A simple method for the assay of colistin in human plasma, using pre-column derivatization with 9-fluorenylmethyl chloroformate in solid-phase extraction cartridges and reversed-phase high-performance liquid chromatography

Colistin plasma concentrations are not associated with better clinical outcomes in patients with pneumonia caused by extremely drug-resistant Pseudomonas aeruginosa

IMPORTANCE

In some cases, colistin is the only treatment option for infections caused by the very drug-resistant Pseudomonas aeruginosa. However, in the past decade, there have been questions concerning its pharmacokinetics and concentration at the site of infection. In this scenario, its use in a difficult-to-treat infection like pneumonia is currently debatable. This is a clinical pharmacokinetic study of colistin in patients with multidrug-resistant P. aeruginosa pneumonia. Our findings demonstrate that colistin exposure is associated with worse clinical outcomes rather than better clinical outcomes, implying that other therapeutic options should be explored in this clinical setting.

Individual Components of Polymyxin B Modeled via Population Pharmacokinetics to Design Humanized Dosage Regimens for a Bloodstream and Lung Infection Model in Immune-Competent Mice

Polymyxin B is a "last-line-of-defense" antibiotic approved in the 1960s. However, the population pharmacokinetics (PK) of its four main components has not been reported in infected mice. We aimed to determine the PK of polymyxin B1, B1-Ile, B2, and B3 in a murine bloodstream and lung infection model of Acinetobacter baumannii and develop humanized dosage regimens. A linear 1-compartment model, plus an epithelial lining fluid (ELF) compartment for the lung model, best described the PK. Clearance and volume of distribution were similar among the four components. The bioavailability fractions were 72.6% for polymyxin B1, 12.0% for B1-Ile, 11.5% for B2, and 3.81% for B3 for the lung model and were similar for the bloodstream model. While the volume of distribution was comparable between both models (17.3 mL for the lung and ~27 mL for the bloodstream model), clearance was considerably smaller for the lung (2.85 mL/h) compared to that of the bloodstream model (5.59 mL/h). The total drug exposure (AUC) in ELF was high due to the saturable binding of polymyxin B presumably to bacterial lipopolysaccharides. However, the modeled unbound AUC in ELF was ~16.7% compared to the total drug AUC in plasma. The long elimination half-life (~4 h) of polymyxin B enabled humanized dosage regimens with every 12 h dosing in mice. Daily doses that optimally matched the range of drug concentrations observed in patients were 21 mg/kg for the bloodstream and 13 mg/kg for the lung model. These dosage regimens and population PK models support translational studies for polymyxin B at clinically relevant drug exposures.

HPLC Determination of Colistin in Human Urine Using Alkaline Mobile Phase Combined with Post-Column Derivatization: Validation Using Accuracy Profiles

In this study, the development, validation, and application of a new liquid chromatography post-column derivatization method for the determination of Colistin in human urine samples is demonstrated. Separation of Colistin was performed using a core–shell C₁₈ analytical column in an alkaline medium in order (i) to be compatible with the o-phthalaldehyde-based post-column derivatization reaction and (ii) to obtain better retention of the analyte. The Colistin derivative was detected spectrofluorometrically (λ_ext/λ_em = 340/460 nm) after post-column derivatization with o-phthalaldehyde and N-acetyl cysteine. The post-column derivatization parameters were optimized using the Box–Behnken experimental design, and the method was validated using the total error concept. The β-expectation tolerance intervals did not exceed the acceptance criteria of ±15%, meaning that 95% of future results would be included in the defined bias limits. The limit of detection of the method was adequate corresponding to 100 nmol·L⁻¹. The mean analytical bias (expressed as relative error) in the spiking levels was suitable, being in the range of −2.8 to +2.5% for both compounds with the percentage relative standard deviation lower than 3.4% in all cases. The proposed analytical method was satisfactorily applied to the analysis of the drug in human urine samples.

Methods for Determination of Meropenem Concentration in Biological Samples

Measuring the concentration of antibiotics in biological samples allow implementation of therapeutic monitoring of these drugs and contribute to the adjustment of the dosing regimen in patients. This increases the effectiveness of antimicrobial therapy, reduces the toxicity of these drugs and prevents the development of bacterial resistance. This review article summarizes current knowledge on methods for determining concentration of meropenem, an antibiotic drug from the group of carbapenems, in different biological samples. It provides a brief discussion of the chemical structure, physicochemical and pharmacokinetic properties of meropenem, different sample preparation techniques, use of apparatus and equipment, knowledge of the advantages and limitations of available methods, as well as directions in which new methods should be developed. This review should facilitate clinical laboratories to select and apply one of the established methods for measuring of meropenem, as well as to provide them with the necessary knowledge to develop new methods for quantification of meropenem in biological samples according to their needs.

Pharmacokinetics and pharmacodynamics of peptide antibiotics

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

Alginate oligosaccharides enhance diffusion and activity of colistin in a mucin-rich environment

In a number of chronic respiratory diseases e.g. cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD), the production of viscous mucin reduces pulmonary function and represents an effective barrier to diffusion of inhaled therapies e.g. antibiotics. Here, a 2-compartment Transwell model was developed to study impaired diffusion of the antibiotic colistin across an artificial sputum (AS) matrix/medium and to quantify its antimicrobial activity against Pseudomonas aeruginosa NH57388A biofilms (alone and in combination with mucolytic therapy). High-performance liquid chromatography coupled with fluorescence detection (HPLC-FLD) revealed that the presence of AS medium significantly reduced the rate of colistin diffusion (> 85% at 48 h; p < 0.05). Addition of alginate oligosaccharide (OligoG CF-5/20) significantly improved colistin diffusion by 3.7 times through mucin-rich AS medium (at 48 h; p < 0.05). Increased diffusion of colistin with OligoG CF-5/20 was shown (using confocal laser scanning microscopy and COMSTAT image analysis) to be associated with significantly increased bacterial killing (p < 0.05). These data support the use of this model to study drug and small molecule delivery across clinically-relevant diffusion barriers. The findings indicate the significant loss of colistin and reduced effectiveness that occurs with mucin binding, and support the use of mucolytics to improve antimicrobial efficacy and lower antibiotic exposure.

