Activity of the new cephalosporin CXA-101 (FR264205) against Pseudomonas aeruginosa isolates from chronically-infected cystic fibrosis patients

Ceftolozane/Tazobactam for Treating Children With Exacerbations of Cystic Fibrosis Due to Pseudomonas aeruginosa: A Review of Available Data

Ceftolozane-tazobactam is a novel fifth-generation cephalosporin/β-lactamase inhibitor combination recently approved for treatment of both complicated intra-abdominal and urinary tract infections in adults. Considering its potent bactericidal activity against Pseudomonas aeruginosa, it might represent an important option also for treating children with exacerbations of cystic fibrosis due to Pseudomonas aeruginosa when other alternative treatments have been exhausted. We hereby review available data on the use of ceftolozane-tazobactam in children, focusing on cystic fibrosis.

In Vitro Activity of Ceftolozane/Tazobactam vs Nonfermenting, Gram-Negative Cystic Fibrosis Isolates

Ceftolozane/tazobactam (C/T) was tested and compared against 93 nonfermenting, Gram-negative clinical isolates from cystic fibrosis specimens. Based on current breakpoints for intra-abdominal and urinary tract infections (which may not be appropriate for pulmonary infections), C/T was found to be the most active agent against P. aeruginosa (95.7% susceptible), followed by piperacillin/tazobactam (89.4% susceptible). For other Gram-negative pathogens included, C/T had varying activity.

Time-Kill Analysis of Ceftolozane/Tazobactam Efficacy Against Mucoid Pseudomonas aeruginosa Strains from Cystic Fibrosis Patients

INTRODUCTION

Mucoid Pseudomonas aeruginosa (MP) strains in cystic fibrosis (CF) patients are thought to initiate the chronic infection stage of CF and are associated with pulmonary function decline.

OBJECTIVES

The purpose of this study was to assess the susceptibility of MP strains to ceftolozane/tazobactam and the efficacy of ceftolozane/tazobactam against MP strains compared with those for standard-of-care antipseudomonal antibiotics.

METHODS

Ten clinical isolates of MP from CF patients were tested for susceptibility with Etest and time-kill analysis with ceftolozane/tazobactam compared with ceftazidime, cefepime, ciprofloxacin, meropenem, tobramycin, and polymyxin B. The physiologic free peak concentrations were used in the time-kill experiments.

RESULTS

Ceftolozane/tazobactam minimum inhibitory concentrations ranged from 0.032 to 1.5 mg/L. In the time-kill analysis, the mean starting inoculum for the isolates was 6.29 ± 0.22 log₁₀ colony forming units (CFU) per milliliter. On average, ceftolozane/tazobactam, cefepime, ciprofloxacin, meropenem, tobramycin, and polymyxin B all demonstrated bactericidal activity. With all isolates taken into account, polymyxin B, tobramycin, meropenem, and ceftolozane/tazobactam 3 g were the most potent, with reductions in inoculum of 5.07 ± 0.45, 4.58 ± 2.2, 4.76 ± 0.71, and 4.17 ± 0.94 log₁₀ CFU/mL, respectively. Ceftolozane/tazobactam 1.5 g, cefepime, and ciprofloxacin reduced the starting inoculum by 3.74 ± 0.99, 3.42 ± 1.4, and 3.23 ± 2.0 log₁₀ CFU/mL, respectively. Despite 90% susceptibility, ceftazidime was bactericidal against seven of ten strains, with an average reduction in starting inoculum of 2.91 ± 2.2 log₁₀ CFU/mL.

CONCLUSION

Ceftolozane/tazobactam activity against MP strains derived from CF patients was comparable to that of standard-of-care agents at both the 1.5-g dose and the 3-g dose. Further in vitro modeling and clinical trials are warranted.

