Effectiveness of tigecycline-based versus colistin- based therapy for treatment of pneumonia caused by multidrug-resistant Acinetobacter baumannii in a critical setting: a matched cohort analysis

Machine learning algorithms to predict colistin-induced nephrotoxicity from electronic health records in patients with multidrug-resistant Gram-negative infection

OBJECTIVES

Colistin-induced nephrotoxicity prolongs hospitalisation and increases mortality. The study aimed to construct machine learning models to predict colistin-induced nephrotoxicity in patients with multidrug-resistant Gram-negative infection.

METHODS

Patients receiving colistin from three hospitals in the Clinical Research Database were included. Data were divided into a derivation cohort (2011-2017) and a temporal validation cohort (2018-2020). Fifteen machine learning models were established by categorical boosting, light gradient boosting machine and random forest. Classifier performances were compared by the sensitivity, F1 score, Matthews correlation coefficient (MCC), area under the receiver operating characteristic (AUROC) curve, and area under the precision-recall curve (AUPRC). SHapley Additive exPlanations plots were drawn to understand feature importance and interactions.

RESULTS

The study included 1392 patients, with 360 (36.4%) and 165 (40.9%) experiencing nephrotoxicity in the derivation and temporal validation cohorts, respectively. The categorical boosting with oversampling achieved the highest performance with a sensitivity of 0.860, an F1 score of 0.740, an MCC of 0.533, an AUROC curve of 0.823, and an AUPRC of 0.737. The feature importance demonstrated that the days of colistin use, cumulative dose, daily dose, latest C-reactive protein, and baseline haemoglobin were the most important risk factors, especially for vulnerable patients. A cutoff colistin dose of 4.0 mg/kg body weight/d was identified for patients at higher risk of nephrotoxicity.

CONCLUSIONS

Machine learning techniques can be an early identification tool to predict colistin-induced nephrotoxicity. The observed interactions suggest a modification in dose adjustment guidelines. Future geographic and prospective validation studies are warranted to strengthen the real-world applicability.

Current Therapeutic Approaches for Multidrug-Resistant and Extensively Drug-Resistant Acinetobacter baumannii Infections

The treatment of Acinetobacter baumannii infections remains a challenge for physicians worldwide in the 21st century. The bacterium possesses a multitude of mechanisms to escape the human immune system. The consequences of A. baumannii infections on morbidity and mortality, as well on financial resources, remain dire. Furthermore, A. baumannii superinfections have also occurred during the COVID-19 pandemic. While prevention is important, the antibiotic armamentarium remains the most essential factor for the treatment of these infections. The main problem is the notorious resistance profile (including resistance to carbapenems and colistin) that this bacterium exhibits. While newer beta lactam/beta-lactamase inhibitors have entered clinical practice, with excellent results against various infections due to Enterobacteriaceae, their contribution against A. baumannii infections is almost absent. Hence, we have to resort to at least one of the following, sulbactam, polymyxins E or B, tigecycline or aminoglycosides, against multidrug-resistant (MDR) and extensively drug-resistant (XDR) A. baumannii infections. Furthermore, the notable addition of cefiderocol in the fight against A. baumannii infections represents a useful addition. We present herein the existing information from the last decade regarding therapeutic advances against MDR/XDR A. baumannii infections.

Genomic Characterization of Mobile Genetic Elements Associated with Multidrug-Resistant Acinetobacter Non-baumannii Species from Southern Thailand

This study investigated the genetic diversity, antimicrobial resistance profiles, and virulence characteristics of Acinetobacter non-baumannii isolates obtained from four hospitals in southern Thailand. Clinical data, genome information, and average nucleotide identity (ANI) were analyzed for eight isolates, revealing diverse genetic profiles and novel sequence types (STs). Minimum spanning tree analysis indicated potential clonal spread of certain STs across different geographic regions. Antimicrobial resistance genes (ARGs) were detected in all isolates, with a high prevalence of genes conferring resistance to carbapenems, highlighting the challenge of antimicrobial resistance in Acinetobacter spp. infections. Mobile genetic elements (MGEs) carrying ARGs were also identified, emphasizing the role of horizontal gene transfer in spreading resistance. Evaluation of virulence-associated genes revealed a diverse range of virulence factors, including those related to biofilm formation and antibiotic resistance. However, no direct correlation was found between virulence-associated genes in Acinetobacter spp. and specific clinical outcomes, such as infection severity or patient mortality. This complexity suggests that factors beyond gene presence may influence disease progression and outcomes. This study emphasizes the importance of continued surveillance and molecular epidemiological studies to combat the spread of multidrug-resistant (MDR) Acinetobacter non-baumannii strains. The findings provide valuable insights into the epidemiology and genetic characteristics of this bacteria in southern Thailand, with implications for infection control and antimicrobial management efforts.

Safety and effectiveness of tigecycline combination therapy in renal transplant patients with infection due to carbapenem-resistant gram-negative bacteria

Background

Carbapenem-resistant gram-negative bacterial (CRGNB) infections are increasing among kidney transplant recipients, and effective therapeutic options are limited. This study aimed to investigate the efficacy and adverse events associated with combination therapy tigecycline in renal transplant patients with CRGNB infections.

Methods

This study retrospectively analyzed 40 Chinese patients with confirmed or suspected CRGNB infections who received tigecycline therapy. The patients' case features and clinical and microbiological data were analyzed.

Results

A total of 40 renal transplant recipients received tigecycline therapy for a median duration of 9 (range, 3-25) days. CRGNB isolates were obtained from the organ preservation solution of the donor kidney in 28 patients, with confirmed transmission in 4 patients. Infections were detected in the bloodstream, urinary tract, sputum, and wound. The most prevalent isolates were Klebsiella pneumoniae (75%, 30/40), Acinetobacter baumannii (15%, 6/40), and Escherichia coli (10%, 4/40). A clinical response was observed in 32 (80%) patients. The 28-day all-cause mortality rate was 7.5% (3/40), while the one-year all-cause mortality rate was 2.5% (1/40). While one patient died owing to severe pancreatitis, no serious adverse events related to tigecycline therapy were reported. However, multiple indices of liver function and pancreatitis precursors increased after treatment with tigecycline compared to before treatment.

Conclusion

Tigecycline therapy appears to be well tolerated in renal transplant recipients with multidrug-resistant bacterial infections. Nevertheless, attention should be paid to adverse reactions related to tigecycline therapy, especially gastrointestinal reactions, and the related laboratory tests should be closely monitored.

Rational use of tigecycline and tigecycline blood concentration monitoring in patients with severe infection

Tigecycline, a tetracycline antibiotic, is widely used against antimicrobial resistance; therefore, medical staff should use tigecycline rationally to improve clinical efficacy and reduce resistance to this drug. The present study aimed to enhance the rate of rational tigecycline usage. The patients were divided into a low-dose (50 mg tigecycline twice daily, every 12 h) and a high-dose group (100 mg twice daily, every 12 h). The blood concentrations of tigecycline were examined and the area under the curve (AUC)_{0-12 h} values of the two groups were calculated. Prescriptions of tigecycline for 40 intensive care unit (ICU) cases were reviewed to evaluate the rationality of tigecycline usage. The peak plasma concentrations (the 7th administration after 1 h) of tigecycline were significantly higher in the high-dose group (2.46±0.43 µg/ml) compared with those in the low-dose group (1.25±0.16 µg/ml). The AUC_{0-12 h} was 16.35±3.09 h µg/ml in the high-dose group and 9.83±1.23 h µg/ml in the low-dose group (P<0.001). There were 29 irrational prescriptions identified, involving: i) Lack of consultation records (n=20); ii) inappropriate usage or dosage (n=17); iii) inappropriate drug selection (n=2); or iv) lack of dynamic laboratory tests to evaluate the efficacy (n=4). The irrational use of tigecycline in ICU patients is common. The rate of rational tigecycline usage can be improved by strengthening the management, training and participation of clinical pharmacists.

