Updated US and European Dose Recommendations for Intravenous Colistin: How Do They Perform?

Advances in the clinical treatment of multidrug-resistant pathogens using polymyxins

OBJECTIVES

Polymyxins are a vital class of antibiotics used to combat multidrug-resistant Gram-negative bacteria. However, their use is limited due to potential nephrotoxicity and the availability of alternative antibiotics. This review aims to examine the properties of polymyxins and the clinical advances in their use for treating infections caused by carbapenem-resistant Gram-negative bacteria (CR-GNB).

METHODS

This review analyses literature on polymyxin properties and various clinical approaches, including intravenous drip infusion, nebulized or dry powder inhalation, and ointment application. Treatment efficacy in terms of bacterial eradication, cure rate and mortality rate are reviewed and evaluated.

RESULTS

Polymyxins have been reintroduced to treat critical infections due to the increasing prevalence of CR-GNB. Clinical trials and studies have confirmed that polymyxins can effectively treat CR-GNB infections when the formulation and administration are appropriate, with acceptable levels of nephrotoxicity.

CONCLUSIONS

In the future, the development of polymyxin formulations will aim to improve their clinical effectiveness while reducing toxicity and side effects and preventing the emergence of polymyxin-resistant strains. Enhanced efficacy and minimized potential side effects can be achieved by developing new polymyxin-delivery systems that provide a smart and controlled release or customized patient administration.

L-carnitine co-administration prevents colistin-induced mitochondrial permeability transition and reduces the risk of acute kidney injury in mice

Colistin is a polymyxin antibiotic currently experiencing renewed clinical interest due to its efficacy in the treatment of multidrug resistant (MDR) bacterial infections. The frequent onset of acute dose-dependent kidney injury, with the potential of leading to long-term renal damage, has limited its use and hampered adequate dosing regimens, increasing the risk of suboptimal plasma concentrations during treatment. The mechanism of colistin-induced renal toxicity has been postulated to stem from mitochondrial damage, yet there is no direct evidence of colistin acting as a mitochondrial toxin. The aim of this study was to evaluate whether colistin can directly induce mitochondrial toxicity and, if so, uncover the underlying molecular mechanism. We found that colistin leads to a rapid permeability transition of mitochondria isolated from mouse kidney that was fully prevented by co-incubation of the mitochondria with desensitizers of the mitochondrial transition pore cyclosporin A or L-carnitine. The protective effect of L-carnitine was confirmed in experiments in primary cultured mouse tubular cells. Consistently, the relative risk of colistin-induced kidney damage, calculated based on histological analysis as well as by the early marker of tubular kidney injury, Kim-1, was halved under co-administration with L-carnitine in vivo. Notably, L-carnitine neither affected the pharmacokinetics of colistin nor its antimicrobial activity against relevant bacterial strains. In conclusion, colistin targets the mitochondria and induces permeability transition thereof. L-carnitine prevents colistin-induced permeability transition in vitro. Moreover, L-carnitine co-administration confers partial nephroprotection in mice treated with colistin, without interfering with its pharmacokinetics and antibacterial activity.

Colistin plasma concentrations are not associated with better clinical outcomes in patients with pneumonia caused by extremely drug-resistant Pseudomonas aeruginosa

IMPORTANCE

In some cases, colistin is the only treatment option for infections caused by the very drug-resistant Pseudomonas aeruginosa. However, in the past decade, there have been questions concerning its pharmacokinetics and concentration at the site of infection. In this scenario, its use in a difficult-to-treat infection like pneumonia is currently debatable. This is a clinical pharmacokinetic study of colistin in patients with multidrug-resistant P. aeruginosa pneumonia. Our findings demonstrate that colistin exposure is associated with worse clinical outcomes rather than better clinical outcomes, implying that other therapeutic options should be explored in this clinical setting.

Treatment and diagnosis of severe KPC-producing Klebsiella pneumoniae infections: a perspective on what has changed over last decades

Antimicrobial resistance is a global health threat. Among Gram-negative bacteria, resistance to carbapenems, a class of β-lactam antibiotics, is usually a proxy for difficult-to-treat resistance, since carbapenem-resistant organisms are often resistant to many classes of antibiotics. Carbapenem resistance in the Gram-negative pathogen Klebsiella pneumoniae is mostly due to the production of carbapenemases, enzymes able to hydrolyze carbapenems, and K. pneumoniae carbapenemase (KPC)-type enzymes are overall the most prevalent carbapenemases in K. pneumoniae. In the last decade, the management of severe infections due to KPC-producing K. pneumoniae (KPC-Kp) in humans has presented many peculiar challenges to clinicians worldwide. In this perspective, we discuss how the treatment of severe KPC-Kp infections has evolved over the last decades, guided by the accumulating evidence from clinical studies, and how recent advances in diagnostics have allowed to anticipate identification of KPC-Kp in infected patients.KEY MESSAGESIn the last decade, the management of severe infections due to KPC-Kp has presented many peculiar challenges to clinicians worldwideFollowing the introduction in clinical practice of novel β-lactam/β-lactamase inhibitor combinations and novel β-lactams active against KPC-producing bacteria, the management of severe KPC-Kp infections has witnessed a remarkable evolutionTreatment of severe KPC-Kp infections is a highly dynamic process, in which the wise use of novel antimicrobials should be accompanied by a continuous refinement based on evolving clinical evidence and laboratory diagnostics.

Pharmacokinetic/pharmacodynamic (PK/PD) simulation for dosage optimization of colistin and sitafloxacin, alone and in combination, against carbapenem-, multidrug-, and colistin-resistant Acinetobacter baumannii

To the best of our knowledge, to date, no study has investigated the optimal dosage regimens of either colistin or sitafloxacin against drug-resistant Acinetobacter baumannii (A. baumannii) infections by using specific parameters. In the current study, we aimed to explore the optimal dosage regimens of colistin and sitafloxacin, either in monotherapy or in combination therapy, for the treatment of carbapenem-, multidrug-, and colistin-resistant A. baumannii infections. A Monte Carlo simulation was applied to determine the dosage regimen that could achieve the optimal probability of target attainment (PTA) and cumulative fraction of response (CFR) (≥90%) based on the specific parameters of each agent and the minimal inhibitory concentration (MIC) of the clinical isolates. This study explored the dosage regimen of 90, 50, 30, and 10 mL/min for patients with creatinine clearance (CrCL). We also explored the dosage regimen for each patient with CrCL using combination therapy because there is a higher possibility of reaching the desired PTA or CFR. Focusing on the MIC90 of each agent in combination therapy, the dosage regimen for colistin was a loading dose of 300 mg followed by a maintenance dose ranging from 50 mg every 48 h to 225 mg every 12 h and the dosage regimen for sitafloxacin was 325 mg every 48 h to 750 mg every 12 h. We concluded that a lower-than-usual dose of colistin based on specific pharmacokinetic data in combination with a higher-than-usual dose of sitafloxacin could be an option for the treatment of carbapenem-, multidrug-, and colistin-resistant. A. baumannii. The lower dose of colistin might show a low probability of adverse reaction, while the high dose of sitafloxacin should be considered. In the current study, we attempted to find if there is a strong possibility of drug selection against crucial drug-resistant pathogen infections in a situation where there is a lack of new antibiotics. However, further study is needed to confirm the results of this simulation study.

Age of Antibiotic Resistance in MDR/XDR Clinical Pathogen of Pseudomonas aeruginosa

Antibiotic resistance in Pseudomonas aeruginosa remains one of the most challenging phenomena of everyday medical science. The universal spread of high-risk clones of multidrug-resistant/extensively drug-resistant (MDR/XDR) clinical P. aeruginosa has become a public health threat. The P. aeruginosa bacteria exhibits remarkable genome plasticity that utilizes highly acquired and intrinsic resistance mechanisms to counter most antibiotic challenges. In addition, the adaptive antibiotic resistance of P. aeruginosa, including biofilm-mediated resistance and the formation of multidrug-tolerant persisted cells, are accountable for recalcitrance and relapse of infections. We highlighted the AMR mechanism considering the most common pathogen P. aeruginosa, its clinical impact, epidemiology, and save our souls (SOS)-mediated resistance. We further discussed the current therapeutic options against MDR/XDR P. aeruginosa infections, and described those treatment options in clinical practice. Finally, other therapeutic strategies, such as bacteriophage-based therapy and antimicrobial peptides, were described with clinical relevance.