In Vitro Activity of Ceftolozane-Tazobactam against Multidrug-Resistant Nonfermenting Gram-Negative Bacilli Isolated from Patients with Cystic Fibrosis

Ceftolozane-tazobactam was tested against 58 multidrug-resistant nonfermenting Gram-negative bacilli (35 Pseudomonas aeruginosa, 11 Achromobacter xylosoxydans, and 12 Stenotrophomonas maltophilia isolates) isolated from cystic fibrosis patients and was compared to ceftolozane alone, ceftazidime, meropenem, and piperacillin-tazobactam. Ceftolozane-tazobactam was the most active agent against P. aeruginosa but was inactive against A. xylosoxydans and S. maltophilia In time-kill experiments, ceftolozane-tazobactam had complete bactericidal activity against 2/6 clinical isolates (33%).

In vitro Activity of Ceftolozane/Tazobactam Alone or with an Aminoglycoside Against Multi-Drug-Resistant Pseudomonas aeruginosa from Pediatric Cystic Fibrosis Patients

INTRODUCTION

Gram-negative multi-drug resistance is an emerging threat among pediatric patients with cystic fibrosis (CF). Ceftolozane/tazobactam (C/T) is an extended-spectrum cephalosporin/beta-lactamase inhibitor combination that has been shown to maintain activity against MDR P. aeruginosa isolates. The understanding of C/T effectiveness in pediatric patients is extremely limited. Minimum inhibitory concentration (MIC) testing and time-kill analyses were performed to better understand the antimicrobial susceptibility and potential role of C/T.

METHODS

Non-duplicate clinical respiratory MDR P. aeruginosa isolates (n = 5) from four pediatric CF patients were identified. MICs were determined for these isolates using CLSI broth microdilution methods. Time-kill analyses were performed using multiples of C/T alone, and combinations of C/T 2× and 8× the MIC with 30 mg/L tobramycin or 80 mg/L amikacin for all isolates. Cell counts were determined by serial dilution plating.

RESULTS

Isolates had variable susceptibilities to C/T (range 0.5-8 mg/L), tobramycin (range 2 to >64 mg/L) and amikacin (range 8 to >256 mg/L). Time-kill analyses revealed an average of 0.71 (range -0.6 to 4.4), 1.50 (range 0.8-2.0) and 2.1 (range 1.2-3.4) log-kill at 4×, 8× and 16× the C/T MIC, respectively. At a tobramycin MIC of 32 mg/L, combination therapy showed synergistic benefit when the isolate was C/T susceptible. C/T and amikacin combination therapy showed synergistic activity at an amikacin MIC >256 mg/L when C/T MIC was 2 mg/L (4.7 log-kill at 2× C/T MIC and 4.0 log-kill at 8× C/T MIC).

CONCLUSION

C/T appears to be a promising treatment option for treatment of MDR P. aeruginosa in pediatric CF patients, both alone and in combination with tobramycin or amikacin. Interestingly, the benefit of C/T combination therapy with amikacin may be more pronounced than with the addition of tobramycin. Further evaluation of such combination regimens in pediatric CF patients is warranted.

Population Pharmacokinetics and Safety of Ceftolozane-Tazobactam in Adult Cystic Fibrosis Patients Admitted with Acute Pulmonary Exacerbation

Ceftolozane-tazobactam has potent activity against Pseudomonas aeruginosa, a pathogen associated with cystic fibrosis (CF) acute pulmonary exacerbations (APE). Due to the rapid elimination of many antibiotics, CF patients frequently have altered pharmacokinetics. In this multicenter, open-label study, we described the population pharmacokinetics and safety of ceftolozane-tazobactam at 3 g every 8 h (q8h) in 20 adult CF patients admitted with APE. Population pharmacokinetics were determined using the nonparametric adaptive grid program in Pmetrics for R. A 5,000-patient Monte Carlo simulation was performed to determine the probability of target attainment (PTA) for the ceftolozane component at 1.5 g and 3 g of ceftolozane-tazobactam q8h across a range of MICs using a primary threshold exposure of 60% free time above the MIC (fT>MIC). In these 20 adult CF patients, ceftolozane and tazobactam concentration data were best described by 2-compartment models, and ceftolozane clearance (CL) was significantly correlated with creatinine clearance (r = 0.71, P < 0.001). These data suggest that ceftolozane and tazobactam clearance estimates in CF patients are similar to those in adults without CF (ceftolozane CF CL, 4.76 ± 1.13 liter/h; tazobactam CF CL, 20.51 ± 4.41 liter/h). However, estimates of the volume of the central compartment (Vc) were lower than those for adults without CF (ceftolozane CF Vc, 7.51 ± 2.05 liters; tazobactam CF Vc, 7.85 ± 2.66 liters). Using a threshold of 60% fT>MIC, ceftolozane-tazobactam regimens of 1.5 g and 3 g q8h should achieve PTAs of ≥90% at MICs up to 4 and 8 μg/ml, respectively. Ceftolozane-tazobactam at 3 g q8h was well tolerated. These observations support additional studies of ceftolozane-tazobactam for Pseudomonas aeruginosa APE in CF patients. (This study has been registered at ClinicalTrials.gov under identifier NCT02421120.).

