Population pharmacokinetics of vancomycin in patients receiving extracorporeal membrane oxygenation

A Population Pharmacokinetic Model for Vancomycin in Adult Patients Receiving Extracorporeal Membrane Oxygenation Therapy

The literature on the pharmacokinetics of vancomycin in patients undergoing extracorporeal membrane oxygenation (ECMO) therapy is sparse. A population pharmacokinetic (PK) model for vancomycin in ECMO patients was developed using a nonlinear mixed effects modeling on the concentration–time profiles of 14 ECMO patients who received intravenous vancomycin. Model selection was based on log‐likelihood criterion, goodness of fit plots, and scientific plausibility. Identification of covariates was done using a full covariate model approach. The pharmacokinetics of vancomycin was adequately described with a two‐compartment model. Parameters included clearance of 2.83 L/hr, limited central volume of distribution 24.2 L, and low residual variability 0.67%. Findings from the analysis suggest that standard dosing recommendations for vancomycin in non‐ECMO patients are adequate to achieve therapeutic trough concentrations in ECMO patients. This further shows that ECMO minimally affects the PK of vancomycin in adults including in higher‐weight patients.

Pharmacokinetics and Dosing of Anti-infective Drugs in Patients on Extracorporeal Membrane Oxygenation: A Review of the Current Literature

PURPOSE

Extracorporeal membrane oxygenation (ECMO) is a cardiopulmonary bypass device that is used to temporarily support the most critically ill of patients with respiratory and/or cardiac failure. Infection and its sequelae may be an indication for ECMO or infections may be acquired while on ECMO and are associated with a mortality >50%. Effective therapy requires optimal dosing. However, optimal dosing can be different in patients on ECMO because the ECMO circuit can alter drug pharmacokinetics. This review assessed the current literature for pharmacokinetic data and subsequent dosing recommendations for anti-infective drugs in patients on ECMO.

METHODS

We searched the PubMed and Embase databases (1965 to February 2016) and included case reports, case series, or studies that provided pharmacokinetic data for anti-infective drugs including antibiotics, antifungals, and antivirals being used to treat patients of all age groups on ECMO. Pharmacokinetic parameters and dosing recommendations based on these data are presented.

FINDINGS

The majority of data on this topic comes from neonatal studies of antibiotics from the 1980s and 1990s. These studies generally demonstrate a larger volume of distribution due to ECMO and therefore higher doses are needed initially. More adult data are now emerging, but with a predominance of case reports and case series without comparison with critically ill controls. The available pharmacokinetic analyses do suggest that volume of distribution and clearance are unchanged in the adult population, and therefore dosing recommendations largely remain unchanged. There is a lack of data on children older than 1 year of age. The data support the importance of therapeutic drug monitoring when available in this population of patients.

IMPLICATIONS

This review found reasonably robust dosing recommendations for some drugs and scant or no data for other important anti-infectives. In order to better determine optimal dosing for patients on ECMO, a systematic approach is needed. Approaches that combine ex vivo ECMO experiments, animal studies, specialized pharmacokinetic modeling, and human clinical trials are being developed.

Pharmacokinetics of Vancomycin in Elderly Patients Aged over 80 Years

Since the 1950s, vancomycin has remained a reference treatment for severe infections caused by Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus Vancomycin is a nephrotoxic and ototoxic drug mainly eliminated through the kidneys. It has a large interindividual pharmacokinetic variability, which justifies monitoring its plasma concentrations in patients. This is especially important in patients aged over 80 years, who frequently have renal impairment. However, the pharmacokinetics of vancomycin in this population is very poorly described in the literature. The objective of this work was to propose a model able to predict the pharmacokinetics of vancomycin in very elderly people. First, a population pharmacokinetic model was carried out using the algorithm NPAG (nonparametric adaptive grid) on a database of 70 hospitalized patients aged over 80 years and treated with vancomycin. An external validation then was performed on 41 patients, and the predictive capabilities of the model were assessed. The model had two compartments and six parameters. Body weight and creatinine clearance significantly influenced vancomycin volume of distribution and body clearance, respectively. The means (± standard deviations) of vancomycin volume of distribution and clearance were 36.3 ± 15.2 liter and 2.0 ± 0.9 liter/h, respectively. In the validation group, the bias and precision were -0.75 mg/liter and 8.76 mg/liter for population predictions and -0.39 mg/liter and 2.68 mg/liter for individual predictions. In conclusion, a pharmacokinetic model of vancomycin in a very elderly population has been created and validated for predicting plasma concentrations of vancomycin.

Pharmacotherapy during pediatric extracorporeal membrane oxygenation: a review

INTRODUCTION

Pediatric critical illness and associated alterations in organ function can change drug pharmacokinetics (PK). Extracorporeal membrane oxygenation (ECMO), a life-saving therapy for severe cardiac and/or respiratory failure, causes additional PK alterations that affect drug disposition.

AREAS COVERED

The purposes of this review are to discuss the PK changes that occur during ECMO, the associated therapeutic implications, and to review PK literature relevant to pediatric ECMO. We discuss various classes of drugs commonly used for pediatric patients on ECMO, including sedatives, analgesics, antimicrobials and cardiovascular drugs. Finally, we discuss future areas of research and recommend strategies for future pediatric ECMO pharmacologic investigations.

EXPERT OPINION

Clinicians caring for pediatric patients treated with ECMO must have an understanding of PK alterations that could lead to either therapeutic failures or increased drug toxicity during this life-saving therapy. Limited data currently exist for optimal drug dosing in pediatric populations who are treated with ECMO. While there are clear challenges to conducting and analyzing data associated with clinical pharmacokinetic-pharmacodynamic studies of children on ECMO, we present techniques to address these challenges. Improved understanding of the physiology and drug disposition during ECMO combined with PK-PD modeling will allow for more adaptable and individualized dosing schemes.

