Polymyxin B and Doxycycline Use in Patients with Multidrug-Resistant Acinetobacter baumannii Infections in the Intensive Care Unit

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.

Doxycycline for Multidrug-Resistant Gram-Negative Bacterial Infection Treatment: A Scoping Review

Introduction

Multidrug-resistant bacterial infections limit available therapeutic options. Doxycycline is an old antibiotic from the tetracycline class that exhibits a wide antibacterial action, including Gram-negative bacteria (GNB), and could be an alternative for the treatment of multidrug-resistant (MDR) Enterobacteriaceae. The study aimed to systematically identify, evaluate, and summarize the results of studies related to outcomes of treatments for MDR-GNB infections in patients treated with doxycycline.

Methods

This review was conducted in four databases during weeks 41-52 of 2022: PubMed, Medline, Scopus, and Web of Science, from the earliest year available on each database to December 2022. Preferred Reporting Items for Systematic Review and Meta-Analysis guidelines were followed in conducting this study, and PICO was used for the research question of this review.

Results

This scoping review found 8 retrospective studies that included 59 patients. Of these, 69% were treated for ventilator-associated pneumonia (VAP), 27% for urinary tract infections, 2% for bloodstream infections, and 2% for wound infections, both of which were associated with VAP. The usual dosage of doxycycline was 100 mg intravenously or orally. Clinical and microbiologic improvements were achieved in 81.3% and 87% of all patients, respectively. The mortality rate was 17.3% and was exclusively due to VAP.

Conclusions

Doxycycline showed promising results in this review; however, randomized clinical trials or prospective cohorts are recommended to demonstrate the efficacy of doxycycline in the treatment of MDR infections with GNB.

Rejuvenating the Activity of Usual Antibiotics on Resistant Gram-Negative Bacteria: Recent Issues and Perspectives

Antibiotic resistance continues to evolve and spread beyond all boundaries, resulting in an increase in morbidity and mortality for non-curable infectious diseases. Due to the failure of conventional antimicrobial therapy and the lack of introduction of a novel class of antibiotics, novel strategies have recently emerged to combat these multidrug-resistant infectious microorganisms. In this review, we highlight the development of effective antibiotic combinations and of antibiotics with non-antibiotic activity-enhancing compounds to address the widespread emergence of antibiotic-resistant strains.

Prevalence of polymyxin-induced nephrotoxicity and its predictors in critically ill adult patients: A meta-analysis

BACKGROUND

Polymyxin-induced nephrotoxicity is a major safety concern in clinical practice due to long-term adverse outcomes and high mortality.

AIM

To conducted a systematic review and meta-analysis of the prevalence and potential predictors of polymyxin-induced nephrotoxicity in adult intensive care unit (ICU) patients.

METHODS

PubMed, EMBASE, the Cochrane Library and Reference Citation Analysis database were searched for relevant studies from inception through May 30, 2022. The pooled prevalence of polymyxin-induced nephrotoxicity and pooled risk ratios of associated factors were analysed using a random-effects or fixed-effects model by Stata SE ver. 12.1. Additionally, subgroup analyses and meta-regression were conducted to assess heterogeneity.

RESULTS

A total of 89 studies involving 12234 critically ill adult patients were included in the meta-analysis. The overall pooled incidence of polymyxin-induced nephrotoxicity was 34.8%. The pooled prevalence of colistin-induced nephrotoxicity was not higher than that of polymyxin B (PMB)-induced nephrotoxicity. The subgroup analyses showed that nephrotoxicity was significantly associated with dosing interval, nephrotoxicity criteria, age, publication year, study quality and sample size, which were confirmed in the univariable meta-regression analysis. Nephrotoxicity was significantly increased when the total daily dose was divided into 2 doses but not 3 or 4 doses. Furthermore, older age, the presence of sepsis or septic shock, hypoalbuminemia, and concomitant vancomycin or vasopressor use were independent risk factors for polymyxin-induced nephrotoxicity, while an elevated baseline glomerular filtration rate was a protective factor against colistin-induced nephrotoxicity.

CONCLUSION

Our findings indicated that the incidence of polymyxin-induced nephrotoxicity among ICU patients was high. It emphasizes the importance of additional efforts to manage ICU patients receiving polymyxins to decrease the risk of adverse outcomes.

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.

European Society of clinical microbiology and infectious diseases (ESCMID) guidelines for the treatment of infections caused by Multidrug-resistant Gram-negative bacilli (endorsed by ESICM -European Society of intensive care Medicine)

SCOPE

These ESCMID guidelines address the targeted antibiotic treatment of 3^rd generation cephalosporin-resistant Enterobacterales (3GCephRE) and carbapenem-resistant Gram-negative bacteria, focusing on the effectiveness of individual antibiotics and on combination vs. monotherapy.

METHODS

An expert panel was convened by ESCMID. A systematic review was performed including randomized controlled trials and observational studies, examining different antibiotic treatment regimens for the targeted treatment of infections caused by the 3GCephRE, carbapenem-resistant Enterobacterales (CRE), carbapenem-resistant Pseudomonas aeruginosa (CRPA) and carbapenem-resistant Acinetobacter baumanni (CRAB). Treatments were classified as head-to-head comparisons between individual antibiotics and monotherapy vs. combination therapy regimens, including defined monotherapy and combination regimens only. The primary outcome was all-cause mortality, preferably at 30 days and secondary outcomes included clinical failure, microbiological failure, development of resistance, relapse/recurrence, adverse events and length of hospital stay. The last search of all databases was conducted in December 2019, followed by a focused search for relevant studies up until ECCMID 2021. Data were summarized narratively. The certainty of the evidence for each comparison between antibiotics and between monotherapy vs. combination therapy regimens was classified by the GRADE recommendations. The strength of the recommendations for or against treatments was classified as strong or conditional (weak).

