Cefiderocol for the Treatment of Adult and Pediatric Patients With Cystic Fibrosis and Achromobacter xylosoxidans Infections

In vitro activity of cefiderocol against Gram-negative pathogens isolated from people with cystic fibrosis and bronchiectasis

OBJECTIVES

Gram-negative pathogens causing respiratory infection in people with cystic fibrosis and bronchiectasis are becoming progressively more resistant to conventional antibiotics. Although cefiderocol is licenced for the treatment of infections due to Gram-negative organisms, there are limited data on the activity of cefiderocol against pathogens associated with chronic respiratory diseases. The aim of this study was to determine the susceptibility of Gram-negative pathogens from cystic fibrosis and bronchiectasis to cefiderocol and comparator antibiotics.

METHODS

Minimal inhibitory concentrations (MICs) of cefiderocol and 15 comparator antibiotics were determined by broth microdilution against 300 respiratory isolates: Burkholderia spp., Stenotrophomonas spp., Achromobacter spp., Ralstonia spp. and Pandoraea spp., and used to calculate the MIC of each antibiotic required to inhibit 50% (MIC50) and 90% (MIC90) of isolates.

RESULTS

The MIC50 and MIC90 of cefiderocol for all 300 isolates tested was 0.25 and 32 mg/L, with 232 (77.3%) isolates having an MIC value ≤2 mg/L. In addition, cefiderocol demonstrated excellent activity against Stenotrophomonas spp. and Achromobacter spp. isolates, with 86.7% and 87.2%, respectively, exhibiting an MIC of 2 mg/L. Tigecycline also demonstrated good activity against all isolates with an MIC50 of <0.5 mg/L.

CONCLUSIONS

These in vitro data demonstrated that cefiderocol had greater activity than most comparator antibiotics and could be an alternative treatment option for respiratory infection caused by these pathogens that has not responded to first-line therapy.

Novel Approaches to Multidrug-Resistant Infections in Cystic Fibrosis

Patients with cystic fibrosis (CF) often develop respiratory tract infections with pathogenic multidrug-resistant organisms (MDROs) such as methicillin-resistant Staphylococcus aureus, and a variety of gram-negative organisms that include Pseudomonas aeruginosa, Burkholderia sp., Stenotrophomonas maltophilia, Achromobacter xylosoxidans, and nontuberculous mycobacteria (NTM). Despite the introduction of new therapies to address underlying cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction, MDRO infections remain a problem and novel antimicrobial interventions are still needed. Therapeutic approaches include improving the efficacy of existing drugs by adjusting the dose based on differences in CF patient pharmacokinetics/pharmacodynamics, the development of inhaled formulations to reduce systemic adverse events, and the use of newer beta-lactam/beta-lactamase combinations. Alternative innovative therapeutic approaches include the use of gallium and bacteriophages to treat MDRO pulmonary infections including those with extreme antibiotic resistance. However, additional clinical trials are required to determine the optimal dosing and efficacy of these different strategies and to identify patients with CF most likely to benefit from these new treatment options.

Performance evaluation of Bruker UMIC® microdilution panel and disc diffusion to determine cefiderocol susceptibility in Enterobacterales, Acinetobacter baumannii, Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Achromobacter xylosoxidans and Burkolderia species

PURPOSE

Cefiderocol susceptibility testing (AST) represents an open challenge for clinical microbiology. Herein, we evaluated the performance of the UMIC® Cefiderocol broth microdilution (BMD) test and disc diffusion on Gram-negative species.

METHODS

UMIC® Cefiderocol BMD test, disc diffusion and reference BMD were in parallel performed on a collection of 256 clinical isolates. Categorical agreement (CA), essential agreement (EA), bias, major errors (MEs) and very major errors (VMEs) were calculated for both AST methods.

RESULTS

The UMIC® Cefiderocol BMD strip exhibited an EA < 90% (85.5%), a CA higher than 90% (93.7%) and a low number of VMEs (n = 4, 4.2%) and MEs (n = 12, 7.4%). UMIC® Cefiderocol identified 96.2% of the resistant isolates [Enterobacterales, (39/40); P. aeruginosa (19/19); A. xylosoxidans (5/6); S. maltophilia (5/6); Burkholderia spp. (8/8)]. Disc diffusion showed a high CA (from 94.9 to 100%) regardless of disc manufacturer in Enterobacterales, P. aeuroginosa, A. baumannii and S. maltophilia. However, high rates of results falling in the area of technical uncertainty (ATU) were observed in Enterobacterales (34/90, 37.8%) and P. aeruginosa (16/40, 40%). Disc diffusion showed a poor performance in A. xylosoxidans and Burkholderia spp. if PK/PD breakpoint was used (overall, 5/9 VMEs; in contrast, the use of P. aeruginosa-specific breakpoints resulted in 100% of CA with 24.6% of results in the ATU).

