Tetracyclines for treating multidrug-resistant Acinetobacter baumannii ventilator-associated pneumonia

Current and novel therapies for management of Acinetobacter baumannii-associated pneumonia

Acinetobacter baumannii is a common pathogen associated with hospital-acquired pneumonia showing increased resistance to carbapenem and colistin antibiotics nowadays. Infections with A. baumannii cause high patient fatalities due to their capability to evade current antimicrobial therapies, emphasizing the urgency of developing viable therapeutics to treat A. baumannii-associated pneumonia. In this review, we explore current and novel therapeutic options for overcoming therapeutic failure when dealing with A. baumannii-associated pneumonia. Among them, antibiotic combination therapy administering several drugs simultaneously or alternately, is one promising approach for optimizing therapeutic success. However, it has been associated with inconsistent and inconclusive therapeutic outcomes across different studies. Therefore, it is critical to undertake additional clinical trials to ascertain the clinical effectiveness of different antibiotic combinations. We also discuss the prospective roles of novel antimicrobial therapies including antimicrobial peptides, bacteriophage-based therapy, repurposed drugs, naturally-occurring compounds, nanoparticle-based therapy, anti-virulence strategies, immunotherapy, photodynamic and sonodynamic therapy, for utilizing them as additional alternative therapy while tackling A. baumannii-associated pneumonia. Importantly, these innovative therapies further require pharmacokinetic and pharmacodynamic evaluation for safety, stability, immunogenicity, toxicity, and tolerability before they can be clinically approved as an alternative rescue therapy for A. baumannii-associated pulmonary infections.

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.

Treatment of ventilator-associated pneumonia due to carbapenem-resistant Gram-negative bacteria with novel agents: a contemporary, multidisciplinary ESGCIP perspective

INTRODUCTION

: In the past 15 years, treatment of VAP caused by carbapenem-resistant Gram-negative bacteria (CR-GNB) has represented an intricate challenge for clinicians.

AREAS COVERED

In this perspective article, we discuss the available clinical data about novel agents for the treatment of CR-GNB VAP, together with general PK/PD principles for the treatment of VAP, in the attempt to provide some suggestions for optimizing antimicrobial therapy of CR-GNB VAP in the daily clinical practice.

EXPERT OPINION

Recently, novel BL and BL/BLI combinations have become available that have shown potent in vitro activity against CR-GNB and have attracted much interest as novel, less toxic, and possibly more efficacious options for the treatment of CR-GNB VAP compared with previous standard of care. Besides randomized controlled trials, a good solution to enrich our knowledge on how to use these novel agents at best in the near future, while at the same time remaining adherent to current evidence-based guidelines, is to improve our collaboration to conduct larger multinational observational studies to collect sufficiently large populations treated in real life with those novel agents for which guidelines currently do not provide a recommendation (in favor or against) for certain causative organisms.

Antimicrobial Stewardship Programs: A Review of Strategies to Avoid Polymyxins and Carbapenems Misuse in Low Middle-Income Countries

Antibiotics misuse and overuse are concerning issues worldwide, especially in low middle-income countries. These practices contribute to the increasing rates of antimicrobial resistance. One efficient strategy to avoid them is antimicrobial stewardship programs. In this review, we focus on the possible approaches to spare the prescription of polymyxins and carbapenems for the treatment of Acinetobacter baumannii, carbapenem-resistant Enterobacterales, and Pseudomonas aeruginosas infections. Additionally, we highlight how to implement cumulative antibiograms and biomarkers to a sooner de-escalation of antibiotics.

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/.

Tigecycline to treat Stenotrophomonas maltophilia ventilator-associated pneumonia in a trauma intensive care unit as a result of a drug shortage: A case series

WHAT IS KNOWN AND OBJECTIVE

Stenotrophomonas maltophilia is an intrinsically multidrug-resistant (MDR) organism which commonly presents as a respiratory tract infection. S. maltophilia is typically treated with high-dose sulfamethoxazole/trimethoprim (SMX/TMP). However, SMX/TMP and other treatment options for S. maltophilia can be limited because of resistance, allergy, adverse events or unavailability of the drug; use of novel agents may be necessary to adequately treat this MDR infection and overcome these limitations.

CASE DESCRIPTION

This small case series describes two patients who underwent treatment with tigecycline for ventilator-associated pneumonia (VAP) caused by S. maltophilia after admission to a trauma intensive care unit. At the time of admission for the two reported patients, a national drug shortage of intravenous (IV) SMX/TMP prevented its use. Tigecycline was chosen as a novel agent to treat S. maltophilia VAP based on culture and susceptibility data, and it was used successfully. Both patients showed clinical signs of improvement with eventual cure and discharge from the hospital after treatment with tigecycline, and one patient demonstrated confirmed microbiological cure with a negative repeat bronchoscopic bronchoalveolar lavage (BAL).

WHAT IS NEW AND CONCLUSION

To our knowledge, this small case series is the first documentation of utilizing tigecycline to treat S. maltophilia VAP in the United States. Although it likely should not be considered as a first-line agent, tigecycline proved to be an effective treatment option in the two cases described in the setting of a national drug shortage of the drug of choice.

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.

Minocycline, focus on mechanisms of resistance, antibacterial activity, and clinical effectiveness: Back to the future

OBJECTIVES

The increasing crisis regarding multidrug-resistant (MDR) and extensively drug-resistant microorganisms leads to appealing therapeutic options.

METHODS

During the last 30 years, minocycline, a wide-spectrum antimicrobial agent, has been effective against MDR Gram-positive and Gram-negative bacterial infections. As with other tetracyclines, the mechanism of action of minocycline involves attaching to the bacterial 30S ribosomal subunit and preventing protein synthesis.

