New colistin population pharmacokinetic data in critically ill patients suggesting an alternative loading dose rationale

Model-Informed Rationale for Early Therapeutic Drug Monitoring of Colistin in Critically Ill Patients

Adequate colistin exposure is important for microbiological clearance. This study was performed in critically ill patients >18 years old to develop a simplified nonparametric pharmacokinetic (PK) model of colistin for routine clinical use and to determine the role of dose optimization. The Non-Parametric Adaptive Grid algorithm within the Pmetrics software package for R was used to develop a PK model from 47 patients, and external validation of the final model was performed in 13 patients. A 1-compartment multiplicative gamma error model with 0-order input and first-order elimination of colistin was developed with creatinine clearance and serum albumin as covariates on elimination rate constant. An R² for observed vs individual predicted colistin concentrations of 0.92 was obtained in the validation cohort. High interindividual variability in colistin steady-state area under the plasma concentration-time curve (AUC) from from 120 hours to 144 hours (coefficient of variation = 80.1%) and a high interoccasion variability (median coefficient of variation of AUC from time 0 to hours predicted every 8 hours for initial 96 hours after starting colistin = 23.8) was predicted in patients who received this antibiotic for a period of over 152 hours (n = 22). With the model-suggested dose regimen, only 20% of simulated profiles achieved AUC from time 0 to 24 hours in the range of 50 to 60 mg • h/L due to high variability in population PK. In this group of patients, steady-state colistin concentrations were predicted to be achieved >96 hours after initiation of colistimethate sodium. This study advocates the need for early and repeated therapeutic drug monitoring and dose optimization in critically ill patients to achieve adequate therapeutic concentration of colistin.

Next-Generation Polymyxin Class of Antibiotics: A Ray of Hope Illuminating a Dark Road

Although new-generation antimicrobials, in particular β-lactam/β-lactamase inhibitors, have largely replaced polymyxins in carbapenem-resistant Gram-negative bacterial infections, polymyxins are still needed for carbapanem-resistant Acinetobacter baumannii infections and in settings where novel agents are not readily available. Despite their potent in vitro activity, the clinical utility of polymyxins is significantly limited by their pharmacokinetic properties and nephrotoxicity risk. There is significant interest, therefore, in developing next-generation polymyxins with activity against colistin-resistant strains and lower toxicity than existing polymyxins. In this review, we aim to present the antibacterial activity mechanisms, in vitro and in vivo efficacy data, and toxicity profiles of new-generation polymyxins, including SPR206, MRX-8, and QPX9003, as well as the general characteristics of old polymyxins. Considering the emergence of colistin-resistant strains particularly in endemic regions, the restoration of the antimicrobial activity of polymyxins via PBT2 is also described in this review.

Prevalence of polymyxin-induced nephrotoxicity and its predictors in critically ill adult patients: A meta-analysis

BACKGROUND

Polymyxin-induced nephrotoxicity is a major safety concern in clinical practice due to long-term adverse outcomes and high mortality.

AIM

To conducted a systematic review and meta-analysis of the prevalence and potential predictors of polymyxin-induced nephrotoxicity in adult intensive care unit (ICU) patients.

METHODS

PubMed, EMBASE, the Cochrane Library and Reference Citation Analysis database were searched for relevant studies from inception through May 30, 2022. The pooled prevalence of polymyxin-induced nephrotoxicity and pooled risk ratios of associated factors were analysed using a random-effects or fixed-effects model by Stata SE ver. 12.1. Additionally, subgroup analyses and meta-regression were conducted to assess heterogeneity.

RESULTS

A total of 89 studies involving 12234 critically ill adult patients were included in the meta-analysis. The overall pooled incidence of polymyxin-induced nephrotoxicity was 34.8%. The pooled prevalence of colistin-induced nephrotoxicity was not higher than that of polymyxin B (PMB)-induced nephrotoxicity. The subgroup analyses showed that nephrotoxicity was significantly associated with dosing interval, nephrotoxicity criteria, age, publication year, study quality and sample size, which were confirmed in the univariable meta-regression analysis. Nephrotoxicity was significantly increased when the total daily dose was divided into 2 doses but not 3 or 4 doses. Furthermore, older age, the presence of sepsis or septic shock, hypoalbuminemia, and concomitant vancomycin or vasopressor use were independent risk factors for polymyxin-induced nephrotoxicity, while an elevated baseline glomerular filtration rate was a protective factor against colistin-induced nephrotoxicity.

CONCLUSION

Our findings indicated that the incidence of polymyxin-induced nephrotoxicity among ICU patients was high. It emphasizes the importance of additional efforts to manage ICU patients receiving polymyxins to decrease the risk of adverse outcomes.

The Role of Colistin in the Era of New β-Lactam/β-Lactamase Inhibitor Combinations

With the current crisis related to the emergence of carbapenem-resistant Gram-negative bacteria (CR-GNB), classical treatment approaches with so-called “old-fashion antibiotics” are generally unsatisfactory. Newly approved β-lactam/β-lactamase inhibitors (BLBLIs) should be considered as the first-line treatment options for carbapenem-resistant Enterobacterales (CRE) and carbapenem-resistant Pseudomonas aeruginosa (CRPA) infections. However, colistin can be prescribed for uncomplicated lower urinary tract infections caused by CR-GNB by relying on its pharmacokinetic and pharmacodynamic properties. Similarly, colistin can still be regarded as an alternative therapy for infections caused by carbapenem-resistant Acinetobacter baumannii (CRAB) until new and effective agents are approved. Using colistin in combination regimens (i.e., including at least two in vitro active agents) can be considered in CRAB infections, and CRE infections with high risk of mortality. In conclusion, new BLBLIs have largely replaced colistin for the treatment of CR-GNB infections. Nevertheless, colistin may be needed for the treatment of CRAB infections and in the setting where the new BLBLIs are currently unavailable. In addition, with the advent of rapid diagnostic methods and novel antimicrobials, the application of personalized medicine has gained significant importance in the treatment of CRE infections.

Clinical Efficacy and Nephrotoxicity of the Loading Dose Colistin for the Treatment of Carbapenem-Resistant Acinetobacter baumannii in Critically Ill Patients

Carbapenem-resistant Acinetobacter baumannii (CRAB) is one of the most common causes of nosocomial infections in critically ill patients. Colistin methanesulfonate (CMS), an inactive prodrug, has been considered as a last-resort treatment for CRAB infection in critically ill patients. The objective of this study was to assess 30-day survival and nephrotoxicity in critically ill patients who received non-loading dose (LD) versus LD of CMS for CRAB infection treatment. Between 2012 and 2017, this retrospective cohort analysis was performed at Chiang Mai University Hospital (CMUH), focusing on critically ill patients with CRAB infection who received either non-LD or LD of CMS. A total of 383 patients met the criteria for inclusion. At the 30th day of treatment, the survival rate of patients in the LD CMS group was 1.70 times (adjusted HR) of those in the non-LD group (95% CI = 1.17-2.50, p = 0.006). Clinical response was significantly higher in the LD CMS group than non-LD CMS group (aHR, 1.35, 95% CI, 1.01-1.82, p = 0.046). In addition, a microbiological response-eradication of pre-treatment isolated pathogens in post-treatment cultures-in patients with LD CMS was 1.57 times that of patients with non-LD CMS (95% CI, 1.15-2.15, p = 0.004). Additionally, there was a significant difference in nephrotoxicity between LD CMS and non-LD CMS (aHR, 1.57, 95% CI, 1.14-2.17, p = 0.006). Based on these results, LD CMS should be used to increase the opportunity of patients to achieve favourable outcomes. However, LD CMS was found associated with an increase in nephrotoxicity, so renal function should be closely monitored when LD colistin was administered.

