Infectious Diseases: Parenteral Polymyxin B Use in Patients with Multidrug-Resistant Gram-Negative Bacteremia and Urinary Tract Infections: A Retrospective Case Series

Engineering a nanoantibiotic system displaying dual mechanism of action

In recent decades, peptide amphiphiles (PAs) have established themselves as promising self-assembling bioinspired materials in a wide range of medical fields. Herein, we report a dual-therapeutic system constituted by an antimicrobial PA and a cylindrical protease inhibitor (LJC) to achieve broad antimicrobial spectrum and to enhance therapeutic efficacy. We studied two strategies: PA-LJC nanostructures (Encapsulation) and PA nanostructures + free LJC (Combination). Computational modeling using a molecular theory for amphiphile self-assembly captures and explains the morphology of PA-LJC nanostructures and the location of encapsulated LJC in agreement with transmission electron microscopy and two-dimensional (2D) NMR observations. The morphology and release profile of PA-LJC assemblies are strongly correlated to the PA:LJC ratio: high LJC loading induces an initial burst release. We then evaluated the antimicrobial activity of our nanosystems toward gram-positive and gram-negative bacteria. We found that the Combination broadens the spectrum of LJC, reduces the therapeutic concentrations of both agents, and is not impacted by the inoculum effect. Further, the Encapsulation provides additional benefits including bypassing water solubility limitations of LJC and modulating the release of this molecule. The different properties of PA-LJC nanostructures results in different killing profiles, and reduced cytotoxicity and hemolytic activity. Meanwhile, details in membrane alterations caused by each strategy were revealed by various microscopy and fluorescent techniques. Last, in vivo studies in larvae treated by the Encapsulation strategy showed better antimicrobial efficacy than polymyxin B. Collectively, this study established a multifunctional platform using a versatile PA to act as an antibiotic, membrane-penetrating assistant, and slow-release delivery vehicle.

Risks of Polymyxin B Nephrotoxicity and Its Precursors in the Intensive Care Unit: A Retrospective Cohort Study

BACKGROUND AND AIM

Polymyxin group antibiotics constitute a part of our limited arsenal in the treatment of multidrug-resistant gram-negative bacteria. However, their use is limited especially due to nephrotoxicity and other side effects. In this study, we primarily aimed to determine the effect of polymyxin B on the rate of nephrotoxicity in critically ill patients, and secondly to identify the factors that facilitate nephrotoxicity caused by polymyxin B.

MATERIALS AND METHODS

The study was designed as a retrospective cohort study and conducted by scanning patients aged 18 years or older who had been admitted to our intensive care unit (ICU) in 2022 and treated with polymyxin B for at least 72 hours. Patients without chronic renal failure and acute kidney injury (AKI) before starting polymyxin B therapy were included and AKI was examined after the use of polymyxin B. The patients were then divided into two groups, those with AKI and those without AKI. We tried to find factors that may facilitate AKI by comparing the two groups.

RESULTS

Of the patients, 26 were female and 34 were male. In 21 of the patients (35%), renal damage of varying degrees developed; these patients belonged to the nephrotoxicity (NT) group, while the rest belonged to the non-nephrotoxicity (non-NT) group. We found that advanced age (p=0.008), low baseline GFR (p=0.01), baseline creatinine (p=0.006), BMI (p=0.011), concomitant diseases (p<0.001), and days of use of polymyxin B (p=0.006) were statistically different between the two groups. In multivariate analysis of univariate analysis, we found that duration of polymyxin B use, BMI, and advanced age were independent risk factors for AKI development.

CONCLUSION

We found that 21 (35%) of 60 intensive care unit patients who had no previous history of kidney injury developed kidney injury after being treated with polymyxin B. We identified advanced age, high BMI, and duration of polymyxin B use as independent risk factors. Therefore, we recommend close monitoring of renal function and prompt intervention, particularly in patients with risk factors, during polymyxin B use.