Guidelines for the diagnosis, treatment, prevention and control of infections caused by carbapenem-resistant gram-negative bacilli

The dissemination of carbapenem-resistant Gram-negative bacilli (CRGNB) is a global public health issue. CRGNB isolates are usually extensively drug-resistant or pandrug-resistant, resulting in limited antimicrobial treatment options and high mortality. A multidisciplinary guideline development group covering clinical infectious diseases, clinical microbiology, clinical pharmacology, infection control, and guideline methodology experts jointly developed the present clinical practice guidelines based on best available scientific evidence to address the clinical issues regarding laboratory testing, antimicrobial therapy, and prevention of CRGNB infections. This guideline focuses on carbapenem-resistant Enterobacteriales (CRE), carbapenem-resistant Acinetobacter baumannii (CRAB), and carbapenem-resistant Pseudomonas aeruginosa (CRPA). Sixteen clinical questions were proposed from the perspective of current clinical practice and translated into research questions using PICO (population, intervention, comparator, and outcomes) format to collect and synthesize relevant evidence to inform corresponding recommendations. The grading of recommendations, assessment, development and evaluation (GRADE) approach was used to evaluate the quality of evidence, benefit and risk profile of corresponding interventions and formulate recommendations or suggestions. Evidence extracted from systematic reviews and randomized controlled trials (RCTs) was considered preferentially for treatment-related clinical questions. Observational studies, non-controlled studies, and expert opinions were considered as supplementary evidence in the absence of RCTs. The strength of recommendations was classified as strong or conditional (weak). The evidence informing recommendations derives from studies worldwide, while the implementation suggestions combined the Chinese experience. The target audience of this guideline is clinician and related professionals involved in management of infectious diseases.

Active Clinical Trials in Hepatic Encephalopathy: Something Old, Something New and Something Borrowed

Hepatic encephalopathy (HE) is a potentially reversible neurocognitive syndrome that occurs in patients with acute or chronic liver disease. Currently, most of the therapies for HE aim to reduce ammonia production or increase its elimination. To date, only two agents have been approved as treatments for HE: lactulose and rifaximin. Many other drugs have also been used, but data to support their use are limited, preliminary or lacking. The aim of this review is to provide an overview and discussion of the current development of treatments for HE. Data from ongoing clinical trials in HE were obtained from the ClinicalTrials.gov website, and a breakdown analysis of studies that were active on August 19th, 2022, was performed. Seventeen registered and ongoing clinical trials for therapeutics targeting HE were identified. More than 75% of these agents are in phase II (41.2%) or in phase III (34.7%). Among them, there are many old acquaintances in the field, such as lactulose and rifaximin, some new entries such as fecal microbiota transplantation and equine anti-thymocyte globulin, an immunosuppressive agent, but also some therapies borrowed from other conditions, such as rifamycin SV MMX and nitazoxanide, two antimicrobial agents FDA approved for the treatment of some types of diarrheas or VE303 and RBX7455, two microbiome restoration therapies, currently used as treatment of high-risk Clostridioides difficile infections. If working, some of these drugs could soon be used as valid alternatives to current therapies when ineffective or be approved as novel therapeutic approaches to improve the quality of life of HE patients.

Hepatic encephalopathy: investigational drugs in preclinical and early phase development

INTRODUCTION

Hepatic encephalopathy (HE) is a neuropsychiatric syndrome, in patients with liver disease, which affects life quality and span. Current treatments are lactulose or rifaximin, acting on gut microbiota. Treatments aiming ammonia levels reduction have been tested with little success.

AREAS COVERED

Pre-clinical research shows that the process inducing HE involves sequentially: liver failure, altered microbiome, hyperammonemia, peripheral inflammation, changes in immunophenotype and extracellular vesicles and neuroinflammation, which alters neurotransmission impairing cognitive and motor function. HE may be reversed using drugs acting at any step: modulating microbiota with probiotics or fecal transplantation; reducing peripheral inflammation with anti-TNFα, autotaxin inhibitors or silymarin; reducing neuroinflammation with sulforaphane, p38 MAP kinase or phosphodiesteras 5 inhibitors, antagonists of sphingosine-1-phosphate receptor 2, enhancing meningeal lymphatic drainage or with extracellular vesicles from mesenchymal stem cells; reducing GABAergic neurotransmission with indomethacin or golexanolone.

EXPERT OPINION

A factor limiting the progress of HE treatment is the lack of translation of research advances into clinical trials. Only drugs acting on microbiota or ammonia reduction have been tested in patients. It is urgent to change the mentality on how to approach HE treatment to develop clinical trials to assess drugs acting on the immune system/peripheral inflammation, neuroinflammation or neurotransmission to improve HE.

Unravelling the Hepatic Elimination Mechanisms of Colistin

PURPOSE

Colistin is an antibiotic which is increasingly used as a last-resort therapy in critically-ill patients with multidrug resistant Gram-negative infections. The purpose of this study was to evaluate the mechanisms underlying colistin's pharmacokinetic (PK) behavior and to characterize its hepatic metabolism.

METHODS

In vitro incubations were performed using colistin sulfate with rat liver microsomes (RLM) and with rat and human hepatocytes (RH and HH) in suspension. The uptake of colistin in RH/HH and thefraction of unbound colistin in HH (fu,hep) was determined. In vitro to in vivo extrapolation (IVIVE) was employed to predict the hepatic clearance (CLh) of colistin.

RESULTS

Slow metabolism was detected in RH/HH, with intrinsic clearance (CLint) values of 9.34± 0.50 and 3.25 ± 0.27 mL/min/kg, respectively. Assuming the well-stirred model for hepatic drug elimination, the predicted rat CLh was 3.64± 0.22 mL/min/kg which could explain almost 70% of the reported non-renal in vivo clearance. The predicted human CLh was 91.5 ± 8.83 mL/min, which was within two-fold of the reported plasma clearance in healthy volunteers. When colistin was incubated together with the multidrug resistance-associated protein (MRP/Mrp) inhibitor benzbromarone, the intracellular accumulation of colistin in RH/HH increased significantly.

CONCLUSION

These findings indicate the major role of hepatic metabolism in the non-renal clearance of colistin, while MRP/Mrp-mediated efflux is involved in the hepatic disposition of colistin. Our data provide detailed quantitative insights into the hereto unknown mechanisms responsible for non-renal elimination of colistin.

Colistin- and amikacin-loaded lipid-based drug delivery systems for resistant gram-negative lung and wound bacterial infections

Antimicrobial resistance (AMR) is a global health issue, which needs to be tackled without further delay. The World Health Organization(WHO) has classified three gram-negative bacteria, Pseudomonas aeruginosa, Klebsiella pneumonia and Acinetobacter baumannii, as the principal responsible for AMR, mainly causing difficult to treat nosocomial lung and wound infections. In this regard, the need for colistin and amikacin, the re-emerged antibiotics of choice for resistant gram-negative infections, will be examined as well as their associated toxicity. Thus, current but ineffective clinical strategies designed to prevent toxicity related to colistin and amikacin will be reported, highlighting the importance of lipid-based drug delivery systems (LBDDSs), such as liposomes, solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs), as efficient delivery strategies for reducing antibiotic toxicity. This review reveals that colistin- and amikacin-NLCs are promising carriers with greater potential than liposomes and SLNs to safely tackle AMR, especially for lung and wound infections.

Dexmedetomidine may reduce the risk of acute kidney injury development in critically ill patients during colistin therapy

INTRODUCTION

Colistin is considered as a last resort therapy for multidrug-resistant gram-negative organisms. It is widely used despite the significant risk of nephrotoxicity. Experimental studies showed the nephroprotective effect of dexmedetomidine, a sedative agent, against colistin toxicity. This study was performed to show the possible nephroprotective effect of dexmedetomidine among critically ill patients who received colistin.

METHODS

Adult (>17 years) patients who were admitted to our surgical and medical intensive care unit (ICU) from March 2018 through March 2021, and who received colistin were included. Patients who receive Colistin therapy or intensive care unit follow-up of <72 h (discharge or death) and Acute kidney injury (AKI) or need hemodialysis prior to colistin therapy at the same hospitalization were excluded. AKI risk factors were examined by grouping patients with and without AKI. Patients, receiving colistin concomitantly with dexmedetomidine were also evaluated.

RESULTS

Of the 139 patients included, 27 (17.8%) patients received dexmedetomidine. Sixty-five patients (47%) had AKI, at a median 5 (4-7) days after the initiation of colistin. Older age, lower baseline estimated glomerular filtration rate, and vasopressor use were associated with a higher risk of AKI, while dexmedetomidine use was associated with a lower risk. In the multivariate regression model, dexmedetomidine use was independently associated with a lower risk of AKI development (OR 0.20 95% CI 0.07-0.59, p = 0.003).

CONCLUSION

In respect to these findings, dexmedetomidine may provide protection against AKI during colistin therapy in critically ill patients.

Pharmacokinetic and pharmacodynamic properties of polymyxin B in Escherichia coli and Klebsiella pneumoniae murine infection models

BACKGROUND

Although polymyxin B has been in use since the late 1950s, there have been limited studies done to unravel its pharmacokinetics (PK) and pharmacodynamics (PD) index.

METHODS

We determined, in neutropenic infected mice, the PK, plasma protein binding and PK/PD index best correlating with efficacy for Escherichia coli and Klebsiella pneumoniae strains.