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.

Colistin induced acute kidney injury in critically ill children: a prospective study utilizing RIFLE criteria

BACKGROUND

Colistin is one of the last resort antibiotic options for resistant gram-negative pathogens. Renal injury is the most common side effect of colistin. Characteristics of nephrotoxicity are well described in adults. However, this data is sparse in children.

OBJECTIVES

In this study we evaluated the incidence, severity, time course and risk factors of colistin nephrotoxicity in a pediatric population.

METHODS

In a prospective study over a 9-month period, children who received intravenous colistin for at least 48 h were evaluated for renal side effect by utilizing Risk-Injury-Failure-Loss-End Stage Kidney Disease (RIFLE) criteria. Children receiving renal replacement therapy (RRT) or received a repeated course of colistin were excluded.

RESULTS

Thirty-seven children were included. Median age of participants was 4.5 months. Overall, 48.6% of the cases developed AKI and consisted 56% in the Risk, 33% in the Injury and 11% in the Failure categories of RIFLE criteria. AKI was reversible while colistin continued and no one required RRT. Mean ± SD time to AKI development was 10.94 ± 7.51 days. Multivariate logistic regression analysis demonstrated that total cumulative dose of colistin was an independent predictor of nephrotoxicity (standardized ß = 1.024, P = 0.034).

CONCLUSION

AKI is a common side effect of colistin therapy in critically ill children developing in nearly half of recipients. However, with the dosage range utilized in this study, in the majority of children, renal injury seemed to be mild to moderate in nature. Given the limited treatment options available in critically ill children with resistant gram-negative pathogens, colistin remains a marvelous therapeutic option. Further studies are required to fully elucidate the risk factors and clinical pictures of colistin-induced nephrotoxicity.

Activity of the combination of colistin and fosfomycin against NDM-1-producing Escherichia coli with variable levels of susceptibility to colistin and fosfomycin in a murine model of peritonitis

BACKGROUND

Alternative treatments are needed against NDM-1-producing Escherichia coli. Colistin (COL) and fosfomycin (FOS) often remain active in vitro but selection of resistant mutants is frequent if used separately. We determined whether the combination of colistin and fosfomycin may be useful to treat infections with NDM-1-producing E. coli with varying levels of resistance.

METHODS

Isogenic derivatives of E. coli CFT073 with blaNDM-1 and variable levels of resistance to colistin and fosfomycin (CFT073-NDM1, CFT073-NDM1-COL and CFT073-NDM1-FOS, respectively) were used. The combination (colistin + fosfomycin) was tested in vitro and in a fatal peritonitis murine model. Mortality and bacterial loads were determined and resistant mutants detected.

RESULTS

Colistin MICs were 0.5, 16 and 0.5 mg/L and fosfomycin MICs were 1, 1 and 32 mg/L against CFT073-NDM1, CFT073-NDM1-COL and CFT073-NDM1-FOS, respectively. In time-kill curves, combining colistin with fosfomycin was synergistic and bactericidal against CFT073-NDM1 and CFT073-NDM1-FOS, with concentrations of 4× MIC (for both drugs), but not against CFT073-NDM1-COL (concentrations of colistin = 0.5× MIC), due to regrowth with fosfomycin-resistant mutants. Mice died less and bacterial counts were lower in spleen with the combination compared with monotherapy against all strains; the combination prevented selection of resistant mutants except for CFT073-NDM1-COL where fosfomycin-resistant mutants were found in all mice.

CONCLUSIONS

Combining colistin and fosfomycin was beneficial in vitro and in vivo against NDM-1-producing E. coli, even with strains less susceptible to colistin and fosfomycin. However, the combination failed to prevent the emergence of fosfomycin-resistant mutants against colistin-resistant strains. Combining colistin and fosfomycin constitutes an alternative for treatment of NDM-1 E. coli, except against colistin-resistant strains.

Population Pharmacokinetics of Colistin Methanesulfonate Sodium and Colistin in Critically Ill Patients: A Systematic Review

Understanding the pharmacokinetics parameter of colistin methanesulfonate sodium (CMS) and colistin is needed to optimize the dosage regimen in critically ill patients. However, there is a scarcity of pharmacokinetics parameters in this population. This review provides a comprehensive understanding of CMS and colistin pharmacokinetics parameters in this population. The relevant studies published in English that reported on the pharmacokinetics of CMS and colistin from 2000 until 2020 were systematically searched using the PubMed and Scopus electronic databases. Reference lists of articles were reviewed to identify additional studies. A total of 252 citation titles were identified, of which 101 potentially relevant abstracts were screened, and 25 full-text articles were selected for detailed analysis. Of those, 15 studies were included for the review. This review has demonstrated vast inter-study discrepancies in colistin plasma concentration and the pharmacokinetics parameter estimates. The discrepancies might be due to complex pathophysiological changes in the population studied, differences in CMS brand used, methodology, and study protocol. Application of loading dose of CMS and an additional dose of CMS after dialysis session was recommended by some studies. In view of inter-patient and intra-patient variability in colistin plasma concentration and pharmacokinetics parameters, personalized colistin dosing for this population is recommended.

Development of novel immunoprophylactic agents against multidrug resistant Gram-negative bacterial infections

The widespread emergence of antibiotic resistance including multidrug resistance in Gram negative (G-) bacterial pathogens poses a critical challenge to the current antimicrobial armamentarium. Antibody-drug conjugates (ADCs), primarily used in anti-cancer therapy, offer a promising treatment alternative due to their ability to deliver a therapeutic molecule while simultaneously activating the host immune response. The Cloudbreak® platform is being used to develop ADCs to treat infectious diseases, composed of a therapeutic targeting moiety (TM) attached via a non-cleavable linker to an effector moiety (EM) to treat infectious diseases. In this proof-of-concept study, 21 novel dimeric peptidic molecules (TMs) were evaluated for activity against a screening panel of G- pathogens. The activity of the TMs were not impacted by existing drug resistance. Potent TMs were conjugated to the Fc fragment of human IgG1 (EM) resulting in 4 novel ADCs. These ADCs were evaluated for immunoprophylactic efficacy in a neutropenic mouse model of deep thigh infection. In colistin-sensitive infections, 3 of the 4 ADCs offered similar protection as therapeutically dosed colistin while CTC-171 offered enhanced protection. The efficacy of these ADCs was unchanged in colistin-resistant infections. Together, these results indicate that the ADCs used here are capable of potent binding to G- pathogens regardless of LPS modifications that otherwise lead to antibiotic resistance and support further exploration of ADCs in the treatment of drug resistant G- bacterial infections.

