-TAZ) affords broad coverage against Pseudomonas aeruginosa. Regrettably, TOL-TAZ resistance has been reported. We sought to identify modifiable risk factors that may reduce the emergence of TOL-TAZ resistance.

METHODS

Twenty-eight patients infected with carbapenem-resistant P. aeruginosa isolates susceptible to TOL-TAZ and treated with ≥72 hours of TOL-TAZ between January 2018 and December 2019 in Baltimore, Maryland were included. The 28 patients had P. aeruginosa isolates available both before and after TOL-TAZ exposure. Cases were defined as patients with at least a four-fold increase in P. aeruginosa TOL-TAZ MICs after exposure to TOL-TAZ. Independent risk factors for the emergence of TOL-TAZ resistance comparing cases and controls were investigated using logistic regression. Whole genome sequencing of paired isolates was used to identify mechanisms of resistance that emerged during TOL-TAZ exposure.

RESULTS

Fourteen patients (50%) had P. aeruginosa isolates which developed high-level TOL-TAZ resistance (i.e., cases). Cases were more likely to have inadequate source control (29% vs. 0%, p=0.04) and were less likely to receive TOL-TAZ as an extended 3-hour infusion (0% vs. 29%; p=0.04). Eighty-six percent of index isolates susceptible to ceftazidime-avibactam (CAZ-AVI) had subsequent P. aeruginosa isolates with high-level resistance to CAZ-AVI, after TOL-TAZ exposure. Common mutations identified in TOL-TAZ resistant isolates involved AmpC, a known binding site for both ceftolozane and ceftazidime, and DNA polymerase.

CONCLUSION

Due to our small sample size, our results remain exploratory but forewarn of the potential emergence of TOL-TAZ resistance during therapy and suggest extending TOL-TAZ infusions may be protective. Larger studies are needed to investigate this association.

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.

Ceftolozane and tazobactam for the treatment of hospital acquired pneumonia

INTRODUCTION

Patients admitted to hospitals are at risk of developing nosocomial infections. These types of infections typically occur in immune-compromised patients. Furthermore, nosocomial infections are frequently caused by resistant organisms, including nonfermenting gram-negative bacilli such as Pseudomonas aeruginosa.

AREAS COVERED

P. aeruginosa is a hazardous pathogen. It can resist numerous antibiotics, due to several resistance mechanisms. It is associated with serious illnesses, particularly hospital-acquired infections including ventilator-associated pneumonia. In the past, only a limited number of anti-pseudomonal drugs were available. However, several therapeutic advancements have been made, in recent years, to target P. aeruginosa, including the development of the new cephalosporin: ceftolozane-tazobactam.

EXPERT OPINION

Ceftolozane-tazobactam is a combination of a novel semi-synthetic fifth-generation cephalosporin with a well-established beta-lactamase inhibitor. From a structural perspective, ceftolozane-tazobactam has attested increased stability to AmpC β-lactamases. Additionally, ceftolozane-tazobactam is less affected by changes in efflux pumps and porin permeability due to an enhanced affinity to certain penicillin-binding proteins (PBPs). This enables the molecule to overcome the most common anti-drug resistant mechanisms of bacteria. According to previous clinical trials conducted, ceftolozane-tazobactam must be considered when treating patients with confirmed or suspected P. aeruginosa respiratory tract infections, either nosocomial pneumonia or ventilator-associated pneumonia.