The Remarkable Innate Resistance of Burkholderia bacteria to Cationic Antimicrobial Peptides: Insights into the Mechanism of AMP Resistance

Gram-negative bacteria belonging to the genus Burkholderia are remarkably resistant to broad-spectrum, cationic, antimicrobial peptides (AMPs). It has been proposed that this innate resistance is related to changes in the outer membrane lipopolysaccharide (OM LPS), including the constitutive, essential modification of outer membrane Lipid A phosphate groups with cationic 4-amino-4-deoxy-arabinose. This modification reduces the overall negative charge on the OM LPS which may change the OM structure and reduce the binding, accumulation, and permeation of cationic AMPs. Similarly, the Gram-negative pathogen Pseudomonas aeruginosa can quickly become resistant to many AMPs by multiple mechanisms, frequently, including activation of the arn operon, which leads, transiently, to the same modification of Lipid A. We recently discovered a set of synthetically evolved AMPs that do not invoke any resistance in P. aeruginosa over multiple passages and thus are apparently not inhibited by aminorabinosylation of Lipid A in P. aeruginosa. Here we test these resistance-avoiding peptides, within a set of 18 potent AMPs, against Burkholderia thailandensis. We find that none of the AMPs tested have measurable activity against B. thailandensis. Some were inactive at concentrations as high as 150 μM, despite all having sterilizing activity at ≤ 10 μM against a panel of common, human bacterial pathogens, including P. aeruginosa. We speculate that the constitutive modification of Lipid A in members of the Burkholderia genus is only part of a broader set of modifications that change the architecture of the OM to provide such remarkable levels of resistance to cationic AMPs.

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.

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.

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.

Clinical use of intravenous polymyxin B for the treatment of patients with multidrug-resistant Gram-negative bacterial infections: An evaluation of the current evidence

OBJECTIVES

The epidemic dimensions of the emergence of multidrug-resistant (MDR) Gram-negative bacterial infections have led to the revival of old antibiotics, including the polymyxins.

METHODS

We performed a review and meta-analysis to evaluate the current literature data regarding the effectiveness and safety of intravenous polymyxin B in patients with MDR Gram-negative bacterial infections and the overall mortality and nephrotoxicity in patients treated with intravenous polymyxin B either as monotherapy or combination therapy.

RESULTS

A total of 5 prospective and 28 retrospective studies, 1 cross-sectional study, 2 retrospective case series and 7 case reports provided data regarding the effectiveness and/or toxicity of intravenous polymyxin B. All-cause mortality of 2910 patients (from 27 studies) who received intravenous polymyxin B was 41.2% (95% CI 35.5-47.0%). All-cause nephrotoxicity of 2994 patients (from 28 studies) treated with intravenous polymyxin B was 40.7% (95% CI 35.0-46.6%). Renal failure among 2111 patients (from 14 studies) was 11.2% (95% CI 8.7-13.9%).

CONCLUSION

Mortality of patients treated with intravenous polymyxin B is similar to the literature-reported mortality of patients treated with intravenous colistin, while nephrotoxicity associated with polymyxin B use is possibly milder compared with colistin use based on literature data. Head-to-head prospective studies would help to clarify the benefit of polymyxin B over colistin. However, a critical evaluation of the existing worldwide literature data supports the need for availability of the intravenous formulation of polymyxin B as a potentially useful option for the treatment of patients with MDR and extensively drug-resistant (XDR) Gram-negative bacterial infections.

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.

Is There a Role for the Therapeutic Drug Monitoring of Colistin? An Overview

Colistin is used as a last-line antibiotic for the treatment of Gram-negative multiresistant bacteria. Due to its high nephrotoxicity, Therapeutic Drug Monitoring (TDM) is recommended for dose adjustment. We aimed to evaluate the available evidence of TDM in patients given colistin to treat Gram-negative infections. In this paper, we offer an overview, using an electronic search of the literature (published up to June 2019, without language restrictions) that compares the clinical outcomes and measurements of colistin TDM. Ultimately, the Therapeutic Drug Monitoring (TDM) of colistin in Plasma could prevent nephrotoxicity risk.

Lipidated Analogs of the LL-37-Derived Peptide Fragment KR12-Structural Analysis, Surface-Active Properties and Antimicrobial Activity

