Quantitative determination of colistin A/B and colistin methanesulfonate in biological samples using hydrophilic interaction chromatography tandem mass spectrometry

Development and validation of a liquid chromatography-tandem mass spectrometry method for the determination of polymixin B1, B2, ile-B1, E1, and E2 in human plasma and its clinical pharmacokinetic application

Polymyxin B (PB) and Polymyxin E (PE, also called colistin) are used as the last treatment resort for multidrug-resistant Gram-negative bacterial infections. The nephrotoxicity and neurotoxicity of polymyxins limit their clinical use, and guidelines recommend therapeutic drug monitoring (TDM) to optimize efficacy and reduce toxicity. However, there are limited analytical methods available for the determination of PB and PE. This study aimed to develop a simple and robust liquid chromatography with tandem mass spectrometry (LC-MS/MS) analytical method for determining the main compounds of PB and PE, namely PB1, PB2, ile-PB1, PE1, and PE2, in human plasma and to investigate of their pharmacokinetics in critically ill patients with the use of PB and PE, respectively. Plasma PB1, PB2, ile-PB1, PE1, and PE2 were chromatographically separated on a Welch LP-C18 column and detected using electrospray ionization mode coupled with multiple reaction monitoring. The calibration curve showed acceptable linearity over 20-10,000 ng/mL for PB1, PE1, and PE2 and 10-5000 ng/mL for PB2 and ile-PB1 in the plasma, respectively. After validation following approved guidelines, this method was successfully applied for PB and PE pharmacokinetic analysis and TDM in critically ill patients. Additionally, the composition of PB1, PB2, ile-PB1, PE1, and PE2 remains unchanged from 0 to 12 h after entering the patient's body.

Full green assay of parenteral dosage forms of polymyxins utilizing xanthene dye: application to content uniformity testing

Due to the lack of other treatment options, a rebirth of polymyxins is urgently required. Colistin (also called polymyxin E) and polymyxin B are the only two examples of this antibiotic class that were effectively employed in such critical situations. In the present work, both of the two studied medications were quantified via a simple, green, and non-extracting spectrophotometric approach based on the formation of ion-pair complexes with Erythrosine B. Without using any organic solvents, the pink color of the created complexes was detected at wavelength = 558 nm. To achieve the highest intensity of absorbance, optimum conditions were established by the screening of many experimental factors such as pH, buffer volume, the volume of Erythrosine B, and the time consumed to undergo the reaction. For Colistin and Polymyxin B respectively, Beer-Lambert's law was observed at the concentration ranges of 1-6, 1-9 µg mL- 1. The technique was approved and validated following ICH recommendations. Lastly, the suggested approach has been successfully implemented to quantify the cited medications colorimetrically, for the first time, in their parenteral dosage forms with excellent recoveries. Also, Content uniformity testing was implemented.

Coacervation in Slow Motion: Kinetics of Complex Micelle Formation Induced by the Hydrolysis of an Antibiotic Prodrug

Colistin methanesulfonate (CMS) is the less-toxic prodrug of highly nephrotoxic colistin. To develop and understand highly necessary new antibiotic formulations, the hydrolysis of CMS to colistin must be better understood. Herein, with the addition of poly(ethylene oxide)-b-poly(methacrylic acid) (PEO-b-PMAA) to CMS, we show that we can follow the hydrolysis kinetics, employing small-angle X-ray scattering (SAXS) through complex coacervation. During this hydrolysis, hydroxy methanesulfonate (HMS) groups from CMS are cleaved, while the newly formed cationic amino groups complex with the anionic charge from the PMAA block. As the hydrolysis of HMS groups is slow, we can follow the complex coacervation process by the gradual formation of complex micelles containing activated antibiotics. Combining mass spectrometry (MS) with SAXS, we quantify the hydrolysis as a function of pH. Upon modeling the kinetic pathways, we found that complexation only happens after complete hydrolysis into colistin and that the process is accelerated under acidic conditions. At pH = 5.0, effective charge switching was identified as the slowest step in the CMS conversion, constituting the rate-limiting step in colistin formation.

