Colistin plus Sulbactam or Fosfomycin against Carbapenem-Resistant Acinetobacter baumannii: Improved Efficacy or Decreased Risk of Nephrotoxicity?

Background

Acinetobacter baumannii has been recognized as a cause of nosocomial infection. To date, polymyxins, the last-resort therapeutic agents for carbapenem-resistant A. baumannii (CRAB). Thus, the small number of effective antibiotic options against CRAB represents a challenge to human health. This study examined the appropriate dosage regimens of colistin alone or in combination with sulbactam or fosfomycin using Monte Carlo simulation with the aims of improving efficacy and reducing the risk of nephrotoxicity.

Materials and Methods

Clinical CRAB isolates were obtained from patients admitted to Phramongkutklao Hospital in 2014 and 2015. The minimum inhibitory concentration (MIC) of colistin for each CRAB isolate was determined using the broth dilution method, whereas those of sulbactam and fosfomycin were determined using the agar dilution method. Each drug regimen was simulated using the Monte Carlo technique to calculate the probability of target attainment (PTA) and the cumulative fraction of response (CFR). Nephrotoxicity based on RIFLE (Risk, Injury, Failure, Loss of kidney function, and End-stage kidney disease) criteria was indicated by colistin trough concentration exceeding ≥3.3 µg/mL.

Results

A total of 50 CRAB isolates were included. The MIC₅₀ and MIC₉₀ were 64 and 128 µg/mL, respectively, for sulbactam, 256 and 2,048 µg/mL, respectively, for fosfomycin, and 1 and 4 µg/mL, respectively, for colistin. In patients with creatinine clearance of 91 – 130 m/min, the dosing regimens of 180 mg every 12 h and 150 mg every 8 h achieved ≥ 90% of target of the area under the free drug plasma concentration–time curve from 0 to 24 hr (fAUC24)/MIC ≥25 against isolates MICs of ≤0.25 and ≤0.5 µg/mL, respectively, and their rates of colistin trough concentration more than ≥3.3 µg/mL were 35 and 54%, respectively. Colistin combined with sulbactam or fosfomycin decreased the colistin MIC of CRAB isolates from 1 – 16 µg/mL to 0.0625 – 1 and 0.0625 – 2 µg/mL, respectively. Based on CFR ≥ 90%, no colistin monotherapy regimens in patients with creatinine clearance of 91 – 130 mL/min were effective against all of the studied CRAB isolates. For improving efficacy and reducing the risk of nephrotoxicity, colistin 150 mg given every 12 h together with sulbactam (≥6 g/day) or fosfomycin (≥18 g/day) was effective in patients with creatinine clearance of 91 – 130 mL/min. Additionally, both colistin combination regimens were effective against five colistin-resistant A. baumannii isolates.

Conclusion

Colistin monotherapy at the maximum recommended dose might not cover some CRAB isolates. Colistin combination therapy appears appropriate for achieving the pharmacokinetic/pharmacodynamic targets of CRAB treatment.

Generation of a novel human dermal substitute functionalized with antibiotic-loaded nanostructured lipid carriers (NLCs) with antimicrobial properties for tissue engineering

BACKGROUND

Treatment of patients affected by severe burns is challenging, especially due to the high risk of Pseudomonas infection. In the present work, we have generated a novel model of bioartificial human dermis substitute by tissue engineering to treat infected wounds using fibrin-agarose biomaterials functionalized with nanostructured lipid carriers (NLCs) loaded with two anti-Pseudomonas antibiotics: sodium colistimethate (SCM) and amikacin (AMK).

RESULTS

Results show that the novel tissue-like substitutes have strong antibacterial effect on Pseudomonas cultures, directly proportional to the NLC concentration. Free DNA quantification, WST-1 and Caspase 7 immunohistochemical assays in the functionalized dermis substitute demonstrated that neither cell viability nor cell proliferation were affected by functionalization in most study groups. Furthermore, immunohistochemistry for PCNA and KI67 and histochemistry for collagen and proteoglycans revealed that cells proliferated and were metabolically active in the functionalized tissue with no differences with controls. When functionalized tissues were biomechanically characterized, we found that NLCs were able to improve some of the major biomechanical properties of these artificial tissues, although this strongly depended on the type and concentration of NLCs.

CONCLUSIONS

These results suggest that functionalization of fibrin-agarose human dermal substitutes with antibiotic-loaded NLCs is able to improve the antibacterial and biomechanical properties of these substitutes with no detectable side effects. This opens the door to future clinical use of functionalized tissues.