RESULTS

This antimicrobial agent has been approved for the treatment of acne vulgaris, some sexually transmitted diseases and rheumatoid arthritis. Although many reports have been published, there remains limited information regarding the prevalence, mechanism of resistance and clinical effectiveness of minocycline.

CONCLUSION

Thus, we summarize here the currently available data concerning pharmacokinetics and pharmacodynamics, mechanism of action and resistance, antibacterial activity and clinical effectiveness of minocycline.

Monotherapy versus combination therapy for multidrug-resistant Gram-negative infections: Systematic Review and Meta-Analysis

Infections caused by carbapenemase-producing, multidrug-resistant (MDR), or extensively drug-resistant (XDR) Gram-negative bacteria constitute a major therapeutic challenge. Whether combination antibiotic therapy is superior to monotherapy remains unknown. In this systematic review and meta-analysis OVID MEDLINE, EMBASE, PubMed, The Cochrane Library, and Scopus databases were searched for randomized controlled trials (RCTs) and observational studies published by December 2016 comparing mono- with combination antibiotic therapy for infections with carbapenemase-producing, MDR, or XDR Gram-negative bacteria. Mortality and clinical cure rates served as primary and secondary outcome measures, respectively. Of 8847 initially identified studies, 53 studies - covering pneumonia (n = 10 studies), blood stream (n = 15), osteoarticular (n = 1), and mixed infections (n = 27) - were included. 41% (n = 1848) of patients underwent monotherapy, and 59% (n = 2666) combination therapy. In case series/cohort studies (n = 45) mortality was lower with combination- vs. monotherapy (RR 0.83, CI 0.73-0.93, p = 0.002, I2 = 24%). Subgroup analysis revealed lower mortality with combination therapy with at least two in-vitro active antibiotics, in blood stream infections, and carbapenemase-producing Enterobacteriaceae. No mortality difference was seen in case-control studies (n = 6) and RCTs (n = 2). Cure rates did not differ regardless of study type. The two included RCTs had a high and unknown risk of bias, respectively. 16.7% (1/6) of case-control studies and 37.8% (17/45) of cases series/cohort studies were of good quality, whereas quality was poor in the remaining studies. In conclusion, combination antimicrobial therapy of multidrug-resistant Gram-negative bacteria appears to be superior to monotherapy with regard to mortality.

The Role of Minocycline in the Treatment of Nosocomial Infections Caused by Multidrug, Extensively Drug and Pandrug Resistant Acinetobacter baumannii: A Systematic Review of Clinical Evidence

Treatment options for multidrug resistant Acinetobacter baumannii strains (MDR-AB) are limited. Minocycline has been used alone or in combination in the treatment of infections associated with AB. A systematic review of the clinical use of minocycline in nosocomial infections associated with MDR-AB was performed according to the PRISMA-P guidelines. PubMed-Medline, Scopus and Web of Science ^TM databases were searched from their inception until March 2019. Additional Google Scholar free searches were performed. Out of 2990 articles, 10 clinical studies (9 retrospective case series and 1 prospective single center trial) met the eligibility criteria. In total, 223 out of 268 (83.2%) evaluated patients received a minocycline-based regimen; and 200 out of 218 (91.7%) patients with available data received minocycline as part of a combination antimicrobial regimen (most frequently colistin or carbapenems). Pneumonia was the most common infection type in the 268 cases (80.6% with 50.4% ventilator-associated pneumonia). The clinical and microbiological success rates following minocycline treatment were 72.6% and 60.2%, respectively. Mortality was 20.9% among 167 patients with relevant data. In this systematic review, minocycline demonstrated promising activity against MDR-AB isolates. This review sets the ground for further studies exploring the role of minocycline in the treatment of MDR-AB associated infections.

Treatment of Achromobacter Ventilator-Associated Pneumonia in Critically Ill Trauma Patients

BACKGROUND

Achromobacter sp are nonfermenting Gram-negative bacilli (NFGNB) that rarely cause severe infections, including ventilator-associated pneumonia (VAP). Data on the treatment of Achromobacter pneumonia are very limited, and the organism has been associated with a high mortality rate. Thus, more data are needed on treating this organism.

OBJECTIVE

To evaluate the treatment of Achromobacter VAP in critically ill trauma patients.

METHODS

This retrospective, observational study evaluated critically ill trauma patients who developed Achromobacter VAP. A previously published pathway for the diagnosis and management of VAP was used according to routine patient care. This included the use of quantitative bronchoscopic bronchoalveolar lavage cultures to definitively diagnose VAP.

RESULTS

A total of 37 episodes of Achromobacter VAP occurred in 34 trauma intensive care unit patients over a 15-year period. The most commonly used definitive antibiotics were imipenem/cilastatin, cefepime, or trimethoprim/sulfamethoxazole. The primary outcome of clinical success was achieved in 32 of 37 episodes (87%). This is similar to previous studies of other NFGNB VAP (eg, Pseudomonas, Acinetobacter) from the study center. Microbiological success was seen in 21 of 28 episodes (75%), and VAP-related mortality was 9% (3 of 34 patients).

CONCLUSIONS

Achromobacter is a rare but potentially serious cause of VAP in critically ill patients. In this study, there was an acceptable success rate compared with other causes of NFGNB VAP in this patient population.