Guidelines for the diagnosis, treatment, prevention and control of infections caused by carbapenem-resistant gram-negative bacilli

The dissemination of carbapenem-resistant Gram-negative bacilli (CRGNB) is a global public health issue. CRGNB isolates are usually extensively drug-resistant or pandrug-resistant, resulting in limited antimicrobial treatment options and high mortality. A multidisciplinary guideline development group covering clinical infectious diseases, clinical microbiology, clinical pharmacology, infection control, and guideline methodology experts jointly developed the present clinical practice guidelines based on best available scientific evidence to address the clinical issues regarding laboratory testing, antimicrobial therapy, and prevention of CRGNB infections. This guideline focuses on carbapenem-resistant Enterobacteriales (CRE), carbapenem-resistant Acinetobacter baumannii (CRAB), and carbapenem-resistant Pseudomonas aeruginosa (CRPA). Sixteen clinical questions were proposed from the perspective of current clinical practice and translated into research questions using PICO (population, intervention, comparator, and outcomes) format to collect and synthesize relevant evidence to inform corresponding recommendations. The grading of recommendations, assessment, development and evaluation (GRADE) approach was used to evaluate the quality of evidence, benefit and risk profile of corresponding interventions and formulate recommendations or suggestions. Evidence extracted from systematic reviews and randomized controlled trials (RCTs) was considered preferentially for treatment-related clinical questions. Observational studies, non-controlled studies, and expert opinions were considered as supplementary evidence in the absence of RCTs. The strength of recommendations was classified as strong or conditional (weak). The evidence informing recommendations derives from studies worldwide, while the implementation suggestions combined the Chinese experience. The target audience of this guideline is clinician and related professionals involved in management of infectious diseases.

Tigecycline-Containing Regimens and Multi Drug-Resistant Acinetobacter baumannii: A Systematic Review and Meta-Analysis

Introduction: The use of tigecycline (TG) for the treatment of Acinetobacter baumannii is controversial. In this systematic review and meta-analysis, we aimed to better explore the safety and efficacy of TG for the treatment of multi drug-resistant (MDR) Acinetobacter. Methods: We searched PubMed/MEDLINE, Scopus, Cochrane Central, and Web of Science to identify studies reporting the clinical and microbiological efficacy and safety of regimens containing TG in patients with drug susceptibility testing (DST)-confirmed MDR A. baumannii, published until December 30, 2022. Observational studies were included if they reported clinical and microbiological efficacy of TG-based regimens. The Newcastle-Ottawa Scale (NOS) and Joana Briggs Institute (JBI) critical appraisal tool were used to assess the quality of included studies. Results: There were 30 observational studies, of which 19 studies were cohort and 11 studies were single group studies. Pooled clinical response and failure rates in the TG-containing regimens group were 58.1 (95% confidence interval [CI] 49.2-66.6) and 40.2 (95% CI 31.1-50.0), respectively. The pooled microbiological response rate was 32.1 (95% CI 19.8-47.5), and the pooled all-cause mortality rate was 41.1 (95% CI 34.1-48.4). Pooled clinical response and failure rates in the colistin-based regimens group were 52.7 (42.7-62.5) and 43.1 (33.1-53.8), respectively. The pooled microbiological response rate was 42.9 (16.2-74.5), and the pooled all-cause mortality rate was 34.3 (26.1-43.5). Conclusions: According to our results, the efficacy of the TG-based regimen is the same as other antibiotics. However, our study showed a high mortality rate and a lower rate of microbiological eradication for TG compared with colistin-based regimen. Therefore, our study does not recommend it for the treatment of MDR A. baumannii. However, this was a prevalence meta-analysis of observational studies, and for better conclusion experimental studies are required.

Synergistic Effects of a Probiotic Culture Extract and Antimicrobial Combinations against Multidrug-Resistant Acinetobacter baumannii

Background and Objectives: Developing effective treatment outcomes for multidrug-resistant Acinetobacter baumannii (MRAB) infections, with colistin and tigecycline the current frontline therapies, is challenging, because of the risk of renal toxicity and low blood concentrations of active ingredients when administered intravenously. This study aimed to identify the effect of combination therapy using conventional antimicrobial agents that are used for treating drug-resistant bacteria and the additional synergistic effect of four probiotic culture extracts isolated from the human body and Lactobacillus preparations. Materials and Methods: The antimicrobial combination and synergistic effect of adding Lactobacillus extract against 33 strains of A. baumannii isolated from pus, urine, and other specimens submitted to the Department of Laboratory Medicine of a university hospital, located in Gyeonggi-do, Korea, was investigated over a 3-year period between January 2017 and December 2019. Results: Antimicrobial susceptibility tests on bacteria isolated in clinical practice demonstrated that 26 strains (79%) were MRAB, while multi-locus sequence typing indicated that ST191 was the predominant type (45%; n = 15). Checkerboard test results demonstrated that combination therapy using meropenem and colistin had the highest synergistic effect (fractional inhibitory concentration index = 0.5), while the time-kill assay test using Lactobacillus spp. culture extract exhibited an inhibitory effect within 1 h and complete inhibition of MRAB within 3 h. Lactobacillus paracasei exhibited the fastest antimicrobial reactivity and longest sustained antimicrobial activity. Conclusion: These findings provide useful foundational data for an appropriate combination of colistin with other antimicrobial agents for treating MRAB infection in clinical settings, and the use of various probiotic culture extracts to reduce the required dosage, and therefore toxicity of colistin.

Successful treatment of pan-drug resistant Acinetobacter baumannii nosocomial meningitis/ventriculitis by combined intravenous and intrathecal colistin-tigecycline administration: a case series

BACKGROUND

This study aims to evaluate the efficacy of combined intraventricular and intravenous co-administration of colistin and tigecycline in the management of pan-drug resistant Acinetobacter baumannii meningitis/ventriculitis.

METHODS

In this case series we report 3 patients with healthcare-associated ventriculitis/meningitis caused by pan-drug resistant Acinetobacter baumannii that were treated with combined colistin and tigecycline administration through both intraventricular and intravenous routes.

RESULTS

All patients were administered colistin intraventricularly at a dose of 250.000 IU q.d. and intravenously at 9 million IU loading dose, followed after 12 hours by maintenance dose of 4.5 million IU every 12 hours and tigecycline intraventricularly at a dose of 10 mg b.i.d. and intravenously at 200 mg loading dose followed after 12 hours by 100 mg every 12 hours. In patients with a calculated creatinine clearance of less than 60 ml/min, according to the Cockcroft-Gault formula, the maintenance dose of colistin was reduced based on a modified formula. All patients had a favourable clinical and microbiological response with evidence of CSF sterilization.

CONCLUSIONS

Taking advantage of the synergistic action of combined colistin and tigecycline through administration both intraventricularly and intravenously may be a promising salvage option for critically ill patients with pan-drug resistant A. baumannii CNS infection.

Efficacy of Fosfomycin-Containing Regimens for Treatment of Bacteremia Due to Pan-Drug Resistant Acinetobacter baumannii in Critically Ill Patients: A Case Series Study

Acinetobacter baumannii (AB) has evolved over the last decades as a major problem in carbapenem-resistant gram-negative nosocomial infections, associated with high mortality rates especially in the intensive care unit (ICU). Recent reports highlight the increasing prevalence of resistance to colistin, a last resort therapeutic option for carbapenem-resistant AB. We retrospectively evaluated the characteristics, treatment regimens and outcomes of twenty patients with pan-drug resistant (PDR) AB primary bacteremia hospitalized in the ICU of the University General Hospital of Patras, during a two-year period (October 2020-September 2022). The 28-day mortality reached 50%. Between survivors and non-survivors, no differences were found regarding age, gender, and Charlson comorbidity index (CCI). However, non-survivors had higher APACHE II scores and higher prevalence of septic shock and COVID-19 infection. A significantly higher percentage in the survivor group received Fosfomycin as part of the combination regimen. Inclusion of fosfomycin in the combination therapeutic regimen was associated with significantly better survival as compared to non-fosfomycin-containing regimens. In view of the increasing prevalence of PDR-AB infections in ICUs, its associated high rates of mortality and the lack of effective treatment options, the observed survival benefit with fosfomycin inclusion in the therapeutic regimen merits further validation in larger prospective studies.