Pharmacometric Approaches to Personalize Use of Primarily Renally Eliminated Antibiotics in Preterm and Term Neonates

Sepsis remains a major cause of mortality and morbidity in neonates, and, as a consequence, antibiotics are the most frequently prescribed drugs in this vulnerable patient population. Growth and dynamic maturation processes during the first weeks of life result in large inter- and intrasubject variability in the pharmacokinetics (PK) and pharmacodynamics (PD) of antibiotics. In this review we (1) summarize the available population PK data and models for primarily renally eliminated antibiotics, (2) discuss quantitative approaches to account for effects of growth and maturation processes on drug exposure and response, (3) evaluate current dose recommendations, and (4) identify opportunities to further optimize and personalize dosing strategies of these antibiotics in preterm and term neonates. Although population PK models have been developed for several of these drugs, exposure-response relationships of primarily renally eliminated antibiotics in these fragile infants are not well understood, monitoring strategies remain inconsistent, and consensus on optimal, personalized dosing of these drugs in these patients is absent. Tailored PK/PD studies and models are useful to better understand relationships between drug exposures and microbiological or clinical outcomes. Pharmacometric modeling and simulation approaches facilitate quantitative evaluation and optimization of treatment strategies. National and international collaborations and platforms are essential to standardize and harmonize not only studies and models but also monitoring and dosing strategies. Simple bedside decision tools assist clinical pharmacologists and neonatologists in their efforts to fine-tune and personalize the use of primarily renally eliminated antibiotics in term and preterm neonates.

Pharmacokinetics of Continuous Infusion Meropenem With Concurrent Extracorporeal Life Support and Continuous Renal Replacement Therapy: A Case Report

Pharmacokinetic parameters can be significantly altered for both extracorporeal life support (ECLS) and continuous renal replacement therapy (CRRT). This case report describes the pharmacokinetics of continuous-infusion meropenem in a patient on ECLS with concurrent CRRT. A 2.8-kg, 10-day-old, full-term neonate born via spontaneous vaginal delivery presented with hypothermia, lethargy, and a ~500-g weight loss from birth. She progressed to respiratory failure on hospital day 2 (HD 2) and developed sepsis, disseminated intravascular coagulation, and liver failure as a result of disseminated adenoviral infection. By HD 6, acute kidney injury was evident, with progressive fluid overload >1500 mL (+) for the admission. On HD 6 venoarterial ECLS was instituted for lung protection and fluid removal. On HD 7 she was initiated on CRRT. On HD 12, a blood culture returned positive and subsequently grew Pseudomonas aeruginosa with a minimum inhibitory concentration (MIC) for meropenem of 0.25 mg/L. She was started on vancomycin, meropenem, and amikacin. A meropenem bolus of 40 mg/kg was given, followed by a continuous infusion of 10 mg/kg/hr (240 mg/kg/day). On HD 15 (ECLS day 9) a meropenem serum concentration of 21 mcg/mL was obtained, corresponding to a clearance of 7.9 mL/kg/min. Repeat cultures from HDs 13 to 15 (ECLS days 7-9) were sterile. This meropenem regimen was successful in providing a target attainment of 100% for serum concentrations above the MIC for ≥40% of the dosing interval and was associated with a sterilization of blood in this complex patient on concurrent ECLS and CRRT circuits.

Trough Concentrations of Vancomycin in Patients Undergoing Extracorporeal Membrane Oxygenation

To investigate the appropriateness of the current vancomycin dosing strategy in adult patients with extracorporeal membrane oxygenation (ECMO), between March 2013 and November 2013, patients who were treated with vancomycin while on ECMO were enrolled. Control group consisted of 60 patients on vancomycin without ECMO, stayed in medical intensive care unit during the same study period and with the same exclusion criteria. Early trough levels were obtained within the fourth dosing, and maintenance levels were measured at steady state. A total of 20 patients were included in the analysis in ECMO group. Sixteen patients received an initial intravenous dose of 1.0 g vancomycin followed by 1.0 g every 12 hours. The non-steady state trough level of vancomycin after starting administration was subtherapeutic in 19 patients (95.00%) in ECMO group as compared with 40 patients (66.67%) in the control group (p = 0.013). Vancomycin clearance was 1.27±0.51 mL/min/kg, vancomycin clearance/creatinine clearance ratio was 0.90 ± 0.37, and elimination rate constant was 0.12 ± 0.04 h^-1. Vancomycin dosingfrequency and total daily dose were significantly increased after clinical pharmacokinetic services of the pharmacist based on calculated pharmacokinetic parameters (from 2.10 ± 0.72 to 2.90 ± 0.97times/day, p = 0.002 and from 32.54 ± 8.43 to 42.24 ± 14.62mg/kg, p = 0.014) in ECMO group in contrast with those (from 2.11 ± 0.69 to 2.37 ± 0.86 times/day, p = 0.071 and from 33.91 ± 11.85 to 31.61 ± 17.50 mg/kg, p = 0.350) in the control group.Although the elimination rate for vancomycin was similar with population parameter of non ECMO patients, the current dosing strategy of our institution for vancomycinin our ICU was not sufficient to achieve the target trough in the initial period in most patients receiving ECMO.

External Evaluation of Population Pharmacokinetic Models of Vancomycin in Neonates: The transferability of published models to different clinical settings

BACKGROUND

Vancomycin is one of the most evaluated antibiotics in neonates using modeling and simulation approaches. However no clear consensus on optimal dosing has been achieved. The objective of the present study was to perform an external evaluation of published models, in order to test their predictive performances in an independent dataset and to identify the possible study-related factors influencing the transferability of pharmacokinetic models to different clinical settings.

METHOD

Published neonatal vancomycin pharmacokinetic models were screened from the literature. The predictive performance of 6 models was evaluated using an independent dataset (112 concentrations from 78 neonates). The evaluation procedures used simulation-based diagnostics (visual predictive check [VPC] and normalized prediction distribution errors [NPDE]).

