Inhaled colistin monotherapy for respiratory tract infections in adults without cystic fibrosis: a systematic review and meta-analysis

Inhaled Alone versus Inhaled Plus Intravenous Polymyxin B for the Treatment of Pneumonia Due to Carbapenem-Resistant Gram-Negative Bacteria: A Prospective Randomized Controlled Trial

Infections due to carbapenem-resistant Gram-negative bacteria (CR-GNB) are associated with considerable morbidity and mortality. Polymyxin B (PMB) is a first-line agent for CR-GNB-associated pneumonia, but limited data exist on the clinical use of inhaled (IH) PMB. A single-center, prospective randomized controlled trial was conducted in China to compare IH PMB alone with IH plus intravenous (IV) PMB between February 2022 and February 2024. The primary outcome was the clinical cure rate. Twenty-two evaluable patients were assigned to the IH group, and 56 patients were included in the IH+IV group. Baseline characteristics were comparable between the two groups. No significant differences were observed in clinical cure rates, favorable clinical outcomes, microbiological outcomes, all-cause mortality, or pneumonia-related mortality. However, IH PMB alone was associated with a lower incidence of nephrotoxicity (P = 0.030). IH PMB demonstrated significantly higher drug concentrations in the epithelial lining fluid (ELF) compared to systemic administration. Patients with immunosuppressive therapy (OR, 0.066; 95% CI, 0.010-0.433; P = 0.005), malignancies (OR, 0.112; 95% CI, 0.016-0.797; P = 0.029), and higher SOFA scores (OR, 0.693; 95% CI, 0.518-0.929; P = 0.014) were less likely to achieve favorable clinical outcomes. Conversely, higher PMB ELF 1-hour concentrations (OR, 1.085; 95% CI, 1.026-1.148; P = 0.004) were associated with more favorable clinical outcomes. The combination of these four indicators demonstrated excellent diagnostic performance (AUC = 0.882). Plasma 1-hour PMB concentrations showed acceptable predictive performance for nephrotoxicity (AUC = 0.766). The potential benefits of IH PMB outweigh the risks, making it an effective treatment for CR-GNB-associated pneumonia in combination with other empirical antimicrobial agents.

Treatment Approaches for Carbapenem-Resistant Acinetobacter baumannii Infections

Carbapenem-resistant Acinetobacter baumannii has been associated with over three hundred thousand annual deaths globally. It is resistant to most available antibiotics and associated with high morbidity and mortality. No global consensus currently exists for treatment strategies that balance safety and efficacy because of heterogeneity of treatment regimens in current clinical practice and scarcity of large-scale controlled studies arising from difficulties in establishing robust clinical outcomes. This review outlines the epidemiology and resistance mechanisms of carbapenem-resistant A. baumannii, then summarizes available clinical data on each approved agent with activity against this pathogen. Emerging treatment options such as cefiderocol and sulbactam-durlobactam show promise, but their success hinges on comprehensive clinical validation and access in regions most impacted by this pathogen. New therapeutic modalities that are in various stages of clinical development are also discussed.

Outcome of intravenous and inhaled polymyxin B treatment in patients with multidrug-resistant gram-negative bacterial pneumonia

PURPOSE

The incidence of pneumonia caused by multidrug-resistant gram-negative bacteria (MDR GNB) is increasing, which imposes significant burden on public health. Inhalation combined with intravenous polymyxins has emerged as a viable treatment option. However, pharmacokinetic studies focusing on intravenous and inhaled polymyxin B (PMB) are limited.

METHODS

This study included seven patients with MDR GNB-induced pneumonia who were treated with intravenous plus inhaled PMB from March 1 to November 30, 2022, in the intensive care unit of the First Affiliated Hospital of Zhejiang University School of Medicine. Clinical outcomes and therapeutic drug monitoring data of PMB in both plasma and epithelial lining fluid (ELF) were retrospectively reviewed.

RESULTS

Median PMB concentrations in the ELF were 7.83 (0.72-66.5), 116.72 (17.37-571.26), 41.1 (3.69-133.78) and 33.82 (0.83-126.68) mg/L at 0, 2, 6 and 12 h, respectively, and were much higher than those detected in the serum. ELF concentrations of PMB at 0, 2, 6 and 12 h were higher than the minimum inhibitory concentrations of pathogens isolated from the patients. Steady-state concentrations of PMB in the plasma were >2 mg/L in most patients. Of the patients, 57.14% were cured and 71.43% showed a favourable microbiological response. The incidence of side effects with PMB was low.

CONCLUSIONS

Inhaled plus intravenous PMB can achieve high ELF concentrations and favourable clinical outcomes without an increased adverse effect profile. This treatment approach appears promising for the treatment of patients with pneumonia caused by MDR-GNB.

Inhaled heparin: Past, present, and future

While heparin has traditionally served as a key anticoagulant in clinical practice for nearly a century, recent years have witnessed a growing interest in its role as a potent antiinflammatory and antiviral agent, as well as an anticancer agent. To address challenges with injection-based delivery, exploring patient-friendly routes such as oral and pulmonary delivery is crucial. This review specifically highlights the multiple therapeutic benefits of inhaled heparin. In summary, this review serves as a valuable source of information, providing deep insights into the diverse therapeutic advantages of inhaled heparin and its potential applications within clinical contexts.

Treatment of infections caused by carbapenem-resistant Acinetobacter baumannii

Patients with severe carbapenem-resistant Acinetobacter baumannii (CRAB) infections currently face significant treatment challenges. When patients display signs of infection and the clinical suspicion of CRAB infections is high, appropriate treatment should be immediately provided. However, current treatment plans and clinical data for CRAB are limited. Inherent and acquired resistance mechanisms, as well as host factors, significantly restrict options for empirical medication. Moreover, inappropriate drug coverage can have detrimental effects on patients. Most existing studies have limitations, such as a restricted sample size, and are predominantly observational or non-randomized, which report significant variability in patient infection severity and comorbidities. Therefore, a gold-standard therapy remains lacking. Current and future treatment options of infections due to CRAB were described in this review. The dose and considerable side effects restrict treatment options for polymyxins, and high doses of ampicillin-sulbactam or tigecycline appear to be the best option at the time of initial treatment. Moreover, new drugs such as durlobactam and cefiderocol have substantial therapeutic capabilities and may be effective salvage treatments. Bacteriophages and antimicrobial peptides may serve as alternative treatment options in the near future. The advantages of a combination antimicrobial regimen appear to predominate those of a single regimen. Despite its significant nephrotoxicity, colistin is considered a primary treatment and is often used in combination with antimicrobials, such as tigecycline, ampicillin-sulbactam, meropenem, or fosfomycin. The Infectious Diseases Society of America (IDSA) has deemed high-dose ampicillin-sulbactam, which is typically combined with high-dose tigecycline, polymyxin, and other antibacterial agents, the best option for treating serious CRAB infections. A rational combination of drug use and the exploration of new therapeutic drugs can alleviate or prevent the effects of CRAB infections, shorten hospital stays, and reduce patient mortality.

In Vitro Evaluation of Colistin Conjugated with Chitosan-Capped Gold Nanoparticles as a Possible Formulation Applied in a Metered-Dose Inhaler

Inhaled colistin is used to treat pneumonia and respiratory infections through nebulization or dry powder inhalers. Nevertheless, the development of a metered-dose inhaler (MDI) for colistin, which could enhance patient convenience and treatment efficacy, has not yet been developed. Colistin is known for its ability to induce cellular toxicity. Gold nanoparticles (AuNPs) can potentially mitigate colistin toxicity. Therefore, this study aimed to evaluate the antimicrobial effectiveness of colistin conjugated with chitosan-capped gold nanoparticles (Col-CS-AuNPs) and their potential formulation for use with MDIs to deliver the aerosol directly to the deep lung. Fourier-transform infrared spectroscopy, nuclear magnetic resonance, and elemental analysis were used to characterize the synthesized Col-CS-AuNPs. Drug release profiles fitted with the most suitable release kinetic model were evaluated. An MDI formulation containing 100 µg of colistin per puff was prepared. The aerosol properties used to determine the MDI performance included the fine particle fraction, mass median aerodynamic diameter, and geometric standard deviation, which were evaluated using the Andersen Cascade Impactor. The delivered dose uniformity was also determined. The antimicrobial efficacy of the Col-CS-AuNP formulation in the MDI was assessed. The chitosan-capped gold nanoparticles (CS-AuNPs) and Col-CS-AuNPs had particle sizes of 44.34 ± 1.02 and 174.50 ± 4.46 nm, respectively. CS-AuNPs effectively entrapped 76.4% of colistin. Col-CS-AuNPs exhibited an initial burst release of up to 60% colistin within the first 6 h. The release mechanism was accurately described by the Korsmeyer-Peppas model, with an R2 > 0.95. The aerosol properties of the Col-CS-AuNP formulation in the MDI revealed a high fine particle fraction of 61.08%, mass median aerodynamic diameter of 2.34 µm, and geometric standard deviation of 0.21, with a delivered dose uniformity within 75-125% of the labeled claim. The Col-CS-AuNP MDI formulation completely killed Escherichia coli at 5× and 10× minimum inhibitory concentrations after 6 and 12 h of incubation, respectively. The toxicity of CS-AuNP and Col-CS-AuNP MDI formulations in upper and lower respiratory tract cell lines was lower than that of free colistin. The stability of the Col-CS-AuNP MDI formulation was maintained for at least 3 months. The Col-CS-AuNP MDI formulation effectively eradicated bacteria over a 12-h period, showing promise for advancing lung infection treatments.

