Battle of polymyxin induced nephrotoxicity: Polymyxin B versus colistin

Corynoxeine Supplementation Ameliorates Colistin-Induced Kidney Oxidative Stress and Inflammation in Mice

This study investigated the protective effects of corynoxeine, a natural alkaline compound, on colistin-caused nephrotoxicity using a murine model. Forty mice were divided randomly into control, corynoxeine-only (20 mg/kg/day, intraperitoneal injection), colistin-only (20 mg/kg/day, intraperitoneal injection), and colistin (20 mg/kg/day) + corynoxeine (5 and 20 mg/kg/day) groups (8 mice in each group). All treatments were maintained for seven consecutive days. Results showed that colistin treatment at 20 mg/kg/day for seven days significantly increased serum urea nitrogen and creatinine levels and induced the loss and degeneration of renal tubular epithelial cells, which were markedly ameliorated by corynoxeine co-treatment at 5 or 20 mg/kg/day. Corynoxeine supplementation also markedly attenuated colistin-induced increases in malondialdehyde levels and decreases in reduced glutathione levels and superoxide dismutase and catalase activities in the kidneys. Furthermore, corynoxeine supplementation significantly decreased the expression of transforming growth factor β (TGF-β) and nicotinamide adenine dinucleotide phosphate hydrogen oxidase 4 (NOX4) proteins and nuclear factor kappa B (NF-κB), interleukin-1beta (IL-1β), IL-6, and tumor necrosis factor-α mRNAs, while it significantly increased the expression of erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) proteins in the kidneys. In conclusion, these results reveal that corynoxeine can protect against colistin-induced nephrotoxicity in mice by inhibiting oxidative stress and inflammation, which may partly be attributed to its ability on the activation of the Nrf2/HO-1 pathway and the inhibition of the TGF-β/NOX4 and NF-κB pathways.

Mefloquine reduces the bacterial membrane fluidity of Acinetobacter baumannii and distorts the bacterial membrane when combined with polymyxin B

Acinetobacter baumannii is a high-priority organism for the development of new antibacterial treatments. We found that the antimalarial medication mefloquine (MFQ) permeabilized the bacterial cell membrane of A. baumannii, decreased membrane fluidity, and caused physical injury to the membrane. MFQ also maintained activity across different pH conditions (pH range: 5-8). Structure-activity relationship analysis using MFQ analogs demonstrated that piperidin-2-yl methanol is required for antibacterial activity. Scanning and transmission electron microscopy demonstrated the compromised morphological and membrane integrity in MFQ-treated cells. MFQ synergized with the membrane permeabilizers polymyxin B and colistin and the MFQ + polymyxin B combination killed bacterial cells more effectively than either treatment alone. MFQ + polymyxin B was effective against other gram-negative bacteria including Escherichia coli, Burkholderia pseudomallei, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Bodipy-cadaverine displacement assays confirmed the active interaction of MFQ with other membrane lipid components, such as lipopolysaccharide, lipid A, lipoteichoic acids, and fatty acids. In all-atom molecular dynamics simulations, lipid interactions facilitated the permeation of MFQ into the simulated Gram-negative membrane. Additionally, positively charged nitrogen in the piperidine group of MFQ seems to enhance interactions with the negatively charged components of the bacterial membrane. MFQ + polymyxin B caused significantly greater curvature in the simulated membrane, indicating greater damage than standalone drug treatment. Finally, in vivo assays showed that MFQ + polymyxin B rescued Galleria mellonella larvae infected with A. baumannii. In conclusion, membrane-active agents such as MFQ may warrant further investigation as a potential components of gram-negative infection treatment, particularly in combination with polymyxin B.

IMPORTANCE

Antimicrobial resistance is a threat globally, and new treatments are urgently needed to combat the rise of multidrug-resistant bacteria. However, the development of anti-infectives has declined over the last two decades due to regulatory, financial and long-term requirement related challenges. In this study, we examined the membrane interactions of the antiparasitic agent mefloquine (MFQ) in combination with polymyxin B, using both in vitro and in silico approaches to evaluate their potential efficacy against gram-negative bacterial infections. We investigated the interaction of MFQ with lipid bilayers to understand the mechanism through which antibacterial activity is exerted. The piperidine moiety of MFQ plays a critical role in its interaction with the lipid bilayer and facilitates membrane permeabilization. In contrast, the membrane permeabilizer polymyxin B is associated with significant neurotoxicity and nephrotoxicity. Our findings highlight the potential of membrane-acting compounds, such as MFQ, to enhance combinatorial activity while mitigating polymyxin B-associated toxicity.

