Efficacy and safety of low-dose colistin in the treatment for infections caused by multidrug-resistant gram-negative bacteria

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

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

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.

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.

Colistina en el tratamiento de infecciones por pseudomonas aeruginosa y acinetobacter baumannii extensivamente resistentes (XDR) en un hospital de tercer nivel

Objetivo: Describir la respuesta clínica y mortalidad general de Colistina en infecciones por Pseudomonas XDR y Acinetobacter XDR en el Hospital Nacional Arzobispo Loayza in Lima, Peru.Métodos: Estudio observacional, descriptivo y retrospectivo. Se incluyeron los registros de pacientes > 18 años, desde junio del 2014 a junio del 2016, que tuvieron infección por Pseudomonas XDR o Acinetobacter XDR confirmada por cultivo, y que recibieron colistina. Se realizó análisis univariado de las características generales de los pacientes; un análisis bivariado con test de Chi2, t-student o ANOVA según corresponda, y además se describió los factores asociados a mortalidad.Resultados. Se incluyeron 56 registros de pacientes, la mediana de la edad fue 46,5 [31,5 a 63,5]. El 48,2% tuvo un cultivo positivo para Pseudomonas XDR y el 51,8% para Acinetobacter XDR. La respuesta clínica favorable fue 85,7% a los 15 días y de 78,6% a los 30 días. La mortalidad intrahospitalaria a los 30 días fue 21,4%, la mortalidad en UCI fue de 30,8% y la nefrotoxicidad fue de 5,4%.Conclusiones. Colistina combinada con otro antimicrobiano tuvo una respuesta clínica favorable en infección por Pseudomonas XDR o Acinetobacter XDR.

Colistin for the treatment of urinary tract infections caused by extremely drug-resistant Pseudomonas aeruginosa: Dose is critical

OBJECTIVES

Optimal dosage regimens of colistin for the treatment of urinary tract infections (UTI) are unknown. Colistimethate sodium (CMS), the inactive prodrug of colistin, is mainly excreted in urine and converts to colistin after filtration by glomeruli, suggesting that concentrations of colistin in urine could be much higher than in plasma. Therefore, there is a need to optimize dosage regimens of intravenous CMS for UTI. The aim of this study was to examine the relationship between AUC/MIC of formed colistin and clinical outcomes in patients with UTI caused by extremely drug resistant (XDR) Pseudomonas aeruginosa.

METHODS

This prospective, observational cohort study involved patients with UTI caused by XDR P. aeruginosa. Clinical cure, bacteriological clearance and acute kidney injury (AKI) were analyzed. Steady-state colistin plasma concentrations (C_ss) were measured using HPLC. Based on the PK/PD of colistin in neutropenic mouse thigh infection models with P. aeruginosa, the optimal AUC/MIC should be ≥60 mg·h/L. According to the pharmacokinetics (PK) in critically-ill patients, the C_ss target of formed colistin in plasma was 2.5 mg/L.

RESULTS

Thirty-three patients were included (24 lower UTI and 9 pyelonephritis). The MIC₅₀ and MIC₉₀ values for colistin were 0.5 and 2 mg/L respectively. Nineteen patients (57.6%) received colistin monotherapy (84.2% lower UTI and 15.8% pyelonephritis). Of these, clinical cure was achieved in 89.5% of cases. Among patients with clinical cure and monotherapy, only 5 (29.4%) attained an optimal plasma AUC/MIC and only 1 (5.9%) the therapeutic level of formed colistin (2.5 mg/L). However, 10 (58.8%) patients showed colistin plasma concentrations above the MIC of the isolated P. aeruginosa. Microbiological eradication was achieved in 76.9% of patients. AKI at the end of treatment was present in 29.4% of patients.

CONCLUSIONS

The currently recommended dosage regimens of CMS showed high efficacy for the treatment of lower complicated UTI caused by XDR P. aeruginosa in non-critically ill patients and in the case of low MIC values, but also a considerable nephrotoxicity rate. Our data suggest that the use of lower CMS doses for lower UTI should be investigated in future studies to minimize the unnecessary nephrotoxicity.

Use of Colistin in Critically Ill Patients

Due to lack of better therapeutic options, colistin use for extensively drug-resistant Gram-negative organisms was revived in the past two decades, including in patients in intensive-care units (ICU). There are multiple knowledge gaps pertaining to the clinical use and utility of colistin in critically-ill patients, but due to lack of options, it is used in these high risk patients. In this chapter, we critically review the various topics pertaining to colistin use in critically-ill patients, while highlighting the (lack of) controlled evidence supporting common current practices pertaining to colistin use by clinicians.

