Antibiotic dosing in the 'at risk' critically ill patient: Linking pathophysiology with pharmacokinetics/pharmacodynamics in sepsis and trauma patients

Therapeutic Drug Monitoring of Antimicrobials in Critically Ill Obese Patients

Obesity is a significant global public health concern that is associated with an elevated risk of comorbidities as well as severe postoperative and nosocomial infections. The treatment of infections in critically ill obese patients can be challenging because obesity affects the pharmacokinetics and pharmacodynamics of antibiotics, leading to an increased risk of antibiotic therapy failure and toxicity due to inappropriate dosages. Precision dosing of antibiotics using therapeutic drug monitoring may help to improve the management of this patient population. This narrative review outlines the pharmacokinetic and pharmacodynamic changes that result from obesity and provides a comprehensive critical review of the current available data on dosage adjustment of antibiotics in critically ill obese patients.

Sequestration of Antimicrobial Agents in Xcoating and Heparin-Coated Extracorporeal Membrane Oxygenation Circuits: An In Vitro Study

Limited data exist to guide antimicrobial therapy commonly prescribed to patients undergoing extracorporeal membrane oxygenation (ECMO). This study aimed to describe the kinetics of the cefazolin, doripenem, daptomycin, and levofloxacin in heparin-coated and Xcoating ECMO circuits. Circuits were primed with bovine whole blood and maintained at a physiological pH and temperature for 24 h. Each antimicrobial agent was added to the whole blood before priming. Equivalent doses of these drugs were added to glass jars containing fresh bovine whole blood as a control. Serial blood samples were collected from the ECMO circuits and controls over 24 h, and drug concentrations were quantified using validated assays. The concentrations of cefazolin, doripenem, daptomycin, and levofloxacin did not decrease significantly over 24 h. Collectively, these antimicrobial agents can be administered without the need to consider sequestration when using either heparin-coated or Xcoating circuits.

β-Lactam Dosing in Critical Patients: A Narrative Review of Optimal Efficacy and the Prevention of Resistance and Toxicity

Antimicrobial prescription in critically ill patients represents a complex challenge due to the difficult balance between infection treatment and toxicity prevention. Underexposure to antibiotics and therapeutic failure or, conversely, drug overexposure and toxicity may both contribute to a worse prognosis. Moreover, changes in organ perfusion and dysfunction often lead to unpredictable pharmacokinetics. In critically ill patients, interindividual and intraindividual real-time β-lactam antibiotic dose adjustments according to the patient's condition are critical. The continuous infusion of β-lactams and the therapeutic monitoring of their concentration have both been proposed to improve their efficacy, but strong data to support their use are still lacking. The knowledge of the pharmacokinetic/pharmacodynamic targets is poor and is mostly based on observational data. In patients with renal or hepatic failure, selecting the right dose is even more tricky due to changes in drug clearance, distribution, and the use of extracorporeal circuits. Intermittent usage may further increase the dosing conundrum. Recent data have emerged linking overexposure to β-lactams to central nervous system toxicity, mitochondrial recovery delay, and microbiome changes. In addition, it is well recognized that β-lactam exposure facilitates resistance selection and that correct dosing can help to overcome it. In this review, we discuss recent data regarding real-time β-lactam antibiotic dose adjustment, options in special populations, and the impacts on mitochondria and the microbiome.

Pharmacokinetics, Pharmacodynamics, and Dosing Considerations of Novel β-Lactams and β-Lactam/β-Lactamase Inhibitors in Critically Ill Adult Patients: Focus on Obesity, Augmented Renal Clearance, Renal Replacement Therapies, and Extracorporeal Membrane Oxygenation

OBJECTIVE

Dose optimization of novel β-lactam antibiotics (NBLA) has become necessary given the increased prevalence of multidrug-resistant infections in intensive care units coupled with the limited number of available treatment options. Unfortunately, recommended dose regimens of NBLA based on PK/PD indices are not well-defined for critically ill patients presenting with special situations (i.e., obesity, extracorporeal membrane oxygenation (ECMO), augmented renal clearance (ARC), and renal replacement therapies (RRT)). This review aimed to discuss and summarize the available literature on the PK/PD attained indices of NBLA among critically ill patients with special circumstances.

DATA SOURCES

PubMed, MEDLINE, Scopus, Google Scholar, and Embase databases were searched for studies published between January 2011 and May 2022.

STUDY SELECTION AND DATA EXTRACTION

Articles relevant to NBLA (i.e., ceftolozane/tazobactam, ceftazidime/avibactam, cefiderocol, ceftobiprole, imipenem/relebactam, and meropenem/vaborbactam) were selected. The MeSH terms of "obesity", "augmented renal clearance", "renal replacement therapy", "extracorporeal membrane oxygenation", "pharmacokinetic", "pharmacodynamic" "critically ill", and "intensive care" were used for identification of articles. The search was limited to adult humans' studies that were published in English. A narrative synthesis of included studies was then conducted accordingly.

DATA SYNTHESIS

Available evidence surrounding the use of NBLA among critically ill patients presenting with special situations was limited by the small sample size of the included studies coupled with high heterogeneity. The PK/PD target attainments of NBLA were reported to be minimally affected by obesity and/or ECMO, whereas the effect of renal functionality (in the form of either ARC or RRT) was more substantial.