Study on the invitro synergistic susceptibility and biofilm inhibition mechanism of ceftazidime-avibactam combined with aztreonam against carbapenem-resistant Klebsiella pneumoniae

Objective

This study aims to investigate the synergistic effects and biofilm inhibition mechanisms of ceftazidime-avibactam (CZA) combined with aztreonam (ATM) against carbapenem-resistant Klebsiella pneumonia (CRKP) commonly found in the local clinical setting, providing new insights for clinical anti-infective strategies.

Methods

We selected a total of 150 non-duplicate clinical isolates of CRKP from multiple hospitals in Ningbo. Common carbapenemase genes were detected using PCR. Broth microdilution and time-kill assays were used to evaluate the in vitro synergistic effects of CZA and ATM, both individually and in combination, on CRKP isolates with different enzyme types, and the fractional inhibitory concentration index (FICI) was calculated. The crystal violet staining method and bacterial cell permeability assay were employed to assess the impact of CZA, ATM, and their combination on the cell structure and biofilm formation capacity of CRKP. Real-time quantitative PCR (qRT-PCR) was used to measure the expression levels of biofilm-related genes (Luxs, mrkA, wbbM, pgaA, and wzm) in CRKP under treatment with CZA, ATM, or their combination.

Results

The comparison of synergistic indices for different enzyme-type CRKP strains with CZA and ATM combination therapy showed a statistically significant difference (p < 0.01). The time-kill assay indicated that the time-kill curves for strains carrying blaKPC-2 and blaNDM-1 resistance genes were similar between the monotherapy and combination therapy groups, while the CZA + ATM combination therapy group showed a significant decrease in bacterial concentration after 4-8 h of cultivation compared to the CZA and ATM monotherapy groups. The crystal violet staining and bacterial cell permeability assays demonstrated that the CZA + ATM combination significantly reduced biofilm formation and increased cellular structure disruption in CRKP. The qRT-PCR results showed that CZA combined with ATM notably decreased the expression levels of biofilm-related genes Luxs, mrkA, wbbM, pgaA, and wzm in CRKP.

Conclusion

The combination of ATM and CZA shows a strong synergistic antibacterial effect against CRKP strains with various enzyme types, with particularly notable synergy in strains carrying the blaKPC-2 resistance gene. Additionally, this combination significantly disrupts the cellular structure of CRKP and inhibits biofilm formation.

Polymyxin B in The Treatment of Infections Caused by Multidrug-Resistant Gram-Negative Bacteria in Children: A Retrospective Case Series and A Literature Review

Background

Multidrug-resistant Gram-negative bacteria (MRGN) pose a significant threat and require priority attention. Polymyxin B (PMB) retains substantial activity against MRGN and makes it potentially the last resort therapy for MRGN infections in children. To assess the effectiveness and safety of PMB in treating MRGN infections in Chinese children.

Methods

Paediatric patients aged 0-18 years who were treated with PMB for MRGN infections were enrolled in the study. These cases were then compared with those identified in a literature review. In logistic regression, three independent variables were used for analyzing clinical effectiveness, and two for nephrotoxicity.

Results

A cohort of 54 children was included in study and 24 eligible literature of 259 children were included in literature review. Out of the 54 patients, 53.7% showed favorable clinical responses, while 13.0% died during their hospitalization, of which 3.7% died within 30 days after receiving PMB. AKI was observed in 25.9% patients with 11.1% risk stage, 7.4% injury stage and 7.4% failure stage. The PMB co-administration with carbapenems was associated with significantly higher effectiveness (odds rate [OR] = 3.16, 95% confidence interval [CI]: 1.02-9.86, P = 0.05) and co-administration with potent diuretic (furosemide) may increase the risk of AKI (OR = 4.91, 95% CI: 0.96-24.98, P = 0.05).

