Colistin serum concentrations after intravenous administration in critically ill patients with serious multidrug-resistant, gram-negative bacilli infections: a prospective, open-label, uncontrolled study

In Vitro Antibiofilm Activity of Fosfomycin Alone and in Combination with Other Antibiotics against Multidrug-Resistant and Extensively Drug-Resistant Pseudomonas aeruginosa

BACKGROUND

Due to its rapid resistance development and ability to form biofilms, treatment of Pseudomonas aeruginosa infections is becoming more complicated by the day. Drug combinations may help reduce both resistance and biofilm formation.

METHODS

Using the microtiter plate assay, we investigated the in vitro inhibition of biofilm formation and the disruption of preformed biofilms in multidrug-resistant and extensively drug-resistant clinical isolates of P. aeruginosa in the presence of peak plasma levels of eight antipseudomonal antibiotics alone and in combination with fosfomycin: ceftazidime, piperacillin/tazobactam, cefepime, imipenem, gentamicin, amikacin, ciprofloxacin and colistin.

RESULTS

Combination therapy was significantly superior to monotherapy in its inhibition of biofilm formation. The highest inhibition rates were observed for combinations with colistin, cefepime and ceftazidime.

CONCLUSION

Our results support fosfomycin combination therapy as an enhanced prophylactic option. Moreover, combinations with β-lactam antibiotics and colistin demonstrated a more potent inhibition effect on biofilm formation than protein synthesis inhibitors.

The NLRP3 Inflammasome Is a Major Cause of Acute Renal Failure Induced by Polypeptide Antibiotics

Drug-induced acute renal failure (ARF) is a public health concern that hinders optimal drug therapy. However, pathological mechanisms of drug-induced ARF remain to be elucidated. Here, we show that a pathological process of drug-induced ARF is mediated by proinflammatory cross-talk between kidney tubular cells and macrophages. Both polymyxin B and colistin, polypeptide antibiotics, frequently cause ARF, stimulated the ERK and NF-κB pathways in kidney tubular cells, and thereby upregulated M-CSF and MCP-1, leading to infiltration of macrophages into the kidneys. Thereafter, the kidney-infiltrated macrophages were exposed to polypeptide antibiotics, which initiated activation of the NLR family pyrin domain containing 3 (NLRP3) inflammasome. Interestingly, blockade of the NLRP3 activation clearly ameliorated the pathology of ARF induced by polypeptide antibiotics, suggesting that a combination of the distinct cellular responses to polypeptide antibiotics in kidney tubular cells and macrophages plays a key role in the pathogenesis of colistin-induced ARF. Thus, our results provide a concrete example of how drugs initiate ARF, which may give insight into the underlying pathological process of drug-induced ARF.

Clinical outcomes of colistin methanesulfonate sodium in correlation with pharmacokinetic parameters in critically ill patients with multi-drug resistant bacteria-mediated infection: A systematic review and meta-analysis

BACKGROUND

Colistin is a viable option for multidrug resistant gram-negative bacteria emerged from inappropriate antibiotic use. Nonetheless, suboptimal colistin concentrations and nephrotoxicity risks hinder its clinical use. Thus, the aim of this study is to investigate clinical outcomes in correlation with pharmacokinetic differences and infection types in critically ill patients on intravenous colistin methanesulfornate sodium (CMS).

METHODS

A systematic literature search of Embase, Google Scholars, and PubMed was performed to identify clinical trials evaluating pharmacokinetic parameters along with clinical outcomes of CMS treatment from inception to July 2023. The pooled analyses of clinical impact of CMS on nephrotoxicity, mortality, clinical cure, and colistin concentration at steady state (Css,avg) were performed. This study was registered in the PROSPERO (CRD 42023456120).

RESULTS

Total of 695 critically ill patients from 17 studies were included. The mortality was substantially lower in clinically cured patients (OR 0.05; 95% CI 0.02 - 0.14), whereas the mortality rate was statistically insignificant between nephrotoxic and non-nephrotoxic patients. Inter-patient variability of pharmacokinetic parameters of CMS and colistin was observed in critically ill patients. The standard mean differences of Css,avg were statistically insignificant between clinically cure and clinically failure groups (standard mean difference (SMD) -0.25; 95% CI -0.69 - 0.19) and between nephrotoxic and non-nephrotoxic groups (SMD 0.67; 95% CI -0.27-1.61). The clinical cure rate is substantially lower in pneumonia patients (OR 0.09; 95% CI 0.01 - 0.56), and pharmacokinetic parameters pertaining to microbiological cure were different among strains.

CONCLUSION

The mortality rate was substantially lower in clinically cured patients with CMS. However, no significant differences in Css,avg of colistin were examined to determine the impact of pharmacokinetic differences on clinical outcomes including mortality rate and nephrotoxicity risk. Nevertheless, the clinical cure rate is substantially lower in patients with respiratory infection than patients with urinary tract infection.

Determining Susceptibility and Potential Mediators of Resistance for the Novel Polymyxin Derivative, SPR206, in Acinetobacter baumannii

With the increase in carbapenem-resistant A. baumannii (CRAB) infections, there has been a resurgence in the use of polymyxins, specifically colistin (COL). Since the reintroduction of COL-based regimens in treating CRAB infections, several COL-resistant A. baumannii isolates have been identified, with the mechanism of resistance heavily linked with the loss of the lipopolysaccharide (LPS) layer of the bacterial outer membrane through mutations in lpxACD genes or the pmrCAB operon. SPR206, a novel polymyxin derivative, has exhibited robust activity against multidrug-resistant (MDR) A. baumannii. However, there is a dearth of knowledge regarding its efficacy in comparison with other A. baumannii-active therapeutics and whether traditional polymyxin (COL) mediators of A. baumannii resistance also translate to reduced SPR206 activity. Here, we conducted susceptibility testing using broth microdilution on 30 A. baumannii isolates (17 COL-resistant and 27 CRAB), selected 14 COL-resistant isolates for genomic sequencing analysis, and performed time-kill analyses on four COL-resistant isolates. In susceptibility testing, SPR206 demonstrated a lower range of minimum inhibitory concentrations (MICs) compared with COL, with a four-fold difference observed in MIC50 values. Mutations in lpxACD and/or pmrA and pmrB genes were detected in each of the 14 COL-resistant isolates; however, SPR206 maintained MICs ≤ 2 mg/L for 9/14 (64%) of the isolates. Finally, SPR206-based combination regimens exhibited increased synergistic and bactericidal activity compared with COL-based combination regimens irrespective of the multiple resistance genes detected. The results of this study highlight the potential utility of SPR206 in the treatment of COL-resistant A. baumannii infections.

In vitro killing of multidrug/extensively drug-resistant Pseudomonas aeruginosa by fosfomycin alone or in combination with antipseudomonal antibiotics

Pseudomonas aeruginosa is a leading cause of nosocomial infections. Given the constant rise in resistance, adequate therapy is increasingly demanding. Fosfomycin recently became an appealing treatment option of bacterial infections due to multidrug-resistant bacteria (MDR). So far, fosfomycin synergy with other antibiotics has been assessed in studies, but only a limited number focused on MDR P. aeruginosa and on the effect of these combinations on the duration of the postantibiotic effect (PAE). We investigated synergy of fosfomycin with an array of antipseudomonal antibiotics using gradient diffusion strip cross method and time-kill method, and their effect on the duration of PAE against 51 variously resistant P. aeruginosa isolates. The highest rate of synergy was observed for combination with ceftazidime (23.4%) and gentamicin (19.1%). The PAE of antibiotic combinations was superior to that of the drugs alone. Our findings indicate that fosfomycin combination therapy may be a valuable treatment alternative.