CONCLUSION

In conclusion, disc diffusion and UMIC® Cefiderocol are valid methods for the determination of cefiderocol susceptibility. Given the high number of results in the ATU by disc diffusion, a combined use of both AST methods may represent a solution to overcome the challenge of cefiderocol susceptibility testing in routine microbiology laboratories.

In vitro and in vivo activity of cefiderocol against Achromobacter spp. and Burkholderia cepacia complex, including carbapenem-non-susceptible isolates

Achromobacter spp. and Burkholderia cepacia complex (Bcc) are rare but diverse opportunistic pathogens associated with serious infections, which are often multidrug resistant. This study compared the in vitro antibacterial activity of the siderophore antibiotic cefiderocol against Achromobacter spp. and Bcc isolates with that of other approved antibacterial drugs, including ceftazidime-avibactam, ciprofloxacin, colistin, imipenem-relebactam, and meropenem-vaborbactam. Isolates were collected in the SIDERO multinational surveillance program. Among 334 Achromobacter spp. isolates [76.6% from respiratory tract infections (RTIs)], cefiderocol had minimum inhibitory concentration (MIC)50/90 of 0.06/0.5 µg/mL overall and 0.5/4 µg/mL against 52 (15.6%) carbapenem-non-susceptible (Carb-NS) isolates. Eleven (3.3%) Achromobacter spp. isolates overall and 6 (11.5%) Carb-NS isolates were not susceptible to cefiderocol. Among 425 Bcc isolates (73.4% from RTIs), cefiderocol had MIC50/90 of ≤0.03/0.5 µg/mL overall and ≤0.03/1 µg/mL against 184 (43.3%) Carb-NS isolates. Twenty-two (5.2%) Bcc isolates overall and 13 (7.1%) Carb-NS isolates were not susceptible to cefiderocol. Cumulative MIC distributions showed cefiderocol to be the most active of the agents tested in vitro against both Achromobacter spp. and Bcc. In a neutropenic murine lung infection model and a humanized pharmacokinetic immunocompetent rat lung infection model, cefiderocol showed significant bactericidal activity against two meropenem-resistant Achromobacter xylosoxidans strains compared with untreated controls (P < 0.05) and vehicle-treated controls (P < 0.05), respectively. Meropenem, piperacillin-tazobactam, ceftazidime, and ciprofloxacin comparators showed no significant activity in these models. The results suggest that cefiderocol could be a possible treatment option for RTIs caused by Achromobacter spp. and Bcc.

Successful Use of Cefiderocol to Treat a Multidrug-resistant Stenotrophomonas maltophilia Ventilator-associated Pneumonia in an Extremely Preterm Neonate

BACKGROUND

Ventilator-associated pneumonia (VAP) caries a morbidity and mortality risk in the preterm neonate, particularly in the context of rising global antimicrobial resistance driving infections due to multidrug-resistant Gram-negative bacteria. Cefiderocol, a siderophilic cephalosporin, has broad Gram-negative antimicrobial activity and central nervous system penetration and is used for the treatment of hospital-acquired pneumonia or VAP in adults. Scarce data exists on its use in neonates.

CASE

A female neonate born at 26 + 6 weeks developed VAP at 21 days of life. She was commenced on corticosteroids, vancomycin and ceftazidime but continued to deteriorate. Sputum cultures yielded Stenotrophomonas maltophilia resistant to trimethoprim/sulfamethoxazole, ciprofloxacin and ceftazidime, with potential susceptibility to cefiderocol. Cerebrospinal fluid showed an elevated white cell count. In view of worsening respiratory and hemodynamic status, antibiotic treatment was changed to cefiderocol monotherapy at 30 mg/kg/dose every 8 hours. Within 72 hours of commencing cefiderocol, the neonate was successfully extubated to variable-flow continuous positive airway pressure and showed ongoing clinical improvement.

CONCLUSIONS

Cefiderocol was integral for the care of our neonate without any immediate adverse safety consequences. We relied on dosing data from a conference abstract, due to the paucity of evidence on the use of novel antimicrobials. This lack of evidence is particularly concerning given preterm neonates are particularly vulnerable to infections with multidrug-resistant Gram-negative organisms due to their immature immune systems, prolonged hospital stay, repeated interventions and antimicrobial exposure.