RESULTS

Differences in predictive performances of models for vancomycin pharmacokinetics in neonates were found. The mean of NPDE for 6 evaluated models were 1.35, -0.22, -0.36, 0.24, 0.66, 0.48, respectively. These differences were explained, at least partly, by taking into account the method used to measure serum creatinine concentrations. The adult conversion factor of 1.3 (enzymatic to Jaffé) was tested with an improvement in the VPC and NPDE, but it still need to be evaluated and validated in neonates. Differences were also identified between analytical methods for vancomycin.

CONCLUSION

The importance of analytical techniques for serum creatinine concentrations and vancomycin as a predictor of vancomycin concentrations in neonates has been confirmed. Dosage individualisation of vancomycin in neonates should consider not only patients' characteristics and clinical conditions, but also the methods used to measure serum creatinine and vancomycin.

Population pharmacokinetics of vancomycin in adult Chinese patients with post-craniotomy meningitis and its application in individualised dosage regimens

PURPOSE

Vancomycin (VCM) is a first-line antibacterial drug used to treat post-craniotomy meningitis (PCM). VCM pharmacokinetic parameters are altered in PCM patients, compared to those in other patients. Although VCM population pharmacokinetics (PPK) has been reported, changes in VCM PPK in adult Chinese PCM patients remain unknown. We developed a VCM PPK model in adult Chinese PCM patients and proposed a new strategy for individualising VCM administration using this model.

METHODS

Data was obtained from a prospective study of 100 adult PCM patients in the Neurosurgery Department of the First Affiliated Hospital of Fujian Medical University. The trough concentrations at steady state were determined by enzyme multiplied immunoassay. Nonlinear mixed-effect model software was employed to develop the PPK model. The final model was evaluated using the bootstrap method and normalised prediction error distribution and through the testing of 20 independent adult PCM patients.

RESULTS

VCM clearance in PCM patients was higher than that observed in other patients. Creatinine clearance affected VCM clearance, whereas no co-administered drugs influenced VCM pharmacokinetics. Trough concentrations were accurately predicted by the final model, while the prediction errors were less than ±32 %. Moreover, a new strategy for individualising VCM regimens using the PPK model was proposed and validated.

CONCLUSIONS

A PPK model was developed to estimate the individual clearance in inpatients receiving intravenously infused VCM and could be used to develop individualised dosing of adult Chinese PCM patients.

Pharmacokinetic considerations for drugs administered in the critically ill

Significant physiological changes are common among critically ill patients. This case-based review describes the consequences of these changes on the selection and dosing of medications.

How to use vancomycin optimally in neonates: remaining questions

In neonates, vancomycin, a narrow-spectrum antibiotic, is the first choice of treatment of late-onset sepsis predominantly caused by Gram-positive bacteria (coagulase-negative staphylococci and enterococci). Although it has been used for >50 years, prescribing the right dose and dosing regimen remains a challenge in neonatal intensive care units for many reasons including high pharmacokinetic variability, increase in the minimal inhibition concentration against staphylococci, lack of consensus on dosing regimen and way of administration (continuous or intermittent), duration of treatment, use of therapeutic drug monitoring, limited data on short- and long-term toxicity, risk of mutant selection and errors of administration linked to concentrated formulations. This article highlights and discusses future research directions, with specific attention given to dosing optimization of vancomycin, including the advantages of modeling and simulation approaches.

Population Pharmacokinetics of Vancomycin in Postoperative Neurosurgical Patients

Neurosurgical procedures may damage the blood-brain barrier to allow more vancomycin distribution into the cerebrospinal fluid (CSF) from blood after intravenous administration. However, a large intersubject variability in CSF vancomycin concentration was observed. We aimed to develop a population pharmacokinetic model to guide vancomycin dosing in patients after neurosurgical operation. Blood and CSF samples were collected and determined from postoperative neurosurgical patients after vancomycin administration. A three-compartment (central, peripheral, and CSF) model was proposed to characterize the pharmacokinetics of vancomycin. A nonlinear mixed-effects modeling approach was applied to fit the blood and CSF data simultaneously. The covariate analysis found that the CSF albumin level was strongly associated with the clearance between central and CSF compartment. Visual predictive check indicated that the proposed population pharmacokinetic model agrees well with the observed vancomycin concentrations. Individualized vancomycin dosage regimens could be developed for postoperative neurosurgical patients with different CSF albumin levels through model simulations. The CSF albumin level is a determinant of CSF vancomycin concentration.

Pharmacokinetics of vancomycin in adults receiving extracorporeal membrane oxygenation

BACKGROUND/PURPOSE

Extracorporeal membrane oxygenation (ECMO) alters the pharmacokinetics (PK) of vancomycin in neonates; but data on adults is limited.

METHODS

This is a prospective, matched cohort, single center, pharmacokinetic study. For each adult patient who received vancomycin therapy in the ECMO group (with either centrifugal pump or roller pump), a control patient was matched by age (≥ 60 years or < 60 years), gender, and creatinine clearance (CLCr) in intensive care units. After vancomycin was administered for at least four doses, serial blood samples were drawn at 0.5 hours, 1 hour, 2 hours, 3 hours, 5 hours, 7 hours, 11 hours, 23 hours, 35 hours, and 47 hours post vancomycin infusion according to the dosing intervals. The serum concentration-time profile was fitted to a noncompartment model and a nonlinear mixed effect model to determine the PK parameters.

RESULTS

Twenty-two critically ill adults without renal replacement therapy were enrolled. There were no significant differences between the ECMO group and the matched group in demographics, renal function, and PK parameters. However, vancomycin clearance in the roller pump group was significantly lower than that in the matched control (0.83 ± 0.43 mL/min/kg vs. 0.97 ± 0.43 mL/min/kg, p = 0.002).