Dose recommendations for intravenous colistin in pediatric patients from a prospective, multicenter, population pharmacokinetic study

OBJECTIVES

The aim of this study was to describe the population pharmacokinetics of intravenous colistin use in children and to propose optimal dosage regimens.

METHODS

A prospective, multicenter, population pharmacokinetic (PPK) study was conducted. Phoenix 64 version 8.3 was used for the PPK analysis. Simulations were performed to estimate the probability of target attainment for patients achieving target plasma colistin average steady-state concentrations (C_ss,avg).

RESULTS

A total of 334 plasma colistin concentrations were obtained from 79 pediatric patients with a median age (interquartile range) of 2.6 years (0.8-6.8 years); 73 (92.4%) were admitted to intensive care units. Colistin pharmacokinetics were adequately described by a one-compartment model with first-order elimination along with serum creatinine (SCr) as a significant covariate in colistin clearance. The simulation demonstrated that the recommended dose of 5 mg of colistin base activity (CBA)/kg/day resulted in 18.2-63.0% probability of achieving a target C_ss,avg of 2 mg/l. With a lower targeted C_ss,avg of 1 mg/l, colistin dosing with 7.5 mg and 5 mg of CBA/kg/day were adequate for children with SCr levels of 0.1-0.3 mg/dl and >0.3 mg/dl, respectively.

CONCLUSIONS

SCr is a significant covariate in colistin clearance in children. Colistin dosing should be selected according to the patient's SCr level and the desired target C_ss,avg.

Optimal control for colistin dosage selection

Optimization of antibiotic administration helps minimizing cases of bacterial resistance. Dosages are often selected by trial and error using a pharmacokinetic (PK) model. However, this is limited to the range of tested dosages, restraining possible treatment choices, especially for the loading doses. Colistin is a last-resort antibiotic with a narrow therapeutic window; therefore, its administration should avoid subtherapeutic or toxic concentrations. This study formulates an optimal control problem for dosage selection of colistin based on a PK model, minimizing deviations of colistin concentration to a target value and allowing a specific dosage optimization for a given individual. An adjoint model was used to provide the sensitivity of concentration deviations to dose changes. A three-compartment PK model was adopted. The standard deviation between colistin plasma concentrations and a target set at 2 mg/L was minimized for some chosen treatments and sample patients. Significantly lower deviations from the target concentration are obtained for shorter administration intervals (e.g. every 8 h) compared to longer ones (e.g. every 24 h). For patients with normal or altered renal function, the optimal loading dose regimen should be divided into two or more administrations to attain the target concentration quickly, with a high first loading dose followed by much lower ones. This regimen is not easily obtained by trial and error, highlighting advantages of the method. The present method is a refined optimization of antibiotic dosage for the treatment of infections. Results for colistin suggest significant improvement in treatment avoiding subtherapeutic or toxic concentrations.

Population Pharmacokinetics and Outcomes of Critically Ill Pediatric Patients Treated with Intravenous Colistin at Higher Than Recommended Doses

Limited pharmacokinetic (PK) data suggest that currently recommended pediatric dosages of colistimethate sodium (CMS) by the Food and Drug Administration and European Medicines Agency may lead to suboptimal exposure, resulting in plasma colistin concentrations that are frequently <2 mg/liter. We conducted a population PK study in 17 critically ill patients 3 months to 13.75 years (median, 3.3 years) old who received CMS for infections caused by carbapenem-resistant Gram-negative bacteria. CMS was dosed at 200,000 IU/kg/day (6.6 mg colistin base activity [CBA]/kg/day; 6 patients), 300,000 IU/kg/day (9.9 mg CBA/kg/day; 10 patients), and 350,000 IU/kg/day (11.6 mg CBA/kg/day; 1 patient). Plasma colistin concentrations were determined using ultraperformance liquid chromatography combined with electrospray ionization-tandem mass spectrometry. Colistin PK was described by a one-compartment disposition model, including creatinine clearance, body weight, and the presence or absence of systemic inflammatory response syndrome (SIRS) as covariates (P < 0.05 for each). The average colistin plasma steady-state concentration (C_ss,avg) ranged from 1.11 to 8.47 mg/liter (median, 2.92 mg/liter). Ten patients had C_ss,avg of ≥2 mg/liter. The presence of SIRS was associated with decreased apparent clearance of colistin (47.8% of that without SIRS). The relationship between the number of milligrams of CBA per day needed to achieve each 1 mg/liter of plasma colistin C_ss,avg and creatinine clearance (in milliliters per minute) was described by linear regression with different slopes for patients with and without SIRS. Nephrotoxicity, probably unrelated to colistin, was observed in one patient. In conclusion, administration of CMS at the above doses improved exposure and was well tolerated. Apparent clearance of colistin was influenced by creatinine clearance and the presence or absence of SIRS.

Colistin Dosing Regimens against Pseudomonas aeruginosa in Critically Ill Patients: An Application of Monte Carlo Simulation

Our aims are to assess various colistin dosing regimens against Pseudomonas aeruginosa (P. aeruginosa) infection in critically ill patients and to propose an appropriate regimen based on microbiological data. A Monte Carlo simulation was performed using the published colistin’s pharmacokinetic parameters of critically ill patients, the published pharmacodynamic target from a mouse thigh infection model, and the minimum inhibitory concentration (MIC) results from a Vietnamese hospital. The probability of target attainment (PTA) of 80% and cumulative fraction of response (CFR) of 90% were used to evaluate the efficacy of each regimen. Of 121 P. aeruginosa laboratory datasets, the carbapenem-resistant P. aeruginosa (CRPA) and the colistin-resistant P. aeruginosa rates were 29.8% and 0.8%, respectively. MIC_50,90 were both 0.5 mg/L. The simulated results showed that at MIC of 2 mg/L, most regimens could not reach the PTA target, particularly in patients with normal renal function (Creatinine clearance (CrCl) ≥ 80 mL/min). At MIC of 0.5 mg/L and 1 mg/L, current recommendations still worked well. On the basis of these results, aside from lung infection, our study recommends three regimens against P. aeruginosa infection at MIC of 0.5 mg/L, 1 mg/L, and 2 mg/L. In conclusion, higher total daily doses and fractionated colistin dosing regimens could be the strategy for difficult-to-acquire PTA cases, while a less aggressive dose might be appropriate for empirical treatment in settings with low MIC_50/90.

Intravenous colistin for the management of multidrug-resistant bacterial infections in Indian patients

Multidrug-resistant Gram-negative bacterial infection is a serious global concern and especially in low and middle-income countries (LMIC) such as India. Colistin, an antimicrobial once abandoned following reports of organ toxicity, has re-emerged as an essential therapeutic agent in the management of these infections. A retrospective review of 162 inpatients was done, focusing on culture-proven multidrug-resistant infections requiring colistin. The overall clinical outcome in 58% of patients was found to be good, with nephrotoxicity and neurotoxicity occurring only in 8 (5%) and 4 (2.5%) patients, respectively. Multivariate analysis revealed an elevated lactate and raised urea to be independent factors associated with poor clinical response. In conclusion, there appears to be strong evidence supporting the use of colistin in the management of multidrug-resistant Gram-negative bacterial infections.