Efficacy and Safety of Colistin versus Tigecycline for Multi-Drug-Resistant and Extensively Drug-Resistant Gram-Negative Pathogens-A Meta-Analysis

Background: We intended to compare the efficacy and safety outcomes of colistin versus tigecycline as monotherapy or combination therapy against multi-drug resistant (MDR) and extensively drug-resistant (XDR) pathogens. Methods: A search was conducted in PubMed, Cochrane CENTRAL, EMBASE, and in the grey literature (i.e., ClinicalTrials.gov and Google Scholar) up to May 2021. Outcomes were clinical response, mortality, infection recurrence, and renal and hepatic toxicity. We pooled odd ratios (OR) using heterogeneity-guided random or fixed models at a statistical significance of p < 0.05. Results: Fourteen observational studies involving 1163 MDR/XDR pathogens, receiving tigecycline versus colistin monotherapy or combination, were included. Base-case analyses revealed insignificant differences in the clinical response, reinfection, and hepatic impairment. The 30-day mortality was significantly relatively reduced with tigecycline monotherapy (OR = 0.35, 95% CI 0.16−0.75, p = 0.007). The colistin monotherapy significantly relatively reduced in-hospital mortality (OR = 2.27, 95%CI 1.24−4.16, p = 0.008). Renal impairment rates were lower with tigecycline monotherapy or in combination, and were lower with monotherapy versus colistin-tigecycline combination. Low-risk of bias and moderate/high evidence quality were associated with all studies. Conclusions: Within the limitations of this study, it can be concluded that there were no statistically significant differences in main efficacy outcomes between colistin and tigecycline monotherapies or combinations against MDR/XDR infections, except for lower rates of 30-day mortality with tigecycline and in-hospital mortality with colistin. Tigecycline was associated with favourable renal toxicity outcomes.

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.

Sulbactam combined with tigecycline improves outcomes in patients with severe multidrug-resistant Acinetobacter baumannii pneumonia

Background

The purpose of this study was to review the treatment plan of patients with multidrug-resistant Acinetobacter baumannii (MDR-AB) pneumonia and analyze the factors associated with patient deaths and the medication regimen.

Methods

We collected 1,823 qualified respiratory specimens that were culture-positive for MDR-AB. 166 patients confirmed to have hospital-acquired MDR-AB pneumonia were selected as the research subjects. The differing clinical characteristics and treatment interventions between the surviving group and death group within 28 days were analyzed.

Results

The mortality rate was high for those aged > 75 years (p = 0.001). Patients who underwent invasive catheter placement (p < 0.001) and mechanical ventilation (p = 0.046) had a higher mortality rate. Combination therapy with tigecycline can reduce the mortality rate (p < 0.001) of MDR-AB pneumonia in patients with carbapenem-resistant AB(CRAB). Combination therapy with sulbactam was shown to reduce the mortality rate (p < 0.001), and high-dose sulbactam (> 3 g/day) might be better than low-dose sulbactam (≤ 3 g/day).

Conclusion

Reducing the time of invasive catheter placement and mechanical ventilation in patients in the intensive care unit (ICU), antimicrobial treatment, combined with tigecycline and sulbactam, might help reduce the mortality rate in patients with severe MDR-AB hospital-acquired pneumonia.

Recommendations and guidelines for the treatment of infections due to multidrug resistant organisms

Antimicrobial drug resistance is one of the major threats to global health. It has made common infections increasingly difficult or impossible to treat, and leads to higher medical costs, prolonged hospital stays and increased mortality. Infection rates due to multidrug-resistant organisms (MDRO) are increasing globally. Active agents against MDRO are limited despite an increased in the availability of novel antibiotics in recent years. This guideline aims to assist clinicians in the management of infections due to MDRO. The 2019 Guidelines Recommendations for Evidence-based Antimicrobial agents use in Taiwan (GREAT) working group, comprising of infectious disease specialists from 14 medical centers in Taiwan, reviewed current evidences and drafted recommendations for the treatment of infections due to MDRO. A nationwide expert panel reviewed the recommendations during a consensus meeting in Aug 2020, and the guideline was endorsed by the Infectious Diseases Society of Taiwan (IDST). This guideline includes recommendations for selecting antimicrobial therapy for infections caused by carbapenem-resistant Acinetobacter baumannii, carbapenem-resistant Pseudomonas aeruginosa, carbapenem-resistant Enterobacterales, and vancomycin-resistant Enterococcus. The guideline takes into consideration the local epidemiology, and includes antimicrobial agents that may not yet be available in Taiwan. It is intended to serve as a clinical guide and not to supersede the clinical judgment of physicians in the management of individual patients.

Pharmacokinetics and pharmacodynamics of peptide antibiotics

Antimicrobial resistance is a major global health challenge. As few new efficacious antibiotics will become available in the near future, peptide antibiotics continue to be major therapeutic options for treating infections caused by multidrug-resistant pathogens. Rational use of antibiotics requires optimisation of the pharmacokinetics and pharmacodynamics for the treatment of different types of infections. Toxicodynamics must also be considered to improve the safety of antibiotic use and, where appropriate, to guide therapeutic drug monitoring. This review focuses on the pharmacokinetics/pharmacodynamics/toxicodynamics of peptide antibiotics against multidrug-resistant Gram-negative and Gram-positive pathogens. Optimising antibiotic exposure at the infection site is essential for improving their efficacy and minimising emergence of resistance.

Infections Due to Acinetobacter baumannii-calcoaceticus Complex: Escalation of Antimicrobial Resistance and Evolving Treatment Options

Bacteria within the genus Acinetobacter (principally A. baumannii-calcoaceticus complex [ABC]) are gram-negative coccobacilli that most often cause infections in nosocomial settings. Community-acquired infections are rare, but may occur in patients with comorbidities, advanced age, diabetes mellitus, chronic lung or renal disease, malignancy, or impaired immunity. Most common sites of infections include blood stream, skin/soft-tissue/surgical wounds, ventilator-associated pneumonia, orthopaedic or neurosurgical procedures, and urinary tract. Acinetobacter species are intrinsically resistant to multiple antimicrobials, and have a remarkable ability to acquire new resistance determinants via plasmids, transposons, integrons, and resistance islands. Since the 1990s, antimicrobial resistance (AMR) has escalated dramatically among ABC. Global spread of multidrug-resistant (MDR)-ABC strains reflects dissemination of a few clones between hospitals, geographic regions, and continents; excessive antibiotic use amplifies this spread. Many isolates are resistant to all antimicrobials except colistimethate sodium and tetracyclines (minocycline or tigecycline); some infections are untreatable with existing antimicrobial agents. AMR poses a serious threat to effectively treat or prevent ABC infections. Strategies to curtail environmental colonization with MDR-ABC require aggressive infection-control efforts and cohorting of infected patients. Thoughtful antibiotic strategies are essential to limit the spread of MDR-ABC. Optimal therapy will likely require combination antimicrobial therapy with existing antibiotics as well as development of novel antibiotic classes.

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.

Infectious Diseases Society of America Guidance on the Treatment of AmpC β-lactamase-Producing Enterobacterales, Carbapenem-Resistant Acinetobacter baumannii, and Stenotrophomonas maltophilia Infections

BACKGROUND

The Infectious Diseases Society of America (IDSA) is committed to providing up-to-date guidance on the treatment of antimicrobial-resistant infections. A previous guidance document focused on infections caused by extended-spectrum β-lactamase-producing Enterobacterales (ESBL-E), carbapenem-resistant Enterobacterales (CRE), and Pseudomonas aeruginosa with difficult-to-treat resistance (DTR-P. aeruginosa). Here, guidance is provided for treating AmpC β-lactamase-producing Enterobacterales (AmpC-E), carbapenem-resistant Acinetobacter baumannii (CRAB), and Stenotrophomonas maltophilia infections.