Minocycline for the Treatment of Multidrug and Extensively Drug-Resistant A. baumannii: A Review

Acinetobacter baumannii can cause life-threatening nosocomial infections associated with high rates of morbidity and mortality. In recent years, the increasing number of infections due to extensively drug-resistant Acinetobacter with limited treatment options has resulted in a need for additional therapeutic agents, and a renaissance of older, neglected antimicrobials. This has led to an increased interest in the use of minocycline to treat these infections. Minocycline has been shown to overcome many resistance mechanisms affecting other tetracyclines in A. baumannii, including tigecycline. Additionally, it has favorable pharmacokinetic and pharmacodynamic properties, as well as excellent in vitro activity against drug-resistant A. baumannii. Available data support therapeutic success with minocycline, while ease of dosing with no need for renal or hepatic dose adjustments and improved safety have made it an appealing therapy. This review will focus on the mechanisms of action and resistance to tetracyclines in A. baumannii, the in vitro activity, pharmacokinetic and pharmacodynamic properties of minocycline against A. baumannii, and finally the clinical experience with minocycline for the treatment of invasive infections due to this pathogen.

Synergistic Effect of Colistin and Rifampin Against Multidrug Resistant Acinetobacter baumannii: A Systematic Review and Meta-Analysis

The existence of infections caused by multidrug resistant (MDR) Acinetobacter baumannii is a growing problem because of the difficulty to treat them. We examined the published literature and focused our analysis on the investigation of the synergism of colistin and rifampin against MDR A. baumannii isolates via systematic review and meta-analysis. A systematic literature search was performed using the following 4 databases (PubMed, Scopus, EMBASE and ISI Web of Sciences). The related articles were evaluated during the period from December 2014 to January 2015. Information based on resistance and sensitivity to antibiotics, the minimum inhibitory concentration and the effects of two antibiotics on each other including synergism, antagonism, relative synergism and additive antagonism were extracted. A meta-analysis of 17 studies including 448 samples was brought into process and 2% (95% CI 0-4%) and 72% (95% CI 56-89%) resistance to colistin and rifampin were observed, respectively. 42% of all isolates showed MIC = 4 µg/ml (95% CI 14-69%) to rifampin and 30% MIC= 2 µg/ml to colistin (95% CI 3.8-78%). MIC₅₀ and MIC₉₀ for both rifampin and colistin were 2 µg/ml and 4 µg/ml, respectively. 63% of the strains demonstrated synergy (95% CI 37-90%), 7% were highlighted as relative synergism (95% CI 0.0- 13%), 3% showed an additive effect (95% CI -0.0-7%) and 14% were indifferent (95% CI 6-23%). The antagonistic effect was not observed in this combination. Synergy rates of time-kill assay in rifampin and colistin combinations were generally higher than those of check bored microdilution and E-test method. The results demonstrated that the combination therapy could be more useful when compared to monotherapy and that this strategy might reduce the resistance rate to rifampin in MDR A. baumannii isolates.

Intravenous Minocycline: A Review in Acinetobacter Infections

Intravenous minocycline (Minocin^®) is approved in the USA for use in patients with infections due to susceptible strains of Gram-positive and Gram-negative pathogens, including infections due to Acinetobacter spp. Minocycline is a synthetic tetracycline derivative that was originally introduced in the 1960s. A new intravenous formulation of minocycline was recently approved and introduced to address the increasing prevalence of multidrug-resistant (MDR) pathogens. Minocycline shows antibacterial activity against A. baumannii clinical isolates worldwide, and exhibits synergistic bactericidal activity against MDR and extensively drug-resistant (XDR) A. baumannii isolates when combined with other antibacterial agents. In retrospective studies, intravenous minocycline provided high rates of clinical success or improvement and was generally well tolerated among patients with MDR or carbapenem-resistant A. baumannii infections. While randomized clinical trial data would be useful to fully establish the place of minocycline in the management of these infections for which there are currently very few available options, clinical trials in patients with infections due to Acinetobacter spp. are difficult to perform. Nevertheless, current data indicate a potential role for intravenous minocycline in the treatment of patients MDR A. baumannii infections, particularly when combined with a second antibacterial agent (e.g. colistin).

Can Pharmacokinetic and Pharmacodynamic Principles Be Applied to the Treatment of Multidrug-Resistant Acinetobacter?

OBJECTIVE:

To discuss treatment options that can be used for treatment of Acinetobacter infections.

DATA SOURCES:

A MEDLINE search (1966-November 2010) was conducted to identify English-language literature on pharmacotherapy of Acinetobacter and the bibliographies of pertinent articles. Programs and abstracts from infectious diseases meetings were also searched. Search terms included Acinetobacter, multidrug resistance, pharmacokinetics, pharmacodynamics, Monte Carlo simulation, nosocomial pneumonia, carbapenems, polymyxins, sulbactam, aminoglycosides, tetracyclines, tigecycline, rifampin, and fluoroquinolones.

DATA SELECTION AND DATA EXTRACTION:

All articles were critically evaluated and all pertinent information was included in this review.

DATA SYNTHESIS:

Multidrug resistant (MDR) Acinetobacter, defined as resistance to 3 or more antimicrobial classes, has increased over the past decade. The incidence of carbapenem-resistant Acinetobacter is also increasing, leading to an increased use of dose optimization techniques and/or alternative antimicrobials, which is driven by local susceptibility patterns. However, Acinetobacter infections that are resistant to all commercially available antibiotics have been reported. General principles are available to guide dose optimization of aminoglycosides, β-lactams, fluoroquinolones, and tigecycline for infections due to gram-negative pathogens. Unfortunately, data specific to patients with Acinetobacter infections are limited. Recent pharmacokinetic-pharmacodynamic information has shed light on colistin dosing. The dilemma with colistin is its concentration-dependent killing, which makes once-daily dosing seem like an attractive option, but its short postantibiotic effect limits a clinician's ability to extend the dosing interval. Localized delivery of antimicrobials is also an attractive option due to the ability to increase drug concentration at the infection site while minimizing systemic adverse events, but more data are needed regarding this approach.