Multidrug-Resistant Pseudomonas aeruginosa Infection in a Child with Cystic Fibrosis

We describe a pediatric cystic fibrosis patient who developed a pulmonary exacerbation due to two multidrug-resistant (MDR) Pseudomonas aeruginosa isolates. In addition to these MDR organisms, the case was further complicated by β-lactam allergy. Despite the MDR phenotype, both isolates were susceptible to an antimicrobial combination.

Combinatorial Pharmacodynamics of Ceftolozane-Tazobactam against Genotypically Defined β-Lactamase-Producing Escherichia coli: Insights into the Pharmacokinetics/Pharmacodynamics of β-Lactam-β-Lactamase Inhibitor Combinations

Despite a dearth of new agents currently being developed to combat multidrug-resistant Gram-negative pathogens, the combination of ceftolozane and tazobactam was recently approved by the Food and Drug Administration to treat complicated intra-abdominal and urinary tract infections. To characterize the activity of the combination product, time-kill studies were conducted against 4 strains ofEscherichia colithat differed in the type of β-lactamase they expressed. The four investigational strains included 2805 (no β-lactamase), 2890 (AmpC β-lactamase), 2842 (CMY-10 β-lactamase), and 2807 (CTX-M-15 β-lactamase), with MICs to ceftolozane of 0.25, 4, 8, and >128 mg/liter with no tazobactam, and MICs of 0.25, 1, 4, and 8 mg/liter with 4 mg/liter tazobactam, respectively. All four strains were exposed to a 6 by 5 array of ceftolozane (0, 1, 4, 16, 64, and 256 mg/liter) and tazobactam (0, 1, 4, 16, and 64 mg/liter) over 48 h using starting inocula of 10(6)and 10(8)CFU/ml. While ceftolozane-tazobactam achieved bactericidal activity against all 4 strains, the concentrations of ceftolozane and tazobactam required for a ≥3-log reduction varied between the two starting inocula and the 4 strains. At both inocula, the Hill plots (R(2)> 0.882) of ceftolozane revealed significantly higher 50% effective concentrations (EC50s) at tazobactam concentrations of ≤4 mg/liter than those at concentrations of ≥16 mg/liter (P< 0.01). Moreover, the EC50s at 10(8)CFU/ml were 2.81 to 66.5 times greater than the EC50s at 10(6)CFU/ml (median, 10.7-fold increase;P= 0.002). These promising results indicate that ceftolozane-tazobactam achieves bactericidal activity against a wide range of β-lactamase-producingE. colistrains.