Fingolimod synergizes and reverses K. pneumoniae resistance to colistin

Klebsiella pneumoniae (K. pneumoniae) infection and the rapid spread of multi-drug resistant (MDR) bacteria pose a serious threat to global healthcare. Polymyxin E (colistin), a group of cationic antimicrobial polypeptides, is currently one of the last resort treatment options against carbapenem-resistant Gram-negative pathogens. The effectiveness of colistin has been compromised due to its intensive use. This study found that fingolimod (FLD), a natural product derivative, exhibited a significant synergistic bactericidal effect on K. pneumoniae when combined with colistin, both in vitro and in vivo. The checkerboard method was employed to assess the in vitro synergistic effect of FLD with colistin. FLD enhanced the susceptibility of bacteria to colistin and lowered effectively minimum inhibitory concentrations (MIC) when compared to colistin MIC, and the fractional inhibitory concentrations (FIC) value was less than 0.3. The time-kill curve demonstrated that the combination treatment of FLD and colistin had significant bactericidal efficacy. The in vitro concurrent administration of colistin and FLD resulted in heightening membrane permeability, compromising cell integrity, diminishing membrane fluidity, and perturbing membrane homeostasis. They also induced alterations in membrane potential, levels of reactive oxygen species, and adenosine triphosphate synthesis, ultimately culminating in bacterial death. Moreover, the combination of FLD with colistin significantly influenced fatty acid metabolism. In the mouse infection model, the survival rate of mice injected with K. pneumoniae was significantly improved to 67% and pathological damage was significantly relieved with combination treatment of FLD and colistin when compared with colistin treatment. This study highlights the potential of FLD in combining with colistin for treating infections caused by MDR isolates of K. pneumoniae.

Carbapenem-resistant Acinetobacter baumannii and Ventilator-associated Pneumonia; Epidemiology, Risk Factors, and Current Therapeutic Approaches

Acinetobacter baumannii is one of the primary pathogens responsible for healthcare-associated infections. It is related to high rates of morbidity and mortality globally, mainly because of its high capacity to develop resistance to antimicrobials. Nowadays, carbapenem-resistant A. baumannii (CRAB) has increased and represents a significant concern among carbapenem-resistant organisms. It is also a key pathogen associated with ventilator-associated pneumonia. CRAB was placed on the critical group of the universal priority list of the World Health Organization for antibiotic-resistant bacteria, to mention the importance of research development and the urgency of new antibiotics. Patients with severe CRAB infections currently face significant treatment challenges. Some approaches have been taken to deal with CRAB, such as combination therapy and the synergistic effect of certain antibiotics, but the best antibiotic regimen is still unknown. In this narrative review, we attempt to clarify the issues, including epidemiology, risk factors, and current treatment options for CRAB.

High-Loading-Dose Colistin with Nebulized Administration for Carbapenem-Resistant Acinetobacter baumannii Pneumonia in Critically Ill Patients: A Retrospective Cohort Study

Carbapenem-resistant Acinetobacter baumannii (CRAB) infections pose a serious threat, with high morbidity and mortality rates. This retrospective cohort study, conducted at Nakornping Hospital between January 2015 and October 2022, aimed to evaluate the efficacy and safety of a high loading dose (LD) of colistin combined with nebulized colistin in critically ill patients with CRAB pneumonia. Of the 261 patients included, 95 received LD colistin, and 166 received LD colistin with nebulized colistin. Multivariate Cox regression analysis, adjusted for baseline covariates using inverse probability weighting, showed no significant difference in 30-day survival between patients who received LD colistin and those who received LD colistin with nebulized colistin (adjusted hazard ratio [aHR]: 1.17, 95% confidence interval [CI]: 0.80-1.72, p = 0.418). Likewise, there were no significant differences in clinical response (aHR: 0.93, 95% CI: 0.66-1.31, p = 0.688), microbiological response (aHR: 1.21, 95% CI: 0.85-1.73, p = 0.279), or nephrotoxicity (aHR: 1.14, 95% CI: 0.79-1.64, p = 0.492) between the two treatment groups. No significant adverse events related to nebulized colistin were reported. These findings suggest that the addition of nebulized colistin may not offer additional benefits in terms of 30-day survival, clinical or microbiological response, or nephrotoxicity in these patients.

Current Therapeutic Approaches for Multidrug-Resistant and Extensively Drug-Resistant Acinetobacter baumannii Infections

The treatment of Acinetobacter baumannii infections remains a challenge for physicians worldwide in the 21st century. The bacterium possesses a multitude of mechanisms to escape the human immune system. The consequences of A. baumannii infections on morbidity and mortality, as well on financial resources, remain dire. Furthermore, A. baumannii superinfections have also occurred during the COVID-19 pandemic. While prevention is important, the antibiotic armamentarium remains the most essential factor for the treatment of these infections. The main problem is the notorious resistance profile (including resistance to carbapenems and colistin) that this bacterium exhibits. While newer beta lactam/beta-lactamase inhibitors have entered clinical practice, with excellent results against various infections due to Enterobacteriaceae, their contribution against A. baumannii infections is almost absent. Hence, we have to resort to at least one of the following, sulbactam, polymyxins E or B, tigecycline or aminoglycosides, against multidrug-resistant (MDR) and extensively drug-resistant (XDR) A. baumannii infections. Furthermore, the notable addition of cefiderocol in the fight against A. baumannii infections represents a useful addition. We present herein the existing information from the last decade regarding therapeutic advances against MDR/XDR A. baumannii infections.

Intrapulmonary and Systemic Pharmacokinetics of Colistin Following Nebulization of Low-Dose Colistimethate Sodium in Patients with Ventilator-Associated Pneumonia Caused by Carbapenem-Resistant Acinetobacter baumannii

Colistimethate sodium (CMS) nebulization is associated with reduced systemic toxicity compared to intravenous injection, with potentially enhanced clinical efficacy. This study aimed to assess the pharmacokinetic (PK) properties of colistin during low-dose CMS nebulization in patients with ventilator-associated pneumonia (VAP) caused by carbapenem-resistant Acinetobacter baumannii. A nonlinear mixed-effects modeling approach was applied to develop population PK models for colistin in both epithelial lining fluid (ELF) and plasma. Twenty patients participated, and 80 ELF and 100 plasma samples were used for model development. Median colistin concentrations measured in ELF were 614-fold, 408-fold, and 250-fold higher than in plasma at 1, 3, and 5 h, respectively. Time courses in both ELF and plasma were best described by a one-compartment model with a Weibull absorption process. When the final model was simulated, the maximum free concentration and area under the free colistin concentration-time curve at steady state over 24 h in the plasma were approximately 1/90 and 1/50 of the corresponding values in ELF at steady state, respectively. For an A. baumannii MIC of 1 mg/L, inhaling 75 mg of CMS at 6 h intervals was deemed appropriate, with dose adjustments needed for MICs exceeding 2 mg/L. Using a nebulizer for CMS resulted in a notably higher exposure of colistin in the ELF than plasma, indicating the potential of nebulization to reduce systemic toxicity while effectively treating VAP.

Advanced pulmonary drug delivery formulations for the treatment of cystic fibrosis

Cystic fibrosis (CF), a fatal genetic condition, causes thick, sticky mucus. It also causes pancreatic dysfunction, bacterial infection, and increased salt loss. Currently available treatments can improve the patient's quality of life. Drug delivery aided by nanotechnology has been explored to alter the pharmacokinetics and toxicity of drugs. In this short review, we aim to summarize various conventional formulations and highlight advanced formulations delivered via the pulmonary route for the treatment of CF. There is considerable interest in advanced drug delivery formulations addressing the various challenges posed by CF. Despite their potential to be translated for clinical use, we anticipate that a significant amount of effort may still be required for translation to the clinic.