CONCLUSION

Vancomycin clearance in patients receiving ECMO with a roller pump was significantly lower than that in the matched cohort. Vancomycin PK parameters in patients on ECMO with a centrifugal pump were comparable to those in the matched control group.

[Use of ECMO in adult patients with cardiogenic shock: a position paper of the Austrian Society of Cardiology]

The use of ECMO to stabilize critically ill patients with severely depressed cardiac function and hemodynamics increased in the last years due to broader availability, better performance and easier implantation of the devices. The present guidelines of the Austrian Society of Cardiology focus on the use of ECMO in adult non-operated patients with cardiac diseases. Not only indications and contraindications are highlighted, but also the equally important issues of monitoring, complication management, measures during implantation and operation, and weaning of the devices are treated in detail. Thereby the present guidelines aim to optimize the use of ECMO in the individual centers, and aim to help current non-ECMO centers in developing a local ECMO-program or to contact ECMO-centers for discussion of individual patients.

Vancomycin population pharmacokinetics during extracorporeal membrane oxygenation therapy: a matched cohort study

Introduction

The aim of this study was to describe the population pharmacokinetics of vancomycin in critically ill patients treated with and without extracorporeal membrane oxygenation (ECMO).

Methods

We retrospectively reviewed data from critically ill patients treated with ECMO and matched controls who received a continuous infusion of vancomycin (35 mg/kg loading dose over 4 hours followed by a daily infusion adapted to creatinine clearance, CrCl)). The pharmacokinetics of vancomycin were described using non-linear mixed effects modeling.

Results

We compared 11 patients treated with ECMO with 11 well-matched controls. Drug dosing was similar between groups. The median interquartile range (IQR) vancomycin concentrations in ECMO and non-ECMO patients were 51 (28 to 71) versus 45 (37 to 71) mg/L at 4 hours; 23 (16 to 38) versus 29 (21 to 35) mg/L at 12 hours; 20 (12 to 36) versus 23 (17–28) mg/L at 24 hours (ANOVA, P =0.53). Median (ranges) volume of distribution (Vd) was 99.3 (49.1 to 212.3) and 92.3 (22.4 to 149.4) L in ECMO and non-ECMO patients, respectively, and clearance 2.4 (1.7 to 4.9) versus 2.3 (1.8 to 3.6) L/h (not significant). Insufficient drug concentrations (that is drug levels <20 mg/dL) were more common in the ECMO group. The pharmacokinetic model (non-linear mixed effects modeling) was prospectively validated in five additional ECMO-treated patients over a 6-month period. Linear regression analysis comparing the observed concentrations and those predicted using the model showed good correlation (r² of 0.67; P <0.001).

Conclusions

Vancomycin concentrations were similar between ECMO and non-ECMO patients in the early phase of therapy. ECMO treatment was not associated with significant changes in Vd and drug clearance compared with the control patients.

Predictive performance of reported population pharmacokinetic models of vancomycin in Chinese adult patients

WHAT IS KNOWN AND OBJECTIVE

There are numerous studies on population pharmacokinetics of vancomycin in adult patients. However, there is no such research for Chinese adult patients. This study was conducted to evaluate the predictive performance of reported population pharmacokinetic models of vancomycin in Chinese adult patients and to identify some models appropriate for our population.

METHODS

A literature search was conducted in PubMed to obtain the population pharmacokinetic models of vancomycin published between December 2010 and September 2012. The models were assessed using concentration data collected from Chinese patients for external validation. Models with relatively poor predictability were excluded from further analysis. The performance of the remaining models was evaluated in patients with different levels of creatinine clearance, age, body weight and sex by Bayesian method. This method was also used to compare the predictive performance based on peak concentration and trough concentration and the predictability based on different number of observed concentrations.

RESULTS

One hundred and sixty-five blood concentrations from 72 Chinese adult patients were collected retrospectively to serve as the test data set. The evaluated models included all those reported in the seven publications reviewed by Marsot et al. and three other studies published after December 2010. Three models with poor performance on external validation were excluded from the next Bayesian analysis. The distribution of covariates in the model building data set had an important effect on prediction. The predictability based on peak/trough concentration was similar among the evaluated models, and no significant difference was found using our data set except for Roberts' model. As expected, an increased number of samples improved the performance of the Bayesian prediction.

WHAT IS NEW AND CONCLUSION

With our data set, the performance of the evaluated models varied. The characteristics of the patient population and distribution of covariates should be given more consideration when choosing a model to predict blood concentrations. The model developed by Purwonugroho et al. using a data set from patients similar to ours is appropriate for Bayesian dose predictions for vancomycin concentrations in our population of Chinese adult patients.

Drug absorption, distribution, metabolism and excretion considerations in critically ill adults

INTRODUCTION

All critically ill patients require medication to treat organ dysfunction. However, the pharmacokinetics of drugs used to treat these patients is complex due to frequent alterations in drug absorption, distribution, metabolism, and excretion (ADME).

AREAS COVERED

This review examines pharmacokinetic aspects of drug administration for adult intensive care unit (ICU) patients. Specifically, the authors examine the ADME changes that occur and which should be considered by clinicians when delivering drug therapy to critically ill patients.

EXPERT OPINION

Dosage pharmacokinetics determined from single-dose or limited-duration administration studies in healthy volunteers may not apply to critically ill patients. Organ dysfunction among these patients may be due to pre-existing disease or the effects of a systemic or locoregional inflammatory response precipitated by their illness. Alterations in pharmacokinetics observed among the critically ill include altered bioavailability after enteral administration, increased volume of distribution and blood-brain barrier permeability and changes in P-glycoprotein and cytochrome P450 enzyme function. However, the effect of these changes on clinically important outcomes remains uncertain and poorly studied. Future investigations should examine not only pharmacokinetic changes among the critically ill, but also whether recognition of these changes and alterations in drug therapy directed as a consequence of their observation alters patient outcomes.