RESULTS

The pharmacokinetic profile showed non-linear PK; dose was significantly correlated with absorption rate and clearance. The inhibitory sigmoid dose-effect model for the fCmax/MIC index of E. coli fitted best, but was only modestly higher than the R2 of %fT>MIC and fAUC/MIC (R2 0.91-0.93). For K. pneumoniae the fAUC/MIC index had the best fit, which was slightly higher than the R2 of %fT>MIC and fCmax/MIC (R2 0.85-0.91). Static targets of polymyxin B fAUC/MIC were 27.5-102.6 (median 63.5) and 5.9-60.5 (median 11.6) in E. coli and in K. pneumoniae isolates, respectively. A 1 log kill effect was only reached in two E. coli isolates and one K. pneumoniae. The PTA with the standard dosing was low for isolates with MIC >0.25 mg/L.

CONCLUSIONS

This study confirms that fAUC/MIC can describe the exposure-response relationship for polymyxin B. The 1 log kill effect was achieved in the minority of the isolates whereas polymyxin B PK/PD targets cannot be attained for the majority of clinical isolates with the standard dosing regimen, indicating that polymyxin B may be not effective against serious infections as monotherapy.

Empirical antibiotic therapy for difficult-to-treat Gram-negative infections: when, how, and how long?

PURPOSE OF REVIEW

To discuss empirical therapy for severe infections due to Gram-negative bacteria with difficult-to-treat resistance (GNB-DTR) in current clinical practice, focusing in particular on the positioning of novel therapeutic agents and rapid diagnostic tests.

RECENT FINDINGS

The current era of novel agents active against GNB-DTR and showing differential activity against specific determinants of resistance is an unprecedented scenario, in which the clinical reasoning leading to the choice of the empirical therapy for treating severe GNB-DTR infections is becoming more complex, but it also allows for enhanced treatment precision.

SUMMARY

Novel agents should be used in line with antimicrobial stewardship principles, aimed at reducing selective pressure for antimicrobial resistance. However, this does not mean that they should not be used. Indeed, excesses in restrictive uses may be unethical by precluding access to the most effective and less toxic treatments for patients with severe GNB-DTR infections. Given these premises (the 'how'), empirical treatment with novel agents should be considered in all patients with risk factors for GNB-DTR and severe clinical presentation of acute infection (the 'when'). Furthermore, empirical novel agents should preferably be continued only for a few hours, until de-escalation, modification, or confirmation (as targeted therapy) is made possible by the results of rapid diagnostic tests (the 'how long').

Isolation, Identification, and Genetic Characterization of Antibiotic Resistance of Salmonella Species Isolated from Chicken Farms

Salmonella is a major cause of foodborne outbreaks. It causes gastroenteritis in humans and animals. This micro-organism causes severe illness in chickens and has a major impact on chicken productivity and the poultry industry. This study aimed to address the prevalence of Salmonella infection in broiler chicken farms in Kafrelsheikh, Gharbia, and Menofeya provinces in Egypt during 2020-2022. This work also aimed to evaluate the genetic characterization and antibiotic resistance of the isolated Salmonella strains. Clinical signs and mortalities were observed and recorded. In total, 832 samples were collected from 52 broiler flocks, including 26 from both one-week-old and 6-week-old chicken farms from different organs (liver, intestinal content, spleen, and gallbladder). The prevalence of Salmonella infections was reported in the study region to be 36.54%. Of the 26 one-week-old farms surveyed, 11 (42.31%) and 8/26 (30.77%) of the six-week-old broiler chicken farms had Salmonella infections. Recovered isolates were serotyped as 9 (47.37%) S. enteritidis O 1,9,12, ad monophasic H: g, m: -, 6 (31.58.%) S. shangani 2, (10.53%) S. gueuletapee 1, (5.26%) S. II (salamae), and 1 (5.26%) untypable. The results showed that Salmonella infection was predominant in one-week-old chicks compared to infection in six-week-old and uninfected flocks. All Salmonella isolates were resistant to ampicillin and erythromycin, while all isolates were sensitive to ciprofloxacin, chloramphenicol, and levofloxacin. The isolates also contained 10.53% (2/19) streptomycin, 10.53% (2/21) gentamicin, 15.79% (3/19) doxycycline, and 26.32% (5/19) lincomycin and colistin. The phenotypically resistant Salmonella samples against ampicillin, erythromycin, and macrolide harbored bla _TEM , bla _SHV , ermB, ereA, mphA, and ermB, respectively. This baseline data on Salmonella spp. prevalence, serotyping, and antibiotic profiles are combined to define the antimicrobial resistance to this endemic disease. Elucidation of the mechanisms underlying this drug resistance should be of general importance in understanding both the treatment and prevention of Salmonella infection in this part of Egypt.

Next-Generation Polymyxin Class of Antibiotics: A Ray of Hope Illuminating a Dark Road

Although new-generation antimicrobials, in particular β-lactam/β-lactamase inhibitors, have largely replaced polymyxins in carbapenem-resistant Gram-negative bacterial infections, polymyxins are still needed for carbapanem-resistant Acinetobacter baumannii infections and in settings where novel agents are not readily available. Despite their potent in vitro activity, the clinical utility of polymyxins is significantly limited by their pharmacokinetic properties and nephrotoxicity risk. There is significant interest, therefore, in developing next-generation polymyxins with activity against colistin-resistant strains and lower toxicity than existing polymyxins. In this review, we aim to present the antibacterial activity mechanisms, in vitro and in vivo efficacy data, and toxicity profiles of new-generation polymyxins, including SPR206, MRX-8, and QPX9003, as well as the general characteristics of old polymyxins. Considering the emergence of colistin-resistant strains particularly in endemic regions, the restoration of the antimicrobial activity of polymyxins via PBT2 is also described in this review.

Causes of polymyxin treatment failure and new derivatives to fill the gap

Polymyxins are a class of antibiotics that were discovered in 1947 from programs searching for compounds effective in the treatment of Gram-negative infections. Produced by the Gram-positive bacterium Paenibacillus polymyxa and composed of a cyclic peptide chain with a peptide-fatty acyl tail, polymyxins exert bactericidal effects through membrane disruption. Currently, polymyxin B and colistin (polymyxin E) have been developed for clinical use, where they are reserved as "last-line" therapies for multidrug-resistant (MDR) infections. Unfortunately, the incidences of strains resistant to polymyxins have been increasing globally, and polymyxin heteroresistance has been gaining appreciation as an important clinical challenge. These phenomena, along with bacterial tolerance to this antibiotic class, constitute important contributors to polymyxin treatment failure. Here, we review polymyxins and their mechanism of action, summarize the current understanding of how polymyxin treatment fails, and discuss how the next generation of polymyxins holds promise to invigorate this antibiotic class.

Neutrophil-mediated delivery of the combination of colistin and azithromycin for the treatment of bacterial infection

Novel treatment strategies are in urgent need to deal with the rapid development of antibiotic-resistant superbugs. Combination therapies and targeted drug delivery have been exploited to promote treatment efficacies. In this study, we loaded neutrophils with azithromycin and colistin to combine the advantages of antibiotic combinations, targeted delivery, and immunomodulatory effect of azithromycin to treat infections caused by Gram-negative pathogens. Delivery of colistin into neutrophils was mediated by fusogenic liposome, while azithromycin was directly taken up by neutrophils. Neutrophils loaded with the drugs maintained the abilitity to generate reactive oxygen species and migrate. In vitro assays demonstrated enhanced bactericidal activity against multidrug-resistant pathogens and reduced inflammatory cytokine production by the drug-loaded neutrophils. A single intravenous administration of the drug-loaded neutrophils effectively protected mice from Pseudomonas aeruginosa infection in an acute pneumonia model. This study provides a potential effective therapeutic approach for the treatment of bacterial infections.

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Neutrophils are loaded with colistin and azithromycin in vitro

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The loaded drugs enhance the bactericidal effect and reduce the inflammatory response

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Drug-loaded neutrophils conferred effective protection against bacterial infection

Pharmacokinetics and Pharmacodynamics of Colistin Methanesulfonate in Healthy Chinese Subjects after Multi-Dose Regimen

Colistin methanesulfonate (CMS) is an important treatment option for infections caused by carbapenem-resistant Gram-negative organisms (CROs). This study evaluated the pharmacokinetic/pharmacodynamic (PK/PD) profiles and safety of CMS in Chinese subjects following a recommended dosage. A total of 12 healthy Chinese subjects received CMS injections at 2.5 mg/kg once every 12 h for 7 consecutive days. The PK/PD profiles of the active form of CMS, colistin, against CROs were analyzed with the Monte Carlo simulation method. No serious adverse events were observed. The average steady-state plasma concentrations of CMS and colistin were 4.41 ± 0.75 μg/mL and 1.27 ± 0.27 μg/mL, and the steady-state exposures (AUC0−12,ss) were 52.93 ± 9.05 h·μg/mL and 15.28 ± 3.29 h·μg/mL, respectively. Colistin, at its minimum inhibitory concentration (MIC) of 0.5 μg/mL, has >90% probability to reduce CROs by ≥1 log. The PK/PD breakpoints for the ≥1 log kill were ≥MIC90 for carbapenem-resistant Klebsiella pneumoniae and Pseudomonas aeruginosa, but were ≤MIC50 for carbapenem-resistant Acinetobacter baumannii. The recommended dose regimen of CMS for 7 consecutive days was safe in Chinese subjects. The systemic exposure of colistin showed a high probability of being sufficient for most CROs, but was not sufficient for some carbapenem-resistant A. baumannii.