RECOMMENDATIONS

The guideline panel reviewed the evidence per pathogen, preferably per site of infection, critically appraising the existing studies. Many of the comparisons were addressed in small observational studies at high risk of bias only. Notably, there was very little evidence on the effects of the new, recently approved, beta-lactam beta-lactamase inhibitors on infections caused by carbapenem-resistant Gram-negative bacteria. Most recommendations are based on very-low and low certainty evidence. A high value was placed on antibiotic stewardship considerations in all recommendations, searching for carbapenem-sparing options for 3GCephRE and limiting the recommendations of the new antibiotics for severe infections, as defined by the sepsis-3 criteria. Research needs are addressed.

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.

Acute toxicity is a dose-limiting factor for intravenous polymyxin B: A safety and pharmacokinetic study in healthy Chinese subjects

OBJECTIVES

Polymyxin B is a last-line antibiotic for multidrug-resistant gram-negative bacterial infections. However, limited safety and pharmacokinetic information is available. We investigated the safety and pharmacokinetics of intravenous polymyxin B in healthy subjects.

METHODS

An open-label, single-dose clinical trial was conducted in healthy Chinese subjects. Polymyxin B (sulphate) was administered intravenously at 0.75 or 1.5 mg/kg (n = 10 per dose, 5 males and 5 females) to examine the safety and pharmacokinetics.

RESULTS

One female subject in the 1.5-mg/kg group discontinued due to abdominal pain during administration. The most frequently reported adverse events were perioral paraesthesia, dizziness, and numbness of extremities (7/10 subjects in the 0.75-mg/kg group, all subjects in the 1.5-mg/kg group). All neurotoxicity-related events dissipated without treatment within a maximum of 23 h. Notably, abdominal pain (3/5) and vulvar pruritus (2/5), colpitis (2/5) or abnormal uterine bleeding (1/5) were reported in female subjects receiving the 1.5-mg/kg dose. In the 0.75-mg/kg group, the total clearance, volume of distribution and half-life of polymyxin B were 0.028±0.002 L/h/kg, 0.219±0.023 L/kg and 5.44±0.741 h, respectively; similar values were observed in the 1.5-mg/kg group. Urinary recovery was 3.7 ± 1.1% and 8.1 ± 1.3% in the 0.75- and 1.5-mg/kg groups, respectively. Population pharmacokinetics of polymyxin B was consistent with a three-compartment model. The clearance and distribution of the central compartment were 0.027 L/h/kg and 0.071 L/kg, respectively.

CONCLUSIONS

This study is the first to examine the safety and pharmacokinetics of polymyxin B in healthy subjects. Our results highlight that acute toxicity is a dose-limiting factor for intravenous polymyxin B.

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.

Propranolol, chlorpromazine and diclofenac restore susceptibility of extensively drug-resistant (XDR)-Acinetobacter baumannii to fluoroquinolones

Nosocomial infections caused by extensively drug-resistant (XDR) or Pan-Drug resistant (PDR) Acinetobacter (A.) baumannii have recently increased dramatically creating a medical challenge as therapeutic options became very limited. The aim of our study was to investigate the antibiotic-resistance profiles and evaluate the various combinations of ciprofloxacin (CIP) or levofloxacin (LEV) with antimicrobial agents and non-antimicrobial agents to combat antimicrobial resistance of XDR A. baumannii. A total of 100 (6.25%) A. baumannii clinical isolates were recovered from 1600 clinical specimens collected from hospitalized patients of two major university hospitals in Upper Egypt. Antimicrobial susceptibility tests were carried out according to CLSI guidelines. Antimicrobial susceptibility testing of the respective isolates showed a high percentage of bacterial resistance to 19 antimicrobial agents ranging from 76 to99%. However, a lower percentage of resistance was observed for only colistin (5%) and doxycycline (57%). The isolates were categorized as PDR (2; 2%), XDR (68; 68%), and multi-drug resistant (MDR) (30; 30%). Genotypic analysis using ERIC-PCR on 2 PDR and 32 selected XDR isolates showed that they were not clonal. Combinations of CIP or LEV with antibiotics (including, ampicillin, ceftriaxone, amikacin, or doxycycline) were tested on these A. baumannii non-clonal isolates using standard protocols where fractional inhibitory concentrations (-FICs) were calculated. Results of the respective combinations showed synergism in 23.5%, 17.65%, 32.35%, 17.65% and 26.47%, 8.28%, 14.71%, 26.47%, of the tested isolates, respectively. CIP or LEV combinations with either chlorpromazine (CPZ) 200 μg/ml, propranolol (PR) in two concentrations, 0.5 mg/ml and 1.0 mg/ml or diclofenac (DIC) 4 mg/ml were carried out and the MIC decrease factor (MDF) of each isolate was calculated and results showed synergism in 44%, 50%, 100%, 100% and 94%, 85%, 100%, 100%, of the tested isolates, respectively. In conclusion, combinations of CIP or LEV with CPZ, PR, or DIC showed synergism in most of the selected PDR and XDR A. baumannii clinical isolates. However, these combinations have to be re-evaluated in vivo using appropriate animal models infected by XDR- or PDR- A. baumannii.