Systematic review on estimated rates of nephrotoxicity and neurotoxicity in patients treated with polymyxins

BACKGROUND

Nephrotoxicity and neurotoxicity are commonly associated with polymyxin treatment; however, the emergence of multidrug-resistant Gram-negative bacteria with limited therapeutic options has resulted in increased use of polymyxins.

OBJECTIVES

To determine the rates of nephrotoxicity and neurotoxicity during polymyxin treatment and whether any factors influence these.

DATA SOURCES

Medline, Embase and Cochrane Library databases were searched on 2 January 2020.

STUDY ELIGIBILITY CRITERIA

Studies reporting nephrotoxicity and/or neurotoxicity rates in patients with infections treated with polymyxins were included. Reviews, meta-analyses and reports not in English were excluded.

PARTICIPANTS

Patients hospitalized with infections treated with systemic or inhaled polymyxins were included. For comparative analyses, patients treated with non-polymyxin-based regimens were also included.

METHODS

Meta-analyses were performed using a random-effects model; subgroup meta-analyses were conducted where data permitted using a mixed-effects model.

RESULTS

In total, 237 reports of randomized controlled trials, cohort and case-control studies were eligible for inclusion; most were single-arm observational studies. Nephrotoxic events in 35,569 patients receiving polymyxins were analysed. Overall nephrotoxicity rate was 0.282 (95% confidence interval (CI) 0.259-0.307). When excluding studies where >50% of patients received inhaled-only polymyxin treatment or nephrotoxicity assessment was by methods other than internationally recognized criteria (RIFLE, KDIGO or AKIN), the nephrotoxicity rate was 0.391 (95% CI 0.364-0.419). The odds of nephrotoxicity were greater with polymyxin therapies compared to non-polymyxin-based regimens (odds ratio 2.23 (95% CI 1.58-3.15); p < 0.001). Meta-analyses showed a significant effect of polymyxin type, dose, patient age, number of concomitant nephrotoxins and use of diuretics, glycopeptides or vasopressors on the rate of nephrotoxicity. Polymyxin therapies were not associated with a significantly different rate of neurotoxicity than non-polymyxin-based regimens (p 0.051). The overall rate of neurotoxicity during polymyxin therapy was 0.030 (95% CI 0.020-0.043).

CONCLUSIONS

Polymyxins are associated with a higher risk of nephrotoxicity than non-polymyxin-based regimens.

ColistinDose, a Mobile App for Determining Intravenous Dosage Regimens of Colistimethate in Critically Ill Adult Patients: Clinician-Centered Design and Development Study

Background

Determining a suitable dose of intravenous colistimethate is challenging because of complicated pharmacokinetics, confusing terminology, and the potential for renal toxicity. Only recently have reliable pharmacokinetic/pharmacodynamic data and dosing recommendations for intravenous colistimethate become available.

Objective

The aim of this work was to develop a clinician-friendly, easy-to-use mobile app incorporating up-to-date dosing recommendations for intravenous colistimethate in critically ill adult patients.

Methods

Swift programming language and common libraries were used for the development of an app, ColistinDose, on the iPhone operating system (iOS; Apple Inc). The compatibility among different iOS versions and mobile devices was validated. Dosing calculations were based on equations developed in our recent population pharmacokinetic study. Recommended doses generated by the app were validated by comparison against doses calculated manually using the appropriate equations.

Results

ColistinDose provides 3 major functionalities, namely (1) calculation of a loading dose, (2) calculation of a daily dose based on the renal function of the patient (including differing types of renal replacement therapies), and (3) retrieval of historical calculation results. It is freely available at the Apple App Store for iOS (version 9 and above). Calculated doses accurately reflected doses recommended in patients with varying degrees of renal function based on the published equations. ColistinDose performs calculations on a local mobile device (iPhone or iPad) without the need for an internet connection.

Conclusions

With its user-friendly interface, ColistinDose provides an accurate and easy-to-use tool for clinicians to calculate dosage regimens of intravenous colistimethate in critically ill patients with varying degrees of renal function. It has significant potential to avoid the prescribing errors and patient safety issues that currently confound the clinical use of colistimethate, thereby optimizing patient treatment.

Polymyxin-induced nephrotoxicity and its predictors: a systematic review and meta-analysis of studies conducted using RIFLE criteria of acute kidney injury

Polymyxins are last-resort antibiotics re-emerged to treat infections caused by multidrug resistant (MDR) and extensively drug-resistant (XDR) Gram-negative bacterial infections. However, polymyxin-associated nephrotoxicity has become the main safety concern. Therefore, we conducted this systematic review and meta-analysis on polymyxin-induced nephrotoxicity and its predictors using studies conducted based on the validated RIFLE (Risk, Injury, Failure, Loss of Function and End-stage renal disease) criteria of acute kidney damage. Literature search was carried out through visiting legitimate databases and indexing services including PubMed, MEDLINE (Ovid®), EMBASE (Ovid®), and Scopus to retrieve relevant studies. Following screening and eligibility evaluation, relevant data were extracted from included studies and analyzed using STATA 15.0 and Rev-Man 5.3. Inverse variance method with random effects pooling model was used for the analysis of outcome measures at 95% confidence interval. Besides, meta-regression, meta-influence, and publication bias analyses were conducted. A total of 48 studies involving 6,199 adult patients aged ≥ 18 years were included for systematic review and meta-analysis. The pooled incidence of polymyxin-induced nephrotoxicity was found to be 45% (95% CI: 41- 49%; I² = 92.52%). Stratifying with RIFLE severity scales, pooled estimates of polymyxin-treated patients identified as 'risk', 'injury' and 'failure' were 17% (95% CI: 14-20%), 13% (95% CI: 11-15%), and 10% (95% CI: 9-11%), respectively. Besides, the pooled incidence of colistin-induced nephrotoxicity was about 48% (95% CI: 42-54%), whereas that of polymyxin B was 38% (95% CI: 32-44%). Likewise, colistin had 37% increased risk of developing nephrotoxicity compared to the polymyxin B treated cohorts (RR = 1.37, 95% CI: 1.13-1.67; I² = 57%). Older age (AOR = 1.03, 95% CI: 1.01-1.05), daily dose (AOR = 1.46, 95% CI: 1.09-1.96), underlying diabetes mellitus (AOR = 1.81, 95% CI: 1.25-2.63), and concomitant nephrotoxic drugs (AOR = 2.31, 95% CI: 1.79-3.00) were independent risk factors for polymyxin-induced nephrotoxicity. Patients with high serum albumin level were less likely (AOR = 0.69, 95% CI: 0.56-0.85] to experience nephrotoxicity compared to those with low albumin level. Despite the resurgence of these antibiotics for the chemotherapy of MDR/XDR-Gram-negative superbugs, the high incidence of nephrotoxicity has become a contemporary clinical concern. Being elderly, high daily dose, having underlying diseases such as diabetes, and use of concomitant nephrotoxic drugs were independent predictors of nephrotoxicity. Therefore, therapeutic drug monitoring should be done to these patients to outweigh the potential benefits of polymyxin therapy from its risk.