Transdermal Delivery of High Molecular Weight Antibiotics to Deep Tissue Infections via Droplette Micromist Technology Device (DMTD)

Wound infection by multidrug-resistant (MDR) bacteria is a major disease burden. Systemic administration of broad-spectrum antibiotics colistin methanesulfonate (CMS) and vancomycin are the last lines of defense against deep wound infections by MDR bacteria. However, systemic administration of CMS and vancomycin are linked to life-threatening vital organ damage. Currently there are no effective topical application strategies to deliver these high molecular weight antibiotics across the stratum corneum. To overcome this difficulty, we tested if high molecular weight antibiotics delivered by Droplette micromist technology device (DMTD), a transdermal delivery device that generates a micromist capable of packaging large molecules, could attenuate deep skin tissue infections. Using green fluorescent protein-tagged E. coli and live tissue imaging, we show that (1) the extent of attenuation of deep-skin E. coli infection was similar when treated with topical DMTD- or systemic IP (intraperitoneal)-delivered CMS; (2) DMTD-delivered micromist did not spread the infection deeper; (3) topical DMTD delivery and IP delivery resulted in similar levels of vancomycin in the skin after a 2 h washout period; and (4) IP-delivered vancomycin was about 1000-fold higher in kidney and plasma than DMTD-delivered vancomycin indicating systemic toxicity. Thus, topical DMTD delivery of these antibiotics is a safe treatment for the difficult-to-treat deep skin tissue infections by MDR bacteria.

Dosing Colistimethate Every 8 h Results in Higher Plasma Concentrations of Active Colistin Than Every 12-Hourly Dosing without Increase in Nephrotoxicity: A Phase 1 Pharmacokinetics Trial in Healthy Adult Volunteers

Despite its use for decades, pharmacokinetic (PK) and safety studies on colistin are limited. We conducted a phase l, open-label trial to evaluate the safety and PK of multiple doses of intravenous (IV) and aerosolized colistimethate sodium (CMS) administered separately and in combination. In total, 31 healthy adults were enrolled into three cohorts of 9, 10, and 12 participants, respectively. Each cohort received increasing doses of CMS over three dosing periods as follows: Period 1 (IV only), 2.5 mg/kg every 12 h (q12h) to 3.3 mg/kg every 8 h (q8h); Period 2 (aerosolized only), 75 mg 2–4 doses, and Period 3 (combined IV aerosolized), in which was Periods 1 and 2 combined. Safety assessments, serum and lung concentrations of colistin analytes (colistin A, colistin B, CMS A, and CMS B), and kidney biomarkers were measured at specified time points. Increasing the CMS dose from 2.5 mg/kg q12h to q8h resulted in a 33% increase in serum colistin A concentrations from 3.9 μg/mL to 5.3 μg/mL—well above the accepted target of 2 μg/mL for 6 h after dosing, without evidence of nephrotoxicity. However, there was an increase in neurotoxicity, primarily perioral and lingual paresthesias, and self-limited ataxia. IV administration did not increase the lung concentrations of colistin.

The necessity of a loading dose when prescribing intravenous colistin in critically ill patients with CRGNB-associated pneumonia: a multi-center observational study

Background

The importance or necessity of a loading dose when prescribing intravenous colistin has not been well established in clinical practice, and approximate one-third to half of patients with carbapenem-resistant gram-negative bacteria (CRGNB) infection did not receive the administration of a loading dose. The aim of this study is to investigate the efficacy and risk of acute kidney injury when prescribing intravenous colistin for critically ill patients with nosocomial pneumonia caused by CRGNB.

Methods

This was a multicenter, retrospective study that recruited ICU-admitted patients who had CRGNB-associated nosocomial pneumonia and were treated with intravenous colistin. Then, we classified the patients into colistin loading dose (N = 85) and nonloading dose groups (N = 127). After propensity-score matching for important covariates, we compared the mortality rate, clinical outcome and microbiological eradication rates between the groups (N = 67).

Results

The loading group had higher percentages of patients with favorable clinical outcomes (55.2% and 35.8%, p = 0.037) and microbiological eradication rates (50% and 27.3%, p = 0.042) at day 14 than the nonloading group. The mortality rates at days 7, 14 and 28 and overall in-hospital mortality were not different between the two groups, but the Kaplan–Meier analysis showed that the loading group had a longer survival time than the nonloading group. Furthermore, the loading group had a shorter length of hospital stay than the nonloading group (52 and 60, p = 0.037). Regarding nephrotoxicity, there was no significant difference in the risk of developing acute kidney injury between the groups.

Conclusions

The administration of a loading dose is recommended when prescribing intravenous colistin for critically ill patients with nosocomial pneumonia caused by CRGNB.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-022-03947-9.

Pharmacokinetics and pharmacodynamics of peptide antibiotics

Antimicrobial resistance is a major global health challenge. As few new efficacious antibiotics will become available in the near future, peptide antibiotics continue to be major therapeutic options for treating infections caused by multidrug-resistant pathogens. Rational use of antibiotics requires optimisation of the pharmacokinetics and pharmacodynamics for the treatment of different types of infections. Toxicodynamics must also be considered to improve the safety of antibiotic use and, where appropriate, to guide therapeutic drug monitoring. This review focuses on the pharmacokinetics/pharmacodynamics/toxicodynamics of peptide antibiotics against multidrug-resistant Gram-negative and Gram-positive pathogens. Optimising antibiotic exposure at the infection site is essential for improving their efficacy and minimising emergence of resistance.

Transcriptomics Reveals How Minocycline-Colistin Synergy Overcomes Antibiotic Resistance in Multidrug-Resistant Klebsiella pneumoniae

Multidrug-resistant Gram-negative bacteria are a rapidly growing public health threat, and the development of novel antimicrobials has failed to keep pace with their emergence. Synergistic combinations of individually ineffective drugs present a potential solution, yet little is understood about the mechanisms of most such combinations. Here, we show that the combination of colistin (polymyxin E) and minocycline has a high rate of synergy against colistin-resistant and minocycline-intermediate or -resistant strains of Klebsiella pneumoniae. Furthermore, using transcriptome sequencing (RNA-Seq), we characterized the transcriptional profiles of these strains when treated with the drugs individually and in combination. We found a striking similarity between the transcriptional profiles of bacteria treated with the combination of colistin and minocycline at individually subinhibitory concentrations and those of the same isolates treated with minocycline alone. We observed a similar pattern with the combination of polymyxin B nonapeptide (a polymyxin B analogue that lacks intrinsic antimicrobial activity) and minocycline. We also found that genes involved in polymyxin resistance and peptidoglycan biosynthesis showed significant differential gene expression in the different treatment conditions, suggesting possible mechanisms for the antibacterial activity observed in the combination. These findings suggest that the synergistic activity of this combination against bacteria resistant to each drug alone involves sublethal outer membrane disruption by colistin, which permits increased intracellular accumulation of minocycline.

The Role of Colistin in the Era of New β-Lactam/β-Lactamase Inhibitor Combinations

With the current crisis related to the emergence of carbapenem-resistant Gram-negative bacteria (CR-GNB), classical treatment approaches with so-called “old-fashion antibiotics” are generally unsatisfactory. Newly approved β-lactam/β-lactamase inhibitors (BLBLIs) should be considered as the first-line treatment options for carbapenem-resistant Enterobacterales (CRE) and carbapenem-resistant Pseudomonas aeruginosa (CRPA) infections. However, colistin can be prescribed for uncomplicated lower urinary tract infections caused by CR-GNB by relying on its pharmacokinetic and pharmacodynamic properties. Similarly, colistin can still be regarded as an alternative therapy for infections caused by carbapenem-resistant Acinetobacter baumannii (CRAB) until new and effective agents are approved. Using colistin in combination regimens (i.e., including at least two in vitro active agents) can be considered in CRAB infections, and CRE infections with high risk of mortality. In conclusion, new BLBLIs have largely replaced colistin for the treatment of CR-GNB infections. Nevertheless, colistin may be needed for the treatment of CRAB infections and in the setting where the new BLBLIs are currently unavailable. In addition, with the advent of rapid diagnostic methods and novel antimicrobials, the application of personalized medicine has gained significant importance in the treatment of CRE infections.