An increasing number of multidrug-resistant pathogens is a serious problem of modern medicine and new antibiotics are highly demanded. In this study, different n-alkyl acids (C2-C14) and aromatic acids (benzoic and trans-cinnamic) were conjugated to the N-terminus of KR12 amide. The effect of this modification on antimicrobial activity (ESKAPE bacteria and biofilm of Staphylococcus aureus) and cytotoxicity (human red blood cells and HaCaT cell line) was examined. The effect of lipophilic modifications on helicity was studied by CD spectroscopy, whereas peptide self-assembly was studied by surface tension measurements and NMR spectroscopy. As shown, conjugation of the KR12-NH2 peptide with C4-C14 fatty acid chains enhanced the antimicrobial activity with an optimum demonstrated by C8-KR12-NH2 (MIC 1-4 μg/mL against ESKAPE strains; MBEC of S. aureus 4-16 μg/mL). Correlation between antimicrobial activity and self-assembly behavior of C14-KR12-NH2 and C8-KR12-NH2 has shown that the former self-assembled into larger aggregated structures, which reduced its antimicrobial activity. In conclusion, N-terminal modification can enhance antimicrobial activity of KR12-NH2; however, at the same time, the cytotoxicity increases. It seems that the selectivity against pathogens over human cells can be achieved through conjugation of peptide N-terminus with appropriate n-alkyl fatty and aromatic acids.

Clinical Use of Polymyxin B

Polymyxin B is another clinically available polymyxin that has re-emerged in clinical practice to treat infections caused by multi-drug (MDR) or extensively-drug-resistant (XDR) Gram-negative bacteria (GNB). Its chemical structure is very similar to the structure of polymyxin E (colistin). However, since the latter is administered as a prodrug, there are major pharmacokinetic differences between both polymyxins that may potentially determine different clinical and microbiological outcomes. Studies addressing clinical or microbiological outcomes in patients treated with polymyxin B for MDR or XDR GNB are reviewed in this chapter.

Mechanisms of Polymyxin-Induced Nephrotoxicity

Polymyxin-induced nephrotoxicity is the major dose-limiting factor and can occur in up to 60% of patients after intravenous administration. This chapter reviews the latest literature on the mechanisms of polymyxin-induced nephrotoxicity and its amelioration. After filtration by glomeruli, polymyxins substantially accumulate in renal proximal tubules via receptor-mediated endocytosis mainly by megalin and PEPT2. It is believed that subsequently, a cascade of interconnected events occur, including the activation of death receptor and mitochondrial apoptotic pathways, mitochondrial damage, endoplasmic reticulum stress, oxidative stress and cell cycle arrest. The current literature shows that oxidative stress plays a key role in polymyxin-induced kidney damage. Use of antioxidants have a potential in the attenuation of polymyxin-induced nephrotoxicity, thereby widening the therapeutic window. Mechanistic findings on polymyxin-induced nephrotoxicity are critical for the optimization of their use in the clinic and the discovery of safer polymyxin-like antibiotics.

Personalizing Polymyxin B Dosing Using an Adaptive Feedback Control Algorithm

Polymyxin B is used as an antibiotic of last resort for patients with multidrug-resistant Gram-negative bacterial infections; however, it carries a significant risk of nephrotoxicity. Herein we present a polymyxin B therapeutic window based on target area under the concentration-time curve (AUC) values and an adaptive feedback control algorithm (algorithm) which allows for the personalization of polymyxin B dosing. The upper bound of this therapeutic window was determined through a pharmacometric meta-analysis of polymyxin B nephrotoxicity data, and the lower bound was derived from murine thigh infection pharmacokinetic (PK)/pharmacodynamic (PD) studies. A previously developed polymyxin B population pharmacokinetic model was used as the backbone for the algorithm. Monte Carlo simulations (MCS) were performed to evaluate the performance of the algorithm using different sparse PK sampling strategies. The results of the nephrotoxicity meta-analysis showed that nephrotoxicity rate was significantly correlated with polymyxin B exposure. Based on this analysis and previously reported murine PK/PD studies, the target AUC_0–24 (AUC from 0 to 24 h) window was determined to be 50 to 100 mg · h/liter. MCS showed that with standard polymyxin B dosing without adaptive feedback control, only 71% of simulated subjects achieved AUC values within this window. Using a single PK sample collected at 24 h and the algorithm, personalized dosing regimens could be computed, which resulted in >95% of simulated subjects achieving AUC_0–24 values within the target window. Target attainment further increased when more samples were used. Our algorithm increases the probability of target attainment by using as few as one pharmacokinetic sample and enables precise, personalized dosing in a vulnerable patient population.

