Clinical and Microbiological Efficacy of Colistin Therapy Alone or in Combination as Treatment for Multidrug ResistantPseudomonas aeruginosaDiabetic Foot Infections with or Without Osteomyelitis

A Real-world Multicenter Outpatient Experience of Ceftolozane/Tazobactam

Background

Ceftolozane/tazobactam (C/T) is indicated for the treatment of complicated intra-abdominal infection (IAI), complicated urinary tract infection (UTI), and hospital-acquired/ventilator-associated bacterial pneumonia caused by susceptible bacteria. As real-world data are limited, we report utilization and associated outcomes of C/T use in the outpatient setting.

Methods

This is a multicenter, retrospective study of patients who received C/T between May 2015 and December 2020. Demographics, infection types, C/T utilization characteristics, microbiology, and health care resource utilization were collected. Clinical success was defined as complete or partial symptom resolution at completion of C/T. Persistent infection and discontinuation of C/T were deemed nonsuccess. Logistic regression analysis was used to identify predictors associated with clinical outcomes.

Results

A total of 126 patients (median age, 59 years; 59% male; median Charlson index, 5) from 33 office infusion centers were identified. Infection types included 27% bone and joint infection (BJI), 23% UTI, 18% respiratory tract infection (RTI), 16% IAI, 13% complicated skin and soft tissue infection (cSSTI), and 3% bacteremia. The median daily dose of C/T was 4.5 g, primarily administered via elastomeric pumps as intermittent infusion. The most common gram-negative pathogen was P. aeruginosa (63%), 66% of which was multidrug-resistant and 45% carbapenem-resistant. Enterobacterales was identified in 26% of isolates, of which 44% were extended-spectrum beta-lactamase producers. The overall clinical success rate of C/T was 84.7%. Nonsuccessful outcomes were due to persistent infections (9.7%) and drug discontinuations (5.6%).

Conclusions

C/T was successfully used in the outpatient setting to treat a variety of serious infections with a high prevalence of resistant pathogens.

Polymyxin combination therapy for multidrug-resistant, extensively-drug resistant, and difficult-to-treat drug-resistant gram-negative infections: is it superior to polymyxin monotherapy?

INTRODUCTION

The increasing prevalence of infections with multidrug-resistant (MDR), extensively-drug resistant (XDR) or difficult-to-treat drug resistant (DTR) Gram-negative bacilli (GNB), including Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella pneumoniae, Enterobacter species, and Escherichia coli poses a severe challenge.

AREAS COVERED

The rapid growing of multi-resistant GNB as well as the considerable deceleration in development of new anti-infective agents have made polymyxins (e.g. polymyxin B and colistin) a mainstay in clinical practices as either monotherapy or combination therapy. However, whether the polymyxin-based combinations lead to better outcomes remains unknown. This review mainly focuses on the effect of polymyxin combination therapy versus monotherapy on treating GNB-related infections. We also provide several factors in designing studies and their impact on optimizing polymyxin combinations.

EXPERT OPINION

An abundance of recent in vitro and preclinical in vivo data suggest clinical benefit for polymyxin-drug combination therapies, especially colistin plus meropenem and colistin plus rifampicin, with synergistic killing against MDR, XDR, and DTR P. aeruginosa, K. pneumoniae and A. baumannii. The beneficial effects of polymyxin-drug combinations (e.g. colistin or polymyxin B + carbapenem against carbapenem-resistant K. pneumoniae and carbapenem-resistant A. baumannii, polymyxin B + carbapenem + rifampin against carbapenem-resistant K. pneumoniae, and colistin + ceftolozan/tazobactam + rifampin against PDR-P. aeruginosa) have often been shown in clinical setting by retrospective studies. However, high-certainty evidence from large randomized controlled trials is necessary. These clinical trials should incorporate careful attention to patient's sample size, characteristics of patient's groups, PK/PD relationships and dosing, rapid detection of resistance, MIC determinations, and therapeutic drug monitoring.

Practical extended use of antimicrobial silver (PExUS)

BACKGROUND

Antimicrobial silver has had a role in wound antisepsis throughout history and, with the rise in acquired antibiotic resistance, silver dressings are once again commonly used. Issues with silver dressings include the important environmental consideration of nanoparticle manufacture, and the significant financial cost of these products. One solution to these problems may be to adopt an opened-but-unused model of wound care whereby dressing materials are used in piecemeal fashion and excess stored in between dressing changes. Due to a lack of literature on the topic, this project was designed with the aim of testing the antimicrobial efficacy of available silver dressings during storage after opening.