Comparison of the clinical efficacy and toxicity of nebulized polymyxin monotherapy and combined intravenous and nebulized polymyxin for the treatment of ventilator-associated pneumonia caused by carbapenem-resistant gram-negative bacteria: a retrospective cohort study

Objective: To investigate the clinical efficacy and toxicity of nebulized polymyxin monotherapy and combined intravenous and nebulized polymyxin for the treatment of VAP caused by CR-GNB. Additionally, among patients treated with nebulized polymyxin monotherapy, we compared the clinical efficacy and toxicity of polymyxin B and polymyxin E. Methods: This study was a single-center, retrospective study. Included patients received aerosolized polymyxin for at least 72 h with or without intravenous polymyxin for the management of CR-GNB VAP. The primary endpoint was clinical cure at the end of polymyxin therapy. Secondary endpoints included AKI incidence, time of bacteria-negative conversion, duration of MV after inclusion, length of stay in ICU, and all-cause ICU mortality. Results: 39 patients treated with nebulized polymyxin monotherapy were assigned to the NL-polymyxin group. 39 patients treated with nebulized polymyxin combined with intravenous use of polymyxin were assigned to the IV-NL-polymyxin group. Among the NL-polymyxin group, 19 patients were treated with polymyxin B and 20 with polymyxin E. The clinical baseline characteristics before admission to the ICU and before nebulization of polymyxin were similar between the two groups. No differences were found between the two study groups in terms of microorganism distribution, VAP cure rate, time of bacteria-negative conversion, duration of MV after inclusion, length of stay in ICU and all-cause ICU mortality. Similarly, survival analysis did not differ between the two groups (χ2 = 3.539, p = 0.06). AKI incidence was higher in the IV-NL-polymyxin group. When comparing the clinical efficacy and toxicity to polymyxin B and polymyxin E, there was no difference between the two groups in terms of VAP cure rate, time of bacteria-negative conversion, duration of MV after inclusion, length of stay in ICU, SOFA score, CPIS, AKI incidence and all-cause ICU mortality. Conclusion: Our study found that nebulized polymyxin monotherapy was non-inferior to combination therapy with intravenous polymyxin in treating CR-GNB-VAP. Furthermore, we observed no differences in clinical efficacy or related toxic side effects between polymyxin B and polymyxin E during nebulized polymyxin therapy as monotherapy. However, future prospective studies with larger sample sizes are required to confirm these findings.

High-Dose Nebulized Colistin Methanesulfonate and the Role in Hospital-Acquired Pneumonia Caused by Gram-Negative Bacteria with Difficult-to-Treat Resistance: A Review

Hospital-acquired pneumonia, including ventilator-associated pneumonia (VAP) due to difficult-to-treat-resistant (DTR) Gram-negative bacteria, contributes significantly to morbidity and mortality in ICUs. In the era of COVID-19, the incidences of secondary nosocomial pneumonia and the demand for invasive mechanical ventilation have increased dramatically with extremely high attributable mortality. Treatment options for DTR pathogens are limited. Therefore, an increased interest in high-dose nebulized colistin methanesulfonate (CMS), defined as a nebulized dose above 6 million IU (MIU), has come into sight. Herein, the authors present the available modern knowledge regarding high-dose nebulized CMS and current information on pharmacokinetics, clinical studies, and toxicity issues. A brief report on types of nebulizers is also analyzed. High-dose nebulized CMS was administrated as an adjunctive and substitutive strategy. High-dose nebulized CMS up to 15 MIU was attributed with a clinical outcome of 63%. High-dose nebulized CMS administration offers advantages in terms of efficacy against DTR Gram-negative bacteria, a favorable safety profile, and improved pharmacokinetics in the treatment of VAP. However, due to the heterogeneity of studies and small sample population, the apparent benefit in clinical outcomes must be proven in large-scale trials to lead to the optimal use of high-dose nebulized CMS.

Navigating Available Treatment Options for Carbapenem-Resistant Acinetobacter baumannii-calcoaceticus Complex Infections

Carbapenem-resistant Acinetobacter baumannii-calcoaceticus complex (CRAB) is one of the top-priority pathogens for new antibiotic development. Unlike other antibiotic-resistant threats, none of the available therapies have been shown to consistently reduce mortality or improve patient outcomes in clinical trials. Antibiotic combination therapy is routinely used in clinical practice; however, the preferred combination has not been defined. This narrative review focuses on evidence-based solutions for the treatment of invasive CRAB infections. We dissect the promise and perils of traditional agents used in combination, such as colistin, sulbactam, and the tetracyclines, and offer clinical pearls based on our interpretation of the available data. Next, we investigate the merits of newly developed β-lactam agents like cefiderocol and sulbactam-durlobactam, which have demonstrated contrasting results in recent randomized clinical trials. The review concludes with the authors' perspective on the evolving treatment landscape for CRAB infections, which is complicated by limited clinical data, imperfect treatment options, and a need for future clinical trials. We propose that effective treatment for CRAB infections requires a personalized approach that incorporates host factors, the site of infection, pharmacokinetic-pharmacodynamic principles, local molecular epidemiology of CRAB isolates, and careful interpretation of antibiotic susceptibility testing results. In most clinical scenarios, a dose-optimized, sulbactam-based regimen is recommended with the addition of at least one other in vitro active agent. Should sulbactam-durlobactam receive regulatory approval, recommendations will need to be re-evaluated with the most recent evidence.

Aerosolized Antibiotics to Manage Ventilator-Associated Infections: A Comprehensive Review

BACKGROUND

Ventilator-associated lower respiratory tract infectious complications in critically ill patients cover a wide spectrum of one disease process (respiratory infection), initiating from tracheal tube and/or tracheobronchial colonization, to ventilator associated tracheobronchitis (VAT) and ventilator-associated pneumonia (VAP). VAP occurence has been associated with increased intensive care unit (ICU) morbidity (ventilator days, as well as length of ICU and hospital stay) and ICU mortality. Therefore, treatments that aim at VAP/VAT incidence reduction are a high priority.

AIM

The aim of the present review is to discuss the current literature concerning two major aspects: (a) can aerosolized antibiotics (AA) administered in a pre-emptive way prevent the occurrence of ventilator-associated infections? and (b) can VAT treatment with aerosolized avert the potential evolution to VAP?

RESULTS

There were identified eight studies that provided data on the use of aerosolized antibiotics for the prevention of VAT/VAP. Most of them report favorable data on reducing the colonisation rate and the progression to VAP/VAT. Another four studies dealt with the treatment of VAT/VAP. The results support the decrease in the incidence to VAP transition and/or the improvement in signs and symptoms of VAP. Moreover, there are concise reports on higher cure rates and microbiological eradication in patients treated with aerosolized antibiotics. Yet, differences in the delivery modality adopted and resistance emergence issues preclude the generalisability of the results.

CONCLUSION

Aerosolized antibiotic therapy can be used to manage ventilator-associated infections, especially those with difficult to treat resistance. The limited clinical data raise the need for large randomized controlled trials to confirm the benefits of AA and to evaluate the impact on antibiotic selection pressure.

Physiologically-based pharmacokinetic modeling to inform dosing regimens and routes of administration of rifampicin and colistin combination against Acinetobacter baumannii

BACKGROUND

Carbapenem-resistant Acinetobacter baumannii (CRAB) is resistant to major antibiotics such as penicillin, cephalosporin, fluoroquinolone and aminoglycoside, and has become a significant nosocomial pathogen. The efficacy of rifampicin and colistin combination against CRAB could be dependent on the administration routes and drug concentrations at the site of infection.

OBJECTIVE

The objective is to predict drug disposition in biological tissues. Treatment efficacy is extrapolated by assessing respective pharmacodynamic (PD) indices, as well as parameters associated with the emergence of resistance.

METHODS

Physiologically-based pharmacokinetic models of rifampicin and colistin were utilized to predict tissue exposures. Dosing regimens and administration routes for combination therapy were evaluated in terms of in vitro antimicrobial susceptibility of A. baumannii associated with targeted PD indices and resistance parameters.

RESULTS

Simulated exposures in blood, heart, lung, skin and brain were consistent with reported penetration rates. The results demonstrated that a combination of colistin and rifampicin using conventional intravenous (i.v.) doses could achieve effective exposures in the blood and skin. However, for lung infections, colistin by inhalation would be required due to low lung penetration from intravenous route. Inhaled colistin alone provided good PD coverage but this practice could encourage the emergence of additional resistance which may be overcome by a combination regimen that includes inhaled colistin.

CONCLUSION

This in silico extrapolation provides valuable information on dosing regimens and routes of administration against CRAB infections in specific tissues. The PBPK modeling approach could be a non-invasive way to inform therapeutic benefits of combination antimicrobial therapy.

Synergistic Activity of Colistin in Combination with Clofoctol against Colistin Resistant Gram-Negative Pathogens

Colistin is a bactericidal antibiotic identified decades ago which is active against a number of Gram-negative pathogens. After early elimination from clinical use due to toxicity issues, colistin has been reintroduced as a last-resort treatment for antibiotic-resistant Gram-negative infections lacking other therapeutic options. Inevitably, colistin resistance has emerged among clinical isolates, making the development of colistin adjuvants extremely beneficial. Clofoctol is a synthetic antibiotic active against Gram-positive bacteria, with low toxicity and high tropism for the airways. Interestingly, clofoctol has been found to have multiple biological activities and has been proposed for the treatment of several obstructive lung diseases, including asthma, lung cancer, and SARS-CoV-2 infection. In this study, the activity of clofoctol as a colistin adjuvant was investigated in Gram-negative lung pathogens that are critical for the high prevalence of multidrug-resistant isolates, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Acinetobacter baumannii. Clofoctol potentiated the bactericidal effect of colistin in all tested strains and reduced colistin MICs below the susceptibility breakpoint in nearly all colistin-resistant strains. Overall, this observation supports the development of inhaled clofoctol-colistin formulations for the treatment of difficult-to-treat airway infections caused by Gram-negative pathogens. IMPORTANCE Colistin is used as a last-resort antibiotic against extensively drug-resistant Gram-negative pathogens. However, colistin resistance is on the rise. Clofoctol is an antibiotic used against Gram-positive bacteria, with low toxicity and high penetration and storage in the airways. Here, a strong synergistic activity of the colistin-clofoctol combination against colistin-resistant Pseudomonas aeruginosa, Klebsiella pneumoniae, and Acinetobacter baumannii isolates is reported, supporting the development of clofoctol-colistin formulations for the therapy of difficult-to-treat airways infections caused by these Gram-negative pathogens.

