Daptomycin pharmacokinetics in adult oncology patients with neutropenic fever. Antimicrob Agents Chemother. 2009;53:428-434. [PMID: 19015332 DOI: 10.1128/aac.00943-08]

Clinical pharmacokinetics of antimicrobials in critical care: a narrative review

INTRODUCTION

The management of critically ill septic patients presents considerable challenges due to multifaceted physiological alterations. Rapid changes such as fluid shifts, hyperdynamic states, and altered renal clearance often require special attention for better clinical outcomes. Vital organ dysfunction, with or without MODS, often necessitates supportive management like RRT, ventilatory support, and ECMO. These interventions can significantly affect the PK/PD of administered antimicrobials, complicating effective treatment.

AREA COVERED

Patient-specific parameters such as age, weight, and comorbid illnesses (e.g. cystic fibrosis, burns, and immunocompromised states) are critical determinants of antimicrobial pharmacokinetics. Understanding PK/PD determinants is crucial for developing optimized dosing regimens that enhance therapeutic efficacy and minimize toxicity in critically ill patients.

EXPERT OPINION

Incorporating pharmacometrics approaches in dose optimization can significantly improve patient outcomes. This review focuses on the nuances of PK/PD for optimized antimicrobial dosing in critically ill septic patients, emphasizing the importance of individualized treatment plans to address the complex and dynamic needs of this patient population. The adoption of these advanced pharmacokinetic and pharmacodynamic principles into clinical practice is essential for advancing patient care and optimizing therapeutic outcomes in critically ill patients.

Advances in antibacterial treatment of adults with high-risk febrile neutropenia

BACKGROUND

High-risk febrile neutropenia (HR-FN) is a life-threatening complication in patients with haematological malignancies or receiving myelosuppressive chemotherapy. Since the last international guidelines were published over 10 years ago, there have been major advances in the understanding and management of HR-FN, including on antibiotic pharmacokinetics and discontinuation/de-escalation strategies.

OBJECTIVES

Summarizing major advances in the field of antibacterial therapy in patients with HR-FN: empirical therapy, pharmacokinetics of antibiotics and antibiotic stewardship.

SOURCES

Narrative review based on literature review from PubMed. We focused on studies published between 2010 and 2023 about the pharmacokinetics of antimicrobials, management of antimicrobial administration, and discontinuation/de-escalation strategies. We did not address antimicrobial prophylaxis, viral or fungal infections.

CONTENT

Several high-quality publications have highlighted important modifications of antibiotic pharmacokinetics in HR-FN, with standard dosages exposing patients to underdosing. These recent clinical and population pharmacokinetics studies help improve management protocols with optimized initial dosing and infusion rules for β-lactams, vancomycin, daptomycin and amikacin; they highlight the potential benefits of therapeutic drug monitoring. A growing body of evidence also shows that antibiotic discontinuation/de-escalation strategies are beneficial for bacterial ecology and patients' outcome. We further discuss methods and limitations for implementation of such protocols in haematology.

IMPLICATIONS

We highlight recent information about the management of antibacterial therapy in HR-FN that might be considered in updated guidelines for HR-FN management.

Daptomycin Population Pharmacokinetics in Patients Affected by Severe Gram-Positive Infections: An Update

Daptomycin pharmacokinetics may not depend on renal function only and it significantly differs between healthy volunteers and severely ill patients. Herein, we propose a population pharmacokinetics model based on 424 plasma daptomycin concentrations collected from 156 patients affected by severe Gram-positive infections during a routine therapeutic drug monitoring protocol. Model building and validation were performed using NONMEM 7.2 (ICON plc), Xpose4 and Perl-speaks-to-NONMEM. The final pop-PK model was a one-compartment first-order elimination model, with a 2.7% IIV for drug clearance (Cl), influence of creatinine clearance on drug clearance and of sex on distribution volume. After model validation, we simulated 10,000 patients with the Monte-Carlo method to predict the efficacy and tolerability of different daptomycin daily dosages. For the most common 6 mg/kg daily dose, the simulated probability of overcoming the toxic minimum concentration (24.3 mg/L) was 14.8% and the efficacy (expressed as a cumulative fraction of response) against methicillin-resistant S. aureus, S. pneumoniae and E. faecium was 95.77%, 99.99% and 68%, respectively. According to the model-informed precision dosing paradigm, pharmacokinetic models such as ours could help clinicians to perform patient-tailored antimicrobial dosing and maximize the odds of therapy success without neglecting toxicity risks.

Optimization of dosing regimens of vancomycin, teicoplanin, linezolid and daptomycin against methicillin-resistant Staphylococcus aureus in neutropenic patients with cancer by Monte Carlo simulations

The objective of this study was to evaluate the efficacy of various dosing regimens of vancomycin, teicoplanin, linezolid and daptomycin against methicillin-resistant Staphylococcus aureus (MRSA) in neutropenic patients with cancer. Monte Carlo simulations were conducted using pharmacokinetic parameters and pharmacodynamic data to determine cumulative fraction of response (CFRs) in terms of area under the concentration-time curve/minimum inhibition concentration target. Currently clinical standard dosing regimens of vancomycin, teicoplanin, linezolid and daptomycin were insufficient to provide expected CFRs against MRSA for neutropenic patients with cancer. The high dosing regimens of vancomycin (3500 mg/d), teicoplanin (800 mg/d) and daptomycin (8 mg/kg/d) could provide CFRs of ≥ 80%, showing a higher treatment success. However, the majority of CFRs with linezolid simulated dosing regimens reached < 80% against MRSA. Therefore, a strategy of high dosages of vancomycin, teicoplanin and daptomycin may be needed to attain optimal therapeutic efficacy against MRSA in neutropenic patients with cancer.