METHODS

Four commonly used silver dressings were tested for antimicrobial activity using a zone of inhibition assay against clinically important pathogens. The assay was performed on opening of dressings and repeated over 3 months in storage at 4, 25 or 37°C. Analysis was performed using repeated measures ANOVA. Swab cultures were taken at each simulated dressing change to detect microbial contamination of the dressings during storage.

RESULTS

There was no effect of time or storage temperature on the zone of inhibition over the 12 week test period. No swabs taken returned culture consistent with microbial contamination of stored dressings.

CONCLUSION

Opened silver dressings maintain antimicrobial activity for at least 12 weeks in storage and are resistant to contamination. An opened-but-unused model for wound care is likely to improve cost-effectiveness while preserving effectiveness and safety.

Antimicrobial silver dressings: a review of emerging issues for modern wound care

Skin is an important barrier to pathogenic microorganisms and plays a critical role in a ctivation of innate immune responses. When the skin barrier is breached following wounding or burn injury, pathogens can invade and complicate healing with infection resulting in delayed healing and symptomatic scarring. Wound infection is a significant problem after burn injury and in patients with chronic wounds. Antimicrobial silver has had a significant role in wound antisepsis throughout history and, given the rise in community acquired antibiotic resistance, silver dressings are now commonly used to combat wound infection. The multi-modal mechanism of action, low potential for toxicity and formation of microbial resistance makes silver dressings suitable tools against a wide array of clinically important microbes. There are, however, a number of issues with silver dressings including a conflicting evidence base, the important environmental consideration of nanoparticle manufacture, and the significant cost of these products. One solution may be to adopt an 'opened-but-unused' means of wound care whereby bulk dressing materials are used piecemeal and stored in between dressing changes to increase the cost-effectiveness and reduced wastage. There is, however, little literature on this topic and so in vitro and clinical research must be performed to consider the efficacy of active ingredient dressings in wound care including silver dressings once opened and stored.

Losing the Battle but Winning the War: Can Defeated Antibacterials Form Alliances to Combat Drug-Resistant Pathogens?

Despite the recent development of antibacterials that are active against multidrug-resistant pathogens, drug combinations are often necessary to optimize the killing of difficult-to-treat organisms. Antimicrobial combinations typically are composed of multiple agents that are active against the target organism; however, many studies have investigated the potential utility of combinations that consist of one or more antibacterials that individually are incapable of killing the relevant pathogen. The current review summarizes in vitro, in vivo, and clinical studies that evaluate combinations that include at least one drug that is not active individually against Pseudomonas aeruginosa, Klebsiella pneumoniae, Acinetobacter baumannii, or Staphylococcus aureus. Polymyxins were often included in combinations against all three of the Gram-negative pathogens, and carbapenems were commonly incorporated into combinations against K. pneumoniae and A. baumannii. Minocycline, sulbactam, and rifampin were also frequently investigated in combinations against A. baumannii, whereas the addition of ceftaroline or another β-lactam to vancomycin or daptomycin showed promise against S. aureus with reduced susceptibility to vancomycin or daptomycin. Although additional clinical studies are needed to define the optimal combination against specific drug-resistant pathogens, the large amount of in vitro and in vivo studies available in the literature may provide some guidance on the rational design of antibacterial combinations.

A Macromolecule Reversing Antibiotic Resistance Phenotype and Repurposing Drugs as Potent Antibiotics

In order to mitigate antibiotic resistance, a new strategy to increase antibiotic potency and reverse drug resistance is needed. Herein, the translocation mechanism of an antimicrobial guanidinium-functionalized polycarbonate is leveraged in combination with traditional antibiotics to afford a potent treatment for drug-resistant bacteria. Particularly, this polymer-antibiotic combination approach reverses rifampicin resistance phenotype in Acinetobacter baumannii demonstrating a 2.5 × 105-fold reduction in minimum inhibitory concentration (MIC) and a 4096-fold reduction in minimum bactericidal concentration (MBC). This approach also enables the repurposing of auranofin as an antibiotic against multidrug-resistant (MDR) Gram-negative bacteria with a 512-fold MIC and 128-fold MBC reduction, respectively. Finally, the in vivo efficacy of polymer-rifampicin combination is demonstrated in a MDR bacteremia mouse model. This combination approach lays foundational ground rules for a new class of antibiotic adjuvants capable of reversing drug resistance phenotype and repurposing drugs against MDR Gram-negative bacteria.

Clinical relevance of in vitro synergistic activity of antibiotics for multidrug-resistant Gram-negative infections: A systematic review

OBJECTIVES

The aim of this review was to investigate the outcomes of patients infected with multidrug-resistant (MDR) or extensively drug-resistant (XDR) Gram-negative bacteria following synergy-guided antibiotic combination therapy (SGACT).