METHODS

A panel of six infectious diseases specialists with expertise in managing antimicrobial-resistant infections formulated questions about the treatment of AmpC-E, CRAB, and S. maltophilia infections. Answers are presented as suggestions and corresponding rationales. In contrast to guidance in the previous document, published data on optimal treatment of AmpC-E, CRAB, and S. maltophilia infections are limited. As such, guidance in this document is provided as "suggested approaches" based on clinical experience, expert opinion, and a review of the available literature. Because of differences in the epidemiology of resistance and availability of specific anti-infectives internationally, this document focuses on the treatment of infections in the United States.

RESULTS

Preferred and alternative treatment suggestions are provided, assuming the causative organism has been identified and antibiotic susceptibility results are known. Approaches to empiric treatment, duration of therapy, and other management considerations are also discussed briefly. Suggestions apply for both adult and pediatric populations.

CONCLUSIONS

The field of antimicrobial resistance is highly dynamic. Consultation with an infectious diseases specialist is recommended for the treatment of antimicrobial-resistant infections. This document is current as of September 17, 2021 and will be updated annually. The most current versions of IDSA documents, including dates of publication, are available at www.idsociety.org/practice-guideline/amr-guidance-2.0/.

In vitro and in vivo Activity of Combinations of Polymyxin B with Other Antimicrobials Against Carbapenem-Resistant Acinetobacter baumannii

Purpose

To study the in vitro and in vivo antibacterial activities of polymyxin B (PB) and other five antimicrobial agents, including imipenem (IMP), meropenem (MEM), tigecycline (TGC), sulbactam (SUL), and rifampicin (RIF), alone or in combination against carbapenem-resistant Acinetobacter baumannii (CRAB).

Methods

Microbroth dilution method was used to determine the minimum inhibitory concentration (MIC) of ten strains of CRAB against six antibacterial drugs, and the checkerboard method was used to determine the fractional inhibitory concentration index (FICI). A mouse pneumonia model was established by intranasal instillation of Ab5075 to evaluate the antibacterial activity in vivo.

Results

The resistance rate of ten CRAB strains to IMP, MEM, and SUL was 100%, that to PB and TGC was 0%, and that to RIF was 20%. When PB was used in combination with the other five antibiotics in vitro, it mainly showed synergistic and additive effects on CRAB. The synergistic effect of PB and RIF was maximal, followed by MEM and IMP but was weak with SUL and TGC. In vivo, compared to the model group (untreated with antibiotics), treatment group (six antibiotics alone and PB combined with the other five antibiotics) reduced the bacterial load in the lung tissue and the serum inflammatory factors (IL-1β, IL-6, and TNF-α). The bacterial load and the inflammatory factors of the combined group decreased significantly than that of the single group (P<0.05). The IL-6 and TNF-α values of the PB combined with the RIF group were significantly lower than the two drugs used individually.

Conclusion

The combination of PB and IMP, MEM, and RIF exerted robust in vitro synergistic effects on CRAB isolates. The combination of PB and the other five antimicrobial agents had a better effect in the mouse pneumonia model than single agent, while the combination of PB and RIF had the best effect.

Clinical Outcomes and Safety of Meropenem-Colistin versus Meropenem-Tigecycline in Patients with Carbapenem-Resistant Acinetobacter baumannii Pneumonia

This study compared the clinical outcomes and safety of meropenem–colistin versus meropenem–tigecycline in the treatment of adult patients with carbapenem-resistant Acinetobacter baumannii (CRAB) pneumonia. A retrospective observational study of patients with CRAB pneumonia was performed at a 1048-bed university-affiliated hospital in the Republic of Korea between June 2013 and January 2020. All adult patients initially treated with meropenem–colistin were compared with those treated with meropenem–tigecycline to evaluate in-hospital mortality and adverse events. Altogether, 66 patients prescribed meropenem–colistin and 24 patients prescribed meropenem–tigecycline were included. All patients had nosocomial pneumonia, and 31.1% had ventilator-associated pneumonia. The minimum inhibitory concentrations of meropenem ≤ 8 μg/mL and tigecycline ≤ 2 μg/mL were 20.0% and 81.1%, respectively. The in-hospital and 28-day mortality rates were 40% and 32%, respectively. In the Cox proportional hazard regression analysis, predictors associated with in-hospital mortality included procalcitonin ≥ 1 ng/mL (adjusted hazard ratio (aHR), 3.39; 95% confidence interval (CI) 1.40–8.19; p = 0.007) and meropenem–colistin combination therapy (aHR, 2.58; 95% CI, 1.07–6.23; p = 0.036). Episodes of nephrotoxicity were significantly more common in the meropenem–colistin group than in the meropenem–tigecycline group (51.5% vs. 12.5%, p = 0.001). Meropenem–tigecycline combination therapy might be a valuable treatment option for patients with CRAB pneumonia.

Treatment of patients with serious infections due to carbapenem-resistant Acinetobacter baumannii: How viable are the current options?

This review critically appraises the published microbiologic and clinical data on the treatment of patients with carbapenem-resistant Acinetobacter baumannii infections. Despite being recognized as an urgent threat pathogen by the CDC and WHO, optimal treatment of patients with serious CRAB infections remains ill-defined. Few commercially available agents exhibit reliable in vitro activity against CRAB. Historically, polymyxins have been the most active agents in vitro, though interpretations of susceptibility data are difficult given issues surrounding MIC testing methodologies and lack of correlation between MICs and clinical outcomes. Most available preclinical and clinical data involve use of polymyxins, tetracyclines, and sulbactam, alone and in combination. As the number of viable treatment options is limited, combination therapy with a polymyxin is often used for patients with CRAB infections, despite the significant risk of nephrotoxicity. However, no treatment regimen has been found to reduce mortality, which exceeds 40% across most studies, or substantially improve clinical response. While some newer agents, such as eravacycline and cefiderocol, have demonstrated in vitro activity, clinical efficacy has not been fully established. New agents with clinically relevant activity against CRAB isolates and favorable toxicity profiles are sorely needed.

Clinical Features and Antimicrobial Susceptibility of Pseudomonas aeruginosa and Acinetobacter baumannii Complex Isolates in Intensive Care Patients with Chronic Obstructive Pulmonary Disease and Community-Acquired Pneumonia in Taiwan

Purpose

Little is known about the features and implications of Pseudomonas aeruginosa (PA) and Acinetobacter baumannii complex (ABC) isolates discovered in patients with chronic obstructive pulmonary disease (COPD) and community-acquired pneumonia (CAP) requiring invasive mechanical ventilation and admission to an intensive care unit. Thus, our study aimed to investigate the clinical characteristics and antimicrobial susceptibilities of PA and ABC isolates cultured from endotracheal aspirates (EAs) in such population.

Patients and Methods

In this retrospective, cross-sectional study, clinical data from medical records were reviewed and collected for analysis.

Results

Of the 262 participants, 17.2% (45/262), 11.5% (30/262), and 27.1% (71/262) had PA, ABC, and any of the two isolates discovered from EA cultures, respectively. Patients with PA isolates were associated with poorer lung function (the Global Initiative for Chronic Obstructive Lung Disease (GOLD) III+IV versus GOLD I+II, odds ratio (OR)=2.39, p= 0.022) and a lower body mass index (per increase of 1 kg/m², OR= 0.93, p= 0.106) while the former was an independent predictor. Moreover, both subjects with ABC isolates and those with any of these two microorganisms were independently associated with a lower serum albumin level (per increase of 1 g/dL, OR= 0.44, p=0.009 and OR= 0.59, p=0.023, respectively). Participants with PA isolates were more likely to have failed weaning (62.2% versus 44.7%, p= 0.048) and death (28.9% versus 12.4%, p= 0.010) than those without PA isolates. The majority of the PA and ABC isolates were susceptible and resistant to all the tested antimicrobials, respectively, except that tigecycline had a reliable activity against ABC.

Conclusion

Our findings provide important information to help intensivists make better treatment decisions in critically ill patients with COPD and CAP.

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.