Acinetobacter baumannii Resistance: A Real Challenge for Clinicians

Acinetobacter baumannii (named in honor of the American bacteriologists Paul and Linda Baumann) is a Gram-negative, multidrug-resistant (MDR) pathogen that causes nosocomial infections, especially in intensive care units (ICUs) and immunocompromised patients with central venous catheters. A. baumannii has developed a broad spectrum of antimicrobial resistance, associated with a higher mortality rate among infected patients compared with other non-baumannii species. In terms of clinical impact, resistant strains are associated with increases in both in-hospital length of stay and mortality. A. baumannii can cause a variety of infections; most involve the respiratory tract, especially ventilator-associated pneumonia, but bacteremia and skin wound infections have also been reported, the latter of which has been prominently observed in the context of war-related trauma. Cases of meningitis associated with A. baumannii have been documented. The most common risk factor for the acquisition of MDR A baumannii is previous antibiotic use, following by mechanical ventilation, length of ICU/hospital stay, severity of illness, and use of medical devices. Current efforts focus on addressing all the antimicrobial resistance mechanisms described in A. baumannii, with the objective of identifying the most promising therapeutic scheme. Bacteriophage- and artilysin-based therapeutic approaches have been described as effective, but further research into their clinical use is required.

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.

Nephrotoxicity prevalence in patients treated with polymyxins: a systematic review with meta-analysis of observational studies

Colistin and polymyxin B are increasingly reintroduced in clinical practice due to the absence of effective antibiotics for the treatment of emerging infections caused by gram-negative bacteria. The synthesis of current evidence on the characteristics of polymyxins, especially regarding nephrotoxicity, is necessary. This study aims to conduct a systematic review and meta-analysis of cohort-type observational studies in order to identify the prevalence of nephrotoxicity in patients treated with either colistin or polymyxin B. PubMed, Scopus, and DOAJ electronic databases were searched, and manual searches were done. Cohort studies evaluating renal damage (nephrotoxicity) in adult patients caused by colistin or polymyxin B were included. Meta-analyses of the prevalence of nephrotoxicity as well as cumulative meta-analysis and meta-regression were conducted. After the systematic searches, 95 cohorts (n = 7911 patients) were included for analysis. The nephrotoxicity prevalence was 26.7% [confidence interval (CI) 95%: 22.8-30.9%] for colistin and 29.8% (CI 23.8-36.7%) for polymyxin B (P = 0.720). The publication year of the studies, the criteria used to classify renal damage, and the nephrotoxicity as primary or secondary outcome showed a significant influence on the adverse event rates.

Comparative efficacy and safety of treatment options for MDR and XDR Acinetobacter baumannii infections: a systematic review and network meta-analysis

Objectives

To comprehensively compare and rank the efficacy and safety of available treatment options for patients with MDR and XDR Acinetobacter baumannii (AB) infection.

Methods

We searched PubMed, Embase and the Cochrane register of trials systematically for studies that examined treatment options for patients with MDR- and XDR-AB infections until April 2016. Network meta-analysis (NMA) was performed to estimate the risk ratio (RR) and 95% CI from both direct and indirect evidence. Primary outcomes were clinical cure and microbiological cure. Secondary outcomes were all-cause mortality and nephrotoxic and non-nephrotoxic adverse events.

Results

A total of 29 studies with 2529 patients (median age 60 years; 65% male; median APACHE II score 19.0) were included. Although there were no statistically significant differences between treatment options, triple therapy with colistin, sulbactam and tigecycline had the highest clinical cure rate. Colistin in combination with sulbactam was associated with a significantly higher microbiological cure rate compared with colistin in combination with tigecycline (RR 1.23; 95% CI 1.03-1.47) and colistin monotherapy (RR 1.21; 95% CI 1.06-1.38). No significant differences in all-cause mortality were noted between treatment options. Tigecycline-based therapy also appeared less effective for achieving a microbiological cure and is not appropriate for treating bloodstream MDR- and XDR-AB infections.

Conclusions

Combination therapy of colistin with sulbactam demonstrates superiority in terms of microbiological cure with a safety profile similar to that of colistin monotherapy. Thus, our findings support the use of this combination as a treatment for MDR- and XDR-AB infections.

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.

Can octapeptin antibiotics combat extensively drug-resistant (XDR) bacteria?

INTRODUCTION

The octapeptins are a family of cyclic lipopeptides first reported in the 1970s then largely ignored. At the time, their reported antibiotic activity against polymyxin-resistant bacteria was a curiosity. Today, the advent of widespread drug resistance in Gram-negative bacteria has prompted their 'rediscovery.' The paucity of new antibiotics in the clinical pipeline is coupled with a global spread of increasing antibiotic resistance, particularly to meropenem and polymyxins B and E (colistin). Areas covered: We review the original discovery of octapeptins, their recent first chemical syntheses, and their mode of action, then discuss their potential as a new class of antibiotics to treat extensively drug-resistant (XDR) Gram-negative infections, with direct comparisons to the closely related polymyxins. Expert commentary: Cyclic lipopeptides in clinical use (polymyxin antibiotics) have significant dose-limiting nephrotoxicity inherent to their chemotype. This toxicity has prevented improved polymyxin analogs from progressing to the clinic, and tainted the perception of lipopeptide antibiotics in general. We argue that the octapeptins are fundamentally different from the polymyxins, with a disparate mode of action, spectra of action against MDR and XDR bacteria and a superior preclinical safety profile. They represent early-stage candidates that can help prime the antibiotic discovery pipeline.