[Development of a Sensitive Enzyme-linked Immunosorbent Assay for Daptomycin]

Daptomycin (DAP) has a completely different mechanism of action compared with conventional drugs for methicillin-resistant Staphylococcus aureus (MRSA) and is widely used as the first-line drug for treatment of dermal soft tissue infection and sepsis caused by MRSA infection in clinical practice. However, DAP has serious side effects, including renal dysfunction and rhabdomyolysis, and thus therapeutic drug monitoring of DAP is recommended. The purpose of this study was to develop an enzyme-linked immunosorbent assay (ELISA) for DAP that is simpler and more sensitive compared with existing assay methods and can be used in pharmacokinetic studies. Anti-DAP antibody was obtained by immunizing mice with an antigen conjugated with mercaptosuccinyl bovine serum albumin using N-(4-maleimidobutyryloxy) succinimide as a heterobifunctional coupling agent. Enzyme labeling of DAP with horseradish peroxidase was performed using pyromellitic dianhydride. The generated antibody and enzyme conjugate were used to develop a highly sensitive and specific ELISA for DAP in human serum. This ELISA shows a linear range of detection from 0.3 to 72.9 ng/mL, and a limit of quantification of approximately 0.3 ng/mL. The developed ELISA should be a valuable tool for pharmacokinetic studies and therapeutic drug monitoring of DAP.

Pharmacodynamic Analysis of Daptomycin-treated Enterococcal Bacteremia: It Is Time to Change the Breakpoint

BACKGROUND

Currently, there is debate over whether the daptomycin susceptibility breakpoint for enterococci (ie, minimum inhibitory concentration [MIC] ≤4 mg/L) is appropriate. In bacteremia, observational data support prescription of high doses (>8 mg/kg). However, pharmacodynamic targets associated with positive patient outcomes are undefined.

METHODS

Data were pooled from observational studies that assessed outcomes in daptomycin-treated enterococcal bacteremia. Patients who received an additional antienterococcal antibiotic and/or a β-lactam antibiotic at any time during treatment were excluded. Daptomycin exposures were calculated using a published population pharmacokinetic model. The free drug area under the concentration-time curve to MIC ratio (fAUC/MIC) threshold predictive of survival at 30 days was identified by classification and regression tree analysis and confirmed with multivariable logistic regression. Monte Carlo simulations determined the probability of target attainment (PTA) at clinically relevant MICs.

RESULTS

Of 114 patients who received daptomycin monotherapy, 67 (58.8%) were alive at 30 days. A fAUC/MIC >27.43 was associated with survival in low-acuity (n = 77) patients (68.9 vs 37.5%, P = .006), which remained significant after adjusting for infection source and immunosuppression (P = .026). The PTA for a 6-mg/kg/day (every 24 hours) dose was 1.5%-5.5% when the MIC was 4 mg/L (ie, daptomycin-susceptible) and 91.0%-97.9% when the MIC was 1 mg/L.

CONCLUSIONS

For enterococcal bacteremia, a daptomycin fAUC/MIC >27.43 was associated with 30-day survival among low-acuity patients. As pharmacodynamics for the approved dose are optimized only when MIC ≤1 mg/L, these data continue to stress the importance of reevaluation of the susceptibility breakpoint.

[Localization and Accumulation Studies of Daptomycin in Rats Kidney Using Immunohistochemistry]

Daptomycin (DAP) has a completely different mechanism of action compared to conventional methicillin-resistant Staphylococcus aureus (MRSA) drugs and is widely used clinically as the first-line drug for the treatment of skin soft tissue infection and sepsis caused by MRSA infection. However, the most serious side effects of DAP include renal dysfunction and rhabdomyolysis. Knowledge of the time sequence of localization of DAP in cells and tissues of animals may help in developing a better understanding of the actual overall pharmacokinetics of DAP. We prepared DAP-specific antibodies by immunizing mice with DAP-GMBS-BSA conjugate. The Anti-DAP antibody was specific for DAP, which enabled us to develop an immunocytochemical method for detecting the uptake of DAP in the rat kidneys. One hour after a single intravenous (i.v.) injection of DAP at 12 mg/kg, immunohistochemical observation showed a strong ring-like positive reaction in the cytoplasm immediately below the microvilli of proximal tubule epithelial cells. The distal tubules and collecting ducts contained DAP-positive and negative cells in the cross section of one tubule. Twenty-four hours after DAP administration, several strong positive reactions of different sizes were observed in the cytoplasm of epithelial cells at the proximal tubule. No staining was detected after 7 days. This study will be a useful tool for analyzing the pharmacokinetics of DAP.

The characteristics and impact indicator of vancomycin pharmacokinetics in cancer patients complicated with severe pneumonia

OBJECTIVE

This study was designed to investigate the characteristics and impact indicator of vancomycin pharmacokinetics in cancer patients complicated with severe pneumonia.

METHODS

Fifty-seven cancer patients complicated with severe pneumonia were included in this research. Vancomycin serum trough concentrations were measured using the fluorescence polarization immunoassay (FPIA) method. The Bayesian estimator was used to calculate the pharmacokinetic parameters.

RESULTS

The average initial therapeutic dose of vancomycin was 15.18 ± 3.29 mg/kg (q12 h). Our study shows that vancomycin initial trough concentrations measured in cancer patients are significantly reduced (6.54 ± 3.11 mg/L; p < 0.0001) compared with the recommended standard vancomycin trough concentration (10-15 or 15-20 mg/L). Meanwhile, the clearance (CL) and volume of distribution (Vd) of vancomycin was increased significantly in cancer patients. Multivariate linear regression analysis revealed that Cys-C was the most important variable for vancomycin trough concentration (r² = 0.439). The relationships between vancomycin trough concentrations and Cys-C were further evaluated after the 57 patients were grouped by cut-off point (1.44 mg/L) of the serum Cys- C levels before vancomycin was administered. Compared with group Early group (Cys-C>1.44 mg/L), Delayed group (Cys-C≤1.44 mg/L) had much lower trough concentrations. Meanwhile, CL and CLcr were significantly increased in Delayed group (Cys-C≤1.44 mg/L). Although the clinical outcomes were similar between two groups, the duration of vasoactive agent in Early group was considerably shorter compared with Delayed group (χ² = 4.213; p < 0.05).