Population Pharmacokinetics of Polymyxin B

Polymyxin B is used as a last treatment resort for multidrug-resistant Gram-negative bacterial infections. The objectives of this study were to examine the population pharmacokinetics of polymyxin B and investigate factor(s) influencing pharmacokinetic variability. Four serial blood samples each were collected from 35 adult patients at steady state. The concentrations of individual polymyxin B components were analyzed using a validated liquid chromatography / tandem mass spectrometry assay and combined to derive total concentrations. A maximum likelihood expectation maximization approach was used to fit the data. Various demographic variables were investigated as potential covariates for clearance and volume of distribution (V_d ) using linear regression analysis. A one-compartment model fit to the data satisfactorily (r²  = 0.96). The best-fit mean ± SD for clearance and V_d were 2.5 ± 1.1 L/h and 34.3 ± 16.4 L, respectively. Creatinine clearance was found to be a statistically significant covariate of clearance, but the magnitude was deemed clinically insignificant.

Methionine Ameliorates Polymyxin-Induced Nephrotoxicity by Attenuating Cellular Oxidative Stress

Polymyxins are a last line of defense against multidrug-resistant Gram-negative pathogens. Recent pharmacological data show that intravenous polymyxins can cause nephrotoxicity in up to 60% of patients, and the plasma concentrations of polymyxins achieved with the currently recommended dosage regimens are suboptimal in a large proportion of patients. Simply increasing the daily dose of polymyxins is not possible due to nephrotoxicity. This study aimed to examine the protective effect of methionine against polymyxin-induced nephrotoxicity. Methionine (400 mg/kg of body weight), polymyxin B (35 mg/kg), a combination of methionine (100 or 400 mg/kg) and polymyxin B, and saline were administered to mice twice daily over 3.5 days. Kidneys were collected immediately at the end of the experiment for histological examination. The effect of methionine on the pharmacokinetics of polymyxin B was investigated in rats. The attenuation of polymyxin B (0.75 mM)-induced mitochondrial superoxide production by methionine (10.0 mM) was examined in rat kidney (NRK-52E) cells. Histological results revealed that the polymyxin-induced nephrotoxicity in mice was ameliorated by methionine in a dose-dependent manner. The methionine doses were well tolerated in the mice and rats, and the pharmacokinetics of polymyxin B in rats were not affected by methionine. In the group receiving polymyxin B-methionine, the total body clearance of polymyxin B was very similar to that in the group receiving polymyxin B alone (3.71 ± 0.57 versus 3.12 ± 1.66 ml/min/kg, P > 0.05). A substantial attenuation of polymyxin-induced mitochondrial superoxide production in NRK-52E cells was observed following pretreatment with methionine. Our results demonstrate that coadministration of methionine significantly ameliorated polymyxin-induced nephrotoxicity and decreased mitochondrial superoxide production in renal tubular cells.

In vitro assessment and multicenter cohort study of comparative nephrotoxicity rates associated with colistimethate versus polymyxin B therapy

Despite concerns of nephrotoxicity, polymyxin antibiotics often remain the only susceptible agents for multidrug-resistant (MDR) Gram-negative bacteria. Colistin has been more commonly used clinically due to a perceived safety benefit. We compared the nephrotoxicity of colistin to polymyxin B. The in vitro cytotoxicity of colistin was compared to polymyxin B in two mammalian renal cell lines. To validate the clinical relevance of the findings, we evaluated adult patients with normal renal function who received a minimum of 72 h of polymyxin therapy in a multicenter study. The primary outcome was the prevalence of nephrotoxicity, as defined by the RIFLE (risk, injury, failure, loss, end-stage kidney disease) criteria. Colistin exhibited an in vitro cytotoxicity profile similar to polymyxin B. A total of 225 patients (121 receiving colistimethate, 104 receiving polymyxin B) were evaluated. Independent risk factors for colistimethate-associated nephrotoxicity included age (odds ratio [OR], 1.04; 95% confidence interval [CI], 1.00 to 1.07; P = 0.03), duration of therapy (OR 1.08; 95% CI, 1.02 to 1.15; P = 0.02), and daily dose by ideal body weight (OR 1.40; 95% CI, 1.05 to 1.88; P = 0.02). In contrast, cystic fibrosis was found to be a protective factor in patients who received colistimethate (OR, 0.03; 95% CI, 0.001 to 0.79; P = 0.04). In a matched analysis based on the risk factors identified (n = 76), the prevalence of nephrotoxicity was higher with colistimethate than with polymyxin B (55.3% versus 21.1%; P = 0.004). Polymyxin B was not found to be more nephrotoxic than colistin and may be the preferred polymyxin for MDR infections. A prospective study comparing the two polymyxins directly is warranted.

