Colistin and polymyxin B in critical care

Reaction-Induced Self-Assembly of Polymyxin Mitigates Cytotoxicity and Reverses Drug Resistance

Polymyxins have been regarded as an efficient therapeutic against many life-threatening, multidrug resistant Gram-negative bacterial infections; however, the cytotoxicity and emergence of drug resistance associated with polymyxins have greatly hindered their clinical potential. Herein, the reaction-induced self-assembly (RISA) of polymyxins and natural aldehydes in aqueous solution is presented. The resulting assemblies effectively mask the positively charged nature of polymyxins, reducing their cytotoxicity. Moreover, the representative PMBA4 (composed of polymyxin B (PMB) and (E)-2-heptenal (A4)) assemblies demonstrate enhanced binding to Gram-negative bacterial outer membranes and exhibit multiple antimicrobial mechanisms, including increased membrane permeability, elevated bacterial metabolism, suppression of quorum sensing, reduced ATP synthesis, and potential reduction of bacterial drug resistance. Remarkably, PMBA4 assemblies reverse drug resistance in clinically isolated drug-resistant strains of Gram-negative bacteria, demonstrating exceptional efficacy in preventing and eradicating bacterial biofilms. PMBA4 assemblies efficiently eradicate Gram-negative bacterial biofilm infections in vivo and alleviate inflammatory response. This RISA strategy offers a practical and clinically applicable approach to minimize side effects, reverse drug resistance, and prevent the emergence of resistance associated with free polymyxins.

Lipid A in outer membrane vesicles shields bacteria from polymyxins

The continuous emergence of multidrug-resistant bacterial pathogens poses a major global healthcare challenge, with Klebsiella pneumoniae being a prominent threat. We conducted a comprehensive study on K. pneumoniae's antibiotic resistance mechanisms, focusing on outer membrane vesicles (OMVs) and polymyxin, a last-resort antibiotic. Our research demonstrates that OMVs protect bacteria from polymyxins. OMVs derived from Polymyxin B (PB)-stressed K. pneumoniae exhibited heightened protective efficacy due to increased vesiculation, compared to OMVs from unstressed Klebsiella. OMVs also shield bacteria from different bacterial families. This was validated ex vivo and in vivo using precision cut lung slices (PCLS) and Galleria mellonella. In all models, OMVs protected K. pneumoniae from PB and reduced the associated stress response on protein level. We observed significant changes in the lipid composition of OMVs upon PB treatment, affecting their binding capacity to PB. The altered binding capacity of single OMVs from PB stressed K. pneumoniae could be linked to a reduction in the lipid A amount of their released vesicles. Although the amount of lipid A per vesicle is reduced, the overall increase in the number of vesicles results in an increased protection because the sum of lipid A and therefore PB binding sites have increased. This unravels the mechanism of the altered PB protective efficacy of OMVs from PB stressed K. pneumoniae compared to control OMVs. The lipid A-dependent protective effect against PB was confirmed in vitro using artificial vesicles. Moreover, artificial vesicles successfully protected Klebsiella from PB ex vivo and in vivo. The findings indicate that OMVs act as protective shields for bacteria by binding to polymyxins, effectively serving as decoys and preventing antibiotic interaction with the cell surface. Our findings provide valuable insights into the mechanisms underlying antibiotic cross-protection and offer potential avenues for the development of novel therapeutic interventions to address the escalating threat of multidrug-resistant bacterial infections.

Resistance mechanisms for Gram-negative bacteria-specific lipopeptides, turnercyclamycins, differ from that of colistin

IMPORTANCE

Bacterial resistance to antibiotics is a crisis. Acinetobacter baumannii is among the CDC urgent threat pathogens in part for this reason. Lipopeptides known as turnercyclamycins are produced by symbiotic bacteria that normally live in marine mollusks, where they may be involved in shaping their symbiotic niche. Turnercyclamycins killed Gram-negative pathogens including drug-resistant Acinetobacter, but how do the mechanisms of resistance compare to other lipopeptide drugs? Here, we define resistance from a truncation of MlaA, a protein involved in regulating bacterial membrane phospholipids. Intriguingly, this resistance mechanism only affected one turnercyclamycin variant, which differed only in two atoms in the lipid tail of the compounds. We could not obtain significant resistance to the second turnercyclamycin variant, which was also effective in an infection model. This study reveals an unexpected subtlety in resistance to lipopeptide antibiotics, which may be useful in the design and development of antibiotics to combat drug resistance.

The Efficacy and Safety of Intravenous Colistin Plus Aerosolized Colistin Versus Intravenous Colistin Alone in Critically Ill Trauma Patients With Multi-Drug Resistant Gram-Negative Bacilli Infection

BACKGROUND AND AIM

Gram-negative bacteria (GNB) with potential multiple drug resistance (MDR) have emerged as a major group of organisms causing ventilator-associated pneumonia (VAP). Higher concentrations are deposited directly in the lungs when antibiotics are given via inhalation, minimizing systemic side effects. This study aims to compare the efficacy and safety of intravenous plus aerosolized colistin versus intravenous (IV) colistin alone in critically ill trauma patients who reported MDR-GNB infection on endotracheal aspirate culture.

METHODS

A hundred patients were recruited in the Intensive Care Unit, Trauma Centre, Institute of Medical Sciences, Banaras Hindu University, Varanasi, and randomly assigned to the control (n=50) group, which received IV colistin plus aerosolized colistin and the intervention group (n = 50), which received IV colistin alone. Changes in total leucocyte count (TLC), renal function test (RFT), endotracheal aspirate culture, 24-hour urine output, length of ICU stay, and 28-day ICU mortality were investigated.

RESULTS

Patients receiving intravenous plus nebulized colistin therapy had a better outcome compared to IV colistin alone in terms of faster eradication of MDR-GNB infection. A rise in serum urea and creatinine levels was seen in both groups, which were significantly higher, along with a decrease in urine output in the group receiving intravenous colistin alone. No significant difference was observed in serum sodium and potassium levels in the RFT protocol, length of ICU stay, or 28-day ICU mortality.

CONCLUSION

Intravenous nebulized colistin could be considered a better alternative therapy for VAP caused by multi-drug-resistant Gram-negative bacteria in the ICU in terms of faster microbiological cure and lesser nephrotoxicity.

Nutraceuticals and network pharmacology approach for acute kidney injury: A review from the drug discovery aspect

Acute kidney injury (AKI) has become a global health issue, with ~12 million reports yearly, resulting in a persistent increase in morbidity and mortality rates. AKI pathophysiology is multifactorial involving oxidative stress, mitochondrial dysfunction, epigenetic modifications, inflammation, and eventually, cell death. Hence, therapies able to target multiple pathomechanisms can aid in AKI management. To change the drug discovery framework from "one drug, one target" to "multicomponent, multitarget," network pharmacology is evolving as a next-generation research approach. Researchers have used the network pharmacology approach to predict the role of nutraceuticals against different ailments including AKI. Nutraceuticals (herbal products, isolated nutrients, and dietary supplements) belong to the pioneering category of natural products and have shown protective action against AKI. Nutraceuticals have recently drawn attention because of their ability to provide physiological benefits with less toxic effects. This review emphasizes the nutraceuticals that exhibited renoprotection against AKI and can be used either as monotherapy or adjuvant with conventional therapies to boost their effectiveness and lessen the adverse effects. Additionally, the study sheds light on the application of network pharmacology as a cost-effective and time-saving approach for the therapeutic target prediction of nutraceuticals against AKI.