CONCLUSIONS

The serum trough concentration of vancomycin was significantly reduced in cancer patients complicated with severe pneumonia. Higher dosage regimen is needed to ensure clinical effectiveness. The Cys-C level measured prior to administration of vancomycin is suggested to be the most suitable parameter to predict whether vancomycin trough concentration is up to standard dosage. Especially for patients with baseline Cys-c less than 1.44 mg/L, it is more likely to need higher dosage algorithm.

Optimizing the Dosing Regimens of Daptomycin Based on the Susceptible Dose-Dependent Breakpoint against Vancomycin-Resistant Enterococci Infection

Daptomycin, a lipopeptide antibiotic, is one of the therapeutic options used for the treatment of vancomycin-resistant enterococci (VRE). Recently, the Clinical and Laboratory Standards Institute (CLSI) M100 30th edition has removed the susceptibility (S) breakpoint for Enterococcus faecium and replaced it with a susceptible dose-dependent (SDD) breakpoint of ≤4 μg/mL, with a suggested dosage of 8–12 mg/kg/day. Herein, we aimed to determine the minimum inhibitory concentration (MIC) values of daptomycin against clinical VRE isolates and to study the appropriate daptomycin dosing regimens among critically ill patients based on the new susceptibility CLSI breakpoint. The MIC determination of daptomycin was performed using E-test strips among clinical VRE strains isolated from patients at the Phramongkutklao Hospital. We used Monte Carlo simulation to calculate the probability of target attainment (PTA) and the cumulative fraction of response (CFR) of the ratio of the free area under the curve to MIC (fAUC_0–24/MIC) > 27.4 and fAUC_0–24/MIC > 20 for survival and microbiological response, respectively, at the first day and steady state. Further, we determined that the simulated daptomycin dosing regimen met the minimum concentration (Cmin) requirements for safety of being below 24.3 mg/L. All of the 48 VRE isolates were E. faecium strains, and the percentiles at the 50th and 90th MIC of daptomycin were 1 and 1.5 μg/mL, respectively. At MIC ≤ 2 μg/mL, a daptomycin dosage of 12 mg/kg/day achieved the PTA target of survival and microbiological response at the first 24 h time point and steady state. For a MIC of 4 μg/mL, none of the dosage regimens achieved the PTA target. For CFR, a dosage of 8–12 mg/kg/day could achieve the 90% CFR target at the first day and steady state. All dosing regimens had a low probability of Cmin being greater than 24.3 mg/L. In conclusion, the MIC of VRE against daptomycin is quite low, and loading and maintenance doses with 8 mg/kg/day were determined to be optimal and safe.

Pharmacodynamic Analysis of Daptomycin-treated Enterococcal Bacteremia: It Is Time to Change the Breakpoint

BACKGROUND

Currently, there is debate over whether the daptomycin susceptibility breakpoint for enterococci (ie, minimum inhibitory concentration [MIC] ≤4 mg/L) is appropriate. In bacteremia, observational data support prescription of high doses (>8 mg/kg). However, pharmacodynamic targets associated with positive patient outcomes are undefined.

METHODS

Data were pooled from observational studies that assessed outcomes in daptomycin-treated enterococcal bacteremia. Patients who received an additional antienterococcal antibiotic and/or a β-lactam antibiotic at any time during treatment were excluded. Daptomycin exposures were calculated using a published population pharmacokinetic model. The free drug area under the concentration-time curve to MIC ratio (fAUC/MIC) threshold predictive of survival at 30 days was identified by classification and regression tree analysis and confirmed with multivariable logistic regression. Monte Carlo simulations determined the probability of target attainment (PTA) at clinically relevant MICs.

RESULTS

Of 114 patients who received daptomycin monotherapy, 67 (58.8%) were alive at 30 days. A fAUC/MIC >27.43 was associated with survival in low-acuity (n = 77) patients (68.9 vs 37.5%, P = .006), which remained significant after adjusting for infection source and immunosuppression (P = .026). The PTA for a 6-mg/kg/day (every 24 hours) dose was 1.5%-5.5% when the MIC was 4 mg/L (ie, daptomycin-susceptible) and 91.0%-97.9% when the MIC was 1 mg/L.

CONCLUSIONS

For enterococcal bacteremia, a daptomycin fAUC/MIC >27.43 was associated with 30-day survival among low-acuity patients. As pharmacodynamics for the approved dose are optimized only when MIC ≤1 mg/L, these data continue to stress the importance of reevaluation of the susceptibility breakpoint.

Development and validation of sensitive and selective quantification of total and free daptomycin in human plasma using ultra-performance liquid chromatography coupled to tandem mass spectrometry

Recently, several studies on pharmacokinetics parameters of daptomycin reported that plasma trough concentration was linked to efficacy and adverse effects, suggesting the usefulness of therapeutic drug monitoring. Although some methods for determining total daptomycin concentration using liquid chromatography coupled to tandem mass spectrometry were established previously, no sensitive quantification method for free drug concentration was established. In this study, we aimed to develop a quantitative method of measuring both total and free daptomycin concentrations using ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS), by which both trough and maximum concentrations can be measured. Plasma samples were prepared by solid phase extraction. Free fractions were obtained by ultrafiltration. The assay fulfilled the requirements of US Food and Drug Administration and the European Medicines Agency for assay validation. The methods for total and free drug showed good fit over wide ranges of 0.5-200 and 0.04-40 μg/mL, with lower limits of quantitation of 0.5 and 0.04 μg/mL, respectively. Recovery rate of free daptomycin from ultrafiltration was approximately 100%. Extraction recovery rates of total and free drug measurements ranged from 57.1 to 67.4% and 54.6 to 62.3%, while matrix effect varied between 111.9 and 118.7% and 104.0 and 127.1%, respectively. The maximum and trough concentrations of total and free daptomycin in plasma from two patients in intensive care unit were successfully determined, demonstrating the feasibility of clinical application of the novel methods for determining plasma total and free daptomycin concentrations. In conclusion, we succeeded to develop a sensitive and selective method using UPLC-MS/MS for quantitative measurement of total and free daptomycin concentrations in plasma.

Population pharmacokinetics and dosing considerations for the use of daptomycin in adult patients with haematological malignancies

Objectives

To assess the population pharmacokinetics (popPK) of daptomycin at the conventional dose of 6 mg/kg/day in a cohort of oncohaematological patients.