Prescribing Ceftolozane/Tazobactam for Pediatric Patients: Current Status and Future Implications

Antibiotics are arguably the greatest medical development of the 20th century but these precious resources are being threatened by the continued rise in infections caused by multidrug-resistant bacteria. There is concern that we are on the precipice of a 'post-antibiotic era'. The situation is exacerbated by a stagnation in the pharmaceutical industry in developing new antibiotics, particularly those with activity against some of the most resistant Gram-negative organisms because of significant economic, scientific, and regulatory barriers. One of the products of recent initiatives to reinvigorate the antibiotic pipeline is the agent ceftolozane/tazobactam. Ceftolozane/tazobactam was approved in December 2014 by the US Food and Drug Administration for the treatment of complicated urinary tract infections and complicated intra-abdominal infections for patients 18 years of age and older. The safety and effectiveness of ceftolozane/tazobactam in pediatric patients has not been established in clinical studies. However, with the rise of highly drug-resistant Gram-negative organisms in children and the current climate of ongoing, multiple, and simultaneous antibiotic shortages--particularly of broad-spectrum antibiotics, the potential off-label role of ceftolozane/tazobactam for children needs to be explored while pediatric studies are ongoing. The objective of this opinion piece is to discuss what is currently known about ceftolozane/tazobactam and its potential implications for use in the pediatric population.

Impact of MIC range for Pseudomonas aeruginosa and Streptococcus pneumoniae on the ceftolozane in vivo pharmacokinetic/pharmacodynamic target

Ceftolozane is a novel cephalosporin with activity against drug-resistant pathogens, including Pseudomonas aeruginosa and Streptococcus pneumoniae. The in vivo investigation reported here tested the limits of this drug against 20 P. aeruginosa and S. pneumoniae isolates across a wide MIC range and defined resistance mechanisms. The times above the MIC (T>MIC) targets for stasis and 1- and 2-log reductions were 31%, 39%, and 42% for P. aeruginosa and 18%, 24%, and 27% for S. pneumoniae, respectively. The 1-log endpoint was achieved for strains with MICs as high as 16 μg/ml.

β-Lactam Antibiotics Renaissance

Since the 1940s β-lactam antibiotics have been used to treat bacterial infections. However, emergence and dissemination of β-lactam resistance has reached the point where many marketed β-lactams no longer are clinically effective. The increasing prevalence of multidrug-resistant bacteria and the progressive withdrawal of pharmaceutical companies from antibiotic research have evoked a strong reaction from health authorities, who have implemented initiatives to encourage the discovery of new antibacterials. Despite this gloomy scenario, several novel β-lactam antibiotics and β-lactamase inhibitors have recently progressed into clinical trials, and many more such compounds are being investigated. Here we seek to provide highlights of recent developments relating to the discovery of novel β-lactam antibiotics and β-lactamase inhibitors.

Pseudomonas aeruginosa ceftolozane-tazobactam resistance development requires multiple mutations leading to overexpression and structural modification of AmpC

We compared the dynamics and mechanisms of resistance development to ceftazidime, meropenem, ciprofloxacin, and ceftolozane-tazobactam in wild-type (PAO1) and mutator (PAOMS, ΔmutS) P. aeruginosa. The strains were incubated for 24 h with 0.5 to 64× MICs of each antibiotic in triplicate experiments. The tubes from the highest antibiotic concentration showing growth were reinoculated in fresh medium containing concentrations up to 64× MIC for 7 consecutive days. The susceptibility profiles and resistance mechanisms were assessed in two isolated colonies from each step, antibiotic, and strain. Ceftolozane-tazobactam-resistant mutants were further characterized by whole-genome analysis through RNA sequencing (RNA-seq). The development of high-level resistance was fastest for ceftazidime, followed by meropenem and ciprofloxacin. None of the mutants selected with these antibiotics showed cross-resistance to ceftolozane-tazobactam. On the other hand, ceftolozane-tazobactam resistance development was much slower, and high-level resistance was observed for the mutator strain only. PAO1 derivatives that were moderately resistant (MICs, 4 to 8 μg/ml) to ceftolozane-tazobactam showed only 2 to 4 mutations, which determined global pleiotropic effects associated with a severe fitness cost. High-level-resistant (MICs, 32 to 128 μg/ml) PAOMS derivatives showed 45 to 53 mutations. Major changes in the global gene expression profiles were detected in all mutants, but only PAOMS mutants showed ampC overexpression, which was caused by dacB or ampR mutations. Moreover, all PAOMS mutants contained 1 to 4 mutations in the conserved residues of AmpC (F147L, Q157R, G183D, E247K, or V356I). Complementation studies revealed that these mutations greatly increased ceftolozane-tazobactam and ceftazidime MICs but reduced those of piperacillin-tazobactam and imipenem, compared to those in wild-type ampC. Therefore, the development of high-level resistance to ceftolozane-tazobactam appears to occur efficiently only in a P. aeruginosa mutator background, in which multiple mutations lead to overexpression and structural modifications of AmpC.