Intravenous polymyxins: Revival with puzzle

With the increasing incidence of multi-drug resistant strains, especially carbapenem resistant strains, polymyxsins (mainly colistin and polymyxin B) based regimens seem to be a revival as an effective treatment of last resort in these infections. Evidence from 47 clinical trials or case series we reviewed showed that polymyxins based regimens are effective and have less toxicity compared with previous trials. When used alone, the mortality of intravenous polymyxsins ranged from 0% to 74.3%, clinical response (cure and improvement) rate was 7-82.1%, and microbiological eradication was 27.3-73.9%. The main reasons for the combination therapy are to get potential synergistic effects and to prevent the selection of heteroresistant strains. Several studies showed combination therapy seemed to be more effective than monotherapy, though a few doubts remain. Clinically, polymyxsins can be used in combination with several antibiotics, such as carberpenem, sulbactam, tigecycline, fosfomycin, glycopeptide, rifampicin and so on, but the optimal combination regimen is yet to be confirmed. The optimal dose of polymyxins is also controversial. With the limited clinical evidence, it's suggested loading dose regimens may be more effective, but more attention should be paid to adverse effects. Although recommended in some studies, high dose polymxins regimens with inconsistent clinical evidence need more trials to confirm. It is important to note that concerning dosing regimens, colistin and polymyxin B are not quite the same. In renal impaired patients polymyxin B should be prescribed without dosing adjustment. Risk of renal failure may increase in the following situations, such as the combination of intravenous colistin plus intravenous vancomycin, higher doses-colistin, and intravenous colistin combined with inhalational colistin. In conclusion, there're still controversies in combination regimens, dosing strategies and so on. Prospective trials of lager sample size are needed.

Systematic Review of Antimicrobial Resistance of Clinical Acinetobacter baumannii Isolates in Iran: An Update

Treatment of Acinetobacter baumannii has become a medical challenge because of the increasing incidence of multiresistant strains and a lack of viable treatment alternatives. This systematic review attempts to investigate the changes in resistance of A. baumannii to different classes of antibiotics in Iran, with emphasis on the antimicrobial activity of polymyxin B (PMB) and colistin (COL). Biomedical databases were searched for English-published articles evaluating microbiological activity of various antimicrobial agents, including PMB and COL. Then, the available data were extracted and analyzed. Thirty-one studies, published from 2009 to 2015, were identified which contain data for 3,018 A. baumannii clinical isolates. With the exception of polymyxins and tigecycline (TIG), there was a high rate of resistance to various groups of antibiotics, including carbapenems. The minimum inhibitory concentration (MIC) ranges for PMB and COL on A. baumannii isolates tested were 0.12-64 μg/ml and 0.001-128 μg/ml, respectively. Polymyxins showed adequate activity with no significant trends in the resistance rate during most of the study period. The incidence of resistance to TIG was estimated low from 2% to 38.4% among the majority of A. baumannii. The present systematic review of the published literatures revealed that multidrug-resistant (including carbapenem-resistant) strains of A. baumannii have increased in Iran. In these circumstances, the older antibiotics, such as COL or PMB, preferably in combination with other antimicrobials (rifampicin, meropenem), could be considered as the therapeutic solution against the healthcare-associated infections. Designing rational dosage regimens for patients to maximize the antimicrobial activity and minimize the emergence and prevalence of resistance is recommended.

Resurgence of Polymyxin B for MDR/XDR Gram-Negative Infections: An Overview of Current Evidence

Polymyxin B has resurged in recent years as a last resort therapy for Gram-negative multidrug-resistant (MDR) and extremely drug resistant (XDR) infections. Understanding newer evidence on polymyxin B is necessary to guide clinical decision making. Here, we present a literature review of polymyxin B in Gram-negative infections with update on its pharmacology.

Resistance to Colistin in Klebsiella Pneumoniae: A 4.0 Strain?

The global rise of multidrug-resistant gram-negative bacteria represents an increasing threat to patient safety. From the first observation of a carbapenem-resistant gram-negative bacteria a global spread of extended-spectrum beta-lactamases and carbapenemases producing Klebsiella pneumoniae has been observed. Treatment options for multidrug-resistant K. pneumoniae are actually limited to combination therapy with some aminoglycosides, tigecycline and to older antimicrobial agents. Unfortunately, the prevalence of colistin-resistant and tigecycline-resistant K. pneumoniae is increasing globally. Infection due to colistin-resistant K. pneumoniae represents an independent risk factor for mortality. Resistance to colistin in K. pneumoniae may be multifactorial, as it is mediated by chromosomal genes or plasmids. The emergence of transmissible, plasmid-mediated colistin resistance is an alarming finding. The absence of new agents effective against resistant Gram-negative pathogens means that enhanced surveillance, compliance with infection prevention procedures, and antimicrobial stewardship programs will be required to limit the spread of colistin-resistant K. pneumoniae.

The safety of polymyxin antibiotics

INTRODUCTION

The emergence of multidrug-resistant gram-negative bacteria has led to the increasing use of polymyxins. Nephrotoxicity and, to a lesser degree, neurotoxicity occur often during systemic polymyxin therapy. Scientific evidence regarding safety associated with polymyxins remains limited.

AREAS COVERED

Case reports/case series, observational studies and clinical trials assessing safety and toxicity of polymyxins were critically reviewed.

