Colistin pharmacokinetics in burn patients during continuous venovenous hemofiltration

Edoxaban pharmacokinetics during in vitro continuous renal replacement therapy

BACKGROUND

To evaluate the clearance of edoxaban during modeled in vitro continuous renal replacement therapy (CRRT), assess protein binding and circuit adsorption, and provide initial dosing recommendations.

METHODS

Edoxaban was added to the CRRT circuit and serial pre-filter bovine blood samples were collected along with post-filter blood and effluent samples. All experiments were performed in duplicate using continuous veno-venous hemofiltration (CVVH) and hemodialysis (CVVHD) modes, with varying filter types, flow rates, and point of CVVH replacement fluid dilution. Concentrations of edoxaban and urea were quantified via liquid chromatography-tandem mass spectrometry. Plasma pharmacokinetic parameters for edoxaban were estimated via noncompartmental analysis. Two and three-way analysis of variance (ANOVA) models were built to assess the effects of mode, filter type, flow rate, and point of dilution on CLCRRT. Linear regression was utilized to provide dosing estimations across CRRT effluent flow rates from 0.5 to 5 L/h. Optimal edoxaban doses were suggested using CLCRRT and population non-renal clearance (CLNR) to estimate total clearance and match the systemic AUC associated with efficacy in the treatment of venous thromboembolism.

RESULTS

Edoxaban clearance from the CRRT circuit occurred primarily via hemofilter adsorption to the HF1400 and M150 filters at 74% and 65%, respectively, while mean percent protein binding was 41%. Multivariate analyses confirmed the lack of influence of CRRT mode, filter type, and point of dilution on the CLCRRT of edoxaban allowing dosing recommendations to be made based on effluent flow rate. Edoxaban doses of 30-45 mg once daily were estimated to achieve target the AUC threshold for flow rates from 0.5 to 5 L/h.

CONCLUSION

For CRRT flow rates most employed in clinical practice, an edoxaban dose of 45 mg once daily is predicted to achieve target systemic exposure thresholds for venous thromboembolism treatment. The safety and efficacy of this proposed dosing warrants further investigation in clinical studies.

High-dose colistin pharmacokinetics in critically ill patients receiving continuous renal replacement therapy

BACKGROUND

Colistin, administered as intravenous colistimethate (CMS), is still used in the critical care setting and current guidelines recommend high dosage CMS in patients undergoing continuous renal replacement therapy (CRRT). Due to the paucity of real-life data, we aimed to describe colistin pharmacokinetic/pharmacodynamic (PK/PD) profile in a cohort of critically ill patients with infections due to carbapenem-resistant (CR) bacteria undergoing CRRT.

RESULTS

All consecutive patients admitted to three Intensive Care Units (ICUs) of a large metropolitan University Hospital, treated with colistin for at least 48 h at the dosage of 6.75 MUI q12, after 9 MIU loading dose, and undergoing CRRT were included. After the seventh dose, patients underwent blood serial sampling during a time frame of 24 h. We included 20 patients, who had CR-Acinetobacter baumannii ventilator-associated pneumonia and were characterized by a median SAPS II and SOFA score of 41 [34.5-59.3] and 9 [6.7-11], respectively. Fifteen patients died during ICU stay and six recovered renal function. Median peak and trough colistin concentrations were 16.6 mcg/mL [14.8-20.6] and 3.9 mcg/mL [3.3-4.4], respectively. Median area under the time-concentration curve (AUC0 - 24) and average steady-state concentration (Css, avg) were 193.9 mcg h/mL [170.6-208.6] and 8.07 mcg/mL [7.1-8.7]. Probability of target attainment of colistin pharmacodynamics according to the fAUC0 - 24/MIC target ≥ 12 was 100% for MIC ≤ 2 mcg/mL and 85% for MIC = 4 mcg/ML, although exceeding the toxicity limit of Css, avg 3-4 mcg/mL.

CONCLUSIONS

In critically ill patients with CR infections undergoing CRRT, recommended CMS dosage resulted in colistin plasmatic levels above bacterial MIC90, but exceeding the safety Css, avg. limit.