Parenteral polymyxins: assessing efficacy and safety in critically ill patients with renal dysfunction

OBJECTIVES

Studies have established the effectiveness and safety of polymyxins in treating multidrug resistant (MDR) pathogens. However, the challenge is whether these nephrotoxic drugs can be administered in compromised renal states. The present study was undertaken to establish their role in such patients. The effectiveness and nephrotoxicity of polymyxins in critically ill-patients harboring MDR Gram-negative bacteria with already compromised renal functions was compared with those with normal renal functions.

MATERIALS AND METHODS

This retrospective cohort study (March 2008-March 2010) was conducted in the intensive care unit of a tertiary care hospital. A total of 48 eligible critically ill-patients receiving polymyxins were enrolled. A comparison was carried out (length of stay in hospital, mortality, renal function) between patients with acute kidney injury (AKI, n = 18; defined by the RIFLE classification) and patients with normal renal function (non-AKI, n = 30).

RESULTS

Patients with baseline AKI had a significantly higher adjusted mortality rate at admission when compared with the non-AKI group. At the end of therapy with polymyxins, 26.66% non-AKI patients developed renal dysfunction while 38.88% of patients in the AKI group had worsening of renal function (P = 0.006). However, there was no significant difference in the length of hospital stay (23.9 ± 13.24 vs. 30.5 ± 22.50; P = 0.406) and overall mortality (44.4% vs. 36.7%; P = 0.76) between two groups.

CONCLUSION

Polymyxins can be administered in AKI patients with favorable results provided used judiciously with strict monitoring of renal functions, dose modification according to creatinine clearance and aggressive fluid management.

Urinary tract infection

The urinary tract is a common source for life-threatening infections. Most patients with sepsis or septic shock from a urinary source have complicated urinary tract infection. This article explains the epidemiology, risk factors, and treatment. Effective management, appropriate collection of microbiology specimens, prompt initiation of antimicrobial therapy, source control, and supportive therapy are described.

Emerging resistance problems and future perspectives in pharmacotherapy for complicated urinary tract infections

INTRODUCTION

Urinary tract infections (UTIs) are among the most common infectious diseases and contribute to high financial burden worldwide. Administration of appropriate antibiotic therapy is the key to achieving good therapeutic outcomes. The authors review the current status of global or regional epidemiology, especially on the antimicrobial resistance and several potential agents against complicated UTIs by multidrug-resistant (MDR) pathogens.

AREAS COVERED

The authors summarized the susceptibility status on several major surveillance programs on uropathogens, focusing on Enterobacteriaceae, Pseudomonas aeruginosa, Acinetobacter baumannii, methicillin-resistant Staphylococcus aureus, and vancomycin-resistant enterococci. Besides, the current perspectives of several potential antimicrobials against MDR uropathogens available for UTIs were also reviewed.

EXPERT OPINION

High resistance to broad-spectrum antibiotics, especially to extended-spectrum β-lactams, carbapenems, and fluoroquinolones among uropathogens emerges as a critical problem in many countries. Appropriate antimicrobial stewardship and continuous surveillance are necessary to monitor the trends of susceptibility for main pathogens. For these MDR uropathogens, polymyxin, fosfomycin, tigecycline, nitrofurantoin, linezolid, and daptomycin might be potential treatments for patients with uncomplicated and complicated UTIs in some countries, although they might not be approved by their regulation. However, more clinical evidence and more extensive meta-analyses are needed to evaluate and confirm the effectiveness of their usage in countries with a high prevalence of multidrug resistance.

Risk factors for treatment failure of polymyxin B monotherapy for carbapenem-resistant Klebsiella pneumoniae infections