Therapeutic Drug Monitoring of Antibiotics in Critically Ill Patients: Current Practice and Future Perspectives With a Focus on Clinical Outcome

PURPOSE

Early initiation of antibiotics is essential for ameliorating infections in critically ill patients. The correct dosage of antibiotics is imperative to ensure their adequate exposure. Critically ill patients have altered pharmacokinetic parameters and are often infected by less susceptible microorganisms. Differences in drug disposition are not considered with standard doses of antibiotics. This can lead to suboptimal antibiotic exposure in critically ill patients. To overcome this problem of suboptimal dosing, therapeutic drug monitoring (TDM) is a strategy commonly used to support individualized dosing of antibiotics. It is routinely used for vancomycin and aminoglycosides in clinical practice. In recent years, it has become apparent that TDM may also be used in other antibiotics.

METHODS

This review summarizes the evidence for TDM of antibiotics in critically ill patients, focuses on clinical outcomes, and summarizes possibilities for optimized TDM in the future.

RESULTS AND CONCLUSION

After reviewing the literature, we can conclude that general TDM implementation is advised for glycopeptides and aminoglycosides, as evidence of the relationship between TDM and clinical outcome is present. For antibiotics, such as beta-lactams, fluoroquinolones, and linezolid, it seems rational to perform TDM in specific patient cases. TDM involving other antibiotics is supported by individual cases, specifically to decrease toxicity. When focusing on future possibilities to improve TDM of antibiotics in critically ill patients, implementation of model-informed precision dosing should be investigated because it can potentially streamline the TDM process. The logistics of TDM, such as turnaround time and available equipment, are challenging but may be overcome by rapid bioanalytical techniques or real-time monitoring of drug concentrations through biosensors in the future. Education, clinical information on targets, and clinical outcome studies are other important factors that facilitate TDM implementation.

Breaking antimicrobial resistance by disrupting extracytoplasmic protein folding

Antimicrobial resistance in Gram-negative bacteria is one of the greatest threats to global health. New antibacterial strategies are urgently needed, and the development of antibiotic adjuvants that either neutralize resistance proteins or compromise the integrity of the cell envelope is of ever-growing interest. Most available adjuvants are only effective against specific resistance proteins. Here, we demonstrate that disruption of cell envelope protein homeostasis simultaneously compromises several classes of resistance determinants. In particular, we find that impairing DsbA-mediated disulfide bond formation incapacitates diverse β-lactamases and destabilizes mobile colistin resistance enzymes. Furthermore, we show that chemical inhibition of DsbA sensitizes multidrug-resistant clinical isolates to existing antibiotics and that the absence of DsbA, in combination with antibiotic treatment, substantially increases the survival of Galleria mellonella larvae infected with multidrug-resistant Pseudomonas aeruginosa. This work lays the foundation for the development of novel antibiotic adjuvants that function as broad-acting resistance breakers.

Antibiotics, like penicillin, are the foundation of modern medicine, but bacteria are evolving to resist their effects. Some of the most harmful pathogens belong to a group called the 'Gram-negative bacteria', which have an outer layer – called the cell envelope – that acts as a drug barrier. This envelope contains antibiotic resistance proteins that can deactivate or repel antibiotics or even pump them out of the cell once they get in. One way to tackle antibiotic resistance could be to stop these proteins from working.

Proteins are long chains of building blocks called amino acids that fold into specific shapes. In order for a protein to perform its role correctly, it must fold in the right way. In bacteria, a protein called DsbA helps other proteins fold correctly by holding them in place and inserting links called disulfide bonds. It was unclear whether DsbA plays a role in the folding of antibiotic resistance proteins, but if it did, it might open up new ways to treat antibiotic resistant infections.

To find out more, Furniss, Kaderabkova et al. collected the genes that code for several antibiotic resistance proteins and put them into Escherichia coli bacteria, which made the bacteria resistant to antibiotics. Furniss, Kaderabkova et al. then stopped the modified E. coli from making DsbA, which led to the antibiotic resistance proteins becoming unstable and breaking down because they could not fold correctly.

Further experiments showed that blocking DsbA with a chemical inhibitor in other pathogenic species of Gram-negative bacteria made these bacteria more sensitive to antibiotics that they would normally resist. To demonstrate that using this approach could work to stop infections by these bacteria, Furniss, Kaderabkova et al. used Gram-negative bacteria that produced antibiotic resistance proteins but could not make DsbA to infect insect larvae. The larvae were then treated with antibiotics, which increased their survival rate, indicating that blocking DsbA may be a good approach to tackling antibiotic resistant bacteria.

According to the World Health Organization, developing new treatments against Gram-negative bacteria is of critical importance, but the discovery of new drugs has ground to a halt. One way around this is to develop ways to make existing drugs work better. Making drugs that block DsbA could offer a way to treat resistant infections using existing antibiotics in the future.

Colistin-Induced Acute Kidney Injury and the Effect on Survival in Patients with Multidrug-Resistant Gram-Negative Infections: Significance of Drug Doses Adjusted to Ideal Body Weight

Background

Colistin is a lifesaving treatment for multidrug-resistant Gram-negative bacterial (MDR-GNB) infections along with its well-known nephrotoxicity. The controversy of colistin-induced acute kidney injury (AKI) on mortality is noted. This study aimed to determine the risk factors and impact of AKI on the survival and significance of colistin dosage.

Methods

A retrospective cohort study was performed in adult patients who received intravenous colistin for MDR-GNB treatment between June 2015 and June 2017. Factors influencing colistin-induced AKI and survival were evaluated by Cox regression analysis. Cut-off levels of the colistin dose per ideal body weight (IBW) that significantly affected clinical outcomes were assessed with linearity trends and receiver operating characteristic analyses.

Results

AKI occurred in 68.5% of 412 enrolled patients with an incidence rate of 10.6 per 100 patients-days and a median time was 6 (3–13) days. Stages I–III of AKI were 38.3, 24.5, and 37.2%. Factors associated with colistin-induced AKI were advanced age, high serum bilirubin, AKI presented before colistin administration, increased daily colistin doses per IBW, and concomitant use of nephrotoxic drugs. Colistin-induced AKI was related to mortality (HR 1.74, 95% CI 1.06–2.86, p=0.028). In the non-AKI before colistin usage subgroup, the total dose and total dose/IBW were >1,500–2,000 mg and 30–35 mg/kg to benefit mortality reduction but were <2,500–3,000 mg and 45–50 mg/kg for risk reduction of AKI. A daily colistin dose/IBW >4.5 mg/kg/day also increased the risk of AKI. In the AKI developed before colistin subgroup, the cut-off values of total colistin dose >1250–1350 mg and total dose/IBW >23.5–24 mg/kg demonstrated significant risks of AKI.

Conclusion

The incidence of AKI after colistin administration was high and impacted mortality. Prevention and early correction of these related factors are mandatory. Careful use of colistin was also both beneficial in mortality and AKI reductions.

Urinary tract infections in patients with renal insufficiency and dialysis - epidemiology, pathogenesis, clinical symptoms, diagnosis and treatment

Epidemiological studies show an increasing number of patients worldwide suffering from chronic kidney diseases (CKD), which are associated with a risk for progression to end-stage kidney disease (ESKD). CKD patients stage 2-5, patients with regular chronic dialysis treatment (hemo- or peritoneal dialysis), and patients suffering from kidney allograft dysfunction are at high risk to develop infections, e.g. urinary tract infections (UTI) and/or sepsis (urosepsis). These groups show metabolic disturbance, chronic inflammation, and impaired immunocompetence. Escherichia coli is still the most common pathogen in UTI. A wide variety of other pathogens may be involved in UTI. Urological interventions, catheterization, as well as repeated courses of antibiotics contribute to an increased challenge of antimicrobial resistance. The diagnosis of UTI in CKD is based on standard clinical and laboratory criteria. Pyuria (≥10 leucocytes/µl) is more often observed in patients with oligoanuria and low bacterial colony counts. The treatment strategies for this population are based on the same principles as in patients with normal renal function. However, drugs cleared by the kidney or by dialysis membranes need dose adjustment. Antimicrobials with potential systemic toxicity and nephrotoxicity should be administered with caution.

Estimation of the Difference in Colistin Plasma Levels in Critically Ill Patients with Favorable or Unfavorable Clinical Outcomes

In recent decades, antimicrobial resistance (AMR) has led to an increased use of therapeutic alternatives. Among these options, colistin continues to be an option for the treatment of multi-resistant (MDR) Gram-negative bacterial infections. However, due to its high toxicity (nephrotoxicity and neurotoxicity) and narrow therapeutic window, colistin treatment must be utilized carefully. Colistin-treated patients have been observed to have higher mortality due to inadequate therapeutic levels. The objective of this study was to estimate the difference in colistin plasma levels in critically ill patients, and its relationship to favorable or unfavorable clinical outcomes. This prospective observational study was conducted between September 2017 and June 2020 at the Universidad de La Sabana Clinic, in patients who had been treated with colistimethate sodium (CMS) for at least 72 h until day 7 of drug treatment in the critical care unit of a university hospital. There were no statistically significant differences in colistin levels between groups with favorable or unfavorable clinical outcomes (0.16 SD vs. 0.54 SD p-value = 0.167). There was higher mortality in patients with subtherapeutic levels (18% vs. 0%), and additionally, there was a greater rate of renal failure in the group with higher therapeutic levels (50% vs. 20.7%). Due to the loss of power of the study, we were unable to demonstrate a possible difference between colistin levels related to favorable or unfavorable clinical outcomes at day 7. However, we recommend further studies to evaluate the impact of measuring levels in terms of mortality and security.