Mechanism of Action of Isopropoxy Benzene Guanidine against Multidrug-Resistant Pathogens

The increasing emergence of antibiotic resistance is an urgent threat to global health care; thus, there is a need for new therapeutics. Guanidine is the preferred functional group for antimicrobial design and development. Herein, the potential antibacterial activity of the guanidine derivative isopropoxy benzene guanidine (IBG) against multidrug-resistant (MDR) bacteria was discovered. The synergistic antibacterial activity of IBG and colistin was determined by checkerboard assay, time-killing curve, and mouse experiments. The antibacterial mechanism of IBG was verified in fluorescent probe experiments, intracellular oxidative phosphorylation assays, and transcriptome analysis. The results showed that IBG displays efficient antibacterial activity against Gram-positive pathogens and Gram-negative pathogens with permeabilized outer membranes. Further mechanistic studies showed that IBG triggers cytoplasmic membrane damage by binding to phosphatidylglycerol and cardiolipin, leading to the dissipation of proton motive force and accumulation of intracellular ATP. IBG combined with low levels of colistin enhances bacterial outer membrane permeability and increases the accumulation of reactive oxygen species, as further evidenced by transcriptome analysis. Furthermore, the efficacy of IBG with colistin against MDR Escherichia coli in three infection models was demonstrated. Together, these results suggest that IBG is a promising adjuvant of colistin, providing an alternative approach to address the prevalent infections caused by MDR Gram-negative pathogens. IMPORTANCE As antibiotic discovery stagnates, the world is facing a growing menace from the emergence of bacteria that are resistant to almost all available antibiotics. The key to winning this race is to explore distinctive mechanisms of antibiotics. Thus, novel efficient antibacterial agents and alternative strategies are urgently required to fill the void in antibiotic development. Compared with the large amount of money and time required to develop new agents, the antibiotic adjuvant strategy is a promising approach to inhibit bacterial resistance and increase killing of bacteria. In this study, we found that the guanidine derivatives IBG not only displayed efficient antibacterial activities against Gram-positive bacteria but also restored colistin susceptibility of Gram-negative pathogens as an antibiotic adjuvant. More in-depth study showed that IBG is a potential lead to overcome antibiotic resistance, providing new insight into future antibiotic discovery and development.

How to Use Nebulized Antibiotics in Severe Respiratory Infections

Difficult-to-treat pulmonary infections caused by multidrug-resistant (MDR) pathogens are of great concern because their incidence continues to increase worldwide and they are associated with high morbidity and mortality. Nebulized antibiotics are increasingly being used in this context. The advantages of the administration of a nebulized antibiotic in respiratory tract infections due to MDR include the potential to deliver higher drug concentrations to the site of infection, thus minimizing the systemic adverse effects observed with the use of parenteral or oral antibiotic agents. However, there is an inconsistency between the large amount of experimental evidence supporting the administration of nebulized antibiotics and the paucity of clinical studies confirming the efficacy and safety of these drugs. In this narrative review, we describe the current evidence on the use of nebulized antibiotics for the treatment of severe respiratory infections.

Use of High-Dose Nebulized Colistimethate in Patients with Colistin-Only Susceptible Acinetobacter baumannii VAP: Clinical, Pharmacokinetic and Microbiome Features

(1) Background: Colistin-only susceptible (COS) Acinetobacter baumannii (AB) ventilator-associated pneumonia (VAP) represents a clinical challenge in the Intensive Care Unit (ICU) due to the negligible lung diffusion of this molecule and the low-grade evidence on efficacy of its nebulization. (2) Methods: We conducted a prospective observational study on 134 ICU patients with COS-AB VAP to describe the 'real life' clinical use of high-dose (5 MIU q8) aerosolized colistin, using a vibrating mesh nebulizer. Lung pharmacokinetics and microbiome features were investigated. (3) Results: Patients were enrolled during the COVID-19 pandemic with the ICU presenting a SAPS II of 42 [32-57]. At VAP diagnosis, the median PaO₂/FiO₂ was 120 [100-164], 40.3% were in septic shock, and 24.6% had secondary bacteremia. The twenty-eight day mortality was 50.7% with 60.4% and 40.3% rates of clinical cure and microbiological eradication, respectively. We did not observe any drug-related adverse events. Epithelial lining fluid colistin concentrations were far above the CRAB minimal-inhibitory concentration and the duration of nebulized therapy was an independent predictor of microbiological eradication (12 [9.75-14] vs. 7 [4-13] days, OR (95% CI): 1.069 (1.003-1.138), p = 0.039). (4) Conclusions: High-dose and prolonged colistin nebulization, using a vibrating mesh, was a safe adjunctive therapeutic strategy for COS-AB VAP. Its right place and efficacy in this setting warrant investigation in interventional studies.

Melatonin ameliorates lung cell inflammation and apoptosis caused by Klebsiella pneumoniae via AMP-activated protein kinase

Klebsiella pneumoniae is a Gram-negative bacterium and the causative agent of several life-threatening nosocomial infections, including pneumonia. K. pneumoniae induces acute lung injury and inflammation in humans that require immediate hospitalization and treatment. Therefore, attenuation of K. pneumoniae-induced inflammation is necessary for the survival of patients. This study investigated the mechanisms by which melatonin abrogated K. pneumoniae-induced inflammation and apoptosis of lung cell lines, HLF-1 and BEAS-2B. Our results showed that in vitro infection of HLF-1 and BEAS-2B cells by K. pneumoniae significantly induced inflammation and apoptosis increased elevated levels of IL-6, CXCL1, CXCL2, and caspase-9 mRNA. However, these effects were abrogated by melatonin treatment. Infection with K. pneumoniae significantly increased the expression of AMP-induced protein kinase (AMPK). Furthermore, AMPK silencing significantly abrogated the suppression of inflammation and apoptosis in melatonin-infected K. pneumoniae lung cells. Melatonin could alleviate K. pneumoniae infection-induced inflammation in three-dimensional lung spheroids. In conclusion, our study demonstrated that melatonin abrogated K. pneumoniae-induced inflammation and apoptosis in lung cells through AMPK. Our study demonstrated the potential of melatonin for therapy against K. pneumoniae infections including pneumonia.

Recommendations and guidelines for the treatment of infections due to multidrug resistant organisms

Antimicrobial drug resistance is one of the major threats to global health. It has made common infections increasingly difficult or impossible to treat, and leads to higher medical costs, prolonged hospital stays and increased mortality. Infection rates due to multidrug-resistant organisms (MDRO) are increasing globally. Active agents against MDRO are limited despite an increased in the availability of novel antibiotics in recent years. This guideline aims to assist clinicians in the management of infections due to MDRO. The 2019 Guidelines Recommendations for Evidence-based Antimicrobial agents use in Taiwan (GREAT) working group, comprising of infectious disease specialists from 14 medical centers in Taiwan, reviewed current evidences and drafted recommendations for the treatment of infections due to MDRO. A nationwide expert panel reviewed the recommendations during a consensus meeting in Aug 2020, and the guideline was endorsed by the Infectious Diseases Society of Taiwan (IDST). This guideline includes recommendations for selecting antimicrobial therapy for infections caused by carbapenem-resistant Acinetobacter baumannii, carbapenem-resistant Pseudomonas aeruginosa, carbapenem-resistant Enterobacterales, and vancomycin-resistant Enterococcus. The guideline takes into consideration the local epidemiology, and includes antimicrobial agents that may not yet be available in Taiwan. It is intended to serve as a clinical guide and not to supersede the clinical judgment of physicians in the management of individual patients.

Secondary Prophylaxis With Inhaled Colistin to Prevent Recurrence of Pseudomonas aeruginosa and Extended-spectrum β-lactamase-producing Enterobacterales Pneumonia in ICU After Lung Transplantation: A Before-and-after Retrospective Cohort Analysis

BACKGROUND

Early pneumonia is an independent risk factor for 1-y mortality after lung transplantation (LTx). Pseudomonas aeruginosa is the most common isolate in early pneumonia and is also associated with an increased risk of chronic lung allograft dysfunction. The aim of our study was to evaluate the efficacy of secondary prophylaxis with inhaled colistin (IC) in preventing the recurrence of P aeruginosa or extended-spectrum β-lactamase-producing Enterobacterales (ESBL-PE) pneumonia in the postoperative period in the intensive care unit after LTx.