CONCLUSIONS:

Increased reliance on dosage optimization, combination therapy, and localized delivery of antimicrobials are methods to pursue positive clinical outcomes in MDR Acinetobacter infections since novel antimicrobials will not be available for several years. Well-designed clinical trials with MDR Acinetobacter are needed to define the best treatment options for these patients.

Anticipating the Unpredictable: A Review of Antimicrobial Stewardship and Acinetobacter Infections

Acinetobacter remains one of the most challenging pathogens in the field of infectious diseases owing primarily to the uniqueness and multiplicity of its resistance mechanisms. This resistance often leads to devastatingly long delays in time to appropriate therapy and increased mortality for patients afflicted with Acinetobacter infections. Selecting appropriate empiric and definitive antibacterial therapy for Acinetobacter is further complicated by the lack of reliability in commercial antimicrobial susceptibility testing devices and limited breakpoint interpretations for available agents. Existing treatment options for infections due to Acinetobacter are limited by a lack of robust efficacy and safety data along with concerns regarding appropriate dosing, pharmacokinetic/pharmacodynamic targets, and toxicity. Antimicrobial stewardship programs are essential to combat this unpredictable pathogen through use of infection prevention, rapid diagnostics, antibiogram-optimized treatment regimens, and avoidance of overuse of antimicrobials. The drug development pipeline includes several agents with encouraging in vitro activity against Acinetobacter, but their place in therapy and contribution to the armamentarium against this pathogen remain to be defined. The objective of this review is to highlight the unique challenge of treating infections due to Acinetobacter and summarize recent literature regarding optimal antimicrobial treatment for this pathogen. The drug development pipeline is also explored for future potentially effective treatment options.

Can minocycline be a carbapenem sparing antibiotic? Current evidence

With the increasing incidence of multidrug-resistant organisms, there is a need for newer antibiotics. However, due to the lack of new antimicrobial agents, it is necessary to re-evaluate the older agents like minocycline which is a second-line antimicrobial agent. In this study, minocycline susceptibility testing was performed for 693 Escherichia coli, 316 Klebsiella spp. and 89 Acinetobacter spp. Among extended spectrum beta-lactamase producing E. coli and Klebsiella spp. percentage susceptibility to minocycline were 76 and 85, respectively. Among the carbapenem resistant E. coli, Klebsiella spp. and Acinetobacter spp. minocycline susceptibility were 52%, 55% and 42%, respectively. Based on the susceptibility profile, minocycline can be considered for treatment of infections by multidrug-resistant organisms.

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

Background:

Multidrug-resistant Acinetobacter baumannii (MDR-Ab) has emerged as an increasingly problematic cause of hospital-acquired infections in the intensive care unit (ICU). MDR-Ab is resistant to most standard antimicrobials but often retains susceptibility to polymyxin B and doxycycline.

Objective:

To evaluate the efficacy and toxicity of polymyxin B and doxycycline in the treatment of MDR-Ab infections.

Methods:

A retrospective chart review was conducted between March 2002 and May 2005 in patients who received doxycycline or polymyxin B for treatment of MDR-Ab infections in ICUs within Grady Memorial Hospital, Atlanta, GA.

Results:

Thirty-seven patients with MDR-Ab infections were treated with polymyxin B or doxycycline. Median age was 41 years and median ICU length of stay was 18 days prior to acquisition of MDR-Ab. Clinical cure was observed in 22 of 29 (76%) evaluable patients treated with polymyxin B and 2 of 4 (50%) patients treated with doxycycline. In patients with follow-up cultures, microbiological cure was observed in 17 of 21 (81%) patients treated with polymyxin B and 2 of 3 (67%) patients treated with doxycycline. Nephrotoxicity developed in 21% (7 of 33) of patients who received polymyxin B. Neurotoxicity was observed in 2 (6%) patients who received polymyxin B. No adverse reactions were observed with doxycycline. Overall, crude mortality was 27% (9 of 33) and 75% (3 of 4) among those who received polymyxin B and doxycycline, respectively. Three (9%) deaths were attributed to polymyxin B treatment failure, and no deaths were attributed to doxycycline treatment failure.

Conclusions:

Polymyxin B was effectively used to treat a substantial proportion of critically ill patients with MDR-Ab infection and was associated with a similar rate of nephrotoxicity as previously reported. Doxycycline monotherapy was used in a limited number of patients for the treatment of MDR-Ab; further evaluation of its efficacy in larger numbers of patients is warranted.

Minocycline and Tigecycline: What Is Their Role in the Treatment of Carbapenem-Resistant Gram-Negative Organisms?

Carbapenem-resistant organisms are increasingly common worldwide, particularly in India and are associated with high mortality rates especially in patients with severe infection such as bacteremia. Existing drugs such as carbapenems and polymyxins have a number of disadvantages, but remain the mainstay of treatment. The tetracycline class of antibiotics was first produced in the 1940s. Minocycline, tetracycline derivative, although licensed for treatment of wide range of infections, has not been considered for treatment of multidrug-resistant organisms until recently and needs further in vivo studies. Tigecycline, a derivative of minocycline, although with certain disadvantages, has been frequently used in the treatment of carbapenem-resistant organisms. In this article, we review the properties of minocycline and tigecycline, the common mechanisms of resistance, and assess their role in the management of carbapenem-resistant organisms.