Methods

Patients underwent serial blood sampling on day 3 of therapy (before dosing and at 0, 0.5, 1, 2, 3, 5, 7, 9 and 12 h after dosing) to assess the pharmacokinetic profile of daptomycin. PopPK and Monte Carlo simulation were performed to define the probability of target attainment (PTA) with 6, 8, 10 and 12 mg/kg/day of the pharmacokinetic/pharmacodynamic target of AUC 24 /MIC >1081.

Results

Thirty patients were recruited. A two-compartment open model with first-order intravenous input and first-order elimination was developed. Estimated creatinine clearance (CL CR ), serum albumin concentration (Alb) and presence of AML were covariates included in the final model. Monte Carlo simulation showed that the conventional 6 mg/kg/day dose resulted in optimal PTAs (≥80%) in the presence of pathogens with an MIC up to 0.5 mg/L only in patients with CL CR 50-100 mL/min/1.73 m 2 , Alb 26-45 g/L and a haematological diagnosis other than AML. Conversely, higher dosages, up to 12 mg/kg/day, were needed to achieve this goal in the presence of pathogens with an MIC of 0.25-0.5 mg/L in all of the other tested scenarios. In patients with CL CR 101-150 mL/min/1.73 m 2 and Alb 15-25 g/L, suboptimal PTAs (<60%) were predicted even with 12 mg/kg/day dosing .

Conclusions

Our study provides a strong rationale for considering daptomycin dosages of ≥ 8 mg/kg/day in several clinical scenarios for oncohaematological patients. In some of these scenarios therapeutic drug monitoring could be a useful adjunct for optimized care.

Role of Daptomycin on Burn Wound Healing in an Animal Methicillin-Resistant Staphylococcus aureus Infection Model

Prolonged hospitalization and antibiotic therapy are risk factors for the development of methicillin-resistant Staphylococcus aureus (MRSA) infections in thermal burn patients. We used a rat model to study the in vivo efficacy of daptomycin in the treatment of burn wound infections by S. aureus, and we evaluated the wound healing process through morphological and immunohistochemical analysis. A copper bar heated in boiling water was applied on a paraspinal site of each rat, resulting in two full-thickness burns. A small gauze was placed over each burn and inoculated with 5 × 10⁷ CFU of S. aureus ATCC 43300. The study included two uninfected control groups with and without daptomycin treatment, an infected control group that did not receive any treatment, and two infected groups treated, respectively, with intraperitoneal daptomycin and teicoplanin. The main outcome measures were quantitative culture, histological evaluation of tissue repair, and immunohistochemical expression of wound healing markers: epidermal growth factor receptor (EGFR) and fibroblast growth factor 2 (FGF-2). The highest inhibition of infection was achieved in the group that received daptomycin, which reduced the bacterial load from 10⁷ CFU/ml to about 10³ CFU/g (P < 0.01). The groups treated with daptomycin showed better overall healing with epithelialization and significantly higher collagen scores than the other groups, and these findings were also confirmed by immunohistochemical data. In conclusion, our results support the hypothesis that daptomycin is an important modulator of wound repair by possibly reducing hypertrophic burn scar formation.

Daptomycin Pharmacokinetics and Pharmacodynamics in Septic and Critically Ill Patients

Infections, including sepsis, are associated with high mortality rates in critically ill patients in the intensive care unit (ICU). Appropriate antibiotic selection and adequate dosing are important for improving patient outcomes. Daptomycin is bactericidal in bloodstream infections caused by Staphylococcus aureus and other Gram-positive pathogens cultured in ICU patients. The drug has concentration-dependent activity, and the area under the curve/minimum inhibitory concentration ratio is the pharmacokinetic/pharmacodynamic (PK/PD) index that best correlates with daptomycin activity, whereas toxicity correlates well with daptomycin plasma trough concentrations (or minimum concentration [C min]). Adequate daptomycin exposure can be difficult to achieve in ICU patients; multiple PK alterations can result in highly variable plasma concentrations, which are difficult to predict. For this reason, therapeutic drug monitoring could help clinicians optimize daptomycin dosing, thus improving efficacy while decreasing the likelihood of serious adverse events. This paper reviews the literature on daptomycin in ICU patients with sepsis, focusing on dosing and PK and PD parameters.

Therapeutic Drug Monitoring of Daptomycin: A Retrospective Monocentric Analysis

BACKGROUND

Daptomycin dose is adjusted to body weight and renal function and is usually not guided by therapeutic drug monitoring. Daptomycin plasma concentration measurement was established at our institution in January 2009 and is now increasingly being used. The aim of this study was to describe and characterize variability in daptomycin exposure during routine clinical therapy.

METHODS

We collected daptomycin plasma concentrations that were measured at our institution during the period January 2009-July 2012. Additional clinical and demographic data and their association with daptomycin exposure were tested by a multilevel linear regression analysis.

RESULTS

A total of 332 daptomycin plasma concentrations were determined in 86 patients. Sixty-six percent (n = 218) of all determinations were trough concentrations (Cmin), and 34% (n = 114) were peak concentrations (Cmax). Cmin ranged 2-68 mg/L (median, 16.7 mg/L), and Cmax 20-236 mg/L (median, 66.2 mg/L). A significant positive association of total dose, albumin, creatinine and a significant negative association of dose interval and intermittent hemodialysis with Cmin were found in the regression analysis. Total dose and intensive care unit (ICU) stay were significantly associated with Cmax (P < 0.05). However, only 28% (P < 0.005) of Cmin variability and 8% (P = 0.08) of Cmax variability were explained by the factors included in the analysis.

CONCLUSIONS

Daptomycin plasma concentrations are often unpredictable as shown by highly variable drug exposure that is only partially explained by dose administered and underlying renal function.