Agents of Last Resort: An Update on Polymyxin Resistance

Polymyxin resistance is a major public health threat, because the polymyxins represent last-line therapeutics for gram-negative pathogens resistant to essentially all other antibiotics. Minimizing any potential emergence and dissemination of polymyxin resistance relies on an improved understanding of mechanisms of and risk factors for polymyxin resistance, infection prevention and stewardship strategies, together with optimization of dosing of polymyxins (eg, combination regimens).

The Pitt Bacteremia Score Predicts Mortality in Nonbacteremic Infections

BACKGROUND

Predicting mortality risk in patients is important in research settings. The Pitt bacteremia score (PBS) is commonly used as a predictor of early mortality risk in patients with bloodstream infections (BSIs). We determined whether the PBS predicts 14-day inpatient mortality in nonbacteremia carbapenem-resistant Enterobacteriaceae (CRE) infections.

METHODS

Patients were selected from the Consortium on Resistance Against Carbapenems in Klebsiella and Other Enterobacteriaceae, a prospective, multicenter, observational study. We estimated risk ratios to analyze the predictive ability of the PBS overall and each of its components individually. We analyzed each component of the PBS in the prediction of mortality, assessed the appropriate cutoff value for the dichotomized score, and compared the predictive ability of the qPitt score to that of the PBS.

RESULTS

In a cohort of 475 patients with CRE infections, a PBS ≥4 was associated with mortality in patients with nonbacteremia infections (risk ratio [RR], 21.9; 95% confidence interval [CI], 7.0, 68.8) and with BSIs (RR, 6.0; 95% CI, 2.5, 14.4). In multivariable analysis, the hypotension, mechanical ventilation, mental status, and cardiac arrest parameters of the PBS were independent risk factors for 14-day all-cause inpatient mortality. The temperature parameter as originally calculated for the PBS was not independently associated with mortality. However, a temperature <36.0°C vs ≥36°C was independently associated with mortality. A qPitt score ≥2 had similar discrimination as a PBS ≥4 in nonbacteremia infections.

CONCLUSIONS

Here, we validated that the PBS and qPitt score can be used as reliable predictors of mortality in nonbacteremia CRE infections.

Population pharmacokinetics of colistin and the relation to survival in critically ill patients infected with colistin susceptible and carbapenem-resistant bacteria

OBJECTIVES

The aim was to analyse the population pharmacokinetics of colistin and to explore the relationship between colistin exposure and time to death.

METHODS

Patients included in the AIDA randomized controlled trial were treated with colistin for severe infections caused by carbapenem-resistant Gram-negative bacteria. All subjects received a 9 million units (MU) loading dose, followed by a 4.5 MU twice daily maintenance dose, with dose reduction if creatinine clearance (CrCL) < 50 mL/min. Individual colistin exposures were estimated from the developed population pharmacokinetic model and an optimized two-sample per patient sampling design. Time to death was evaluated in a parametric survival analysis.

RESULTS

Out of 406 randomized patients, 349 contributed pharmacokinetic data. The median (90% range) colistin plasma concentration was 0.44 (0.14-1.59) mg/L at 15 minutes after the end of first infusion. In samples drawn 10 hr after a maintenance dose, concentrations were >2 mg/L in 94% (195/208) and 44% (38/87) of patients with CrCL ≤120 mL/min, and >120 mL/min, respectively. Colistin methanesulfonate sodium (CMS) and colistin clearances were strongly dependent on CrCL. High colistin exposure to MIC ratio was associated with increased hazard of death in the multivariate analysis (adjusted hazard ratio (95% CI): 1.07 (1.03-1.12)). Other significant predictors included SOFA score at baseline (HR 1.24 (1.19-1.30) per score increase), age and Acinetobacter or Pseudomonas as index pathogen.

DISCUSSION

The population pharmacokinetic model predicted that >90% of the patients had colistin concentrations >2 mg/L at steady state, but only 66% at 4 hr after start of treatment. High colistin exposure was associated with poor kidney function, and was not related to a prolonged survival.

Extensive Therapeutic Drug Monitoring of Colistin in Critically Ill Patients Reveals Undetected Risks

(1) Background: With the rise of multi-/pan-drug resistant (MDR/PDR) pathogens, the less utilized antibiotic Colistin has made a comeback. Colistin fell out of favor due to its small therapeutic range and high potential for toxicity. Today, it is used again as a last resort substance in treating MDR/PDR pathogens. Although new guidelines with detailed recommendations for Colistin dosing are available, finding the right dose in critically ill patients with renal failure remains difficult. Here, we evaluate the efficiency of the current guidelines' recommendations by using high resolution therapeutic drug monitoring of Colistin. (2) Methods: We analyzed plasma levels of Colistin and its prodrug colisthimethate sodium (CMS) in 779 samples, drawn from eight PDR-infected ICU patients, using a HPLC-MS/MS approach. The impact of renal function on proper Colistin target levels was assessed. (3) Results: CMS levels did not correlate with Colistin levels. Over-/Underdosing occurred regardless of renal function and mode of renal replacement therapy. Colistin elimination half-time appeared to be longer than previously reported. (4) Conclusion: Following dose recommendations from the most current guidelines does not necessarily lead to adequate Colistin plasma levels. Use of Colistin without therapeutic drug monitoring might be unsafe and guideline adherence does not warrant efficient target levels in critically ill patients.

Efficacy and safety of colistin loading dose: a meta-analysis

Objectives

Colistin represents a polypeptide used for the treatment of MDR microorganisms, although the optimal dosing strategy is under investigation. The present meta-analysis aims to determine whether the administration of a colistin loading dose in patients receiving high-dose maintenance regimens changes the rates of treatment success and the risk of nephrotoxicity.

Methods

Medline, Scopus, CENTRAL, Clinicaltrials.gov and Google Scholar were systematically searched from inception to 18 November 2019. Studies were considered eligible if they reported clinical outcomes among patients receiving high-dose colistin therapy with and without the administration of a loading dose. Meta-analysis was performed by fitting a random-effects model.

Results

Eight (three prospective and five retrospective cohort) studies were included, comprising 1115 patients. The administration of a colistin loading dose was associated with significantly higher microbiological [risk ratio (RR) = 1.23, 95% CI = 1.10–1.39] but not clinical (RR = 1.04, 95% CI = 0.87–1.24) success. No significant associations were calculated for nephrotoxicity (RR = 1.31, 95% CI = 0.90–1.91) and mortality (RR = 1.03, 95% CI = 0.82–1.29) risk. The results remained stable after adjustments for small sample size, credibility ceilings, publication bias and risk of bias.

Conclusions

Observational evidence suggests that the administration of a colistin loading dose in patients receiving high maintenance dosage regimens is significantly associated with higher rates of microbiological response, but does not change clinical cure, mortality or nephrotoxicity risk. The dosing regimen that would provide the optimal balance between treatment efficacy and safety needs to be determined by future randomized controlled trials.