An LC-MS/MS method for simultaneous analysis of the cystic fibrosis therapeutic drugs colistin, ivacaftor and ciprofloxacin

Inhaled antibiotics such as colistin and ciprofloxacin are increasingly used to treat bacterial lung infections in cystic fibrosis patients. In this study, we established and validated a new HPLC-MS/MS method that could simultaneously detect drug concentrations of ciprofloxacin, colistin and ivacaftor in rat plasma, human epithelial cell lysate, cell culture medium, and drug transport media. An aliquot of 200 μL drug-containing rat plasma or cell culture medium was treated with 600 μL of extraction solution (acetonitrile containing 0.1% formic acid and 0.2% trifluoroacetic acid (TFA)). The addition of 0.2% TFA helped to break the drug-protein bonds. Moreover, the addition of 0.1% formic acid to the transport medium and cell lysate samples could significantly improve the response and reproducibility. After vortexing and centrifuging, the sample components were analyzed by HPLC-MS/MS. The multiple reaction monitoring mode was used to detect the following transitions: 585.5-101.1 (colistin A), 578.5-101.1 (colistin B), 393.2-337.2 (ivacaftor), 332.2-314.2 (ciprofloxacin), 602.3-101.1 (polymyxin B1 as internal standard (IS)) and 595.4-101.1 (polymyxin B2 as IS). The running time of a single sample was only 6 min, making this a time-efficient method. Linear correlations were found for colistin A at 0.029-5.82 μg/mL, colistin B at 0.016-3.14 μg/mL, ivacaftor at 0.05-10.0 μg/mL, and ciprofloxacin at 0.043-8.58 μg/mL. Accuracy, precision, and stability of the method were within the acceptable range. This method would be highly useful for research on cytotoxicity, animal pharmacokinetics, and in vitro drug delivery.

Estimation of the Difference in Colistin Plasma Levels in Critically Ill Patients with Favorable or Unfavorable Clinical Outcomes

In recent decades, antimicrobial resistance (AMR) has led to an increased use of therapeutic alternatives. Among these options, colistin continues to be an option for the treatment of multi-resistant (MDR) Gram-negative bacterial infections. However, due to its high toxicity (nephrotoxicity and neurotoxicity) and narrow therapeutic window, colistin treatment must be utilized carefully. Colistin-treated patients have been observed to have higher mortality due to inadequate therapeutic levels. The objective of this study was to estimate the difference in colistin plasma levels in critically ill patients, and its relationship to favorable or unfavorable clinical outcomes. This prospective observational study was conducted between September 2017 and June 2020 at the Universidad de La Sabana Clinic, in patients who had been treated with colistimethate sodium (CMS) for at least 72 h until day 7 of drug treatment in the critical care unit of a university hospital. There were no statistically significant differences in colistin levels between groups with favorable or unfavorable clinical outcomes (0.16 SD vs. 0.54 SD p-value = 0.167). There was higher mortality in patients with subtherapeutic levels (18% vs. 0%), and additionally, there was a greater rate of renal failure in the group with higher therapeutic levels (50% vs. 20.7%). Due to the loss of power of the study, we were unable to demonstrate a possible difference between colistin levels related to favorable or unfavorable clinical outcomes at day 7. However, we recommend further studies to evaluate the impact of measuring levels in terms of mortality and security.

Development of ELISA formats for polymyxin B monitoring in serum of critically ill patients

Treating infections in critically ill patients often requires the use of last-line antibacterial drugs such as polymyxins with a narrow therapeutic window and high toxicity. In critically ill patients, the drug pharmacokinetics changes significantly, and as a result, the antibiotic concentrations in blood and infection foci become suboptimal, which leads to therapeutic failures or toxic manifestations. For timely dosage adjustments, a competitive ELISA-based method using antibodies to polymyxin В (PMB) was developed. Among the several considered assays, a direct antibody-coated format was selected for its short duration (1.5 h) and the best agreement with the LC-MS/MS data (R² = 98 %). The assay dynamic measurement range (IC₂₀-IC₈₀) could be substantially shifted by changing the ratio of immunoreagents. To conveniently measure the therapeutic range of PMB concentrations, it was adjusted to 5.0-192 ng/mL, allowing the samples to be analyzed after a simple 100-fold dilution with the assay buffer. The ELISA sensitivity expressed in half-inhibition concentration (IC₅₀) and the limit of detection were 30.6 and 1.8 ng/mL, respectively. The assay cross-reactivity towards the related analogue colistin (COL) was 95 %, and this compound could also be adequately quantified by the same assay. The PMB and COL recovery from the spiked serum samples was similar and constituted 98-109 %. The trial drug monitoring was carried out in 3 patients with Gram-negative sepsis, and the established pharmacokinetic profiles of PMB revealed the necessity for individual dosage adjustment.