Pharmacokinetics of oseltamivir and oseltamivir carboxylate in critically ill patients receiving continuous venovenous hemodialysis and/or extracorporeal membrane oxygenation

STUDY OBJECTIVE

To investigate oseltamivir and oseltamivir carboxylate pharmacokinetics in critically ill patients who were receiving continuous venovenous hemodialysis (CVVHD) and/or extracorporeal membrane oxygenation (ECMO).

DESIGN

Prospective, open-label, pharmacokinetic study.

SETTING

Intensive care units of an academic medical center.

PATIENTS

Thirteen critically ill patients aged 13 years or older with suspected or confirmed H1N1 influenza who had a prescription for oseltamivir and were concurrently receiving CVVHD and/or ECMO between October 2009 and January 2010.

INTERVENTION

Oseltamivir 150 mg was administered nasogastrically or nasoenterically every 12 hours. Blood samples were collected at baseline and at 1, 2, 4, 6, 8, 10, and 12 hours after administration of the fourth oseltamivir dose or subsequent doses. In patients receiving CVVHD, effluent also was collected at the same time points. Urine was collected throughout the 12-hour dosing interval.

MEASUREMENTS AND MAIN RESULTS

Eight patients received CVVHD only, four patients received both CVVHD and ECMO, and one patient received ECMO only. Pharmacokinetic parameters for the patient who received only ECMO were not reported. The median maximum plasma concentration and area under the plasma concentration-time curve for the 12-hour dosing interval (AUC(0-12) ) for the remaining 12 patients were 83.4 ng/ml and 216 ng•hour/ml, respectively, for oseltamivir and 2000 ng/ml and 21,500 ng•hour/ml, respectively, for oseltamivir carboxylate. Mean clearance due to CVVHD was 33.8 ml/minute for oseltamivir and 50.2 ml/minute for oseltamivir carboxylate. For patients who received ECMO, no substantial differences between pre- and post-ECMO oxygenator plasma concentrations were found for oseltamivir or oseltamivir carboxylate.

CONCLUSION

Although the optimal pharmacokinetic-pharmacodynamic targets for oseltamivir carboxylate remain unclear, in the patients receiving CVVHD with or without ECMO, a regimen of oseltamivir 150 mg every 12 hours yielded a median oseltamivir carboxylate AUC(0-12) considerably higher than would be expected in non-critically ill patients receiving the same dosage regimen.

Effect of hypothermia and extracorporeal life support on drug disposition in neonates

Extracorporeal membrane oxygenation (ECMO) is a valuable treatment modality in neonates with reversible cardiopulmonary failure in therapy-resistant pulmonary hypertension after perinatal asphyxia, septic shock or ECMO cardiopulmonary resuscitation. Neonates with severe perinatal asphyxia are currently treated with therapeutic hypothermia to improve neurological outcome. Consequently, therapeutic hypothermia may be indicated in the neonatal ECMO population. Both ECMO and hypothermia have been associated with changes in drug disposition. However, little is known about the combined effects of these treatment modalities. This review will explore the available literature, identify possible changes in pharmacokinetics and make suggestions for future research directions.

Sequestration of drugs in the circuit may lead to therapeutic failure during extracorporeal membrane oxygenation

Introduction

Extracorporeal membrane oxygenation (ECMO) is a supportive therapy, with its success dependent on effective drug therapy that reverses the pathology and/or normalizes physiology. However, the circuit that sustains life can also sequester life-saving drugs, thereby compromising the role of ECMO as a temporary support device. This ex vivo study was designed to determine the degree of sequestration of commonly used antibiotics, sedatives and analgesics in ECMO circuits.

Methods

Four identical ECMO circuits were set up as per the standard protocol for adult patients on ECMO. The circuits were primed with crystalloid and albumin, followed by fresh human whole blood, and were maintained at a physiological pH and temperature for 24 hours. After baseline sampling, fentanyl, morphine, midazolam, meropenem and vancomycin were injected into the circuit at therapeutic concentrations. Equivalent doses of these drugs were also injected into four polyvinylchloride jars containing fresh human whole blood for drug stability testing. Serial blood samples were collected from the ECMO circuits and the controls over 24 hours and the concentrations of the study drugs were quantified using validated assays.

Results

Four hundred samples were analyzed. All study drugs, except meropenem, were chemically stable. The average drug recoveries from the ECMO circuits and the controls at 24 hours relative to baseline, respectively, were fentanyl 3% and 82%, morphine 103% and 97%, midazolam 13% and 100%, meropenem 20% and 42%, vancomycin 90% and 99%. There was a significant loss of fentanyl (p = 0.0005), midazolam (p = 0.01) and meropenem (p = 0.006) in the ECMO circuit at 24 hours. There was no significant circuit loss of vancomycin at 24 hours (p = 0.26).

Conclusions

Sequestration of drugs in the circuit has implications on both the choice and dosing of some drugs prescribed during ECMO. Sequestration of lipophilic drugs such as fentanyl and midazolam appears significant and may in part explain the increased dosing requirements of these drugs during ECMO. Meropenem sequestration is also problematic and these data support a more frequent administration during ECMO.

The impact of extracorporeal life support and hypothermia on drug disposition in critically ill infants and children

Extracorporeal membrane oxygenation (ECMO) support is an established lifesaving therapy for potentially reversible respiratory or cardiac failure. In 10% of all pediatric patients receiving ECMO, ECMO therapy is initiated during or after cardiopulmonary resuscitation. Therapeutic hypothermia is frequently used in children after cardiac arrest, despite the lack of randomized controlled trials that show its efficacy. Hypothermia is frequently used in children and neonates during cardiopulmonary bypass (CPB). By combining data from pharmacokinetic studies in children on ECMO and CPB and during hypothermia, this review elucidates the possible effects of hypothermia during ECMO on drug disposition.

