Changes in the serum protein binding of vancomycin in patients with methicillin-resistant Staphylococcus aureus infection: the role of serum alpha 1-acid glycoprotein levels

Evaluation of the pharmacokinetics of liposomal amphotericin B and analysis of the relationship between pharmacokinetics, efficacy and safety in patients with hematological diseases

INTRODUCTION

This study aimed to identify factors responsible for changes in blood concentrations of a liposomal formulation of amphotericin B (AMPH-B, L-AMB) and analyze the relationships between blood concentrations and efficacy or toxicity.

METHODS

L-AMB was administered to 30 patients being treated for hematological diseases. AMPH-B plasma concentrations were determined right before the initiation (Cmin) and at the end (Cmax) of infusion on at least 1 day, beginning on Day 3 of L-AMB treatment. The relationships of Cmin divided by dose (C/D ratio) to body weight, age, hepatic function, renal function, serum albumin, C-reactive protein (CRP), response, hypokalemia, and renal impairment were evaluated.

RESULTS

C/D ratio was not correlated with age, hepatic function, renal function, or serum albumin. Body weight adjusted C/D ratio was negatively correlated with CRP. Cmax and Cmin were compared between responders and non-responders, those with or without hypokalemia, and those with or without renal impairment. A higher Cmax in patients with hypokalemia was the only significant difference seen.

CONCLUSIONS

The negative correlation between CRP and plasma concentrations was likely caused by higher distribution of L-AMB from the blood to infected tissue in patients with a greater degree of infection, with a resulting decrease in plasma concentrations. AMPH-B plasma concentrations were not related to response. Higher Cmax of AMPH-B were observed in patients with hypokalemia, but no relationship between plasma concentration and renal toxicity was observed, suggesting that AMPH-B plasma concentrations appear to be minimally related to PD when used as L-AMB.

Updated antimicrobial dosing recommendations for obese patients

The prevalence of obesity has increased considerably in the last few decades. Pathophysiological changes in obese patients lead to pharmacokinetic (PK) and pharmacodynamic (PD) alterations that can condition the correct exposure to antimicrobials if standard dosages are used. Inadequate dosing in obese patients can lead to toxicity or therapeutic failure. In recent years, additional antimicrobial PK/PD data, extended infusion strategies, and studies in critically ill patients have made it possible to obtain data to provide a better dosage in obese patients. Despite this, it is usually difficult to find information on drug dosing in this population, which is sometimes contradictory. This is a comprehensive review of the dosing of different types of antimicrobials (antibiotics, antifungals, antivirals, and antituberculosis drugs) in obese patients, where the literature on PK and possible dosing strategies in obese adults was critically assessed.

Involvement of the effect of renal hypoperfusion medications on vancomycin trough concentration: A secondary analysis using a retrospective observational data

This study examined the association between vancomycin (VCM) trough concentration and confounding factors including renal hypoperfusion medications which include angiotensin-converting enzyme inhibitors/angiotensin receptor blockers, loop/thiazide diuretics, or non-steroidal anti-inflammatory drugs. This secondary analysis included patients aged >15 years who were administered VCM intravenously between June 2015 and August 2017 at the Tokyo Women's Medical University Medical Center East. We investigated predictors for three (initial, mean, and final) dose-normalized VCM trough concentration (dose-normalized VCM_trough ) as outcome using a multiple linear regression analysis. In total, 208 patients were analysed (use of loop/thiazide diuretics: 48 [23%]). Multiple linear regression analysis revealed that the initial dose-normalized VCM_trough was negatively correlated with estimated glomerular filtration rate (eGFR) (p = 0.028) and positively correlated with the use of loop/thiazide diuretics (p = 0.003). Meanwhile, there was a positive correlation between the mean dose-normalized VCM_trough and age (p = 0.023). The mean dose-normalized VCM_trough was negatively correlated with eGFR (p < 0.001) and serum albumin (p < 0.001). The final dose-normalized VCM_trough was positively associated with age (p = 0.034) and negatively associated with eGFR (p = 0.032) and serum albumin (p = 0.007). Clinicians should closely monitor VCM trough concentration while receiving VCM and loop/thiazide diuretics.