Polymyxin combination therapy for multidrug-resistant, extensively-drug resistant, and difficult-to-treat drug-resistant gram-negative infections: is it superior to polymyxin monotherapy?

INTRODUCTION

The increasing prevalence of infections with multidrug-resistant (MDR), extensively-drug resistant (XDR) or difficult-to-treat drug resistant (DTR) Gram-negative bacilli (GNB), including Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella pneumoniae, Enterobacter species, and Escherichia coli poses a severe challenge.

AREAS COVERED

The rapid growing of multi-resistant GNB as well as the considerable deceleration in development of new anti-infective agents have made polymyxins (e.g. polymyxin B and colistin) a mainstay in clinical practices as either monotherapy or combination therapy. However, whether the polymyxin-based combinations lead to better outcomes remains unknown. This review mainly focuses on the effect of polymyxin combination therapy versus monotherapy on treating GNB-related infections. We also provide several factors in designing studies and their impact on optimizing polymyxin combinations.

EXPERT OPINION

An abundance of recent in vitro and preclinical in vivo data suggest clinical benefit for polymyxin-drug combination therapies, especially colistin plus meropenem and colistin plus rifampicin, with synergistic killing against MDR, XDR, and DTR P. aeruginosa, K. pneumoniae and A. baumannii. The beneficial effects of polymyxin-drug combinations (e.g. colistin or polymyxin B + carbapenem against carbapenem-resistant K. pneumoniae and carbapenem-resistant A. baumannii, polymyxin B + carbapenem + rifampin against carbapenem-resistant K. pneumoniae, and colistin + ceftolozan/tazobactam + rifampin against PDR-P. aeruginosa) have often been shown in clinical setting by retrospective studies. However, high-certainty evidence from large randomized controlled trials is necessary. These clinical trials should incorporate careful attention to patient's sample size, characteristics of patient's groups, PK/PD relationships and dosing, rapid detection of resistance, MIC determinations, and therapeutic drug monitoring.

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.

Pharmacokinetic Characteristics of Nebulized Colistimethate Sodium Using Two Different Types of Nebulizers in Critically Ill Patients with Ventilator-Associated Respiratory Infections

Background: Rising antimicrobial resistance has led to a revived interest in inhaled colistin treatment in the critically ill patient with ventilator-associated respiratory infection (VARI). Nebulization via vibrating mesh nebulizers (VMNs) is considered the current standard-of-care, yet the use of generic jet nebulizers (JNs) is more widespread. Few data exist on the intrapulmonary pharmacokinetics of colistin when administered through VMNs, while there is a complete paucity regarding the use of JNs. Methods: In this study, 18 VARI patients who received 2 million international units of inhaled colistimethate sodium (CMS) through a VMN were pharmacokinetically compared with six VARI patients who received the same drug dose through a JN, in the absence of systemic CMS administration. Results: Surprisingly, VMN and JN led to comparable formed colistin exposures in the epithelial lining fluid (ELF) (median (IQR) AUC0-24: 86.2 (46.0-185.9) mg/L∙h with VMN and 91.5 (78.1-110.3) mg/L∙h with JN). The maximum ELF concentration was 10.4 (4.7-22.6) mg/L and 7.4 (6.2-10.3) mg/L, respectively. Conclusions: Based on our results, JN might be considered a viable alternative to the theoretically superior VMN. Therapeutic drug monitoring in the ELF can be advised due to the observed low exposure, high variability, and appreciable systemic absorption.

Anti-infective Medicines Use in Children and Neonates With Pre-existing Kidney Dysfunction: A Systematic Review

Background

Dosing recommendations for anti-infective medicines in children with pre-existing kidney dysfunction are derived from adult pharmacokinetics studies and adjusted to kidney function. Due to neonatal/pediatric age and kidney impairment, modifications in renal clearance and drug metabolism make standard anti-infective dosing for children and neonates inappropriate, with a risk of drug toxicity or significant underdosing. The aim of this study was the systematic description of the use of anti-infective medicines in pediatric patients with pre-existing kidney impairment.

Methods

A systematic review of the literature was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The EMBASE, Medline and Cochrane databases were searched on September 21st, 2021. Studies in all languages reporting data on pre-defined outcomes (pharmacokinetics-PK, kidney function, safety and efficacy) regarding the administration of anti-infective drugs in children up to 18 years with pre-existing kidney dysfunction were included.

Results

29 of 1,792 articles were eligible for inclusion. There were 13 case reports, six retrospective studies, nine prospective studies and one randomized controlled trial (RCT), reporting data on 2,168 pediatric patients. The most represented anti-infective class was glycopeptides, with seven studies on vancomycin, followed by carbapenems, with five studies, mostly on meropenem. Antivirals, aminoglycosides and antifungals counted three articles, followed by combined antibiotic therapy, cephalosporins, lipopeptides with two studies, respectively. Penicillins and polymixins counted one study each. Nine studies reported data on patients with a decreased kidney function, while 20 studies included data on kidney replacement therapy (KRT). Twenty-one studies reported data on PK. In 23 studies, clinical outcomes were reported. Clinical cure was achieved in 229/242 patients. There were four cases of underdosing, one case of overdosing and 13 reported deaths.

Conclusion

This is the first systematic review providing evidence of the use of anti-infective medicines in pediatric patients with impaired kidney function or requiring KRT. Dosing size or interval adjustments in pediatric patients with kidney impairment vary according to age, critical illness status, decreased kidney function and dialysis type. Our findings underline the relevance of population PK in clinical practice and the need of developing predictive specific models for critical pediatric patients.

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.

Dose Optimization of Colistin: A Systematic Review

Colistin is considered a last treatment option for multi-drug and extensively resistant Gram-negative infections. We aimed to assess the available data on the dosing strategy of colistin. A systematic review was performed to identify all published studies on the dose optimization of colistin. Grey literature and electronic databases were searched. Data were collected in a specified form and the quality of the included articles was then assessed using the Newcastle-Ottawa scale for cohort studies, the Cochrane bias tool for randomized clinical trials (RCT), and the Joanna Briggs Institute (JBI) critical checklist for case reports. A total of 19 studies were included, of which 16 were cohort studies, one was a RCT, and two were case reports. A total of 18 studies proposed a dosing regimen for adults, while only one study proposed a dosing schedule for pediatric populations. As per the available evidence, a loading dose of 9 million international units (MIU) of colistin followed by a maintenance dose of 4.5 MIU every 12 h was considered the most appropriate dosing strategy to optimize the safety and efficacy of treatment and improve clinical outcomes. This review supports the administration of a loading dose followed by a maintenance dose of colistin in severe and life-threatening multi-drug Gram-negative bacterial infections.

Prospective observational study of the impact of plasma colistin levels in patients with carbapenem-resistant Acinetobacter baumannii pneumonia

OBJECTIVES

Colistin, an important drug to treat carbapenem-resistant Acinetobacter baumannii (CRAB) infections, has a narrow therapeutic window with nephrotoxicity. This study was conducted to determine the importance of colistin concentrations in predicting nephrotoxicity when treating CRAB pneumonia with colistin.

METHODS

A prospective cohort study was performed in one teaching hospital from May 2015 to January 2018. Patients with CRAB pneumonia were treated with intravenous colistin methanesulfonate (CMS) at 2.5-5.0 mg/kg/day. On Days 3 and 4, plasma colistin and CMS concentrations were determined by six serial blood samples (immediately prior to dosing and 1 h and 4 h after the end of infusion).