Colistin conditioning surfaces combined with antimicrobial treatment to prevent ventilator-associated infections

Biofilm formation on endotracheal tubes (ETT) is an important factor in the development of ventilator-associated pneumonia (VAP). This work aimed to investigate the effectiveness of colistin (COL) against the early stages of biofilm formation by Pseudomonas aeruginosa. Two strategies were used: pre-conditioning the adhesion surfaces with COL before biofilm formation and growing biofilms in its presence. The combined effect of treating P. aeruginosa 24-hours old biofilms with Ciprofloxacin (CIP) or colistin (COL) on clean and COL-conditioned surfaces was also assessed. Random deposition of COL residues altered the physico-chemical properties of the adhesion surfaces and impaired biofilm formation. Moreover, as a consequence of the reduced amount of biofilms attached to COL conditioned surfaces, adhered cells became more exposed to the subsequent action of CIP or COL, suggesting a combined outcome of prophylactic and therapeutic COL-based strategies. Results highlighted the promising use of COL to prevent the establishment of biofilms on ETT.

In vitro research of combination therapy for multidrug-resistant Klebsiella pneumoniae bloodstream infections

Objective

Multidrug-resistant Klebsiella pneumoniae (MDR KP) bloodstream infections are a serious problem. The objective of this study was to investigate the effects of appropriate combination therapies on MDR KP bloodstream infections.

Methods

MDR KP strains isolated from clinical samples were assessed for antibiotic susceptibility using the broth microdilution method. Twenty consecutive MDR KP clinical isolates from patients with bloodstream infections were examined in this study. The experiments were conducted at the Bacterial Laboratory of Tongde Hospital from March to August 2021. Antibiotic combination tests were performed using the minimum inhibitory concentration (MIC) test, and the sum of the fractional inhibitory concentration was used to assess synergy.

Results

Following treatment with a combination of two antibiotic agents, the MIC50 and MIC90 values decreased compared with that before treatment. MIC50 decreased by at least 50%, with one value reduced to 6.25% of the pretreatment value. None of the antibiotic combinations were antagonistic. Combination of polymyxin B with rifampicin or tigecycline had a synergistic effect on 70% and 65% of the strains, respectively.

Conclusions

In vitro combination therapies with two active drug agents (polymyxin B plus rifampicin or tigecycline) had a better effect on MDR KP infections compared with that in other regimens.

Updates on the global dissemination of colistin-resistant Escherichia coli: An emerging threat to public health

Colistin drug resistance is an emerging public health threat worldwide. The adaptability, existence and spread of colistin drug resistance in multiple reservoirs and ecological environmental settings is significantly increasing the rate of occurrence of multidrug resistant (MDR) bacteria such as Escherichia coli (E. coli). Here, we summarized the reports regarding molecular and biological characterization of mobile colistin resistance gene (mcr)-positive E. coli (MCRPEC), originating from diverse reservoirs, including but not limited to humans, environment, waste water treatment plants, wild, pets, and food producing animals. The MCRPEC revealed the abundance of clinically important resistance genes, which are responsible for MDR profile. A number of plasmid replicon types such as IncI2, IncX4, IncP, IncX, and IncFII with a predominance of IncI2 were facilitating the spread of colistin resistance. This study concludes the distribution of multiple sequence types of E. coli carrying mcr gene variants, which are possible threat to "One Health" perspective. In addition, we have briefly explained the newly known mechanisms of colistin resistance i.e. plasmid-encoded resistance determinant as well as presented the chromosomally-encoded resistance mechanisms. The transposition of ISApl1 into the chromosome and existence of intact Tn6330 are important for transmission and stability for mcr gene. Further, genetic environment of co-localized mcr gene with carbapenem-resistance or extended-spectrum β-lactamases genes has also been elaborated, which is limiting human beings to choose last resort antibiotics. Finally, environmental health and safety control measures along with spread mechanisms of mcr genes are discussed to avoid further propagation and environmental hazards of colistin resistance.

Pulmonary biofilm-based chronic infections and inhaled treatment strategies

Certain pulmonary diseases, such as cystic fibrosis (CF), non-CF bronchiectasis, chronic obstructive pulmonary disease, and ventilator-associated pneumonia, are usually accompanied by respiratory tract infections due to the physiological alteration of the lung immunological defenses. Recurrent infections may lead to chronic infection through the formation of biofilms. Chronic biofilm-based infections are challenging to treat using antimicrobial agents. Therefore, effective ways to eradicate biofilms and thus relieve respiratory tract infection require the development of efficacious agents for biofilm destruction, the design of delivery carriers with biofilm-targeting and/or penetrating abilities for these agents, and the direct delivery of them into the lung. This review provides an in-depth description of biofilm-based infections caused by pulmonary diseases and focuses on current existing agents that are administered by inhalation into the lung to treat biofilm, which include i) inhalable antimicrobial agents and their combinations, ii) non-antimicrobial adjuvants such as matrix-targeting enzymes, mannitol, glutathione, cyclosporin A, and iii) liposomal formulations of anti-biofilm agents. Finally, novel agents that have shown promise against pulmonary biofilms as well as traditional and new devices for pulmonary delivery of anti-biofilm agents into the lung are also discussed.

Formulation of chitosan coated nanoliposomes for the oral delivery of colistin sulfate: in vitro characterization, 99mTc-radiolabeling and in vivo biodistribution studies

Colistin sulfate is a very important antibiotic for the treatment of multidrug-resistant Gram-negative infections. Unfortunately, it has low oral bioavailability and several side effects following parenteral administration. The present study aims to develop chitosan-coated colistin nanoliposomes to improve the stability in the gastrointestinal tract and to enhance the oral delivery of colistin. The chitosan-coated colistin nanoliposomes were obtained via thin-film evaporation and electrostatic deposition methods using either Span 60, Tween 65 or Tween 80 as surfactants with different cholesterol: surfactant: soya lecithin ratios. The influence of systems variables was further characterized by vesicle size analysis, zeta potential (ZP), poly dispersibility index (PDI), and also their entrapment efficiency percentage (EE %) was evaluated. Various systems were formed with vesicle sizes in the nano-range, 155.64 ± 12.53 nm to 315.64 ± 15.90 nm, and EE % of 45.2 ± 2.9% to 81.8 ± 2.9%. Moreover, the ZP value of the prepared nanoliposomes switched from a negative to a positive value after chitosan coating. To track the released colistin in vivo, technetium 99m (^99mTc) was incorporated into the optimum system (S-3) system via direct coupling with colistin. Chitosan-coated ^99mTc-colistin nanoliposome, ^99mTc-colistin suspension, and ^99mTc-chitosan-coated nanoliposomes (placebo) were administered orally into bacterial infection (Escherichia coli) bearing mice. The biodistribution results showed that chitosan-coated nanoliposome significantly enhanced the bioavailability of colistin compared to colistin suspension (the commercially available). Moreover, the system effectively improved the localization of colistin at the infected muscle. In conclusion, this approach offers a promising tool for enhanced oral delivery of colistin.