Greater optimisation of pharmacokinetic/pharmacodynamic parameters through a loading dose of intravenous colistin in paediatric patients

Use of colistin in children is rising in line with the increase of multidrug-resistant Gram-negative bacteria (MDR-GNB). In adults, a colistin loading dose is recommended to achieve therapeutic concentrations within 12-24 h. Here we aimed to describe the pharmacokinetic (PK) parameters of a loading dose versus a recommended initial dose of intravenous colistimethate sodium (CMS) in paediatric patients. A prospective, open-label, PK study was conducted in paediatric patients (age 2-18 years) with normal renal function. Patients (n = 20) were randomly assigned to receive either a CMS loading dose (LD group) of 4 mg of colistin base activity (CBA)/kg/dose or a standard initial dose (NLD group) of 2.5 mg (12-h interval) or 1.7 mg (8-h interval) of CBA/kg/dose. Serial blood samples were collected. Plasma concentrations of formed colistin were measured by LC-MS/MS. PK parameters were reported. Acute kidney injury (AKI) was monitored by serum creatinine and urine NGAL. The median (interquartile range) age and body weight were 8.5 (3.5-11.3) years and 21.5 (13.5-20.0) kg. The mean (standard deviation) of first-dose PK parameters of the LD group versus the NLD group were: C_max, 6.1 (2.4) vs. 4.1 (1.3) mg/L; AUC_0-t, 26.5 (12.5) vs. 13.5 (3.6) mg/L·h; V_d, 0.7 (0.4) vs. 0.6 (0.3) L/kg; and t_1/2, 2.9 (0.6) vs. 2.6 (0.4) h. No patient developed AKI by serum creatinine criteria. A CMS loading dose is beneficial for improvement of colistin exposure without increased AKI. A higher daily dose of CMS should be considered, especially for MDR-GNB treatment.

International Consensus Guidelines for the Optimal Use of the Polymyxins: Endorsed by the American College of Clinical Pharmacy (ACCP), European Society of Clinical Microbiology and Infectious Diseases (ESCMID), Infectious Diseases Society of America (IDSA), International Society for Anti-infective Pharmacology (ISAP), Society of Critical Care Medicine (SCCM), and Society of Infectious Diseases Pharmacists (SIDP)

The polymyxin antibiotics colistin (polymyxin E) and polymyxin B became available in the 1950s and thus did not undergo contemporary drug development procedures. Their clinical use has recently resurged, assuming an important role as salvage therapy for otherwise untreatable gram-negative infections. Since their reintroduction into the clinic, significant confusion remains due to the existence of several different conventions used to describe doses of the polymyxins, differences in their formulations, outdated product information, and uncertainties about susceptibility testing that has led to lack of clarity on how to optimally utilize and dose colistin and polymyxin B. We report consensus therapeutic guidelines for agent selection and dosing of the polymyxin antibiotics for optimal use in adult patients, as endorsed by the American College of Clinical Pharmacy (ACCP), Infectious Diseases Society of America (IDSA), International Society of Anti-Infective Pharmacology (ISAP), Society for Critical Care Medicine (SCCM), and Society of Infectious Diseases Pharmacists (SIDP). The European Society for Clinical Microbiology and Infectious Diseases (ESCMID) endorses this document as a consensus statement. The overall conclusions in the document are endorsed by the European Committee on Antimicrobial Susceptibility Testing (EUCAST). We established a diverse international expert panel to make therapeutic recommendations regarding the pharmacokinetic and pharmacodynamic properties of the drugs and pharmacokinetic targets, polymyxin agent selection, dosing, dosage adjustment and monitoring of colistin and polymyxin B, use of polymyxin-based combination therapy, intrathecal therapy, inhalation therapy, toxicity, and prevention of renal failure. The treatment guidelines provide the first ever consensus recommendations for colistin and polymyxin B therapy that are intended to guide optimal clinical use.

A Randomized Clinical Trial Evaluating the Efficacy of Colistin Loading Dose in Critically Ill Children

Objective:

Pharmacokinetic and clinical studies recommend applying loading dose of colistin for the treatment of severe infections in the critically ill adults. Pharmacokinetic studies of colistin in children also highlight the need for a loading dose. However, there are no clinical studies evaluating the effectiveness of colistin loading dose in children.

Methods:

In a randomized trial, children with ventilator-associated pneumonia or central line-associated bloodstream infection (CLABSI) for whom colistin was initiated, were enrolled. Patients were randomized into two groups; loading dose and conventional dose treatment arms. In the conventional treatment arm, colistimethate sodium was initiated with maintenance dose. In the loading dose group, colistimethate sodium was commenced with a loading dose of 150,000 international unit/kg, then on the maintenance dose. Both treatment arms also received meropenem as combination therapy. Primary outcomes were overall efficacy, clinical improvement and microbiological cure. Secondary outcomes were colistin-induced nephrotoxicity and development of resistance.

Findings:

Thirty children completed this study. There was a significantly higher overall efficacy in the group received loading dose (42.9 vs. 6.3%, P = 0.031). There weren’t any significant differences in the clinical and microbiological endpoints. In the subgroup of children with CLABSI, results illustrated a trend toward (though statistically nonsignificant) better clinical cure for patients receiving loading dose.

Conclusion:

This preliminary study suggests that colistin loading dose might have some benefits in critically ill children, specifically in children with CLABSI. Further trials are required to elucidate colistin best dosing strategy in critically ill children with severe infections.

An Approach to Measuring Colistin Plasma Levels Regarding the Treatment of Multidrug-Resistant Bacterial Infection

Antimicrobial resistance to antibiotic treatment has significantly increased during recent years, causing this to become a worldwide public health problem. More than 70% of pathogenic bacteria are resistant to at least one of the currently used antibiotics. Polymyxin E (colistin) has recently been used as a “last line” therapy when treating Gram-negative multi-resistant bacteria. However, little is known about these molecules’ pharmacological use as they have been discontinued because of their high toxicity. Recent research has been focused on determining colistimethate sodium’s pharmacokinetic parameters to find the optimal dose for maintaining a suitable benefit–risk balance. This review has thus been aimed at describing the use of colistin on patients infected by multi-drug resistant bacteria and the importance of measuring this drug’s plasma levels in such patients.

Differences in Colistin Administration and Bacterial and Treatment Outcomes in Critically Ill Patients

The desired target steady-state average colistin concentration (C_ss,avg) to balance between therapeutic effectiveness and nephrotoxicity is largely unclear. The objective of this study was to evaluate the effect of the desired target colistin C_ss,avg on the effectiveness and safety of IV colistin therapy in critically ill patients. Overall, 153 critically ill patients (71% males) receiving IV colistin were retrospectively analyzed. The desired target colistin C_ss,avg was estimated based on the daily colistin dose and creatinine clearance of each patient. No significant predictor for clinical cure was identified. However, microbiological outcome was significantly associated with pneumonia compared to bacteremia (odds ratio [OR] 0.092, 95% confidence interval [CI] [0.033-0.251], P < 0.001) and the use of IV colistin loading dose (OR 2.783, 95% CI [1.126-6.880], P = 0.027). Colistin-associated nephrotoxicity was significantly less likely to occur in patients who received inhaled colistin close to the time of IV colistin therapy (OR 0.331, CI [0.119-0.925], P = 0.035). The desired target C_ss,avg of colistin was not associated with treatment outcomes or the risk of nephrotoxicity. Loading dose and inhaled colistin use near the time of IV colistin therapy may be considered to maximize therapeutic effectiveness and minimize the risk of colistin-associated nephrotoxicity, respectively.