RESULTS

The 25 patients included in the analysis had hospital-acquired pneumonia caused by CRAB. Nephrotoxicity occurred in five patients (20%) on Day 7. There was no difference in clinical characteristics of patients with or without nephrotoxicity. The maximum plasma CMS concentration (mean ± standard deviation) was significantly higher in patients with nephrotoxicity on Day 7 than those without nephrotoxicity (15.3 ± 4.2 mg/L vs. 8.3 ± 3.8 mg/L; P = 0.014). The maximum plasma colistin concentration (C_max,col) was significantly higher in the nephrotoxicity group on Day 7 (4.8 ± 2.0 mg/L vs. 2.1 ± 1.0 mg/L; P = 0.002). C_max,col was lower in patients with microbiological failure than those without microbiological failure (1.92 mg/L vs. 3.01 mg/L; P = 0.038).

CONCLUSION

This study confirmed that plasma levels of CMS and colistin, especially maximum levels, are important for predicting nephrotoxicity in patients with CRAB pneumonia. [ClinicalTrials.gov ID NCT02482961].

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.

Trough polymyxin B plasma concentration is an independent risk factor for its nephrotoxicity

AIMS

Data regarding clinical pharmacokinetic/toxicodynamic (PK/TD) of polymyxin B is short of direct quantitative data. This study aims to investigate the risk factors of polymyxin B associated acute kidney injury (AKI) and to assess the relationship between polymyxin B plasma levels and its nephrotoxicity.

METHODS

A retrospective study was performed in adult patients treated with polymyxin B. Risk factors associated with AKI and plasma trough concentrations of polymyxin B were identified via medical record review. A multivariate logistic regression model was established and the risk of polymyxin B-associated AKI were predicted by a receiver operating characteristic curve, with maximal Youden index used to identify safety thresholds among the study population.

RESULTS

Fifty-four adult patients were included in the study. AKI was detected in 14 patients during polymyxin B treatment (25.9%, 14 out of 54). C_min (odds ratio [OR] 2.071; 95% confidence interval [CI] 1.235-3.472) and baseline serum creatinine (OR 1.024; 95% CI 1.005-1.043) were significant independent risk factors for developing AKI. The area under the ROC curve of the combined predictor was larger based on the above factors. When the Youden index was at maximum, the optimal cut-off point was 6.678 of the ROC curve. When C_min  ≥ 3.13 mg/L, the probability of AKI was more than 50%.

CONCLUSION

In this study, when the calculated combined predictor value was >6.678, there was an increased risk of AKI. Maintaining a polymyxin B C_min level below 3.13 mg/L may be helpful in reducing the incidence of polymyxin B associated nephrotoxicity.

In Vitro Synergy of Colistin in Combination with Meropenem or Tigecycline against Carbapenem-Resistant Acinetobacter baumannii

Acinetobacter baumannii is currently classified as one of six pathogens that contribute to increased patient mortality. Thus, exploratory studies navigating alternative treatment strategies are of supreme interest. Herein, we completed minimum inhibitory concentration (MIC) testing, and time-kill analyses (TKA) on 50 carbapenem-resistant Acinetobacterbaumannii isolates including 28 colistin-resistant isolates. Upon testing of MEM or TGC in the presence of sub-inhibitory COL against the 50 isolates, there was a median 2-fold reduction in MEM and TGC MICs. In the TKAs, the COL+MEM combination was synergistic in 45 (90%) isolates and bactericidal in 43 (86%) isolates at 24 hours, whereas the COL+TGC combination TKAs demonstrated synergy in 32 (64%) isolates and bactericidal activity was shown in 28 (56%) isolates. Additionally, sulbactam (SUL) and TGC were added to the COL+MEM dual therapy regimen to assess the possible utility of a triple therapy regimen against five non-responsive isolates. The COL+MEM+SUL and COL+MEM+TGC regimens effectively restored synergy in (5/5) 100% of the isolates. The results of this study demonstrate the potential utility of COL combinations in the treatment of carbapenem-resistant isolates.

Aerosolized plus intravenous colistin vs intravenous colistin alone for the treatment of nosocomial pneumonia due to multidrug-resistant Gram-negative bacteria: A retrospective cohort study

OBJECTIVE

To compare the effectiveness and safety of aerosolized (AER) plus intravenous (IV) colistin with IV colistin alone in patients with nosocomial pneumonia (NP) due to multidrug-resistant (MDR) Gram-negative bacteria.

METHODS

This was a retrospective cohort study of adults with NP who received IV colistin alone or in combination with AER colistin. The primary endpoint was clinical cure at end of therapy. Secondary endpoints included microbiological eradication, in-hospital mortality and nephrotoxicity.

RESULTS

In total, 135 patients were included in this study: 65 patients received AER plus IV colistin and 70 patients received IV colistin alone. Baseline characteristics were similar between the two groups. Clinical cure was achieved in 42 (65%) patients who received AER plus IV colistin and 26 (37%) patients who received IV colistin alone (P = 0.01). Among a total of 88 patients who were microbiologically evaluable, 27 (42%) patients who received AER plus IV colistin and 12 (17%) patients who received IV colistin alone attained favourable microbiological outcomes (P = 0.022). In-hospital mortality (43% vs 59%, P = 0.072) was higher in patients who received IV colistin alone, but the difference was not significant. Renal injury occurred in 31% of patients who received AER plus IV colistin and in 41% of patients who received IV colistin alone (P = 0.198).

CONCLUSION

AER colistin can be considered as salvage therapy as an adjunct to IV administration for the treatment of patients with NP due to MDR Gram-negative pathogens.

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.

In vitro and in vivo Effect of Antimicrobial Agent Combinations Against Carbapenem-Resistant Klebsiella pneumoniae with Different Resistance Mechanisms in China

Objective

This study aimed to evaluate the in vitro and in vivo effects of different combinations of antimicrobial agents against carbapenemase-producing and non-producing Klebsiella pneumoniae from China.

Methods

A checkerboard assay of meropenem (MEM), amikacin (AK), tigecycline (TGC), colistin (COL) and their combinations was carried out against 58 clinical carbapenem-resistant K. pneumoniae (CRKp) isolates, including 11 carbapenemase-non-producing K. pneumoniae isolates and 21 isolates producing KPC-2 enzyme, 11 NDM-1, 13 IMP, one VIM-1 and one OXA-48. The checkerboard assay was analyzed by the fractional inhibitory concentration index (FICI). A time-kill assay and Galleria mellonella infection model were conducted to evaluate the in vitro and in vivo effects of the four drugs alone and in combination.

Results

In the checkerboard assay, TGC+AK and MEM+AK combinations showed the highest synergistic effect against KPC-2 and NDM-1 carbapenemase-producing isolates, with synergy+partial synergy (defined as FICI <1) rates of 76.2% and 71.4% against KPC-2 producers, and 54.5% and 81.8% against NDM-1 producers. TGC+AK and MEM+COL combinations showed the highest rate of synergistic effect against IMP-producing isolates. Against carbapenemase-non-producing isolates, TGC+COL and TGC+AK combinations showed the highest rate of synergy effect (63.6% and 54.5%). MEM+AK showed a synergistic effect against one VIM-1 producer (FICI=0.31) and an additivite effect (FICI=1) against one OXA-48 producer. In the time-kill assay, COL+AK, COL+TGC, COL+MEM and AK+TGC showed good synergistic effects against the KPC-2-producing isolate D16. COL+MEM and COL+TGC combinations showed good effects against the NDM-1-producing isolate L13 and IMP-4-producing isolate L34. Against the carbapenemase-non-producing isolate Y105, MEM+TGC and COL+AK showed high synergistic effects, with log₁₀CFU/mL decreases of 6.2 and 5.5 compared to the most active single drug. In the G. mellonella survival assay, MEM-based combinations had relatively high survival rates, especially when combined with colistin, against KPC-2 producers (90% survival rate) and with amikacin against metallo-beta-lactamase producers (95-100% survival rate).

Conclusion

Our study suggests that different antimicrobial agent combinations should be considered against CRKp infections with different resistance mechanisms.