Implementation of Modern Therapeutic Drug Monitoring and Lipidomics Approaches in Clinical Practice: A Case Study with Colistin Treatment

Nowadays, lipidomics plays a crucial role in the investigation of novel biomarkers of various diseases. Its implementation into the field of clinical analysis led to the identification of specific lipids and/or significant changes in their plasma levels in patients suffering from cancer, Alzheimer's disease, sepsis, and many other diseases and pathological conditions. Profiling of lipids and determination of their plasma concentrations could also be helpful in the case of drug therapy management, especially in combination with therapeutic drug monitoring (TDM). Here, for the first time, a combined approach based on the TDM of colistin, a last-resort antibiotic, and lipidomic profiling is presented in a case study of a critically ill male patient suffering from Pseudomonas aeruginosa-induced pneumonia. Implementation of innovative analytical approaches for TDM (online combination of capillary electrophoresis with tandem mass spectrometry, CZE-MS/MS) and lipidomics (liquid chromatography-tandem mass spectrometry, LC-MS/MS) was demonstrated. The CZE-MS/MS strategy confirmed the chosen colistin drug dosing regimen, leading to stable colistin concentrations in plasma samples. The determined colistin concentrations in plasma samples reached the required minimal inhibitory concentration of 1 μg/mL. The complex lipidomics approach led to monitoring 545 lipids in collected patient plasma samples during and after the therapy. Some changes in specific individual lipids were in good agreement with previous lipidomics studies dealing with sepsis. The presented case study represents a good starting point for identifying particular individual lipids that could correlate with antimicrobial and inflammation therapeutic management.

Novel method for determination of colistin sulfate in human plasma by high-performance liquid chromatography-tandem mass spectrometry and its clinical applications in critically ill patients

Colistin is a last-resort antibiotic used for treating infections caused by carbapenem-resistant Gram-negative bacteria, particularly in critically patients, nevertheless its therapeutic window is narrow, and requires monitoring. A determination method suitable for clinical detection is conducive to ensure its efficacy and safety of patients with severe infection. We developed and validated a concise and accurate high-performance liquid chromatography-tandem mass spectrometry method for the determination of colistin A and B in human plasma. We used a Kinetex C18 column (50 mm × 2.1 mm, 2.6 μm) with acetonitrile (containing 0.1% formic acid) as the protein precipitant and water (containing 0.2% formic acid and 5 mmol/L ammonium formate) - acetonitrile (containing 0.2% formic acid) as the gradient elution. The calibration curves were linear over concentration ranges of 0.06-4.00 μg/mL (colistin A) and 0.1-7.0 μg/mL (colistin B). The precision, accuracy, matrix effect, extraction recovery, and stability were all validated. This method was applied to the therapeutic drug monitoring for 50 critically ill patients. The trough, peak, and average steady-state concentrations of these patients were 0.8 ± 0.4, 1.4 ± 0.5, and 1.0 ± 0.4 μg/mL, respectively. And the concentrations of colistin in human plasma were closely related to the patient's renal function.

Applications of tandem mass spectrometry (MS/MS) in antimicrobial peptides field: Current state and new applications

Antimicrobial peptides (AMPs) constitute a group of small molecular peptides that exhibit a wide range of antimicrobial activity. These peptides are abundantly present in the innate immune system of various organisms. Given the rise of multidrug-resistant bacteria, microbiological studies have identified AMPs as potential natural antibiotics. In the context of antimicrobial resistance across various human pathogens, AMPs hold considerable promise for clinical applications. However, numerous challenges exist in the detection of AMPs, particularly by immunological and molecular biological methods, especially when studying of newly discovered AMPs in proteomics. This review outlines the current status of AMPs research and the strategies employed in their development, considering resent discoveries and methodologies. Subsequently, we focus on the advanced techniques of mass spectrometry for the quantification of AMPs in diverse samples, and analyzes their application, advantages, and limitations. Additionally, we propose suggestions for the future development of tandem mass spectrometry for the detection of AMPs.