Efficacy of Ceftolozane-Tazobactam in Combination with Colistin against Extensively Drug-Resistant Pseudomonas aeruginosa, Including High-Risk Clones, in an In Vitro Pharmacodynamic Model

Combination therapy is an attractive therapeutic option for extensively drug-resistant (XDR) Pseudomonas aeruginosa infections. Colistin has been the only treatment available for these infections for many years, but its results are suboptimal. Ceftolozane-tazobactam (C/T) is a newly available therapeutic option that has shown good antipseudomonal activity, even against a number of XDR P. aeruginosa strains. However, data about combinations containing C/T are scarce. The aim of this study was to analyze the activity of C/T and colistin alone and in combination against a collection of XDR P. aeruginosa strains containing 24 representative clinical isolates from a multicentre Spanish study. Twenty-four time-kill experiments performed over 24 h were conducted in duplicate to determine the effects of colistin and C/T alone and combined. An in vitro pharmacodynamic chemostat model then was used to validate this combination against three selected XDR P. aeruginosa ST175 isolates with different susceptibility levels to C/T. Static time-kill assays demonstrated superior synergistic or additive effect for C/T plus colistin against 21 of the 24 isolates studied. In the in vitro dynamic pharmacokinetic/pharmacodynamic (PK/PD) model, the C/T regimen of 2/1 g every 8 h with a steady-state concentration of 2 mg/liter colistin effectively suppressed the bacterial growth at 24 h. Additive or synergistic interactions were observed for C/T plus colistin against XDR P. aeruginosa strains and particularly against C/T-resistant strains. C/T plus colistin may be a useful treatment for XDR P. aeruginosa infections, including those caused by high risk-clones resistant to C/T.

Use of continuous infusion ceftolozane-tazobactam with therapeutic drug monitoring in a patient with cystic fibrosis

PURPOSE

The safe and effective use of ceftolozane-tazobactam delivered via continuous infusion in a cystic fibrosis (CF) patient with reduced body weight and presumed augmented renal clearance is reported.

SUMMARY

A 30-year-old woman with CF was admitted for acute pulmonary exacerbations with positive respiratory cultures for Pseudomonas aeruginosa and extended-spectrum β-lactamase-producing Escherichia coli. Susceptibility testing confirmed multidrug resistance, and the patient was transitioned to ceftolozane-tazobactam for definitive therapy. A novel strategy of administering ceftolozane-tazobactam 6 g by continuous i.v. infusion over 24 hours was initiated during hospitalization and continued at discharge for a total of 10 days. Therapeutic drug monitoring over the first 36 hours of the continuous infusion confirmed adequate exposure. The patient had clinical resolution with return to baseline of pulmonary function tests and no noted adverse drug events.

CONCLUSION

A continuous infusion regimen of ceftolozane-tazobactam was successfully used in a CF patient with augmented renal clearance.

Clinical and Safety Evaluation of Continuously Infused Ceftolozane/Tazobactam in the Outpatient Setting

Background

Ceftolozane/tazobactam (C/T) is a novel cephalosporin/β-lactamase inhibitor currently dosed by 8-hour intervals to treat complicated and multidrug-resistant Pseudomonas aeruginosa infections in inpatients. This dosing strategy limits the ability to transition patients to outpatient antimicrobial therapy. There are limited data in the literature to support continuous infusion (CI) dosing.

Methods

This study is a retrospective chart review of patients who received CI C/T at an infusion center part of a community health system. Patients were evaluated from August 2016 through January 2018. Patients were included in the study if they were ≥18 years old and received their entire course of C/T as a CI in the outpatient setting. Patients were excluded if they received any part of their therapy as an inpatient.

Results

The primary outcome evaluated was symptom resolution. Secondary outcomes evaluated were microbiologic resolution as well as patient satisfaction. Seven patients received either 4.5 or 9 grams of continuous infusion C/T every 24 hours in the outpatient setting over the study period. For the primary outcome, 6 of 7 patients had symptom resolution. For the secondary outcomes, 3 of 3 patients had microbiologic resolution, and patient satisfaction scores were overall positive among respondents.

Conclusions

Ceftolozane/tazobactam delivered as a continuous infusion may be a safe, effective, and convenient way to treat infections caused by P aeruginosa. This novel treatment regimen can be an option for patients to avoid hospital admission or discharge to complete therapy as an outpatient.