A physicochemical assessment of the thermal stability of dextrin-colistin conjugates

Attachment of polysaccharide carriers is increasingly being used to achieve precision delivery and improved effectiveness of protein and peptide drugs. Although it is clear that their clinical effectiveness relies on the purity and integrity of the conjugate in storage, as well as following administration, instability of polysaccharide-based conjugates can reduce the protective efficacy of the polymer, which may adversely affect the bioactive's potency. As a model, these studies used dextrin-colistin conjugates, with varying degrees of polymer modification (1, 2.5 and 7.5 mol% succinoylation) to assess the effect of storage temperature (- 20, 4, 21 and 37 °C) and duration (up to 12 months) on saccharide and colistin release and antimicrobial activity. Estimation of the proportion of saccharide release (by comparison of area under the curve from size exclusion chromatograms) was more pronounced at higher temperatures (up to 3 and 35% at - 20 °C and 37 °C, respectively after 12 months), however, repeated freeze-thaw did not produce any measurable release of saccharides, while addition of amylase (20, 100, 500 IU/L) caused rapid release of saccharides (> 70% total within 24 h). At all temperatures, conjugates containing the lowest degree of succinoylation released the highest proportion of free colistin, which increased with storage temperature, however no trend in saccharide release was observed. Despite the clear physical effects of prolonged storage, antimicrobial activity of all samples was only altered after storage at 37 °C for 12 months (> threefold decreased activity). These results demonstrate significant release of saccharides from dextrin-colistin conjugates during prolonged storage in buffered solution, especially at elevated temperature, which, in most cases, did not affect antimicrobial activity. These findings provide vital information about the structure-activity relationship of dextrin-colistin conjugates, prior to full-scale commercial development, which can subsequently be applied to other polysaccharide-protein and -peptide conjugates.

Colistimethate Acidic Hydrolysis Revisited: Arrhenius Equation Modeling Using UPLC-QToF MS

Colistimethate (CMS), the prodrug of polymyxin E (colistin), is an antibiotic widely used as a last-line therapy against multidrug resistant Gram-negative bacteria, but little is known about its pharmacokinetics as its administration has stopped as a result of high neuro- and nephro-toxicity. The measurement of CMS levels in patients’ biological fluids is of great importance in order to find the optimal dose regimen reducing the drug toxicity. Until now, CMS assay methods are based on the indirect determination after its hydrolysis to colistin (CS). Herein, the aim is to find the optimal conditions for the complete hydrolysis of CMS to CS. The reaction was studied at accelerated conditions: 40 °C, 50 °C, and 60 °C, and the results were evaluated by assessing the Arrhenius equation and computation employing the Tenua software. A validated analytical methodology based on ultra-performance liquid chromatography (UPLC) coupled to a hybrid quadrupole time of flight (QToF) instrument is developed for the simultaneous measurement of CMS and CS. The current methodology resulted in complete hydrolysis, in contrast with the previously reported one.

Systemic pharmacokinetics and safety of high doses of nebulized colistimethate sodium in critically ill patients with hospital-acquired and ventilator-associated pneumonia

OBJECTIVES

To assess the pharmacokinetics of formed colistin in plasma and the safety of two different high doses of colistimethate sodium administered via nebulization in critically ill surgical patients with hospital-acquired pneumonia (HAP) or ventilator-associated pneumonia (VAP).

PATIENTS AND METHODS

Formed colistin plasma concentrations were measured in critically ill surgical patients with pneumonia treated with two different doses of nebulized colistimethate sodium (3 MIU/8 h versus 5 MIU/8 h). Adverse events possibly related to nebulized colistimethate sodium were recorded.

RESULTS

Twenty-seven patients (15 in the 3 MIU/8 h group and 12 in the 5 MIU/8 h group) were included. Colistin plasma concentrations were unquantifiable (<0.1 mg/L) in eight (53.3%) patients in the 3 MIU/8 h group and in seven patients (58.3%) in the 5 MIU/8 h group. Median (IQR) quantifiable colistin plasma concentrations before nebulization and at 1, 4 and 8 h were 0.17 (0.12-0.33), 0.20 (0.11-0.24), 0.17 (0.12-0.23) and 0.17 (0.11-0.32) mg/L, respectively, in the 3 MIU/8 h group and 0.20 (0.11-0.35), 0.24 (0.12-0.44), 0.24 (0.10-0.49) and 0.23 (0.11-0.44) mg/L, respectively, in the 5 MIU/8 h group, with no differences between the two groups at any time. Renal impairment during nebulized treatment was observed in three patients in each group, but was unlikely to be related to colistimethate sodium treatment. Nebulized colistimethate sodium therapy was well tolerated and no bronchospasms or neurotoxicity events were observed.

CONCLUSIONS

In this limited observational case series of critically ill patients with HAP or VAP treated with high doses of nebulized colistimethate sodium, systemic exposure was minimal and the treatment was well tolerated.

Steady-state pharmacokinetic and pharmacodynamic profiling of colistin in critically ill patients with multi-drug-resistant gram-negative bacterial infections, along with differences in clinical, microbiological and safety outcome

Limited data are present regarding the steady-state pharmacokinetics and pharmacodynamics of colistin in critically ill patients suffering from multi-drug-resistant gram-negative bacterial (MDR-GNB) infections. We aimed to profile the steady-state pharmacokinetics and pharmacodynamics of colistin in critically ill patients with MDR-GNB infections, along with determining the predictors that could influence the clinical, microbiological and safety outcome. We recruited 30 critically ill patients suffering from MDR-GNB infections in our prospective open-label study. Intravenous colistimethate sodium (CMS) 2 million IU was administered concurrently with inhalational CMS 1 million IU every 8 hours. Steady-state plasma colistin levels were measured. Logistic regression analysis was used to identify various predictors of clinical, microbiological and safety outcome. A large variability was observed in the steady-state colistin pharmacokinetic/pharmacodynamic parameters, along with the factors that influenced the clinical, microbiological and safety outcome. In conclusion, steady-state colistin pharmacokinetic and pharmacodynamic parameters observed in our study were largely consistent with those reported in previous studies. High acute physiology and chronic health evaluation II scores were associated with poor clinical outcome. Log-transformed colistin maximum concentration, area under the plasma concentration curve for 8 hours, apparent total body clearance and apparent volume of distribution were significantly associated with the safety outcome.