Treatment of Resistant Gram-negative bacilli in children

Resistance of Gram-negative bacteria to the most widely used antibiotics, particularly β-lactams, is now considered as major public health problem. The main resistance mechanisms to β-lactams in Enterobacterales are the production of extended spectrum β-lactamases (ESBL) or carbapenemases, which hydrolyze virtually all β-lactams. However, a substantial proportion of carbapenem-resistant Gram-negative bacilli do not produce carbapenemase but combine overproduction of a cephalosporinase and/or ESBL with very low penem hydrolysis and reduced outer membrane permeability. The arrival of new antibacterial agents active on some of these multidrug-resistant strains, such as new β-lactam inhibitors, has marked a turning point in treatment and represents real progress. In-depth knowledge of resistance mechanisms is crucial to the choice of the most effective molecule, and their prescription requires close collaboration between microbiologists, infectious disease specialists and intensive care physicians. While these compounds are significantly more active against resistant strains than those previously available, their spectrum of activity does not cover all resistance mechanisms in Gram-negatives, nor in other bacterial species potentially involved in polymicrobial infections. The use of these new compounds does not alter antibiotic regimens in terms of duration and indication of combined antibiotic therapy, which remain very limited.

An Overview of Cefiderocol's Therapeutic Potential and Underlying Resistance Mechanisms

Antimicrobial resistance continues to increase globally and treatment of difficult-to-treat (DTT) infections, mostly associated with carbapenem-resistant (CR) Pseudomonas aeruginosa, CR Acinetobacter baumannii, and CR- and third-generation-cephalosporins-resistant Enterobacterales remains a challenge for the clinician. The recent approval of cefiderocol has broaden the armamentarium for the treatment of patients with DTT infections. Cefiderocol is a siderophore cephalosporin that has shown excellent antibacterial activity, in part due to its innovative way of cell permeation. It is relatively stable compared to most commonly found carbapenamases. However, some resistant mechanisms to cefiderocol have already been identified and reduced susceptibility has developed during patient treatment, highlighting that the clinical use of cefiderocol must be rational. In this review, we summarize the current available treatments against the former resistant bacteria, and we revise and discuss the mechanism of action of cefiderocol, underlying the biological function of siderophores, the therapeutic potential of cefiderocol, and the mechanisms of resistance reported so far.

New Antimicrobials for the Treatment of Neonatal Sepsis Caused by Multi-Drug-Resistant Bacteria: A Systematic Review

BACKGROUND

Infections by multi-drug-resistant (MDR) organisms are sharply increasing in newborns worldwide. In low and middle-income countries, a disproportionate amount of neonatal sepsis caused by MDR Gram negatives was recently reported. Newborns with infections by MDR organisms with limited treatment options may benefit from novel antimicrobials.

METHODS

We performed a literature search investigating the use in newborns, infants and children of novel antimicrobials for the treatment of MDR Gram negatives, namely ceftazidime/avibactam, ceftolozane/tazobactam, cefiderocol, meropenem/vaborbactam, imipenem/relebactam, and Gram positives with resistance of concern, namely ceftaroline and dalbavancin. PubMed, EMBASE, and Web of Science were searched.

RESULTS

A total of 50 records fulfilled the inclusion criteria. Most articles were case reports or case series, and ceftazidime/avibactam was the most studied agent. All studies showed favorable efficacy and safety profile in newborns and across different age cohorts.

CONCLUSIONS

novel antibiotics may be considered in newborns for the treatment of MDR Gram negatives with limited treatment options and for Gram positives with resistance concerns. Further studies are needed to address their effectiveness and safety in newborns.

Antimicrobial Strategies for Cystic Fibrosis

Lung infection is the leading cause of death in cystic fibrosis (CF), and antimicrobial therapies are the backbone of infection management. While many different strategies may be applied, rigorous microbiological surveillance, intensive eradication therapy, and long-term maintenance therapy based on inhaled antibiotics may be considered the main strategy for infection control in individuals with CF. While most of the existing evidence is based on infection with Pseudomonas aeruginosa, other important pathogens causing lung inflammation and deterioration exist and should be treated despite the evidence gap. In this chapter, we describe the approaches to the antimicrobial treatment of the most important pathogens in CF and the evidence behind.