How to: screening for mcr-mediated resistance to colistin

BACKGROUND

Colistin belongs to the last-resort antibiotics. The discovery of plasmid-bound colistin resistance mediated by the mcr-gene(s) is of great concern because, given its biological potential, there is a risk of its rapid spread.

OBJECTIVES

To discuss the current literature on the methods for the screening for mcr-mediated resistance to colistin.

SOURCES

Literature was drawn from a search of PubMed from 1 January 2016 to 26 April 2021.

CONTENT

The selective culture-based or culture-independent approach can be used for the screening of mcr-mediated resistance to colistin in clinical samples. Rapid Polymyxin NP, Colistin Drop or Colistin Agar Spot tests are applicable for the selection of isolates with a suspected resistance to colistin that has to be confirmed by broth microdilution. The mcr-mediated resistance to colistin can be confirmed by the detection of the causal gene(s) or by phenotype using EDTA-colistin broth disc elution; production of the MCR-1 enzyme can be confirmed with lateral flow immunoassay, using matrix-assisted laser desorption/ionization time-of flight or liquid chromatography-based mass spectrometry. Whole-genome sequencing (WGS) is the ultimate typing method. When a WGS platform is not available at a healthcare facility, a WGS-outsourced service, in combination with freely available bioinformatics tools, allows for the characterization of the mcr-gene(s) carrying isolates.

IMPLICATIONS

mcr-mediated colistin resistance should be monitored through active targeted screening. The broth microdilution method is required for colistin susceptibility testing but as only a selected number of clinical isolates are tested, colistin resistance, including mcr-mediated, may remain undetected. In mcr-1-positive Escherichia coli isolates, the MIC to colistin can range from 2 to 8 mg/L, so it is proposed that Enterobacterales with a colistin MIC of 2 mg/L should also be included in the mcr-mediated colistin resistance screening and those with a confirmed mcr-genotype and/or MCR-phenotype should be considered to be colistin-resistant.

Population Pharmacokinetics of Colistin Methanesulfonate Sodium and Colistin in Critically Ill Patients: A Systematic Review

Understanding the pharmacokinetics parameter of colistin methanesulfonate sodium (CMS) and colistin is needed to optimize the dosage regimen in critically ill patients. However, there is a scarcity of pharmacokinetics parameters in this population. This review provides a comprehensive understanding of CMS and colistin pharmacokinetics parameters in this population. The relevant studies published in English that reported on the pharmacokinetics of CMS and colistin from 2000 until 2020 were systematically searched using the PubMed and Scopus electronic databases. Reference lists of articles were reviewed to identify additional studies. A total of 252 citation titles were identified, of which 101 potentially relevant abstracts were screened, and 25 full-text articles were selected for detailed analysis. Of those, 15 studies were included for the review. This review has demonstrated vast inter-study discrepancies in colistin plasma concentration and the pharmacokinetics parameter estimates. The discrepancies might be due to complex pathophysiological changes in the population studied, differences in CMS brand used, methodology, and study protocol. Application of loading dose of CMS and an additional dose of CMS after dialysis session was recommended by some studies. In view of inter-patient and intra-patient variability in colistin plasma concentration and pharmacokinetics parameters, personalized colistin dosing for this population is recommended.

Optimizing Antimicrobial Drug Dosing in Critically Ill Patients

A fundamental step in the successful management of sepsis and septic shock is early empiric antimicrobial therapy. However, for this to be effective, several decisions must be addressed simultaneously: (1) antimicrobial choices should be adequate, covering the most probable pathogens; (2) they should be administered in the appropriate dose, (3) by the correct route, and (4) using the correct mode of administration to achieve successful concentration at the infection site. In critically ill patients, antimicrobial dosing is a common challenge and a frequent source of errors, since these patients present deranged pharmacokinetics, namely increased volume of distribution and altered drug clearance, which either increased or decreased. Moreover, the clinical condition of these patients changes markedly over time, either improving or deteriorating. The consequent impact on drug pharmacokinetics further complicates the selection of correct drug schedules and dosing during the course of therapy. In recent years, the knowledge of pharmacokinetics and pharmacodynamics, drug dosing, therapeutic drug monitoring, and antimicrobial resistance in the critically ill patients has greatly improved, fostering strategies to optimize therapeutic efficacy and to reduce toxicity and adverse events. Nonetheless, delivering adequate and appropriate antimicrobial therapy is still a challenge, since pathogen resistance continues to rise, and new therapeutic agents remain scarce. We aim to review the available literature to assess the challenges, impact, and tools to optimize individualization of antimicrobial dosing to maximize exposure and effectiveness in critically ill patients.

Optimal control for colistin dosage selection

Optimization of antibiotic administration helps minimizing cases of bacterial resistance. Dosages are often selected by trial and error using a pharmacokinetic (PK) model. However, this is limited to the range of tested dosages, restraining possible treatment choices, especially for the loading doses. Colistin is a last-resort antibiotic with a narrow therapeutic window; therefore, its administration should avoid subtherapeutic or toxic concentrations. This study formulates an optimal control problem for dosage selection of colistin based on a PK model, minimizing deviations of colistin concentration to a target value and allowing a specific dosage optimization for a given individual. An adjoint model was used to provide the sensitivity of concentration deviations to dose changes. A three-compartment PK model was adopted. The standard deviation between colistin plasma concentrations and a target set at 2 mg/L was minimized for some chosen treatments and sample patients. Significantly lower deviations from the target concentration are obtained for shorter administration intervals (e.g. every 8 h) compared to longer ones (e.g. every 24 h). For patients with normal or altered renal function, the optimal loading dose regimen should be divided into two or more administrations to attain the target concentration quickly, with a high first loading dose followed by much lower ones. This regimen is not easily obtained by trial and error, highlighting advantages of the method. The present method is a refined optimization of antibiotic dosage for the treatment of infections. Results for colistin suggest significant improvement in treatment avoiding subtherapeutic or toxic concentrations.

Population Pharmacokinetics and Outcomes of Critically Ill Pediatric Patients Treated with Intravenous Colistin at Higher Than Recommended Doses

Limited pharmacokinetic (PK) data suggest that currently recommended pediatric dosages of colistimethate sodium (CMS) by the Food and Drug Administration and European Medicines Agency may lead to suboptimal exposure, resulting in plasma colistin concentrations that are frequently <2 mg/liter. We conducted a population PK study in 17 critically ill patients 3 months to 13.75 years (median, 3.3 years) old who received CMS for infections caused by carbapenem-resistant Gram-negative bacteria. CMS was dosed at 200,000 IU/kg/day (6.6 mg colistin base activity [CBA]/kg/day; 6 patients), 300,000 IU/kg/day (9.9 mg CBA/kg/day; 10 patients), and 350,000 IU/kg/day (11.6 mg CBA/kg/day; 1 patient). Plasma colistin concentrations were determined using ultraperformance liquid chromatography combined with electrospray ionization-tandem mass spectrometry. Colistin PK was described by a one-compartment disposition model, including creatinine clearance, body weight, and the presence or absence of systemic inflammatory response syndrome (SIRS) as covariates (P < 0.05 for each). The average colistin plasma steady-state concentration (C_ss,avg) ranged from 1.11 to 8.47 mg/liter (median, 2.92 mg/liter). Ten patients had C_ss,avg of ≥2 mg/liter. The presence of SIRS was associated with decreased apparent clearance of colistin (47.8% of that without SIRS). The relationship between the number of milligrams of CBA per day needed to achieve each 1 mg/liter of plasma colistin C_ss,avg and creatinine clearance (in milliliters per minute) was described by linear regression with different slopes for patients with and without SIRS. Nephrotoxicity, probably unrelated to colistin, was observed in one patient. In conclusion, administration of CMS at the above doses improved exposure and was well tolerated. Apparent clearance of colistin was influenced by creatinine clearance and the presence or absence of SIRS.