EXPERT OPINION

Polymyxins are drugs with a narrow therapeutic range. Nephrotoxicity is associated with both host factors and polymyxin exposure, and recent studies suggest that the relative risk of nephrotoxicity is similar for colistin and polymyxin B. Studies that have examined the safety of polymyxins have several limitations. Considering the available evidence, toxicities that may develop while on polymyxin therapy most often are mild to moderate in magnitude and reversible in nature. Strategies to minimize toxicity associated with polymyxins have evolved and include avoidance of toxic medications, careful dosing, use of critical care, therapeutic drug monitoring and development of polymyxin derivatives. However, given that polymyxin use has re-emerged in an era of increased antimicrobial resistance, the presence of other treatment modalities may be limited. Therefore, clinicians must consider overall risk to benefit ratio of continuing versus stopping polymyxin treatment and optimize minimization strategies to reduce polymyxin-induced toxicities.

Tetracyclines for multidrug-resistant Acinetobacter baumannii infections

Multidrug-resistant (MDR) Acinetobacter baumannii infections have emerged as a serious threat worldwide. As novel agents have yet to be developed, understanding the effectiveness and safety of older antibiotics has become a priority. The purpose of this systematic review was to summarise the available clinical evidence on the use of tetracyclines for the treatment of A. baumannii infections. Ten retrospective studies regarding doxycycline and minocycline for the treatment of 185 A. baumannii infections (of which 65.4% were respiratory infections and 13% were bloodstream infections) in 156 patients were available. In most cases (86.4%), tetracyclines were administered in combination with another agent. The usual dosage of doxycycline or minocycline was 100mg intravenous or per os twice daily (usually with a 200mg loading dose for minocycline). Clinical success was achieved in 120 (76.9%) of 156 patients; in 87 (71.9%) of 121 respiratory infections and in 21 (87.5%) of 24 bloodstream infections. Twenty-two deaths occurred in 100 recorded cases. Microbiological eradication was attained in 72 (71.3%) of 101 available cases and documented microbiological eradication was reached in 59 (66.3%) of 89 available cases. Adverse events were noted in only 1 of 88 cases. Overall, although tetracycline-containing regimens showed encouraging results, more data from larger comparative trials are required to establish a role for these antibiotics in the treatment of MDR A. baumannii infections.

Multi-drug resistant gram negative infections and use of intravenous polymyxin B in critically ill children of developing country: retrospective cohort study

Background

Patients in pediatric intensive care Units (PICU) are susceptible to infections with antibiotic resistant organisms which increase the morbidity, mortality and cost of care.

To describe the clinical characteristics and mortality in patients with Multi-Drug Resistant (MDR) gram negative organisms. We also report safety of Polymyxin B use in these patients.

Methods

Files of patients admitted in PICU of Aga Khan University Hospital, from January 2010 to December 2011, one month to 15 years of age were reviewed. Demographic and clinical features of patients with MDR gram negative infections, antibiotic susceptibility pattern of isolates, discharge disposition and adverse effects of Polymyxin B were recorded.

Results

A total of 44.8/1000(36/803) admitted patients developed MDR gram negative infections, of which 47.2%(17/36) were male, with mean age of 3.4 yrs(+/−4.16). Acinetobacter Species (25.5%) was the most frequently isolated MDR organisms followed by Klebsiella Pneumoniae (17%). Sensitivity of isolates was 100% to Polymyxin B, followed by Imipenem (50%), and piperacillin/tazobactem (45%). The crude mortality rate of patients with MDR gram negative infections was 44.4% (16/36). Fourteen of 36 patients received Polymyxin B and 57.1%; (8/14) of them were cured. Nephrotoxicity was observed in 21.4% (3/14) cases, none of the patients showed signs of neuropathy.

Conclusion

Our study highlights high rates of Carbapenem resistant gram negative isolates, leading to increasing use of Polymyxin B as the only drug to combat against these critically ill children. Therefore, we emphasizeon Stewardship of Antibiotics and continuous surveillance system as strategies in overall management of these critically ill children.

Efficacy and safety of polymyxins for the treatment of Acinectobacter baumannii infection: a systematic review and meta-analysis

BACKGROUND

Multi-drug resistance among Acinetobacter baumannii increases the need for polymyxins. We conducted a meta-analysis aimed to assess the efficacy and safety of polymyxins for the treatment of Acinetobacter baumannii infection.

METHODS

We searched PUBMED, EMBASE, the Cochrane Central Register of Controlled Trials (CENTRAL), CNKI, Chinese Biomedical Literature Database up to November 1, 2013, to identify published studies, and we searched clinical trial registries to identify completed unpublished studies. Randomized controlled trials and cohort studies were considered for inclusion. Data were extracted on clinical response, microbiological response, mortality, length of stay and adverse events.

RESULTS

12 controlled studies, comparing 677 patients, were included. Although clinical (odds ratio 1.421, 95% confidence interval 0.722-2.797) and microbiological (OR 1.416, 95% CI 0.369-5.425) response rates favored the polymyxins group, these differences were not significant. Treatment with polymyxins vs. controls did not affect hospital mortality (OR 0.506, 95% CI 0.101-2.536), lengths of hospital stay (standard mean difference -0.221, 95% CI 0.899-0.458) or nephrotoxicity (OR 1.192, 95% CI 0.436-3.261). The combination of polymyxins with other antibiotics achieved similar clinical response rates to its monotherapy regimen (OR 0.601, 95% CI 0.320-1.130).

CONCLUSIONS

Our results suggest that polymyxins may be as safe and as efficacious as standard antibiotics for the treatment of A. baumannii infection. There is no strong evidence that combination regimen of polymyxins is superior to monotherapy regimen.

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.