Microbial Epidemiology of the Cystic Fibrosis Airways: Past, Present, and Future

Progressive obstructive lung disease secondary to chronic airway infection, coupled with impaired host immunity, is the leading cause of morbidity and mortality in cystic fibrosis (CF). Classical pathogens found in the airways of persons with CF (pwCF) include Pseudomonas aeruginosa, Staphylococcus aureus, the Burkholderia cepacia complex, Achromobacter species, and Haemophilus influenzae. While traditional respiratory-tract surveillance culturing has focused on this limited range of pathogens, the use of both comprehensive culture and culture-independent molecular approaches have demonstrated complex highly personalized microbial communities. Loss of bacterial community diversity and richness, counteracted with relative increases in dominant taxa by traditional CF pathogens such as Burkholderia or Pseudomonas, have long been considered the hallmark of disease progression. Acquisition of these classic pathogens is viewed as a harbinger of advanced disease and postulated to be driven in part by recurrent and frequent antibiotic exposure driven by frequent acute pulmonary exacerbations. Recently, CF transmembrane conductance regulator (CFTR) modulators, small molecules designed to potentiate or restore diminished protein levels/function, have been successfully developed and have profoundly influenced disease course. Despite the multitude of clinical benefits, structural lung damage and consequent chronic airway infection persist in pwCF. In this article, we review the microbial epidemiology of pwCF, focus on our evolving understanding of these infections in the era of modulators, and identify future challenges in infection surveillance and clinical management.

Real-Life Data on the Effectiveness and Safety of Cefiderocol in Severely Infected Patients: A Case Series

INTRODUCTION

Real-life data about cefiderocol use to treat extensively drug-resistant bacteria are scarce. We aim to report our early experience in patients with difficult-to-treat infections and limited therapeutic options.

METHODS

Patients treated with cefiderocol from March 2018 to April 2022 in a tertiary-care hospital in Spain were included. Demographic, clinical, and microbiological data were collected up to 90 days after the end of treatment or until death. Survival status was recorded at 30 and 90 days.

RESULTS

Ten patients were included, seven of them critically ill. Ventilator-associated pneumonia (40%) and bacteremia (40%) were the main infections. Multidrug-resistant or extensively drug-resistant P. aeruginosa was the most frequently isolated pathogen (70%, of which six patients were infected with bacteria with difficult-to-treat resistance), followed by A. baumannii, E. coli, and A. xylosoxidans (10% each). Seven patients received combination therapy. Clinical and microbiological cures were achieved in 90% and 80% of patients, respectively. Two previously susceptible strains (20%) developed resistance to cefiderocol. Overall, 30-day and 90-day mortality rates were 10% and 50%, respectively, although two out of five patients died due to the infection. No serious adverse events were reported, except for one patient who developed thrombocytopenia.

CONCLUSION

Cefiderocol seems to be an effective and safe rescue therapy for patients infected with difficult-to-treat pathogens, although there is a definite risk of the emergence of resistance.

The Role of MMPs in the Era of CFTR Modulators: An Additional Target for Cystic Fibrosis Patients?

Cystic fibrosis (CF) is a high-prevalence disease characterized by significant lung remodeling, responsible for high morbidity and mortality worldwide. The lung structural changes are partly due to proteolytic activity associated with inflammatory cells such as neutrophils and macrophages. Matrix metalloproteases (MMPs) are the major proteases involved in CF, and recent literature data focused on their potential role in the pathogenesis of the disease. In fact, an imbalance of proteases and antiproteases was observed in CF patients, resulting in dysfunction of protease activity and loss of lung homeostasis. Currently, many steps forward have been moved in the field of pharmacological treatment with the recent introduction of triple-combination therapy targeting the CFTR channel. Despite CFTR modulator therapy potentially being effective in up to 90% of patients with CF, there are still patients who are not eligible for the available therapies. Here, we introduce experimental drugs to provide updates on therapy evolution regarding a proportion of CF non-responder patients to current treatment, and we summarize the role of MMPs in pathogenesis and as future therapeutic targets of CF.