Role of newer and re-emerging older agents in the treatment of infections caused by carbapenem-resistant Enterobacteriaceae

Antimicrobial resistance has been identified by the World Health Organization as "one of the three greatest threats to human health." Gram negative bacteria in particular drive this alarming trend. Carbapenem-resistant Enterobacteriaceae (CRE) such as Escherichia coli, Klebsiella pneumoniae, and Enterobacter species are of particular importance as they are associated with poor clinical outcomes and are common causes for a variety of infections including bacteremia, urinary tract infection, intra-abdominal infections and pneumonia. CRE are difficult to treat as carbapenem resistance is often accompanied by resistance to additional drug classes. For example, CRE may be extensively drug resistant or even pandrug resistant. Unfortunately, CRE infections have increased over the past 15 y while new and effective antibiotics have not kept pace. Recently, however, new agents have become available to help treat CRE infection, and several more are under development. This article reviews the efficacy, safety, and pharmacokinetic issues around 4 emerging agents to treat CRE - ceftazidime-avibactam, fosfomycin, tigecycline, and minocycline. In addition, an overview of agents in the antibiotic pipeline - meropenem-vaborbactam, imipenem-relebactam, plazomicin, and eravacycline is provided. More established agents, such as those in the polymyxin class and aminoglycoside class (other than the pipeline agent plazomicin), are not addressed here.

Antibiotic regimens for treatment of infections due to multidrug-resistant Gram-negative pathogens: An evidence-based literature review

Evidences regarding the efficacy of different antibiotic regimens proposed for treatment of multidrug-resistant (MDR) Gram-negative pathogens have been reviewed. Available data in Scopus, Medline, EMBASE, the Cochrane central register of controlled trials, and Cochrane database of systematic reviews have been collected. Several antibiotic regimens are proposed for treatment of MDR Gram-negative infections (defined as nonsusceptibility to at least one agent in three or more antimicrobial categories). The most challenging issue is the treatment of carbapenem-resistant (CR) Gram-negative pathogens. A carbapenem plus either colistin or tigecycline was the most effective regimen for treatment of CR Gram-negative pathogens with low-level resistance (minimal inhibitory concentration [MIC] ≤ 8 mg/L). However, in high-level resistance (MIC > 8 mg/L), combination of colistin and tigecycline showed promising effect.

In vitro activity of minocycline alone or in combination in multidrug-resistant Acinetobacter baumannii isolates

Minocycline (MIN) usually shows good activity against Acinetobacter baumannii strains. The reintroduction to the market of intravenous MIN provides an additional agent to the limited options for the treatment of A. baumannii infections. The activity of MIN as a single agent and in combination with rifampicin (RIF), colistin (COL) or imipenem (IMI) was evaluated by means of killing curves and 24  h-time-kill curves in five A. baumannii isolates which were selected on the basis of different antimicrobial resistance profiles. MIN showed bacteriostatic activity in three isolates (2 ×  or 16 ×  MIC) and bactericidal activity in the other isolates (64 ×  MIC). In isolates harbouring the tetB gene, the associations studied were always indifferent. However, in isolates not harbouring tetB, the use of MIN in combination showed a rapid synergistic effect (at 4  h) in four out of nine combinations (two with RIF and one each with IMI and COL). At 24  h, this effect was observed in six out of nine combinations (two in each association). MIN in combination with RIF, IMI and COL showed bactericidal synergy in most of the isolates which did not harbour the tetB gene, but the combinations were not synergistic in tetB-positive isolates.

Carbapenem-resistance in gram-negative bacilli and intravenous minocycline: an antimicrobial stewardship approach at the Detroit Medical Center

In the era of carbapenem-resistance in Acinobacter baumannii and Enterobacteriaceae, there are limited treatment options for these pathogens. It is essential that clinicians fully assess all available therapeutic alternatives for these multidrug-resistant organisms. We herein describe the approach of the antimicrobial stewardship team at the Detroit Medical Center (DMC) for the evaluation and use of intravenous (IV) minocycline for the treatment of these resistant organisms, given potential advantages of IV minocycline over tigecycline and doxycycline. In vitro analyses at the DMC demonstrated good activity against A. baumannii (78% susceptibility), including 74% of carbapenem-resistant strains, but limited activity against our carbapenem-resistant K.pneumoniae (12% susceptibility.) Based in part on these results, IV minocycline was added to the formulary, primarily for the treatment of carbapenem-resistant A. baumannii. Early experience has been positive: 6/9 (67%) of patients who received IV minocycline had infections due to these organisms cured, including 6/7 (86%) who received doses of 200 mg twice daily.

A review of intravenous minocycline for treatment of multidrug-resistant Acinetobacter infections

Options for treatment of multidrug-resistant (MDR) Acinetobacter baumannii infections are extremely limited. Minocycline intravenous is active against many MDR strains of Acinetobacter, and Clinical and Laboratory Standards Institute breakpoints exist to guide interpretation of minocycline susceptibility results with Acinetobacter. In addition, minocycline intravenous holds a US Food and Drug Administration indication for treatment of infections caused by Acinetobacter. There is an accumulating amount of literature reporting successful use of minocycline intravenous for treatment of serious MDR Acinetobacter infections, particularly for nosocomial pneumonia. These results, coupled with the generally favorable tolerability of minocycline intravenous, support its use as a viable therapeutic option for treatment of MDR Acinetobacter infections.