Validation of a novel murine wound model of Acinetobacter baumannii infection

Patients recovering from traumatic injuries or surgery often require weeks to months of hospitalization, increasing the risk for wound and surgical site infections caused by ESKAPE pathogens, which include A. baumannii (the ESKAPE pathogens are Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species). As new therapies are being developed to counter A. baumannii infections, animal models are also needed to evaluate potential treatments. Here, we present an excisional, murine wound model in which a diminutive inoculum of a clinically relevant, multidrug-resistant A. baumannii isolate can proliferate, form biofilms, and be effectively treated with antibiotics. The model requires a temporary, cyclophosphamide-induced neutropenia to establish an infection that can persist. A 6-mm-diameter, full-thickness wound was created in the skin overlying the thoracic spine, and after the wound bed was inoculated, it was covered with a dressing for 7 days. Uninoculated control wounds healed within 13 days, whereas infected, placebo-treated wounds remained unclosed beyond 21 days. Treated and untreated wounds were assessed with multiple quantitative and qualitative techniques that included gross pathology, weight loss and recovery, wound closure, bacterial burden, 16S rRNA community profiling, histopathology, peptide nucleic acid-fluorescence in situ hybridization, and scanning electron microscopy assessment of biofilms. The range of differences that we are able to identify with these measures in antibiotic- versus placebo-treated animals provides a clear window within which novel antimicrobial therapies can be assessed. The model can be used to evaluate antimicrobials for their ability to reduce specific pathogen loads in wounded tissues and clear biofilms. Ultimately, the mouse model approach allows for highly powered studies and serves as an initial multifaceted in vivo assessment prior to testing in larger animals.

To study the clinical efficacy and nephrotoxicity along with the risk factors for acute kidney injury associated with parenteral polymyxin B

Aim:

The aim of this study was to evaluate the clinical efficacy and nephrotoxicity along with the risk factors for acute kidney injury (AKI) associated with the parenteral polymyxin B in patients with the multidrug resistance (MDR) gram −ve infections in a tertiary Intensive care unit (ICU).

Materials and Methods:

A retrospective cohort study (March 2010-October 2011) was conducted in Medical ICU of a 23 bedded tertiary care hospital in Northern India.

Results:

Out of 71 ICU patients who were administered polymyxin B, only 32 (M:F = 1:0.8) met the inclusion criteria. Patients with concurrent administration of nephrotoxic drugs were excluded from the study. Mean age of patients was 48.53 ± 13.90 years ranging from 16 years to 68 years. 6 out of 32 (18.7%) patients progressed to AKI, whereas renal functions remained normal in 26 (81.2%) patients. No statistically significant difference was observed in mortality between AKI and non AKI patients at the end of therapy (33.3% vs. 26.9%, P value 0.756). Older age (62.33 ± 11.90 vs. 45.34 ± 2.45, P value 0.005) was found to be an independent risk factor for causing nephrotoxicity.

Conclusion:

In the present scenario of rising infections with MDR gram −ve micro-organisms, this pilot study suggests that polymyxin B can be used effectively and safely in patients not receiving other nephrotoxic drugs, with cautious administration in older patients as they are more vulnerable to nephrotoxicity caused by polymyxin B.

Pharmacokinetics and efficacy of liposomal polymyxin B in a murine pneumonia model

Polymyxin B (PB) is increasingly used as the last treatment for multidrug-resistant (MDR) Gram-negative bacterial infections. In this study, serum and epithelial lining fluid (ELF) pharmacokinetics and the efficacy of a PB liposomal formulation were investigated. Two groups of 24 Swiss Webster mice were intravenously administered PB liposomes or PB aqueous solution at ca. 3 mg/kg. Serum and ELF samples were collected for up to 6 h to quantify major PB components. Three groups of neutropenic mice (n = 6/group) were infected with a clinical MDR Pseudomonas aeruginosa strain followed by intravenous administration of PB liposomes or PB aqueous solution at 3 mg/kg every 6 h or sham (drug-free) liposomes every 6 h. Bacterial burden in animal lung tissues was quantified after 24 h of therapy and was compared using one-way ANOVA. Survival of infected animals over time (n = 10/group) was evaluated by Kaplan-Meier analysis and log-rank test. In the pharmacokinetic study, the AUC ratio in ELF between liposome and aqueous solution groups ranged from 4.6 to 11.1 for various major PB components. In the efficacy study, for strain PA 9019 a significantly lower bacterial burden was seen in the liposomal group (3.8 ± 0.7 vs. 7.9 ± 0.8 log(10)CFU/g in the aqueous solution group), which subsequently prolonged survival of infected animals. In this study, treatment with a PB liposomal formulation yielded higher drug penetration into pulmonary ELF, which resulted in superior efficacy. However, further investigations on the clinical utility of the PB liposomal formulation are warranted.

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.

Carbapenem-resistant Enterobacteriaceae: a review of treatment and outcomes

The emergence of carbapenem resistance in Enterobacteriaceae is an important threat to global health. Reported outcomes of infections with carbapenem-resistant Enterobacteriaceae (CRE) are poor. Very few options remain for the treatment of these virulent organisms. Antibiotics which are currently in use to treat CRE infections include aminoglycosides, polymyxins, tigecycline, fosfomycin, and temocillin. In addition, the role of combination therapy, including carbapenem containing regimens, remains to be defined. There are several important concerns regarding all of these treatment options such as limited efficacy, increasing reports of resistance, and specific toxicities. Data from retrospective studies favor combination therapy over single-agent therapy for the treatment of CRE bloodstream infections. In summary, new antibiotics are greatly needed, as is additional prospective research.