Conclusion

PMB has advantages in treating MRGN infections in paediatric patients, showing favorable clinical responses and pathogen clearance. AKI is a notable safety concern. The small sample size might hinder reliable identification of factors affecting clinical effectiveness and adverse effects.

Size-controlled antimicrobial peptide drug delivery vehicles through complex coacervation

Due to the escalating threat of the pathogens' capability of quick adaptation to antibiotics, finding new alternatives is crucial. Although antimicrobial peptides (AMPs) are highly potent and effective, their therapeutic use is limited' as they are prone to enzymatic degradation, are cytotoxic and have low retention. To overcome these challenges, we investigate the complexation of the cationic AMP colistin with diblock copolymers poly(ethylene oxide)-b-poly(methacrylic acid) (PEO-b-PMAA) forming colistin-complex coacervate core micelles (colistin-C3Ms). We present long-term stable kinetically controlled colistin-C3Ms that can be prepared from several block lengths of PEO-b-PMAA polymers, where the polymerisation degree governs the overall micellar size. To achieve precise control over size and polydispersity, which are crucial for drug delivery applications, we investigate the hybridisation of PEO-b-PMAA polymers with varying chain lengths or PMAA homopolymers in ternary complex coacervation systems with colistin. This results in size-tunable colistin-C3Ms, ranging, depending on the mixing ratios, from micellar sizes of 26 nm to 100 nm. With size tunability at rather narrow size distributions and high stability, ternary colistin-C3Ms offer potential advancements in C3M drug delivery, paving the way for more effective and targeted treatments for bacterial infections in precision medicine.

Mefloquine reduces the bacterial membrane fluidity of Acinetobacter baumannii and distorts the bacterial membrane when combined with polymyxin B

Acinetobacter baumannii is a high-priority organism for the development of new antibacterial treatments. We found that the antimalarial medication mefloquine (MFQ) permeabilized the bacterial cell membrane of A. baumannii , decreased membrane fluidity, and caused physical injury to the membrane. MFQ also maintained activity across different pH conditions (PH range 5-8). Structure-activity relationship analysis using MFQ analogs demonstrated that piperidin-2-yl methanol is required for antibacterial activity. Scanning and transmission electron microscopy demonstrated the compromised morphological and membrane integrity in MFQ treated cells. MFQ synergized with the membrane permeabilizers polymyxin B and colistin and the MFQ+polymyxin B combination killed bacterial cells more effectively than either treatment alone. MFQ+polymyxin B was effective against other Gram-negative bacteria including Escherisia coli, Burkholderia pseudomallei, Klebsiella pneumoniae, and Pseudomonas auroginosa . Bodipy-cadaverine displacement assays confirmed the active interaction of MFQ with other membrane lipid components, such as lipopolysaccharide, lipid A, lipoteichoic acids, and fatty acids. In all-atom molecular dynamics simulations, lipid interactions facilitated the permeation of MFQ into the simulated Gram-negative membrane. Additionally, positively charged nitrogen in the piperidine group of MFQ seems to enhance interactions with the negatively charged components of the bacterial membrane. MFQ+polymyxin B caused significantly greater curvature in the simulated membrane, indicating greater damage than standalone drug treatment. Finally, in vivo assays showed that MFQ+polymyxin B rescued Galleria mellonella larvae infected with A. baumannii . In conclusion, membrane-active agents such as MFQ may warrant further investigation as potential component of Gram-negative infection treatment, particularly in combination with polymyxin B.

Importance

Antimicrobial resistance is a threat globally, and new treatments are urgently needed to combat the rise of multidrug-resistant bacteria. However, the development of anti-infectives has declined over the last two decades due to regulatory, financial and long-term requirement related challenges. In this study, we examined the membrane interactions of the antiparasitic agent mefloquine in combination with polymyxin B, using both in vitro and in silico approaches to evaluate their potential efficacy against Gram-negative bacterial infections. We investigated the interaction of MFQ with lipid bilayers to understand the mechanism through which antibacterial activity is exerted. The piperidine moiety of MFQ plays a critical role in its interaction with the lipid bilayer and facilitates membrane permeabilization. In contrast, the membrane permeabilizer polymyxin B is associated with significant neurotoxicity and nephrotoxicity. Our findings highlight the potential of membrane-acting compounds, such as MFQ, to enhance combinatorial activity while mitigating polymyxin B-associated toxicity.