Novel Approaches to Multidrug-Resistant Infections in Cystic Fibrosis

Patients with cystic fibrosis (CF) often develop respiratory tract infections with pathogenic multidrug-resistant organisms (MDROs) such as methicillin-resistant Staphylococcus aureus, and a variety of gram-negative organisms that include Pseudomonas aeruginosa, Burkholderia sp., Stenotrophomonas maltophilia, Achromobacter xylosoxidans, and nontuberculous mycobacteria (NTM). Despite the introduction of new therapies to address underlying cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction, MDRO infections remain a problem and novel antimicrobial interventions are still needed. Therapeutic approaches include improving the efficacy of existing drugs by adjusting the dose based on differences in CF patient pharmacokinetics/pharmacodynamics, the development of inhaled formulations to reduce systemic adverse events, and the use of newer beta-lactam/beta-lactamase combinations. Alternative innovative therapeutic approaches include the use of gallium and bacteriophages to treat MDRO pulmonary infections including those with extreme antibiotic resistance. However, additional clinical trials are required to determine the optimal dosing and efficacy of these different strategies and to identify patients with CF most likely to benefit from these new treatment options.

Comparative analysis of microbial communities in different growth stages of Dermacentor nuttalli

Ticks were identified as arthropods that are pathogenic vectors. Dermacentor nuttalli is one of the dominant tick species in Inner Mongolia, and it carries and transmits a wide range of pathogenic microorganisms. However, at present, only the detection of D. nuttalli adult ticks and D. nuttalli different developmental stages carrying one specific pathogen, or the next-generation sequencing of D. nuttalli adult ticks were available. In this study, we investigated the microbial community structures of D. nuttalli in different growth stages under laboratory artificial feeding conditions. Total DNA was extracted from seven growth stages (female adult ticks, eggs, larval ticks, engorged larval ticks, nymphal ticks, engorged nymphal ticks, and second-generation adult ticks) obtained from laboratory artificial feeding of engorged D. nuttalli female ticks in Inner Mongolia. Then, the 16S rDNA V3-V4 hypervariable region was amplified to construct an Illumina PE250 library. Finally, 16S rRNA sequencing was performed on Illumina Novaseq 6000 platform. The sequencing data were analyzed using molecular biology software and platforms. The Illumina PE250 sequencing results showed that the egg stage had the highest diversity and number of species (28.74%, 98/341), while the engorged nymph stage had the lowest diversity and number of species (9.72%, 21/216). A total of 387 genera of 22 phyla were annotated in D. nuttalli, with 9 phyla and 57 genera found throughout all 7 growth stages. The dominant phylum was Proteobacteria; the dominant genera were Arsenophonus and Rickettsia; and the genera with the highest relative abundance in the 7 growth stages were Pseudomonas, Paenalcaligenes, Arsenophonus, Arsenophonus, Pseudomonas, Arsenophonus, and Rickettsia, respectively. Among the 23 exact species annotated, Brucella melitensis exhibits pathogeny that poses a serious threat to humans and animals. In this study, the microbial community composition at different growth stages of D. nuttalli was comprehensively analyzed for the first time.

Cefiderocol to manage chronic, multi-drug-resistant Burkholderia cepacia complex infection in a patient with cystic fibrosis: a case report

In cystic fibrosis (CF) patients, Gram-negative Burkholderia cepacia complex (Bcc) infections are associated with recurrent pulmonary exacerbations. Bcc organisms are innately resistant to many antibiotics, and infection with B. cenocepacia is a contraindication to lung transplantation. We report a CF patient with severe lung disease, colonized with Bcc, with a history of around nine exacerbations per year for over 10 years, for whom antibiotic regimens (including targeted and broad-spectrum antibiotics) had not cleared infection or extended the interval between exacerbations. After receiving a 2 week cefiderocol-containing regimen, the patient remained stable for more than 5 months without the need for additional antibiotics or hospital admissions for respiratory exacerbations.

Safety and efficacy of cefiderocol for off-label treatment indications: A systematic review

PURPOSE

Cefiderocol is a siderophore cephalosporin recently approved by the United States Food and Drug Administration for the treatment of hospital- and ventilator-acquired bacterial pneumonia and complicated urinary tract infections. However, there is potential for cefiderocol utility for a variety of other infections. The purpose of this systematic review was to identify literature examining the safety and efficacy of cefiderocol for off-label indications.

METHODS

The PRISMA guidelines were utilized for reporting. Databases searched included PubMed, Scopus, and Embase, from inception to September 2021. Manuscripts describing cefiderocol off-label use in clinical settings were included. Exclusion criteria were studies focused on labeled indications, animal studies, pharmacodynamic/pharmacokinetic studies, in vitro or laboratory studies, and manuscripts in languages other than English or Arabic. Each stage of review utilized two independent investigators, with conflicts resolved and critical appraisal performed. Data regarding presentation, clinical course, and infection characteristics were extracted and descriptively analyzed.