Polymyxins are reserved for salvage therapy of infections caused by carbapenem-resistant Klebsiella pneumoniae (CRKP). Though synergy has been demonstrated for the combination of polymyxins with carbapenems or tigecycline, in vitro synergy tests are nonstandardized, and the clinical effect of synergy remains unclear. This study describes outcomes for patients with CRKP infections who were treated with polymyxin B monotherapy. We retrospectively reviewed the medical records of patients with CRKP infections who received polymyxin B monotherapy from 2007 to 2011. Clinical, microbiology, and antimicrobial treatment data were collected. Risk factors for treatment failure were identified by logistic regression. Forty patients were included in the analysis. Twenty-nine of 40 (73%) patients achieved clinical cure as defined by clinician-documented improvement in signs and symptoms of infections, and 17/32 (53%) patients with follow-up culture data achieved microbiological cure. End-of-treatment mortality was 10%, and 30-day mortality was 28%. In a multivariate analysis, baseline renal insufficiency was associated with a 6.0-fold increase in clinical failure after adjusting for septic shock (odds ratio [OR] = 6.0; 95% confidence interval [CI] = 1.22 to 29.59). Breakthrough infections with organisms intrinsically resistant to polymyxins occurred in 3 patients during the treatment. Eighteen of 40 (45%) patients developed a new CRKP infection a median of 23 days after initial polymyxin B treatment, and 3 of these 18 infections were polymyxin resistant. The clinical cure rate achieved in this retrospective study was 73% of patients with CRKP infections treated with polymyxin B monotherapy. Baseline renal insufficiency was a risk factor for treatment failure after adjusting for septic shock. Breakthrough infections with organisms intrinsically resistant to polymyxin B and development of resistance to polymyxin B in subsequent CRKP isolates are of concern.

Polymyxin B Induces Apoptosis in Kidney Proximal Tubular Cells

The nephrotoxicity of polymyxins is a major dose-limiting factor for treatment of infections caused by multidrug-resistant Gram-negative pathogens. The mechanism(s) of polymyxin-induced nephrotoxicity is not clear. This study aimed to investigate polymyxin B-induced apoptosis in kidney proximal tubular cells. Polymyxin B-induced apoptosis in NRK-52E cells was examined by caspase activation, DNA breakage, and translocation of membrane phosphatidylserine using Red-VAD-FMK [Val-Ala-Asp(O-Me) fluoromethyl ketone] staining, a terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) assay, and double staining with annexin V-propidium iodide (PI). The concentration dependence (50% effective concentration [EC₅₀]) and time course for polymyxin B-induced apoptosis were measured in NRK-52E and HK-2 cells by fluorescence-activated cell sorting (FACS) with annexin V and PI. Polymyxin B-induced apoptosis in NRK-52E cells was confirmed by positive labeling from Red-VAD-FMK staining, TUNEL assay, and annexin V-PI double staining. The EC₅₀ (95% confidence interval [CI]) of polymyxin B for the NRK-52E cells was 1.05 (0.91 to 1.22) mM and was 0.35 (0.29 to 0.42) mM for HK-2 cells. At lower concentrations of polymyxin B, minimal apoptosis was observed, followed by a sharp rise in the apoptotic index at higher concentrations in both cell lines. After treatment of NRK-52E cells with 2.0 mM polymyxin B, the percentage of apoptotic cells (mean ± standard deviation [SD]) was 10.9% ± 4.69% at 6 h and reached plateau (>80%) at 24 h, whereas treatment with 0.5 mM polymyxin B for 24 h led to 93.6% ± 5.57% of HK-2 cells in apoptosis. Understanding the mechanism of polymyxin B-induced apoptosis will provide important information for discovering less nephrotoxic polymyxin-like lipopeptides.

A validated ultra-performance liquid chromatography-tandem mass spectrometry method for the quantification of polymyxin B in mouse serum and epithelial lining fluid: application to pharmacokinetic studies

OBJECTIVES

A rapid, sensitive and robust ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed for the quantification of four major polymyxin B components (polymyxin B1, polymyxin B2, polymyxin B3 and isoleucine-polymyxin B1) in serum and epithelial lining fluid (ELF) samples.

METHODS

A Waters Acquity UPLC HSS C18 column was used with 0.1% formic acid in water/acetonitrile as mobile phases. Analysis was performed in a positive ionization mode with multiple-reactions monitoring scan type. Five percent trichloroacetic acid was used to precipitate proteins in biological samples and to increase the sensitivity of detection.

RESULTS

Our results showed a linear concentration range of 0.0065-3.2 mg/L for all the major polymyxin B components in both serum and ELF, respectively; the interday variation was <10% and the accuracy was 88%-115%. The validated method was used to characterize the pharmacokinetics (serum and ELF) of polymyxin B in mice.