Cost-effectiveness analysis of low versus high dose colistin in the treatment of multi-drug resistant pneumonia in Saudi Arabia

Background Gram negative pathogens are increasingly resistant to commonly used first line antibiotics and colistin is in most cases the only medicine available. There is very limited information available comparing the effectiveness and costs of low versus high dose colistin with studies showing efficacy with both doses and with variable levels of adverse effects. The absence of a definite dosing strategy makes a model to compare low dose and high dose colistin invaluable in making decisions regarding the appropriate use of colistin. Objective This study was designed to evaluate the cost effectiveness of low versus high dose colistin in the treatment of Pneumonia caused by colistin-only sensitive gram negative bacteria from the perspective of a tertiary care hospital in Saudi Arabia. Setting 300-bed tertiary care hospital in Saudi Arabia. Method A retrospective review was conducted to compare the costs and outcomes of treatment of pneumonia with low versus high dose colistin. The model followed an average patient from initiation of treatment until clinical cure or failure. Main outcome measures The main outcomes were cure, nephrotoxicity, total direct costs per episode, cost per additional cure and cost per nephrotoxicity avoided. Results There was no significant difference between high and low dose colistin with regards to clinical cure (30% vs. 21%; p = 0.292). Significantly more patients experienced nephrotoxicity with high versus low dose colistin (30% vs. 8%; p = 0.004). With low dose colistin the incremental costs per nephrotoxicity avoided was SAR-3056.28. One-way sensitivity analyses did not change the overall results. Conclusion Low dose was not inferior to high dose colistin in terms of clinical cure and had a lower incidence of nephrotoxicity resulting in significant cost avoidance.

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.

Staphylococcus aureus and MRSA Growth and Biofilm Formation after Treatment with Antibiotics and SeNPs

Methicillin-resistant Staphylococcus aureus (MRSA) is a dangerous pathogen resistant to β-lactam antibiotics. Due to its resistance, it is difficult to manage the infections caused by this strain. We examined this issue in terms of observation of the growth properties and ability to form biofilms in sensitive S. aureus and MRSA after the application of antibiotics (ATBs)-ampicillin, oxacillin and penicillin-and complexes of selenium nanoparticles (SeNPs) with these ATBs. The results suggest the strong inhibition effect of SeNPs in complexes with conventional ATBs. Using the impedance method, a higher disruption of biofilms was observed after the application of ATB complexes with SeNPs compared to the group exposed to ATBs without SeNPs. The biofilm formation was intensely inhibited (up to 99%±7% for S. aureus and up to 94%±4% for MRSA) after application of SeNPs in comparison with bacteria without antibacterial compounds whereas ATBs without SeNPs inhibited S. aureus up to 79%±5% and MRSA up to 16%±2% only. The obtained results provide a basis for the use of SeNPs as a tool for the treatment of bacterial infections, which can be complicated because of increasing resistance of bacteria to conventional ATB drugs.

Risk Factors for Colistin-Associated Acute Kidney Injury: A Multicenter Study from Turkey

The aim of this study was to investigate the incidence of acute kidney injury (AKI) and risk factors due to colistin use in patients infected with multidrug-resistant pathogens. This multicenter, retrospective, observational study was conducted in Turkey, at 5 different research and university hospitals. Cox regression analyses were performed, to determine independent predictors of AKI. From April 2012 to July 2014, a total of 216 patients aged between 18-94 years, treated with colistimethate sodium (CMS) were included in the study. The mean age of the patients was 60.3 ± 20.1 years. The overall incidence of AKI was 34.3% (74/216) at any time during treatment. Concomitant use of loop diuretics, baseline creatinine level, and CMS dosage were independently associated with AKI. According to our results, patients with higher baseline creatinine levels, or patients who had to use concomitant loop diuretics may need to be monitored more closely, and dose adjustment should be done promptly. More comprehensive studies are, however, still needed to evaluate the efficacy of low-dose colistin since higher doses tend to increase the risk of AKI.

Evaluation of the Etest method for detecting colistin susceptibility of multidrug-resistant Gram-negative isolates in Vietnam

The minimum inhibitory concentrations (MICs) of colistin for 241 multidrug-resistant (MDR) Gram-negative pathogens were determined by the Etest and by the broth microdilution method (BMD). The two methods showed essential agreements of 76% (77/102) for Acinetobacter baumannii, 90% (36/40) for Pseudomonas aeruginosa and 84% (83/99) for Enterobacteriaceae isolates, with categorical agreements of 100%, 98%, and 100%, respectively. Of the 241 isolates, none showed a very major error and one (0.4%) showed a major error. MICs ranged from 0.125 to 0.5 μg/ml for all A. baumannii and most Enterobacteriaceae isolates, and from 1 to 2 μg/ml for most P. aeruginosa isolates. Of the 40 P. aeruginosa isolates, 27 (68%) showed higher colistin MICs by the Etest than by the BMD. In contrast, 77% (78/102) of the A. baumannii and 57% (56/99) of the Enterobacteriaceae isolates showed lower colistin MICs by the Etest than by the BMD. The Etest is a reliable and easy-to-use method to measure colistin MICs of MDR Gram-negative pathogens in clinical laboratories and can be used following validation by microdilution methods.