RESULTS

The search identified a total of 985 records, narrowed to a final set of 27 studies. Among studies included were 18 (66.7%) case reports, 8 (29.6%) case series, and 1 (3.7%) phase 3 clinical trial. Cefiderocol was most frequently used off-label for bacteremia/sepsis with or without an identified source in 51 (67.1%) out of a total of 76 included patients. Among case series/reports with available data, 43 of 53 patients (81.1%) received combination antibiotic therapy. The most common pathogens identified included multi/extensively drug-resistant Pseudomonas aeruginosa and/or Acinetobacter baumannii. Various clinical end points were reported, while microbiological end points were reported in 18 (66.7%) studies. Cefiderocol-related side effects were uncommon and rarely use-limiting.

CONCLUSIONS

This systematic review depicts relative clinical effectiveness of off-label cefiderocol, most commonly for P. aeruginosa and A. baumannii infections as combination antibiotic therapy. Further study is needed to elucidate the safety and efficacy of cefiderocol across an expanded set of patients and indications.

Cefiderocol for the Treatment of Multidrug-Resistant Gram-Negative Bacteria: A Systematic Review of Currently Available Evidence

Cefiderocol is a novel synthetic siderophore-conjugated antibiotic that hijacks the bacterial iron transport systems facilitating drug entry into cells, achieving high periplasmic concentrations. This systematic review analyzed the currently available literature on cefiderocol. It summarized in vitro susceptibility data, in vivo antimicrobial activity, pharmacokinetics/pharmacodynamics (PK/PD), clinical efficacy, safety and resistance mechanisms of cefiderocol. Cefiderocol has potent in vitro and in vivo activity against multidrug-resistant (MDR) Gram-negative bacteria, including carbapenem-resistant isolates. But New Delhi Metallo-β-lactamase (NDM)- positive isolates showed significantly higher MICs than other carbapenemase-producing Enterobacterales, with a susceptible rate of 83.4% for cefiderocol. Cefiderocol is well-tolerated, and the PK/PD target values can be achieved using a standard dose regimen or adjusted doses according to renal function. Clinical trials demonstrated that cefiderocol was non-inferiority to the comparator drugs in treating complicated urinary tract infection and nosocomial pneumonia. Case reports and series showed that cefiderocol was a promising therapeutic agent in carbapenem-resistant infections. However, resistant isolates and reduced susceptibility during treatment to cefiderocol have already been reported. In conclusion, cefiderocol is a promising powerful weapon for treating MDR recalcitrant infections.

The indispensable role of pharmacy services and medication therapy management in cystic fibrosis

Care for people with cystic fibrosis (PWCF) is highly complex and requires a multidisciplinary approach where the pharmacist plays a vital role. The purpose of this manuscript is to serve as a guideline for pharmacists and pharmacy technicians who provide care for PWCF by providing background and current recommendations for the use of cystic fibrosis (CF)-specific medications in both the acute and ambulatory care settings. The article explores current literature surrounding the role of pharmacists and pharmacy technicians, proven pharmacy models to emulate, and pharmacokinetic idiosyncrasies unique to the CF population while also identifying areas of future research. Clinical recommendations for the use of CF-specific medications are broken down by organ system including mechanism of action, adverse events, dosages, and monitoring parameters. The article also includes quick reference tables essential to the acute and chronic medication therapy management of PWCF.

Role of AxyABM overexpression in acquired resistance in Achromobacter xylosoxidans

BACKGROUND

Acquired antimicrobial resistance among Achromobacter isolates from cystic fibrosis (CF) patients is frequent. Data concerning the mechanisms involved are scarce. The role of the AxyXY-OprZ and AxyEF-OprN Resistance Nodulation Division (RND) efflux systems has been demonstrated, but not that of AxyABM.

OBJECTIVES

To explore the role of efflux systems in the acquired multiresistance observed in a one-step mutant selected after ofloxacin exposure.

METHODS

The in vitro resistant mutant NCF-39-Bo2 and its parental strain NCF-39 (MICs of meropenem of 8 and 0.19 mg/L, of ceftazidime of 12 and 3 mg/L, of cefiderocol of 0.094 and 0.032 mg/L and of ciprofloxacin of 8 and 1.5 mg/L, respectively) were investigated by RNA-seq and WGS. Gene inactivation and reverse transcription quantitative PCR (RT-qPCR) were used to explore the role of the efflux systems of interest.