Evaluation of the Synergistic Antibacterial Effects of Fosfomycin in Combination with Selected Antibiotics against Carbapenem-Resistant Acinetobacter baumannii

The spread of multi-drug resistant (MDR) pathogens and the lagging pace in the development of novel chemotherapeutic agents warrant the use of combination therapy as a reliable, cost-effective interim option. In this study, the synergistic effects of fosfomycin in combination with other antibiotics were assessed. Of the 193 isolates, 90.6% were non-susceptible to fosfomycin, with minimum inhibitory concentrations (MICs) of ≥128 µg/mL. Antibacterial evaluation of fosfomycin-resistant isolates indicated multi-drug resistance to various antibiotic classes. Combinations of fosfomycin with 12 commonly used antibiotics synergistically inhibited most fosfomycin-resistant isolates. The fractional inhibitory concentration index indicated that combining fosfomycin with either aminoglycosides, glycylcyclines, fluoroquinolones, or colistin resulted in 2- to 16-fold reduction in the MIC of fosfomycin. Time-kill kinetics further confirmed the synergistic bactericidal effects of fosfomycin in combination with either amikacin, gentamicin, tobramycin, minocycline, tigecycline, or colistin, with more than 99.9% reduction in bacterial cells. Fosfomycin-based combination therapy might serve as an alternative option for the treatment of MDR A. baumannii. Further steps including in vivo efficacy and toxicity in experimental models of infection are required prior to clinical applications.

Efficacy of Lysophosphatidylcholine as Direct Treatment in Combination with Colistin against Acinetobacter baumannii in Murine Severe Infections Models

The stimulation of the immune response to prevent the progression of an infection may be an adjuvant to antimicrobial treatment. Here, we aimed to evaluate the efficacy of lysophosphatidylcholine (LPC) treatment in combination with colistin in murine experimental models of severe infections by Acinetobacter baumannii. We used the A. baumannii Ab9 strain, susceptible to colistin and most of the antibiotics used in clinical settings, and the A. baumannii Ab186 strain, susceptible to colistin but presenting a multidrug-resistant (MDR) pattern. The therapeutic efficacies of one and two LPC doses (25 mg/kg/d) and colistin (20 mg/kg/8 h), alone or in combination, were assessed against Ab9 and Ab186 in murine peritoneal sepsis and pneumonia models. One and two LPC doses combined with colistin and colistin monotherapy enhanced Ab9 and Ab186 clearance from spleen, lungs and blood and reduced mice mortality compared with those of the non-treated mice group in both experimental models. Moreover, one and two LPC doses reduced the bacterial concentration in tissues and blood in both models and increased mice survival in the peritoneal sepsis model for both strains compared with those of the colistin monotherapy group. LPC used as an adjuvant of colistin treatment may be helpful to reduce the severity and the resolution of the MDR A. baumannii infection.

Systematic review on estimated rates of nephrotoxicity and neurotoxicity in patients treated with polymyxins

BACKGROUND

Nephrotoxicity and neurotoxicity are commonly associated with polymyxin treatment; however, the emergence of multidrug-resistant Gram-negative bacteria with limited therapeutic options has resulted in increased use of polymyxins.

OBJECTIVES

To determine the rates of nephrotoxicity and neurotoxicity during polymyxin treatment and whether any factors influence these.

DATA SOURCES

Medline, Embase and Cochrane Library databases were searched on 2 January 2020.

STUDY ELIGIBILITY CRITERIA

Studies reporting nephrotoxicity and/or neurotoxicity rates in patients with infections treated with polymyxins were included. Reviews, meta-analyses and reports not in English were excluded.

PARTICIPANTS

Patients hospitalized with infections treated with systemic or inhaled polymyxins were included. For comparative analyses, patients treated with non-polymyxin-based regimens were also included.

METHODS

Meta-analyses were performed using a random-effects model; subgroup meta-analyses were conducted where data permitted using a mixed-effects model.

RESULTS

In total, 237 reports of randomized controlled trials, cohort and case-control studies were eligible for inclusion; most were single-arm observational studies. Nephrotoxic events in 35,569 patients receiving polymyxins were analysed. Overall nephrotoxicity rate was 0.282 (95% confidence interval (CI) 0.259-0.307). When excluding studies where >50% of patients received inhaled-only polymyxin treatment or nephrotoxicity assessment was by methods other than internationally recognized criteria (RIFLE, KDIGO or AKIN), the nephrotoxicity rate was 0.391 (95% CI 0.364-0.419). The odds of nephrotoxicity were greater with polymyxin therapies compared to non-polymyxin-based regimens (odds ratio 2.23 (95% CI 1.58-3.15); p < 0.001). Meta-analyses showed a significant effect of polymyxin type, dose, patient age, number of concomitant nephrotoxins and use of diuretics, glycopeptides or vasopressors on the rate of nephrotoxicity. Polymyxin therapies were not associated with a significantly different rate of neurotoxicity than non-polymyxin-based regimens (p 0.051). The overall rate of neurotoxicity during polymyxin therapy was 0.030 (95% CI 0.020-0.043).

CONCLUSIONS

Polymyxins are associated with a higher risk of nephrotoxicity than non-polymyxin-based regimens.

ColistinDose, a Mobile App for Determining Intravenous Dosage Regimens of Colistimethate in Critically Ill Adult Patients: Clinician-Centered Design and Development Study

Background

Determining a suitable dose of intravenous colistimethate is challenging because of complicated pharmacokinetics, confusing terminology, and the potential for renal toxicity. Only recently have reliable pharmacokinetic/pharmacodynamic data and dosing recommendations for intravenous colistimethate become available.

Objective

The aim of this work was to develop a clinician-friendly, easy-to-use mobile app incorporating up-to-date dosing recommendations for intravenous colistimethate in critically ill adult patients.

Methods

Swift programming language and common libraries were used for the development of an app, ColistinDose, on the iPhone operating system (iOS; Apple Inc). The compatibility among different iOS versions and mobile devices was validated. Dosing calculations were based on equations developed in our recent population pharmacokinetic study. Recommended doses generated by the app were validated by comparison against doses calculated manually using the appropriate equations.

Results

ColistinDose provides 3 major functionalities, namely (1) calculation of a loading dose, (2) calculation of a daily dose based on the renal function of the patient (including differing types of renal replacement therapies), and (3) retrieval of historical calculation results. It is freely available at the Apple App Store for iOS (version 9 and above). Calculated doses accurately reflected doses recommended in patients with varying degrees of renal function based on the published equations. ColistinDose performs calculations on a local mobile device (iPhone or iPad) without the need for an internet connection.

Conclusions

With its user-friendly interface, ColistinDose provides an accurate and easy-to-use tool for clinicians to calculate dosage regimens of intravenous colistimethate in critically ill patients with varying degrees of renal function. It has significant potential to avoid the prescribing errors and patient safety issues that currently confound the clinical use of colistimethate, thereby optimizing patient treatment.

Treatment of infections caused by Gram-negative pathogens: current status on the pharmacokinetics/pharmacodynamics of parenteral and inhaled polymyxins in patients

Polymyxins are increasingly used as a last resort for the treatment of infections caused by multidrug-resistant Gram-negative bacteria in patients. Over the last decade, significant progress has been made in understanding the pharmacokinetics/pharmacodynamics/toxicodynamics (PK/PD/TD) of parenteral and inhaled polymyxins. This mini-review provides an overview of polymyxin chemistry, different dose definitions, and the latest research on their clinical use, toxicities, and PK/PD after intravenous and inhalation administration. Optimising the PK/PD/TD of polymyxins in patients is critical to maximise their efficacy while minimising toxicities and the emergence of resistance.