TRIAL REGISTRATION

This trial was registered in ClinicalTrials.gov on 23/07/2021 with the ID NCT04995133 (https//clinicaltrials.gov/study/NCT04995133).

Pharmacokinetics, Pharmacodynamics, and Dose Optimization of Cefiderocol during Continuous Renal Replacement Therapy

BACKGROUND

The need for continuous renal replacement therapy (CRRT) in critically ill patients with serious infections is associated with clinical failure, emergence of resistance, and excess mortality. These poor outcomes are attributable in large part to subtherapeutic antimicrobial exposure and failure to achieve target pharmacokinetic/pharmacodynamic (PK/PD) thresholds during CRRT. Cefiderocol is a novel siderophore cephalosporin with broad in vitro activity against resistant pathogens and is often used to treat critically ill patients, including those receiving CRRT, despite the lack of data to guide dosing in this population.

OBJECTIVE

The aim of this study was to evaluate the PK and PD of cefiderocol during in vitro and in vivo CRRT and provide optimal dosing recommendations.

METHODS

The PK and dialytic clearance of cefiderocol was evaluated via an established in vitro CRRT model across various modes, filter types, and effluent flow rates. These data were combined with in vivo PK data from nine patients receiving cefiderocol while receiving CRRT from phase III clinical trials. Optimal dosing regimens and their respective probability of target attainment (PTA) were assessed via an established population PK model with Bayesian estimation and 1000-subject Monte Carlo simulations at each effluent flow rate.

RESULTS

The overall mean sieving/saturation coefficient during in vitro CRRT was 0.90 across all modes, filter types, effluent flow rates, and points of replacement fluid dilution tested. Adsorption was negligible at 10.9%. Three-way analysis of variance (ANOVA) and multiple linear regression analyses demonstrated that effluent flow rate is the primary driver of clearance during CRRT and can be used to calculate optimal cefiderocol doses required to match the systemic exposure observed in patients with normal renal function. Bayesian estimation of these effluent flow rate-based optimal doses in nine patients receiving CRRT from the phase III clinical trials of cefiderocol revealed comparable mean (± standard deviation) area under the concentration-time curve values as patients with normal renal function (1709 ± 539 mg·h/L vs. 1494 ± 58.4 mg·h/L; p = 0.26). Monte Carlo simulations confirmed these doses achieved >90% PTA against minimum inhibitory concentrations ≤4 mg/L at effluent flow rates from 0.5 to 5 L/h.

CONCLUSION

The optimal dosing regimens developed from this work have been incorporated into the prescribing information for cefiderocol, making it the first and only antimicrobial with labeled dosing for CRRT. Future clinical studies are warranted to confirm the efficacy and safety of these regimens.

Dose Optimization of Colistin: A Systematic Review

Colistin is considered a last treatment option for multi-drug and extensively resistant Gram-negative infections. We aimed to assess the available data on the dosing strategy of colistin. A systematic review was performed to identify all published studies on the dose optimization of colistin. Grey literature and electronic databases were searched. Data were collected in a specified form and the quality of the included articles was then assessed using the Newcastle-Ottawa scale for cohort studies, the Cochrane bias tool for randomized clinical trials (RCT), and the Joanna Briggs Institute (JBI) critical checklist for case reports. A total of 19 studies were included, of which 16 were cohort studies, one was a RCT, and two were case reports. A total of 18 studies proposed a dosing regimen for adults, while only one study proposed a dosing schedule for pediatric populations. As per the available evidence, a loading dose of 9 million international units (MIU) of colistin followed by a maintenance dose of 4.5 MIU every 12 h was considered the most appropriate dosing strategy to optimize the safety and efficacy of treatment and improve clinical outcomes. This review supports the administration of a loading dose followed by a maintenance dose of colistin in severe and life-threatening multi-drug Gram-negative bacterial infections.

Correlation of antimicrobial fraction unbound and sieving coefficient in critically ill patients on continuous renal replacement therapy: a systematic review

Background

Fraction unbound has been used as a surrogate for antimicrobial sieving coefficient (SC) to predict extracorporeal clearance in critically ill patients on continuous renal replacement therapy (CRRT), but this is based largely on expert opinion.