METHODS

A systematic review of PubMed and Scopus databases was performed. Published studies of any design reporting outcomes of patients with MDR Gram-negative bacteria treated with SGACT were included. Two reviewers independently assessed the relevancy and quality of the retrieved articles and extracted the available data.

RESULTS

Nineteen reports (530 patients) were included. Eleven case reports/series described 26 cases of systemic infection due to MDR Gram-negative bacteria treated with SGACT. Five deaths were reported, two of which were attributed to the infection. Six studies (including one randomised controlled trial) provided comparative data for patients treated with SGACT and those treated with unguided combination therapy (UCT) or active monotherapy. In the pooled analysis of unadjusted data from these studies (504 patients), there was no difference between SGACT and UCT or monotherapy (OR=0.47, 95% CI 0.21-1.04; I²=52%). Analysis of adjusted data showed that SGACT was significantly associated with survival (OR=0.44, 95% CI 0.20-0.98; I²=54%).

CONCLUSION

These limited but promising findings warrant further investigation of SGACT in the outcome of patients with MDR Gram-negative infections in well-designed trials.

Two for the price of one: emerging carbapenemases in a returning traveller to New York City

We report a case of a complex orthopaedic infection in a patient returning to New York City from Bangladesh where he was involved in a serious motor vehicle accident. He developed extensive osteomyelitis with a carbapenem-resistant Klebsiella pneumoniae The isolate was unique due to the coexistence of New Delhi metallo-β-lactamase-1 and Oxacillinase type-181 carbapenemases, which are relatively uncommon in North America and were presumably acquired in Bangladesh. Herein, we explore challenges associated with management of carbapenem-resistant Enterobacteriaceae infections, including limited available data on effective antimicrobial therapy. We also highlight the added value of rapid diagnostic technology in guiding clinical management. Ultimately, the patient required both aggressive surgical management and combination therapy with aztreonam and ceftazidime-avibactam for true source control and favourable clinical outcome.

Understanding Diabetic Foot Infection and its Management

Diabetic Foot Ulcers (DFUs), a dreadful micro-vascular complication is liable for substantial increase in morbidity and mortality. DFU is a complicated amalgam of neuropathy, peripheral arterial diseases, foot deformities and infection. Spanning the spectrum from superficial cellulitis, microbial flora leads to chronic ostemyelitis and gangrenous extremity lower limb amputations. Wounds without affirmation of soft tissue or bone infection do not require antibiotic therapy. Treatment of mild and moderate infection requires empiric therapy covering gram-positive cocci, whereas severe or infection caused by drug resistant organisms needs broad spectrum anti-microbial targeting aggressive gram-negative aerobes and obligate anaerobes. Definitive therapy employed should be based on culture reports and clinical response. Evaluation of bone infection requires imaging by plain radiographs or MRI to increase sensitivity and specificity. Surgical interventions are must and may range from minor debridement to resections or revascularization and major amputations depending upon wound severity. On time and forceful management of diabetic foot ulcers by employing multidisciplinary management approaches focusing on prevention, learning, regular foot assessment, aggressive intervention, and optimal use of therapeutic footwear can often prevent exacerbation of the difficulty and eliminate the potential for amputation. Here, we review recent studies addressing diabetic foot infections with emphasis on pathophysiology, exclusive risk factors; evaluation including physical inspection, laboratory investigations, relevant treatment strategies and assessment of infection severity.

Culture-Based Screening of Aerobic Microbiome in Diabetic Foot Subjects and Developing Non-healing Ulcers

The study was carried on diabetic foot patients to deduce clinical attributes, the occurrence of the range of aerobic microbial flora and to assess their comparative in vitro susceptibility to the customarily used antimicrobials. We also studied the potential risk factors involved in the development of non-healing ulcers. A total of 87 organisms were isolated from 70 specimens, including Escherichia coli (19.5%) among the Gram-negative and Staphylococcus aureus (18.4%) among the Gram-positive as the predominant aerobes explored. Pseudomonas aeruginosa and E. coli were predominant isolates of non-healing ulcers. The antimicrobial sensitivity pattern revealed that vancomycin (100%) and amikacin (90.4%) exhibited highest sensitivity to Gram-positive cocci, while all strains of P. aeruginosa were sensitive toward imipenem (100%). The prevalent uncontrolled glycemic status, altered lipid spectra, the existence of neuropathy, and peripheral vascular disease, suggested predisposition toward the development of non-healing lesions. The study has underlined the need for continuous surveillance of bacteria and their antimicrobial sensitivity blueprints to provide the basis for empirical therapy and to minimize the risk of complications. Further, stringent clinical evaluation, and medical history will help in revealing the risk of developing non-healing status in diabetic foot ulcers.