Colistin Dosing Regimens against Pseudomonas aeruginosa in Critically Ill Patients: An Application of Monte Carlo Simulation

Our aims are to assess various colistin dosing regimens against Pseudomonas aeruginosa (P. aeruginosa) infection in critically ill patients and to propose an appropriate regimen based on microbiological data. A Monte Carlo simulation was performed using the published colistin’s pharmacokinetic parameters of critically ill patients, the published pharmacodynamic target from a mouse thigh infection model, and the minimum inhibitory concentration (MIC) results from a Vietnamese hospital. The probability of target attainment (PTA) of 80% and cumulative fraction of response (CFR) of 90% were used to evaluate the efficacy of each regimen. Of 121 P. aeruginosa laboratory datasets, the carbapenem-resistant P. aeruginosa (CRPA) and the colistin-resistant P. aeruginosa rates were 29.8% and 0.8%, respectively. MIC_50,90 were both 0.5 mg/L. The simulated results showed that at MIC of 2 mg/L, most regimens could not reach the PTA target, particularly in patients with normal renal function (Creatinine clearance (CrCl) ≥ 80 mL/min). At MIC of 0.5 mg/L and 1 mg/L, current recommendations still worked well. On the basis of these results, aside from lung infection, our study recommends three regimens against P. aeruginosa infection at MIC of 0.5 mg/L, 1 mg/L, and 2 mg/L. In conclusion, higher total daily doses and fractionated colistin dosing regimens could be the strategy for difficult-to-acquire PTA cases, while a less aggressive dose might be appropriate for empirical treatment in settings with low MIC_50/90.

Clinical and Laboratory Standards Institute and European Committee on Antimicrobial Susceptibility Testing Position Statements on Polymyxin B and Colistin Clinical Breakpoints

Recent data on polymyxin pharmacokinetics, pharmacodynamics, toxicity, and clinical outcomes suggest these agents have limited clinical utility. Pharmacokinetics-pharmacodynamics data show a steady-state concentration of 2 μg/mL is required for killing bacteria with colistin minimum inhibitory concentrations of 2 μg/mL. Less than 50% of patients with normal renal function achieve this exposure, and it is associated with high risk of nephrotoxicity. This exposure does not achieve bacterial stasis in pneumonia models. Randomized and observational studies consistently demonstrate increased mortality for polymyxins compared with alternative agents. The Clinical and Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) are 2 global organizations that establish interpretive criteria for in vitro susceptibility data. CLSI has recently taken the step to eliminate the "susceptible" interpretive category for the polymyxins, whereas EUCAST maintains this interpretive category. This viewpoint describes the opinions of these organizations and the data that were used to inform their perspectives.

Outcomes of Adjunctive Therapy with Intravenous Cefoperazone-Sulbactam for Ventilator-Associated Pneumonia Due to Carbapenem-Resistant Acinetobacter baumannii

Introduction

The efficacy of adjunctive therapy with cefoperazone-sulbactam (CEP-SUL) for ventilator-associated pneumonia (VAP) due to carbapenem-resistant A. baumannii (CRAB) is unclear.

Methods

We retrospectively analyzed the therapeutic effect of adding CEP-SUL to standard regimens for VAP due to CRAB. Patients with VAP due to CRAB strains that were susceptible to CEP-SUL were enrolled into the study. The patients were divided into two groups: those who receive cefoperazone-sulbactam (CEP-SUL⁺), and those who did not receive cefoperazone-sulbactam (CEP-SUL). Mortality rates and resource utilization of these two groups were compared. Factors associated with mortality were explored.

Results

Eighty patients were enrolled into the study, 52 CEP-SUL⁺ and 28 CEP-SUL^-. The baseline characteristics of the two groups were comparable, except for median Acute Physiology and Chronic Health Evaluation (APACHE) II score which was significantly higher for CEP-SUL⁺. Thirty-day, and in-hospital mortality rates for CEP-SUL⁺ were significantly lower than CEP-SUL^- with values of 35%, 39% and 61%, 68%, for CEP-SUL⁺ and CEP-SUL^-, respectively. The survival rate for CEP-SUL⁺ was significantly higher compared with CEP-SUL^- (P < 0.001). The number of hospital days, ventilator days since diagnosis of VAP and hospital costs were lower for CEP-SUL⁺.

Conclusion

Overall results suggested that patients with VAP due to CRAB strains who received adjunctive therapy with CEP-SUL had lower mortality rates and resource utilization compared with CEP-SUL^-.

Treatment outcome and adverse effects of colistin in adult patients with carbapenem-resistant gram-negative bacteremia from Pakistan

BACKGROUND

Polymyxins (colistin) have emerged for the treatment of carbapenem resistant (CR) gram-negative infections. There is a paucity of data on treatment outcomes and adverse effects of high-dose colistin treatment in Pakistan. The aim of this study was to determine the efficacy and toxicity of colistin in CR bacteremia, including patients with renal failure and on hemodialysis, and to determine patient outcomes.

METHODS

This prospective cohort study was performed from May to December 2017 at Sindh Institute of Urology and Transplantation, Karachi, Pakistan. Patients aged >18 years with documented gram-negative bacteremia were included. Data were compared between those who received colistin and those who did not, including risk factors for CR bacteremia, bacterial clearance, adverse effects, and all-cause mortality up to 14 days of follow-up.

RESULTS

The study included 137 patients, 73 (53.3%) in the colistin group and 64 (46.7%) in the non-colistin group. Patients in the colistin group were 1.47 times more likely to have died by day 14 of follow-up as compared to those in the non-colistin group (19.2% vs 7.8%; relative risk 1.47, p= 0.05). Patients in both groups achieved more than 80% bacteriological clearance. The colistin group patients were less likely to have received appropriate empirical antibiotics as compared to the non-colistin group patients (4.1% vs 62.5%; relative risk 0.09, p< 0.001). Factors significantly associated with mortality were inappropriate empirical antibiotics and acute renal failure. Of the 73 patients in the colistin group, 27 (37.0%) developed reversible neurological adverse effects. Patients with renal insufficiency, not on hemodialysis, were evaluated for colistin nephrotoxicity. Creatinine decreased from 8.08 mg/dl at baseline to 4.85 mg/dl on day 7 in the colistin group, and from 6.5 mg/dl to 3.9 mg/dl in the non-colistin group. Patients with normal renal function had no significant rise in serum creatinine.

CONCLUSIONS

Colistin is efficacious in clearing bacteremia even in patients with impaired renal function. The adverse effects were found to be minimal and reversible. We recommend the use of colistin in combination with carbapenems for CR gram-negative bacteria in renal failure. Most importantly, however, this study highlights the role of empirical colistin treatment in patients with risk factors for CR bacteremia.

Successful treatment of carbapenemase producing Enterobacteriaceae peritonitis: 'Old therapy for a new bug'

Multidrug-resistant organisms cause significant morbidity and mortality. Infections due to resistant gram-negative bacilli are increasingly being reported. For years, carbapenem antibiotics have been successfully used to treat infections due to resistant Enterobacteriaceae, such as Escherichia coli and Klebsiella pneumoniae, including those producing extended spectrum β-lactamases, a subset of β-lactamase enzymes that confer broad resistance to penicillins and cephalosporins. More recently, carbapenem-resistant Enterobacteriaceae have emerged as pathogenic organisms, which confer broad resistance to most β-lactam antibiotics including 'last-line' carbapenems. However, different types of carbapenemases confer diverse spectra of antibiotic resistance. Here, we describe the case of an 84-year-old lady on peritoneal dialysis (PD) for 3 years who, on developing carbapenem-resistant Klebsiella pneumoniae PD peritonitis, was successfully treated with colistin, an antimicrobial agent first used in the 1950s.

Effects of Different Component Contents of Colistin Methanesulfonate on the Pharmacokinetics of Prodrug and Formed Colistin in Human

PURPOSES

To evaluate the effects of component contents in different colistin methanesulfonate (CMS) formulas on their clinical pharmacokinetics of the prodrug CMS and the formed colistin.

METHODS

Two CMS formulas (CTTQ and Parkedale) were investigated in a single dose, randomized, open-label, crossover study conducted in 18 healthy Chinese subjects. Both CMS formulas met the requirements of European Pharmacopoeia 9.2 with 12.1% difference in the two major active components (CMS A and CMS B). The PK parameters after a single intravenous infusion of CMS at 2.5 mg/kg were calculated and the steady-state plasma colistin concentrations (C_ss,avg) following multiple dosing, once every 12 h for 7 days, were simulated with the non-compartment model.

RESULTS

The systemic exposure (AUC_0-inf) of CMS were 59.49 ± 5.90 h·μg/mL and 51.09 ± 4.70 h·μg/mL, and the AUC_0-inf of colistin were 15.39 ± 2.63 h·μg/mL and 12.36 ± 2.10 h·μg/mL for CTTQ and Parkedale, respectively. The ratios (90% CI) of geometric mean of AUC_0-inf of CTTQ to Parkedale were 116.38% (112.95%, 119.91%) and 124.49% (120.76%, 128.35%) for CMS and colistin, respectively. The predicted C_ss,avg (95% CI) were 0.92 (0.85, 0.99) μg/mL and 0.74 (0.69, 0.79) μg/mL for CTTQ and Parkedale, respectively.