RESULTS

RNA-seq showed that the AxyABM efflux system was overproduced (about 40-fold) in the in vitro mutant NCF-39-Bo2 versus its parental strain NCF-39. A substitution in AxyR, the putative regulator of AxyABM, was detected in NCF-39-Bo2. Gene inactivation of axyB (encoding the transporter component) in NCF-39-Bo2 led to a decrease in MICs of ciprofloxacin (5-fold), meropenem (64-fold), ceftazidime (12-fold) and cefiderocol (24-fold). Inactivation of axyB in the clinical isolate AXX-H2 harbouring a phenotype of resistance close to that of NCF-39-Bo2 enhanced the activity of the same molecules, especially meropenem.

CONCLUSIONS

AxyABM overproduction is involved in acquired resistance of Achromobacter to ciprofloxacin, meropenem and ceftazidime, antibiotics widely used in CF patients, and increases the MIC of the new promising antibiotic cefiderocol.

Pharmacokinetics/Pharmacodynamics and tolerability of cefiderocol in the clinical setting

Cefiderocol is a new cephalosporin with a catechol in its chemical structure faciliting its access to the interior of bacteria through iron channels. In addition, it is broadly stable to beta-lactamases. The pharmacokinetic profile is a beta-lactam one: no oral absorption, and with a wide distribution within the vascular space and the interstitial fluid of well vascularized tissues, reaching therapeutic concentrations in the alveolar lavage fluid and within the macrophage. The binding of cefiderocol to human plasma proteins, primarily albumin, is moderate (range 40-60%). The terminal elimination half-life in healthy adult subjects was 2 to 3 hours. Cefiderocol is mainly renally eliminated, so dose adjustments are recommended in subjects with moderate / severe renal impairment, in case of dialysis, and probably in patients with external clearance. Like other beta-lactams, the PK / PD parameter that has been shown to best correlate with efficacy is the efficacy time of unbound plasma concentrations (%fT>MIC), which must be close to 100% to achieve a bactericidal effect. This is possible with 2 g in a 3-hour infusion every 8 hours. In controlled trials appears to be well tolerated, similar to comparators: meropenem or imipenem-cilastatin. Cefiderocol has no apparent clinically significant effect on ECG parameters nor on plasma iron values.

Clinical experience of cefiderocol

Infections by antibiotic-resistant microorganisms could be considered a "stealth pandemic" that we fight daily in most hospitals. Some estimates suggest that today 700,000 deaths per year can be attributed to antimicrobial resistance. By the year 2050, it is estimated that this will increase to ten million deaths per year as a result of infections by multidrug-resistant microorganisms. In this context, the availability of antimicrobial therapy that is effective against these pathogens is essential to be able to "save the lives" of our patients. Cefiderocol, a new cephalosporin with a different mechanism of action, will be an essential treatment in many infections caused by resistant aerobic gram-negative bacteria. Cefiderocol has been used to treat patients with complicated urinary tract infections (cUTI); hospital-acquired pneumonia (HAP), ventilator-associated pneumonia (VAP), healthcare-associated pneumonia (HAP); in patients with sepsis and bacteremia, some without an identified primary focus of infection.

Clinical Pharmacokinetics and Pharmacodynamics of Cefiderocol

Cefiderocol is a new broad-spectrum cephalosporin antibiotic with promising activity against various Gram-negative bacteria including carbapenem-resistant strains. A chlorocatechol group in the C-3 side chain provides cefiderocol with a siderophore activity, improving its stability against β-lactamases and facilitating the transportation of cefiderocol across outer bacterial membranes. Cefiderocol shows linear pharmacokinetics over a broad range of clinically relevant doses, with unchanged renal excretion constituting the main route of elimination. Geometric means (coefficient of variation) of the volume of distribution and clearance in individuals with normal kidney function were 15.8 (15%) L and 4.70 (27%) L/h, respectively. In patients with end-stage renal disease, clearance was 1.10 (24%) L/h. Time above the minimum inhibitory concentration is the main predictor of efficacy. There is no evidence for clinically relevant interactions of cefiderocol with other drugs mediated by metabolizing enzymes or drug transporters. Simulations based on population pharmacokinetic modeling suggest that dosing regimens should be adjusted based on kidney function to optimize therapeutic exposure to cefiderocol. Clinical efficacy trials indicated that cefiderocol is non-inferior to imipenem/cilastatin in the treatment of complicated urinary tract infections and acute uncomplicated pyelonephritis, and to meropenem in the treatment of nosocomial pneumonia. In the one study currently available, cefiderocol performed similarly to the best available therapy in the treatment of severe carbapenem-resistant Gram-negative infections regarding clinical and microbiological efficacy. In summary, cefiderocol shows favorable pharmacokinetic/pharmacodynamic properties and an acceptable safety profile, suggesting that cefiderocol might be a viable option to treat infections with bacteria resistant to other antibiotics.