Effect of obesity on the pharmacokinetics of antimicrobials in critically ill patients: A structured review

The increased prevalence of obesity presents challenges for clinicians aiming to provide optimised antimicrobial dosing in the intensive care unit. Obesity is likely to exacerbate the alterations to antimicrobial pharmacokinetics when the chronic diseases associated with obesity exist with the acute pathophysiological changes associated with critical illness. The purpose of this paper is to review the potential pharmacokinetic (PK) changes of antimicrobials in obese critically ill patients and the implications for appropriate dosing. We found that hydrophilic antimicrobials (e.g. β-lactams, vancomycin, daptomycin) were more likely to manifest altered pharmacokinetics in critically ill patients who are obese. In particular for β-lactam antibiotics, obesity is associated with a larger volume of distribution (V(d)). In obese critically ill patients, piperacillin is also associated with a lower drug clearance (CL). For doripenem, these PK changes have been associated with reduced achievement of pharmacodynamic (PD) targets when standard drug doses are used. For vancomycin, increases in Vd are associated with increasing total body weight (TBW), meaning that the loading dose should be based on TBW even in obese patients. For daptomycin, an increased Vd is not considered to be clinically relevant. For antifungals, little data exist in obese critically ill patients; during fluconazole therapy, an obese patient had a lower V(d) and higher CL than non-obese comparators. Overall, most studies suggested that standard dosage regimens of most commonly used antimicrobials are sufficient to achieve PD targets. However, it is likely that larger doses would be required for pathogens with higher minimum inhibitory concentrations.

Measuring unbound versus total vancomycin concentrations in serum and plasma: methodological issues and relevance

BACKGROUND

Studies on the unbound fraction (fu) of vancomycin report highly variable results. Great controversy also exists about the correlation between unbound and total vancomycin concentrations. As differences in (pre-)analytic techniques may explain these findings, we investigated the impact of the procedure used to isolate unbound vancomycin in serum/plasma on fu and the correlation between total and unbound concentrations.

METHODS

Patient samples (n = 39) were analyzed for total and unbound vancomycin concentrations after ultrafiltration (UF, Centrifree at 4°C and 37°C) or equilibrium dialysis (ED, using a Fast Micro-Equilibrium Dialyzer at 37°C) on an Architect i2000SR. To investigate correlations with potential binding proteins, total protein, albumin, alpha-1-acid glycoprotein, and IgA concentrations were also measured.

RESULTS

The median fu after ED was 72.5% [interquartile range (IQR), 68.7%-75.0%]. Ultrafiltration at 4°C and 37°C resulted in a median fu of 51.6% (IQR, 48.6%-54.8%) and 75.2% (IQR, 69.3%-78.6%), respectively, with no significant difference between unbound vancomycin concentrations after ED and UF at 37°C (P = 0.13). Unbound concentrations obtained through ED and UF correlated linearly (4°C: r = 0.9457; 37°C: r = 0.9478; both P < 0.0001). Linear mixed-model regression showed that total vancomycin as such was the predominant determinant for the unbound concentration, allowing a reliable prediction (mean bias ± SD, 5.0% ± 7.6%). The studied protein concentrations were of no added value in predicting the unbound concentration.

CONCLUSIONS

Vancomycin fu after UF at 4°C was on average 30.6% lower than that after UF at 37°C, demonstrating the importance of temperature during UF. Ultrafiltration at 37°C resulted in unbound vancomycin concentrations equivalent with ED. As the unbound concentration could be reliably predicted based on total vancomycin concentrations as such, measurement of unbound vancomycin concentrations has little added value over measurements of total vancomycin concentrations.

Determination of the free and total concentrations of vancomycin by two-dimensional liquid chromatography and its application in elderly patients