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.

Therapeutic drug monitoring of polymyxin B by LC-MS/MS in plasma and urine

Background: A robust and rapid method for therapeutic drug monitoring (TDM) is urgently needed for polymyxin B, which is a last-line antibiotic for multidrug-resistant gram-negative bacteria infection. Methodology: A 3-min run of LC-MS/MS method was established to determine the main components of polymyxin B (polymyxin B1 and B2) in human plasma or urine. Solid-phase extraction was employed to eliminate the matrix effect from complicated samples from patients. Results: The calibration range was 0.050-5.00 and 0.0110-0.549 μg/ml for polymyxin B1 and B2, respectively, in plasma and urine. The precision and accuracy of quality controls, matrix effect, extraction recovery and stability were all validated and satisfied with the ICH requirements. The method was successfully applied to a pharmacokinetic study in healthy subjects and TDM in patients. Conclusion: The rapid LC-MS/MS method was validated for polymyxin B in plasma and urine, and robust for TDM.

Efficacy of Ceftolozane-Tazobactam in Combination with Colistin against Extensively Drug-Resistant Pseudomonas aeruginosa, Including High-Risk Clones, in an In Vitro Pharmacodynamic Model

Combination therapy is an attractive therapeutic option for extensively drug-resistant (XDR) Pseudomonas aeruginosa infections. Colistin has been the only treatment available for these infections for many years, but its results are suboptimal. Ceftolozane-tazobactam (C/T) is a newly available therapeutic option that has shown good antipseudomonal activity, even against a number of XDR P. aeruginosa strains. However, data about combinations containing C/T are scarce. The aim of this study was to analyze the activity of C/T and colistin alone and in combination against a collection of XDR P. aeruginosa strains containing 24 representative clinical isolates from a multicentre Spanish study. Twenty-four time-kill experiments performed over 24 h were conducted in duplicate to determine the effects of colistin and C/T alone and combined. An in vitro pharmacodynamic chemostat model then was used to validate this combination against three selected XDR P. aeruginosa ST175 isolates with different susceptibility levels to C/T. Static time-kill assays demonstrated superior synergistic or additive effect for C/T plus colistin against 21 of the 24 isolates studied. In the in vitro dynamic pharmacokinetic/pharmacodynamic (PK/PD) model, the C/T regimen of 2/1 g every 8 h with a steady-state concentration of 2 mg/liter colistin effectively suppressed the bacterial growth at 24 h. Additive or synergistic interactions were observed for C/T plus colistin against XDR P. aeruginosa strains and particularly against C/T-resistant strains. C/T plus colistin may be a useful treatment for XDR P. aeruginosa infections, including those caused by high risk-clones resistant to C/T.

Rapid one-step enzyme immunoassay and lateral flow immunochromatographic assay for colistin in animal feed and food

Background

Colistin (polymyxin E) is a kind of peptide antibiotic which has been approved in animal production for the purposes of disease prevention, treatment, and growth promotion. However, the wide use of colistin in animal feed may accelerate the spread of colistin-resistance gene MCR-1 from animal production to human beings, and its residue in animal-origin food may also pose serious health hazards to humans. Thus, it is necessary to develop corresponding analytical methods to monitor the addition of colistin in animal feed and the colistin residue in animal-origin food.

Results

A one-step enzyme-linked immunosorbent assay (ELISA) and a lateral flow immunochromatographic assay (LFIA) for colistin were developed based on a newly developed monoclonal antibody. The ELISA showed a 50% inhibition value (IC₅₀) of 9.7 ng/mL with assay time less than 60 min, while the LFIA had a strip reader-based detection limit of 0.87 ng/mL in phosphate buffer with assay time less than 15 min. For reducing the non-specific adsorption of colistin onto sample vial, the components of sample extraction solution were optimized and proved to greatly improve the assay accuracy. The spiked recovery experiment showed that the recoveries of colistin from feed, milk and meat samples were in the range of 77.83% to 113.38% with coefficient of variations less than 13% by ELISA analysis and less than 18% by LFIA analysis, respectively. Furthermore, actual sample analysis indicated that the two immunoassays can produce results consistent with instrumental analysis.

Conclusions

The developed assays can be used for rapid qualitative or quantitative detection of colistin in animal feed and food.

Electronic supplementary material

The online version of this article (10.1186/s40104-019-0389-7) contains supplementary material, which is available to authorized users.

Colistin for the treatment of urinary tract infections caused by extremely drug-resistant Pseudomonas aeruginosa: Dose is critical

OBJECTIVES

Optimal dosage regimens of colistin for the treatment of urinary tract infections (UTI) are unknown. Colistimethate sodium (CMS), the inactive prodrug of colistin, is mainly excreted in urine and converts to colistin after filtration by glomeruli, suggesting that concentrations of colistin in urine could be much higher than in plasma. Therefore, there is a need to optimize dosage regimens of intravenous CMS for UTI. The aim of this study was to examine the relationship between AUC/MIC of formed colistin and clinical outcomes in patients with UTI caused by extremely drug resistant (XDR) Pseudomonas aeruginosa.

METHODS

This prospective, observational cohort study involved patients with UTI caused by XDR P. aeruginosa. Clinical cure, bacteriological clearance and acute kidney injury (AKI) were analyzed. Steady-state colistin plasma concentrations (C_ss) were measured using HPLC. Based on the PK/PD of colistin in neutropenic mouse thigh infection models with P. aeruginosa, the optimal AUC/MIC should be ≥60 mg·h/L. According to the pharmacokinetics (PK) in critically-ill patients, the C_ss target of formed colistin in plasma was 2.5 mg/L.