Objectives

To examine relationships between package insert-derived fraction unbound (Fu-P), study-specific fraction unbound (Fu-S), and SC in critically ill patients receiving CRRT.

Methods

English-language studies containing patient-specific in vivo pharmacokinetic parameters for antimicrobials in critically ill patients requiring CRRT were included. The primary outcome included correlations between Fu-S, Fu-P, and SC. Secondary outcomes included correlations across protein binding quartiles, serum albumin, and predicted in-hospital mortality, and identification of predictors for SC through multivariable analysis.

Results

Eighty-nine studies including 32 antimicrobials were included for analysis. SC was moderately correlated to Fu-S (R2 = 0.55, P < 0.001) and Fu-P (R2 = 0.41, P < 0.001). SC was best correlated to Fu-S in first (<69%) and fourth (>92%) quartiles of fraction unbound and above median albumin concentrations of 24.5 g/L (R2 = 0.71, P = 0.07). Conversely, correlation was weaker in patients with mortality estimates greater than the median of 55% (R2 = 0.06, P = 0.84). SC and Fu-P were also best correlated in the first quartile of antimicrobial fraction unbound (R2 = 0.66, P < 0.001). Increasing Fu-P, flow rate, membrane surface area, and serum albumin, and decreasing physiologic charge significantly predicted increasing SC.

Conclusions

Fu-S and Fu-P were both reasonably correlated to SC. Caution should be taken when using Fu-S to calculate extracorporeal clearance in antimicrobials with 69%–92% fraction unbound or with >55% estimated in-hospital patient mortality. Fu-P may serve as a rudimentary surrogate for SC when Fu-S is unavailable.

Evaluation of Pseudomonas aeruginosa pathogenesis and therapeutics in military-relevant animal infection models

Modern combat-related injuries are often associated with acute polytrauma. As a consequence of severe combat-related injuries, a dysregulated immune response results in serious infectious complications. The gram-negative bacterium Pseudomonas aeruginosa is an opportunistic pathogen that often causes life-threatening bloodstream, lung, bone, urinary tract, and wound infections following combat-related injuries. The rise in the number of multidrug-resistant P. aeruginosa strains has elevated its importance to civilian clinicians and military medicine. Development of novel therapeutics and treatment options for P. aeruginosa infections is urgently needed. During the process of drug discovery and therapeutic testing, in vivo testing in animal models is a critical step in the bench-to-bedside approach, and required for Food and Drug Administration approval. Here, we review current and past literature with a focus on combat injury-relevant animal models often used to understand infection development, the interplay between P. aeruginosa and the host, and evaluation of novel treatments. Specifically, this review focuses on the following animal infection models: wound, burn, bone, lung, urinary tract, foreign body, and sepsis.

Pharmacokinetics and dialytic clearance of apixaban during in vitro continuous renal replacement therapy

Background

To evaluate the transmembrane clearance (CL_TM) of apixaban during modeled in vitro continuous renal replacement therapy (CRRT), assess protein binding and circuit adsorption, and provide initial dosing recommendations.

Methods

Apixaban was added to the CRRT circuit and serial pre-filter bovine blood samples were collected along with post-filter blood and effluent samples. All experiments were performed in duplicate using continuous veno-venous hemofiltration (CVVH) and hemodialysis (CVVHD) modes, with varying filter types, flow rates, and point of CVVH replacement fluid dilution. Concentrations of apixaban and urea were quantified via liquid chromatography-tandem mass spectrometry. Plasma pharmacokinetic parameters for apixaban were estimated via noncompartmental analysis. CL_TM was calculated via the estimated area under the curve (AUC) and by the product of the sieving/saturation coefficient (SC/SA) and flow rate. Two and three-way analysis of variance (ANOVA) models were built to assess the effects of mode, filter type, flow rate, and point of dilution on CL_TM by each method. Optimal doses were suggested by matching the AUC observed in vitro to the systemic exposure demonstrated in Phase 2/3 studies of apixaban. Linear regression was utilized to provide dosing estimations for flow rates from 0.5–5 L/h.