In Vitro Activity of 22 Antibiotics against Achromobacter Isolates from People with Cystic Fibrosis. Are There New Therapeutic Options?

Bacteria belonging to the genus Achromobacter are increasingly isolated from respiratory samples of people with cystic fibrosis (PWCF). The management of this multidrug-resistant genus is challenging and characterised by a lack of international recommendations, therapeutic guidelines and data concerning antibiotic susceptibility, especially concerning the newer antibiotics. The objective of this study was to describe the antibiotic susceptibility of Achromobacter isolates from PWCF, including susceptibility to new antibiotics. The minimum inhibitory concentrations (MICs) of 22 antibiotics were determined for a panel of 23 Achromobacter isolates from 19 respiratory samples of PWCF. Two microdilution MIC plates were used: EUMDROXF^® plate (Sensititre) and Micronaut-S Pseudomonas MIC^® plate (Merlin) and completed by a third method if necessary (E-test^® or UMIC^®). Among usual antimicrobial agents, the most active was imipenem (70% susceptibility). Trimethoprim-sulfamethoxazole, piperacillin and tigecycline (65%, 56% and 52% susceptibility, respectively) were still useful for the treatment of Achromobacter infections. Among new therapeutic options, β-lactams combined with a β-lactamase-inhibitor did not bring benefits compared to β-lactam alone. On the other hand, cefiderocol appeared as a promising therapeutic alternative for managing Achromobacter infections in PWCF. This study provides the first results on the susceptibility of clinical Achromobacter isolates concerning new antibiotics. More microbiological and clinical data are required to establish the optimal treatment of Achromobacter infections.

Optimization of antibiotics for cystic fibrosis pulmonary exacerbations due to highly resistant nonlactose fermenting Gram negative bacilli: Meropenem-vaborbactam and cefiderocol

We are writing this letter to provide an update of published information on antibiotics for cystic fibrosis (CF) pulmonary exacerbations to the State of the Art articles by Zobell et al. Information on meropenem-vaborbactam and cefiderocol were not available when the original articles were published. These new antibiotics, approved in 2017 and 2019, possess antipseudomonal properties like the other carbapenems and cephalosporins in the original articles however, existing literature refers to their use for other less common bacteria. As patients with CF age, the microorganisms in their bacterial cultures change and some can colonize multiple or uncommon bacterial species including, Burkholderia, Achromobacter, and Stenotrophomonas spp. In 2019, these nonlactose fermenting bacterial species made up for approximately 15% of respiratory microorganisms cultured in pediatric patients. Though infrequent, compared to Staphylococcus aureus or Pseudomonas aeruginosa, these bacteria are opportunistic pathogens and patients at the highest risk for these infections include those with CF. Like other Gram negative bacteria, Burkholderia, Achromobacter, and Stenotrophomonas spp., are frequently drug resistant and can make treatment extremely challenging, thus it is crucial that data for treatment of these less common pathogens be evaluated.

New Perspectives on Antimicrobial Agents: Cefiderocol

Bacterial resistance to carbapenem agents has reached alarming levels. Accordingly, collaborative efforts between national and international organizations and the pharmaceutical industry have led to an impressive expansion of commercially available β-lactam agents in recent years. No available agent comes close to the broad range of activity afforded by cefiderocol, a novel siderophore-cephalosporin conjugate. The novelty of and need for cefiderocol are clear, but available clinical data are conflicting, leaving infectious diseases specialists puzzled as to when to prescribe this agent in clinical practice. After a brief overview of cefiderocol pharmacokinetics and pharmacodynamics, safety data, cefiderocol susceptibility testing, and putative mechanisms of cefiderocol resistance, this review focuses on determining cefiderocol's role in the management of specific pathogens, including carbapenem-resistant Acinetobacter baumannii complex, carbapenem-resistant Pseudomonas aeruginosa, carbapenem-resistant Enterobacterales, and less commonly identified glucose-nonfermenting organisms such as Stenotrophomonas maltophilia, Burkholderia species, and Achromobacter species. Available preclinical, clinical trial, and postmarketing data are summarized for each organism, and each section concludes with our opinions on where to position cefiderocol as a clinical therapeutic.