RESULTS

Thirty-three patients were included (24 lower UTI and 9 pyelonephritis). The MIC₅₀ and MIC₉₀ values for colistin were 0.5 and 2 mg/L respectively. Nineteen patients (57.6%) received colistin monotherapy (84.2% lower UTI and 15.8% pyelonephritis). Of these, clinical cure was achieved in 89.5% of cases. Among patients with clinical cure and monotherapy, only 5 (29.4%) attained an optimal plasma AUC/MIC and only 1 (5.9%) the therapeutic level of formed colistin (2.5 mg/L). However, 10 (58.8%) patients showed colistin plasma concentrations above the MIC of the isolated P. aeruginosa. Microbiological eradication was achieved in 76.9% of patients. AKI at the end of treatment was present in 29.4% of patients.

CONCLUSIONS

The currently recommended dosage regimens of CMS showed high efficacy for the treatment of lower complicated UTI caused by XDR P. aeruginosa in non-critically ill patients and in the case of low MIC values, but also a considerable nephrotoxicity rate. Our data suggest that the use of lower CMS doses for lower UTI should be investigated in future studies to minimize the unnecessary nephrotoxicity.

A Review of the Clinical Pharmacokinetics of Polymyxin B

Polymyxin B remains an antibiotic of last resort because of its toxicities. Although newer therapies are becoming available, it is anticipated that resistance to these agents will continue to emerge, and understanding the safest and most efficacious manner to deliver polymyxin B will remain highly important. Recent data have demonstrated that polymyxin B may be less nephrotoxic than colistin. Pharmacokinetically, polymyxin B is primarily eliminated via non-renal pathways, and most do not recommend adjusting the dose for renal impairment. However, some recent studies suggest a weak relationship between polymyxin B clearance and patient creatinine clearance. This review article will describe the clinical pharmacokinetics of polymyxin B and address relevant issues in chemistry and assays available.

Colistin Use in Patients with Chronic Kidney Disease: Are We Underdosing Patients?

Colistin is administered as its inactive prodrug colistimethate (CMS). Selection of an individualized CMS dose for each patient is difficult due to its narrow therapeutic window, especially in patients with chronic kidney disease (CKD). Our aim was to analyze CMS use in patients with CKD. Secondary objectives were to assess the safety and efficacy of CMS in this special population. In this prospective observational cohort study of CMS-treated CKD patients, CKD was defined as the presence of a glomerular filtration rate (GFR) < 60 mL/min/m² for more than 3 months. The administered doses of CMS were compared with those recently published in the literature. Worsened CKD at the end of treatment (EOT) was evaluated with the RIFLE (Risk, Injury, Failure, Loss of kidney function, and End-stage kidney disease) criteria. Colistin plasma concentrations (C_ss) were measured using high-performance liquid chromatography. Fifty-nine patients were included. Thirty-six (61.2%) were male. The median age was 76 (45–95) years and baseline GFR was 36.6 ± 13.6. The daily mean CMS dosage used was compared with recently recommended doses (3.36 vs. 6.07; p < 0.001). Mean C_ss was 0.9 (0.2–2.9) mg/L, and C_ss was <2 mg/L in 50 patients (83.3%). Clinical cure was achieved in 43 (72.9%) patients. Worsened renal function at EOT was present in 20 (33.9%) patients and was reversible in 10 (52.6%). The CMS dosages used in this cohort were almost half those currently recommended. The mean achieved C_ss were under the recommended target of 2 mg/dL. Despite this, clinical cure rate was high. In this patient cohort, the incidence of nephrotoxicity was similar to those found in other recent studies performed in the general population and was reversible in 52.6%. These results suggest that CMS is safe and effective in patients with CKD and may encourage physicians to adjust dosage regimens to recent recommendations in order to optimize CMS treatments.

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.

Rapid, simple, and clinically applicable high-performance liquid chromatography method for clinical determination of plasma colistin concentrations

Background

Since both the antibacterial effects and common adverse effects of colistin are concentration-dependent, determination of the most appropriate dosage regimen and administration method for colistin therapy is essential to ensure its efficacy and safety. We aimed to establish a rapid and simple high-performance liquid chromatography (HPLC)-based system for the clinical determination of colistin serum concentrations.

Methods

Extraction using a solid-phase C18 cartridge, derivatisation with 9-fluorenylmethyl chloroformate, and elution with a short reversed-phase Cl8 column effectively separated colistin from an internal standard. The HPLC apparatus and conditions were as follows: analytical column, Hydrosphere C18; sample injection volume, 50 μL; column temperature, 40 °C; detector, Shimadzu RF-5300 fluorescence spectrophotometer (excitation wavelength, 260 nm; emission wavelength, 315 nm); mobile phase, acetonitrile/tetrahydrofuran/distilled water (50,14,20, v/v/v); flow-rate, 1.6 mL/min.

Results

The calibration curves obtained for colistin were linear in the concentration range of 0.10–8.0 μg/mL. The regression equation was y = 0.6496× − 0.0141 (r² = 0.9999). The limit of detection was ~ 0.025 μg/mL, and the assay intra- and inter-day precisions were 0.87–3.74% and 1.97–6.17%, respectively. The analytical peaks of colistin A, colistin B, and the internal standard were resolved with adequate peak symmetries, and their retention times were approximately 8.2, 6.8, and 5.4 min, respectively. Furthermore, the assay was successfully applied to quantify the plasma colistin levels of a haemodialysis patient.

Conclusion

The assay is a simple, rapid, accurate, selective, clinically applicable HPLC-based method for the quantification of colistin in human plasma.