METHODS

We conducted a before-and-after retrospective cohort study by including all patients who underwent LTx between January 2015 and December 2020 in our center. Secondary prophylaxis with IC was instituted in January 2018 (observation period from January 2015 to December 2017, intervention period from January 2018 to December 2020).

RESULTS

A total of 271 lung transplants were included (125 in the observation period and 146 in the intervention period). The patients were predominately male (64.2%) with a median age of 57 y and received double LTx (67.9%) for chronic obstructive pulmonary disease/emphysema (36.2%) or interstitial lung disease (48.3%). The proportion of patients who experienced at least 1 recurrence of P aeruginosa or ESBL-PE pneumonia was significantly lower in the intervention period than in the observation period (0.7% versus 7.2%, P = 0.007).

CONCLUSIONS

Our study suggests a potential benefit of secondary prophylaxis with IC to prevent the recurrence of P aeruginosa or ESBL-PE pneumonia in the intensive care unit after LTx.

Aerosolized antibiotics in the treatment of hospital-acquired pneumonia/ventilator-associated pneumonia

Aerosolized antibiotics are being increasingly used to treat respiratory infections, especially those caused by drug-resistant pathogens. Their use in the treatment of hospital-acquired pneumonia and ventilator-associated pneumonia in critically ill patients is especially significant. They are also used as an efficient alternative to overcome the issues caused by systemic administration of antibiotics, including the occurrence of drug-resistant strains, drug toxicity, and insufficient drug concentration at the target site. However, the rationale for the use of aerosolized antibiotics is limited owing to their insufficient efficacy and the potential for underestimated risks of developing side effects. Despite the lack of availability of high-quality evidence, the use of aerosolized antibiotics is considered as an attractive alternative treatment approach, especially in patients with multidrug-resistant pathogens. In this review, we have discussed the effectiveness and side effects of aerosolized antibiotics as well as the latest advancements in this field and usage in the Republic of Korea.

An Evidence-Based Multidisciplinary Approach Focused on Creating Algorithms for Targeted Therapy of Infection-Related Ventilator-Associated Complications (IVACs) Caused by Pseudomonas aeruginosa and Acinetobacter baumannii in Critically Ill Adult Patients

(1) Background: To develop evidence-based algorithms for targeted antibiotic therapy of infection-related ventilator-associated complications (IVACs) caused by non-fermenting Gram-negative pathogens. (2) Methods: A multidisciplinary team of four experts had several rounds of assessments for developing algorithms devoted to targeted antimicrobial therapy of IVACs caused by two non-fermenting Gram-negative pathogens. A literature search was performed on PubMed-MEDLINE (until September 2021) to provide evidence for supporting therapeutic choices. Quality and strength of evidence was established according to a hierarchical scale of the study design. Six different algorithms with associated recommendations in terms of therapeutic choice and dosing optimization were suggested according to the susceptibility pattern of two non-fermenting Gram-negative pathogens: multi-susceptible Pseudomonas aeruginosa (PA), multidrug-resistant (MDR) metallo-beta-lactamase (MBL)-negative-PA, MBL-positive-PA, carbapenem-susceptible Acinetobacter baumannii (AB), and carbapenem-resistant AB. (3) Results: Piperacillin–tazobactam or fourth-generation cephalosporins represent the first therapeutic choice in IVACs caused by multi-susceptible PA. A carbapenem-sparing approach favouring the administration of novel beta-lactam/beta-lactamase inhibitors should be pursued in the management of MDR-MBL-negative PA infections. Cefiderocol should be used as first-line therapy for the management of IVACs caused by MBL-producing-PA or carbapenem-resistant AB. Fosfomycin-based combination therapy, as well as inhaled colistin, could be considered as a reasonable alternative for the management of IVACs due to MDR-PA and carbapenem-resistant AB. (4) Conclusions: The implementation of algorithms focused on prompt revision of antibiotic regimens guided by results of conventional and rapid diagnostic methodologies, appropriate place in therapy of novel beta-lactams, implementation of strategies for sparing the broadest-spectrum antibiotics, and pharmacokinetic/pharmacodynamic optimization of antibiotic dosing regimens is strongly suggested.

Contemporary Perspective on the Treatment of Acinetobacter baumannii Infections: Insights from the Society of Infectious Diseases Pharmacists

The purpose of this narrative review is to bring together the most recent epidemiologic, preclinical, and clinical findings to offer our perspective on best practices for managing patients with A. baumannii infections with an emphasis on carbapenem-resistant A. baumannii (CRAB). To date, the preferred treatment for CRAB infections has not been defined. Traditional agents with retained in vitro activity (aminoglycosides, polymyxins, and tetracyclines) are limited by suboptimal pharmacokinetic characteristics, emergence of resistance, and/or toxicity. Recently developed and US Food and Drug Administration (FDA)-approved β-lactam/β-lactamase inhibitor agents do not provide enhanced activity against CRAB. On balance, cefiderocol and eravacycline demonstrate potent in vitro activity and are well tolerated, but clinical data for patients with CRAB infections do not yet support widespread use. Given that CRAB has the capacity to infect vulnerable patients and preferred regimens have not been identified, we advocate for combination therapy. Our preferred regimen for critically ill patients infected, or considered to be at high risk for CRAB, includes meropenem, polymyxin B, and ampicillin/sulbactam. Importantly, site of infection, severity of illness, and local epidemiology are essential factors to be considered in selecting combination therapies. Molecular mechanisms of resistance may unveil preferred combinations at individual centers; however, such data are often unavailable to treating clinicians and have not been linked to improved clinical outcomes. Combination strategies may also pose an increased risk for antibiotic toxicity and Clostridioides difficile infection, and should therefore be balanced by understanding patient goals of care and underlying health conditions. Promising therapies that are in clinical development and/or under investigation include durlobactam-sulbactam, cefiderocol combination regimens, and bacteriophage therapy, which may over time eliminate the need for the continued use of polymyxins. Future goals for CRAB management include pathogen-focused treatment paradigms that are based on molecular mechanisms of resistance, local susceptibility rates, and the availability of well-tolerated, effective treatment options.

The Human Innate Immune Protein Calprotectin Elicits a Multimetal Starvation Response in Pseudomonas aeruginosa

To combat infections, the mammalian host limits availability of essential transition metals such as iron (Fe), zinc (Zn), and manganese (Mn) in a strategy termed "nutritional immunity." The innate immune protein calprotectin (CP) contributes to nutritional immunity by sequestering these metals to exert antimicrobial activity against a broad range of microbial pathogens. One such pathogen is Pseudomonas aeruginosa, which causes opportunistic infections in vulnerable populations, including individuals with cystic fibrosis. CP was previously shown to withhold Fe(II) and Zn(II) from P. aeruginosa and induce Fe and Zn starvation responses in this pathogen. In this work, we performed quantitative, label-free proteomics to further elucidate how CP impacts metal homeostasis pathways in P. aeruginosa. We report that CP induces an incomplete Fe starvation response, as many Fe-containing proteins that are repressed by Fe limitation are not affected by CP treatment. The Zn starvation response elicited by CP seems to be more complete than the Fe starvation response and includes increases in Zn transporters and Zn-independent proteins. CP also induces the expression of membrane-modifying proteins, and metal depletion studies indicate this response results from the sequestration of multiple metals. Moreover, the increased expression of membrane-modifying enzymes upon CP treatment correlates with increased tolerance to polymyxin B. Thus, the response of P. aeruginosa to CP treatment includes both single- and multimetal starvation responses and includes many factors related to virulence potential, broadening our understanding of this pathogen's interaction with the host. IMPORTANCE Transition metal nutrients are critical for growth and infection by all pathogens, and the innate immune system withholds these metals from pathogens to limit their growth in a strategy termed "nutritional immunity." While multimetal depletion by the host is appreciated, the majority of studies have focused on individual metals. Here, we use the innate immune protein calprotectin (CP), which complexes with several metals, including iron (Fe), zinc (Zn), and manganese (Mn), and the opportunistic pathogen Pseudomonas aeruginosa to investigate multimetal starvation. Using an unbiased label-free proteomics approach, we demonstrate that multimetal withholding by CP induces a regulatory response that is not merely additive of individual metal starvation responses, including the induction of lipid A modification proteins.

Current and Emerging Therapies to Combat Cystic Fibrosis Lung Infections

The ultimate aim of any antimicrobial treatment is a better infection outcome for the patient. Here, we review the current state of treatment for bacterial infections in cystic fibrosis (CF) lung while also investigating potential new treatments being developed to see how they may change the dynamics of antimicrobial therapy. Treatment with antibiotics coupled with regular physical therapy has been shown to reduce exacerbations and may eradicate some strains. Therapies such as hypertonic saline and inhaled PulmozymeTM (DNase-I) improve mucus clearance, while modifier drugs, singly and more successfully in combination, re-open certain mutant forms of the cystic fibrosis transmembrane conductance regulator (CFTR) to enable ion passage. No current method, however, completely eradicates infection, mainly due to bacterial survival within biofilm aggregates. Lung transplants increase lifespan, but reinfection is a continuing problem. CFTR modifiers normalise ion transport for the affected mutations, but there is conflicting evidence on bacterial clearance. Emerging treatments combine antibiotics with novel compounds including quorum-sensing inhibitors, antioxidants, and enzymes, or with bacteriophages, aiming to disrupt the biofilm matrix and improve antibiotic access. Other treatments involve bacteriophages that target, infect and kill bacteria. These novel therapeutic approaches are showing good promise in vitro, and a few have made the leap to in vivo testing.