Colistin, mechanisms and prevalence of resistance

BACKGROUND

Infections caused by multi-drug-resistant Gram-negative bacteria, particularly Acinetobacter baumannii, Pseudomonas aeruginosa and Klebsiella pneumoniae, that cause nosocomial infections, represent a growing problem worldwide. The rapid increase in the prevalence of Gram-negative pathogens that are resistant to fluoroquinolones and aminoglycosides as well as all β-lactams, including carbapenems, monobactam, cephalosporins and broad-spectrum penicillins, has prompted the reconsideration of colistin as a valid therapeutic option. Colistin is an old class of cationic, which act by disrupting the bacterial membranes resulting in cellular death. Although there has been a significant recent increase in the data gathered on colistin, focusing on its chemistry, antibacterial activity, mechanism of action and resistance, pharmacokinetics, pharmacodynamics and new clinical application, the prevalence of colistin resistance has been very little reported in the literature. This review concentrates on recent literature aimed at optimizing the clinical use of this important antibiotic.

METHODS

The available evidence from various studies (microbiological and clinical studies, retrieved from the PubMed, and Scopus databases) regarding the mechanisms and prevalence of resistance was evaluated.

RESULTS

Increasing use of colistin for treatment of infections caused by these bacteria has led to the emergence of colistin resistance in several countries worldwide. Although resistance to polymyxins is generally less than 10%, it is higher in the Mediterranean and South-East Asia (Korea and Singapore), where colistin resistance rates are continually increasing.

CONCLUSION

There is a critical need for effective infection prevention and control measures and strict use of antibiotics in the world to control the rise and spread of colistin resistance.

In diabetic foot infections antibiotics are to treat infection, not to heal wounds

INTRODUCTION

Diabetic foot ulcers, especially when they become infected, are a leading cause of morbidity and may lead to severe consequences, such as amputation. Optimal treatment of these diabetic foot problems usually requires a multidisciplinary approach, typically including wound debridement, pressure off-loading, glycemic control, surgical interventions and occasionally other adjunctive measures.

AREAS COVERED

Antibiotic therapy is required for most clinically infected wounds, but not for uninfected ulcers. Unfortunately, clinicians often prescribe antibiotics when they are not indicated, and even when indicated the regimen is frequently broader spectrum than needed and given for longer than necessary. Many agents are available for intravenous, oral or topical therapy, but no single antibiotic or combination is optimal. Overuse of antibiotics has negative effects for the patient, the health care system and society. Unnecessary antibiotic therapy further promotes the problem of antibiotic resistance.

EXPERT OPINION

The rationale for prescribing topical, oral or parenteral antibiotics for patients with a diabetic foot wound is to treat clinically evident infection. Available published evidence suggests that there is no reason to prescribe antibiotic therapy for an uninfected foot wound as either prophylaxis against infection or in the hope that it will hasten healing of the wound.

A new strategy to fight antimicrobial resistance: the revival of old antibiotics

The increasing prevalence of hospital and community-acquired infections caused by multidrug-resistant (MDR) bacterial pathogens is limiting the options for effective antibiotic therapy. Moreover, this alarming spread of antimicrobial resistance has not been paralleled by the development of novel antimicrobials. Resistance to the scarce new antibiotics is also emerging. In this context, the rational use of older antibiotics could represent an alternative to the treatment of MDR bacterial pathogens. It would help to optimize the armamentarium of antibiotics in the way to preserve new antibiotics and avoid the prescription of molecules known to favor the spread of resistance (i.e., quinolones). Furthermore, in a global economical perspective, this could represent a useful public health orientation knowing that several of these cheapest “forgotten” antibiotics are not available in many countries. We will review here the successful treatment of MDR bacterial infections with the use of old antibiotics and discuss their place in current practice.

Clinical Outcomes of Multidrug Resistant Pseudomonas aeruginosa Infection and the Relationship With Type III Secretion System in Patients With Diabetic Foot

The objective was to analyze the clinical outcomes of multidrug resistant Pseudomonas aeruginosa (MDRPA) infection and determine the relationship between type III secretion system (TTSS) and MDRPA in diabetic foot (DF) patients. A total of 117 patients infected with P aeruginosa were recruited and grouped into MDRPA and non-MDRPA group according to antimicrobial susceptibility testing. TTSS genes were detected by polymerase chain reaction (PCR). Potential risk factors for MDRPA infection were examined using univariate and multivariate analyses. Clinical outcomes were compared on the basis of MDRPA or TTSS virulence gene. Previous antibiotic therapy, previous hospitalization and osteomyelitis were associated with MDRPA infection. MDRPA group had a higher amputation/toe rate (32.6% vs 16.2%) and lower healing rate (20.9% vs 41.9%) than non-MDRPA group ( P = .032). A significantly higher proportion of exoU was present in MDRPA group (75.0% vs 25.0%, P < .05) than non-MDRPA group. Patients infected with exoU isolates had a lower healing rate and higher amputation/toe rate (25.0% vs 65.2%, 33.3% vs 8.7%, P < .05) than infected with exoS isolates. The exoU gene was predominance among MDRPA strains. The poor clinical outcomes of MDRPA infection in patients with DF were attributable to exoU gene.