Dose Optimization of Colistin Combinations against Carbapenem-Resistant Acinetobacter baumannii from Patients with Hospital-Acquired Pneumonia in China by Using an In Vitro Pharmacokinetic/Pharmacodynamic Model

Colistin-based combination therapy has become an important strategy to combat the carbapenem-resistant Acinetobacter baumannii (CRAB). However, the optimal dosage regimen selection for the combination with maximum efficacy is challenging. Checkerboard assay was employed to evaluate the synergy of colistin in combination with meropenem, rifampin, fosfomycin, and minocycline against nine carbapenem-resistant A. baumannii isolates (MIC of meropenem [MIC_MEM], ≥32 mg/liter) isolated from Chinese hospital-acquired pneumonia (HAP) patients. A static time-kill assay, in vitro dynamic pharmacokinetic/pharmacodynamic (PK/PD) model, and semimechanistic PK/PD modeling were conducted to predict and validate the synergistic effect of the most efficacious combination. Both checkerboard and static time-kill assays demonstrated the superior synergistic effect of the colistin-meropenem combination against all CRAB isolates. In the in vitro PK/PD model, the dosage regimen of 2 g meropenem daily via 3-h infusion combined with steady-state 1 mg/liter colistin effectively suppressed the bacterial growth at 24 h with a 2-log₁₀ decrease, compared with the initial inocula against two CRAB isolates. The semimechanistic PK/PD model predicted that more than 2 mg/liter colistin combined with meropenem (2 g, 3-h infusion) was required to achieve the killing below the limit of detection (<LOD; i.e., 1 log₁₀CFU/ml) at 24 h with an MIC_MEM of ≥32 mg/liter. Colistin combined with meropenem exerted synergistic killing against CRAB even with an MIC_MEM of ≥32 mg/liter and MIC of colistin (MIC_CST) of ≤1 mg/liter. However, it is predicted that a higher concentration of colistin combined with meropenem was crucial to kill bacteria to <LOD. Our study provides important PK/PD information for optimization of the colistin and meropenem combination against CRAB.

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.

Population Pharmacokinetics of Intravenous Colistin in Pediatric Patients: Implications for the Selection of Dosage Regimens

Background

Intravenous colistin is widely used to treat infections in pediatric patients. Unfortunately, there is a paucity of pharmacological information to guide the selection of dosage regimens. The daily dose recommended by the US Food and Drug Administration (FDA) and European Medicines Agency (EMA) is the same body weight–based dose traditionally used in adults. The aim was to increase our understanding of the patient factors that influence the plasma concentration of colistin, and assess the likely appropriateness of the FDA and EMA dosage recommendations.

Methods

There were 5 patients, with a median age of 1.75 (range 0.1–6.25) years, a median weight of 10.7 (2.9–21.5) kg, and a median creatinine clearance of 179 (44–384) mL/min/1.73m2, who received intravenous infusions of colistimethate each 8 hours. The median daily dose was 0.21 (0.20–0.21) million international units/kg, equivalent to 6.8 (6.5–6.9) mg of colistin base activity per kg/day. Plasma concentrations of colistimethate and formed colistin were subjected to population pharmacokinetic modeling to explore the patient factors influencing the concentration of colistin.

Results

The median, average, steady-state plasma concentration of colistin (Css,avg) was 0.88 mg/L; individual values ranged widely (0.41–3.50 mg/L), even though all patients received the same body weight–based daily dose. Although the daily doses were ~33% above the upper limit of the FDA- and EMA-recommended dose range, only 2 patients achieved Css,avg ≥2mg/L; the remaining 3 patients had Css,avg <1mg/L. The pharmacokinetic covariate analysis revealed that clearances of colistimethate and colistin were related to creatinine clearance.

Conclusions

The FDA and EMA dosage recommendations may be suboptimal for many pediatric patients. Renal functioning is an important determinant of dosing in these patients.

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.

Pharmacokinetics of colistin in patients with multidrug-resistant Gram-negative infections: A pilot study

Background & objectives

There is little information concerning intravenously (i.v.) administered colistin in patients with multidrug-resistant (MDR) Gram-negative infections. Thus, this pilot prospective study was undertaken to characterize efficacy and pharmacokinetics of colistin in patients with MDR Gram-negative infections.

Methods

Nine patients with age >12 yr and MDR Gram-negative infections were included, of whom six were given colistin at the doses of 2 MU, while three patients were given 1 MU i.v. dose every 8 h. Blood samples were collected at different time intervals. Determination of colistin concentration was done by a ultra-high-performance liquid chromatography/mass spectrometry/selected reaction monitoring assay.

Results

The area under the plasma concentration-versus-time curve over eight hours (AUC_0-8) for colistin after the 1^st dose ranged from 3.3 to 16.4 mg×h/l (median, 4.59). After the 5^th dose, AUC_0-8for colistin ranged from 4.4 to 15.8 mg×h/l (median, 6.0). With minimal inhibitory concentration (MIC) value of 0.125 mg/l, AUC_0-8/MIC ranged from 26.7 to 131.4 (median, 36.7) and 35.5 to 126.0 (median, 48.0) after the 1^st and the 5^th doses of 2 MU every 8 h, respectively.

Interpretation & conclusions

As there is a paucity of information on AUC/MIC for colistin, it may not be possible to conclude whether AUC/MIC values in our patients were adequate. There is a microbiological clearance of organism, which goes in favour of the dosing schedule being adequate. Further studies need to be done to understand the pharmacokinetics of colistin in patients with infections.

Colistin Heteroresistance and Involvement of the PmrAB Regulatory System in Acinetobacter baumannii

Multidrug-resistant Acinetobacter baumannii infection has recently emerged as a worldwide clinical problem, and colistin is increasingly being used as a last-resort therapy. Despite its favorable bacterial killing, resistance and heteroresistance (HR) to colistin have been described. The purpose of the present study was to investigate the role of the PmrAB regulatory pathway in laboratory-selected mutants representative of global epidemic strains. From three unrelated A. baumannii clinical strains (sequence types 2, 3, and 20), eight colistin-resistant mutants were selected. Half of the mutants showed HR to colistin according to the reference method (population analysis profiling), whereas the other half exhibited stable resistance. M12I mutation within pmrA and M308R, S144KLAGS, and P170L mutations for pmrB were associated with HR to colistin, while T235I, A226T, and P233S mutations within pmrB were associated with stable resistance. The transcript levels of the pmrCAB operon were upregulated in all the mutants. Compensatory mutations were explored for some mutants. A single mutant (T235I mutant) displayed a compensatory mutation through ISAba1 mobilization within the pmrB gene that was associated with the loss of colistin resistance. The mutant resistance phenotype associated with T235I was partially restored in a trans-complementation assay turning to HR. The level of colistin resistance was correlated with the level of expression of pmrC in the trans-complemented strains. This report shows the role of different mutations in the PmrAB regulatory pathway and warns of the development of colistin HR that could be present but not easily detected through routine testing.