Advances in the therapy of bacterial bloodstream infections

BACKGROUND

Advances in the diagnostic and therapeutic management of patients with bloodstream infections (BSIs) have been achieved in the last years, improving clinical outcome. However, mortality associated with some pathogens, such as Staphylococcus aureus and Enterococcus spp., is still high. In addition, the spread of antibiotic resistance, mainly among Gram-negative bacteria, reduces treatment options in some circumstances. Therefore, interest in new drugs, combination regimens and optimal dosing schedules is rising.

OBJECTIVES

Our aim is to summarize the current evidence on available antibiotic regimens for patients with bacterial BSI, focusing on drug choice, combination regimens and optimal dosing schedules. We selected bacteria that are difficult to manage because of virulence factors (i.e. methicillin-susceptible S. aureus), tolerance to antibiotic activity (i.e. Enterococcus faecalis), and/or susceptibility patterns (i.e. methicillin-resistant S. aureus, vancomycin-resistant enterococci, carbapenem-resistant Enterobacteriaceae, multidrug-resistant Pseudomonas aeruginosa and carbapenem-resistant Acinetobacter baumannii).

SOURCES

MEDLINE search with English language and publication in the last 5 years as limits.

CONTENT AND IMPLICATIONS

The literature gaps on the use of new drugs, the uncertainties regarding the use of combination regimens, and the need to optimize dosing schedules in some circumstances (e.g. augmented renal clearance, renal replacement therapy, high inoculum BSI sources, and isolation of bacteria showing high MICs) have been revised.

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

PURPOSE

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

METHODS

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

FINDINGS

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

IMPLICATIONS

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

Epidemiology and Treatment of Multidrug-Resistant and Extensively Drug-Resistant Pseudomonas aeruginosa Infections

In recent years, the worldwide spread of the so-called high-risk clones of multidrug-resistant or extensively drug-resistant (MDR/XDR) Pseudomonas aeruginosa has become a public health threat. This article reviews their mechanisms of resistance, epidemiology, and clinical impact and current and upcoming therapeutic options. In vitro and in vivo treatment studies and pharmacokinetic and pharmacodynamic (PK/PD) models are discussed. Polymyxins are reviewed as an important therapeutic option, outlining dosage, pharmacokinetics and pharmacodynamics, and their clinical efficacy against MDR/XDR P. aeruginosa infections. Their narrow therapeutic window and potential for combination therapy are also discussed. Other "old" antimicrobials, such as certain β-lactams, aminoglycosides, and fosfomycin, are reviewed here. New antipseudomonals, as well as those in the pipeline, are also reviewed. Ceftolozane-tazobactam has clinical activity against a significant percentage of MDR/XDR P. aeruginosa strains, and its microbiological and clinical data, as well as recommendations for improving its use against these bacteria, are described, as are those for ceftazidime-avibactam, which has better activity against MDR/XDR P. aeruginosa, especially strains with certain specific mechanisms of resistance. A section is devoted to reviewing upcoming active drugs such as imipenem-relebactam, cefepime-zidebactam, cefiderocol, and murepavadin. Finally, other therapeutic strategies, such as use of vaccines, antibodies, bacteriocins, anti-quorum sensing, and bacteriophages, are described as future options.

Recognizing and Overcoming Resistance to New Beta-Lactam/Beta-Lactamase Inhibitor Combinations

PURPOSE OF REVIEW

To describe the mechanisms and clinical relevance of emergent resistance to three recently introduced beta-lactamase inhibitor combinations (BLICs) active against resistant Gram-negative organisms: ceftolozane-tazobactam, ceftazidime-avibactam, and meropenem-vaborbactam.