Clinical use of intravenous polymyxin B for the treatment of patients with multidrug-resistant Gram-negative bacterial infections: An evaluation of the current evidence

OBJECTIVES

The epidemic dimensions of the emergence of multidrug-resistant (MDR) Gram-negative bacterial infections have led to the revival of old antibiotics, including the polymyxins.

METHODS

We performed a review and meta-analysis to evaluate the current literature data regarding the effectiveness and safety of intravenous polymyxin B in patients with MDR Gram-negative bacterial infections and the overall mortality and nephrotoxicity in patients treated with intravenous polymyxin B either as monotherapy or combination therapy.

RESULTS

A total of 5 prospective and 28 retrospective studies, 1 cross-sectional study, 2 retrospective case series and 7 case reports provided data regarding the effectiveness and/or toxicity of intravenous polymyxin B. All-cause mortality of 2910 patients (from 27 studies) who received intravenous polymyxin B was 41.2% (95% CI 35.5-47.0%). All-cause nephrotoxicity of 2994 patients (from 28 studies) treated with intravenous polymyxin B was 40.7% (95% CI 35.0-46.6%). Renal failure among 2111 patients (from 14 studies) was 11.2% (95% CI 8.7-13.9%).

CONCLUSION

Mortality of patients treated with intravenous polymyxin B is similar to the literature-reported mortality of patients treated with intravenous colistin, while nephrotoxicity associated with polymyxin B use is possibly milder compared with colistin use based on literature data. Head-to-head prospective studies would help to clarify the benefit of polymyxin B over colistin. However, a critical evaluation of the existing worldwide literature data supports the need for availability of the intravenous formulation of polymyxin B as a potentially useful option for the treatment of patients with MDR and extensively drug-resistant (XDR) Gram-negative bacterial infections.

Colistin Update on Its Mechanism of Action and Resistance, Present and Future Challenges

Colistin has been extensively used since the middle of the last century in animals, particularly in swine, for the control of enteric infections. Colistin is presently considered the last line of defense against human infections caused by multidrug-resistant Gram-negative organisms such as carbapenemase-producer Enterobacterales, Acinetobacter baumanni, and Pseudomonas aeruginosa. Transferable bacterial resistance like mcr-genes was reported in isolates from both humans and animals. Researchers actively seek strategies to reduce colistin resistance. The definition of guidelines for colistin therapy in veterinary and human medicine is thus crucial. The ban of colistin use in swine as a growth promoter and for prophylactic purposes, and the implementation of sustainable measures in farm animals for the prevention of infections, would help to avoid resistance and should be encouraged. Colistin resistance in the human-animal-environment interface stresses the relevance of the One Health approach to achieve its effective control. Such measures should be addressed in a cooperative way, with efforts from multiple disciplines and with consensus among doctors, veterinary surgeons, and environment professionals. A revision of the mechanism of colistin action, resistance, animal and human use, as well as colistin susceptibility evaluation is debated here.

Plasmid-Determined Colistin Resistance in the North African Countries: A Systematic Review

We have conducted a systematic review to update available information on plasmid-mediated colistin resistance (mobilized colistin resistance [mcr]) genes in North African countries. We have searched the articles of PubMed, Scopus, and Web of Science databases reporting plasmid-mediated colistin resistance bacteria isolated in North African countries. After searching and selection, 30 studies that included 208 mcr-positive isolates were included. Different mcr-positive strains frequencies were recorded and ranged from 2% in clinical isolates to 12.3% in environmental samples. Escherichia coli was the predominant species recorded and these microorganisms showed high resistance to ciprofloxacin and cotrimoxazole. IncHI2 plasmids are probably the key vectors responsible for the dissemination of mcr genes in these countries. This review highlighted that the mcr-positive isolates are circulating in different ecological niches with different frequencies. Therefore, actions should be implemented to prevent the dissemination of the mcr genes within and outside of these countries, such as microbiological and molecular surveillance programs and restriction use of colistin in farming.

The Efflux Pump MexXY/OprM Contributes to the Tolerance and Acquired Resistance of Pseudomonas aeruginosa to Colistin

The intrinsic resistance of Pseudomonas aeruginosa to polymyxins in part relies on the addition of 4-amino-4-deoxy-l-arabinose (Ara4N) molecules to the lipid A of lipopolysaccharide (LPS), through induction of operon arnBCADTEF-ugd (arn) expression. As demonstrated previously, at least three two-component regulatory systems (PmrAB, ParRS, and CprRS) are able to upregulate this operon when bacteria are exposed to colistin. In the present study, gene deletion experiments with the bioluminescent strain PAO1::lux showed that ParRS is a key element in the tolerance of P. aeruginosa to this last-resort antibiotic (i.e., resistance to early drug killing). Other loci of the ParR regulon, such as those encoding the efflux proteins MexXY (mexXY), the polyamine biosynthetic pathway PA4773-PA4774-PA4775, and Ara4N LPS modification process (arnBCADTEF-ugd), also contribute to the bacterial tolerance in an intricate way with ParRS. Furthermore, we found that both stable upregulation of the arn operon and drug-induced ParRS-dependent overexpression of the mexXY genes accounted for the elevated resistance of pmrB mutants to colistin. Deletion of the mexXY genes in a constitutively activated ParR mutant of PAO1 was associated with significantly increased expression of the genes arnA, PA4773, and pmrA in the absence of colistin exposure, thereby highlighting a functional link between the MexXY/OprM pump, the PA4773-PA4774-PA4775 pathway, and Ara4N-based modification of LPS. The role played by MexXY/OprM in the adaptation of P. aeruginosa to polymyxins opens new perspectives for restoring the susceptibility of resistant mutants through the use of efflux inhibitors.

Effect of an activated charcoal product (DOAC Stop™) intended for extracting DOACs on various other APTT-prolonging anticoagulants

Background

The aim of the study was to investigate the specificity of an activated charcoal-based product (DOAC Stop™) initially intended for the specific extraction of direct oral anticoagulants (DOACs) from test plasmas on a range of other anticoagulants.

Methods

Test plasmas were prepared by adding various anticoagulants to pooled normal plasma at concentrations prolonging an activated partial thromboplastin time (APTT) test by a factor of 1.5–3. These plasmas were treated with DOAC Stop™ for 5 and 20 min. Then APTTs were repeated and residual anticoagulant concentrations estimated from dose-response curves.

Results

The activated charcoal (AC)-based product was found to extract DOACs efficiently. It also bound the intravenous anticoagulants argatroban and lepirudin, but it had no effect on heparin, enoxaparin or danaparoid in plasma. Among other APTT-inhibiting agents that might be present in test plasmas from patients, it extracted protamine, aprotinin and polymyxin. It had no effect on annexin V, thrombomodulin, a typical lupus anticoagulant, a factor VIII antibody, activated protein C or its activator, but it did bind some cationic inhibitors of the APTT with molecular weight below approximately 30 kDa.