Clinical and microbiological efficacy and toxicity of colistin in patients infected with multidrug-resistant gram-negative pathogens

Polymyxins have recently again become important because of multidrug-resistant (MDR) gram-negative pathogens. The aim of this study was to evaluate the clinical and microbiological efficacy and toxicity of different dosages of colistin in patients infected with MDR microorganisms that were sensitive only to colistin. The study was conducted in the 1,200-bed Ankara Numune Training and Research Hospital. Patients with normal renal function who received colistin for 48 h or more were retrospectively evaluated. Clinical response was defined as resolution of fever and clinical and laboratory findings. Microbiological response was defined as bacteriological eradication from the infection site. Nephrotoxicity was defined as at least two consecutive serum creatinine measurements with an increase of 0.5 mg/dl from baseline at least 24 h apart after 2 or more days of colistin therapy. Twenty-four patients were included in the study: total clinical response was obtained in 17 of 24 (70.8 %) patients and microbiological response in 15 of 24 (62.5 %) patients. Patients were grouped according to colistin dosage of 3 × 1 million units (MU) versus 3 × 2 MU. Clinical response rates were 69.2 % and 72.7 %, respectively (p = 0.65). Microbiological response rate was similar (p = 0.62). Nephrotoxicity was revealed in 1 of 13 patients (7.7 %) for the 3 × 1 MU group and 2 of 11 patients (18.2 %) in the 3 × 2 MU group (p = 0.57). The nephrotoxicity rate was greater with higher dosages of colistin, but the difference was not statistically significant. Renal function of patients receiving higher dosages of colistin should be more closely monitored.

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.

Confronting multidrug-resistant Acinetobacter baumannii: a review

Multidrug-resistant Acinetobacter baumannii (MDR-AB) infections are difficult to treat owing to the extremely limited armamentarium. The present review reports all available treatment options against MDR-AB, including single molecules, combination schemes, and alternative modes of antimicrobial administration. Additionally, a group of recently reported peptides with anti-MDR-AB activity is described.

Safety and efficacy of intravenous colistin (colistin methanesulphonate) for severe multidrug-resistant Gram-negative bacterial infections

Multidrug-resistant (MDR) bacterial infections are increasing in Taiwan hospitals, prompting the common use of colistin. In this study, the safety and efficacy of intravenous (i.v.) colistin was assessed. The medical records of patients receiving colistin for treatment of MDR Gram-negative bacterial infections between January 2006 and September 2008 at a Taiwan medical centre were reviewed retrospectively. Demographics, clinical presentation, causative organism, adverse events and outcomes were recorded. Of the 115 patient records analysed, 74 patients (64%) were treated in the Intensive Care Unit. Common underlying diseases were hypertension (49%), chronic pulmonary disease (46%), chronic kidney disease (33%) and malignancy (31%). Lower respiratory tract infections were most common (71%), followed by primary bloodstream infections (12%), urinary tract infections (8.7%) and others (7.8%). Successful treatment with i.v. colistin against MDR Gram-negative bacterial infections occurred in 59 patients (51%). Multivariate analysis showed that a higher Acute Physiology and Chronic Health Evaluation (APACHE) II score (odds ratio=1.14; 95% confidence interval 1.02-1.28; P=0.02) was independently associated with a poor clinical response. Overall, 12 (14%) of 84 patients presented nephrotoxicity and 4 patients (3.5%) had neurotoxicity. In conclusion, colistin is an effective antimicrobial agent for severe infections caused by MDR Gram-negative bacteria. Clinical outcomes are associated with the severity of infection and underlying diseases. Compared with previous reports, this study showed a lower incidence of nephrotoxicity and neurotoxicity.

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.

Neurotoxicity in patients treated with intravenous polymyxin B: Two case reports

PURPOSE

Two cases of reversible neurotoxicity associated with the administration of intravenous polymyxin B are described.

SUMMARY

In the first case, a 60-year-old, obese, white woman with a medical history of recurring urinary tract infections, nephrolithiasis, and chronic renal insufficiency was admitted for parenteral antibiotics for dysuria and hematuria despite outpatient management with oral antibiotics. Her urinalysis revealed pyuria and large blood content. The corresponding urine culture contained >or=100,000 colony-forming units/mL of multidrug-resistant (MDR) Klebsiella pneumoniae. The patient was treated with polymyxin B at 20,000 units/kg i.v. as a loading dose and then 10,000 units/kg i.v. daily based on her renal function. The patient experienced oral paresthesia that resolved upon discontinuation of the infusion with no further complications. In the second case, a 57-year-old white man with hypertension and ascending cholangitis was admitted. He required percutaneous drainage of an infected pancreatic cyst and received polymyxin B at 25,000 units/kg i.v. as a loading dose and then 15,000 units/kg i.v. daily in addition to imipenem-cilastatin based on the sensitivities of two organisms (Escherichia coli and MDR K. pneumoniae) isolated from the abdominal drainage. For his pancreatic abscess, the patient received a prolonged course of polymyxin B, which was well tolerated for the first four weeks. On day 30 of the polymyxin B, the patient reported oral and lower extremity paresthesias. The symptoms resolved upon discontinuation of the polymyxin B.

CONCLUSION

Two patients developed symptoms of neurotoxicity after receiving intravenous polymyxin B for the treatment of MDR gram-negative infections.