Steady-state pharmacokinetic and pharmacodynamic profiling of colistin in critically ill patients with multi-drug-resistant gram-negative bacterial infections, along with differences in clinical, microbiological and safety outcome

Limited data are present regarding the steady-state pharmacokinetics and pharmacodynamics of colistin in critically ill patients suffering from multi-drug-resistant gram-negative bacterial (MDR-GNB) infections. We aimed to profile the steady-state pharmacokinetics and pharmacodynamics of colistin in critically ill patients with MDR-GNB infections, along with determining the predictors that could influence the clinical, microbiological and safety outcome. We recruited 30 critically ill patients suffering from MDR-GNB infections in our prospective open-label study. Intravenous colistimethate sodium (CMS) 2 million IU was administered concurrently with inhalational CMS 1 million IU every 8 hours. Steady-state plasma colistin levels were measured. Logistic regression analysis was used to identify various predictors of clinical, microbiological and safety outcome. A large variability was observed in the steady-state colistin pharmacokinetic/pharmacodynamic parameters, along with the factors that influenced the clinical, microbiological and safety outcome. In conclusion, steady-state colistin pharmacokinetic and pharmacodynamic parameters observed in our study were largely consistent with those reported in previous studies. High acute physiology and chronic health evaluation II scores were associated with poor clinical outcome. Log-transformed colistin maximum concentration, area under the plasma concentration curve for 8 hours, apparent total body clearance and apparent volume of distribution were significantly associated with the safety outcome.

Clinical efficacy and pharmacokinetics of colistimethate sodium and colistin in critically ill patients in an Indian hospital with high endemic rates of multidrug-resistant Gram-negative bacterial infections: A prospective observational study

BACKGROUND

Safe and effective use of colistin requires robust pharmacokinetic (PK) and pharmacodynamic (PD) data to guide dosing.

AIM

To evaluate the pharmacokinetics of colistimethate sodium and colistin in critically ill patients and correlate with clinical efficacy and renal function.

MATERIALS AND METHODS

Twenty critically ill adult patients with colistin-susceptible multidrug-resistant (MDR) infections and normal renal function treated with intravenous colistimethate sodium - at a 9 million units (270 mg CBA) loading dose followed by maintenance (MD) of 3 million units t.i.d, 24 hours later - were evaluated for clinical cure (CC) at the end of therapy. Patient characteristics and plasma colistin levels at 0, 0.5, 1, 2, 4, 8 and 12 hours after the loading dose and at 1, 2 and 8 hours after the eighth and ninth infusion of MD were evaluated. Colistimethate sodium and colistin levels were measured by high-performance liquid chromatography and tandem mass spectrometry (HPLC-MS/MS).

RESULTS

Among the 20 patients who were evaluated, 60% had pneumonia. Predominant pathogens were Klebsiella pneumoniae and Acinetobacter spp. Clinical cure was 50% (10/20). Mean peak loading dose concentrations were 3 ± 1.1 mg/L (1.75-5.14) and 2.37 ± 1.2 mg/L (1.52-5.54) for 'cure' and 'failure' groups, respectively (p = 0.13), while mean steady-state (Cssavg) concentrations were 2.25 ± 1.3 mg/L and 1.78 ± 1.1 mg/L in 'cure' and 'failure' groups, respectively (p = 0.19). Nephrotoxicity was 5% on day 7 of therapy. However, bacteriological cure could not be correlated with PK/PD.

CONCLUSIONS

Subtherapeutic Cssavg with clinical failure and lower efficacy without significant nephrotoxicity highlights the need for therapeutic drug monitoring to guide colistin dosing.

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.

Quantification of Colistin in Plasma by Liquid Chromatography-Tandem Mass Spectrometry: Application to a Pharmacokinetic Study

Colistin is a polymixin antibiotic (polymixin E) that is produced by Bacillus colistinus bacteria. The aim of the present study was to develop and validate a method to quantify colistin levels in plasma using high performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) technique and then apply it in experimental animals (rats) to investigate the pharmacokinetic profile of colistin in this species. Polymyxin B was used as an internal standard (IS) and the quantitation was carried out using ESI + interface and employing multiple reaction monitoring (MRM) mode. A mobile phase consisting of acetonitrile:water:formic acid (30:70:0.1%; v/v/v) was employed and Zorbax eclipse plus C18 (1.8 µm, 2.1 mm i.d. x 50 mm) was the optimal column for this method and utilized at a flow rate of 0.2 mL/min. The full scan mass spectra of precursor/product ions of colistin A were at m/z 585.5 > 100.8, for colistin B at m/z 578.8 > 101 and for the IS at m/z 602.8 > 101. The lower limit of quantification (LLOQ) was 0.5 µg/mL. The method demonstrated acceptable intra-run and inter-run precision and accuracy for both colistin A and colistin B. Colistin was stable when assessed for long-term stability, freeze-thaw stability and autosampler stability. However, it was not stable when stored at room temperature. The matrix effect evaluation showed minimal or no effect. Incurred sample reanalysis findings were within acceptable ranges (<20% of the nominal concentration). The pharmacokinetic parameters of colistin were investigated in rats using the present method. The developed method for colistin demonstrates that it is rapid, sensitive, specific, accurate, precise, and reliable.

A coup d'état by NDM-producing Klebsiella pneumoniae overthrows the major bacterial population during KPC-directed therapy

The objective of this study was to utilize a co-culture hollow-fiber infection model (HFIM) to characterize the interplay between a small, difficult-to-detect, New Delhi metallo-β-lactamase-producing Klebsiella pneumoniae (NDM-Kp) minor population and a larger K. pneumoniae carbapenemase (KPC)-producing K. pneumoniae population in the presence of KPC-directed antibacterial therapy. Selective plating onto agar with ceftazidime-avibactam was used to track the density of the NDM-Kp population. Susceptibility testing and the Verigene System failed to identify the small initial NDM-Kp population. However, a ceftazidime-avibactam Etest detected resistant colonies that were confirmed to be NDM-Kp. In the HFIM, all of the investigated drug regimens caused regrowth within 24 h and resulted in >10⁹ CFU/mL of NDM-Kp. Our study demonstrates that the HFIM is a powerful tool for studying the population dynamics of multiple pathogens during antimicrobial exposure and also highlights that difficult-to-detect minor populations of drug-resistant bacteria may cause treatment failure without appropriate antibacterial therapy.

Extensive Therapeutic Drug Monitoring of Colistin in Critically Ill Patients Reveals Undetected Risks

(1) Background: With the rise of multi-/pan-drug resistant (MDR/PDR) pathogens, the less utilized antibiotic Colistin has made a comeback. Colistin fell out of favor due to its small therapeutic range and high potential for toxicity. Today, it is used again as a last resort substance in treating MDR/PDR pathogens. Although new guidelines with detailed recommendations for Colistin dosing are available, finding the right dose in critically ill patients with renal failure remains difficult. Here, we evaluate the efficiency of the current guidelines' recommendations by using high resolution therapeutic drug monitoring of Colistin. (2) Methods: We analyzed plasma levels of Colistin and its prodrug colisthimethate sodium (CMS) in 779 samples, drawn from eight PDR-infected ICU patients, using a HPLC-MS/MS approach. The impact of renal function on proper Colistin target levels was assessed. (3) Results: CMS levels did not correlate with Colistin levels. Over-/Underdosing occurred regardless of renal function and mode of renal replacement therapy. Colistin elimination half-time appeared to be longer than previously reported. (4) Conclusion: Following dose recommendations from the most current guidelines does not necessarily lead to adequate Colistin plasma levels. Use of Colistin without therapeutic drug monitoring might be unsafe and guideline adherence does not warrant efficient target levels in critically ill patients.