Design of experiments guided multivariate calibration for the quantitation of injectable colistimethate sodium by ultra performance liquid chromatography - High resolution mass spectrometry

Colistimethate sodium (CMS) is a widely administrated old-generation prodrug for the treatment of the life-threatening infections caused by multi-resistant Gram-negative bacteria. Until now, the quality control procedure of the CMS commercial products is based on microbiological assays. The aim of the study is the development of a chemical analysis methodology based on liquid chromatography - mass spectrometry (LC-MS) that could be used for the quality control of CMS products. The careful optimization of the LC and QToF-MS parameters was deemed crucial, as CMS is known to be a very complex mixture. Thus, a two stage Design of Experiments (DoE) pipeline has been followed, aiming towards the separation of the mixture components. According to the DoE results, a baseline-resolved chromatogram revealing more than 20 compounds was achieved. The separation was performed using a Waters Acquity BEH C8 column employing gradient elution. The mobile phase consisted of aq. ammonium formate 0.005 M (pH 6) (solvent A) and methanol/acetonitrile 79/21 (v/v) (solvent B). A second optimization experiment for the MS signal was employed in order to achieve maximum sensitivity. The singly charged signals were monitored for the validation in the positive ion mode. The calibration curve range was 50-110 μg mL^-1, corresponding to the 80-120% of the nominal CMS amount in the commercial products. Due to the complexity of the CMS chromatograms and the corresponding spectrum of each chromatographic peak, untargeted and targeted approaches were performed employing the MZmine software. Furthermore, apart from the classical univariate statistical analysis, partial least squares regression (PLS-R) model was also employed, as the variables were more than the observations. The developed methodology has been employed to analyze several batches and inconsistences have been discovered.

Use of colistin in adult patients: A cross-sectional study

OBJECTIVES

The aim of this study was to assess colistin use in a country endemic for multidrug-resistant Gram-negative bacteria (MDR-GNB).

METHODS

Colistin prescription patterns were evaluated in 22 Italian centres. Factors associated with use of colistin in combination with other anti-MDR-GNB agents were also assessed.

RESULTS

A total of 221 adults receiving colistin were included in the study. Their median age was 64 years (interquartile range 52-73 years) and 134 (61%) were male. Colistin was mostly administered intravenously (203/221; 92%) and mainly for targeted therapy (168/221; 76%). The most frequent indications for colistin therapy were bloodstream infection and lower respiratory tract infection. Intravenous colistin was administered in combination with at least another anti-MDR-GNB agent in 80% of cases (163/203). A loading dose of 9 MU of colistimethate was administered in 79% of patients receiving i.v. colistin and adequate maintenance doses in 85%. In multivariable analysis, empirical therapy [odds ratio (OR) = 3.25, 95% confidence interval (CI) 1.24-8.53;P = 0.017] and targeted therapy for carbapenem-resistant Enterobacterales infection (OR = 4.76, 95% CI 1.69-13.43; P = 0.003) were associated with use of colistin in combination with other agents, whilst chronic renal failure (OR = 0.39, 95% CI 0.17-0.88; P =  0.024) was associated with use of colistin monotherapy.

CONCLUSION

Colistin remains an important option for severe MDR-GNB infections when other treatments are not available. Despite inherent difficulties in optimising its use owing to peculiar pharmacokinetic/pharmacodynamic characteristics, colistin was mostly used appropriately in a country endemic for MDR-GNB.

Potential pitfalls in LC-MS/MS quantification of colistin for therapeutic drug monitoring of patients treated with colistimethate

Starting from a warning of possible artificially high plasma colistin concentrations observed in clinical samples in our recently published LC-MS/MS method, we reviewed our analytical assay and demonstrated, for the first time, that caution must be paid to ionization conditions employed in the MS system. The artefact reported here demonstrates that additional experiments should be performed in the course of validation of LC-MS/MS methods to be used in samples containing both colistin and colistimethate.

Clinical Pharmacokinetics, Pharmacodynamics and Toxicodynamics of Polymyxins: Implications for Therapeutic Use

The availability of sensitive, accurate and specific analytical methods for the measurement of polymyxins in biological fluids has enabled an understanding of the pharmacokinetics of these important antibiotics in healthy humans and patients. Colistin is administered as its inactive prodrug colistin methanesulfonate (CMS) and has especially complex pharmacokinetics. CMS undergoes conversion in vivo to the active entity colistin, but the rate of conversion varies from brand to brand and possibly from batch to batch. The extent of conversion is generally quite low and depends on the relative magnitudes of the conversion clearance and other clearance pathways for CMS of which renal excretion is a major component. Formed colistin in the systemic circulation undergoes very extensive tubular reabsorption; the same mechanism operates for polymyxin B which is administered in its active form. The extensive renal tubular reabsorption undoubtedly contributes to the propensity for the polymyxins to cause nephrotoxicity. While there are some aspects of pharmacokinetic behaviour that are similar between the two clinically used polymyxins, there are also substantial differences. In this chapter, the pharmacokinetics of colistin, administered as CMS, and polymyxin B are reviewed, and the therapeutic implications are discussed.