A robust two-dimensional liquid chromatography (2D-LC) method for determining the free and total concentrations of vancomycin in plasma was developed and validated. The 2D-LC system, which exhibited a strong capacity for inhibiting interference, comprised a unique RP1-IEX-RP2 column system and an "Assistant Flow" configuration. Ultrafiltration technology was employed to separate free vancomycin from the protein-bound fraction in human plasma. The influence of ultrafiltration conditions on the free vancomycin concentration was evaluated. The calibration curve was linear over the 0.195-49.92μg/ml range for the free and total vancomycin concentrations. The within- and between-run precision ranges were 1.5-3.9% and 2.0-4.7% for the total concentration, 1.4-3.3% and 2.4-4.0% for the free concentration, respectively. Ultrafiltration was susceptible to variations in the experimental conditions, including the centrifugation time, the centrifugal force, and the nominal molecular weight limit of the ultrafiltration membrane. A total of 101 serum samples from 84 elderly patients were analyzed by this method. The free vancomycin concentration was 5.88±3.75μg/ml (range: 0.240-16.79μg/ml), the total concentration was 12.36±5.36μg/ml (range: 2.16-27.14μg/ml), and the unbound fraction was 45.6±18.8% (range: 11.1-96.9%). There was a poor correlation between the free and total vancomycin concentrations (R(2)=0.596, p<0.05). This method appears to be sensitive, precise, selective, and suitable for use in protein-binding studies of vancomycin.

Accuracy of the analysis of free vancomycin concentration by ultrafiltration in various disease states

The different ultrafiltrate volume results in different unbound vancomycin fractions as determined by centrifugal ultrafiltration and hollow fiber centrifugal ultrafiltration.

Unbound fraction of vancomycin in intensive care unit patients

Published data on the unbound fraction of vancomycin in patient samples exhibit high variability. In the present study, a robust ultrafiltration method was developed and applied to 102 clinical samples from 22 intensive care unit patients who were treated with continuous infusion of vancomycin. A validated HPLC method was used for determination of total and unbound concentrations. The mean unbound fraction was 67.2% (standard deviation 7.5%, range 47.2-92.1%) and independent of total concentration of vancomycin or of albumin. The unbound fraction was significantly correlated (r = +0.67, P = .0009) with the renally filtered fraction (drug clearance/creatinine clearance), providing functional evidence for the validity of the measurements. Ultrafiltration proved to be susceptible to variations in the experimental conditions such as pH, temperature and centrifugal force. The measured unbound fraction increased from 60% at pH 6 to 100% at pH 9, from 57% at 4°C to 80% at 37°C, and was 76% at 1,000 g compared with 45% at 10,000 g. Lack of standardization may therefore partly explain the variable results reported in the literature.

fAUC/MIC is the most predictive pharmacokinetic/pharmacodynamic index of colistin against Acinetobacter baumannii in murine thigh and lung infection models

OBJECTIVES

To elucidate the pharmacokinetic/pharmacodynamic (PK/PD) index that predicts colistin efficacy against Acinetobacter baumannii in neutropenic murine thigh and lung infection models, and to determine the extent of the emergence of resistance in vivo to colistin.

METHODS

PK/PD of colistin was studied in thigh and lung infection models against A. baumannii ATCC 19606 and two multidrug-resistant clinical isolates (two of the three strains were colistin heteroresistant). Dose fractionation studies were conducted over a daily dose range of 1-160 mg/kg colistin sulphate. Bacterial burden in tissues was measured at 24 h. Non-linear least squares regression analyses were employed to determine the PK/PD index (fAUC/MIC, fC(max)/MIC or fT(>MIC)) best correlating with the efficacy of colistin in each model. Real-time population analysis profiles were conducted for tissue samples to monitor the emergence of resistance.

RESULTS

The fAUC/MIC was the PK/PD index that correlated best with efficacy in both thigh (R(2) = 0.90) and lung (R(2) = 0.80) infection models. The fAUC/MIC targets required to achieve stasis and 1 log kill against the three strains were 1.89-7.41 and 6.98-13.6 in the thigh infection model, respectively, while the corresponding values were 1.57-6.52 and 8.18-42.1 in the lung infection model. Amplification of colistin-resistant subpopulations was revealed for all strains in both models after 24 h colistin treatment.

CONCLUSIONS

This study indicates the importance of achieving adequate time-averaged exposure to colistin and defined target fAUC/MIC values for various magnitudes of kill. Amplification of resistant subpopulations indicates the importance of investigating rational combinations with colistin. The results will facilitate efforts to optimize colistin use in humans.