Pharmacokinetic and Pharmacodynamic Considerations of Antibiotics of Last Resort in Treating Gram-Negative Infections in Adult Critically Ill Patients

PURPOSE OF REVIEW

We provide an overview of antimicrobials that are considered last resort for the treatment of resistant gram-negative infections in adult critically ill patients. The role in therapy, pharmacodynamic (PD) goals, and pharmacokinetic (PK) changes in critical illness for aminoglycosides, polymyxins, tigecycline, fosfomycin, and fluoroquinolones are summarized.

RECENT FINDINGS

Altered PK in septic patients in the intensive care unit (ICU) is observed with many of our agents of last resort. Based on the available literature, dosage adjustments may be required to optimize PK parameters and meet PD targets for most effective bacterial killing. Data is limited, studies are conducted in heterogeneous patient populations, and conclusions are frequently conflicting. Strategic dosing regimens such as high-dose extended interval dosing of aminoglycosides or loading doses with colistin and polymyxin B are examples of ways to optimize antibiotic PK in critically ill patients. Benefits of these strategies must be balanced with risks of increased toxicity. Patients with resistant gram-negative infections may present with septic shock in the ICU. Sepsis can significantly alter the PK of antibiotics and require dosage adjustments to attain optimal drug levels. An understanding of PK and PD properties of these agents of last resort will help to maximize therapeutic efficacy while minimizing toxic effects.

Colistin resistance among blood culture isolates at a tertiary care centre in Hungary

OBJECTIVES

The emergence of colistin resistance has been detected worldwide in recent years. Whilst colistin susceptibility has been tested in carbapenem resistant Enterobacteriaceae as well as multidrug-resistant Pseudomonas spp. and Acinetobacter spp. during routine laboratory practice, the overall rate of colistin resistance was unknown in our centre. The aim of this retrospective study was to reveal the prevalence of colistin resistance among clinically significant blood culture isolates in two different periods (2010-2011 and 2016) in our laboratory.

METHODS

Consecutive non-duplicate strains (n=776) were screened for colistin resistance using agar plates containing 4mg/L colistin. Strains cultured on colistin-containing plates were further examined. Minimum inhibitory concentrations (MICs) of colistin-tolerant subcultures and original cultures were determined in parallel by the broth microdilution method. Screening for mcr-1-mediated colistin resistance was performed by PCR.

RESULTS

The rate of colistin resistance was 0.6%, 1.3% and 2.6% in Enterobacteriaceae, Pseudomonas spp. and Acinetobacter spp., respectively; colistin-resistant subpopulations were found in 17%, 27% and 20% of isolates, respectively, with low frequency. Seven colistin-resistant strains were found, among which was an mcr-1-positive Escherichia coli isolated from a blood sample of a haemato-oncology patient in 2011. All Stenotrophomonas maltophilia isolates were resistant to colistin.

CONCLUSIONS

The low prevalence of colistin resistance was in accordance with European data. The prevalence of heteroresistance was significantly higher, but the clinical significance of the phenomenon is unclear. We have identified the first mcr-1-positive E. coli strain in Hungary. mcr-1 has been in Hungary since 2011 but has not yet expanded.

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.

Pharmacodynamic and pharmacokinetic considerations in the treatment of critically Ill patients infected with carbapenem-resistant Enterobacteriaceae

Carbapenem-Resistant Enterobacteriaceae (CRE) are an emerging healthcare crisis. Infections due to CRE are associated with high morbidity and mortality, especially in critically ill patients. Due to the multi-drug resistant nature of these infections only limited treatment options are available. Antimicrobials that have been described for the treatment of CRE infections include carbapenems, polymyxins, fosfomycin, tigecycline, aminoglycosides, and ceftazidime-avibactam. Given the limited treatment options it is imperative the pharmacokinetic and pharmacodynamics (PK-PD) characteristics of these agents are considered to optimize treatment regimens. This review will focus on the PK-PD challenges of the current treatment options for CRE infections.

Effects of colistin on biofilm matrices of Escherichia coli and Staphylococcus aureus

Biofilms are the preferred environment of micro-organisms on various surfaces such as catheters and heart valves, are associated with numerous difficult-to-treat and recurrent infections, and confer an extreme increase in antibiotic tolerance to most compounds. The aim of this study was to evaluate how colistin affects both the extracellular biofilm matrix and the embedded bacteria in biofilms of methicillin-resistant Staphylococcus aureus (MRSA), a species with intrinsic resistance to colistin, and colistin-susceptible Escherichia coli. Biofilms of MRSA and E. coli were treated with different concentrations of colistin. The minimum biofilm eradication concentration (MBEC) and the effectiveness of colistin at reducing the planktonic fraction were defined as the remaining viable bacteria measured as CFU/mL. In addition, biofilm-embedded cells were LIVE/DEAD-stained and were analysed by confocal laser scanning microscopy (CLSM). Quantification of the biofilm CLSM images was conducted using an open-access in-house algorithm (qBA). In contrast to MRSA, E. coli biofilms and planktonic cells were significantly reduced by colistin in a concentration-dependent manner. Nevertheless, colistin has been shown to exert a matrix-reducing effect following treatment both in laboratory strains and clinical isolates of MRSA and E. coli. Because exposure to colistin rapidly triggered the emergence of highly resistant clones, monotherapy with colistin should be applied with caution. These results suggest that colistin destabilises the biofilm matrix structure even in species with intrinsic colistin resistance, such as S. aureus, leading to the release of planktonic cells that are more susceptible to antibiotics.

Revival of old antibiotics: needs, the state of evidence and expectations

The gap between the emergence of antibiotic resistance and new antibiotic development has drawn attention to old antibiotics whose spectrum of coverage frequently comprises highly resistant bacteria. However, these antibiotics have frequently not undergone the structured process of antibiotic development of modern antibiotics, from pharmacokinetic/pharmacodynamic (PK/PD) studies establishing safe and effective dosing, establishment of susceptibility breakpoints, to clinical trials establishing clinical safety and effectiveness. In this review, we highlight the gaps for which we need old antibiotics in community- and hospital-acquired infections. Reviewing recently published and ongoing randomised controlled trials (RCTs) shows advances in our understanding of the efficacy and effectiveness of oral fosfomycin, mecillinam and nitrofurantoin for cystitis, and of trimethoprim/sulfamethoxazole for complicated skin infections caused by methicillin-resistant Staphylococcus aureus (MRSA) in the community. Summarising older evidence shows the inferiority of chloramphenicol versus modern antibiotics for severe infections. We lack studies on severe infections caused by carbapenem-resistant Gram-negative bacteria and other multidrug-resistant (MDR) bacteria in hospitalised and critically ill patients; ongoing studies assessing colistin and intravenous fosfomycin might fill in some gaps. In the re-development process of old antibiotics, we mandate modern PK/PD studies comprising special populations as well as RCTs addressing the target population of patients in need of these antibiotics powered to examine patient-relevant outcomes. Structured antibiotic re-development from the laboratory to evidence-based treatment recommendations requires public funding, multidisciplinary collaboration, international co-ordination, and methods to streamline the recruitment of critically ill patients infected by MDR bacteria.

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.