Results

Mean adsorption to the HF1400 and M150 filters differed significantly at 38 and 13%, respectively, while mean (± standard deviation, SD) percent protein binding was 70.81 ± 0.01%. Effect of CVVH point of dilution did not differ across filter types, although CL_TM was consistently significantly higher during CRRT with the HF1400 filter compared to the M150. The three-way ANOVA demonstrated improved fit when CL_TM values calculated by AUC were used (adjusted R² 0.87 vs. 0.52), and therefore, these values were used to generate optimal dosing recommendations. Linear regression revealed significant effects of filter type and flow rate on CL_TM by AUC, suggesting doses of 2.5–7.5 mg twice daily (BID) may be needed for flow rates ranging from 0.5–5 L/h, respectively.

Conclusion

For CRRT flow rates most commonly employed in clinical practice, the standard labeled 5 mg BID dose of apixaban is predicted to achieve target systemic exposure thresholds. The safety and efficacy of these proposed dosing regimens warrants further investigation in clinical studies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-021-02248-7.

Polymyxins interaction to the human serum albumin: A thermodynamic and computational study

Polymyxin B and E (colistin), are a group of cationic charged cyclic antibiotic lipopeptides that are frequently used in the clinics to treat infections caused by the multidrug-resistant gram-negative bacteria. Since the interactions with the blood plasma drug-transport proteins may play a critical role in determining their pharmacological and pharmacokinetic profiles, we studied the binding properties of polymyxins to the human serum albumin (HSA) under simulated physiological conditions by the combination of biophysical approaches, such as isothermal titration calorimetry (ITC), fluorescence anisotropy, circular dichroism (CD) buttressed by computational studies. The HSA binding to the polymyxins was relatively strong (K_a ≈ 1.0 × 10⁷ M^-1). Molecular docking indicated that polymyxins bind to the cleft of HSA between domains I and III via the electrostatic interactions. This evidence was further confirmed by the entropy-driven interaction for the polymyxins bound HSA. Far UV-CD experiments showed that the secondary structure of HSA doesn't alter and its stable structure is preserved. Collectively, these investigations revealed that the polymyxins bind preferentially to the partially unfolded intermediate forms of the protein structure; however, HSA molecule does not undergo any significant conformational changes upon binding. This is promising as it may limit the unfavorable side effects of the medicine. On the whole, the results provide quantitative and qualitative insight of the binding interaction between HSA and polymyxins, which is important in understanding their effect as therapeutic agents.

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.

High-volume hemofiltration in adult burn patients with septic shock and acute kidney injury: a multicenter randomized controlled trial

BACKGROUND

Sepsis and septic shock occur commonly in severe burns. Acute kidney injury (AKI) is also common and often results as a consequence of sepsis. Mortality is unacceptably high in burn patients who develop AKI requiring renal replacement therapy and is presumed to be even higher when combined with septic shock. We hypothesized that high-volume hemofiltration (HVHF) as a blood purification technique would be beneficial in this population.

METHODS

We conducted a multicenter, prospective, randomized, controlled clinical trial to evaluate the impact of HVHF on the hemodynamic profile of burn patients with septic shock and AKI involving seven burn centers in the United States. Subjects randomized to the HVHF were prescribed a dose of 70 ml/kg/hour for 48 hours while control subjects were managed in standard fashion in accordance with local practices.

RESULTS

During a 4-year period, a total of nine subjects were enrolled for the intervention during the ramp-in phase and 28 subjects were randomized, 14 each into the control and HVHF arms respectively. The study was terminated due to slow enrollment. Ramp-in subjects were included along with those randomized in the final analysis. Our primary endpoint, the vasopressor dependency index, decreased significantly at 48 hours compared to baseline in the HVHF group (p = 0.007) while it remained no different in the control arm. At 14 days, the multiple organ dysfunction syndrome score decreased significantly in the HVHF group when compared to the day of treatment initiation (p = 0.02). No changes in inflammatory markers were detected during the 48-hour intervention period. No significant difference in survival was detected. No differences in adverse events were noted between the groups.