Tigecycline antibacterial activity, clinical effectiveness, and mechanisms and epidemiology of resistance: narrative review

Tigecycline is unique glycylcycline class of semisynthetic antimicrobial agents developed for the treatment of polymicrobial infections caused by multidrug-resistant Gram-positive and Gram-negative pathogens. Tigecycline evades the main tetracycline resistance genetic mechanisms, such as tetracycline-specific efflux pump acquisition and ribosomal protection, via the addition of a glycyclamide moiety to the 9-position of minocycline. The use of the parenteral form of tigecycline is approved for complicated skin and skin structure infections (excluding diabetes foot infection), complicated intra-abdominal infections, and community-acquired bacterial pneumonia in adults. New evidence also suggests the effectiveness of tigecycline for the treatment of severe Clostridioides difficile infections. Tigecycline showed in vitro susceptibility to Coxiella spp., Rickettsia spp., and multidrug-resistant Neisseria gonnorrhoeae strains which indicate the possible use of tigecycline in the treatment of infections caused by these pathogens. Except for intrinsic, or often reported resistance in some Gram-negatives, tigecycline is effective against a wide range of multidrug-resistant nosocomial pathogens. Herein, we summarize the currently available data on tigecycline pharmacokinetics and pharmacodynamics, its mechanism of action, the epidemiology of tigecycline resistance, and its clinical effectiveness.

Polymyxin Monotherapy vs. Combination Therapy for the Treatment of Multidrug-resistant Infections: A Systematic Review and Meta-analysis

Objectives

The objective of this review was to compare the effectiveness of Colistin monotherapy and combination therapy for the treatment of multidrug-resistant gram-negative bacterial infections.

Data sources

PubMed, Cochrane Library.

Study eligibility interventions and exclusions

In this systematic review, we included all retrospective and prospective studies and randomized controlled trials (RCTs) that compared intravenous polymyxin monotherapy and combination therapy with any other antibiotic for treating multidrug-resistant infections. Studies using inhaled polymyxins with 5 or less than 5 patients were excluded. The primary outcome was 30-day all-cause mortality and if not reported at day 30 we extracted and documented the closest time point. Both crude outcome rates and adjusted effect estimates were extracted for mortality.

Study appraisal data extraction and synthesis

Search string used was "(Colistin OR polymyxin) AND (Enterobacteriaceae OR Klebsiella OR Acinetobacter OR Escherichia coli OR Pseudomonas) AND (random OR prospective OR retrospective OR cohort OR observational OR blind)." Thirty-nine studies were included in our analysis; out of which 6 RCTs were included and 9 studies used carbapenem as the adjunctive antibiotic. Each study was screened and reviewed for eligibility independently by two authors and data extrapolated on an Excel sheet.

Results

The meta-analysis of polymyxin monotherapy vs. combination therapy in multidrug-resistant infections yielded an odds ratio (OR) of 0.81 (95% confidence interval [CI]: 0.65-1.01) with minimal heterogeneity (I ² = 40%), whereas pooled analysis of this comparison in studies that included carbapenem as combination therapy yielded an OR of 0.64 (CI: 0.40-1.03; I ² = 62%). Likewise, the pooled analysis of the RCTs yielded an OR of 0.82 (95% CI: 0.58-1.16, I ² = 22%). All these showed no statistical significance. However, it was seen that polymyxin combination therapy was more effective in multidrug-resistant infections compared to polymyxin monotherapy. The effectiveness was more glaring when carbapenems were used as the combination drug instead of any other antibiotic and more so in many in vitro studies that used polymyxin combination therapy.

Conclusion

Although statistically insignificant, it would be prudent to use polymyxin combination therapy to treat multidrug-resistant gram-negative bacilli (GNB) infection over monotherapy with preference to use carbapenem as the adjunct alongside polymyxins.

How to cite this article

Samal S, Mishra SB, Patra SK, Rath A, Dash A, Nayak B, et al. Polymyxin Monotherapy vs. Combination Therapy for the Treatment of Multidrug-resistant Infections: A Systematic Review and Meta-analysis. Indian J Crit Care Med 2021;25(2):199-206.

Synergistic Effect of Tazobactam on Amikacin MIC in Acinetobacter baumannii Isolated from Burn Patients in Tehran, Iran

BACKGROUND

Burn is still an important global public health challenge. Wound colonization of antibiotic resistant bacteria such as Acinetobacter baumannii can lead to high morbidity and mortality in burn patients. The aim of this study was to evaluate the inhibitory effect of tazobactam on efflux pump, which can cause aminoglycoside resistant in A. baumannii isolated from burn patients.

METHODS

In this study, 47 aminoglycoside resistant A. baumannii spp. were obtained from burn patients, admitted to the Shahid Motahari Burns Hospital in Tehran, Iran, during June-August 2018. The inhibitory effect of tazobactam against adeB such as efflux pump was evaluated by Minimum Inhibitory Concentration (MIC) determination of amikacin alone and in combination with tazobactam. Fractional Inhibitory Concentration index (FIC) was used to determine the efficacy of tazobactam/ amikacin combination. Further, semi-quantitative Real- Time PCR was performed to quantify the expression rates of the adeB gene before and after addition of tazobactam/amikacin.

RESULTS

The MIC values were significantly reduced when a combined amikacin and tazobactam was utilized. The most common interaction observed was synergistic (78.2%), followed by.additive effects (21.8%), as per FIC results. The adeB mRNA expression levels were found to be downregulated in 60.7% of isolates treated with tazobactam.

CONCLUSION

Tazobactam can have impact on resistance to aminoglycoside by inhibiting efflux pump. Thus, the combination of tazobactam with amikacin can be used as an alternative treatment approach in multidrug resistant A. baumannii infections.

Influence of severity of infection on the effect of appropriate antimicrobial therapy for Acinetobacter baumannii bacteremic pneumonia

Background

The impact of appropriate antimicrobial therapy for A. baumannii bacteremic pneumonia has not been well established due to the inclusion of the three phenotypically indistinguishable Acinetobacter species and confounding factors including underlying diseases and severity of infection. This retrospective study aimed to evaluate the impact of appropriate antimicrobial therapy on 14-day mortality in A. baumannii bacteremic pneumonia patients after adjusting for risk factors.

Methods

This study was conducted at five medical centers in Taiwan between July 2012 and June 2016. A. baumannii species identification was performed using reference molecular methods. Risk factors for 14-day mortality were analyzed via logistic regression. The interaction between the Acute Physiology and Chronic Health Evaluation (APACHE) II score and appropriate antimicrobial therapy was assessed using the logistic model.

Results

A total of 336 patients with monomicrobial A. baumannii bacteremic pneumonia were included in this study. The overall 14-day mortality rate was 47.3%. The crude mortality of appropriate antimicrobial therapy was 35.9% (57 of 151 patients). Appropriate antimicrobial therapy was associated with a lower mortality after multivariate adjustment (odds ratio [OR], 0.57; 95% confidence interval [CI], 0.34–0.97; p = 0.04), and the effect was influenced by APACHE II score (OR for interaction term, 0.0098; 95% CI, 0.0005–0.1885; p = 0.002). Further analysis demonstrated that appropriate antimicrobial therapy significantly reduced 14-day mortality among the patients with an APACHE II score > 35 (OR 0.0098; 95% CI 0.0005–0.1885).

Conclusion

Appropriate antimicrobial therapy decreases 14-day mortality of the most severely ill patients with A. baumannii bacteremic pneumonia.

Efficacy and safety of tigecycline in treatment of pneumonia caused by MDR Acinetobacter baumannii: a systematic review and meta-analysis

BACKGROUND

Use of tigecycline in treating MDR Acinetobacter baumannii (MDRAB) remains controversial.

OBJECTIVES

To comprehensively assess the safety and efficacy of tigecycline in pneumonia caused by Acinetobacter baumannii.

METHODS

PubMed, Embase, Web of Science and Cochrane library databases were searched up to 12 March 2019. Studies were included if they compared tigecycline-based regimens with other antibiotic regimens for treating AB pulmonary infections and we pooled the clinical outcomes, microbiological response, adverse events or mortality.