LTX-315 is a novel broad-spectrum antimicrobial peptide against clinical multidrug-resistant bacteria

INTRODUCTION

Infections stemming from multidrug-resistant bacteria present a substantial threat to public health today. Discovering or synthesizing novel compounds is crucial to alleviate this pressing situation.

OBJECTIVE

The main purpose of this study is to verify the antibacterial activity of LTX-315 and explore its primary action mode.

METHODS

Through antibacterial phenotype assay screening, we obtained a potent compound named LTX-315 from diverse drug libraries, 10,926 compounds in total. Then, the bactericidal effect and its action mode were explored through biochemical and chemistry methods such as atime-killing curve, scanning electronic microscopy, isothermal titration calorimetry analysis, and nuclear magnetic resonance. Finally, the efficacy in vivo of LTX-315 against drug-resistant bacteria was proved through amice infection model.

RESULTS

In this study, LTX-315, an oncolytic peptide, was discovered to effectively eliminate gram-positive and gram-negative pathogens, even for those multidrug-resistant strains. Through strong electrostatic interactions, LTX-315 can bind to the membrane component phosphatidylglycerol (PG) with extremely high affinity (nanomolar level). Strikingly, in contrast to the typical electrostatic interactions of antibacterial peptides, the indole group of LTX-315, situated near the alkyl chain, exhibits significantly enhanced recognition and interaction with PG due to the hydrophobic effect of the alkyl chain. Furthermore, it exerts various impacts on cell membranes, including damaging integrity, increasing permeability, and decreasing membrane fluidity. Additionally, microscopy revealed significant cell disintegration. The influence, in turn, disrupts several physiological activities inside cells, such as increasing the reactive oxygen species level, ultimately leading to cell death. Finally, the efficacy of LTX-315 in vivo against multidrug-resistant and hypervirulent Klebsiella pneumoniae was demonstrated.

CONCLUSION

The unique mechanism of LTX-315 involves high-affinity binding to PG and subsequent membrane disruption, providing a novel approach against multidrug-resistant bacteria compared to conventional antibiotics. As a potential candidate, it shows promise in effectively treating bacterial infections, particularly those caused by drug-resistant bacteria, thereby addressing the escalating challenge of antibiotic resistance worldwide.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Pharmacokinetic study of polymyxin B in healthy subjects and subjects with renal insufficiency

Polymyxin B is a viable option for treating antibiotic-resistant infections; however, current data on its pharmacokinetics, particularly in patients with renal insufficiency, remain inconclusive and necessitates further investigation. To address this gap, we conducted an open-label, single-center, single-dose, parallel-group pharmacokinetic study. Participants received an intravenous dose of 0.75 mg/kg of polymyxin B and were categorized based on their renal function: those with normal function (creatinine clearance [CLcr] ≥ 90 mL/min), mild renal insufficiency (CLcr 60-89 mL/min), and end-stage kidney disease patients on intermittent hemodialysis (IHD) (CLcr < 10 mL/min). The pharmacokinetic parameters assessed included the area under the curve (AUC), maximum concentration (Cmax), clearance rate (CL), volume of distribution (Vz), and half-life (t1/2). Results indicated that subjects with mild renal insufficiency exhibited pharmacokinetic profiles similar to healthy individuals. Nevertheless, in patients undergoing long-term IHD, we observed significant differences: the AUC was 58% higher, Cmax was 29% lower, CL was 42% lower, Vz was 60% larger, and t1/2 was extended by 10 h compared to healthy controls. Secondary outcomes revealed good tolerability of polymyxin B across all groups, with no serious adverse effects related to renal function. In summary, while kidney function may have a slight impact on the pharmacokinetic of polymyxin B, it does not compromise the drug's therapeutic effectiveness.