CONCLUSION

The difference in component content in the two CMS formulas had a significant (P < 0.001) impact on the systemic exposure of colistin in human, thus, warranted essential considerations in clinical applications.

RESTORE-IMI 1: A Multicenter, Randomized, Double-blind Trial Comparing Efficacy and Safety of Imipenem/Relebactam vs Colistin Plus Imipenem in Patients With Imipenem-nonsusceptible Bacterial Infections

Background

The β-lactamase inhibitor relebactam can restore imipenem activity against imipenem-nonsusceptible gram-negative pathogens. We evaluated imipenem/relebactam for treating imipenem-nonsusceptible infections.

Methods

Randomized, controlled, double-blind, phase 3 trial. Hospitalized patients with hospital-acquired/ventilator-associated pneumonia, complicated intraabdominal infection, or complicated urinary tract infection caused by imipenem-nonsusceptible (but colistin- and imipenem/relebactam-susceptible) pathogens were randomized 2:1 to 5–21 days imipenem/relebactam or colistin+imipenem. Primary endpoint: favorable overall response (defined by relevant endpoints for each infection type) in the modified microbiologic intent-to-treat (mMITT) population (qualifying baseline pathogen and ≥1 dose study treatment). Secondary endpoints: clinical response, all-cause mortality, and treatment-emergent nephrotoxicity. Safety analyses included patients with ≥1 dose study treatment.

Results

Thirty-one patients received imipenem/relebactam and 16 colistin+imipenem. Among mITT patients (n = 21 imipenem/relebactam, n = 10 colistin+imipenem), 29% had Acute Physiology and Chronic Health Evaluation II scores >15, 23% had creatinine clearance <60 mL/min, and 35% were aged ≥65 years. Qualifying baseline pathogens: Pseudomonas aeruginosa (77%), Klebsiella spp. (16%), other Enterobacteriaceae (6%). Favorable overall response was observed in 71% imipenem/relebactam and 70% colistin+imipenem patients (90% confidence interval [CI] for difference, –27.5, 21.4), day 28 favorable clinical response in 71% and 40% (90% CI, 1.3, 51.5), and 28-day mortality in 10% and 30% (90% CI, –46.4, 6.7), respectively. Serious adverse events (AEs) occurred in 10% of imipenem/relebactam and 31% of colistin+imipenem patients, drug-related AEs in 16% and 31% (no drug-related deaths), and treatment-emergent nephrotoxicity in 10% and 56% (P = .002), respectively.

Conclusions

Imipenem/relebactam is an efficacious and well-tolerated treatment option for carbapenem-nonsusceptible infections.

Clinical Trials Registration

NCT02452047.

New perspectives in the antibiotic treatment of mechanically ventilated patients with infections from Gram-negatives

Introduction: Ventilator-associated pneumonia (VAP) is a common and potentially fatal complication of mechanical ventilation that is often caused by multidrug-resistant (MDR) Gram-negative bacteria (GNB). Despite the repurposing of older treatments and the novel antimicrobials, many resistance mechanisms cannot be confronted, and novel therapies are needed.Areas covered: We searched the literature for keywords regarding the treatment of GNB infections in mechanically ventilated patients. This narrative review presents new data on antibiotics and non-antibiotic approaches focusing on Phase 3 trials against clinically significant GNB that cause VAP.Expert opinion: Ceftazidime-avibactam, meropenem-vaborbactam, and imipenem-relebactam stand out as new options for infections by Klebsiella pneumoniae carbapenemase-producing bacteria, whereas ceftolozane-tazobactam adds therapeutic flexibility in Pseudomonas aeruginosa infections with multiple resistance mechanisms. Ceftazidime-avibactam and ceftolozane-tazobactam have relevant literature. Aztreonam-avibactam holds promise for the treatment of infections by metallo-β-lactamase (MBL)-producing organisms. Recently approved cefiderocol possesses an extended antibacterial spectrum, including KPC- and MBL-producers. However, recently published data have toned down optimism about treating VAP caused by carbapenem-resistant Acinetobacter baumannii. For the latter, eravacycline may provide additional hope, pending pertinent data. Non-antibiotic treatments currently being considered as adjunct therapeutic approaches are welcome. Nevertheless, they will hopefully substitute current antimicrobials in the future.

Cure of Limb-Threatening XDR Pseudomonas aeruginosa Infection: Combining Genome Sequencing, Therapeutic Drug Level Monitoring, and Surgical Debridement

We describe a case of limb-threatening osteomyelitis and metalware infection with carbapenemase-producing extensively drug-resistant Pseudomonas aeruginosa successfully cured with aggressive surgical debridement and combined intravenous fosfomycin and colistin. Real-time therapeutic drug monitoring was used to maximize probability of efficacy and minimize potential for toxicity.

Imipenem/Cilastatin/Relebactam Alone and in Combination against Pseudomonas aeruginosa in the In Vitro Pharmacodynamic Model

Combination therapy may enhance imipenem/cilastatin/relebactam's (I/R) activity against Pseudomonas aeruginosa and suppress resistance development. Human-simulated unbound plasma concentrations of I/R at 1.25 g every 6 h (h), colistin at 360 mg daily, and amikacin at 25 mg/kg daily were reproduced alone and in combination against six imipenem-nonsusceptible P. aeruginosa isolates in an in vitro pharmacodynamic model over 24 h. For I/R alone, the mean reductions in CFU ± the standard errors by 24 h were -2.52 ± 0.49, -1.49 ± 0.49, -1.15 ± 0.67, and -0.61 ± 0.10 log₁₀ CFU/ml against isolates with MICs of 1/4, 2/4, 4/4, and 8/4 μg/ml, respectively. Amikacin alone also resulted in 24 h CFU reductions consistent with its MIC, while colistin CFU reductions did not differ. Resistant subpopulations were observed after 24 h in 1, 4, and 3 I/R-, colistin-, and amikacin-exposed isolates, respectively. The combination of I/R and colistin resulted in synergistic (n = 1) or additive (n = 2) interactions against three isolates with 24-h CFU reductions ranging from -2.62 to -4.67 log₁₀ CFU/ml. The combination of I/R and amikacin exhibited indifferent interactions against all isolates, with combined drugs achieving -0.51- to -3.33-log₁₀ CFU/ml reductions. No resistant subpopulations were observed during I/R and colistin combination studies, and when added to amikacin, I/R prevented the emergence of amikacin resistance. Against these six multidrug-resistant P. aeruginosa, I/R alone achieved significant CFU reductions against I/R-susceptible isolates. Combinations of I/R plus colistin resulted in additivity or synergy against some P. aeruginosa, whereas the addition of amikacin did not provide further antibacterial efficacy against these isolates.

Bi-Functional Alginate Oligosaccharide-Polymyxin Conjugates for Improved Treatment of Multidrug-Resistant Gram-Negative Bacterial Infections

The recent emergence of resistance to colistin, an antibiotic of last resort with dose-limiting toxicity, has highlighted the need for alternative approaches to combat infection. This study aimed to generate and characterise alginate oligosaccharide (“OligoG”)–polymyxin (polymyxin B and E (colistin)) conjugates to improve the effectiveness of these antibiotics. OligoG–polymyxin conjugates (amide- or ester-linked), with molecular weights of 5200–12,800 g/mol and antibiotic loading of 6.1–12.9% w/w, were reproducibly synthesised. In vitro inflammatory cytokine production (tumour necrosis factor alpha (TNFα) ELISA) and cytotoxicity (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) of colistin (2.2–9.3-fold) and polymyxin B (2.9–27.2-fold) were significantly decreased by OligoG conjugation. Antimicrobial susceptibility tests (minimum inhibitory concentration (MIC), growth curves) demonstrated similar antimicrobial efficacy of ester- and amide-linked conjugates to that of the parent antibiotic but with more sustained inhibition of bacterial growth. OligoG–polymyxin conjugates exhibited improved selectivity for Gram-negative bacteria in comparison to mammalian cells (approximately 2–4-fold). Both OligoG–colistin conjugates caused significant disruption of Pseudomonas aeruginosa biofilm formation and induced bacterial death (confocal laser scanning microscopy). When conjugates were tested in an in vitro “time-to-kill” (TTK) model using Acinetobacter baumannii, only ester-linked conjugates reduced viable bacterial counts (~2-fold) after 4 h. Bi-functional OligoG–polymyxin conjugates have potential therapeutic benefits in the treatment of multidrug-resistant (MDR) Gram-negative bacterial infections, directly reducing toxicity whilst retaining antimicrobial and antibiofilm activities.

Agents of Last Resort: An Update on Polymyxin Resistance

Polymyxin resistance is a major public health threat, because the polymyxins represent last-line therapeutics for gram-negative pathogens resistant to essentially all other antibiotics. Minimizing any potential emergence and dissemination of polymyxin resistance relies on an improved understanding of mechanisms of and risk factors for polymyxin resistance, infection prevention and stewardship strategies, together with optimization of dosing of polymyxins (eg, combination regimens).