Synergistic activity of an OmpA inhibitor and colistin against colistin-resistant Acinetobacter baumannii: mechanistic analysis and in vivo efficacy

Objectives

Preventing bacterial contact with host cells can provide an additional approach to tackling MDR Acinetobacter baumannii. Recently, we identified AOA-2 as a potential blocker of A. baumannii outer membrane protein A without presenting bactericidal activity. Here, we aimed to study whether AOA-2 can increase the activity of colistin against colistin-resistant A. baumannii in vitro and in vivo.

Methods

Reference and clinical A. baumannii strains susceptible and resistant to colistin (CST-S and CST-R) were used. Microdilution and time-kill curve assays were performed to determine the synergy between AOA-2 and colistin. SDS-PAGE assays with CST-S and CST-R outer membrane proteins and MALDI-TOF-TOF (MS-MS/MS) analysis were performed to determine the AOA-2 and colistin synergy mechanism. In a murine peritoneal sepsis model, the therapeutic efficacy of AOA-2 (10 mg/kg/24 h) in combination with a sub-optimal dose of colistin (10 mg/kg/24 h) against CST-R was evaluated by determining the bacterial load in tissues and blood, and mouse survival.

Results

We showed that AOA-2 increased the in vitro colistin susceptibility of reference and clinical CST-S and CST-R strains. This combination also enhanced their killing activity after 24 h of drug exposure. This synergy is mediated by the overexpression of Omp25. In vivo, the combination of AOA-2 with colistin significantly reduced the bacterial load in tissues and blood, and increased mouse survival, compared with colistin monotherapy.

Conclusions

We identified a novel class of antimicrobial agents that has proven to be effective in combination with colistin in an experimental model of severe infection by CST-R A. baumannii.

Rational Combinations of Polymyxins with Other Antibiotics

Combinations of antimicrobial agents are often used in the management of infectious diseases. Antimicrobial agents used as part of combination therapy are often selected empirically. As regrowth and the emergence of polymyxin (either colistin or polymyxin B) resistance has been observed with polymyxin monotherapy, polymyxin combination therapy has been suggested as a possible means by which to increase antimicrobial activity and reduce the development of resistance. This chapter provides an overview of preclinical and clinical investigations of CMS/colistin and polymyxin B combination therapy. In vitro data and animal model data suggests a potential clinical benefit with many drug combinations containing clinically achievable concentrations of polymyxins, even when resistance to one or more of the drugs in combination is present and including antibiotics normally inactive against Gram-negative organisms. The growing body of data on the emergence of polymyxin resistance with monotherapy lends theoretical support to a benefit with combination therapy. Benefits include enhanced bacterial killing and a suppression of polymyxin resistant subpopulations. However, the complexity of the critically ill patient population, and high rates of treatment failure and death irrespective of infection-related outcome make demonstrating a potential benefit for polymyxin combinations extremely challenging. Polymyxin combination therapy in the clinic remains a heavily debated and controversial topic. When combinations are selected, optimizing the dosage regimens for the polymyxin and the combinatorial agent is critical to ensure that the benefits outweigh the risk of the development of toxicity. Importantly, patient characteristics, pharmacokinetics, the site of infection, pathogen and resistance mechanism must be taken into account to define optimal and rational polymyxin combination regimens in the clinic.

Clinical Pharmacokinetics, Pharmacodynamics and Toxicodynamics of Polymyxins: Implications for Therapeutic Use

The availability of sensitive, accurate and specific analytical methods for the measurement of polymyxins in biological fluids has enabled an understanding of the pharmacokinetics of these important antibiotics in healthy humans and patients. Colistin is administered as its inactive prodrug colistin methanesulfonate (CMS) and has especially complex pharmacokinetics. CMS undergoes conversion in vivo to the active entity colistin, but the rate of conversion varies from brand to brand and possibly from batch to batch. The extent of conversion is generally quite low and depends on the relative magnitudes of the conversion clearance and other clearance pathways for CMS of which renal excretion is a major component. Formed colistin in the systemic circulation undergoes very extensive tubular reabsorption; the same mechanism operates for polymyxin B which is administered in its active form. The extensive renal tubular reabsorption undoubtedly contributes to the propensity for the polymyxins to cause nephrotoxicity. While there are some aspects of pharmacokinetic behaviour that are similar between the two clinically used polymyxins, there are also substantial differences. In this chapter, the pharmacokinetics of colistin, administered as CMS, and polymyxin B are reviewed, and the therapeutic implications are discussed.

Pharmacokinetics of colistin in patients with multidrug-resistant Gram-negative infections: A pilot study

Background & objectives

There is little information concerning intravenously (i.v.) administered colistin in patients with multidrug-resistant (MDR) Gram-negative infections. Thus, this pilot prospective study was undertaken to characterize efficacy and pharmacokinetics of colistin in patients with MDR Gram-negative infections.

Methods

Nine patients with age >12 yr and MDR Gram-negative infections were included, of whom six were given colistin at the doses of 2 MU, while three patients were given 1 MU i.v. dose every 8 h. Blood samples were collected at different time intervals. Determination of colistin concentration was done by a ultra-high-performance liquid chromatography/mass spectrometry/selected reaction monitoring assay.

Results

The area under the plasma concentration-versus-time curve over eight hours (AUC_0-8) for colistin after the 1^st dose ranged from 3.3 to 16.4 mg×h/l (median, 4.59). After the 5^th dose, AUC_0-8for colistin ranged from 4.4 to 15.8 mg×h/l (median, 6.0). With minimal inhibitory concentration (MIC) value of 0.125 mg/l, AUC_0-8/MIC ranged from 26.7 to 131.4 (median, 36.7) and 35.5 to 126.0 (median, 48.0) after the 1^st and the 5^th doses of 2 MU every 8 h, respectively.

Interpretation & conclusions

As there is a paucity of information on AUC/MIC for colistin, it may not be possible to conclude whether AUC/MIC values in our patients were adequate. There is a microbiological clearance of organism, which goes in favour of the dosing schedule being adequate. Further studies need to be done to understand the pharmacokinetics of colistin in patients with infections.

Polymyxins: Antibacterial Activity, Susceptibility Testing, and Resistance Mechanisms Encoded by Plasmids or Chromosomes

Polymyxins are well-established antibiotics that have recently regained significant interest as a consequence of the increasing incidence of infections due to multidrug-resistant Gram-negative bacteria. Colistin and polymyxin B are being seriously reconsidered as last-resort antibiotics in many areas where multidrug resistance is observed in clinical medicine. In parallel, the heavy use of polymyxins in veterinary medicine is currently being reconsidered due to increased reports of polymyxin-resistant bacteria. Susceptibility testing is challenging with polymyxins, and currently available techniques are presented here. Genotypic and phenotypic methods that provide relevant information for diagnostic laboratories are presented. This review also presents recent works in relation to recently identified mechanisms of polymyxin resistance, including chromosomally encoded resistance traits as well as the recently identified plasmid-encoded polymyxin resistance determinant MCR-1. Epidemiological features summarizing the current knowledge in that field are presented.

Pharmacodynamics of colistin and fosfomycin: a 'treasure trove' combination combats KPC-producing Klebsiella pneumoniae

Objectives

KPC-producing Klebsiella pneumoniae are an emerging public health problem around the globe. We defined the combinatorial pharmacodynamics and ability to suppress resistance of two 'old' antibiotics, fosfomycin and colistin, in time-kill experiments and hollow-fibre infection models (HFIM).

Methods

Two KPC-2-producing K. pneumoniae isolates were used: one susceptible to both colistin and fosfomycin (KPC 9A: MIC colistin 0.25 mg/L and MIC fosfomycin ≤8 mg/L) and the other resistant to colistin and susceptible to fosfomycin (KPC 5A: MIC colistin 64 mg/L and MIC fosfomycin 32 mg/L). Time-kill experiments assessed an array of colistin and fosfomycin concentrations against both isolates. Colistin and fosfomycin pharmacokinetics from critically ill patients were simulated in the HFIM to define the pharmacodynamic activity of humanized regimens over 5 days against KPC 9A.