Influence of taurine haloamines (TauCl and TauBr) on the development of Pseudomonas aeruginosa biofilm: a preliminary study

Biofilms are consortia of microorganisms (sessile cells) that form on various surfaces including mucosal membranes or teeth. Bacterial biofilms cause many human infections such as chronic sinusitis, acne vulgaris, periodontal diseases, and chronic wounds. These infections are persistent as they show increased resistance to antibiotics and host defense system. Taurine chloramine (TauCl) and taurine bromamine (TauBr) are the physiological products of activated neutrophils, resulting from the reaction between taurine with hypochlorous acid (HOCl) and hypobromous acid (HOBr), respectively. It has been shown in vitro that taurine haloamines exert antimicrobial properties against various pathogenic bacteria. Moreover, clinical studies have shown that both haloamines are effective in the local treatment of skin and mucose infections, including biofilm-related infections. Nevertheless, it has been not tested yet whether they can kill bacteria hidden in biofilm or disrupt biofilm structure. In this study we have investigated the capacity of TauCl and TauBr to inhibit in vitro the formation of P. aeruginosa biofilm. We have also tested their ability to destroy the mature biofilm. Our results suggest that TauBr is able to inhibit in vitro the formation of P. aeruginosa biofilm but cannot destroy the mature biofilm and effectively killed hidden bacteria. In further studies, the combined effect of TauBr and DNase, one of suggested biofilm inhibitors, was tested. Together, we conclude that TauBr is a better than TauCl candidate for local therapy of biofilm-related infections. However, a combined therapy, an application of TauBr together with other anti-biofilm agents (e.g., DNase), seems to be more promising.

The use of intravenous colistin among children in the United States: results from a multicenter, case series

BACKGROUND

A rapid increase in multidrug-resistant Gram-negative infections has led to a reemergence of colistin use globally. Although it is well described among adults, colistin use and its associated toxicities in children are poorly understood. We report findings from the largest case series of pediatric colistin use to date.

METHODS

We queried pediatric infectious diseases specialists from the Emerging Infections Network to identify members who had prescribed intravenous colistin within the past 7 years. We collected relevant demographic and clinical data. Bivariate analyses and multivariable logistic regression were performed.

RESULTS

Two hundred twenty-nine pediatric infectious diseases specialists completed the survey (84% response); 22% had prescribed colistin to children. Among respondents, 92 cases of colistin use from 25 institutions were submitted. The most commonly targeted organisms were multidrug-resistant Pseudomonas (67.4%), multidrug-resistant Acinetobacter -baumanii (11.9%), carbapenemase-producing Enterobacteriaceae (13.0%) and extended-spectrum β-lactamase producing Enterobacteriaceae (5.4%). Development of resistance to colistin was observed in 20.5% of patients. Additional antimicrobial therapy was administered to 84% of patients, and 22% of children experienced nephrotoxicity (not associated with dosage or interval of colistin prescribed). Renal function returned to baseline in all patients. Children aged ≥13 years had approximately 7 times the odds of developing nephrotoxicity than younger children, even after controlling for receipt of additional nephrotoxic agents (odds ratio 7.16; 95% confidence interval: 1.51-14.06; P = 0.013). Four children exhibited reversible neurotoxicity.

CONCLUSIONS

Most pediatric infectious diseases specialists have no experience prescribing colistin. Colistin use in children has been associated primarily with nephrotoxicity and, to a lesser extent, neurotoxicity, both of which are reversible. Emergence of resistance to colistin is concerning.

Combination therapy for treatment of infections with gram-negative bacteria

Combination antibiotic therapy for invasive infections with Gram-negative bacteria is employed in many health care facilities, especially for certain subgroups of patients, including those with neutropenia, those with infections caused by Pseudomonas aeruginosa, those with ventilator-associated pneumonia, and the severely ill. An argument can be made for empiric combination therapy, as we are witnessing a rise in infections caused by multidrug-resistant Gram-negative organisms. The wisdom of continued combination therapy after an organism is isolated and antimicrobial susceptibility data are known, however, is more controversial. The available evidence suggests that the greatest benefit of combination antibiotic therapy stems from the increased likelihood of choosing an effective agent during empiric therapy, rather than exploitation of in vitro synergy or the prevention of resistance during definitive treatment. In this review, we summarize the available data comparing monotherapy versus combination antimicrobial therapy for the treatment of infections with Gram-negative bacteria.