Intravenous combined with aerosolised polymyxins vs intravenous polymyxins monotherapy for ventilator-associated pneumonia: A systematic review and meta-analysis

Polymyxins were applied via different administration routes to treat ventilator-associated pneumonia (VAP) caused by carbapenem-resistant Gram-negative bacteria (CR-GNB). The potential benefits of aerosolised polymyxins as adjunctive treatment for patients are contradictory. This review assessed the safety and efficacy of intravenous (IV) combined with aerosolised polymyxins vs IV polymyxins monotherapy in patients with VAP caused by CR-GNB. Two reviewers independently evaluated and extracted data from PubMed, Embase, Cochrane library and Web of Science. The primary outcome was all-cause mortality and secondary outcomes included clinical cure rate, clinical improvement rate, microbiological eradication rate and nephrotoxicity. Differences for dichotomous outcomes were expressed as odds ratios (ORs) with 95% confidence intervals (CIs). Eleven eligible studies were included. The results showed that compared with IV polymyxins monotherapy, IV plus aerosolised polymyxins therapy significantly reduced all-cause mortality rate (OR = 0.75, 95% CI 0.57-0.99, P = 0.045) and improved clinical improvement rate (OR = 1.62, 95% CI 1.02-2.60, P = 0.043) and microbial eradication rate (OR = 2.07, 95% CI 1.40-3.05, P = 0.000). However, there were no significant differences in terms of clinical cure rate (OR = 1.59, 95% CI 0.96-2.63, P = 0.072) and nephrotoxicity (OR = 1.14, 95% CI 0.80-1.63, P = 0.467) for IV plus aerosolised polymyxins therapy. Subgroup analysis revealed that the clinical improvement rate was significantly improved in case-control studies. Aerosolised polymyxins may be a useful adjunct to IV polymyxins for patients with CR-GNB VAP.

Action enhancement of antimicrobial peptides by their combination with enzymes hydrolyzing fungal quorum molecules

Recently, the lactonase activity of several enzymes (lactonase AiiA, organophosphate hydrolase (His6-OPH) and New Delhi metallo-β-lactamase (NDM-1)) was revealed in the hydrolysis of lactone-containing fungal Quorum Sensing molecules (FQSM). This study was aimed at the investigation of possible use of these enzymes as components of antifungal combinations with antimicrobial peptides (AMPs) to increase their action efficiency against various fungi. For this, the interaction of various AMPs with AiiA, NDM-1 or His6-OPH, as well as the effect of AMPs on the catalytic characteristics of these enzymes in the hydrolysis of FQSM in enzyme/AMP combinations, were studied using in silico computer modeling methods. Enzymes combinations with 3 AMPs Bacitracin, Colistin and Polymyxin B were selected as the most rational in terms of maintaining the effectiveness of AMP and the catalytic activity of enzymes. The antifungal action of the selected combinations against cells of mycelial fungi and yeast was studied in vitro. It was found that combinations of the enzymes AiiA, His6-OPH and NDM-1 with Bacitracin, Colistin and Polymyxin B provide a significant increase in the action efficiency (up to 5000 times) of both AMPs and enzymes against fungi. The most effective variants were obtained for Polymyxin B in multicomponent combinations with enzymes.

A pilot clinical risk model to predict polymyxin-induced nephrotoxicity: a real-world, retrospective cohort study

OBJECTIVES

Polymyxin-induced nephrotoxicity (PIN) is a major safety concern and challenge in clinical practice, which limits the clinical use of polymyxins. This study aims to investigate the risk factors and to develop a scoring tool for the early prediction of PIN.

METHODS

Data on critically ill patients who received intravenous polymyxin B or colistin sulfate for over 24 h were collected. Logistic regression with the least absolute shrinkage and selection operator (LASSO) was used to identify variables that are associated with outcomes. The eXtreme Gradient Boosting (XGB) classifier algorithm was used to further visualize factors with significant differences. A prediction model for PIN was developed through binary logistic regression analysis and the model was assessed by temporal validation and external validation. Finally, a risk-scoring system was developed based on the prediction model.