Pharmacokinetic/pharmacodynamic investigation of colistin against Pseudomonas aeruginosa using an in vitro model

Colistin plays a key role in treatment of serious infections by Pseudomonas aeruginosa. The aims of this study were to (i) identify the pharmacokinetic/pharmacodynamic (PK/PD) index (i.e., the area under the unbound concentration-time curve to MIC ratio [fAUC/MIC], the unbound maximal concentration to MIC ratio [fC(max)/MIC], or the cumulative percentage of a 24-h period that unbound concentrations exceed the MIC [fT(>MIC)]) that best predicts colistin efficacy and (ii) determine the values for the predictive PK/PD index required to achieve various magnitudes of killing effect. Studies were conducted in a one-compartment in vitro PK/PD model for 24 h using P. aeruginosa ATCC 27853, PAO1, and the multidrug-resistant mucoid clinical isolate 19056 muc. Six intermittent dosing intervals, with a range of fC(max) colistin concentrations, and two continuous infusion regimens were examined. PK/PD indices varied from 0.06 to 18 for targeted fC(max)/MIC, 0.36 to 312 for fAUC/MIC, and 0 to 100% for fT(>MIC). A Hill-type model was fit to killing effect data, which were expressed as the log(10) ratio of the area under the CFU/ml curve for treated regimens versus control. With fC(max) values equal to or above the MIC, rapid killing was observed following the first dose; substantial regrowth occurred by 24 h with most regimens. The overall killing effect was best correlated with fAUC/MIC (R(2) = 0.931) compared to fC(max)/MIC (R(2) = 0.868) and fT(>MIC) (R(2) = 0.785). The magnitudes of fAUC/MIC required for 1- and 2-log(10) reductions in the area under the CFU/ml curve relative to growth control were 22.6 and 30.4, 27.1 and 35.7, and 5.04 and 6.81 for ATCC 27853, PAO1, and 19056 muc, respectively. The PK/PD targets identified will assist in designing optimal dosing strategies for colistin.

Colistin in the 21st century

PURPOSE OF REVIEW

Colistin is a 50-year-old antibiotic that is being used increasingly as a 'last-line' therapy to treat infections caused by multidrug-resistant Gram-negative bacteria, when essentially no other options are available. Despite its age, or because of its age, there has been a dearth of knowledge on its pharmacological and microbiological properties. This review focuses on recent studies aimed at optimizing the clinical use of this old antibiotic.

RECENT FINDINGS

A number of factors, including the diversity in the pharmaceutical products available, have hindered the optimal use of colistin. Recent advances in understanding of the pharmacokinetics and pharmacodynamics of colistin, and the emerging knowledge on the relationship between the pharmacokinetics and pharmacodynamics, provide a solid base for optimization of dosage regimens. The potential for nephrotoxicity has been a lingering concern, but recent studies provide useful new information on the incidence, severity and reversibility of this adverse effect. Recent approaches to the use of other antibiotics in combination with colistin hold promise for increased antibacterial efficacy with less potential for emergence of resistance.

SUMMARY

Because few, if any, new antibiotics with activity against multidrug-resistant Gram-negative bacteria will be available within the next several years, it is essential that colistin is used in ways that maximize its antibacterial efficacy and minimize toxicity and development of resistance. Recent developments have improved use of colistin in the 21st century.

Elucidation of the pharmacokinetic/pharmacodynamic determinant of colistin activity against Pseudomonas aeruginosa in murine thigh and lung infection models

Colistin is increasingly used as last-line therapy against Gram-negative pathogens. The pharmacokinetic (PK)/pharmacodynamic (PD) index that best correlates with the efficacy of colistin remains undefined. The activity of colistin against three strains of Pseudomonas aeruginosa was studied in neutropenic mouse thigh and lung infection models. The PKs of unbound colistin were determined from single-dose PK studies together with extensive plasma protein binding analyses. Dose-fractionation studies were conducted over 24 h with a dose range of 5 to 160 mg/kg of body weight/day. The bacterial burden in the thigh or lung was measured at 24 h after the initiation of treatment. Relationships between antibacterial effect and measures of exposure to unbound (f) colistin (area under the concentration-time curve [fAUC/MIC], maximum concentration of drug in plasma [fC(max)]/MIC, and the time that the concentration in plasma is greater than the MIC [fT > MIC]) were examined by using an inhibitory sigmoid maximum-effect model. Nonlinearity in the PKs of colistin, including its plasma protein binding, was observed. The PK/PD index that correlated best with its efficacy was fAUC/MIC in both the thigh infection model (R(2) = 87%) and the lung infection model (R(2) = 89%). The fAUC/MIC targets required to achieve 1-log and 2-log kill against the three strains were 15.6 to 22.8 and 27.6 to 36.1, respectively, in the thigh infection model, while the corresponding values were 12.2 to 16.7 and 36.9 to 45.9 in the lung infection model. The findings of this in vivo study indicate the importance of achieving adequate time-averaged exposure to colistin. The results will facilitate efforts to define the more rational design of dosage regimens for humans.