RECENT FINDINGS

Despite their recent introduction into practice, clinical reports of resistance to BLICs among typically susceptible organisms have already emerged, in some cases associated with therapeutic failure. The resistance mechanisms vary by agent, including mutations in beta-lactamase active sites, upregulation of efflux pumps, and alterations in the structure or expression of porin channels. These changes may confer cross-resistance or, rarely, increased susceptibility to related agents. Clinicians need to be aware of the potential for initial or emergent resistance to BLICs and ensure appropriate antimicrobial susceptibility testing is performed. Dose optimization and novel combinations of agents may play a role in preventing and managing resistance. Recently approved BLICs have provided important new therapeutic options against resistant Gram-negative organisms, but are already coming up against emergent resistance. Awareness of the potential for resistance, early detection, and dose optimization may be important in preserving the utility of these agents.

The "Old" and the "New" Antibiotics for MDR Gram-Negative Pathogens: For Whom, When, and How

The recent expansion of multidrug resistant and pan-drug-resistant pathogens poses significant challenges in the treatment of healthcare associated infections. An important advancement, is a handful of recently launched new antibiotics targeting some of the current most problematic Gram-negative pathogens, namely carbapenem-producing Enterobacteriaceae (CRE) and carbapenem-resistant P. aeruginosa (CRPA). Less options are available against carbapenem-resistant Acinetobacter baumannii (CRAB) and strains producing metallo-beta lactamases (MBL). Ceftazidime-avibactam signaled a turning point in the treatment of KPC and partly OXA- type carbapenemases, whereas meropenem-vaborbactam was added as a potent combination against KPC-producers. Ceftolozane-tazobactam could be seen as an ideal beta-lactam backbone for the treatment of CRPA. Plazomicin, an aminoglycoside with better pharmacokinetics and less toxicity compared to other class members, will cover important proportions of multi-drug resistant pathogens. Eravacycline holds promise in the treatment of infections by CRAB, with a broad spectrum of activity similar to tigecycline, and improved pharmacokinetics. Novel drugs and combinations are not to be considered "panacea" for the ongoing crisis in the therapy of XDR Gram-negative bacteria and colistin will continue to be considered as a fundamental companion drug for the treatment of carbapenem-resistant Enterobacteriaceae (particularly in areas where MBL predominate), for the treatment of CRPA (in many cases being the only in vitro active drug) as well as CRAB. Aminoglycosides are still important companion antibiotics. Finally, fosfomycin as part of combination treatment for CRE infections and P. aeruginosa, deserves a greater attention. Optimal conditions for monotherapy and the "when and how" of combination treatments integrating the novel agents will be discussed.

New treatments of multidrug-resistant Gram-negative ventilator-associated pneumonia

Ventilator-associated pneumonia (VAP) remains an important clinical problem globally, being associated with significant morbidity and mortality. As management of VAP requires adequate and timely antibiotic administration, global emergence of antimicrobial resistance poses serious challenges over our ability to maintain this axiom. Development of antimicrobials against MDR Gram-negative pathogens has therefore emerged as a priority and some new antibiotics have been marketed or approach late stage of development. The aim of this review is to analyse new therapeutic options from the point view of potential treatment of VAP. Among recently developed antimicrobials presented herein, it is obvious that we will have promising therapeutic options against VAP caused by Enterobacteriaceae excluding those producing metallo-β-lactamases, against which only cefiderocol and aztreonam/avibactam are expected to be active. Against infections caused by carbapenem non-susceptible Pseudomonas aeruginosa, ceftolozane/tazobactam and to a lesser extend ceftazidime/avibactam may cover a proportion of current medical needs, but there still remain a considerable proportion of strains which harbor other resistance mechanisms. Murepavadin and cefiderocol hold promise against this particularly notorious pathogen. Finally, Acinetobacter baummannii remains a treatment-challenge. Eravacycline, cefiderocol and probably plazomicin seem to be the most promising agents against this difficult-to treat pathogen, but we have still a long road ahead, to see their position in clinical practice and particularly in VAP. In summary, despite persisting and increasing unmet medical needs, several newly approved and forthcoming agents hold promise for the treatment of VAP and hopefully will enrich our antimicrobial arsenal in the next few years. Targeted pharmacokinetic and clinical studies in real-life scenario of VAP are important to position these new agents in clinical practice, whereas vigilant use will ensure their longevity in our armamentarium.