Current control and treatment of multidrug-resistant Acinetobacter baumannii infections

Institutional outbreaks caused by Acinetobacter baumannii strains that have acquired multiple mechanisms of antimicrobial drug resistance constitute a growing public-health problem. Because of complex epidemiology, infection control of these outbreaks is difficult to attain. Identification of potential common sources of an outbreak, through surveillance cultures and epidemiological typing studies, can aid in the implementation of specific control measures. Adherence to a series of infection control methods including strict environmental cleaning, effective sterilisation of reusable medical equipment, attention to proper hand hygiene practices, and use of contact precautions, together with appropriate administrative guidance and support, are required for the containment of an outbreak. Effective antibiotic treatment of A baumannii infections, such as ventilator-associated pneumonia and bloodstream infections, is also of paramount importance. Carbapenems have long been regarded as the agents of choice, but resistance rates have risen substantially in some areas. Sulbactam has been successfully used in the treatment of serious A baumannii infections; however, the activity of this agent against carbapenem-resistant isolates is decreasing. Polymyxins show reliable antimicrobial activity against A baumannii isolates. Available clinical reports, although consisting of small-sized studies, support their effectiveness and mitigate previous concerns for toxicity. Minocycline, and particularly its derivative, tigecycline, have shown high antimicrobial activity against A baumannii, though relevant clinical evidence is still scarce. Several issues regarding the optimum therapeutic choices for multidrug-resistant A baumannii infections need to be clarified by future research.

Polymyxins: A Review of the Current Status Including Recent Developments

Introduction: Polymyxins have become the drug of choice for treatment of multidrug-resistant gram-negative bacilli infections in Singapore, simply because these pathogens are only susceptible to either aminoglycosides and polymyxins, or polymyxins only. Furthermore, there is no new antibiotic in the pipeline that targets these difficult-to-treat infections. Materials and Methods: All published literatures (up to end of February 2008) regarding polymyxins are included for review. Results: This review serves to give a summary of polymyxins from the current available literature, highlighting relevant clinical studies and information that help to guide informed prescription of polymyxins, should the need arise. Conclusions: However, there are substantial information gaps that needed to be filled urgently, to preserve the clinical utility of this very last line of antibiotic. Key words: Acinetobacter baumannii, Colistin, Multidrug resistance, Polymyxin B, Pseudomonas aeruginosa

Acinetobacter baumannii: emergence of a successful pathogen

Acinetobacter baumannii has emerged as a highly troublesome pathogen for many institutions globally. As a consequence of its immense ability to acquire or upregulate antibiotic drug resistance determinants, it has justifiably been propelled to the forefront of scientific attention. Apart from its predilection for the seriously ill within intensive care units, A. baumannii has more recently caused a range of infectious syndromes in military personnel injured in the Iraq and Afghanistan conflicts. This review details the significant advances that have been made in our understanding of this remarkable organism over the last 10 years, including current taxonomy and species identification, issues with susceptibility testing, mechanisms of antibiotic resistance, global epidemiology, clinical impact of infection, host-pathogen interactions, and infection control and therapeutic considerations.

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

Background

Parenteral polymyxin use declined after the 1960s, due to safety concerns. An increase in multidrug-resistant (MDR) gram-negative infections and a shortage of new agents have prompted increased use of parenteral polymyxin.

Objective

TO describe our clinical experience with parenteral polymyxin B for MDR gram-negative bacteremia and urinary tract infection (UTI).

Methods

Paper pharmacy records were used to identify patients aged 18 years or older, presence of MDR gram-negative bacteremia or UTI, and use of parenteral polymyxin B for at least 48 hours. Electronic and paper patient records were then retrospectively reviewed. Polymyxin B susceptibility was evaluated using the Kirby-Bauer method. MDR isolates were defined as resistant to at least 3 antimicrobial classes, excluding polymyxin B. Microbiologic clearance was defined by 1 repeat urine or 2 repeat blood cultures that were sterile or growing different organisms. Secondary outcomes included hospital mortality and nephrotoxicity, defined as an increase in serum creatinine of 0.5 mg/dL or more, or a 50% reduction in creatinine clearance.

Results:

Seventeen infections in 16 patients were treated with polymyxin B (1 pt. had 2 infections that were analyzed separately). Microbiologic clearance occurred in 14 of 16 (88%) cases of MDR gram-negative bacteremia or UTI in which repeat cultures were done. Ten of 16 patients died (all-cause mortality 63%). Five patients required hemodialysis prior to polymyxin B use. Six (55%) of the remaining 11 patients with baseline renal insufficiency developed nephrotoxicity, and none of them required hemodialysis. The mean ± SD number of days from the initiation of therapy to the onset of nephrotoxicity was 7.5 ± 2.3 (range 4–10) days. Three (50%) of 6 patients with nephrotoxicity died.

Conclusions:

Our data suggest that polymyxin B may be effective for MDR gram-negative infections in patients with limited therapeutic options, but precautions should be taken to avoid toxicity.

Acinetobacter baumannii: epidemiology, antimicrobial resistance, and treatment options

Multidrug-resistant Acinetobacter baumannii is recognized to be among the most difficult antimicrobial-resistant gram-negative bacilli to control and treat. Increasing antimicrobial resistance among Acinetobacter isolates has been documented, although definitions of multidrug resistance vary in the literature. A. baumannii survives for prolonged periods under a wide range of environmental conditions. The organism causes outbreaks of infection and health care-associated infections, including bacteremia, pneumonia, meningitis, urinary tract infection, and wound infection. Antimicrobial resistance greatly limits the therapeutic options for patients who are infected with this organism, especially if isolates are resistant to the carbapenem class of antimicrobial agents. Because therapeutic options are limited for multidrug-resistant Acinetobacter infection, the development or discovery of new therapies, well-controlled clinical trials of existing antimicrobial regimens and combinations, and greater emphasis on the prevention of health care-associated transmission of multidrug-resistant Acinetobacter infection are essential.