Nebulized Colistin in Ventilator-Associated Pneumonia and Tracheobronchitis: Historical Background, Pharmacokinetics and Perspectives

Clinical evidence suggests that nebulized colistimethate sodium (CMS) has benefits for treating lower respiratory tract infections caused by multidrug-resistant Gram-negative bacteria (GNB). Colistin is positively charged, while CMS is negatively charged, and both have a high molecular mass and are hydrophilic. These physico-chemical characteristics impair crossing of the alveolo-capillary membrane but enable the disruption of the bacterial wall of GNB and the aggregation of the circulating lipopolysaccharide. Intravenous CMS is rapidly cleared by glomerular filtration and tubular excretion, and 20-25% is spontaneously hydrolyzed to colistin. Urine colistin is substantially reabsorbed by tubular cells and eliminated by biliary excretion. Colistin is a concentration-dependent antibiotic with post-antibiotic and inoculum effects. As CMS conversion to colistin is slower than its renal clearance, intravenous administration can lead to low plasma and lung colistin concentrations that risk treatment failure. Following nebulization of high doses, colistin (200,000 international units/24h) lung tissue concentrations are > five times minimum inhibitory concentration (MIC) of GNB in regions with multiple foci of bronchopneumonia and in the range of MIC breakpoints in regions with confluent pneumonia. Future research should include: (1) experimental studies using lung microdialysis to assess the PK/PD in the interstitial fluid of the lung following nebulization of high doses of colistin; (2) superiority multicenter randomized controlled trials comparing nebulized and intravenous CMS in patients with pandrug-resistant GNB ventilator-associated pneumonia and ventilator-associated tracheobronchitis; (3) non-inferiority multicenter randomized controlled trials comparing nebulized CMS to intravenous new cephalosporines/ß-lactamase inhibitors in patients with extensive drug-resistant GNB ventilator-associated pneumonia and ventilator-associated tracheobronchitis.

Antimicrobial Stewardship: A Review for Internal Medicine Physicians

Antimicrobial stewardship is the need of the hour to prevent the collapse of our health care system at the hands of a pandemic of resistant pathogens. Inappropriate and indiscriminate abuse of antibiotics has left very few options for prescribing physicians as most of the pathogens, particularly gram-negative, are resistant to the major antibiotics. This article reviews the importance of Antimicrobial Stewardship Programs (ASP) for internal medicine physicians and residents. Commonly encountered clinical scenarios are discussed. Appropriate indications of antibiotics, pathogen-guided prescriptions, adverse effects of common antibiotics, and options to use newer antibiotics are reviewed. The role of a health care team is highlighted. The evidence-based steps taken to ensure ASPs implementation are reiterated to serve as an educational guide for medical residents and physicians.

Rescuing the Last-Line Polymyxins: Achievements and Challenges

Antibiotic resistance is a major global health challenge and, worryingly, several key Gram negative pathogens can become resistant to most currently available antibiotics. Polymyxins have been revived as a last-line therapeutic option for the treatment of infections caused by multidrug-resistant Gram negative bacteria, in particular Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacterales. Polymyxins were first discovered in the late 1940s but were abandoned soon after their approval in the late 1950s as a result of toxicities (e.g., nephrotoxicity) and the availability of "safer" antibiotics approved at that time. Therefore, knowledge on polymyxins had been scarce until recently, when enormous efforts have been made by several research teams around the world to elucidate the chemical, microbiological, pharmacokinetic/pharmacodynamic, and toxicological properties of polymyxins. One of the major achievements is the development of the first scientifically based dosage regimens for colistin that are crucial to ensure its safe and effective use in patients. Although the guideline has not been developed for polymyxin B, a large clinical trial is currently being conducted to optimize its clinical use. Importantly, several novel, safer polymyxin-like lipopeptides are developed to overcome the nephrotoxicity, poor efficacy against pulmonary infections, and narrow therapeutic windows of the currently used polymyxin B and colistin. This review discusses the latest achievements on polymyxins and highlights the major challenges ahead in optimizing their clinical use and discovering new-generation polymyxins. To save lives from the deadly infections caused by Gram negative "superbugs," every effort must be made to improve the clinical utility of the last-line polymyxins. SIGNIFICANCE STATEMENT: Antimicrobial resistance poses a significant threat to global health. The increasing prevalence of multidrug-resistant (MDR) bacterial infections has been highlighted by leading global health organizations and authorities. Polymyxins are a last-line defense against difficult-to-treat MDR Gram negative pathogens. Unfortunately, the pharmacological information on polymyxins was very limited until recently. This review provides a comprehensive overview on the major achievements and challenges in polymyxin pharmacology and clinical use and how the recent findings have been employed to improve clinical practice worldwide.

Polymyxins for the treatment of lower respiratory tract infections: lessons learned from the integration of clinical pharmacokinetic studies and clinical outcomes

The global rise in nosocomial pneumonia caused by multidrug-resistant (MDR) Gram-negative pathogens and the increasingly limited antibiotic treatment options are growing threats to modern medicine. As a result, older antibiotics such as polymyxins are being used as last-resort drugs for MDR nosocomial pneumonia. Polymyxins are bactericidal against most aerobic Gram-negative bacilli. High-dose intravenous (IV) adminsitration of polymyxins, however, results in subtherapeutic concentrations at the site of infection making treatment challenging. Alternative forms of polymyxin delivery have been considered in order to better achieve the necessary concentrations at the site of infection. Several studies have evaluated the effectiveness of aerosolised polymyxins in patients with nosocomial pneumonia caused by MDR Gram-negative pathogens such as Pseudomonas aeruginosa, Acinetobacter baumannii and Klebsiella pneumoniae. Here we evaluated the pharmacokinetic data supporting the use of inhaled polymyxins in nosocomial pneumonia and provide insight into the limitations and challenges that future studies should address. We have also reviewed the literature published between 2006 and 2020 on the use of aerosolised polymyxins for the treatment of nosocomial pneumonia, including ventilator-associated pneumonia, in patients without cystic fibrosis to evaluate their safety and efficacy as monotherapy or as an adjunct to IV antimicrobials. This review highlights the need for well-designed multicentre studies with standardised methodologies to further evaluate the effectiveness of inhaled polymyxins and to provide reliable pharmacokinetic/pharmacodynamic data in order to redefine appropriate dosing strategies.

Comparisons of adverse event reporting for colistin versus polymyxin B using the US Food and Drug Administration Adverse Event Reporting System (FAERS)

Background: The polymyxins (colistin and polymyxin B) have recently reemerged in clinical practice. With the same antimicrobial activities, colistin has been more frequently prescribed in most countries, although available evidence on their nephrotoxicity is conflicting.Methods: The US Food and Drug Administration Adverse Event Reporting System (FAERS) data from Q1-2004 to Q1-2020 were used to identify adverse events (AE) reports. We described the reporting patterns and compare the reporting rates of serious AEs, acute kidney diseases (AKD), and death between colistin and polymyxin B using reporting odds ratios (RORs).Results: The annual number of AE reports increased over time for both drugs. Heterogeneity in reporting characteristics was observed in age and reporter region. RORs of serious, AKD, and death AEs were significantly higher for both drugs versus other drugs. RORs of serious and AKD AEs were higher for colistin compared to polymyxin B (p = 0.0479 and p = 0.0306, respectively), but no difference in death RORs was detected (p = 0.2211).Conclusions: This study showed higher reporting rates of serious AEs and AKD for colistin than polymyxin B, but no difference in death. The findings support future research with stronger study design and larger sample size for the safety comparison between colistin and polymyxin B.

Safety of Nebulized Colistin Solution as Adjunctive Treatment of Lower Respiratory Tract Infections

BACKGROUND

Systemic colistin is often utilized for management of drug resistant lower respiratory tract infections (LRTI). Nebulized administration of colistin allows direct instillation of active agent to maximize concentrations and limit systemic toxicities. Current literature supports efficacy of nebulized colistin as adjunctive treatment for LRTI. However, there is a paucity of data surrounding safety of this administration technique.

METHODS

The electronic medical record (EMR) was queried to identify patients treated with nebulized colistin between January 1, 2016 and December 31, 2018. The data collected from the EMR and hospital adverse drug reaction (ADR) reporting systems included: demographics, dose, serum creatinine (SCr), concomitant nephrotoxins, infecting pathogen, treatment-emergent ADRs, and drug toxicities. The primary outcome was prevalence of renal, neurologic, or respiratory ADRs secondary to nebulized colistin.