Ceftolozane/tazobactam for the treatment of multidrug resistant Pseudomonas aeruginosa: experience from the Balearic Islands

A prospective, descriptive observational study of consecutive patients treated with ceftolozane/tazobactam in the reference hospital of the Balearic Islands (Spain), between May 2016 and September 2017, was performed. Demographic, clinical, and microbiological variables were recorded. The later included resistance profile, molecular typing, and whole genome sequencing of isolates showing resistance development. Fifty-eight patients were treated with ceftolozane/tazobactam. Thirty-five (60.3%) showed respiratory tract infections, 21 (36.2%) received monotherapy, and 37 (63.8%) combined therapy for ≥ 72 h, mainly with colistin (45.9%). In 46.6% of the patients, a dose of 1/0.5 g/8 h was used, whereas 2/1 g/8 h was used in 41.4%. In 56 of the cases (96.6%), the initial Pseudomonas aeruginosa isolates recovered showed a multidrug resistant (MDR) phenotype, and 50 of them (86.2%) additionally met the extensively drug resistant (XDR) criteria and were only susceptible colistin and/or aminoglycosides (mostly amikacin). The epidemic high-risk clone ST175 was detected in 50% of the patients. Clinical cure was documented in 37 patients (63.8%) and resistance development in 8 (13.8%). Clinical failure was associated with disease severity (SOFA), ventilator-dependent respiratory failure, XDR profile, high-risk clone ST175, negative control culture, and resistance development. In 6 of the 8 cases, resistance development was caused by structural mutations in AmpC, including some mutations described for the first time in vivo, whereas in the other 2, by mutations in OXA-10 leading to the extended spectrum OXA-14. Although further clinical experience is still needed, our results suggest that ceftolozane/tazobactam is an attractive option for the treatment of MDR/XDR P. aeruginosa infections.

Multidrug-Resistant Pseudomonas Infections: Hard to Treat, But Hope on the Horizon?

PURPOSE OF REVIEW

As the sixth most common nosocomial pathogen in the USA, Pseudomonas aeruginosa poses a significant threat to patients within the healthcare system. Its intrinsic and acquired resistance mechanisms also significantly limit the choices for antimicrobial therapy, prompting an increase in the research and development of antibacterial agents with enhanced activity against multidrug-resistant (MDR) P. aeruginosa. While many approved and pipeline antibiotics have activity against wild-type P. aeruginosa, only four new antibiotics have promising activity against MDR P. aeruginosa: ceftazidime-avibactam (Avycaz®), ceftolozane-tazobactam (Zerbaxa®), cefiderocol, and imipenem-cilastatin/relebactam. The goal of this paper is to review the epidemiology and mechanisms of resistance in P. aeruginosa as well as explore the newly approved and pipeline agents that overcome these mechanisms of resistance.

RECENT FINDINGS

Ceftazidime-avibactam and ceftolozane-tazobactam are currently FDA-approved and available for use, while cefiderocol and imipenem-cilastatin/relebactam are in development. Current evidence suggests ceftazidime-avibactam and ceftolozane-tazobactam both may have a role in treatment of MDR P. aeruginosa infections. Ceftolozane-tazobactam appears to be modestly more potent against P. aeruginosa, but emergence of resistance has been noted in various reported cases. Trials are ongoing for cefiderocol and imipenem-cilastatin/relebactam and early results appear promising. The aforementioned agents fill important gaps in the antibiotic armamentarium, particularly for patients with MDR P. aeruginosa infections who otherwise have extremely limited and often toxic antibiotic options. However, resistance to all of these agents will likely emerge, and additional antibiotic development is warranted to provide sufficient options to successfully manage MDR P. aeruginosa infections.