Pharmacokinetics and safety of fluconazole in young infants supported with extracorporeal membrane oxygenation

BACKGROUND

Candida infections are a leading cause of infectious disease-related death in infants supported with extracorporeal membrane oxygenation (ECMO). The ECMO circuit can alter drug pharmacokinetics; thus, standard fluconazole dosing in children on ECMO may result in suboptimal drug exposure. This study determined the pharmacokinetics of fluconazole in infants on ECMO.

METHODS

Infants <120 days of age received either intravenous fluconazole prophylaxis (25 mg/kg once a week) or treatment (12 mg/kg daily) while on ECMO. Paired plasma samples were collected preoxygenator and postoxygenator around doses 1 and 2 to calculate pharmacokinetic indices and describe oxygenator extraction. A 1-compartment model was fit to the data using nonlinear regression. Surrogate pharmacodynamic targets for efficacy were evaluated.

RESULTS

Ten infants were enrolled. After dose 1 (n = 9), the median clearance was 17 mL/kg/h, the median volume of distribution was 1.5 L/kg and the median exposure in the first 24 hours (area under the curve from 0 to 24 hours) was 322 h × mg/L. After multiple doses (n = 7), the median clearance was 22 mL/kg/h, the median volume of distribution was 1.9 L/kg and the area under the curve from 0 to 24 hours was 352 h × mg/L. After dose 1, 78% of infants achieved the prophylaxis target, whereas only 11% achieved the therapeutic target. Oxygenator extraction of fluconazole was minimal (-2.0%, standard deviation 15.0), and extraction was not correlated with age of the ECMO circuit (ρ= -0.05). There were no adverse events related to fluconazole.

CONCLUSIONS

Infants on ECMO had higher volume of distribution but similar clearance when compared with historical controls not on ECMO. In infants on ECMO, a fluconazole dose of 25 mg/kg weekly provides adequate exposure for prophylaxis against Candida infections. However, higher doses may be needed for treatment.

Clinical pharmacokinetics of vancomycin in the neonate: a review

Neonatal sepsis is common and is a major cause of morbidity and mortality. Vancomycin is the preferred treatment of several neonatal staphylococcal infections. The aim of this study was to review published data on vancomycin pharmacokinetics in neonates and to provide a critical analysis of the literature. A bibliographic search was performed using PubMed and Embase, and articles with a publication date of August 2011 or earlier were included in the analysis. Vancomycin pharmacokinetic estimates, which are different in neonates compared with adults, also exhibit extensive inter-neonatal variability. In neonates, several vancomycin dosing schedules have been proposed, mainly based on age (i.e., postmenstrual and postnatal), body weight or serum creatinine level. Other covariates [e.g., extracorporeal membrane oxygenation (ECMO), indomethacin or ibuprofen, and growth restriction] of vancomycin pharmacokinetics have been reported in neonates. Finally, vancomycin penetrates cerebrospinal fluid (range = 7-42%). Renal function drives vancomycin pharmacokinetics. Because either age or weight is the most relevant covariate of renal maturation, these covariates should be considered first in neonatal vancomycin dosing guidelines and further adjusted by renal dysfunction indicators (e.g., ECMO and ibuprofen/indomethacin). In addition to the prospective validation of available dosing guidelines, future studies should focus on the relevance of therapeutic drug monitoring and on the value of continuous vancomycin administration in neonates.

Pharmacokinetic changes in patients receiving extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation (ECMO) is a form of prolonged cardiopulmonary bypass used to temporarily sustain cardiac and/or respiratory function in critically ill patients. Extracorporeal membrane oxygenation further complicates the management of critically ill patients who already have profound physiologic derangements with consequent altered pharmacokinetics. The purpose of this study is to identify and critically review the published literature describing pharmacokinetics in the presence of ECMO. This review revealed a dearth of data describing pharmacokinetics during ECMO in critically ill adults, with most of the available data originating in neonates. Of concern, the present data indicate substantial variability and a lack of predictability in drug behavior in the presence of ECMO. The most common mechanisms by which ECMO affects pharmacokinetics are sequestration in the circuit, increased volume of distribution, and decreased drug elimination. While lipophilic drugs and highly protein-bound drugs (eg, voriconazole and fentanyl) are significantly sequestered in the circuit, hydrophilic drugs (eg, β-lactam antibiotics, glycopeptides) are significantly affected by hemodilution and other pathophysiologic changes that occur during ECMO. Although the published literature is insufficient to make any meaningful recommendations for adjusting therapy for drug dosing, this review systematically describes the available data enabling clinicians to make conclusions based on available data. Furthermore, this review serves to highlight the need for well-designed and conducted clinical and laboratory-based studies to provide the data from which robust dosing guidance can be developed to improve clinical outcomes in this most unwell cohort of patients.

Population pharmacokinetics of vancomycin in Thai patients

Population pharmacokinetics of vancomycin in Thai adult patients was determined by non-linear mixed-effects approach using 319 vancomycin serum concentrations from 212 patients. The data were best fitted by a two-compartment model and it was used to examine the effect of patient characteristics on the vancomycin pharmacokinetics. In the final model, there was a linear relationship between vancomycin clearance, CL (L/h), and creatinine clearance calculated by Cockcroft-Gault equation, CL_Cr (mL/min): CL  =0.044  ×  CL_Cr. Meanwhile, volume of central compartment, V₁ (L), was linearly related with the age (years old): V₁ = 0.542  × Age. Intercompartment clearance (Q) and volume of peripheral compartment (V₂) was 6.95 L/h and 44.2 L, respectively. The interindividual variability for CL, V₁, Q, and V₂ was 35.78, 20.93, 39.50, and 57.27%, respectively. Whereas, the intraindividual variability was 4.51 mg/L. Final model then was applied to predict serum vancomycin concentrations on validation group. Predictive performance revealed a bias of −1.43 mg/L (95% CI: −5.82–2.99) and a precision of 12.2 mg/L (95% CI: −1.60–26.16). In conclusion, population pharmacokinetic of vancomycin in Thai adult patients was developed. The model could be used to create vancomycin dosage regimen in the type of patient similar with the present study.