CONCLUSIONS

This is the first report, to date, examining the individual pharmacokinetics of various polymyxin B components in mice. Our results revealed no considerable differences in clearances among the components. The limited exposure of polymyxin B in ELF observed was consistent with the less favourable efficacy of polymyxin B reported for the treatment of pulmonary infections. This method can be used to further examine the pharmacokinetics of polymyxin B in a variety of clinical and experimental settings.

Novel polymyxin derivatives are less cytotoxic than polymyxin B to renal proximal tubular cells

The emergence of very multiresistant Gram-negative bacterial strains has reinstated polymyxins (polymyxin B, colistin), pentacationic lipopeptides, in the therapy, in spite of their nephrotoxicity. Extensive tubular reabsorption concentrates polymyxin in proximal tubular cells. The novel polymyxin derivatives NAB739, NAB7061 and NAB741 have their cyclic part identical to that of polymyxin B, but their side chain consists of uncharged octanoyl-threonyl-d-serinyl, octanoyl-threonyl-aminobutyryl, and acetyl-threonyl-D-serinyl respectively. In this study, we compared the toxicities of NAB739, NAB7061 and NAB741 with that of polymyxin B by using the porcine renal proximal tubular cell line LLC-PK1 electroporated or incubated with the selected compound. Both the ability to cause cell necrosis (quantified as the leakage of lactate dehydrogenase) and the ability to cause apoptosis (as quantified by counting apoptotic nuclei) were assessed. In electroporated cells, polymyxin B induced total (>85%) necrosis of the cells at 0.016 mM, whereas an approx. 8-fold concentration of NAB739 and NAB7961 and an approx. 32-fold concentration of NAB741 was required for the same effect. In cells treated without electroporation (incubated), polymyxin B elicited a marked degree (approx. 50%) of necrosis at 0.5mM, whereas the NAB compounds were inert even at 1mM. Neither polymyxin B nor the NAB compounds induced apoptosis.

Incidence and predictors of acute kidney injury associated with intravenous polymyxin B therapy

BACKGROUND

Increases in multidrug-resistance among gram-negative organisms have necessitated the use of polymyxins. To date, the incidence of acute kidney injury (AKI) associated with polymyxin B has not been evaluated using RIFLE criteria.

METHODS

Adult patients who received polymyxin B were retrospectively evaluated to determine the incidence of AKI during polymyxin B therapy using RIFLE criteria. Predictors of AKI were identified by comparing characteristics of patients with and without AKI.

RESULTS

A total of 73 patients were included. The incidence of AKI was 60%. Ten (14%) patients discontinued therapy due to nephrotoxicity. Median duration of polymyxin B was 11 days with a median cumulative dose of 18 mg/kg. Concomitant nephrotoxins were received in 69 (95%). Patients with AKI had a higher median cumulative dose (1578 mg vs. 800 mg; p = 0.02), a higher body mass index (BMI) (27.2 vs. 24.5 kg/m(2); p = 0.03), and were more likely to receive vancomycin (82% vs. 55%; p = 0.03) compared to those without AKI. After controlling for polymyxin B duration, independent predictors of AKI were higher BMI and concomitant vancomycin.

CONCLUSIONS

The incidence of AKI during polymyxin B therapy was 60%. Further studies are needed to define dosing parameters that maximize efficacy and minimize nephrotoxicity.

Comparative effectiveness of aminoglycosides, polymyxin B, and tigecycline for clearance of carbapenem-resistant Klebsiella pneumoniae from urine

Carbapenem-resistant Klebsiella pneumoniae (CRKP) is an increasingly common cause of health care-associated urinary tract infections. Antimicrobials with in vitro activity against CRKP are typically limited to polymyxins, tigecycline, and often, aminoglycosides. We conducted a retrospective cohort study of cases of CRKP bacteriuria at New York-Presbyterian Hospital from January 2005 through June 2010 to compare microbiologic clearance rates based on the use of polymyxin B, tigecycline, or an aminoglycoside. We constructed three active antimicrobial cohorts based on the active agent used and an untreated cohort of cases that did not receive antimicrobial therapy with Gram-negative activity. Microbiologic clearance was defined as having a follow-up urine culture that did not yield CRKP. Cases without an appropriate follow-up culture or that received multiple active agents or less than 3 days of the active agent were excluded. Eighty-seven cases were included in the active antimicrobial cohorts, and 69 were included in the untreated cohort. The microbiologic clearance rate was 88% in the aminoglycoside cohort (n = 41), compared to 64% in the polymyxin B (P = 0.02; n = 25), 43% in the tigecycline (P < 0.001; n = 21), and 36% in the untreated (P < 0.001; n = 69) cohorts. Using multivariate analysis, the odds of clearance were lower for the polymyxin B (odds ratio [OR], 0.10; P = 0.003), tigecycline (OR, 0.08; P = 0.001), and untreated (OR, 0.14; P = 0.003) cohorts than for the aminoglycoside cohort. Treatment with an aminoglycoside, when active in vitro, was associated with a significantly higher rate of microbiologic clearance of CRKP bacteriuria than treatment with either polymyxin B or tigecycline.