RESULTS

One prospective study and nine retrospective studies were included in this meta-analysis. The results showed similar clinical cure rates (OR = 1.04, 95% CI = 0.60-1.81; P = 0.89) and mortality rates (OR = 1.11, 95% CI = 0.65-1.89; P = 0.71) comparing tigecycline groups with the control groups. However, a significantly lower microbiological eradication rate was found in the tigecycline groups (OR = 0.43, 95% CI = 0.27-0.66; P = 0.0001). Incidence of nephrotoxicity in tigecycline-based regimens was significantly lower than in colistin-based regimens (OR = 0.34, 95% CI = 0.16-0.74, I2 = 35%, P = 0.006). There were no randomized controlled trials (RCTs) included; incomplete safety data and regional bias caused by the majority of the studies originating in China are the main limitations of this meta-analysis.

CONCLUSIONS

Tigecycline can be used for treating MDRAB pulmonary infections owing to efficacy similar to that of other antibiotics. Moreover, tigecycline did not show a higher risk of mortality. Considering the lower microbiological eradication rate for tigecycline, which is likely to induce antimicrobial resistance, well-designed RCTs for high-dose tigecycline in treating pneumonia caused by AB are still needed.

Effect of pharmacokinetic/pharmacodynamic ratio on tigecycline clinical response and toxicity in critically ill patients with multidrug-resistant Gram-negative infections

Introduction:

The information about the pharmacokinetics and optimal dose of tigecycline in critically ill patients with severe underlying diseases is limited and controversial. In this study, we evaluate the pharmacokinetic parameters of tigecycline in critically ill patients with multidrug-resistant Gram-negative infection and explore the association between the pharmacokinetic/pharmacodynamic ratio and treatment response.

Methods:

A prospective study was designed including critically ill patients treated with tigecycline for multidrug-resistant Gram-negative infections. Blood samples were collected at day 3–5 of treatment, and pharmacokinetics parameters were evaluated using NONMEM^® software. Relationship between area under the free concentration–time curve and minimum inhibitory concentration ratio (fAUC/MIC) and treatment failure was evaluated. Association between tigecycline fAUC and hepatobiliary toxicity was also investigated.

Results:

Twenty-five critically ill patients were included in the study. In the pharmacokinetic model, weight and total bilirubin level were found to be significant predictors of tigecycline clearance. Fifteen (60.0%) patients achieved an fAUC/MIC ratio >4.5, seven (28.0%) an fAUC/MIC > 6.96 and only three (12.0%) an fAUC/MIC > 17.9. No differences in fAUC/MIC ratio were obtained between those patients with and without clinical failure (5.28 (IC95%: 2.57–7.94) vs 8.71 (3.57–13.84)). fAUC values were higher in those patients who suffered hepatobiliary disorders (7.63 (3.93–11.34) vs 17.63 (7.85–26.28) mg/L/h).

Conclusion:

An important percentage of critically ill patients with multidrug-resistant Gram-negative infection treated with tigecycline do not achieve an appropriate pharmacokinetic/pharmacodynamic value. Tigecycline fAUC seems to be associated with hepatobiliary disorders in this study population. The effect of fAUC/MIC ratio on clinical response remains unclear.

Comparative efficacy and safety of combination therapy with high-dose sulbactam or colistin with additional antibacterial agents for multiple drug-resistant and extensively drug-resistant Acinetobacter baumannii infections: A systematic review and network meta-analysis

OBJECTIVES

This study aimed to compare the efficacy and safety of combination therapy with high-dose sulbactam or colistin with additional antibacterial agents for treating multidrug-resistant or extensively drug-resistant Acinetobacter baumannii (MDR-AB or XDR-AB) infections.

METHODS

We systematically searched PubMed, Embase, Cochrane, and Web of Science (through March 30, 2020) for studies that examined high-dose sulbactam or colistin with additional antibacterial agents as therapy for patients with infections with MDR-AB and XDR-AB. Through a network meta-analysis (NMA), using both direct and indirect evidence, we determined risk ratios and 95% confidence intervals. Primary outcomes included clinical improvement, clinical cure, microbiological eradication, and mortality from any cause. Secondary outcomes included nephrotoxicity.

RESULTS

The NMA included 18 studies and 1835 patients. We found that high-dose sulbactam (≥6 g per day), combined with another single antibacterial agent (levofloxacin or tigecycline), which were the highest ranking in clinical improvement and clinical cure. Still colistin-based combination in drug-resistant Acinetobacter baumannii therapy occupied the main position (the number of studies and patients) in most studies. Colistin combined with additional antibacterial agents was associated with a higher risk of nephrotoxicity.

CONCLUSIONS

Therapeutic regimens including high-dose sulbactam in combination with additional antibacterial agents (including colistin) might be one of the promising options for the treatment of MDR-AB or XDR-AB infections and high-quality study will be needed to confirm clinical efficacy.

How should we treat acinetobacter pneumonia?

PURPOSE OF REVIEW

To describe recent data about Acinetobacter baumannii pneumonia epidemiology and the therapeutic options including adjunctive nebulized therapy.

RECENT FINDINGS

A. baumannii is a major cause of nosocomial pneumonia in certain geographic areas affecting mainly debilitated patients, with prolonged hospitalization and broad-spectrum antimicrobials. Inappropriate empirical treatment has clearly been associated with increased mortality in A. baumannii pneumonia. Carbapenems may not be considered the treatment of choice in areas with high rates of carbapenem-resistant A. baumannii. Nowadays, polymyxins are the antimicrobials with the greatest level of in-vitro activity. Colistin is the antimicrobial most widely used although polymyxin B is associated with less renal toxicity. It is clear that lung concentrations of polymyxins are suboptimal in a substantial proportion of patients. This issue has justified the use of combination therapy or adjunctive nebulized antibiotics. Current evidence does not allow us to recommend combination therapy for A. baumannii pneumonia. Regarding nebulized antibiotics, it seems reasonable to use in patients who are nonresponsive to systemic antibiotics or A. baumannii isolates with colistin minimum inhibitory concentrations close to the susceptibility breakpoints. Cefiderocol, a novel cephalosporin active against A. baumannii, may represent an attractive therapeutic option if ongoing clinical trials confirm preliminary results.

SUMMARY

The optimal treatment for multidrug-resistant A. baumannii pneumonia has not been established. New therapeutic options are urgently needed. Well designed, randomized controlled trials must been conducted to comprehensively evaluate the effectiveness and safety of nebulized antibiotics for the treatment of A. baumannii pneumonia.

Managing Acinetobacter baumannii infections

PURPOSE OF REVIEW

We reviewed recent data about epidemiology of Acinetobacter baumannii, resistance mechanisms, and therapeutic options for severe infections caused by multidrug-resistant strains.

RECENT FINDINGS

A. baumannii is a major cause of nosocomial infections affecting mainly to debilitating patients in the ICU, although the spread to regular wards and to long-term care facilities is increasing. It is characterized by its great persistence in the environment and to have an extraordinary capability to develop resistance to all antimicrobials.Carbapenems may not be considered the treatment of choice in areas with high rates of carbapenem-resistant A. baumannii. Nowadays, polymyxins are the antimicrobials with the greatest level of in-vitro activity against A. baumannii. Colistin is the most widely used in clinical practice although polymyxin B seems to be associated with less renal toxicity. Colistin is administered intravenously as its inactive prodrug colistimethate. A loading dose of 9 million IU and subsequently high, extended-interval maintenance doses (4.5 million IU/12 h) are recommended. Combination therapy instead of monotherapy increases the rates of microbiological eradication although no clinical study has demonstrated a reduction in clinical outcomes (mortality or length of stay).

SUMMARY

The optimal treatment for multidrug-resistant A. baumannii nosocomial infections has not been established. There are no compelling data to recommend combination therapy for severe A. baumannii infections.