Vancomycin: a review of population pharmacokinetic analyses

Despite nearly five decades of clinical use, vancomycin has retained a significant and uncontested niche in the antibacterial arsenal because of its consistent activity against almost all Gram-positive bacteria. Nevertheless, major vancomycin toxicities have been reported in the literature - in particular, nephrotoxicity and ototoxicity. Vancomycin pharmacokinetics have been described in numerous studies for 25 years. This review presents a synthesis of the reported population pharmacokinetic models of vancomycin. The objective was to determine if there was a consensus on a structural model and which covariates were identified. A literature search was conducted from the PubMed database, from its inception through December 2010, using the following terms: 'vancomycin', 'pharmacokinetic(s)', 'population', 'model(ling)' and 'nonlinear mixed effect'. Articles were excluded if they were not pertinent. The reference lists of all selected articles were also evaluated. Twenty-five articles were included in this review: 15 models concerned paediatric patients and ten models were conducted in adults. In neonates and infants, the pharmacokinetics of vancomycin were mainly described by a one-compartment model, whereas in adults, a two-compartment model was preferentially used. Various covariates were tested but only three (age, creatinine clearance [CL(CR)] and body weight) were included in almost all of the described models. After inclusion of these covariates, the mean (range) values of the interindividual variability in the clearance and volume of distribution were 30% (15.6-45%) and 23% (12.6-48%), respectively. The mean (range) value of the residual variability was 20% (7-39.6%). This review highlights the numerous population pharmacokinetic models of vancomycin developed in recent decades and concludes with relevant information for clinicians and researchers. To optimize vancomycin dosage, this review points out the relevant covariates according to the target population. In adults, dosage optimization depends on CL(CR) and body weight, while in children, it depends on age, body weight and CL(CR). For future population pharmacokinetic studies, a sensitive liquid chromatography-tandem mass spectrometry method could be used and new covariates such as cardiac output or possible renal transporters could be tested. Finally, we suggest that external evaluation should be the first step in a pharmacokinetic analysis of vancomycin rather than describing a new model.

Pediatric cardiovascular drug dosing in critically ill children and extracorporeal membrane oxygenation

Cardiovascular disease in children is common and results in significant morbidity and mortality. The sickest children with cardiovascular disease may require support with extracorporeal membrane oxygenation (ECMO), which provides life-saving assistance for children with refractory cardiorespiratory failure. Many classes of cardiovascular drugs are used in children, but very few of these agents have been well studied in children. The knowledge gap is even more pronounced in children supported by ECMO. Pharmacokinetic (PK) data collected to date (primarily from antibiotics and sedatives) suggest that the ECMO circuit has the potential to significantly alter the PK of drugs including changes in clearance and volume of distribution. Of all cardiovascular drugs administered to children supported by ECMO, only 11 have been partially studied and reported in the medical literature. Esmolol, amiodarone, nesiritide, bumetanide, sildenafil, and prostaglandin E1 seem to require dosing modifications in children supported by ECMO, whereas it seems that hydralazine, nicardipine, furosemide, epinephrine, and dopamine can be dosed similarly to children not supported by ECMO. However, trials evaluating the PK of these drugs in patients supported by ECMO are extremely limited (ie, case reports), and therefore, definitive dosing recommendations are not plausible. Research efforts should focus on evaluating the PK of drugs in patients on ECMO to avoid therapeutic failures or unnecessary toxicities.

A systematic review on pharmacokinetic changes in critically ill patients: role of extracorporeal membrane oxygenation

OBJECTIVE

Several factors including disease condition and different procedures could alter pharmacokinetic profile of drugs in critically ill patients. For optimizing patient's outcome, changing in dosing regimen is necessary. Extracorporeal Membrane Oxygenation (ECMO) is one of the procedures which could change pharmacokinetic parameters.The aim of this review was to evaluate the effect of ECMO support on pharmacokinetic parameters and subsequently pharmacotherapy.

METHOD

A systematic review was conducted by reviewing all papers found by searching following key words; extracorporeal membrane oxygenation, ECMO, pharmacokinetic and pharmacotherapy in bibliography database.

RESULTS

Different drug classes have been studied; mostly antibiotics. Almost all of the studies have been performed in neonates (as a case series). ECMO support is associated with altered pharmacokinetic parameters that may result in acute changes in plasma concentrations with potentially unpredictable pharmacological effect. Altreation in volume of distribution, protein binding, renal or hepatic clearance and sequestration of drugs by ECMO circuit may result in higher or lower doses requirement during ECMO. As yet, definite dosing guideline is not available. ECMO is extensively used recently for therapy and as a procedure affects pharmacokinetics profile along with other factors in critically ill patients. For optimizing the pharmacodynamic response and outcome of patients, drug regimen should be individualized through therapeutic drug monitoring whenever possible.

Determinants of drug absorption in different ECMO circuits

Purpose

The aim of this in vitro study was to evaluate potential determinants of drug loss in different ECMO circuits.

Methods

Midazolam, morphine, fentanyl, paracetamol, cefazolin, meropenem and vancomycin were injected into three neonatal roller pump, two paediatric roller pump and two clinically used neonatal roller pump circuits, all with a silicone membrane, and two neonatal centrifugal pump circuits with polypropylene hollow-fibre membranes. Serial blood samples were taken from a post-oxygenator site. Drug recovery was calculated as the ratio between the determined and the theoretical maximum concentration. The latter was obtained by dividing dose by theoretical circuit volume.