Daptomycin: Physicochemical, Analytical, and Pharmacological Properties

Daptomycin is the first approved member of a new class of antimicrobials, the cyclic lipopeptides, and presents selective action against gram-positive bacteria, including methicillin- and vancomycin-resistant strains. Considering that resistance to daptomycin is rare, the drug has become very important for current clinical practice. This review covers daptomycin's physicochemical characteristics, antibacterial spectrum, mechanism of action, pharmacokinetics, clinical applications, side effects, drug interactions, and the analytical methods used to measure daptomycin in pharmaceutical products and biologic samples. Special attention has been given to therapeutic drug monitoring reports, as studies have shown its highly variable pharmacokinetics in specific circumstances, such as in patients suffering from critical illness, morbid obesity, severe sepsis, and kidney injury. For the same reason, methods described for therapeutic drug monitoring of daptomycin in the special patient population have been reviewed. In addition, the review presents a discussion of environmentally friendly analytical methods for daptomycin, which are necessary to reduce the impact of our activities on the environment. However, it was observed that there is a gap in the literature in this regard and further research involving the development of "green" methodologies for the analysis of daptomycin is necessary. The review will be useful to the clinical community in assisting with the responsible use of daptomycin, which is critical to prevent the emergence of resistant strains.

Pharmacokinetics of Cefepime in Patients with Cancer and Febrile Neutropenia in the Setting of Hematologic Malignancies or Hematopoeitic Cell Transplantation

STUDY OBJECTIVE

To evaluate the steady-state pharmacokinetic parameters of standard cefepime dosing regimens in a hematologic malignancy and hematopoietic cell transplant patient population with febrile neutropenia.

DESIGN

Open-label, single-center, prospective pharmacokinetic study.

SETTING

National Cancer Institute-designated cancer center.

PATIENTS

Nine adults with hematologic malignancies or hematopoietic cell transplants who had febrile neutropenia and were admitted to a hematology-oncology service between January and July 2014.

INTERVENTION

Patients received empirical cefepime 2 g every 8 hours, administered as a 30-minute intravenous infusion, for febrile neutropenia.

MEASUREMENTS AND MAIN RESULTS

Steady-state cefepime serum concentrations were measured after at least 2 days of continuous therapy. Venous blood samples were intensively sampled between 0 and 8 hours after the start of the 30-minute infusion at steady state. Seven of the nine patients had a hematologic malignancy diagnosis of acute leukemia, lymphoma, or myeloma, and two patients had a germ cell tumor diagnosis. Noncompartmental analysis revealed mean ± SD parameters as follows at steady state: area under the plasma concentration-time curve from 0-8 hours 222.9 ± 72.9 mg hour/L, maximum concentration 120.9 ± 21.8 mg/L, clearance 9.7 ± 3.7 L/hour, apparent volume of distribution 19.2 ± 4.65 L, and elimination half-life 1.4 ± 0.3 hours. A one-compartment pharmacokinetic model identified a mean ± SD volume of distribution of 20.9 ± 1.3 L and an elimination rate constant of 0.39 ± 0.03 hour(-1) . The mean estimated percentage of time that drug concentration remains above the pathogen minimum inhibitory concentration (fT>MIC) in serum was 55%, 77%, and 99% at MICs of 16, 8, and 4 mg/L, respectively.

CONCLUSION

Patients with hematologic malignancies or hematopoietic cell transplants who had febrile neutropenia demonstrated homogeneous calculated cefepime volumes and clearances. The population parameters presented in this study may aid in the calculation of patient-specific fT>MIC for similar patients.

Population pharmacokinetics of arbekacin in different infectious disease settings and evaluation of dosing regimens

The efficacy of arbekacin in patients with MRSA infections is influenced by the peak concentration (Cpeak)/MIC ratio (≧8). A daily arbekacin dose of 4-6 mg/kg is primarily used for the treatment of MRSA infection. However, clinical pharmacokinetic studies of arbekacin that evaluate changes in patients with different infectious diseases have been limited. This study was to evaluate the pharmacokinetics of arbekacin in different infectious diseases and to evaluate its dosing regimens. This work describes a single-centre, retrospective study. The pharmacokinetic parameters of arbekacin were calculated from individual serum-concentration data using WinNonlin ver. 6.3. A total of 331 serum samples were obtained from 170 patients. Our drug concentration-time data were well described by a two-compartment open model. The final model showed that drug clearance was related to creatinine clearance and that the total distribution volume (Vd) was related to actual body weight and the presence of bacteremia. The individual Vd in bacteremia patients was significantly higher than those of other patients (bacteremia: 29.7 ± 0.5 L, pneumonia: 20.8 ± 0.4 L, other infections: 21.4 ± 0.4 L; p < 0.05). Additionally, Monte Carlo simulation showed that target (Cpeak/MIC ≧ 8) attainment was only 10.1%, even at a dose of 6 mg/kg, especially for MRSA bacteremia patients with an arbekacin MIC = 2 μg/mL. In conclusion, our study revealed that the Vd may be higher in bacteremia patients than in patients with other infectious diseases. Therefore, an increase in the daily dose of arbekacin should be considered for bacteremia patients.

Daptomycin for Gram-positive Infections in Patients with Neutropenia: Clinical Experience from a European Outcomes Registry

Introduction

The aim of this analysis was to describe in real-world settings the clinical outcomes and safety associated with daptomycin treatment in patients with neutropenia and Gram-positive infections.

Methods

Patients with an absolute neutrophil count (ANC) ≤1000 cells/mm³ who received at least one dose of daptomycin between 2006 and 2012 were selected from a non-interventional, multicenter, retrospective registry (European Cubicin^® Outcome Registry and Experience; EU-CORE^SM).

Results

Of the 6075 patients enrolled in EU-CORE, 446 (7.3%) had an ANC ≤ 1000 cells/mm³ at baseline or during daptomycin therapy; they were all included in efficacy and safety populations. Half of the patients had severe neutropenia (ANC ≤ 100 cells/mm³). Most patients had hematologic malignancy (60.5%), an immunosuppressed state (39.7%) or had undergone a transplant (27.8%). The most common primary infections were bacteremia (42.2%) and complicated skin and soft tissue infection (13.9%). Cultures were positive for 68.6% (254/370) of patients with available culture results; coagulase-negative staphylococci (43.7%; 111/254) and Staphylococcus aureus (18.9%; 48/254) were the most commonly isolated primary pathogens. Median duration of daptomycin therapy was 10.0 (range 1–98) days. Most patients (82.8%) received antibiotics concomitantly with daptomycin; the most common were carbapenems (51.2%), penicillins (42.1%), and aminoglycosides (19.9%). The overall clinical success rate (cured or improved) associated with daptomycin was 77.1%. Adverse events possibly related to daptomycin treatment were reported in seven (1.6%) patients and led to drug discontinuation in 27 (6.1%) patients.