Conclusions

The AC-based product extracted DOACs efficiently with no effect on heparin-type anticoagulants. It did bind argatroban and hirudin-type anticoagulants, which might occur in plasmas from some inpatients, and APTT results obtained after its use should be interpreted after due consideration of patient medications.

The aqueous extract of aged black garlic ameliorates colistin-induced acute kidney injury in rats

The use of colistin in the treatment of multidrug-resistant Gram-negative bacterial infections is restricted due to nephrotoxicity. We investigated the effects of aged black garlic extract (ABGE) on colistin-induced kidney injury in rats. Rats were assigned to four groups. Normal saline was intraperitoneally and intragastrically injected for control group. ABGE was intragastrically injected for garlic group. Ten mg/kg of colistin was intraperitoneally injected for 6 consecutive days for colistin group. One percent of ABGE was done 30 min prior to colistin injection for treatment group. Rats were sacrificed on the next day after last colistin injection. Colistin injection increased the serum levels of blood urea nitrogen and creatinine; however, ABGE prevented deterioration of these serum levels. ABGE also alleviated tubular damage, including vacuolation and necrosis. TUNEL-positive cells were observed less frequently for the ABGE-treated groups. CD68 positive cells were significantly decreased by pretreatment with ABGE. Levels of oxidative stress biomarkers such as 8-hydroxydeoxyguanosine and malondialdehyde were lower in the ABGE-treated groups. Levels of NF-κB, inducible NO synthase, COX-2, and TGF-β1 were lower in rats that had been treated with ABGE injection. Renal levels of IL-1β and TNF-α were increased by colistin administration whereas renal SOD, catalase, and GSH levels were restored by ABGE administration. These results suggest that ABGE, which has antioxidant and anti-inflammatory properties, might be a potential therapeutic agent to prevent renal toxicity of colistin.

Effects of Colistin and Bacteriocins Combinations on the In Vitro Growth of Escherichia coli Strains from Swine Origin

Escherichia coli strains from swine origin, either susceptible or resistant to colistin, were grown under planktonic and biofilm cultures. After which, they were treated with antibacterial agents including nisin and enterocin DD14 bacteriocins, colistin and their combinations. Importantly, the combination of colistin, enterocin DD14 and nisin eradicated the planktonic and biofilm cultures of E. coli CIP54127 and the E. coli strains with colistin-resistance phenotype such as E. coli 184 (mcr-1 ⁺) and E. coli 289 (mcr-1 ^-), suggesting therefore that bacteriocins from lactic acid bacteria could be used as agents with antibiotic augmentation capability.

Colistin versus Colistin Combined with Ampicillin-Sulbactam for Multiresistant Acinetobacter baumannii Ventilator-associated Pneumonia Treatment: An Open-label Prospective Study

Background:

Retrospective studies have reported good clinical success rates using colistin as monotherapy to treat Acinetobacter baumannii ventilator-associated pneumonia (VAP), comparable to that obtained with colistin combined with other antibiotics. However, inadequate penetration into the pulmonary parenchyma for colistin has been shown in animal models.

Aim:

The aim of the study was to study prospectively the outcome, measured as clinical response and survival, of intravenously administered colistin versus colistin combined with high-dose ampicillin-sulbactam in Intensive Care Unit (ICU) patients with multiresistant A. baumannii VAP.

Methods and Subjects:

This prospective, open-label, randomized study included consecutive patients who developed microbiologically documented VAP due to A. baumannii with carbapenem-resistant strains but susceptible to colistin and ampicillin-sulbactam. Seventy-four patients were screened, but finally, 39 participants were enrolled and finished the study Patients received colistin (Group A – 19 patients) or colistin and ampicillin/sulbactam (Group B – 20 patients). The clinical response of VAP was assessed on day 4^th to 5^th of treatment (early response). If therapy was considered unsuccessful after this period, ampicillin/sulbactam was added in Group A or changed therapy in B.

Results:

Early cure rates in Group A and B were 15.8% and 70%, respectively (P = 0.001). Multiple regression analysis revealed that combination treatment (odds ratio [OR]: 43.6, 95% confidence interval [CI]: 3.594–530.9) and Sequential Organ Failure Assessment score <8 (OR: 0.022, 95% CI: 0.001–0.43) were independently associated with favorable clinical response. APACHE II score ≤15 (OR: 0.049, 95% CI: 0.003–0.0942) and an early favorable response to treatment (OR: 244.4, 95% CI: 2.151–27850.9) were associated with survival and discharge from ICU.

Conclusion:

Combination therapy with colistin and a high dose of ampicillin/sulbactam was associated with a more favorable clinical response to VAP due to carbapenem-resistant A. baumannii than colistin monotherapy.

Minocycline attenuates colistin-induced neurotoxicity via suppression of apoptosis, mitochondrial dysfunction and oxidative stress

Background

Neurotoxicity is an adverse effect patients experience during colistin therapy. The development of effective neuroprotective agents that can be co-administered during polymyxin therapy remains a priority area in antimicrobial chemotherapy. The present study investigates the neuroprotective effect of the synergistic tetracycline antibiotic minocycline against colistin-induced neurotoxicity.

Methods

The impact of minocycline pretreatment on colistin-induced apoptosis, caspase activation, oxidative stress and mitochondrial dysfunction were investigated using cultured mouse neuroblastoma-2a (N2a) and primary cortical neuronal cells.

Results

Colistin-induced neurotoxicity in mouse N2a and primary cortical cells gives rise to the generation of reactive oxygen species (ROS) and subsequent cell death via apoptosis. Pretreatment of the neuronal cells with minocycline at 5, 10 and 20 μM for 2 h prior to colistin (200 μM) exposure (24 h), had an neuroprotective effect by significantly decreasing intracellular ROS production and by upregulating the activities of the anti-ROS enzymes superoxide dismutase and catalase. Minocycline pretreatment also protected the cells from colistin-induced mitochondrial dysfunction, caspase activation and subsequent apoptosis. Immunohistochemical imaging studies revealed colistin accumulates within the dendrite projections and cell body of primary cortical neuronal cells.

Conclusions

To our knowledge, this is first study demonstrating the protective effect of minocycline on colistin-induced neurotoxicity by scavenging of ROS and suppression of apoptosis. Our study highlights that co-administration of minocycline kills two birds with one stone: in addition to its synergistic antimicrobial activity, minocycline could potentially ameliorate unwanted neurotoxicity in patients undergoing polymyxin therapy.