A quantitative method for determination of colistin E2 methanesulphonate in human plasma by 15N-labeled colistin E2

The single-component colistin E2, with superior antibacterial activity and lower toxicity, was being developed as the latest generation of polymyxin drugs. However, colistin E2 has not been tested quantitatively in biological matrices. In this study, based on the quantitative detection of colistin methanesulphonate (CMS) and colistin by Zhao et al., 15N-labeled colistin E2 was used as an internal standard (IS) for a more accurate quantitative detection of CMS E2 in human plasma. A rapid ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) assay method was developed for determination of CMS E2 and colistin E2 in human plasma. After pretreatment of plasma samples by 96-well SPE Supra-Clean Weak Cation Exchange (WCX) plate, the formed colistin E2 was detected and quantified by UHPLC-MS/MS system. All plasma lots were found to be free of interferences with the analyte. The matrix has no effect on the quantitation of the analyte. No significant effect of the carryover was observed. The dilution integrity was demonstrated in plasma samples without the loss of accuracy and precision. The lower limit of quantification (LLOQ) was 0.0300 mg/L for colistin E2 in plasma with accuracy (relative error, 5.1-12.7%) and precision (relative standard deviation,  - 5.7-9.3%). Stability of CMS E2 and colistin E2 was demonstrated in biological samples before and during sample treatment, and in the extract. Furthermore, this method was successfully applied to the analysis of plasma samples obtained from Chinese healthy volunteers receiving a single intravenous CMS E2 dose of 5 mg/kg. In conclusion, the detection method was characterized by speed and high accuracy, which laid a solid foundation for the subsequent development of CMS E2 drug.

Unravelling the Hepatic Elimination Mechanisms of Colistin

PURPOSE

Colistin is an antibiotic which is increasingly used as a last-resort therapy in critically-ill patients with multidrug resistant Gram-negative infections. The purpose of this study was to evaluate the mechanisms underlying colistin's pharmacokinetic (PK) behavior and to characterize its hepatic metabolism.

METHODS

In vitro incubations were performed using colistin sulfate with rat liver microsomes (RLM) and with rat and human hepatocytes (RH and HH) in suspension. The uptake of colistin in RH/HH and thefraction of unbound colistin in HH (fu,hep) was determined. In vitro to in vivo extrapolation (IVIVE) was employed to predict the hepatic clearance (CLh) of colistin.

RESULTS

Slow metabolism was detected in RH/HH, with intrinsic clearance (CLint) values of 9.34± 0.50 and 3.25 ± 0.27 mL/min/kg, respectively. Assuming the well-stirred model for hepatic drug elimination, the predicted rat CLh was 3.64± 0.22 mL/min/kg which could explain almost 70% of the reported non-renal in vivo clearance. The predicted human CLh was 91.5 ± 8.83 mL/min, which was within two-fold of the reported plasma clearance in healthy volunteers. When colistin was incubated together with the multidrug resistance-associated protein (MRP/Mrp) inhibitor benzbromarone, the intracellular accumulation of colistin in RH/HH increased significantly.

CONCLUSION

These findings indicate the major role of hepatic metabolism in the non-renal clearance of colistin, while MRP/Mrp-mediated efflux is involved in the hepatic disposition of colistin. Our data provide detailed quantitative insights into the hereto unknown mechanisms responsible for non-renal elimination of colistin.