Conclusion

The study results suggest that daptomycin is an effective therapeutic option for the treatment of a broad range of Gram-positive infections in patients with neutropenia, and has a good safety profile.

Funding

This study was funded by Novartis Pharma AG.

Electronic supplementary material

The online version of this article (doi:10.1007/s12325-015-0231-3) contains supplementary material, which is available to authorized users.

Rapid Turbidimetric Assay to Determine the Potency of Daptomycin in Lyophilized Powder

Daptomycin is an important antimicrobial for clinical practice, mainly because it remains very active against Gram-positive resistant strains, such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci. Development of microbiological methods for the analysis of antimicrobials is highly recommended, since they can provide important information about their biological activities, which physicochemical methods are not able to provide. Considering that there are no studies in the literature describing microbiological methods for the analysis of daptomycin, the aim of this work was to validate a microbiological method for the quantitation of daptomycin by the turbidimetric assay. Staphylococcus aureus was used as the test microorganism, and the brain heart infusion broth was used as the culture medium. The validation of the method was performed according to the ICH guidelines, and it was shown to be linear, precise, robust, accurate and selective, over a concentration range of 8.0 to 18.0 µg mL-1. Student's t-test showed the interchangeability of the proposed method with a previously-validated HPLC method. The developed turbidimetric method described in this paper is a convenient alternative for the routine quality control of daptomycin in its pharmaceutical dosage form.

Origin of de novo daptomycin non susceptible enterococci

The emergence of daptomycin non-susceptible enterococci (DNSE) poses both treatment and infection control challenges. Clinicians should be vigilant that DNSE may be isolated from patients with or without (de novo DNSE) prior use of daptomycin. Recent epidemiological data suggest the presence of a community reservoir for DNSE which may be associated with environmental, foodborne and agricultural exposures. The mechanisms of nonsusceptibility to daptomycin have not been well characterized and may not parallel those for Staphylococcus aureus. The identification of daptomycin resistance genes in anaerobes, in farm animals and in an ecosystem that has been isolated for million years, suggest that the environmental reservoir for de novo DNSE may be larger than previously thought. Herein, the limited available scientific evidence regarding the possible origin of de novo DNSE is discussed. The current existing evidence is not sufficient to draw firm conclusions on the origin of DNSE. Further studies to determine the mechanisms of de novo daptomycin nonsusceptibility among enterococci are needed.

Impact of hospital guideline for weight-based antimicrobial dosing in morbidly obese adults and comprehensive literature review

WHAT IS KNOWN AND OBJECTIVE

Obesity is a significant burden on the healthcare system in the United States, and determining the appropriate antimicrobial dosing regimen in morbidly obese patients is challenging. Morbidly obese patients have documented differences in pharmacokinetic and pharmacodynamic properties compared to normal-weight patients, which impact antibiotic efficacy and toxicity. The Food and Drug Administration does not recognize obesity as a special population and does not require pharmaceutical companies to perform studies specific to obese patients. However, there are an increasing number of post-approval studies in obese patients, and this manuscript reviews available clinical and pharmacokinetic literature regarding weight-based antimicrobial agents. Additionally, we describe a single-centre approach to optimize dosing in morbidly obese patients.

METHODS

A comprehensive literature search was performed on 15 weight-based antimicrobials in the setting of obesity: acyclovir, aminoglycosides, amphotericin B, cidofovir, colistimethate, daptomycin, flucytosine, foscarnet, ganciclovir, quinupristin/dalfopristin, trimethoprim/sulfamethoxazole, vancomycin and voriconazole. A weight-based antimicrobial dosing guideline for morbidly obese patients was developed. An analysis of guideline compliance and cost analysis were performed following guideline implementation.

RESULTS AND DISCUSSION

This review describes the pharmacokinetic changes that occur in obese patients, including increased volume of distribution, altered hepatic metabolism, renal excretion and changes in protein binding. The majority of weight-based antimicrobials result in increased serum concentrations in morbidly obese patients compared to normal-weight patients when the calculated dose is based on actual body weight.

WHAT IS NEW AND CONCLUSION

This review demonstrates different antibiotic pharmacokinetic properties are altered in obese patients that could impact efficacy and toxicity. A single-centre guideline for weight-based antimicrobial dosing in obesity was developed and provides recommendations for using ideal body weight, adjusted body weight or actual body weight when calculating antimicrobial doses. However, more research is needed to better elucidate optimal dosing of weight-based antimicrobials in obesity, with particular focus on efficacy and toxicity.

Antimicrobial treatment of febrile neutropenia: pharmacokinetic-pharmacodynamic considerations

Patients with cancer or hematologic diseases are particularly at risk of infection leading to high morbidity, mortality and costs. Extensive data show that optimization of the administration of antimicrobials according to their pharmacokinetic and pharmacodynamic parameters improves clinical outcome. Evidence is growing that when pharmacokinetic and pharmacodynamic parameters are used to target not only clinical cure but also eradication, the selection resistance is also contained. This is of particular importance in patients with neutropenia in whom increasing rates of drug-resistant Gram-negative bacteria have been reported, particularly Pseudomonas aeruginosa. Based on experimental and clinical studies, pharmacokinetic and pharmacodynamic parameters are discussed in this review for each antibiotic used in febrile neutropenia in order to help physicians improve dosing and optimization of antimicrobial agents.