Development of HPLC with fluorescent detection using NBD-F for the quantification of colistin sulfate in rat plasma and its pharmacokinetic applications

Colistin sulfate, composed of a mixture of colistin A sulfate (CLA) and colistin B sulfate (CLB), is available for treating life-threatening infections caused by multidrug-resistant Gram-negative bacteria. In this study, the CLA and CLB were quantified separately. Colistin sulfate was extracted from rat plasma with a solid-phase extraction C₁₈ cartridge and reacted with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F), and the fluorescent derivatives were subjected to reversed-phase high-performance liquid chromatography analysis and used to investigate the pharmacokinetics of CLA and CLB in rat plasma. The recovery rates of CLA and CLB were 41.2 ± 4.4 and 45.5 ± 3.1%, respectively. The recovery rate calculated from the total area of CLA and CLB was 43.9 ± 3.6%. When 2 mm NBD-F and 10 mm boric acid buffer (pH 9.5) were added to colistin sulfate, the highest recovery rate was obtained. The best heating time was 5 min at 60°C. The lower limits of quantification for CLA, CLB and the total area of CLA and CLB were 0.05, 0.05 and 0.1 μg/mL; the coefficients of variations were 13.5, 14.5 and 14.1%, respectively. This method was found to have acceptable linearity, precision and accuracy, and has been successfully applied to a pharmacokinetic study in rat plasma.

Polymyxins: Antibacterial Activity, Susceptibility Testing, and Resistance Mechanisms Encoded by Plasmids or Chromosomes

Polymyxins are well-established antibiotics that have recently regained significant interest as a consequence of the increasing incidence of infections due to multidrug-resistant Gram-negative bacteria. Colistin and polymyxin B are being seriously reconsidered as last-resort antibiotics in many areas where multidrug resistance is observed in clinical medicine. In parallel, the heavy use of polymyxins in veterinary medicine is currently being reconsidered due to increased reports of polymyxin-resistant bacteria. Susceptibility testing is challenging with polymyxins, and currently available techniques are presented here. Genotypic and phenotypic methods that provide relevant information for diagnostic laboratories are presented. This review also presents recent works in relation to recently identified mechanisms of polymyxin resistance, including chromosomally encoded resistance traits as well as the recently identified plasmid-encoded polymyxin resistance determinant MCR-1. Epidemiological features summarizing the current knowledge in that field are presented.

Agents of Last Resort: Polymyxin Resistance

Polymyxin resistance is a major public health threat, as the polymyxins represent "last-line" therapeutics for Gram-negative pathogens resistant to essentially all other antibiotics. Improved understanding of mechanisms of, and risk factors for, polymyxin resistance, as well as infection prevention and stewardship strategies, together with optimization of dosing of polymyxins including in combination regimens, can help to limit the emergence and dissemination of polymyxin resistance.

Urinary Concentrations of Colistimethate and Formed Colistin after Intravenous Administration in Patients with Multidrug-Resistant Gram-Negative Bacterial Infections

Limited information is available on the urinary excretion of colistin in infected patients. This study aimed to investigate the pharmacokinetics of colistimethate sodium (CMS) and formed colistin in urine in patients with multidrug-resistant (MDR) Gram-negative bacterial infections. A pharmacokinetic study was conducted on 12 patients diagnosed with an infection caused by an extremely drug-resistant (XDR) P. aeruginosa strain and treated with intravenous CMS. Fresh urine samples were collected at 2-h intervals, and blood samples were collected predose (C_{min ss}) and at the end of the CMS infusion (C_{max ss}) for measurement of concentrations of CMS and formed colistin using high-performance liquid chromatography (HPLC). CMS urinary recovery was determined as the summed amount of CMS and formed colistin recovered in urine for each 2-h interval divided by the CMS dose. There were 12 enrolled patients, 9 of whom were male (75%). Data [median (range)] were as follows: age, 65.5 (37 to 86) years; colistimethate urinary recovery 0 to 6 h, 42.6% (2.9% to 72.8%); range of concentrations of colistin in urine, <0.1 to 95.4 mg/liter; C_{min ss} and C_{max ss} of colistin in plasma, 0.9 (<0.2 to 1.4) and 0.9 (<0.2 to 1.4) mg/liter, respectively. In 6/12 (50%) patients, more than 40% of the CMS dose was recovered in the urine within the first 6 h after CMS administration. This study demonstrated rapid urinary excretion of CMS in patients within the first 6 h after intravenous administration. In all but one patient, the concentrations of formed colistin in urine were above the MIC for the most predominant isolate of P. aeruginosa in our hospital. Future studies are warranted for optimizing CMS dosage regimens in urinary tract infection (UTI) patients.

Pharmacokinetics/Pharmacodynamics of Pulmonary Delivery of Colistin against Pseudomonas aeruginosa in a Mouse Lung Infection Model

Colistin is often administered by inhalation and/or the parenteral route for the treatment of respiratory infections caused by multidrug-resistant (MDR) Pseudomonas aeruginosa However, limited pharmacokinetic (PK) and pharmacodynamic (PD) data are available to guide the optimization of dosage regimens of inhaled colistin. In the present study, PK of colistin in epithelial lining fluid (ELF) and plasma was determined following intratracheal delivery of a single dose of colistin solution in neutropenic lung-infected mice. The antimicrobial efficacy of intratracheal delivery of colistin against three P. aeruginosa strains (ATCC 27853, PAO1, and FADDI-PA022; MIC of 1 mg/liter for all strains) was examined in a neutropenic mouse lung infection model. Dose fractionation studies were conducted over 2.64 to 23.8 mg/kg of body weight/day. The inhibitory sigmoid model was employed to determine the PK/PD index that best described the antimicrobial efficacy of pulmonary delivery of colistin. In both ELF and plasma, the ratio of the area under the unbound concentration-time profile to MIC (fAUC/MIC) was the PK/PD index that best described the antimicrobial effect in mouse lung infection (R² = 0.60 to 0.84 for ELF and 0.64 to 0.83 for plasma). The fAUC/MIC targets required to achieve stasis against the three strains were 684 to 1,050 in ELF and 2.15 to 3.29 in plasma. The histopathological data showed that pulmonary delivery of colistin reduced infection-caused pulmonary inflammation and preserved the integrity of the lung epithelium, although colistin introduced mild pulmonary inflammation in healthy mice. This study showed pulmonary delivery of colistin provides antimicrobial effects against MDR P. aeruginosa lung infections superior to those of parenteral administrations. For the first time, our results provide important preclinical PK/PD information for optimization of inhaled colistin therapy.