Substantial Targeting Advantage Achieved by Pulmonary Administration of Colistin Methanesulfonate in a Large-Animal Model

Colistin, administered as its inactive prodrug colistin methanesulfonate (CMS), is often used in multidrug-resistant Gram-negative pulmonary infections. The CMS and colistin pharmacokinetics in plasma and epithelial lining fluid (ELF) following intravenous and pulmonary dosing have not been evaluated in a large-animal model with pulmonary architecture similar to that of humans. Six merino sheep (34 to 43 kg body weight) received an intravenous or pulmonary dose of 4 to 8 mg/kg CMS (sodium) or 2 to 3 mg/kg colistin (sulfate) in a 4-way crossover study. Pulmonary dosing was achieved via jet nebulization through an endotracheal tube cuff. CMS and colistin were quantified in plasma and bronchoalveolar lavage fluid (BALF) samples by high-performance liquid chromatography (HPLC). ELF concentrations were calculated via the urea method. CMS and colistin were comodeled in S-ADAPT. Following intravenous CMS or colistin administration, no concentrations were quantifiable in BALF samples. Elimination clearance was 1.97 liters/h (4% interindividual variability) for CMS (other than conversion to colistin) and 1.08 liters/h (25%) for colistin. On average, 18% of a CMS dose was converted to colistin. Following pulmonary delivery, colistin was not quantifiable in plasma and CMS was detected in only one sheep. Average ELF concentrations (standard deviations [SD]) of formed colistin were 400 (243), 384 (187), and 184 (190) mg/liter at 1, 4, and 24 h after pulmonary CMS administration. The population pharmacokinetic model described well CMS and colistin in plasma and ELF following intravenous and pulmonary administration. Pulmonary dosing provided high ELF and low plasma colistin concentrations, representing a substantial targeting advantage over intravenous administration. Predictions from the pharmacokinetic model indicate that sheep are an advantageous model for translational research.

Luteolin ameliorates colistin-induced nephrotoxicity in the rat models

INTRODUCTION AND AIM

To study the protective, preventive effect of luteolin from colistin-induced nephrotoxicity.

MATERIAL AND METHOD

Four different treatment options were tested on rats: colistin, luteolin, and a combination of colistin and luteolin, intraperitoneally as two doses a day, for seven days. Another group of rats were used as the control and treated with sterile saline. Serum creatinine levels were measured before and after treatment. Histological changes and colistin-induced apoptosis (Insitu BrdU-red DNA Fragmentation Assay Kit) of the renal tissues were examined after the scarification procedure.

RESULTS

In the Colistin Group, post-treatment creatinine levels were statistically higher than the pretreatment levels (p = .001). In the remaining groups, no significant changes were observed. Cells that undergo apoptosis were counted and it was shown that all groups except the colistin-treated group had a similar number of apoptotic cells, whereas the colistin-treated group had statistically higher number of apoptotic cells compared to other groups (p = .0001). Renal histological damage was also measured and the score of the colistin treated group was higher as compared to other groups.

CONCLUSION

The results obtained from this study demonstrated us that luteolin was capable of preventing colistin-induced nephrotoxicity and that this effect was significant at histopathological level.

Bio-Inspired Coating Strategies for the Immobilization of Polymyxins to Generate Contact-Killing Surfaces

Microbial colonization of indwelling devices remains a major concern in modern healthcare. Developing approaches to prevent biomaterial-associated infections (BAI) is, therefore, in great demand. This study aimed to immobilize two antimicrobial peptides (polymyxins B and E) onto polydimethylsiloxane (PDMS) using two polydopamine (pDA)-based approaches: the conventional two-step method involving the deposition of a pDA layer to which biomolecules are immobilized, and a one-step method where peptides are dissolved together with dopamine before its polymerization. Surface characterization confirms the immobilization of polymyxins onto PDMS at a non-toxic concentration. Immobilization of polymyxins using a one-step pDA-based approach is able to prevent Pseudomonas aeruginosa adhesion and kill a significant fraction of the adherent ones. Living cells adhered to these modified surfaces exhibit the same susceptibility pattern as cells adhered to unmodified surfaces, highlighting no resistance development. Results suggest that polymyxins immobilization holds a great potential as an additional antimicrobial functionality in the design of biomaterials.

In vitro and in vivo efficacy, toxicity, bio-distribution and resistance selection of a novel antibacterial drug candidate

A synthetic antimicrobial peptide was identified as a possible candidate for the development of a new antibacterial drug. The peptide, SET-M33L, showed a MIC₉₀ below 1.5 μM and 3 μM for Pseudomonas aeruginosa and Klebsiella pneumoniae, respectively. In in vivo models of P. aeruginosa infections, the peptide and its pegylated form (SET-M33L-PEG) enabled a survival percentage of 60–80% in sepsis and lung infections when injected twice i.v. at 5 mg/Kg, and completely healed skin infections when administered topically. Plasma clearance showed different kinetics for SET-M33L and SET-M33L-PEG, the latter having greater persistence two hours after injection. Bio-distribution in organs did not show significant differences in uptake of the two peptides. Unlike colistin, SET-M33L did not select resistant mutants in bacterial cultures and also proved non genotoxic and to have much lower in vivo toxicity than antimicrobial peptides already used in clinical practice. The characterizations reported here are part of a preclinical development plan that should bring the molecule to clinical trial in the next few years.

Efficacy and Toxicity of High-Dose Colistin in Multidrug-Resistant Gram-Negative Bacilli Infections: A Comparative Study of a Matched Series

BACKGROUND

Colistimethate sodium (CMS) is the commercialized form of colistin that is effective against multiresistant Gram-negative bacilli. Its main side effects are nephrotoxicity and neurotoxicity. Pharmacodynamic dosages showed that they were infratherapeutic. Therefore, strategies with higher doses were proposed. The aim of this study was to assess the efficiency and toxicity of higher-dose CMS by comparing two treatment strategies: high-dose CMS versus standard-dose CMS.

METHODS

A prospective and comparative study of two matched groups was conducted. Fourty-six patients in each group were matched for age, severity and nature of infection. In the high-dose colistin group, CMS was administered at a loading dose of 9 MIU followed by a maintenance dose of 4.5 MIU/12 h. In the second group, retrospectively analyzed, colistin was administered at 6 MIU/day. For each group, clinical results, bacteriological eradication and daily creatinine clearance were recorded. Primary outcome measures were clinical cure defined as disappearance of infectious signs and eradication of microorganisms in all the follow-up cultures. Secondary outcome measures were incidence of acute renal failure and mortality.

RESULTS

Ninety-two patients were analyzed by matching. There was a higher cure rate in the high-dose group (63 vs. 41.3%, p = 0.04). No higher risk of nephrotoxicity was found by increasing daily doses of colistin (32.2 versus 26%, p = 0.64). Similarly, there was no significant difference in the time to onset of renal failure (8.32 vs. 11 days, p = 1) or in the requirement of hemodialysis (26.6 vs. 41%, p = 1).

CONCLUSION

The high-dose colistin regimen is more efficient, without significant renal or neurological toxicity.

Impact of empirical antimicrobial therapy on the outcome of critically ill patients with Acinetobacter bacteremia

RATIONALE:

Empirical antimicrobial therapy (EAT) for Acinetobacter infections may not be appropriate as it tends to be multidrug-resistant. This study evaluated the relationship between appropriate EAT and the outcomes of Intensive Care Unit (ICU) patients with Acinetobacter bacteremia.

METHODS:

This is a retrospective study of patients admitted to a medical-surgical ICU (2005-2010) and developed Acinetobacter bacteremia during the stay. Patients were categorized according to EAT appropriateness, defined as administration of at least one antimicrobial agent to which the Acinetobacter was susceptible before susceptibility results were known. The relation between EAT appropriateness and outcomes was evaluated.