CONCLUSIONS

HVHF was effective in reversing shock and improving organ function in burn patients with septic shock and AKI, and appears safe. Whether reversal of shock in these patients can improve survival is yet to be determined.

TRIAL REGISTRATION

Clinicaltrials.gov NCT01213914 . Registered 30 September 2010.

Outcome analysis of colistin-treated burn center patients

OBJECTIVES

Intravenous colistimethate sodium (CMS) use in burn center patients is increasing due to the emergence of multidrug-resistant gram-negative bacteria. However, optimal dosing strategies and factors that may contribute to treatment failure are limited. The purpose of this study was to determine factors that may contribute to treatment failure in colistin-treated burn center patients.

METHODS

This retrospective, observational study included burn center patients that received ≥48h of intravenous CMS between June 1, 2009 and June 30, 2014. Data was collected utilizing the institution's electronic medical record system. Statistical analysis included demographic, univariable, and multivariable analysis to determine factors that may predict clinical failure of burn center patients requiring intravenous CMS.

RESULTS

Eighty-one patients were included in this study, with 55 patients (68%) achieving clinical success. A total daily dose (TDD) of >5mg/kg ideal body weight (IBW) was associated with significantly less clinical failure (odds ratio=0.21; 95% CI, 0.05, 0.91). Additionally, clinical failure was significantly higher in patients with wounds as the primary source of infection, creatinine clearances of 91-120mL/min, and those receiving renal replacement therapy. No difference was observed in nephrotoxicity when comparing TDD >5mg/kg IBW and TDD ≤5mg/kg IBW.

CONCLUSIONS

Clinical success was significantly higher with larger intravenous CMS doses in burn center patients. Higher CMS doses were not found to be associated with increased nephrotoxicity within this patient group.

Unveiling the Synergistic Interaction Between Liposomal Amphotericin B and Colistin

Patients with multiple comorbidities are often administered simultaneously or sequentially antifungals and antibacterial agents, without full knowledge of the consequences of drug interactions. Considering the clinical relevance of liposomal amphotericin B (L-AMB), the association between L-AMB and six antibacterial agents was evaluated against four clinical isolates and one type strain of Candida spp. and two clinical isolates and one type strain of Aspergillus fumigatus. In order to evaluate such combined effects, the minimal inhibitory concentration (MIC) of L-AMB was determined in the presence of 0.5-, 1-, 2-, and 4-fold peak plasma concentrations of each of the antibacterial drugs. Since the L-AMB/colistin (CST) association was the most synergic, viability assays were performed and the physiological status induced by this association was characterized. In addition, computational molecular dynamics studies were also performed in order to clarify the molecular interaction. The maximum synergistic effect with all antibacterial agents, except CST, was reached at fourfold the usual peak plasma concentrations, resulting in 2-to 8-fold L-AMB MIC reduction for Candida and 2-to 16-fold for Aspergillus. For CST, the greatest synergism was registered at peak plasma concentration (3 mg/L), with 4-to 8-fold L-AMB MIC reduction for Candida and 16-to 32-fold for Aspergillus. L-AMB at subinhibitory concentration (0.125 mg/L) combined with CST 3 mg/L resulted in: a decrease of fungal cell viability; an increase of cell membrane permeability; an increase of cellular metabolic activity soon after 1 h of exposure, which decreased until 24 h; and an increase of ROS production up to 24 h. From the molecular dynamics studies, AMB and CST molecules shown a propensity to form a stable molecular complex in solution, conferring a recognition and binding added value for membrane intercalation. Our results demonstrate that CST interacts synergistically with L-AMB, forming a stable complex, which promotes the fungicidal activity of L-AMB at low concentration.

Intravenous Antibiotic and Antifungal Agent Pharmacokinetic-Pharmacodynamic Dosing in Adults with Severe Burn Injury

PURPOSE

Despite advances in the care of patients with severe burn injury, infection-related morbidity and mortality remain high and can potentially be reduced with antimicrobial dosing optimized for the infecting pathogen. However, anti-infective dose selection is difficult because of the highly abnormal physiologic features of burn patients, which can greatly affect the pharmacokinetic (PK) disposition of these agents. We review published PK data from burn patients and offer evidence-based dosing recommendations for antimicrobial agents in burn-injured patients.