Update on Acinetobacter species: mechanisms of antimicrobial resistance and contemporary in vitro activity of minocycline and other treatment options

Among Acinetobacter species, A. baumannii and other closely related species are commonly implicated in nosocomial infections. These organisms are usually multidrug resistant (MDR), and therapeutic options to treat A. baumannii infections are very limited. Clinicians have been resorting to older antimicrobial agents to treat infections caused by MDR A. baumannii, and some of these agents have documented toxicity and/or are not optimized for the infection type to be treated. Recent clinical experience supported by antimicrobial susceptibility data suggests that minocycline has greater activity than other tetracyclines and glycylcyclines against various MDR pathogens that have limited therapeutic options available, including Acinetobacter species. An intravenous formulation of minocycline has recently become available for clinical use, and in contrast to most older tetracyclines, minocycline has high activity against Acinetobacter species. In this report, we summarized some of the characteristics of the tetracycline class, and quantified the minocycline activity against contemporary (2007-2011) isolates and its potential therapeutic role against a collection of 5477 A. baumannii and other relevant gram-negative organisms when compared directly with tetracycline, doxycycline, and other broad-spectrum antimicrobial agents. Acinetobacter baumannii strains were highly resistant to all agents tested, with the exception of minocycline (79.1% susceptible) and colistin (98.8% susceptible). Minocycline (minimum inhibitory concentration that inhibits 50% and 90% of the isolates [MIC(50/90)]: 1/8 µg/mL) displayed greater activity than doxycycline (MIC(50/90): 2/>8 µg/mL) and tetracycline hydrochloride (HCL) (only 30.2% susceptible) against A. baumannii isolates, and was significantly more active than other tetracyclines against Burkholderia cepacia, Escherichia coli, Serratia marcescens, and Stenotrophomonas maltophilia isolates. In vitro susceptibility testing using tetracycline HCL as a surrogate for the susceptibility other tetracyclines fails to detect minocycline-susceptible isolates and the potential utility of minocycline for the treatment of many MDR A. baumannii infections and other difficult-to-treat species, where there are often limited choices of antimicrobials.

Treatment options for carbapenem-resistant and extensively drug-resistant Acinetobacter baumannii infections

Acinetobacter baumannii is a leading cause of healthcare-associated infections worldwide. Because of various intrinsic and acquired mechanisms of resistance, most β-lactam agents are not effective against many strains, and carbapenems have played an important role in therapy. Recent trends show many infections are caused by carbapenem-resistant or even extensively drug-resistant (XDR) strains, for which effective therapy is not well established. Evidence to date suggests that colistin constitutes the backbone of therapy, but the unique pharmacokinetic properties of colistin have led many to suggest the use of combination antimicrobial therapy. However, the combination of agents and dosing regimens that delivers the best clinical efficacy while minimizing toxicity is yet to be defined. Carbapenems, sulbactam, rifampin and tigecycline have been the most studied in the context of combination therapy. Most data regarding therapy for invasive, resistant A. baumannii infections come from uncontrolled case series and retrospective analyses, though some clinical trials have been completed and others are underway. Early institution of appropriate antimicrobial therapy is shown to consistently improve survival of patients with carbapenem-resistant and XDR A. baumannii infection, but the choice of empiric therapy in these infections remains an open question. This review summarizes the most current knowledge regarding the epidemiology, mechanisms of resistance, and treatment considerations of carbapenem-resistant and XDR A. baumannii.

Optimum treatment strategies for carbapenem-resistant Acinetobacter baumannii bacteremia

Carbapenem-resistant Acinetobacter baumannii (CRAB) constitutes an increasing problem worldwide. CRAB bacteremia is associated with a high fatality rate and its optimal treatment has not been established. Early institution of appropriate therapy is shown to improve survival of patients with CRAB bloodstream infection. Regrettably, treatment options are limited. Little information exists about the efficacy of sulbactam for the treatment of CRAB bacteremia. Colistin and tigecycline possess good in vitro activity and represent in many cases the only therapeutic options although clinical data are scarce. The need for a loading dose of colistin has been recently demonstrated to rapidly achieve therapeutic levels. The use of combination therapy is also a matter of debate but current evidence do not support its routine use.

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.

Therapy of Infections due to Carbapenem-Resistant Gram-Negative Pathogens

The prevalence of carbapenem-resistant gram-negative bacterial pathogens (CRGNs) has increased dramatically during the last 10 years, but the optimal treatment for CRGN infections is not well established due to the relative scarcity of robust clinical data. The polymyxins remain the most consistently active agents against CRGNs in vitro. Tigecycline, based on its in vitro antibacterial spectrum, could also be considered as a therapeutic option in the treatment of infections caused by certain CRGNs. Other agents, including aminoglycosides, rifampin, trimethoprim-sulfamethoxazole, fosfomycin and fluoroquinolones, could be considered as monotherapy or combination therapy against CRGNs in appropriate contexts, as combination therapy with two or more in vitro active drugs appears to be more effective than monotherapy based on some clinical data. Several promising new agents are in late-stage clinical development, including ceftolozane-tazobactam, ceftazidime-avibactam and plazomicin. Given the shortage of adequate treatment options, containment of CRGNs should be pursued through implementation of adequate infection prevention procedures and antimicrobial stewardship to reduce the disease burden and prevent future outbreaks of CRGNs.

Is minocycline a solution for multidrug-resistant Acinetobacter baumannii?