Results

In time-kill experiments, synergy was demonstrated for all colistin/fosfomycin combinations containing >8 mg/L fosfomycin against the double-susceptible KPC strain, 9A. Synergy versus KPC strain 5A was only achieved at the highest concentrations of colistin (4 mg/L) and fosfomycin (512 mg/L) at 48 h. In the HFIM, colistin or fosfomycin monotherapies resulted in rapid proliferation of resistant subpopulations; KPC 9A regrew by 24 h. In contrast to the monotherapies, the colistin/fosfomycin combination resulted in a rapid 6.15 log 10  cfu/mL reduction of KPC 9A by 6 h and complete suppression of resistant subpopulations until 120 h.

Conclusions

Colistin and fosfomycin may represent an important treatment option for KPC-producing K. pneumoniae otherwise resistant to traditional antibiotics.

In vitro Pharmacokinetics/Pharmacodynamics Evaluation of Fosfomycin Combined with Amikacin or Colistin against KPC2-Producing Klebsiella pneumoniae

Objectives: The emergence of carbapenem-resistant Enterobacteriaceae, especially Klebsiella pneumoniae, has become a major concern in clinic settings. Combination therapy is gaining momentum to counter the secondary resistance and potential suboptimal efficacy of monotherapy. The aim of this study was to evaluate the bactericidal effect of fosfomycin (FM), amikacin (AMK), or colistin (COL) alone and combinations against KPC2-producing K. pneumoniae using dynamic model by simulating human pharmacokinetics in vitro. Methods: The Pharmacokinetics Auto Simulation System 400 system was employed to simulate different dosing regimens of FM, AMK, and COL alone and combination. Bacterial growth recovery time (RT) and the area between the control growth and antibacterial killing curves (IE) were used as unbiased and comprehensive means for determining the antimicrobial effect. Results: We observed that COL alone was much pronounced than FM or AMK against KPC-Kp. IE of FM (8 g every 8 h) plus AMK (15 mg/kg once-daily) and FM (8 g every 8 h) plus COL (75,000 IU/kg every 12 h) were higher (>170 and >200 LogCFU/mL·h^-1, respectively) than that of monotherapies against sensitive strains. Of note, the rate of resistance was lower when using the combination of FM (8 g every 8 h) plus COL (75,000 IU/kg every 12 h) than using COL (75,000 IU/kg every 12 h) alone. Conclusions: The combination of FM (8 g every 8 h) plus AMK (15 mg/kg once-daily) and FM (8 g every 8 h) plus COL (75,000 IU/kg every 12 h) were effective at maximizing bacterial killing and suppressing emergence of resistance.

Can Pharmacokinetic and Pharmacodynamic Principles Be Applied to the Treatment of Multidrug-Resistant Acinetobacter?

OBJECTIVE:

To discuss treatment options that can be used for treatment of Acinetobacter infections.

DATA SOURCES:

A MEDLINE search (1966-November 2010) was conducted to identify English-language literature on pharmacotherapy of Acinetobacter and the bibliographies of pertinent articles. Programs and abstracts from infectious diseases meetings were also searched. Search terms included Acinetobacter, multidrug resistance, pharmacokinetics, pharmacodynamics, Monte Carlo simulation, nosocomial pneumonia, carbapenems, polymyxins, sulbactam, aminoglycosides, tetracyclines, tigecycline, rifampin, and fluoroquinolones.

DATA SELECTION AND DATA EXTRACTION:

All articles were critically evaluated and all pertinent information was included in this review.

DATA SYNTHESIS:

Multidrug resistant (MDR) Acinetobacter, defined as resistance to 3 or more antimicrobial classes, has increased over the past decade. The incidence of carbapenem-resistant Acinetobacter is also increasing, leading to an increased use of dose optimization techniques and/or alternative antimicrobials, which is driven by local susceptibility patterns. However, Acinetobacter infections that are resistant to all commercially available antibiotics have been reported. General principles are available to guide dose optimization of aminoglycosides, β-lactams, fluoroquinolones, and tigecycline for infections due to gram-negative pathogens. Unfortunately, data specific to patients with Acinetobacter infections are limited. Recent pharmacokinetic-pharmacodynamic information has shed light on colistin dosing. The dilemma with colistin is its concentration-dependent killing, which makes once-daily dosing seem like an attractive option, but its short postantibiotic effect limits a clinician's ability to extend the dosing interval. Localized delivery of antimicrobials is also an attractive option due to the ability to increase drug concentration at the infection site while minimizing systemic adverse events, but more data are needed regarding this approach.

CONCLUSIONS:

Increased reliance on dosage optimization, combination therapy, and localized delivery of antimicrobials are methods to pursue positive clinical outcomes in MDR Acinetobacter infections since novel antimicrobials will not be available for several years. Well-designed clinical trials with MDR Acinetobacter are needed to define the best treatment options for these patients.

Strategies to enhance rational use of antibiotics in hospital: a guideline by the German Society for Infectious Diseases

Introduction

In the time of increasing resistance and paucity of new drug development there is a growing need for strategies to enhance rational use of antibiotics in German and Austrian hospitals. An evidence-based guideline on recommendations for implementation of antibiotic stewardship (ABS) programmes was developed by the German Society for Infectious Diseases in association with the following societies, associations and institutions: German Society of Hospital Pharmacists, German Society for Hygiene and Microbiology, Paul Ehrlich Society for Chemotherapy, The Austrian Association of Hospital Pharmacists, Austrian Society for Infectious Diseases and Tropical Medicine, Austrian Society for Antimicrobial Chemotherapy, Robert Koch Institute.

Materials and methods

A structured literature research was performed in the databases EMBASE, BIOSIS, MEDLINE and The Cochrane Library from January 2006 to November 2010 with an update to April 2012 (MEDLINE and The Cochrane Library). The grading of recommendations in relation to their evidence is according to the AWMF Guidance Manual and Rules for Guideline Development.

Conclusion

The guideline provides the grounds for rational use of antibiotics in hospital to counteract antimicrobial resistance and to improve the quality of care of patients with infections by maximising clinical outcomes while minimising toxicity. Requirements for a successful implementation of ABS programmes as well as core and supplemental ABS strategies are outlined. The German version of the guideline was published by the German Association of the Scientific Medical Societies (AWMF) in December 2013.

Impact of colistin plasma levels on the clinical outcome of patients with infections caused by extremely drug-resistant Pseudomonas aeruginosa

BACKGROUND

Colistin has a narrow therapeutic window with nephrotoxicity being the major dose-limiting adverse effect. Currently, the optimal doses and therapeutic plasma levels are unknown.

METHODS

Prospective observational cohort study, including patients infected by colistin-susceptible P. aeruginosa treated with intravenous colistimethate sodium (CMS). Clinical data and colistin plasma levels at steady-state (C_ss) were recorded. The primary and secondary end points were clinical cure and 30-day all-cause mortality.

RESULTS

Ninety-one patients were included. Clinical cure was observed in 72 (79%) patients. The mean (SD) C_ss was 1.49 (1.4) mg/L and 2.42 (1.5) mg/L (p = 0.01) in patients who achieved clinical cure and those who not, respectively. Independent risk factors for clinical failure were male sex (OR 5.88; 95% CI 1.09-31.63), APACHE II score (OR 1.15; 95% CI 1.03-1.27) and nephrotoxicity at the EOT (OR 9.13; 95% CI 95% 2.06-40.5). The 30-day mortality rate was 30.8%. Risk factors for 30-day mortality included the APACHE II score (OR 1.98; 95% CI 1-1.20), the McCabe score (OR 2.49; 95% CI 1.14-5.43) and the presence of nephrotoxicity at the end of treatment (EOT) (OR 3.8; 95% CI 1.26-11.47).