RESULTS

Thirty-two patients were administered nebulized colistin during the study period. Approximately 19% of patients had baseline chronic kidney disease. Cultures were positive in 29 patients of which 11 organisms were resistant to all tested antimicrobials. Three patients experienced acute kidney injury (AKI), 1 patient experienced a neurologic reaction, and 1 patient experienced a respiratory reaction, though none were considered treatment-related.

CONCLUSION

The results of our study signify localized administration of colistin results in a low incidence of systemic adverse events. Nebulized colistin is a safe adjunct for managing LRTI.

Systemic pharmacokinetics and safety of high doses of nebulized colistimethate sodium in critically ill patients with hospital-acquired and ventilator-associated pneumonia

OBJECTIVES

To assess the pharmacokinetics of formed colistin in plasma and the safety of two different high doses of colistimethate sodium administered via nebulization in critically ill surgical patients with hospital-acquired pneumonia (HAP) or ventilator-associated pneumonia (VAP).

PATIENTS AND METHODS

Formed colistin plasma concentrations were measured in critically ill surgical patients with pneumonia treated with two different doses of nebulized colistimethate sodium (3 MIU/8 h versus 5 MIU/8 h). Adverse events possibly related to nebulized colistimethate sodium were recorded.

RESULTS

Twenty-seven patients (15 in the 3 MIU/8 h group and 12 in the 5 MIU/8 h group) were included. Colistin plasma concentrations were unquantifiable (<0.1 mg/L) in eight (53.3%) patients in the 3 MIU/8 h group and in seven patients (58.3%) in the 5 MIU/8 h group. Median (IQR) quantifiable colistin plasma concentrations before nebulization and at 1, 4 and 8 h were 0.17 (0.12-0.33), 0.20 (0.11-0.24), 0.17 (0.12-0.23) and 0.17 (0.11-0.32) mg/L, respectively, in the 3 MIU/8 h group and 0.20 (0.11-0.35), 0.24 (0.12-0.44), 0.24 (0.10-0.49) and 0.23 (0.11-0.44) mg/L, respectively, in the 5 MIU/8 h group, with no differences between the two groups at any time. Renal impairment during nebulized treatment was observed in three patients in each group, but was unlikely to be related to colistimethate sodium treatment. Nebulized colistimethate sodium therapy was well tolerated and no bronchospasms or neurotoxicity events were observed.

CONCLUSIONS

In this limited observational case series of critically ill patients with HAP or VAP treated with high doses of nebulized colistimethate sodium, systemic exposure was minimal and the treatment was well tolerated.

Inhaled colistin for the treatment of nosocomial pneumonia due to multidrug-resistant Gram-negative bacteria: A real-life experience in tertiary care hospitals in Saudi Arabia

Background

Nosocomial pneumonia (NP) due to multidrug-resistant (MDR) Gram-negative pathogens, has continued to rise over the last several decades. Parenteral administration of colistin results in poor alveolar penetration and subtherapeutic concentration; therefore, direct drug deposition at site of infection may improve the effectiveness while minimizing the systemic exposure. The aim of this study is to describe the safety and effectiveness of inhaled colistin for the treatment of NP caused by MDR Gram-negative pathogens.

Method

Patients who received inhaled colistin from May 2015 to May 2019 at 2 different tertiary care hospitals in Riyadh, Saudi Arabia were identified from pharmacy databases and their charts were retrospectively reviewed.

Results

86 patients were enrolled in this study. The mean age was 56 ± 20 years. The mean Acute Physiology and Chronic Health Evaluation (APACHE II) was 17 ± 5. The responsible pathogens for NP were Pseudomonas aeruginosa (60%) Acinetobacter baumannii (28%), and Klebsiella pneumoniae (9%). Most patients (76/86) received concomitant intravenous antibiotics. Mean colistin total daily dose was 6 ± 3 million international units divided into 2-3 doses. Mean inhaled colistin duration of therapy was 11 ± 6 days. Favorable clinical outcome was achieved in 51 (59%) patients while favorable microbiological outcome occurred in 29 (34%) patients. Death due to all causes was noted in 39 (45%) cases. Renal injury occurred in 19 (22%) patients, all received concomitant intravenous colistin.

Conclusion

Inhaled colistin can be considered as salvage therapy as adjunct to intravenous administration for treatment of patients with NP due to MDR Gram-negative pathogens.

Inherent colistin resistance in genogroups of the Enterobacter cloacae complex: epidemiological, genetic and biochemical analysis from the BSAC Resistance Surveillance Programme

Background

Polymyxins have re-entered use against problem Gram-negative bacteria. Resistance rates are uncertain, with estimates confounded by selective testing.

Methods

The BSAC Resistance Surveillance Programme has routinely tested colistin since 2010; we reviewed data up to 2017 for relevant Enterobacterales (n = 10 914). Unexpectedly frequent resistance was seen among the Enterobacter cloacae complex isolates (n = 1749); for these, we investigated relationships to species, genome, carbon source utilization and LPS structure.

Results

Annual colistin resistance rates among E. cloacae complex isolates were 4.4%–20%, with a rising trend among bloodstream organisms; in contrast, annual rates for Escherichia coli and Klebsiella spp. (including K. aerogenes) generally remained &lt;2%. WGS split the E. cloacae complex isolates into seven genogroup clusters, designated A–G. Among isolates assigned to genogroups A–D, 47/50 sequenced were colistin resistant, and many of those belonging to genogroups A–C identified as E. asburiae. Isolates belonging to genogroups E–G consistently identified as E. cloacae and were rarely (only 3/45 representatives sequenced) colistin resistant. Genogroups F and G, the predominant colistin-susceptible clusters, were metabolically distinct from other clusters, notably regarding utilization or not of l-fucose, formic acid, d-serine, adonitol, myo-inositol, l-lyxose and polysorbates. LPS from resistant organisms grown without colistin pressure lacked substitutions with 4-amino-arabinose or ethanolamine but was more structurally complex, with more molecular species present.

Conclusions

Colistin resistance is frequent in the E. cloacae complex and increasing among bloodstream isolates. It is associated with: (i) particular genomic and metabolic clusters; (ii) identification as E. asburiae; and (iii) with more complex LPS architectures.

International Consensus Guidelines for the Optimal Use of the Polymyxins: Endorsed by the American College of Clinical Pharmacy (ACCP), European Society of Clinical Microbiology and Infectious Diseases (ESCMID), Infectious Diseases Society of America (IDSA), International Society for Anti-infective Pharmacology (ISAP), Society of Critical Care Medicine (SCCM), and Society of Infectious Diseases Pharmacists (SIDP)

The polymyxin antibiotics colistin (polymyxin E) and polymyxin B became available in the 1950s and thus did not undergo contemporary drug development procedures. Their clinical use has recently resurged, assuming an important role as salvage therapy for otherwise untreatable gram-negative infections. Since their reintroduction into the clinic, significant confusion remains due to the existence of several different conventions used to describe doses of the polymyxins, differences in their formulations, outdated product information, and uncertainties about susceptibility testing that has led to lack of clarity on how to optimally utilize and dose colistin and polymyxin B. We report consensus therapeutic guidelines for agent selection and dosing of the polymyxin antibiotics for optimal use in adult patients, as endorsed by the American College of Clinical Pharmacy (ACCP), Infectious Diseases Society of America (IDSA), International Society of Anti-Infective Pharmacology (ISAP), Society for Critical Care Medicine (SCCM), and Society of Infectious Diseases Pharmacists (SIDP). The European Society for Clinical Microbiology and Infectious Diseases (ESCMID) endorses this document as a consensus statement. The overall conclusions in the document are endorsed by the European Committee on Antimicrobial Susceptibility Testing (EUCAST). We established a diverse international expert panel to make therapeutic recommendations regarding the pharmacokinetic and pharmacodynamic properties of the drugs and pharmacokinetic targets, polymyxin agent selection, dosing, dosage adjustment and monitoring of colistin and polymyxin B, use of polymyxin-based combination therapy, intrathecal therapy, inhalation therapy, toxicity, and prevention of renal failure. The treatment guidelines provide the first ever consensus recommendations for colistin and polymyxin B therapy that are intended to guide optimal clinical use.

Ventilator-Associated Tracheobronchitis: To Treat or Not to Treat?

Ventilator-associated tracheobronchitis (VAT) is an infection commonly affecting mechanically ventilated intubated patients. Several studies suggest that VAT is associated with increased duration of mechanical ventilation (MV) and length of intensive care unit (ICU) stay, and a presumptive increase in healthcare costs. Uncertainties remain, however, regarding the cost/benefit balance of VAT treatment. The aim of this narrative review is to discuss the two fundamental and inter-related dilemmas regarding VAT, i.e., (i) how to diagnose VAT? and (ii) should we treat VAT? If yes, should we treat all cases or only selected ones? How should we treat in terms of antibiotic choice, route, treatment duration?

In vitro synergism of colistin in combination with N-acetylcysteine against Acinetobacter baumannii grown in planktonic phase and in biofilms

Objectives

To investigate the potential synergism of colistin in combination with N-acetylcysteine against Acinetobacter baumannii strains grown in planktonic phase or as biofilms.