New validated spectrofluorimetric protocol for colistin assay through condensation with 2,2-dihydroxyindan-1,3-dione: application to content uniformity testing

A new, cost-effective and sensitive spectroscopic assay for the quantification of Colistin Sulfate (CS) and its prodrug colistimethate sodium (CMS) has been developed and validated. The validated technique depends on the condensation of the studied drug with 2,2-dihydroxyindan-1,3-dione (ninhydrin) and phenylacetaldehyde using Teorell and Stenhagen buffer (pH = 6) to yield a fluorescent product that is estimated at emission wavelength (λ em = 474 nm) after excitation wavelength (λ ex = 390 nm). The reaction's affecting factors were carefully studied and adjusted accurately. Over the following range (0.4-2.4 μg mL-1), the produced calibration plot looked rectilinear, and the estimated limits of detection and quantification (LOD and LOQ) were 0.051 & 0.154 μg mL-1 respectively. The recommended approach was utilized to evaluate market products containing the investigated drug. Moreover, content uniformity testing was employed as a new procedure not found in the previously reported fluorimetric technique.

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.

Salvage Parenteral Antibiotics for Multidrug-Resistant (MDR) Gram-Negative Bacteria; A Fluorescamine-Based Technique for Ultrasensitive Spectrofluorimetric Measurement of Polymyxins; Human Plasma Application

Polymyxins (PMS), namely Colistin (CS) and Polymyxin B (Poly B), are antimicrobial drugs that recently used to treat multi-resistant gram-negative bacteria infections and their resurgence owing to a lack of new antibiotics. A speedy, simple, and ultrasensitive spectrofluorimetric screening of PMS in pharmaceutical formulations and biological fluids was urgently required from this point forward. A reaction between fluorescamine and the aliphatic amino moiety found in both drugs was performed in a slightly alkaline borate buffer (pH 8.5) resulted in highly fluorescent products measured at λ_em 460 (after λ_ex 390.5 nm). Linear calibration curves were constructed over the concentration range of 70 to 1800 ng mL^-1 and 100 to 1400 ng mL^-1 , with slope values of 0.273 and 0.286, correlation coefficients of 0.9998 and 0.9997, and determination coefficient of 0.9997 and 0.9994 for Poly B and CS, respectively. The ultra sensitivity of the proposed method was demonstrated by the very low limits of quantifications values of 67.56 ng mL^-1 and 94.89 ng mL^-1 for Poly B and CS, respectively. The cited drugs were successfully determined in their intravenous market preparations by the prescribed method. Moreover, due to the high sensitivity, the suggested method was employed to assay the investigated drugs in biological fluids.

The first spectrofluorimetric approach for quantification of colistin sulfate and its prodrug colistimethate sodium in pharmaceutical dosage form and human plasma

A new, accurate, nonextractive, and sensitive fluorimetric approach was proposed and validated for the first time estimation of colistin sulfate and its inactive prodrug colistimethate sodium in its bulk form, pharmaceutical formulations, and human plasma. The approach relied on condensation between acetylacetone/formaldehyde and the primary amino moiety of nonfluorescent colistin in Teorell and Stenhagen buffer (pH 2.8) by the Hantzsch reaction to form a highly fluorescent dihydropyridine derivative. The fluorescent product was measured at 460 nm (λ_ex  = 402 nm). A plot of relative fluorescence intensity (RFI) versus concentration was rectilinear over the range 200-4000 ng ml^-1 with excellent correlation (r) and determination (r² ) coefficients of 0.9999 and 0.9998, respectively. The limit of detection (LOD) and limit of quantitation (LOQ) were 40.91 and 123.99 ng ml^-1 , respectively. The present procedure was useful for determination of colistin sulfate either in powder form for suspension or in its parenteral prodrug colistimethate sodium in vial formulation. The investigated approach was applied for in vitro quantification of this drug in spiked human plasma, with a per cent mean recovery of 98.24 ± 1.34. The proposed method is reliable, selective, and does not require tedious sample pretreatment steps, expensive instrumentation, or harmful reagents, all of which make it ideally suited for use in quality control laboratories.