ABSTRACT:

Minocycline is an old, safe, second-line antimicrobial agent that has drawn attention over the last few years as a possible therapeutic option against multidrug-resistant Acinetobacter baumannii (MDRAB) clinical isolates. Recent in vitro and in vivo results indicate that minocycline is a valid, alternative treatment option for minocycline-susceptible MDRAB. Although effective alone, its administration as monotherapy should be avoided. Combinations with other antimicrobials can reduce the MIC of each component, present synergism and minimize the risk for drug resistance. Owing to its limited solubility in urine, it should be avoided for urinary pathogens. The present article reports all available information regarding its use as a therapeutic option against MDRAB.

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.

Revisiting "older" antimicrobials in the era of multidrug resistance

Infections due to multidrug-resistant (MDR) organisms continue to increase, and the antimicrobial pipeline remains unacceptably lean. Given this challenge, it is has become necessary to use older antimicrobials for treatment of MDR pathogens despite concerns regarding toxicity and the lack of clinical efficacy data. In some cases, older antimicrobials offer potential advantages compared with new agents, including lower cost and better in vitro activity. In this review, we focus on the pharmacology, in vitro activity, and clinical experience of older agents, including colistin, minocycline, trimethoprim-sulfamethoxazole, and fosfomycin. We also discuss some new antimicrobial agents that are used to treat MDR pathogens. As MDR pathogens continue to outpace the development of new antimicrobials, it will become imperative to develop strategies regarding the optimal use of older agents in terms of monotherapy versus combination therapy, dosing regimens, and treatment of invasive infections caused by these pathogens.

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.

Antimicrobial Treatment and Clinical Outcomes of Carbapenem-Resistant Acinetobacter baumannii Ventilator-Associated Pneumonia

Objectives: Carbapenem-resistant (CR) Acinetobacter baumannii is an important pathogen in ventilator-associated pneumonia (VAP), but therapeutic options are limited. We describe the clinical outcomes of the largest case series of CR-Acinetobacter VAP reported to date. Methods: A retrospective analysis of 55 participants with CR-Acinetobacter VAP from July 2004 to December 2007 was undertaken. The primary endpoint was clinical response or microbiological eradication. Secondary endpoint was treatment-associated nephrotoxicity defined as ≥50% increase in serum creatinine or an increase of ≥0.5 mg/dL during therapy. Results: Forty-two (76.4%) participants achieved clinical response at the completion of therapy. Clinical responses were achieved in 60.0% of sulbactam-based, 66.7% of polymyxin-based, 77.8% of aminoglycoside-based, 80.6% of minocycline-based, and 90.0% of tigecycline-based regimens. Follow-up sputum cultures were available in 6 of 10 tigecycline-treated participants with 4 of 6 isolates developing intermediate resistance to tigecycline while on therapy. Ten (18.2%) participants without preexisting renal disease developed treatment-associated nephrotoxicity. Baseline serum creatinine was 0.9 ± 0.1 mg/dL (range: 0.6-1.0 mg/dL) at the start of therapy and peaked at 1.9 ± 0.5 mg/dL (range: 1.6-3.0 mg/dL) during therapy. After excluding other potential concomitant renal toxic agents, nephrotoxicity developed in 6 of 30 (20.0%) and 4 of 7 (57.1%) participants treated with an aminoglycoside-or polymyxin-based regimen, respectively. Conclusions: Our results demonstrated that CR-Acinetobacter VAP can be effectively treated with second-line agents. However, colistin-related nephrotoxicity was much higher than recently reported and decreased susceptibility to tigecycline emerged on therapy demonstrating the limitations of alternative regimens.

Minocycline--an old drug for a new century: emphasis on methicillin-resistant Staphylococcus aureus (MRSA) and Acinetobacter baumannii

The epidemiology of nosocomial and community-acquired infections has changed in recent years. Methicillin-resistant Staphylococcus aureus (MRSA), especially community-associated MRSA (CA-MRSA), has emerged as a gram-positive organism with an increasing impact in clinical practice. Infections with Acinetobacter baumannii have become a major cause of morbidity and mortality. Minocycline has significant in vitro activity against MRSA and A. baumannii that is comparable with agents currently used against these organisms. The absence of an intravenous (i.v.) minocycline formulation in recent years has limited its use in seriously ill patients infected with these organisms. However, minocycline i.v. has recently been reintroduced to the US market. The objective of this study was to review available information on the chemistry, mechanism of action, in vitro activity, resistance mechanisms, pharmacokinetics, tolerability and efficacy of minocycline against MRSA and A. baumannii. This article provides suggestions for future studies and potential uses of minocycline and is designed to trigger interest in systematic clinical evaluation of minocycline for patients infected with these organisms. In conclusion, minocycline is an old drug that has the potential to become an important part of the armamentarium against emerging infections such as CA-MRSA and A. baumannii. Owing to its promising profile against these clinically important pathogens as well as excellent pharmacokinetic properties, minocycline merits evaluation in serious infections.

High-dose ampicillin-sulbactam as an alternative treatment of late-onset VAP from multidrug-resistant Acinetobacter baumannii

The increased incidence of multidrug-resistant (MDR) Acinetobacter baumannii ventilator-associated pneumonia in critically ill patients poses a severe therapeutic problem. The aim of this study was to evaluate the efficacy and safety of 2 high-dose treatment regimens of ampicillin-sulbactam (A/S) for MDR Acinetobacter baumannii VAP. We undertook a randomized, prospective trial of critically ill patents with (MDR) Acinetobacter baumannii VAP. Patients were randomly assigned to 1 of 2 treatment regimens of A/S (at a rate 2:1 every 8 h): 1) group A, 18/9 g daily dose (n = 14); and 2) group B, 24/12 g daily dose (n = 13). The duration of therapy was 8+/-2 d for both groups. A total of 27 patients were enrolled in the study. Clinical improvement was seen in 66.7% of the study population in 9/14 (64.3%) of group A patients and 9/13 (69.2%) of group B patients, respectively. Bacteriological success was achieved in 77.8% of the study population (12/14, 85.7% of group A) and in 9/13 (69.2%) of group B patients. The 14-d mortality rate was 25.9% and the all cause 30-d mortality was 48.1%. Both mortality rates did not differ significantly between the 2 groups. No major adverse reactions were recorded. We concluded that clinical and bacteriological results of the study support the use of high-dose regimen of ampicillin-sulbactam for MDR Acinetobacter baumannii VAP.