METHODS

Because most infections occur at least 48 hours after initial burn injury and anti-infective therapy often lasts ≥10 days, we reviewed published data informing PK-pharmacodynamic (PD) dosing of anti-infectives administered during the second, hypermetabolic stage of burn injury, in those with >20% total body surface area burns, and in those with normal or augmented renal clearance (estimated creatinine clearance ≥130 mL/min). Analyses were performed using 10,000-patient Monte Carlo simulations, which uses PK variability observed in burn patients and MIC data to determine the probability of reaching predefined PK-PD targets. The probability of target attainment, defined as the likelihood that an anti-infective dosing regimen would achieve a specific PK-PD target at the single highest susceptible MIC, and the cumulative fraction of response, defined as the population probability of target attainment given a specific dose and a distribution of MICs, were calculated for each recommended anti-infective dosing regimen.

FINDINGS

Evidence-based doses were derived for burn-injured patients for 15 antibiotics and 2 antifungal agents. Published data were unavailable or insufficient for several agents important to the care of burn patients, including newer antifungal and antipseudomonal agents. Furthermore, available data suggest that antimicrobial PK properties in burned patients is highly variable. We recommend that, where possible, therapeutic drug monitoring be performed to optimize PK-PD parameter achievement in individual patients.

IMPLICATIONS

Given the high variability in PK disposition observed in burn patients, doses recommended in the package insert may not achieve PK-PD parameters associated with optimal infectious outcomes. Our study is limited by the necessity for fixed assumptions in depicting this highly variable patient population. New rapid-turnaround analytical technology is needed to expand the menu of antimicrobial agents for which therapeutic drug monitoring is available to guide dose modification within a clinically actionable time frame.

Colistin Use in Patients With Reduced Kidney Function

Colistin (polymyxin E) is a mainly concentration-dependent bactericidal antimicrobial active against multidrug-resistant Gram-negative bacteria. After being abandoned over the past 30 years due to its neuro- and nephrotoxicity, colistin has been reintroduced recently as a last-resort drug for the treatment of multidrug-resistant Gram-negative bacteria infections in combination with other antimicrobials. Unfortunately, although renal toxicity is a well-known dose-related adverse effect of colistin, relatively few studies are currently available on its peculiar pharmacodynamic/pharmacokinetic properties in clinical settings at high risk for drug accumulation, such as acute or chronic kidney disease. In these specific contexts, the risk for underdosing is also substantial because colistin can be easily removed by dialysis/hemofiltration, especially when the most efficient modalities of renal replacement therapy (RRT) are used in critically ill patients. For this reason, recent recommendations in patients undergoing RRT have shifted toward higher dosing regimens, and therapeutic drug monitoring is advised. This review aims to summarize the main issues related to chemical structure, pharmacodynamics/pharmacokinetics, and renal toxicity of colistin. Moreover, recent data and current recommendations concerning colistin dosing in patients with reduced kidney function, with special regard to those receiving RRT such as dialysis or hemofiltration, are also discussed.

Polymyxin B versus colistin: an update

Polymyxin B and colistin (polymyxin E) are polypeptide antibiotics that were developed in the 1940s, but fell into disfavor due to their high toxicity rates. These two antibiotics were previously regarded to be largely equivalent, due to similarities in their chemical structure and spectrum of activity. In recent years, several pertinent differences, especially in terms of potency and disposition, have been revealed between polymyxin B and colistin. These differences are mainly attributed to the fact that polymyxin B is administered parenterally in its active form, while colistin is administered parenterally as an inactive pro-drug, colistimethate. In this review, we summarize the similarities and differences between polymyxin B and colistin. We also discuss the potential clinical implications of these findings, and provide our perspectives on how polymyxins should be employed to preserve their utility in this era of multi-drug resistance.

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).