Polymyxins and their novel derivatives

The emerging very multiresistant Gram-negative bacteria cause remarkable therapeutic challenges. There are no novel classes of agents in clinical development for the treatment of Gram-negative infections. Polymyxins (polymyxin B and colistin) were abandoned in the seventies but are now back in the therapy as the last resort. Their nephrotoxicity may complicate the therapy or even necessitate its discontinuation. Less toxic polymyxin derivatives would be highly welcome. Novel derivatives lack in strategic positions two of the five cationic charges of polymyxins, differ from polymyxins in their renal handling and affinity to kidney brush-border membrane, and are in preclinical studies. Less characterized other recent derivatives, also reviewed here, have increased the collective knowledge on the structure-function relationships in polymyxins. Acquired resistance to polymyxins has been encountered. However, the resistance mechanism compromises the function of the bacterial outer membrane as a permeability barrier to other noxious agents.

Gram-negative bloodstream infections

Gram-negative bloodstream infection (BSI) is both dangerous and challenging. The incidence of Gram-negative BSI rises with age in both men and women, but there are still some gender differences in terms of aetiology and acquisition. Clinical elements such as organ dysfunction are helpful in determining prognosis. During the last few years we have observed dramatic increases in resistance among Gram-negative organisms, including those causing bloodstream infections. Gram-negative pathogens producing extended-spectrum beta-lactamases are now common, and are associated with high rates of inadequate empirical treatment and mortality. In addition, carbapenem resistance is increasing, leaving clinicians with limited therapeutic options. Better knowledge of local epidemiology can help to optimize therapies. The use of cefepime has been questioned based on a recent meta-analysis showing increased mortality in patients treated with the drug. However, an analysis performed by the US Food and Drug Administration has not confirmed these results. Unfortunately, antimicrobial development has not kept pace with resistance, particularly for Gram-negative pathogens. We need therefore to better utilize current antibiotics and undertake rigorous infection control measures to prevent these life-threatening infections.

Prevalence and risk factors for acute kidney injury associated with parenteral polymyxin B use

BACKGROUND

The main adverse effect of polymyxin B is nephrotoxicity. There are few data on polymyxin-associated renal injury.

OBJECTIVE

To assess the prevalence of and risk factors for acute kidney injury (AKI) in patients treated with polymyxin B.

METHODS

The studied population included 114 patients who received at least 3 consecutive days of intravenous polymyxin B and had baseline serum creatinine (SCr) and at least one further SCr measurement during treatment. AKI was defined as an SCr increase to 1.8 mg/dL or greater in patients with baseline SCr less than 1.5 mg/dL, or an increase greater than or equal to 50% in baseline SCr when it was already greater than or equal to 1.5 mg/dL, or need for dialysis.

RESULTS

AKI developed in 22% of the patients. They were older, had a higher baseline SCr, had a higher frequency of baseline SCr greater than or equal to 1.5 mg/dL, used other nephrotoxic drugs and furosemide more often, and required vasoactive drugs and mechanical ventilation more frequently. Progression to renal failure was significantly more probable when the bacteria were isolated in the abdomen, catheter, or blood. AKI patients had a higher mortality rate (92% vs 53%; p < 0.001). Logistic regression identified abnormal baseline SCr (odds ratio [OR] 3.51); need for vasoactive drugs (OR 3.03); and abdomen, blood, or catheter as the infection site (OR 3.82) as independent risk factors for AKI.

CONCLUSIONS

Patients who developed AKI had a strikingly elevated mortality rate. Polymyxin B should be used with extreme caution in patients who have an abnormal baseline SCr; use vasoactive drugs; or have abdomen, blood, or catheter as the infection site.