Population pharmacokinetics and dosing optimization of vancomycin in children with malignant hematological disease

An increase in vancomycin dose has been proposed in adults with malignant hematological disease. As pediatric data are limited, our aim was to evaluate the population pharmacokinetics of vancomycin in order to define the appropriate dosing regimen in children with malignant hematological disease. Vancomycin concentrations were collected prospectively during therapeutic monitoring. Population pharmacokinetic analysis was performed using NONMEM software. Seventy children (age range, 0.3 to 17.7 years) were included. With the current recommended dosing regimen of 40 to 60 mg/kg/day, 53 children (76%) had subtherapeutic steady-state trough concentrations (Css/min of <10 mg/liter). A one-compartment model with first-order elimination was developed. Systematic covariate analysis identified that weight significantly influenced clearance (CL) and volume of distribution (V) with power functions of 0.677 for CL and 0.838 for V. Vancomycin CL also significantly increased with increases in creatinine clearance and seemed to be higher in children with malignant hematological disease than in the general pediatric population. The model was validated internally. Its predictive performance was further confirmed in an external validation by Bayesian estimation. A patient-tailored dosing regimen was developed based on the final pharmacokinetic model and showed that a higher proportion of patients reached the target Css/min than with the traditional mg/kg-basis dose (60% versus 49%) and that the risks associated with underdosing or overdosing were reduced. This is the first population pharmacokinetic study of vancomycin in children with malignant hematological disease. An optimized dosing regimen, taking into account patient weight, creatinine clearance, and susceptibility of the pathogens involved, could routinely be used to individualize vancomycin therapy in this vulnerable population.

Daptomycin use in neutropenic patients with documented gram-positive infections

PURPOSE

The goal of this study was to describe the outcomes associated with daptomycin treatment of documented gram-positive infections in patients with neutropenia.

METHODS

All patients with neutropenia (≤500 cells/m(3)) and at least one documented gram-positive culture from 2006-2009 were identified from a retrospective, multicenter, and observational registry (Cubicin(®) Outcome Registry and Experience (CORE(®))). Investigators assessed patient outcome (cured, improved, failed, nonevaluable) at the end of daptomycin therapy. All patients were included in the safety analysis.

RESULTS

The efficacy population had 186 patients; 159 (85 %) patients had either cure (n = 108, 58 %) or improved (n = 51, 27 %) as an outcome. Success rates (cure plus improved) by the lowest WBC during daptomycin were 98/116 (84 %) for ≤100 cells/m(3) and 61/70 (87 %) for 101-499 cells/m(3), P = 0.6. Most patients had cancer; 135/186 (73 %) had hematological malignancy; 26/186 (14 %) had solid tumors, and 9 (5 %) had both. One hundred fifty-six (84 %) patients received other antibiotics before daptomycin treatment; 82 % vancomycin, of which 31 % failed vancomycin. The most common infections were bacteremia (78 %), skin and skin structure infections (8 %), and urinary tract infections/pyelonephritis (6 %). The most common pathogens were vancomycin-resistant Enterococcus faecium (47 %), methicillin-resistant Staphylococcus aureus (20 %), and coagulase-negative staphylococci (19 %). The median (min, max) initial daptomycin dose was 6 mg/kg (3.6, 8.3). The median (min, max) daptomycin duration of therapy was 14 days (1, 86). Possibly related adverse events occurred in 12/209 patients (6 %), and 13 patients (6 %) discontinued daptomycin due to adverse event.

CONCLUSIONS

The results suggest that daptomycin appeared useful and well tolerated in neutropenic patients, and the degree of neutropenia did not affect daptomycin success rates. Comparative clinical trials are needed to confirm these findings.

Pharmacokinetics of daily daptomycin in critically ill patients undergoing continuous renal replacement therapy

BACKGROUND

The optimal daptomycin dosing regimen for critically ill patients undergoing continuous renal replacement therapy (CRRT) has still to be established.

METHODS

Daptomycin pharmacokinetics was determined in 9 patients after administration of 6 mg/kg/day over 5 days.

RESULTS

At steady state, which was reached by day 3, the area under the curve over 24 h (AUC24h) was 667.4 ± 356.6 mg·h/l, and the maximum concentration (Cmax) was 66.9 ±25.3 mg/l. Mean CRRT clearance accounted for 48% (range 32-67%) of total clearance (mean 10.2 ml/min, range 6.1-18 ml/min). Significant correlations were observed between Cmax, minimum concentration (Cmin) and AUC24h (R(2) = 0.91, p < 0.001, and R(2) = 0.94, p < 0.001) and between albumin plasma concentration and free daptomycin (R(2) = 0.7, p = 0.009).

CONCLUSION

No significant accumulation occurred with a daily daptomycin dose of 6 mg/kg in patients undergoing CRRT with an effluent flow rate of >30 ml/kg/h. The quantification of trough concentrations (Cmin) appears to be a good surrogate to estimate AUC24h and to monitor daptomycin treatment in patients undergoing CRRT.

Simultaneous quantification of antimicrobial agents for multidrug-resistant bacterial infections in human plasma by ultra-high-pressure liquid chromatography-tandem mass spectrometry

Antibiotic-resistant bacterial infection is one of the most serious clinical problems worldwide. Vancomycin, teicoplanin, daptomycin, and colistin are glycopeptide and lipopeptide antibiotics that are frequently used to treat multidrug-resistant bacterial infections. Therapeutic drug monitoring is recommended to ensure both safety and efficacy and to improve clinical outcomes. This study developed a fast, simple, and sensitive ultra-high-pressure liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method for the simultaneous determination of the concentrations of these four drugs in human plasma. The sample preparation process includes a simple protein denaturation step using acetonitrile, followed by an 11-fold dilution with 0.1% formic acid. Eight target peaks for the four drugs can be analyzed within 3 min using a Kinetex™ 2.6 μm C18 column. The mass spectrometry parameters were optimized, and two transitions for each target peak were used for multiple reaction monitoring, which provided high sensitivity and specificity. The UHPLC-MS/MS method was validated over clinical concentration ranges. The intra-day and inter-day precisions for the ratio of the peak area of each analyte to the peak area of the internal standard were all below 12.7 and 14.7% relative standard deviations, respectively. The accuracy at low, medium, and high concentrations of the eight target peaks was between 89.3 and 110.7%. The standard curves for the analytes were linear and had coefficients of determination higher than 0.997. The limits of detection were all below 70 ng mL(-1). The use of this method to analyze patient plasma samples confirmed that it is effective for the therapeutic drug monitoring of these four drugs and can be used to improve the therapeutic efficacy and safety of treatment with antibiotics.