Antimicrobial resistance in internal medicine wards

Antimicrobial resistance is a global medical problem, affecting most bacterial pathogens. The major challenges are currently posed by methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), Enterobacteriaceae producing extended-spectrum-beta-lactamases (ESBL) and carbapenemases, and multi-resistant strains of Pseudomonas aeruginosa and Acinetobacter baumannii. Therapeutic options are very limited and, in some cases, virtually unavailable. This article provides an overview of the recent epidemiological trends exhibited by the most important multi-resistant pathogens, and of the treatment options that are currently available for these infections.

2012 Infectious Diseases Society of America clinical practice guideline for the diagnosis and treatment of diabetic foot infections

Foot infections are a common and serious problem in persons with diabetes. Diabetic foot infections (DFIs) typically begin in a wound, most often a neuropathic ulceration. While all wounds are colonized with microorganisms, the presence of infection is defined by ≥2 classic findings of inflammation or purulence. Infections are then classified into mild (superficial and limited in size and depth), moderate (deeper or more extensive), or severe (accompanied by systemic signs or metabolic perturbations). This classification system, along with a vascular assessment, helps determine which patients should be hospitalized, which may require special imaging procedures or surgical interventions, and which will require amputation. Most DFIs are polymicrobial, with aerobic gram-positive cocci (GPC), and especially staphylococci, the most common causative organisms. Aerobic gram-negative bacilli are frequently copathogens in infections that are chronic or follow antibiotic treatment, and obligate anaerobes may be copathogens in ischemic or necrotic wounds. Wounds without evidence of soft tissue or bone infection do not require antibiotic therapy. For infected wounds, obtain a post-debridement specimen (preferably of tissue) for aerobic and anaerobic culture. Empiric antibiotic therapy can be narrowly targeted at GPC in many acutely infected patients, but those at risk for infection with antibiotic-resistant organisms or with chronic, previously treated, or severe infections usually require broader spectrum regimens. Imaging is helpful in most DFIs; plain radiographs may be sufficient, but magnetic resonance imaging is far more sensitive and specific. Osteomyelitis occurs in many diabetic patients with a foot wound and can be difficult to diagnose (optimally defined by bone culture and histology) and treat (often requiring surgical debridement or resection, and/or prolonged antibiotic therapy). Most DFIs require some surgical intervention, ranging from minor (debridement) to major (resection, amputation). Wounds must also be properly dressed and off-loaded of pressure, and patients need regular follow-up. An ischemic foot may require revascularization, and some nonresponding patients may benefit from selected adjunctive measures. Employing multidisciplinary foot teams improves outcomes. Clinicians and healthcare organizations should attempt to monitor, and thereby improve, their outcomes and processes in caring for DFIs.

Pharmacokinetics and pharmacodynamics of 'old' polymyxins: what is new?

'Old' colistin and polymyxin B are increasingly used as last-line therapy against multidrug-resistant Gram-negative bacteria Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae. For intravenous administration, colistin is dosed as its inactive prodrug colistin methanesulfonate (sodium), while polymyxin B is used as its sulfate (active antibacterial). Over the last decade, significant progress has been made in understanding their chemistry, pharmacokinetics (PK), and pharmacodynamics (PD). The first scientifically based dosing suggestions are now available for colistin methanesulfonate to generate a desired target steady-state plasma concentration of formed colistin in various categories of critically ill patients. As simply increasing polymyxin dosage regimens is not an option for optimizing their PK/PD due to nephrotoxicity, combination therapy with other antibiotics has great potential to maximize the efficacy of polymyxins while minimizing emergence of resistance. We must pursue rational approaches to the use of polymyxins and other existing antibiotics through the application of PK/PD principles.

Medical management of diabetic foot infections

Diabetic foot infections (DFIs) are a commonly encountered medical problem. They are associated with an increased frequency and length of hospitalization and risk for lower-extremity amputation. Furthermore, they have substantial economic consequences. Patients with diabetes mellitus are particularly susceptible to foot infections because of neuropathy, vascular insufficiency, and diminished neutrophil function. The approach to managing DFIs starts with determining if an infection exists. If an infection exists, then the type, severity, extent of infection, and risk factors for resistant organisms should be determined through history, physical examination, and additional laboratory and radiological testing. Optimal management requires surgical debridement, pressure offloading, effective antibiotic therapy, wound care and moisture, maintaining good vascular supply, and correction of metabolic abnormalities, such as hyperglycemia, through a multidisciplinary team. Empiric antibiotics for DFIs vary based on the severity of the infection, but must include anti-staphylococcal coverage.