Methods

Sixteen strains were investigated, including nine colistin-susceptible (MIC range 0.5–1 mg/L) and seven colistin-resistant (MIC range 16–256 mg/L) strains. Synergism of colistin in combination with N-acetylcysteine was investigated by chequerboard assays. The activity of colistin/N-acetylcysteine combinations was further evaluated by time–kill assays with planktonic cultures (three colistin-resistant strains and one colistin-susceptible strain) and by in vitro biofilm models (three colistin-resistant and three colistin-susceptible strains).

Results

Chequerboard assays revealed a relevant synergism of colistin/N-acetylcysteine combinations with all colistin-resistant strains, whereas no synergism was observed with colistin-susceptible strains. Time–kill assays showed a concentration-dependent potentiation of colistin activity by N-acetylcysteine against colistin-resistant strains, with eradication of the culture by combinations of N-acetylcysteine at 8000 mg/L plus colistin at 2 or 8 mg/L. A static effect during the first 8 h of incubation was demonstrated with the colistin-susceptible strain exposed to 0.25 × MIC colistin plus 8000 mg/L N-acetylcysteine. A remarkable antibiofilm synergistic activity of 8 mg/L colistin plus 8000 mg/L N-acetylcysteine was demonstrated with all colistin-resistant and colistin-susceptible strains. The effects were greater with colistin-resistant strains (marked reduction of viable biofilm cells was observed at sub-MIC colistin concentrations).

Conclusions

N-acetylcysteine, at concentrations achievable by topical administration, was shown to revert the colistin-resistant phenotype in A. baumannii, and to exert a relevant activity against biofilms of colistin-susceptible and colistin-resistant A. baumannii strains.

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.

Size Distribution of Colistin Delivery by Different Type Nebulizers and Concentrations During Mechanical Ventilation

Although aerosol delivery through mechanical ventilators has been used to administer various medications, little is known of administration with colistin. This in vitro evaluation aimed to evaluate size distribution of colistin delivery by different types of nebulizers and concentrations during mechanical ventilation. Colistin methanesulfonate (colistin) for injection was dissolved in 6 mL of distilled water to produce a low concentration (L; 156 mg) and a high concentration (H; 312 mg). A dose volume of 6 mL was placed in a vibrating mesh nebulizer (VMN) and a jet nebulizer (JN). The inhaled mass (mean ± SD) of the VMN-L (53.80 ± 14.79 mg) was greater than both the JN-L (19.82 ± 3.34 mg, P = 0.001) and JN-H (31.72 ± 4.48 mg, P = 0.017). The nebulization time of the VMN-L (42.35 ± 2.30 min) was two times longer than the JN-L (21.12 ± 0.8 min) or JN-H (21.65 ± 0.42 min; P < 0.001). The mass median aerodynamic distal to the endotracheal tube was within a similar range at 2.03 to 2.26 μm (P = 0.434), independent of neb or formulation concentration. In conclusion, the VMN-L yields greater inhaled mass than the JN with either concentration. Therefore, a standard nominal dose of colistin results in a higher delivered dose during mechanical ventilation with a VMN compared with a JN and may be considered the preferred device. If JN must be used, multiple doses of low concentration colistin may compensate for poor delivery performance.

Emerging therapies against infections with Pseudomonas aeruginosa

Infections with Pseudomonas aeruginosa have been marked with the highest priority for surveillance and epidemiological research on the basis of parameters such as incidence, case fatality rates, chronicity of illness, available options for prevention and treatment, health-care utilization, and societal impact. P. aeruginosa is one of the six ESKAPE pathogens that are the major cause of nosocomial infections and are a global threat because of their capacity to become increasingly resistant to all available antibiotics. This review reports on current pre-clinical and clinical advances of anti-pseudomonal therapies in the fields of drug development, antimicrobial chemotherapy, vaccines, phage therapy, non-bactericidal pathoblockers, outer membrane sensitizers, and host defense reinforcement.

In Vitro Synergism of Colistin and N-acetylcysteine against Stenotrophomonas maltophilia

Stenotrophomonas maltophilia is an emerging global opportunistic pathogen, responsible for a wide range of human infections, including respiratory tract infections. Intrinsic multidrug resistance and propensity to form biofilms make S. maltophilia infections recalcitrant to treatment. Colistin is among the second-line options in case of difficult-to-treat S. maltophilia infections, with the advantage of being also administrable by nebulization. We investigated the potential synergism of colistin in combination with N-acetylcysteine (NAC) (a mucolytic agent with antioxidant and anti-inflammatory properties) against S. maltophilia grown in planktonic phase and biofilm. Eighteen S. maltophilia clinical isolates (comprising three isolates from cystic fibrosis (CF) and two trimethoprim-sulfamethoxazole (SXT)-resistant strains) were included. Checkerboard assays showed a synergism of colistin/NAC combinations against the strains with colistin Minimum Inhibitory Concentration (MIC) >2 µg/mL (n = 13), suggesting that NAC could antagonize the mechanisms involved in colistin resistance. Nonetheless, time–kill assays revealed that NAC might potentiate colistin activity also in case of lower colistin MICs. A dose-dependent potentiation of colistin activity by NAC was also clearly observed against S. maltophilia biofilms, also at sub-MIC concentrations. Colistin/NAC combinations, at concentrations likely achievable by topical administration, might represent a valid option for the treatment of S. maltophilia respiratory infections and should be examined further.

Shifting Gears: The Future of Polymyxin Antibiotics

The manuscripts contained in this special edition of Antibiotics represent a current review of the polymyxins as well as highlights from the 3rd International Polymyxin Conference, which was held in Madrid, Spain, April 25 to 26, 2018. The role of the polymyxin antibiotics has evolved over time based on the availability of alternative agents. After high rates of nephrotoxicity caused the drug class to fall out of favor, polymyxins were once against utilized in the 21st century to combat drug-resistant pathogens. However, the introduction of safer agents with activity against drug-resistant organisms has brought the future utility of polymyxins into question. The present review investigates the future niche of polymyxins by evaluating currently available and future treatment options for difficult-to-treat pathogens. The introduction of ceftazidime-avibactam, meropenem-vaborbactam and plazomicin are likely to decrease polymyxin utilization for infections caused by Enterobacteriaceae. Similarly, the availability of ceftolozane-tazobactam will reduce the use of polymyxins to counter multidrug-resistant Pseudomonas aeruginosa. In contrast, polymyxins will likely continue be an important option for combatting carbapenem-resistant Acinetobacter baumannii until better options become commercially available. Measuring polymyxin concentrations in patients and individualizing therapy may be a future strategy to optimize clinical outcomes while minimizing nephrotoxicity. Inhaled polymyxins will continue to be an adjunctive option for pulmonary infections but further clinical trials are needed to clarify the efficacy of inhaled polymyxins. Lastly, safer polymyxin analogs will potentially be an important addition to the antimicrobial armamentarium.

A Breath of Fresh Air in the Fog of Antimicrobial Resistance: Inhaled Polymyxins for Gram-Negative Pneumonia

Despite advancements in therapy, pneumonia remains the leading cause of death due to infectious diseases. Novel treatment strategies are desperately needed to optimize the antimicrobial therapy of patients suffering from this disease. One such strategy that has recently garnered significant attention is the use of inhaled antibiotics to rapidly achieve therapeutic concentrations directly at the site of infection. In particular, there is significant interest in the role of inhaled polymyxins for the treatment of nosocomial pneumonia, including ventilator-associated pneumonia, due to their retained activity against multi-drug resistant Gram-negative pathogens, including Acinetobacter baumannii and Pseudomonas aeruginosa. This review will provide a comprehensive overview of the pharmacokinetic/pharmacodynamic profile, clinical outcomes, safety, and potential role of inhaled polymyxins in clinical practice.

Molecular Characterization of Mucus Binding

Binding of small molecules to mucus membranes in the body has an important role in human health, as it can affect the diffusivity and activity of any molecule that acts in a mucosal environment. The binding of drugs and of toxins and signaling molecules from mucosal pathogens is of particular clinical interest. Despite the importance of mucus-small molecule binding, there is a lack of data revealing the precise chemical features of small molecules that lead to mucus binding. We developed a novel equilibrium dialysis assay to measure the binding of libraries of small molecules to mucin and other mucus components, substantially increasing the throughput of small molecule binding measurements. We validated the biological relevance of our approach by quantifying binding of the antibiotic colistin to mucin, and showing that this binding was associated with inhibition of colistin's bioactivity. We next used a small molecule microarray to identify 2,4-diaminopyrimidine as a mucin binding motif and confirmed the importance of this motif for mucin binding using equilibrium dialysis. Furthermore, we showed that, for molecules with this motif, binding to mucins and the mucus-associated biopolymers DNA and alginate is modulated by differences in hydrophobicity and charge. Finally, we showed that molecules lacking the motif exhibited different binding trends from those containing the motif. These results open up the prospect of routine testing of small molecule binding to mucus and optimization of drugs for clinically relevant mucus binding properties.