Nitrite modulates bacterial antibiotic susceptibility and biofilm formation in association with airway epithelial cells

Pseudomonas aeruginosa is the major pathogenic bacteria in cystic fibrosis and other forms of bronchiectasis. Growth in antibiotic-resistant biofilms contributes to the virulence of this organism. Sodium nitrite has antimicrobial properties and has been tolerated as a nebulized compound at high concentrations in human subjects with pulmonary hypertension; however, its effects have not been evaluated on biotic biofilms or in combination with other clinically useful antibiotics. We grew P. aeruginosa on the apical surface of primary human airway epithelial cells to test the efficacy of sodium nitrite against biotic biofilms. Nitrite alone prevented 99% of biofilm growth. We then identified significant cooperative interactions between nitrite and polymyxins. For P. aeruginosa growing on primary CF airway cells, combining nitrite and colistimethate resulted in an additional log of bacterial inhibition compared to treating with either agent alone. Nitrite and colistimethate additively inhibited oxygen consumption by P. aeruginosa. Surprisingly, whereas the antimicrobial effects of nitrite in planktonic, aerated cultures are nitric oxide (NO) dependent, antimicrobial effects under other growth conditions are not. The inhibitory effect of nitrite on bacterial oxygen consumption and biofilm growth did not require NO as an intermediate as chemically scavenging NO did not block growth inhibition. These data suggest an NO-radical independent nitrosative or oxidative inhibition of respiration. The combination of nebulized sodium nitrite and colistimethate may provide a novel therapy for chronic P. aeruginosa airway infections, because sodium nitrite, unlike other antibiotic respiratory chain "poisons," can be safely nebulized at high concentration in humans.

Colistin- and Polymyxin-Induced Nephrotoxicity

With the reintroduction of colistimethate and polymyxin B into clinical practice, a review of their individual and comparative nephrotoxicity attributes as reported in contemporary literature was undertaken. Given variability in definitions used for acute kidney injury, a particular focus was placed on studies utilizing the Risk-Injury-Failure-Loss-End Stage Kidney Disease (RIFLE) criteria of assessment to provide for standardized comparison. Primary risk factors examined included the influence of dosing and the receipt of concomitant nephrotoxins. The typical severity and time course of renal injury that develops were also analyzed. Nephrotoxicity rates with colistimethate appear to approach 50%, and could be of lower frequency and severity with polymyxin B based on limited literature. Acute kidney injury generally appears to be mild to moderate in magnitude and reversible in nature, though as many as 20% of patients experiencing it may require renal replacement therapy of some duration. The majority of studies showed some relationship with dosing- variably reported as being associated with daily dose or cumulative exposure. Traditional nephrotoxic agents did not appear to confer additional risk individually in the majority of investigations, though receipt of multiple concurrent nephrotoxins did yield a relationship in several. Further studies will be required to better characterize the renal adverse effect profile of these agents, particularly in the case of polymyxin B.

Utilization of colistin for treatment of multidrug-resistant Pseudomonas aeruginosa

BACKGROUND

Colistin is uncommonly used in clinical practice; however, the emergence of multidrug-resistant organisms has rekindled interest in this potentially toxic therapeutic option. The present study describes the authors' experience with colistin in the management of patients who were infected with metallo-beta-lactamase (MBL)-producing Pseudomonas aeruginosa within the Calgary Health Region (Calgary, Alberta).

METHOD

Adult patients who received colistimethate sodium (colistin) between January 2000 and December 2005 were identified via pharmacy records, and their charts were reviewed retrospectively. Patients with cystic fibrosis were excluded. Patient demographics, clinical course and relevant laboratory data were extracted.

RESULTS

Twenty-eight courses of colistin were received by 22 patients. The majority of these treatments were directed at MBL-producing Pseudomonas. One-half of the patients received nebulized colistin. Intravenous (IV) colistin was administered to 12 patients for a mean +/- SD of 14.7+/-13.8 days (range 3.7 to 46 days). The highest IV dose used was 125 mg every 6 h or 6 mg/kg/day. Eight of 12 patients (67%) treated with IV colistin responded either fully or partially. Two patients received IV colistin as outpatients. Adverse effects considered to be due to colistin included drug fever, nephrotoxicity and neurotoxicity. Five of nine patients (56%) who had complete data available for evaluation had at least a doubling of creatinine levels from baseline.

CONCLUSION

Patients in the present study received both IV and nebulized colistin for multidrug-resistant P aeruginosa. The use of IV colistin was associated with a favourable response, but mild nephrotoxicity occurred in two-third of patients. It was concluded that colistin may be a useful drug when choices are limited.

Colistin Therapy in a 23-Week Gestational-Age Neonate with Multidrug-Resistant Acinetobacter baumannii Pneumonia

Multidrug-resistant pathogens are becoming more difficult to treat with significantly increasing infection rates. The lack of new antibiotics to combat these strains has led to the resurgence of older antibiotics. This case highlights the first reported use of colistimethate sodium treatment in a 23-week gestational-age neonate with multidrug-resistant Acinetobacter baumannii pneumonia who developed acute renal failure and seizures shortly after initiation of treatment.