RESULTS:

Sixty patients developed Acinetobacter bacteremia in the 6-year period (age = 50 ± 19 years; 62% males; Acute Physiology and Chronic Health Evaluation II score = 28 ± 9; 98.3% with central lines; 67% in shock and 59% mechanically ventilated) on average on day 23 of ICU and day 38 of hospital stay. All isolates were resistant to at least three of the tested antimicrobials. Appropriate EAT was administered to 60% of patients, mostly as intravenous colistin. Appropriate EAT was associated with lower ICU mortality risk (odds ratio: 0.15; 95% confidence interval: 0.03-0.96) on multivariate analysis.

CONCLUSIONS:

In this 6-year cohort, Acinetobacter bacteremia was related to multidrug-resistant strains. Appropriate EAT was associated with decreased ICU mortality risk.

Phospholipase A1 modulates the cell envelope phospholipid content of Brucella melitensis, contributing to polymyxin resistance and pathogenicity

A subset of bacterial pathogens, including the zoonotic Brucella species, are highly resistant against polymyxin antibiotics. Bacterial polymyxin resistance has been attributed primarily to the modification of lipopolysaccharide; however, it is unknown what additional mechanisms mediate high-level resistance against this class of drugs. This work identified a role for the Brucella melitensis gene bveA (BMEII0681), encoding a predicted esterase, in the resistance of B. melitensis to polymyxin B. Characterization of the enzymatic activity of BveA demonstrated that it is a phospholipase A1 with specificity for phosphatidylethanolamine (PE). Further, lipidomic analysis of B. melitensis revealed an excess of PE lipids in the bacterial membranes isolated from the bveA mutant. These results suggest that by lowering the PE content of the cell envelope, BveA increases the resistance of B. melitensis to polymyxin B. BveA was required for survival and replication of B. melitensis in macrophages and for persistent infection in mice. BveA family esterases are encoded in the genomes of the alphaproteobacterial species that coexist with the polymyxin-producing bacteria in the rhizosphere, suggesting that maintenance of a low PE content in the bacterial cell envelope may be a shared persistence strategy for association with plant and mammalian hosts.

The ADMIN-ICU survey: a survey on antimicrobial dosing and monitoring in ICUs

OBJECTIVES

There is little evidence and few guidelines to inform the most appropriate dosing and monitoring for antimicrobials in the ICU. We aimed to survey current practices around the world.

METHODS

An online structured questionnaire was developed and sent by e-mail to obtain information on local antimicrobial prescribing practices for glycopeptides, piperacillin/tazobactam, carbapenems, aminoglycosides and colistin.

RESULTS

A total of 402 professionals from 328 hospitals in 53 countries responded, of whom 78% were specialists in intensive care medicine (41% intensive care, 30% anaesthesiology, 14% internal medicine) and 12% were pharmacists. Vancomycin was used as a continuous infusion in 31% of units at a median (IQR) daily dose of 25 (25-30) mg/kg. Piperacillin/tazobactam was used as an extended infusion by 22% and as a continuous infusion by 7%. An extended infusion of carbapenem (meropenem or imipenem) was used by 27% and a continuous infusion by 5%. Colistin was used at a daily dose of 7.5 (3.9-9) million IU (MIU)/day, predominantly as a short infusion. The most commonly used aminoglycosides were gentamicin (55%) followed by amikacin (40%), with administration as a single daily dose reported in 94% of the cases. Gentamicin was used at a daily dose of 5 (5-6) mg/day and amikacin at a daily dose of 15 (15-20) mg/day. Therapeutic drug monitoring of vancomycin, piperacillin/tazobactam and meropenem was used by 74%, 1% and 2% of the respondents, respectively. Peak aminoglycoside concentrations were sampled daily by 28% and trough concentrations in all patients by 61% of the respondents.

CONCLUSIONS

We found wide variability in reported practices for antibiotic dosing and monitoring. Research is required to develop evidence-based guidelines to standardize practices.

Pseudomonas aeruginosa high-level resistance to polymyxins and other antimicrobial peptides requires cprA, a gene that is disrupted in the PAO1 strain

The arn locus, found in many Gram-negative bacterial pathogens, mediates resistance to polymyxins and other cationic antimicrobial peptides through 4-amino-l-arabinose modification of the lipid A moiety of lipopolysaccharide. In Pseudomonas aeruginosa, several two-component regulatory systems (TCSs) control the arn locus, which is necessary but not sufficient for these resistance phenotypes. A previous transposon mutagenesis screen to identify additional polymyxin resistance genes that these systems regulate implicated an open reading frame designated PA1559 in the genome of the P. aeruginosa PAO1 strain. Resequencing of this chromosomal region and bioinformatics analysis for a variety of P. aeruginosa strains revealed that in the sequenced PAO1 strain, a guanine deletion at the end of PA1559 results in a frameshift and truncation of a full-length open reading frame that also encompasses PA1560 in non-PAO1 strains, such as P. aeruginosa PAK. Deletion analysis in the PAK strain showed that this full-length open reading frame, designated cprA, is necessary for polymyxin resistance conferred by activating mutations in the PhoPQ, PmrAB, and CprRS TCSs. The cprA gene was also required for PmrAB-mediated resistance to other cationic antimicrobial peptides in the PAK strain. Repair of the mutated cprA allele in the PAO1 strain restored polymyxin resistance conferred by an activating TCS mutation. The deletion of cprA did not affect the arn-mediated lipid A modification, indicating that the CprA protein is necessary for a different aspect of polymyxin resistance. This protein has a domain structure with a strong similarity to the extended short-chain dehydrogenase/reductase family that comprises isomerases, lyases, and oxidoreductases. These results suggest a new avenue through which to pursue targeted inhibition of polymyxin resistance.

Synergistic effect of membrane-active peptides polymyxin B and gramicidin S on multidrug-resistant strains and biofilms of Pseudomonas aeruginosa

Multidrug-resistant Pseudomonas aeruginosa is a major cause of severe hospital-acquired infections. Currently, polymyxin B (PMB) is a last-resort antibiotic for the treatment of infections caused by Gram-negative bacteria, despite its undesirable side effects. The delivery of drug combinations has been shown to reduce the required therapeutic doses of antibacterial agents and thereby their toxicity if a synergistic effect is present. In this study, we investigated the synergy between two cyclic antimicrobial peptides, PMB and gramicidin S (GS), against different P. aeruginosa isolates, using a quantitative checkerboard assay with resazurin as a growth indicator. Among the 28 strains that we studied, 20 strains showed a distinct synergistic effect, represented by a fractional inhibitory concentration index (FICI) of ≤0.5. Remarkably, several clinical P. aeruginosa isolates that grew as small-colony variants revealed a nonsynergistic effect, as indicated by FICIs between >0.5 and ≤0.70. In addition to inhibiting the growth of planktonic bacteria, the peptide combinations significantly decreased static biofilm growth compared with treatment with the individual peptides. There was also a faster and more prolonged effect when the combination of PMB and GS was used compared with single-peptide treatments on the metabolic activity of pregrown biofilms. The results of the present study define a synergistic interaction between two cyclic membrane-active peptides toward 17 multidrug-resistant P. aeruginosa and biofilms of P. aeruginosa strain PAO1. Thus, the application of PMB and GS in combination is a promising option for a topical medication and in the prevention of acute and chronic infections caused by multidrug-resistant or biofilm-forming P. aeruginosa.