Population pharmacokinetics of daptomycin in patients affected by severe Gram-positive infections

A population pharmacokinetic analysis of daptomycin was performed based on therapeutic drug monitoring (TDM) data from 58 patients receiving doses of 4-12 mg/kg for the treatment of severe Gram-positive infections. At a daily dose of 8 mg/kg, daptomycin plasma concentrations (mean ± S.D.) were 76.9 ± 9.8 mg/L at the end of infusion and 52.7 ± 15.4 mg/L and 11.4 ± 5.4 mg/L at 0.5 h and 23 h after drug administration, respectively. The final model was a one-compartmental model with first-order elimination, with estimated clearance (CL) of 0.80 ± 0.14 L/h and a volume of distribution (V(d)) of 0.19 ± 0.05 L/kg. Creatinine clearance (CL(Cr)) was identified as having a significant influence on daptomycin CL, and a decrease in CL(Cr) of 30 mL/min from the median value (80 mL/min) was associated with a reduction of daptomycin CL from 0.80 L/h to 0.73 L/h. These results confirm that the presence of severe infection may be associated with an altered disposition of daptomycin, with an increased Vd. MICs were available in 41 patients and results showed that 38 and 31 subjects achieved AUC/MIC values associated with bacteriostatic (>400) and bactericidal effects (>800), respectively. Of note, 31 of these 41 subjects experienced a clinical improvement or were cured. Although daptomycin pharmacokinetics may be influenced by infections, effective AUC/MIC values were achieved in the majority of patients. The present model may be applied in clinical settings for a TDM routine on the basis of a sparse blood sampling protocol.

Meta-analysis of randomized controlled trials of vancomycin for the treatment of patients with gram-positive infections: focus on the study design

OBJECTIVE

To study the effectiveness and safety of vancomycin compared with that of other antibiotics for the treatment of gram-positive infections.

METHODS

Major electronic databases were searched. Data from published randomized controlled trials (January 1, 1950, to September 15, 2011) were pooled using a meta-analytic method.

RESULTS

Fifty-three trials comparing vancomycin with linezolid, daptomycin, quinupristin-dalfopristin, tigecycline, ceftaroline, ceftobiprole, telavancin, teicoplanin, iclaprim, and dalbavancin were included in the meta-analysis. Individual antibiotics were as effective as vancomycin, except for linezolid, which was more effective than vancomycin for the treatment of skin and soft tissue infections (odds ratio [OR], 1.61; 95% confidence interval [CI], 1.07-2.43). Comparators were as effective as vancomycin in the intent-to-treat population (OR, 1.08; 95% CI, 0.98-1.18) but were more effective in the clinically evaluable population (OR, 1.14; 95% CI, 1.02-1.27) when all infections were pooled. When available data from all trials were pooled, no differences were noted when patients with febrile neutropenia (OR, 1.07; 95% CI, 0.82-1.39), pneumonia (OR, 1.10; 95% CI, 0.87-1.37), bacteremia (OR, 1.05; 95% CI, 0.76-1.45), and skin and soft tissue infections (OR, 1.11; 95% CI, 0.89-1.39) were studied. Comparators were more effective in open-label (OR, 1.28; 95% CI, 1.08-1.50) but not in double-blind trials (OR, 1.04; 95% CI, 0.90-1.20). Total adverse events attributed to studied antibiotics (OR, 1.07; 95% CI, 0.90-1.28) and patients withdrawn from trials (OR, 0.86; 95% CI, 0.68-1.09) were similar in the compared groups. Mortality was not different between vancomycin and comparator antibiotics when all trials were included in the analysis (OR, 1.09; 95% CI, 0.96-1.23). Comparators were associated with higher mortality in open-label (OR, 1.27; 95% CI, 1.05-1.54) but not double-blind trials (OR, 0.96; 95% CI, 0.80-1.14).

CONCLUSION

On the basis mainly of data from open-label trials, vancomycin is a treatment choice that is as effective as other available antibiotics for patients with gram-positive infections. Study design seems to make a major contribution to the outcome.

Management of gram-positive bacterial infections in patients with cancer

Bacterial infections, particularly those due to gram-positive bacteria, continue to predominate in patients with cancer. Coagulase-negative and coagulase-positive staphylococci and enterococci remain as common pathogenic microorganisms. Clostridium difficile has emerged as a significant pathogen. Major clinical syndromes include vascular catheter-related infection, febrile neutropenia, diarrhea and colitis. Rising antimicrobial resistance among gram-positive bacteria is of serious concern. The clinical utility of penicillin against streptococci and vancomycin against coagulase-negative and coagulase-positive staphylococci and enterococci may be rapidly diminishing. Liberal empiric use of vancomycin during neutropenic fever needs careful reconsideration. Newer promising anti-gram-positive bacterial drugs with activity against methicillin-resistant staphylococci include daptomycin, linezolid, tigecycline and telavancin. However, toxicity concerns, limited data in immunocompromised populations and high cost prevent the widespread use of these drugs among patients with cancer.

Case report of a successful treatment of methicillin-resistant Staphylococcus aureus (MRSA) bacteremia and MRSA/vancomycin-resistant Enterococcus faecium cholecystitis by daptomycin

A 72-year-old man, receiving 8 mg daptomycin/kg body weight/day for methicillin-resistant Staphylococcus aureus (MRSA) bacteremia, was diagnosed with MRSA/vancomycin-resistant Enterococcus faecium (VRE) cholecystitis (daptomycin MIC values, 1 and 2 mg/liter, respectively). After the fifth drug dose, the bile concentration of daptomycin was 66 mg/liter 5 min after drug administration, with the biliary concentration/MIC values higher than 30 for both bacterial strains. Therefore, daptomycin achieved therapeutic levels in bile, hence suggesting a role for the drug in the treatment of MRSA/VRE cholecystitis.