Is colistin-associated acute kidney injury clinically important in adults? A systematic review and meta-analysis

Colistin is the last-resort antimicrobial agent against infections caused by multidrug-resistance Gram-negative bacteria (MDR-GNB). However, a differing risk of colistin-associated acute kidney injury (CA-AKI) has been demonstrated without affecting mortality, thus the association and its importance needs to be questioned. To assess the impact of this adverse effect, a meta-analysis comparing colistin with other antibiotics in treating MDR-GNB infections was conducted. The PubMed, Embase and Cochrane Library electronic databases were searched up to 31 December 2018 for cohort studies and randomised controlled trials with at least two arms with one arm containing colistin-based treatment. The primary endpoint was the incidence of AKI. The secondary endpoint was 30-day all-cause mortality. A total of 34 studies, including 26 regarding colistin-based therapy versus other antibiotics and 9 regarding colistin monotherapy versus combination therapy, were included. The incidence of CA-AKI was 32.3%. Colistin was associated with an 82% higher incidence of AKI than other antibiotics [odd ratio (OR) = 1.82, 95% confidence interval (CI) 1.13-2.92; P = 0.01]. Most CA-AKI events were mild and reversible without a higher rate of mortality or the requirement for renal replacement therapy (RRT). Only 1.0% of patients required RRT for > 4 weeks. Compared with colistin monotherapy, combination therapy was associated with a significantly lower incidence of AKI (OR = 1.46, 95% CI 1.10-1.94; P = 0.009), particularly in combination with a carbapenem (OR = 1.97, 95% CI 1.30-2.99; P = 0.001). In conclusion, CA-AKI might not be an important limitation of colistin in MDR-GNB therapy.

Colistin-sparing approaches with newer antimicrobials to treat carbapenem-resistant organisms: Current evidence and future prospects

Antimicrobial resistance is on the rise across the globe. Increasing incidence of infections due to carbapenem resistance organisms is becoming difficult to treat, due to the limited availability of therapeutic agents. Very few agents such as colistin, fosfomycin, tigecycline and minocycline are widely used, despite its toxicity. However, with the availability of novel antimicrobials, beta-lactam/beta-lactamase inhibitor-based and non-beta-lactam-based agents could be of great relief. This review covers three important aspects which include (i) current management of carbapenem-resistant infections, (ii) determination of specific types of carbapenemases produced by multidrug-resistant and extensively drug-resistant Gram-negative pathogens and (iii) the currently available novel beta-lactam/beta-lactamase inhibitors and non-beta-lactam-based agents' laboratory findings, clinical outcome and implications.

Extensive drug resistant Acinetobacter baumannii: a comparative study between non-colistin based combinations

Background The Gastrointestinal Surgery Center (GISC)-Mansoura University, faced a series of extensive drug resistant (XDR) A. baumannii cases, that were microbiologically resistant to penicillins, cephalosporins, fluoroquinolones, aminoglycosides, carbapenems and tigecycline. Colistin would have been a last resort therapy in such situation, however, intravenous polymyxins E (colistin) is relatively unavailable in Egypt. Many practitioners tried to form antibiotic combinations from the available antibiotics to overcome the resistance mechanisms of the pathogen. Objective Evaluate the clinical outcomes of these combinations retrospectively. Setting The study took place at the GISC, which is an academic specialized center affiliated with Mansoura University-Egypt. Method Clinical data were collected from the patients' files, where the subjects were classified into two major groups according to the therapeutic intervention. Group 1 included 24 patients divided into 4 subgroups. The first was treated by a Cephalosporin with a Fluoroquinolone (1A), The second was treated by a Carbapenem with a Fluoroquinolone (1B), The third was treated by a B-lactam with an Aminoglycoside (1C) and the fourth was treated by Carbapenem with a Glycylcycline (1D). Group 2 included 6 patients, treated with Tigecycline and Ampicillin-Sulbactam. Main outcome measure Primary outcomes are the A. baumannii microbiological culture negativity after 14 days of therapy and the 30 days' survival after the antibiotic course, while the secondary outcomes are the expected therapies' side effects. Results Group 2 is associated with significant higher primary outcomes without a significant difference regarding the secondary outcomes. Conclusion The combination of Tigecycline and Ampicillin-Sulbactam, appears to be a clinically effective therapy against XDR A. baumannii, despite each agent being resistant alone, without alerting adverse effects.

Acinetobacter Pneumonia: Improving Outcomes With Early Identification and Appropriate Therapy

In an era of increasing antimicrobial resistance, Acinetobacter distinguishes itself as one of the most resistant Gram-negative bacteria responsible for significant morbidity and mortality. New solutions are needed to combat the detrimental effects of increasing rates of antimicrobial resistance. Using empiric broad-spectrum antibiotics in patients deemed at risk for infections caused by multidrug-resistant pathogens may protect against attributable mortality, but this temporary solution furthers the risk of antimicrobial resistance. In this article we will review relevant strategies to aid with early identification and appropriate treatment of Acinetobacter pneumonia while preserving antibiotic susceptibility.

Clinical experience with tigecycline in the treatment of hospital-acquired pneumonia caused by multidrug resistant Acinetobacter baumannii

Background

Tigecycline, with broad in vitro antibacterial activity, has been widely used off-label for nosocomial pneumonia caused by multi-drug resistant Acinetobacter baumannii (MDRAB). However, many concerns have been raised about the efficacy of tigecycline treatment as the inconsistent results from previous clinical studies.

Methods

This retrospective study evaluated the outcome of adult patients with monomicrobial MDRAB nosocomial pneumonia treated with tigecycline between 2015 and 2017. Results.

A total of 77 patients was eligible for this study, and the overall clinical success and 30-day survival rates were 70.03 and 70.13%, respectively, however, the microbiological eradication rate was relatively low (48%). Multivariate analysis indicated that shorter duration of tigecycline use associated with increased clinical failure, whereas higher CURB65 scores, mechanical ventilation and tigecycline resistant to MDRAB have significant association with 30-day mortality.

Conclusions

Our results suggest that tigecycline is one of the potential choices for the treatment of hospital-acquired pneumonia caused by MDRAB, especially with a MIC≤2 mg/L. In addition, a longer duration of tigecycline treatment may be required to insure better clinical outcomes.

Evaluation of the ratio of the estimated area under the concentration-time curve to minimum inhibitory concentration (estimated AUIC) as a predictor of the outcome for tigecycline treatment for pneumonia due to multidrug-resistant bacteria in an intensive care unit

OBJECTIVES

Based on pharmacokinetics/pharmacodynamics (PK/PD) and the minimum inhibitory concentration (MIC) of tigecycline (TGC), dose increases have been advocated to maximize the efficacy against pneumonia that is suspected to be due to multidrug-resistant (MDR) bacteria in an intensive care unit. This practice-based study explored the relationship between the predicted PK parameter, the ratio of the area under the concentration-time curve to the 24 h of dosing/minimum inhibitory concentration (AUC_0-24/MIC or AUIC), and the clinical and microbiological outcomes in critically ill patients with pneumonia due to MDR bacteria.

METHODS

We conducted a prospective cohort study of the treatment of pneumonia due to MDR bacteria in an intensive care unit. The study patients were recruited and assigned to either TGC standard dose (SD, 50 mg q12 h) or high dose (HD, 100 mg q12 h) for the treatment of pneumonia due to MDR bacteria depending on the doctors' decisions. The relationships between the PK/PD parameters and outcomes were examined.

RESULTS

Over the study period, 105 patients were included in the study. Whereas C1/2, Cmin, MIC and AUC were dramatically higher in the HD group than in the SD group (all P < 0.05), the Cmax and AUIC had no difference in both groups (all P > 0.05). The patients in the HD group had a higher clinical cure rate than those in the SD group (P = 0.029), but the bacterial eradication rate and survival rate of the patients in the HD group were not better than those in SD group (P = 0.279 and 0.416, respectively). The Cmax, C1/2, Cmin and AUC in the cured group were higher than those in failure group (all P < 0.05). The MICs were dramatically higher in the failure group than those in cure group (P = 0.0001), which led to significantly lower AUICs (P = 0.0001). In the ROC analysis, the areas of Cmax, C1/2, Cmin, AUC, negative-MIC and AUIC under the ROC curve were 0.64, 0.69, 0.67, 0.66, 0.73 and 0.82, respectively. The sensitivity was ascertained to be 75% and the specificity was 89% when the AUIC cut-off value was considered to be 10.12. Moreover, the sensitivity was ascertained to be 63% and the specificity was 80% when the MIC cut-off value was considered to be 1.75 mg/L.