RESULTS

Of 508 patients, 161 (31.6%) patients developed PIN. Polymyxin type, loading dose, septic shock, concomitant vasopressors and baseline blood urea nitrogen (BUN) level were identified as significant predictors of PIN. All validation exhibited great discrimination, with the AUC of 0.742 (95% CI: 0.696-0.787) for internal validation, of 0.708 (95% CI: 0.605-0.810) for temporal validation and of 0.874 (95% CI: 0.759-0.989) for external validation, respectively. A simple risk-scoring tool was developed with a total risk score ranging from -3 to 4, corresponding to a risk of PIN from 0.79% to 81.24%.

CONCLUSIONS

This study established a prediction model for PIN. Before using polymyxins, the simple risk-scoring tool can effectively identify patients at risk of developing PIN within a range of 7% to 65%.

Acute kidney injury with intravenous colistin sulfate compared with polymyxin B in critically ill patients: A real-world, retrospective cohort study

BACKGROUND

Polymyxins have re-emerged as a last-resort therapeutic option for infections caused by carbapenem-resistant gram-negative bacteria. Nephrotoxicity induced by polymyxins is a significant limitation of its use in the clinic. Polymyxin B and colistin sulfate are two widely used active formulations of polymyxins. However, there is a lack of studies conducting a comparative assessment of nephrotoxicity between the two formulations. This study aimed to compare the nephrotoxicity of polymyxin B and colistin sulfate in critically ill patients.

METHODS

We conducted a retrospective cohort study among critically ill patients who received intravenous polymyxin B or colistin sulfate for over 48 h from January 2017 to January 2024. The primary outcome was the incidence of acute kidney injury (AKI) associated with polymyxins, and the secondary outcome was 30-day all-cause mortality. Additionally, the risk factors of polymyxins-induced AKI and 30-day all-cause mortality were identified by Cox proportional hazard regression analysis.

RESULTS

A total of 473 patients were included in this study. The overall incidence of AKI was significantly higher in patients who received polymyxin B compared to those who received colistin sulfate in the unmatched cohort (20.8% vs. 9.0%, p = 0.002) and in the propensity score matching cohort (21.1% vs. 7.0%, p = 0.004), respectively. However, there was no significant difference in 30-day all-cause mortality between the two groups. Polymyxin type, septic shock, and concomitant use of vasopressors were identified as independent risk factors for polymyxin-induced AKI.

CONCLUSIONS

The prevalence of AKI was higher among patients who received polymyxin B compared to those treated with colistin sulfate. However, there was no significant difference in 30-day all-cause mortality between the two groups. Further prospective, multicenter studies with larger sample sizes are needed to validate these findings.

Pharmacokinetics and Nephrotoxicity of Polymyxin MRX-8 in Rats: A Novel Agent against Resistant Gram-Negative Bacteria

MRX-8 is a novel polymyxin for carbapenem-resistant Gram-negative infections that has been recently evaluated in Phase I clinical trials. Herein, its pharmacokinetics (PK) and nephrotoxicity in rats are reported for the first time. This study aimed at pre-clinical PK and safety assessments. An LC-MS/MS method was developed to determine concentrations of MRX-8 and its major deacylation metabolite, MRX-8039, in rat plasma. Animals were administered a single dose of MRX-8 (2, 4, 6, and 8 mg/kg) or comparator polymyxin B (PMB) (4 and 8 mg/kg) to compare the kidney injury known for the polymyxin drug class. Nephrotoxicity was evaluated using serum creatinine, blood urea nitrogen (BUN) biomarkers, and renal histopathology. In rats, MRX-8 displayed linear PK within the range of 2-8 mg/kg, with approximately 4% of MRX-8 converted to MRX-8039. MRX-8 induced only mild increases in serum creatinine and BUN levels, with an apparent decrease in nephrotoxicity within 24 h, in contrast to PMB, which exhibited a significant and more persistent toxicity. Additional nephrotoxicity biomarkers (plasma NGAL and urinary NGAL, KIM-1, and TIMP-1) have confirmed attenuated MRX-8 kidney injury. Histopathology has revealed significantly greater cellular/tissue toxicity for PMB as compared to MRX-8 (variances of p = 0.008 and p = 0.048 vs. saline control, respectively). Thus, MRX-8 induces a mild and reversible kidney injury in rats compared to PMB. These data support a continued evaluation of the novel polymyxin in human trials.