Potential Impact of Vancomycin Pulmonary Distribution on Treatment Outcomes in Patients with Methicillin-ResistantStaphylococcus aureusPneumonia

Vancomycin as the drug of choice for treatment of methicillin-resistant Staphylococcus aureus (MRSA) pneumonia has been called into question on the basis of therapeutic failures. In patients with MRSA pneumonia, treatment failures are probably due to the complex interplay of variables affecting the host-antimicrobial-pathogen interrelationship. However, it has been suggested that decreased penetration of vancomycin into the lungs may contribute. This review explores physiochemical and physiologic variables that affect pulmonary penetration and describes methods used in quantifying pulmonary vancomycin concentrations. Most important, findings are evaluated in the clinical context of the chemotherapeutic options available for treatment of MRSA pneumonia. The possibility of increased serum vancomycin concentrations as a method to optimize current treatment outcomes is also explored.

Antibiotic management of ventilator-associated pneumonia due to antibiotic-resistant gram-positive bacterial infection

Gram-positive cocci, in particular Staphylococcus aureus, account for as much as one-third of all cases of hospital-acquired pneumonia, and treatment has become increasingly complex as the proportion of resistant isolates has increased. Methicillin-resistant S. aureus is of particular concern because this pathogen is now associated with hospital-acquired, ventilator-associated, community-acquired, and healthcare-associated pneumonia. Antibiotic therapy for ventilator-associated pneumonia is challenging because it can be caused by multiple pathogens, which can be resistant to multiple drugs. This article reviews the epidemiology of ventilator-associated pneumonia and describes options for antibiotic treatment. Particular attention is paid to pneumonia due to methicillin-resistant S. aureus. Studies suggest that vancomycin, the traditional treatment for ventilator-associated pneumonia, may not be the best option for this type of pneumonia and that other antibiotics, such as linezolid and clindamycin, might be better choices. New antibiotics with activity against methicillin-resistant S. aureus are under investigation and may soon become available for clinical use. Studies are needed to define the optimal choice of antibiotic for pneumonias caused by this organism, and these choices will need to be balanced with the need to minimize the emergence of resistance.

Use of Photoaffinity Labeling and Site-directed Mutagenesis for Identification of the Key Residue Responsible for Extraordinarily High Affinity Binding of UCN-01 in Human α1-Acid Glycoprotein

7-Hydroxystaurosporine (UCN-01) is a protein kinase inhibitor anticancer drug currently undergoing a phase II clinical trial. The low distribution volumes and systemic clearance of UCN-01 in human patients have been found to be caused in part by its extraordinarily high affinity binding to human alpha1-acid glycoprotein (hAGP). In the present study, we photolabeled hAGP with [3H]UCN-01 without further chemical modification. The photolabeling specificity of [3H]UCN-01 was confirmed by findings in which other hAGP binding ligands inhibited formation of covalent bonds between hAGP and [3H]UCN-01. The amino acid sequence of the photolabeled peptide was concluded to be SDVVYTDXK, corresponding to residues Ser-153 to Lys-161 of hAGP. No PTH derivatives were detected at the 8th cycle, which corresponded to the 160th Trp residue. This strongly implies that Trp-160 was photolabeled by [3H]UCN-01. Three recombinant hAGP mutants (W25A, W122A, and W160A) and wild-type recombinant hAGP were photolabeled by [3H]UCN-01. Only mutant W160A showed a marked decrease in the extent of photoincorporation. These results strongly suggest that Trp-160 plays a prominent role in the high affinity binding of [3H]UCN-01 to hAGP. A docking model of UCN-01 and hAGP around Trp-160 provided further details of the binding site topology.