Systemic antimicrobial therapy in osteomyelitis

Appropriately designed antibiotic regimens are critical to the management of all stages of osteomyelitis, although goals of therapy may vary in different stages of infection. The most important consideration for antibiotic selection is spectrum of action. Route of administration by intravenous or oral route is less important than drug levels that are achievable at the site of infection. Outpatient parenteral therapy and use of oral agents has simplified delivery of long-term treatment regimens. There are few high-quality studies that compare specific treatment regimens or durations of therapy, and recommendations for drugs and duration of antibiotic therapy are based on expert opinion, case series, and extrapolations from animal models. Intravenous beta-lactams are the treatment of choice for methicillin-susceptible Staphylococcus aureus, but there are also oral options available. Vancomycin has been the treatment of choice for methicillin-resistant Staphylococcus aureus osteomyelitis, but there are several newer parenteral and oral agents for treatment of methicillin-resistant Staphylococcus aureus including linezolid and daptomycin. Rifampin combined with other staphylococcal agents may increase cure rates, especially for device-associated infections. Oral fluoroquinolones and parenteral beta-lactam agents can be used for treatment of gram-negative osteomyelitis, but increasing resistance has complicated management of these infections.

Management of diabetic foot infections in an era of increasing microbial resistance

Diabetic foot infections cause substantial morbidity, incur significant costs, and may lead to amputation. Resistant organisms, particularly methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant gram-negative organisms, are becoming more prevalent. Optimal management of diabetic foot infections is multimodal, and includes not only antimicrobial therapy but also biomechanical support and offloading, local wound care, glycemic control, assessment and treatment of underlying vascular disease, and surgical therapy when warranted. Antimicrobial therapy should be targeted at the likely etiologic agents and should take into consideration the depth and severity of infection. With expansion of the reservoir of resistant organisms, obtaining reliable deep cultures can help focus antimicrobial therapy against the dominant pathogens. Newer agents against resistant gram-positive and gram-negative organisms show promise in the treatment of diabetic foot infections.

Rifampin combination therapy for nonmycobacterial infections

The increasing emergence of antimicrobial-resistant organisms, especially methicillin-resistant Staphylococcus aureus (MRSA), has resulted in the increased use of rifampin combination therapy. The data supporting rifampin combination therapy in nonmycobacterial infections are limited by a lack of significantly controlled clinical studies. Therefore, its current use is based upon in vitro or in vivo data or retrospective case series, all with major limitations. A prominent observation from this review is that rifampin combination therapy appears to have improved treatment outcomes in cases in which there is a low organism burden, such as biofilm infections, but is less effective when effective surgery to obtain source control is not performed. The clinical data support rifampin combination therapy for the treatment of prosthetic joint infections due to methicillin-sensitive S. aureus (MSSA) after extensive debridement and for the treatment of prosthetic heart valve infections due to coagulase-negative staphylococci. Importantly, rifampin-vancomycin combination therapy has not shown any benefit over vancomycin monotherapy against MRSA infections either clinically or experimentally. Rifampin combination therapy with daptomycin, fusidic acid, and linezolid needs further exploration for these severe MRSA infections. Lastly, an assessment of the risk-benefits is needed before the addition of rifampin to other antimicrobials is considered to avoid drug interactions or other drug toxicities.

New information about the polymyxin/colistin class of antibiotics

Infections by multidrug resistant Gram-negative bacilli (MDR-GNB) have become a major threat for patients hospitalized in intensive care units, representing a prevalent cause of morbimortality in the critically ill, since these microorganisms have developed resistance to most available antimicrobial agents. In this respect, very few therapeutic innovations have been developed in recent years, and it is not foreseen that any new drugs will be commercialized in the near future. Tigecycline represents an effective alternative in this setting, but lacks activity against Pseudomonas aeruginosa, and its use has not been validated for all organ-specific infections. Frequently, only old antibiotics like colistin remain a valid option. New pharmaceutical formulations and dosage regimens of polymyxins have considerably reduced the toxicity previously attributed to these antimicrobials, and have made it possible to reintroduce them into clinical practice. Nonetheless, the effectiveness of polymyxins is still suboptimal, and the expansion of heteroresistance and pan-drug-resistant strains of gram-negative bacilli is of concern. Improvements in dosing, alternative methods of administration and different synergic antimicrobial combinations have been proposed in recent literature, among other measures, to enhance the effectiveness of polymyxins. The latest data regarding polymyxins and their clinical use are discussed in this review.