Ceftolozane/tazobactam: a novel antipseudomonal cephalosporin and β-lactamase-inhibitor combination

The management of infections caused by multidrug-resistant Gram-negative bacteria, particularly Pseudomonas aeruginosa, continues to be a significant challenge to clinicians. Ceftolozane/tazobactam is a novel antibacterial and β-lactamase-inhibitor combination that has shown appreciable activity against wild-type Enterobacteriaceae and potent activity against P. aeruginosa. Moreover, ceftolozane/tazobactam has not demonstrated cross-resistance to other antimicrobial classes, particularly those affected by extended-spectrum β-lactamases, AmpC β-lactamase, a loss in porin channels, or the overexpression of efflux pumps in P. aeruginosa. Ceftolozane/tazobactam has completed two Phase II clinical trials in complicated intra-abdominal and complicated urinary tract infections. A Phase III, multicenter, prospective, randomized, open-label study has been initiated to evaluate the safety and efficacy of ceftolozane/tazobactam versus piperacillin/tazobactam for the treatment of ventilator-associated pneumonia. A Medline search of articles from inception to May 2013 and references for selected citations was conducted. Data from abstracts presented at conferences were also appraised. This article reviews the antimicrobial, pharmacokinetic, and pharmacodynamic profile of ceftolozane/tazobactam, and discusses its potential role in therapy.

Pharmacokinetics and pharmacodynamics of once-daily administration of intravenous tobramycin in adult patients with cystic fibrosis hospitalized for an acute pulmonary exacerbation

The serum pharmacokinetic profile of intravenous (i.v.) tobramycin administration was characterized for a sample of nine adult patients with cystic fibrosis (CF) who were hospitalized for an acute pulmonary exacerbation. Current recommended i.v. tobramycin dosing protocols are predicted through modeling and simulation to be suboptimal. Empirical tobramycin regimens of ≥15 mg/kg of body weight administered i.v. once daily should be evaluated for adult patients with CF to optimize outcomes.

Affinity of the new cephalosporin CXA-101 to penicillin-binding proteins of Pseudomonas aeruginosa

CXA-101, previously designated FR264205, is a new antipseudomonal cephalosporin. The objective of this study was to determine the penicillin-binding protein (PBP) inhibition profile of CXA-101 compared to that of ceftazidime (PBP3 inhibitor) and imipenem (PBP2 inhibitor). Killing kinetics, the induction of AmpC expression, and associated changes on cell morphology were also investigated. The MICs for CXA-101, ceftazidime, and imipenem were 0.5, 1, and 1 microg/ml, respectively. Killing curves revealed that CXA-101 shows a concentration-independent bactericidal activity, with concentrations of 1x the MIC (0.5 microg/ml) producing a > 3-log reduction in bacterial load after 8 h of incubation. Live-dead staining showed that concentrations of CXA-101 as low as 0.5x the MIC stopped bacterial septation and induced an intense filamentation, which is consistent with the documented high affinity of PBP3. CXA-101 was found to be a potent PBP3 inhibitor and showed affinities > or = 2-fold higher than those of ceftazidime for all of the essential PBPs (1b, 1c, 2, and 3). Compared to imipenem, in addition to the obvious inverse PBP2/PBP3 affinities, CXA-101 showed a significantly higher affinity for PBP1b but a lower affinity for PBP1c. Furthermore, CXA-101, like ceftazidime and in contrast to imipenem, was found to be a very weak inducer of AmpC expression, consistent with the low PBP4 affinity documented.