Estimation of serum-free 50-percent inhibitory concentrations for human immunodeficiency virus protease inhibitors lopinavir and ritonavir

Using measured free fraction and 50% inhibitory concentration (IC50) values for the human immunodeficiency virus protease inhibitors lopinavir (LPV) and ritonavir (RTV) in tissue culture media with various protein concentrations ranging from 5 to 50%, we estimated serum-free IC50 values for each drug. The range of serum-free IC50 values (0.64 to 0.77 ng/ml for LPV and 3.0 to 5.0 ng/ml for RTV) did not exhibit a trend with increasing protein concentrations, despite a 10-fold difference in the free fraction value (0.006 to 0.063) for LPV and a 5-fold difference in the free fraction value (0.013 to 0.057) for RTV. The mean serum-free IC50 by the MTT-MT4 assay (0.69 ng/ml for LPV and 4.0 ng/ml for RTV) may be the most accurate parameter for the estimation of the inhibitory quotient (IQ), a relative measure of in vivo potency defined as the ratio of the minimal free drug concentration in plasma (C(trough,free)) for a specific patient population and the serum-free IC50. Using this approach, we calculated the average IQs for protease inhibitor-naïve patients for LPV and RTV to be 67 and 5.6, respectively.

Human alpha-1-glycoprotein and its interactions with drugs

For about half a century, the binding of drugs to plasma albumin, the "silent receptor," has been recognized as one of the major determinants of drug action, distribution, and disposition. In the last decade, the binding of drugs, especially but not exclusively basic entities, to another plasma protein, alpha 1-acid glycoprotein (AAG), has increasingly become important in this regard. The present review points out that hundreds of drugs with diverse structures bind to this glycoprotein. Although plasma concentration of AAG is much lower than that of albumin, AAG can become the major drug binding macromolecule in plasma with significant clinical implications. Also, briefly reviewed are the physiological, pathological, and genetic factors that influence binding, the role of AAG in drug-drug interactions, especially the displacement of drugs and endogenous substances from AAG binding sites, and pharmacokinetic and clinical consequences of such interactions. It can be predicted that in the future, rapid automatic methods to measure binding to albumin and/or AAG will routinely be used in drug development and in clinical practice to predict and/or guide therapy.

The obese patient in the ICU

Data from recent surveys indicate that a staggering 34.9% of US adults are overweight. Obese adults are at in increased risk for many chronic medical conditions, and this increases the likelihood of admission to an ICU. The critically ill obese patient presents the ICU team with many unique problems. Obesity may result in significant alterations of pulmonary and cardiac function, as well as the handling of many drugs. An appreciation of these and other changes is essential in the management of the obese ICU patient. The purpose of this article is to review some of the basic concepts related to the treatment of obese patients in the ICU.

A closer look at vancomycin, teicoplanin, and antimicrobial resistance

The worldwide increase in the incidence of resistant Gram-positive infections has renewed interest in the glycopeptide class of antimicrobial agents. Two glycopeptides are available in many parts of the world--vancomycin and teicoplanin. These two agents appear to differ in several respects, including: potential for selecting microbial resistance, dosing convenience, safety, and efficacy in severe infection. Teicoplanin appears to have lower toxicity and greater convenience; however, its widespread acceptance has been plagued by concerns over antimicrobial resistance, efficacy, and appropriate dosing. A review of available studies suggests that teicoplanin, when dosed at 6 mg/kg/day, is better tolerated than vancomycin 15 mg/kg/q12h; however, at these doses, it appears to be somewhat less effective than vancomycin in serious Staphylococcus aureus infection, such as endocarditis. Although higher doses of teicoplanin, 12 mg/kg/day to 30 mg/kg/day, have been associated with efficacy comparable to that of vancomycin in serious S. aureus infections, such doses may eliminate some of the safety advantages conferred by lower teicoplanin doses. Teicoplanin has been associated with resistance among coagulase-negative staphylococci and the selection of resistance in S. aureus. There is some evidence that widespread use of teicoplanin might accelerate the development of S. aureus resistance to both teicoplanin and vancomycin. The selection of an appropriate glycopeptide in an individual patient should be based not only on convenience, but also on a determination of optimal efficacy, safety at an efficacious dose, and the potential for resistance.