CONCLUSION

In this series of patients with infections caused by XDR P. aeruginosa infections, C_ss is not observed to be related to clinical outcome.

Colistin Dosage without Loading Dose Is Efficacious when Treating Carbapenem-Resistant Acinetobacter baumannii Ventilator-Associated Pneumonia Caused by Strains with High Susceptibility to Colistin

OBJECTIVES

This study aims to analyze the mortality and the length of ICU stay (LOS) of A. baumannii VAP compared to respiratory colonization in patients with mechanical ventilation (MV).

METHODS

A prospective cohort study was performed in an ICU of adult patients (February 2010-June 2011). One hundred patients on MV with A. baumannii in lower respiratory airways were recruited, and classified as VAP or airways colonization according to CPIS criteria, with a punctuation ≥6. LOS, 30-days mortality, A. baumannii bacteremia, and clinical features including antibiotic therapy were recorded. Multivariate analysis (linear and Cox regression) and survival analysis (Kaplan-Meier curves) were performed.

RESULTS

Fifty-seven VAP and 43 colonized A. baumannii patients were analyzed. Among the A. baumannii strains, 99% were non-susceptible to carbapenems and the MIC90 of colistin was 0.12 mg/l. Therapy was appropriate in 94.6% of VAP patients, most of them with colistin 6 MIU/day, although in 13 (23.6%) cases colistin was started 48 hours after the onset of VAP. Mortality was similar in both groups (VAP 24.6% vs. colonized 27.9%, p = 0.7). Bacteremia and acute kidney insufficiency were associated with decreased survival (p = 0.02 and p = 0.04, respectively) in VAP patients. LOS was 21.5 (11.5-42.75) vs. 9 (6-22) days for VAP and colonized patients (p = 0.004). VAP (p = 0.003) and age (p = 0.01) were independently related to a longer LOS.

CONCLUSIONS

Multidrug-resistant A. baumannii VAP treated with colistin does not have a different mortality compared to lower airways colonization, among patients on mechanical-ventilation, in a setting of high susceptibility to colistin of A. baumannii.

Colistin loading dose: evaluation of the published pharmacokinetic and clinical data

Colistin (polymyxin E) has been widely used since the beginning of the century as a last-option antibiotic for the treatment of patients with multidrug-resistant and extensively-drug resistant bacterial infections. However, colistin dosing is troublesome because each batch of the drug contains a mixture of components and because it is administered as the inactive pro-drug colistimethate sodium (CMS), which has different pharmacokinetic (PK) properties from the active drug. Significant inter-individual and intra-individual variability in colistin plasma concentrations have been observed in all available studies. Low plasma concentrations of the drug during the first hours from initiation of administration suggested that a loading dose would be appropriate. However, other PK studies challenge this approach. Clinical data from randomised controlled trials are not available, whilst data from observational studies do not support higher effectiveness of a loading dose. In this review, we summarise the available data regarding the administration of a loading dose and discuss the issues surrounding the potential advantages and disadvantages as well as the context within which such an approach could be beneficial to patients.

Management of Adults With Hospital-acquired and Ventilator-associated Pneumonia: 2016 Clinical Practice Guidelines by the Infectious Diseases Society of America and the American Thoracic Society

It is important to realize that guidelines cannot always account for individual variation among patients. They are not intended to supplant physician judgment with respect to particular patients or special clinical situations. IDSA considers adherence to these guidelines to be voluntary, with the ultimate determination regarding their application to be made by the physician in the light of each patient's individual circumstances.These guidelines are intended for use by healthcare professionals who care for patients at risk for hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP), including specialists in infectious diseases, pulmonary diseases, critical care, and surgeons, anesthesiologists, hospitalists, and any clinicians and healthcare providers caring for hospitalized patients with nosocomial pneumonia. The panel's recommendations for the diagnosis and treatment of HAP and VAP are based upon evidence derived from topic-specific systematic literature reviews.

Efficacy of Lysophosphatidylcholine in Combination with Antimicrobial Agents against Acinetobacter baumannii in Experimental Murine Peritoneal Sepsis and Pneumonia Models

Immune response stimulation to prevent infection progression may be an adjuvant to antimicrobial treatment. Lysophosphatidylcholine (LPC) is an immunomodulator involved in immune cell recruitment and activation. In this study, we aimed to evaluate the efficacy of LPC in combination with colistin, tigecycline, or imipenem in experimental murine models of peritoneal sepsis and pneumonia. We used Acinetobacter baumannii strain Ab9, which is susceptible to colistin, tigecycline, and imipenem, and multidrug-resistant strain Ab186, which is susceptible to colistin and resistant to tigecycline and imipenem. Pharmacokinetic and pharmacodynamic parameters for colistin, tigecycline, and imipenem and the 100% minimal lethal dose (MLD100) were determined for both strains. The therapeutic efficacies of LPC, colistin (60 mg/kg of body weight/day), tigecycline (10 mg/kg/day), and imipenem (180 mg/kg/day), alone or in combination, were assessed against Ab9 and Ab186 at the MLD100 in murine peritoneal sepsis and pneumonia models. The levels of pro- and anti-inflammatory cytokines, i.e., tumor necrosis factor alpha (TNF-α) and interleukin-10 (IL-10), were determined by enzyme-linked immunosorbent assay (ELISA) for the same experimental models after inoculating mice with the MLD of both strains. LPC in combination with colistin, tigecycline, or imipenem markedly enhanced the bacterial clearance of Ab9 and Ab186 from the spleen and lungs and reduced bacteremia and mouse mortality rates (P < 0.05) compared with those for colistin, tigecycline, and imipenem monotherapies. Moreover, at 4 h post-bacterial infection, Ab9 induced higher TNF-α and lower IL-10 levels than those with Ab186 (4 μg/ml versus 3 μg/ml [P < 0.05] and 2 μg/ml versus 3.4 μg/ml [P < 0.05], respectively). LPC treatment combined with colistin, tigecycline, or imipenem modestly reduced the severity of infection by A. baumannii strains with different resistance phenotypes compared to LPC monotherapy in both experimental models.

Efficacy and Safety of a Colistin Loading Dose, High-Dose Maintenance Regimen in Critically Ill Patients With Multidrug-Resistant Gram-Negative Pneumonia

INTRODUCTION

Emergence of multidrug-resistant (MDR) gram-negative (GN) pathogens and lack of novel antibiotics have increased the use of colistin, despite unknown optimal dosing. This study aimed to evaluate the safety and efficacy of a colistin loading dose, high-dose (LDHD) maintenance regimen in patients with MDR-GN pneumonia.

METHODS

A retrospective cohort analysis was performed comparing critically ill patients with MDR-GN pneumonia pre- and postimplementation of a colistin LDHD guideline with a primary outcome of clinical cure. Safety was assessed using incidence of acute kidney injury (AKI) based on RIFLE (risk, injury, failure, loss, end-stage renal disease) criteria.

RESULTS

Seventy-two patients met the inclusion criteria (42 preimplementation and 30 postimplementation). Clinical cure was achieved in 23 (55%) patients in the preimplementation group and 20 (67%) patients in the postimplementation group ( P = .31). AKI occurred in 50% of the patients during the preimplementation period and 58% during the postimplementation period ( P = .59) with no difference in initiation rates of renal replacement therapy.

CONCLUSION

The increased clinical cure rate after implementation of the colistin LDHD guideline did not reach statistical significance. The LDHD guideline, however, was not associated with an increased incidence of AKI, despite higher intravenous colistin doses. Opportunity exists to optimize colistin dosage while balancing toxicity, but larger studies are warranted.