Impact of colistin plasma levels on the clinical outcome of patients with infections caused by extremely drug-resistant Pseudomonas aeruginosa

BACKGROUND

Colistin has a narrow therapeutic window with nephrotoxicity being the major dose-limiting adverse effect. Currently, the optimal doses and therapeutic plasma levels are unknown.

METHODS

Prospective observational cohort study, including patients infected by colistin-susceptible P. aeruginosa treated with intravenous colistimethate sodium (CMS). Clinical data and colistin plasma levels at steady-state (C_ss) were recorded. The primary and secondary end points were clinical cure and 30-day all-cause mortality.

RESULTS

Ninety-one patients were included. Clinical cure was observed in 72 (79%) patients. The mean (SD) C_ss was 1.49 (1.4) mg/L and 2.42 (1.5) mg/L (p = 0.01) in patients who achieved clinical cure and those who not, respectively. Independent risk factors for clinical failure were male sex (OR 5.88; 95% CI 1.09-31.63), APACHE II score (OR 1.15; 95% CI 1.03-1.27) and nephrotoxicity at the EOT (OR 9.13; 95% CI 95% 2.06-40.5). The 30-day mortality rate was 30.8%. Risk factors for 30-day mortality included the APACHE II score (OR 1.98; 95% CI 1-1.20), the McCabe score (OR 2.49; 95% CI 1.14-5.43) and the presence of nephrotoxicity at the end of treatment (EOT) (OR 3.8; 95% CI 1.26-11.47).

CONCLUSION

In this series of patients with infections caused by XDR P. aeruginosa infections, C_ss is not observed to be related to clinical outcome.

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.

Lipopeptides as therapeutics: applications and in vivo quantitative analysis

A number of novel lipopeptides have been studied for their possible therapeutic potential. These studies should be supported by the appropriate analytical tools not only for novel potential drugs but also for their metabolites, precursors and side products. Lipopeptides have specific physicochemical properties that make them successful in medical applications. However, there are some difficulties with their qualitative and quantitative analyses in biological samples. Therefore, reliable, sensitive and robust analytical methods are in high demand. The main interest of our review is to describe a selection of specific and important properties of lipopeptides, and the analytical methods currently utilized for their characterization and determination in biological samples. A comparison of the pros and cons of immunomethods versus LC-MS methods is discussed in detail.

Pharmacokinetics of Colistin Following a Single Dose of Intravenous Colistimethate Sodium in Critically Ill Neonates

In this study, we sought to evaluate the pharmacokinetics of colistin after intravenous administration of colistimethate sodium (CMS) in the critically ill neonates with Gram-negative bacterial infections. A single intravenous dose of CMS [approximately 150,000 IU/kg, equivalent to 5 mg/kg colistin base activity (CBA)] was administered to 7 critically ill neonates. Mean (±SD) maximum plasma colistin concentration and area under the time-concentration curve from 0 to infinity were 3.0 ± 0.7 µg/mL and 25.3 ± 10.4 µg·h/mL, respectively. Time to maximum concentration, half-life, apparent volume of distribution and clearance were 1.3 ± 0.9 hours, 9.0 ± 6.5 hours, 7.7 ± 9.3 L/kg and 0.6 ± 0.3 L/h/kg, respectively. After a dose regimen of 5 mg/kg CBA every 24 hours, the average concentration expected at steady state is 1.1 ± 0.4 µg/mL. In critically ill neonates, a single intravenous dose of 5 mg CBA/kg (approximately 150,000 IU/kg of CMS) resulted in suboptimal plasma concentrations of colistin. According to our pharmacokinetics data, the dosage of CMS currently used in critically ill neonates is insufficient.

Colistin: Revival of an Old Polymyxin Antibiotic

Colistin (polymyxin E) is a positively charged deca-peptide antibiotic that disrupts the integrity of the outer membrane of the cell wall of gram-negative bacteria by binding to the lipid A moiety of lipopolysaccharides, resulting in cell death. The endotoxic activity of lipopolysaccharides is simultaneously inhibited. Colistin is increasingly being prescribed as rescue treatment for infections with multidrug-resistant bacilli. Nephrotoxicity and, to a lesser degree, neurotoxicity occur often during systemic colistin therapy, and have severely limited its application in the past. However, these side effects are largely reversible and can be managed through close monitoring. The prodrug colistimethate sodium (CMS) is less toxic and is, therefore, the preferred formulation for parenteral administration. Importantly, resistance to colistin seems to emerge often unless it is combined with another antibiotic, but further studies into this phenomenon are necessary. Pharmacokinetic and pharmacodynamic properties have received little attention, partly because of the physicochemical peculiarities of polymyxin antibiotics, especially their propensity to stick to other molecules and surfaces. The ratio between the area under the curve of free colistin and the pathogen's Minimal Inhibitory Concentration (MIC) best predicts microbiological and clinical responses, but more studies are needed in this area. Likewise, further standardization is needed in production and labeling of colistin formulations, and in the way the susceptibility of bacteria to colistin is determined.