Spread of multidrug-resistant Acinetobacter baumannii and Pseudomonas aeruginosa clones in patients with ventilator-associated pneumonia in an adult intensive care unit at a university hospital

Background

In Brazil, ventilator-associated pneumonia (VAP) caused by carbapenem resistant Acinetobacter baumannii and Pseudomonas aeruginosa isolates are associated with significant mortality, morbidity and costs. Studies on the clonal relatedness of these isolates could lay the foundation for effective infection prevention and control programs.

Objectives

We sought to study the epidemiological and molecular characteristics of A. baumannii vs. P. aeruginosa VAP in an adult intensive care unit (ICU).

Methods

It was conducted a cohort study of patients with VAP caused by carbapenem resistant A. baumannii and P. aeruginosa during 14 months in an adult ICU. Genomic studies were used to investigate the clonal relatedness of carbapenem resistant OXA-23-producing A. baumannii and P. aeruginosa clinical isolates. The risk factors for acquisition of VAP were also evaluated. Clinical isolates were collected for analysis as were samples from the environment and were typed using pulsed field gel electrophoresis.

Results

Multivariate logistic regression analysis identified trauma diagnosed at admission and inappropriate antimicrobial therapy as independent variables associated with the development of A. baumannii VAP and hemodialysis as independent variable associated with P. aeruginosa VAP. All carbapenem resistant clinical and environmental isolates of A. baumannii were OXA-23 producers. No MBL-producer P. aeruginosa was detected. Molecular typing revealed a polyclonal pattern; however, clone A (clinical) and H (surface) were the most frequent among isolates of A. baumannii tested, with a greater pattern of resistance than other isolates. In P. aeruginosa the most frequent clone I was multi-sensitive.

Conclusion

These findings suggest the requirement of constant monitoring of these microorganisms in order to control the spread of these clones in the hospital environment.

Colistin treatment in carbapenem-resistant Acinetobacter baumannii pneumonia patients: Incidence of nephrotoxicity and outcomes

Colistimethate sodium (CMS) is increasingly used to treat multidrug-resistant Gram-negative bacilli infections. However, the incidence of CMS-associated nephrotoxicity has not been evaluated in patients with carbapenem-resistant Acinetobacter baumannii (CRAB) pneumonia. This retrospective study included 120 patients with CRAB pneumonia treated with intravenous CMS for ≥72 h. The objective of the study was to determine risk factors for CMS-induced nephrotoxicity and 30-day mortality in patients with CRAB pneumonia. Of the 120 patients with CRAB pneumonia, 61 (51%) developed nephrotoxicity. Multivariate analysis showed that dose per ideal body weight (IBW) [odds ratio (OR)=1.28, 95% confidence interval (CI) 1.01-1.62; P=0.04], Charlson co-morbidity index (OR=1.31, 95% CI 1.06-1.60; P=0.01) and septic shock (OR=3.16, 95% CI 1.32-7.60; P=0.01) were associated with CMS-associated nephrotoxicity. Thirty-day mortality was 33% (39/120). Multivariate analysis showed that higher daily doses of CMS per IBW [hazard ratio (HR)=0.81, 95% CI 0.67-0.98; P=0.03] and longer duration of CMS therapy (HR=0.86, 95% CI 0.79-0.95; P=0.002) were associated with increased survival. Septic shock (HR=3.91, 95% CI 1.95-7.83; P<0.001) and corticosteroid use (HR=3.49, 95% CI 1.67-7.28; P=0.001) were associated with decreased survival in patients with CRAB pneumonia. Higher daily doses of CMS per IBW, Charlson comorbidity index and septic shock were significant risk factors for CMS-associated nephrotoxicity. However, CMS-associated nephrotoxicity does not appear to have an impact on mortality.

Colistin for lung infection: an update

Increasing incidence of resistance of gram-negative bacteria against even newer antibiotic including carbapenem has generated interest in the old antibiotic colistin, which are being used as salvage therapy in the treatment of multidrug resistant infection. Colistin has excellent bactericidal activity against most gram-negative bacilli. It has shown persist level in the liver, kidney, heart, and muscle; while it is poorly distributed to the bones, cerebrospinal fluid, lung parenchyma, and pleural cavity. Being an old drug, colistin was never gone through the drug development process needed for compliance with competent regulatory authorities that resulted in very much limited understanding of pharmacokinetic (PK) and pharmacodynamic (PD) parameters, such as C_max/MIC ratio, AUC/MIC and T > MIC that could predict the efficacy of colistin. In available PK/PD studies of colistin, mean maximum serum concentration (C_max) of colistin were found just above the MIC breakpoint at steady states that would most probably lead to suboptimal for killing the bacteria, even at dosages of 3.0 million international units (MIU) i.e., 240 mg of colistimethate sodium (CMS) intravenously every 8 h. These finding stresses to use high loading as well as high maintenance dose of intravenous colistin. It is not only suboptimal plasma concentration of colistin but also poor lung tissue concentration, which has been demonstrated in recent studies, poses major concern in using intravenous colistin. Combination therapy mainly with carbapenems shows synergistic effect. In recent studies, inhaled colistin has been found promising in treatment of lung infection due to MDR gram-negative bacteria. New evidence shows less toxicity than previously reported.

Engineered cationic antimicrobial peptides to overcome multidrug resistance by ESKAPE pathogens

Multidrug resistance constitutes a threat to the medical achievements of the last 50 years. In this study, we demonstrated the abilities of two de novo engineered cationic antibiotic peptides (eCAPs), WLBU2 and WR12, to overcome resistance from 142 clinical isolates representing the most common multidrug-resistant (MDR) pathogens and to display a lower propensity to select for resistant bacteria in vitro compared to that with colistin and LL37. The results warrant an exploration of eCAPs for use in clinical settings.

Axinellamines as broad-spectrum antibacterial agents: scalable synthesis and biology

Antibiotic-resistant bacteria present an ongoing challenge to both chemists and biologists as they seek novel compounds and modes of action to out-maneuver continually evolving resistance pathways, especially against Gram-negative strains. The dimeric pyrrole-imidazole alkaloids represent a unique marine natural product class with diverse primary biological activity and chemical architecture. This full account traces the strategy used to develop a second-generation route to key spirocycle 9, culminating in a practical synthesis of the axinellamines and enabling their discovery as broad-spectrum antibacterial agents, with promising activity against both Gram-positive and Gram-negative bacteria. While their detailed mode of antibacterial action remains unclear, the axinellamines appear to cause secondary membrane destabilization and impart an aberrant cellular morphology consistent with the inhibition of normal septum formation. This study serves as a rare example of a natural product initially reported to be devoid of biological activity surfacing as an active antibacterial agent with an intriguing mode of action.

Evaluation of efficacy of natural astaxanthin and vitamin E in prevention of colistin-induced nephrotoxicity in the rat model

OBJECTIVE

We evaluated the effect of astaxanthin (ASX) and vitamin E (vit E) on colistin methanesulfonate (CMS) induced-nephrotoxicity in rats.