Rifampicin combined regimens for gram-negative infections: data from the literature

Multidrug-resistant (MDR) gram-negative bacterial infections are associated with high morbidity and mortality. Given the lack of availability of new highly effective antimicrobial drugs against multiresistant strains, combination regimens are administered that include rifampicin for its demonstrated in vitro synergism with multiple drugs. A literature review was performed of clinical studies reporting the use of rifampicin in the treatment of MDR gram-negative bacterial infections. Nineteen studies were found, including only one randomised controlled study. Data in the literature on combined therapeutic regimens with rifampicin are limited and refer mostly to uncontrolled studies. Therefore, the real clinical benefit of using rifampicin-containing therapies for the treatment of gram-negative multiresistant bacteria in terms of clinical outcome and survival rates still needs to be assessed.

Intravenous colistimethate (colistin) use in critically ill children without cystic fibrosis

INTRODUCTION

The increasing frequency of infections caused by multidrug-resistant (MDR) Gram-negative bacteria has led to the reappraisal of colistimethate use.

METHODS

We present a case series of critically ill pediatric patients without cystic fibrosis who received intravenous colistimethate treatment. All available relevant medical records were reviewed.

RESULTS

Seven children without cystic fibrosis (mean age 7.7 years; 2 female), admitted to the intensive care unit of a tertiary-care pediatric hospital in Athens, Greece, were identified to have received intravenous colistimethate during October 2004 to May 2008. MDR Acinetobacter baumannii, Pseudomonas aeruginosa, and/or Klebsiella pneumoniae were isolated from blood and/or bronchial secretions specimens in 6 of 7 reported patients. All isolates were susceptible to colistin. All 7 patients received intravenous colistimethate in a dosage of 5 mg/kg daily (divided in 3 equal doses, administered every 8 hours). Five children received colistimethate for 10 days and the remaining 2 for 2 and 23 days, respectively. The infections caused by MDR Gram-negative bacteria were improved in 6 children with microbiologically documented infections. Five of the 7 children were discharged from the ICU. The remaining 2 children died (1 of them had received colistimethate for 2 days); their death was not attributed to MDR Gram-negative infection. No nephrotoxicity or other type of toxicity of colistimethate was noted in this case-series.

CONCLUSIONS

Although the small number of included cases precludes any firm conclusions, our study suggests that colistimethate may have a role for the treatment of infections caused by MDR Gram-negative bacteria in critically ill pediatric patients.

Re-emergence of colistin in today's world of multidrug-resistant organisms: personal perspectives

BACKGROUND

Infections due to multidrug-resistant Gram-negative bacteria (including Acinetobacter baumannii, Pseudomonas aeruginosa, and Klebsiella pneumoniae) are being reported with increasing frequency from various parts of the world.

OBJECTIVE

To share personal perspectives on the clinical use of colistin based on the available evidence reported in the literature as well as on knowledge obtained through our clinical experience with the use of colistin in a considerable number of patients during the past 7 years.

METHODS

Literature review and personal experience.

RESULTS/CONCLUSION

During the last decade, clinicians in several countries have resorted to colistin (polymyxin E), an antibiotic that has been shown to be clinically effective and acceptably safe for intravenous, aerosolized, and intrathecal/intraventricular administration. However, more data are needed to answer important clinical questions, including the appropriate colistin dosage, comparison of colistin monotherapy with combination therapy, and the possible preventive and therapeutic role of aerosolized colistin.

New developments in diagnosing and treating diabetic foot infections

Foot infections are common in persons with diabetes and are often the proximate cause of lower extremity amputation. There have been many publications in the past few years dealing with the appropriate ways to diagnose and treat diabetic foot infections. This review presents information gathered from a comprehensive, ongoing surveillance of the literature (published and abstracts) over the past 4 years. Prospective studies have now defined the epidemiology of diabetic foot infections, as well as methods to score and classify the wounds. Several recently published guidelines can assist clinicians in managing these infections. The etiologic agents of infection have been well-defined, and the prevalence of multi-drug-resistance pathogens is growing. Molecular methods offer great promise for quicker and more sensitive diagnosis of infection. New antimicrobial agents, both systemic and topical, as well as novel local treatments, have been shown to be effective in various studies. Improved methods of deploying older agents have added to the variety of treatment approaches now available. Several adjunctive treatments may benefit some patients but their role is as yet unclear. While there is much yet to learn about the most cost-effective ways to diagnose and treat diabetic foot infections the main effort is now to disseminate the available information and facilitate employing the evidence-based guideline recommendations.