Results

Average drug recoveries at 180 min in three neonatal silicone membrane roller pump circuits were midazolam 0.62%, morphine 23.9%, fentanyl 0.35%, paracetamol 34.0%, cefazolin 84.3%, meropenem 82.9% and vancomycin 67.8%. There was a significant correlation between the lipophilicity of the drug expressed as log P and the extent of drug absorption, p < 0.001. The recovery of midazolam and fentanyl in centrifugal pump circuits with hollow-fibre membrane oxygenator was significantly higher compared to neonatal roller pump circuits with silicone membranes: midazolam 63.4 versus 0.62%, fentanyl 33.8 versus 0.35%, p < 0.001. Oxygenator size and used circuits do not significantly affect drug losses.

Conclusions

Significant absorption of drugs occurs in the ECMO circuit, correlating with increased lipophilicity of the drug. Centrifugal pump circuits with hollow-fibre membrane oxygenators show less absorption for all drugs, most pronounced for lipophilic drugs. These results suggest that pharmacokinetics and hence optimal doses of these drugs may be altered during ECMO.

Vancomycin dosing assessment in intensive care unit patients based on a population pharmacokinetic/pharmacodynamic simulation

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT * Despite the frequent use of vancomycin in intensive care unit (ICU) patients, few studies aimed at characterizing vancomycin population pharmacokinetics have been performed in this critical population. * Population pharmacokinetics coupled with pharmacodynamic analysis, in order to optimize drug exposure and hence antibacterial effectiveness, has been little applied in these specific patients. WHAT THIS STUDY ADDS * Our population model characterized the pharmacokinetic profile of vancomycin in adult ICU patients, higher distribution volume values (V) being observed when the patient's serum creatinine (Cr(Se)) was greater than 1 mg dl(-1). * Age and creatinine clearance (CL(cr)) were identified as the main covariates explaining the pharmacokinetic variability in vancomycin CL. * Our pharmacokinetic/pharmacodynamic (PK/PD) simulation should aid clinicians to select initial vancomycin doses that will maximize the rate of response in the ICU setting, taking into account the patient's age and renal function as well as the susceptibility of Staphylococcus aureus. AIM To estimate the vancomycin pharmacokinetic profile in adult ICU patients and to assess vancomycin dosages for increasing the likelihood of optimal exposure. METHODS Five hundred and sixty-nine concentration-time data from 191 patients were analysed using a population pharmacokinetic approach (NONMEN). External model evaluation was made in 46 additional patients. The 24 h area under the concentration-time curve (AUC(0,24 h)) was derived from the final model. Minimum inhibitory concentration (MIC) values for S. aureus were obtained from the EUCAST database. AUC(0,24 h) : MIC >/= 400 was considered as PK/PD efficacy index. The probability of different dosages attaining the target considering different strains of S. aureus and patient subgroups was estimated with Monte Carlo simulation. RESULTS Vancomycin CL showed a significant dependence on patient age and renal function whereas Cr(Se) > 1 mg dl(-1) increased V more than twofold. For our representative ICU patient, 61 years, 73 kg, Cr(Se)= 1.4 mg dl(-1), measured CL(Cr)= 74.7 ml min(-1), the estimated values were CL = 1.06 ml min(-1) kg(-1) and V= 2.04 l kg(-1). The cumulative fraction of response for a standard vancomycin dose (2 g day(-1)) was less than 25% for VISA strains, and 33% to 95% for susceptible S. aureus, depending on patient characteristics. CONCLUSIONS Simulations provide useful information regarding the initial assessment of vancomycin dosing, the conventional dosing regimen probably being suboptimal in adult ICU patients. A graphic approach provides the recommended dose for any selected probability of attaining the PK/PD efficacy target or to evaluate the cumulative fraction of response for any dosing regimen in this population.

Pharmacotherapy during neonatal extracorporeal membrane oxygenation: toward an evidence-based approach

Van der Vorst and coworkers recently illustrated the large variability in furosemide regimens used in their unit. This finding at least suggests that we need more data on the pharmacokinetics and pharmacodynamics of this drug in neonates during treatment with extracorporeal membrane oxygenation, in order to ensure quality of care and safety, and to promote evidence-based prescription. The implementation of population pharmacokinetic models can further increase both the feasibility of such studies and the relevance of the results generated.

Pharmacokinetic/pharmacodynamic analysis of vancomycin in ICU patients

AIMS

To identify the variables affecting vancomycin pharmacokinetics in medical ICU patients and to evaluate the potential efficacy of dosage schedules by PK/PD analysis.

DESIGN

A retrospective pharmacokinetic analysis of serum levels obtained in routine vancomycin monitoring was performed.

SETTING

A 12-bed general ICU of a university teaching hospital.

PATIENTS

Forty-six vancomycin-treated ICU patients fitting the following criteria: over 18 years old; more than three concentration data per patient; absence of renal replacement support, cardiac surgery and neoplastic disorders.

INTERVENTIONS

Clinical information was collected from the patients' medical records. Details of vancomycin therapy, dosage and blood sampling times were obtained from pharmacokinetic reports. Population analysis were made by the standard two-stage approach.

MEASUREMENTS AND MAIN RESULTS

Vancomycin clearance and distribution volume were estimated individually assuming a one-compartment pharmacokinetic model. PK/PD analysis was performed by Monte Carlo simulation. In the ICU patients, higher Vd (nearly twice the quoted value of 0.72 l/kg) and different vancomycin clearance-creatinine clearance relationship were found. Renal function, the APACHE score, age and serum albumin accounted for more than 65% of drug clearance variability. Vancomycin standard dosages led to a 33% risk of not achieving the recommended AUC(24h)/MIC breakpoint for Staphylococcus aureus.

CONCLUSIONS

The population kinetics and PK/PD analyses based on Monte Carlo simulation procedures offer an excellent tool for selecting the therapeutic option with the highest probability of clinical success in ICU patients.