Management of Meningitis Caused by Multi Drug-Resistant Acinetobacter Baumannii: Clinical, Microbiological and Pharmacokinetic Results in a Patient Treated with Colistin Methanesulfonate

This paper reports on a 71- year-old Caucasian male who underwent neurosurgery for an oligodendroglioma, followed by a cranial-sinus fistula and cerebrospinal fluid rhinorrhea. The clinical course was complicated due to an extensively drug-resistant Acinetobacter baumannii meningitis. The patient was treated with colistin methanesulfonate, intrathecal for 24 days and intravenous for 46 days. In addition, the patient received meropenem and teicoplanin to treat a urinary tract infection and a bacterial aspiration pneumonia. Cerebrospinal fluid trough colistin levels resulted above the MIC of A. baumannii. Colistin cerebrospinal fluid concentration did not increase over the treatment period. Meningitis was cured and A. baumannii eradicated. No side effects from the antimicrobial therapy were observed. In conclusion, this case highlights the issues in treating infections caused by resistant Gram negative bacteria and supports previous findings on the efficacy, pharmacokinetic and tolerability of intravenous and intrathecal colistin treatments.

Pulmonary and Systemic Pharmacokinetics of Colistin Following a Single Dose of Nebulized Colistimethate in Mechanically Ventilated Neonates

The purpose of this study was to evaluate the pulmonary and systemic pharmacokinetics of colistin following a single dose of nebulized colistimethate sodium (CMS) in mechanically ventilated neonates. We administered a single dose of nebulized CMS (approximately 120,000 IU/kg of CMS, equivalent to 4 mg/kg colistin base activity) to 6 ventilated neonates with ventilator-associated pneumonia. The median gestational age was 39 weeks (range, 32-39 weeks). Mean (± SD) tracheal aspirate colistin maximum concentration (Cmax), area under the concentration-time curve (AUC 0-24) and t1/2 were 24.0 ± 8.2 μg/mL, 147.6 ± 53.5 μg · hours/mL and 9.8 ± 5.5 hours, respectively. The plasma concentrations of colistin were low. In neonates, a single nebulized dose of CMS (120,000 IU) resulted in high local concentrations for at least 12 hours and low systemic concentrations of colistin. Twice daily nebulization might be more appropriate.

Preliminary method for direct quantification of colistin methanesulfonate by attenuated total reflectance Fourier transform infrared spectroscopy

Colistin use has increased in response to the advent of infections caused by multidrug-resistant organisms. It is administered parenterally as an inactive prodrug, colistin methanesulfonate (CMS). Various formulations of CMS and labeling conventions can lead to confusion about colistin dosing, and questions remain about the pharmacokinetics of CMS. Since CMS does not have strong UV absorbance, current methods employ a laborious process of chemical conversion to colistin followed by precolumn derivatization to detect formed colistin by high-performance liquid chromatography. Here, we report a method for direct quantification of colistin methanesulfonate by attenuated total reflectance Fourier transform infrared spectroscopy (ATR FTIR).

Drug release from an oromucosal paste for the selective decontamination of the oropharynx (in ICU patients and healthy volunteers)

Selective oropharyngeal decontamination (SOD) is used in many ICUs in the Netherlands and some other European countries. While its clinical effect has been studied intensively, no studies have been done to assess the biopharmaceutical aspects of the paste, i.e. it is not known which local concentrations exist. For this study, five healthy volunteers were subjected to 400mg of the generally used paste. Ten ICU patients were treated according to the normal standard in the ICU of the University Medical Center Utrecht. Salivary levels of the various substances were measured over time using two separate analytical methods. Also the microbial burden of the oropharynx was assessed. The results show significant variation in release, both ICU patients and healthy volunteers. The antimicrobials tobramycin and colistin showed a relatively fast release, while nystatin exhibited a controlled release-like pattern. Amphotericin B is hardly released from the formulation. The concentration of the antimicrobial agents drop to sub-MIC levels relatively fast. From a biopharmaceutical perspective, amphotericin B should be replaced by nystatin. The application of the mouth paste is subject to massive variation in daily practice; each nurse applies a different amount, in a different way. In addition, the formulation is hard to apply and unpleasant with regards to the taste and feel for the conscious patients. This is not a clinical study, but a study that aimed to give a biopharmaceutical justification for SOD Both the clinical practice and the clinically determined levels of drugs enable critical evaluation of the outcome of clinical studies performed until now.

Extracorporeal clearance of colistin methanesulphonate and formed colistin in end-stage renal disease patients receiving intermittent haemodialysis: implications for dosing

OBJECTIVES

Colistin, administered intravenously as its inactive prodrug colistin methanesulphonate (CMS), is being increasingly used. However, there is very limited information available on the impact of haemodialysis (HD) on the pharmacokinetics of CMS and formed colistin.

PATIENTS AND METHODS

A single 30 min intravenous dose of CMS (150 mg of colistin base activity) was administered to 10 patients undergoing HD. HD was performed from 1.5 to 5.5 h after the start of the CMS infusion. Serial blood samples were collected over 50 h, additional blood samples pre- and post-dialysis membrane at three timepoints during HD, dialysate samples at four timepoints during HD, and a cumulative urine sample over 24 h. CMS and colistin were determined by HPLC. Population modelling and determination of HD clearance by multiple methods was conducted.

RESULTS

The average amount of CMS recovered in the dialysate was 30.6% of the dose administered. The concentrations of CMS and colistin in the plasma and the amounts of CMS recovered in the dialysate were well described by the population disposition model. The clearance of CMS by dialysis as estimated by population analysis based on systemic plasma concentrations and amounts in the dialysate was 4.26 L/h (26% coefficient of variation). The dialysis clearance determined from the pre- and post-membrane plasma concentrations was 5.67 L/h (21%) for CMS and 3.99 L/h (44%) for colistin. Thus, CMS clearance by dialysis from trans-cartridge extraction was ∼30% higher than when calculated based on the amount in dialysate, suggesting adsorption to the membrane.

CONCLUSIONS

Due to the extensive removal of CMS by dialysis, HD should be conducted at the end of a dosing interval and a supplemental dose should be administered.