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.

[In vitro antimicrobial synergy against imipenem-resistant Acinetobacter baumannii]

BACKGROUND

Most imipenem-resistant Acinetobacter baumannii (IRAB) isolates are multiresistant, leaving few options for an effective antimicrobial therapy. We purposed to select possible candidates for the combinations of antimicrobials that are synergistic in vitro for inhibitory or bactericidal activities against IRAB and evaluate the usefulness of double disk synergy test (DDS) in predicting synergistic bactericidal activity.

METHODS

Fifty-five IRAB isolates recovered from patients during the period from August 1999 to November 2000 were tested for susceptibilities to amikacin, gentamicin, tobramycin, piperacillin, piperacillin/tazobactam, cefotaxime, cefepime, cefoperazone/sulbactam (C/S), imipenem, meropenem, ciprofloxacin, levofloxacin, trimethoprim/sulfamethoxazole, chloramphenicol, minocycline, and colistin by the Clinical and Laboratory Standard Institute agar dilution method. Three isolates showing different susceptibility profiles were tested for antimicrobial synergy by DDS and then by timekill study (TKS) using DDS-positive combinations.

RESULTS

Colistin, C/S, and minocycline were active in 50 (90.9%), 50, and 44 (80.0%) isolates, respectively, and all the other drugs were active in less than 20% of isolates. Minocycline-imipenem, minocycline-C/S, minocycline-amikacin, imipenem-tobramycin, C/S-amikacin, and C/S-tobramycin combinations showed synergistic inhibitory or bactericidal activity by TKS when the same combinations were synergistic in DDS; however, C/S-imipenem was found synergistic on DDS, but not by TKS.

CONCLUSIONS

Colistin, C/S, and minocycline were relatively active against IRAB. DDS might help predict the synergistic antimicrobial effect of TKS if one of the combinations was susceptible.

Comparative time-kill study of doxycycline, tigecycline, sulbactam, and imipenem against several clones of Acinetobacter baumannii

To assess potential alternative options for the treatment of infections caused by Acinetobacter baumannii, we performed time-kill studies of doxycycline and tigecycline using several isolates recovered from patients residing in 10 different cities in Argentina. Imipenem and sulbactam were also included for comparison purposes. Eleven isolates representing 5 distinctive clones, or isolates with different susceptibility patterns within the same clone, were selected. Tubes containing cation-supplemented Mueller-Hinton broth with and without antibiotics were seeded with a log-phase inoculum of roughly 5 x 10(5) CFU/mL. By using the viable counts determined at 2-, 4-, 6-, 8-, and 24-h intervals after inoculation, a 24-h time-kill curve was constructed for each isolate. No bactericidal activity (defined as a >or=3-log(10) CFU/mL decrease in the viable cell counts with respect to the original inoculum) was observed at any time with sulbactam (4 microg/mL) or tigecycline (1 microg/mL), whereas low bactericidal rate (18% of the isolates) was shown for doxycycline (1 microg/mL) and sulbactam (16 microg/mL) after 24 h of incubation. Doxycycline (4 microg/mL) and tigecycline (8 microg/mL) displayed bactericidal activity at 24 h of incubation against 36% and 54% of the isolates, respectively, including the carbapenem-resistant isolate. Corresponding values for imipenem (1 and 4 microg/mL) against the 10 carbapenem-susceptible isolates were 60% and 90%, respectively. The present study confirms the in vitro efficacy of imipenem against A. baumannii, suggests that doxycycline could be a suitable, cost-effective, alternative option in some instances, and sheds light on the potential role of tigecycline in the treatment of infections with this organism.

Old antibiotics for infections in critically ill patients

PURPOSE OF REVIEW

The alarming epidemic of multidrug-resistant bacteria and the reluctance of the pharmaceutical industry to invest in the development of new antibiotics have forced clinicians to reintroduce forgotten antibiotics into their practice. This review highlights the effectiveness and safety of older antibiotics when used in the treatment of infections of critically ill patients.

RECENT FINDINGS

Polymyxins emerged as useful antibiotics for the treatment of infections due to multidrug-resistant Gram-negative bacteria, in particular Acinetobacter baumannii, Pseudomonas aeruginosa and Klebsiella pneumoniae. The nephrotoxicity and neurotoxicity associated with their use are less frequent and serious than previously reported. In addition, aerosolized polymyxins may be a useful weapon in the treatment of hospital-acquired pneumonia. Fosfomycin and chloramphenicol have a wide antimicrobial spectrum, are used extensively in Europe and Africa, respectively, and may have an expanded role in our antimicrobial arsenal. Fusidic acid remains active against various staphylococcal strains, while isepamicin (an aminoglycoside used in some European countries) is slightly more effective than amikacin against some Gram-negative bacteria.

SUMMARY

The declining investment of the pharmaceutical industry in the development of new antibiotics and the increasing antimicrobial resistance create a fertile ground for the study and, probably, revival of older antibiotics for use, especially in critically ill patients.