METHODS

Animals were treated with sterile saline, 300000 or 450 000 IU/kg/day of CMS, CMS + ASX (20 mg/kg), CMS + vit E (100 mg/kg), or CMS + 1 ml/kg olive oil (OO) for 7 days. The plasma/urine creatinine (Cr) level, urine γ-glutamyl-transferase (GGT) level, and renal tissue activities in malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and reductase (GSH), as well as renal histology were performed.

RESULTS

CMS induced a tubular damage, increased the GGT and MDA levels, and decreased the activities of SOD, CAT, GPx and GSH. Co-treatment with ASX or vit E restored all biochemical parameters cited above and improved the histopathological damage.

CONCLUSION

Nephrotoxicity induced by CMS might be due to oxidative damage. The improvement by ASX or vit E seems to be related to their antioxidant properties.

New dosing strategies for an old antibiotic: pharmacodynamics of front-loaded regimens of colistin at simulated pharmacokinetics in patients with kidney or liver disease

Increasing evidence suggests that colistin monotherapy is suboptimal at currently recommended doses. We hypothesized that front-loading provides an improved dosing strategy for polymyxin antibiotics to maximize killing and minimize total exposure. Here, we utilized an in vitro pharmacodynamic model to examine the impact of front-loaded colistin regimens against a high bacterial density (10(8) CFU/ml) of Pseudomonas aeruginosa. The pharmacokinetics were simulated for patients with hepatic (half-life [t1/2] of 3.2 h) or renal (t1/2 of 14.8 h) disease. Front-loaded regimens (n=5) demonstrated improvement in bacterial killing, with reduced overall free drug areas under the concentration-time curve (fAUC) compared to those with traditional dosing regimens (n=14) with various dosing frequencies (every 12 h [q12h] and q24h). In the renal failure simulations, front-loaded regimens at lower exposures (fAUC of 143 mg · h/liter) obtained killing activity similar to that of traditional regimens (fAUC of 268 mg · h/liter), with an ∼97% reduction in the area under the viable count curve over 48 h. In hepatic failure simulations, front-loaded regimens yielded rapid initial killing by up to 7 log10 within 2 h, but considerable regrowth occurred for both front-loaded and traditional regimens. No regimen eradicated the high bacterial inoculum of P. aeruginosa. The current study, which utilizes an in vitro pharmacodynamic infection model, demonstrates the potential benefits of front-loading strategies for polymyxins simulating differential pharmacokinetics in patients with hepatic and renal failure at a range of doses. Our findings may have important clinical implications, as front-loading polymyxins as a part of a combination regimen may be a viable strategy for aggressive treatment of high-bacterial-burden infections.

Parenteral polymyxins: assessing efficacy and safety in critically ill patients with renal dysfunction

OBJECTIVES

Studies have established the effectiveness and safety of polymyxins in treating multidrug resistant (MDR) pathogens. However, the challenge is whether these nephrotoxic drugs can be administered in compromised renal states. The present study was undertaken to establish their role in such patients. The effectiveness and nephrotoxicity of polymyxins in critically ill-patients harboring MDR Gram-negative bacteria with already compromised renal functions was compared with those with normal renal functions.

MATERIALS AND METHODS

This retrospective cohort study (March 2008-March 2010) was conducted in the intensive care unit of a tertiary care hospital. A total of 48 eligible critically ill-patients receiving polymyxins were enrolled. A comparison was carried out (length of stay in hospital, mortality, renal function) between patients with acute kidney injury (AKI, n = 18; defined by the RIFLE classification) and patients with normal renal function (non-AKI, n = 30).

RESULTS

Patients with baseline AKI had a significantly higher adjusted mortality rate at admission when compared with the non-AKI group. At the end of therapy with polymyxins, 26.66% non-AKI patients developed renal dysfunction while 38.88% of patients in the AKI group had worsening of renal function (P = 0.006). However, there was no significant difference in the length of hospital stay (23.9 ± 13.24 vs. 30.5 ± 22.50; P = 0.406) and overall mortality (44.4% vs. 36.7%; P = 0.76) between two groups.

CONCLUSION

Polymyxins can be administered in AKI patients with favorable results provided used judiciously with strict monitoring of renal functions, dose modification according to creatinine clearance and aggressive fluid management.

Macrocyclic drugs and synthetic methodologies toward macrocycles

Macrocyclic scaffolds are commonly found in bioactive natural products and pharmaceutical molecules. So far, a large number of macrocyclic natural products have been isolated and synthesized. The construction of macrocycles is generally considered as a crucial and challenging step in the synthesis of macrocyclic natural products. Over the last several decades, numerous efforts have been undertaken toward the synthesis of complex naturally occurring macrocycles and great progresses have been made to advance the field of total synthesis. The commonly used synthetic methodologies toward macrocyclization include macrolactonization, macrolactamization, transition metal-catalyzed cross coupling, ring-closing metathesis, and click reaction, among others. Selected recent examples of macrocyclic synthesis of natural products and druglike macrocycles with significant biological relevance are highlighted in each class. The primary goal of this review is to summarize currently used macrocyclic drugs, highlight the therapeutic potential of this underexplored drug class and outline the general synthetic methodologies for the synthesis of macrocycles.

Polymyxin resistance of Pseudomonas aeruginosa phoQ mutants is dependent on additional two-component regulatory systems

Pseudomonas aeruginosa can develop resistance to polymyxin as a consequence of mutations in the PhoPQ regulatory system, mediated by covalent lipid A modification. Transposon mutagenesis of a polymyxin-resistant phoQ mutant defined 41 novel loci required for resistance, including two regulatory systems, ColRS and CprRS. Deletion of the colRS genes, individually or in tandem, abrogated the polymyxin resistance of a ΔphoQ mutant, as did individual or tandem deletion of cprRS. Individual deletion of colR or colS in a ΔphoQ mutant also suppressed 4-amino-L-arabinose addition to lipid A, consistent with the known role of this modification in polymyxin resistance. Surprisingly, tandem deletion of colRS or cprRS in the ΔphoQ mutant or individual deletion of cprR or cprS failed to suppress 4-amino-L-arabinose addition to lipid A, indicating that this modification alone is not sufficient for PhoPQ-mediated polymyxin resistance in P. aeruginosa. Episomal expression of colRS or cprRS in tandem or of cprR individually complemented the Pm resistance phenotype in the ΔphoQ mutant, while episomal expression of colR, colS, or cprS individually did not. Highly polymyxin-resistant phoQ mutants of P. aeruginosa isolated from polymyxin-treated cystic fibrosis patients harbored mutant alleles of colRS and cprS; when expressed in a ΔphoQ background, these mutant alleles enhanced polymyxin resistance. These results define ColRS and CprRS as two-component systems regulating polymyxin resistance in P. aeruginosa, indicate that addition of 4-amino-L-arabinose to lipid A is not the only PhoPQ-regulated biochemical mechanism required for resistance, and demonstrate that colRS and cprS mutations can contribute to high-level clinical resistance.