CONCLUSIONS

The AUIC and MIC are associated with tigecycline treatment outcomes in pneumonia due to MDR bacteria, and aiming to achieve an individualized AUIC ≥ 10.12 when MIC < 1.75 mg/L could improve outcomes.

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.

Safety and efficacy of colistin alone or in combination in adults with Acinetobacter baumannii infection: A systematic review and meta-analysis

This review comprehensively assessed the safety and efficacy of colistin alone or in combination in adults with Acinetobacter baumannii infection. PubMed, Embase and the Cochrane Library were searched from inception to March 2018 for studies evaluating colistin monotherapy compared with other antibiotic therapy or colistin-based combination therapy for the treatment of A. baumannii infection in adults. Efficacy outcomes were clinical response and microbiological cure. Safety outcomes were mortality and nephrotoxic adverse events. A total of 4 randomised controlled trials (RCTs) and 14 observational studies were identified, including 7 reporting colistin versus other antibiotics and 12 reporting colistin monotherapy versus colistin-based combination therapy. Overall clinical response, microbiological response and mortality did not differ significantly between colistin monotherapy versus other antibiotics. However, the incidence of nephrotoxicity was significantly higher in colistin monotherapy (OR = 2.50, 95% CI 1.05-5.98; P = 0.04). No significant differences were detected in clinical response and >28-day mortality between colistin monotherapy and combination therapy. However, colistin-based combination therapy showed an increased microbiological response (OR = 0.49, 95% CI 0.32-0.74; P = 0.0009) and decreased incidence of nephrotoxicity (OR = 1.66, 95% CI 0.99-2.78; P =0.05). In conclusion, colistin alone is as effective as other antibiotics for the treatment of A. baumannii infection but has a higher risk of nephrotoxicity. Colistin-based combination therapy demonstrated a microbiological benefit and no higher risk of nephrotoxicity compared with monotherapy. High-quality RCTs are still needed to confirm the beneficial role of colistin-based combination therapy.

Characteristics and Outcomes of Acinetobacter baumannii Infections in Patients with HIV: A Matched Case-Control Study

Acinetobacter baumannii (AB) infection is an increasing global threaten to hospitalized patients, especially those with impaired immune function. Still, few studies addressed the disease burdens and outcomes of AB infection in HIV patients. We aimed to describe characteristics and outcomes of AB infections in patients with HIV, measure the impact of AB infection on 28-day mortality in HIV patients, as well as assess the predictors of 28-day survival among HIV patients with AB pneumonia. A retrospective study with HIV/AB co-infected patients was conducted at Shanghai Public Health Clinical Center (SPHCC), China. Patients with AB pneumonia were further analyzed for predictors of mortality, as well as an additional 1:1 case-control study to determine the fatality of AB pneumonia compared with pneumonia of other pathogens. We found the incidence of AB infection was 17.4 cases per 100 person-years among all hospitalized HIV patients. Hospital mortality rate was 37.5% (21/56). There was a higher 28-day mortality rate in HIV patients with pneumonia due to AB than other pathogens (34% vs 16%, P = 0.03). APACHE II score was independently associated with 28-day survival by multivariate logistic regression (P = 0.031). Our findings indicate that AB infection is incident and can be fatal in HIV seropositive population. AB infection is an independent risk factor of mortality in patients with HIV and pneumonia. A lower APACHE II score on admission predicts a higher 28-day survival rate among HIV/AB co-infected patients.

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.

Tigecycline in the treatment of multidrug-resistant Acinetobacter baumannii meningitis: Results of the Ege study

OBJECTIVES

In this study we retrospectively reviewed A. baumannii meningitis cases treated with tigecycline including regimens and evaluated the efficacy of tigecycline in the therapy.

PATIENTS AND METHODS

Study was performed in seven tertiary-care educational hospitals from five cities of Turkey and one center from France. We extracted data and outcomes of all adult (aged >18) patients with culture proven A. baumannii meningitis treated with tigecycline including antibiotic therapy until April 2016.

RESULTS

A total of 23 patients (15 male and eight female) fulfilled our inclusion criteria. All Acinetobacter strains were carbapenem-resistant and susceptible to tigecycline. Six cases received tigecycline monotherapy while 17 received tigecycline including combination therapy (10 with colistin, 4 with netilmicin, 3 with amikacin, 4 with meropenem). Seven of 23 cases (30%) died during the tigecycline including therapy (1 in monotherapy, 4 in colistin, 2 in netilmicin, 1 amikacin, one case received tigecycline + netilmicin followed by tigecycline + colistin). Hence, overall end of treatment (EOT) success was 70%. However, since further 27% died due to additional nosocomial infections, overall clinical success (relieved symptoms at the EOT and one-month post-therapy survival without any relapse or reinfection) decreased to 43%.

CONCLUSION

We conclude that tigecycline may be an alternative in the salvage treatment of nosocomial multidrug-resistant Acinetobacter spp. meningitis. Acinetobacter spp. Meningitis.

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.

Emergence of antimicrobial resistance among Acinetobacter species: a global threat

PURPOSE OF REVIEW

Bacteria within the genus Acinetobacter [principally Acinetobacter baumannii-calcoaceticus complex (ABC)] are Gram-negative coccobacilli that may cause serious nosocomial infections (particularly ventilator-associated pneumonia and infections of the bloodstream, urinary tract, and wounds) as well as community-acquired infections (often skin/soft tissue infections in the context of trauma). Within the past two decades, Acinetobacter spp. have been responsible for an increasing number of infections in intensive care units (ICUs) globally. Treatment of Acinetobacter infections is difficult, as Acinetobacter spp. are intrinsically resistant to multiple antimicrobial agents, and have a remarkable ability to acquire new resistance determinants via multiple mechanisms.

RECENT FINDINGS

Since the 1990s, global resistance to antimicrobials has escalated dramatically among ABC. Global spread of multidrug-resistant (MDR) A. baumannii strains reflects dissemination of a few clones between hospitals, geographic regions, and continents; this spread is amplified by excessive use of antibiotics. Many isolates are resistant to all antimicrobials except colistin (polymyxin E), and some infections are untreatable with existing antimicrobial agents.

SUMMARY

Antimicrobial resistance poses a serious threat to control infections due to ABC. Strategies to curtail environmental colonization with MDR-ABD will require aggressive infection control efforts and cohorting of infected patients. Thoughtful antibiotic strategies are essential to limit the consequences and spread of MDR-ABC. Optimal therapy will likely require combination antimicrobial therapy of existing antibiotics as well as development of novel antibiotic classes.

Pharmacokinetic and Pharmacodynamic Considerations of Antibiotics of Last Resort in Treating Gram-Negative Infections in Adult Critically Ill Patients

PURPOSE OF REVIEW

We provide an overview of antimicrobials that are considered last resort for the treatment of resistant gram-negative infections in adult critically ill patients. The role in therapy, pharmacodynamic (PD) goals, and pharmacokinetic (PK) changes in critical illness for aminoglycosides, polymyxins, tigecycline, fosfomycin, and fluoroquinolones are summarized.

RECENT FINDINGS

Altered PK in septic patients in the intensive care unit (ICU) is observed with many of our agents of last resort. Based on the available literature, dosage adjustments may be required to optimize PK parameters and meet PD targets for most effective bacterial killing. Data is limited, studies are conducted in heterogeneous patient populations, and conclusions are frequently conflicting. Strategic dosing regimens such as high-dose extended interval dosing of aminoglycosides or loading doses with colistin and polymyxin B are examples of ways to optimize antibiotic PK in critically ill patients. Benefits of these strategies must be balanced with risks of increased toxicity. Patients with resistant gram-negative infections may present with septic shock in the ICU. Sepsis can significantly alter the PK of antibiotics and require dosage adjustments to attain optimal drug levels. An understanding of PK and PD properties of these agents of last resort will help to maximize therapeutic efficacy while minimizing toxic effects.