CONCLUSION

Critically ill patients presenting with special circumstances might be at risk of altered NBLA pharmacokinetics, particularly in the settings of ARC and RRT. More robust, well-designed trials are still required to define effective dose regimens able to attain therapeutic PK/PD indices of NBLA when utilized in those special scenarios, and thus aid in improving the patients' outcomes.

Optimizing Antimicrobial Drug Dosing in Critically Ill Patients

A fundamental step in the successful management of sepsis and septic shock is early empiric antimicrobial therapy. However, for this to be effective, several decisions must be addressed simultaneously: (1) antimicrobial choices should be adequate, covering the most probable pathogens; (2) they should be administered in the appropriate dose, (3) by the correct route, and (4) using the correct mode of administration to achieve successful concentration at the infection site. In critically ill patients, antimicrobial dosing is a common challenge and a frequent source of errors, since these patients present deranged pharmacokinetics, namely increased volume of distribution and altered drug clearance, which either increased or decreased. Moreover, the clinical condition of these patients changes markedly over time, either improving or deteriorating. The consequent impact on drug pharmacokinetics further complicates the selection of correct drug schedules and dosing during the course of therapy. In recent years, the knowledge of pharmacokinetics and pharmacodynamics, drug dosing, therapeutic drug monitoring, and antimicrobial resistance in the critically ill patients has greatly improved, fostering strategies to optimize therapeutic efficacy and to reduce toxicity and adverse events. Nonetheless, delivering adequate and appropriate antimicrobial therapy is still a challenge, since pathogen resistance continues to rise, and new therapeutic agents remain scarce. We aim to review the available literature to assess the challenges, impact, and tools to optimize individualization of antimicrobial dosing to maximize exposure and effectiveness in critically ill patients.

Optimizing the Use of Antibiotic Agents in the Pediatric Intensive Care Unit: A Narrative Review

Antibiotics are one of the most prescribed drug classes in the pediatric intensive care unit, yet the incidence of inappropriate antibiotic prescribing remains high in critically ill children. Optimizing the use of antibiotics in this population is imperative to guarantee adequate treatment, avoid toxicity and the occurrence of antibiotic resistance, both on a patient level and on a population level. Antibiotic stewardship encompasses all initiatives to promote responsible antibiotic usage and the PICU represents a major target environment for antibiotic stewardship programs. This narrative review provides a summary of the available knowledge on the optimal selection, duration, dosage, and route of administration of antibiotic treatment in critically ill children. Overall, more scientific evidence on how to optimize antibiotic treatment is warranted in this population. We also give our personal expert opinion on research priorities.

A survey of antibiotic administration practices involving patients with sepsis in UK critical care units

Background Alternative administration methods are emerging as a key area of research to improve clinical efficacy of antibiotics and address concerns regarding multi-drug resistance. Extended intermittent infusions or continuous infusions of antibiotics exhibiting time-dependent kill characteristics may be favourable in critically ill septic patients, but more evidence is needed to determine best practice. Objective To find out whether any common practice exists for intravenous antibiotic administration in critical care units across UK NHS Trusts, and identify factors influencing the adoption of extended or continuous infusions. Setting UK hospitals. Method UK critical care pharmacists were invited to participate in a survey on behalf of all 240 critical care units via a UK Clinical Pharmacy Association message board. The survey focused on administration practices for 22 antibacterial agents. Main outcome measure Antibiotic administration method. Results Responses were received covering 64 units, a response rate of 26.2%. Common, but not uniform administration methods were apparent for 17/22 antibiotics. Four antibiotics (piperacillin/tazobactam, doripenem, meropenem and vancomycin) were more likely to be administered as continuous or extended-intermittent infusions. Choice of administration method was especially influenced by altered pk/pd properties in sepsis or severe burns patients, or by the presence of organisms requiring high minimal inhibitory concentrations. Conclusion Unlicensed alternative practices of antibiotic administration are widespread but only weak evidence exists of any patient benefit, such as reduced length of stay in critical care, and none showing improvement in mortality. Further research is needed to determine whether extended infusion methods offer clinically meaningful advantages over shorter licenced administration methods in patients in critical care units.

Population Pharmacokinetics of Unbound Ceftolozane and Tazobactam in Critically Ill Patients without Renal Dysfunction

Evaluation of dosing regimens for critically ill patients requires pharmacokinetic data in this population. This prospective observational study aimed to describe the population pharmacokinetics of unbound ceftolozane and tazobactam in critically ill patients without renal impairment and to assess the adequacy of recommended dosing regimens for treatment of systemic infections. Patients received 1.5 or 3.0 g ceftolozane-tazobactam according to clinician recommendation.

Evaluation of dosing regimens for critically ill patients requires pharmacokinetic data in this population. This prospective observational study aimed to describe the population pharmacokinetics of unbound ceftolozane and tazobactam in critically ill patients without renal impairment and to assess the adequacy of recommended dosing regimens for treatment of systemic infections. Patients received 1.5 or 3.0 g ceftolozane-tazobactam according to clinician recommendation. Unbound ceftolozane and tazobactam plasma concentrations were assayed, and data were analyzed with Pmetrics with subsequent Monte Carlo simulations. A two-compartment model adequately described the data from twelve patients. Urinary creatinine clearance (CL_CR) and body weight described between-patient variability in clearance and central volume of distribution (V), respectively. Mean ± standard deviation (SD) parameter estimates for unbound ceftolozane and tazobactam, respectively, were CL of 7.2 ± 3.2 and 25.4 ± 9.4 liters/h, V of 20.4 ± 3.7 and 32.4 ± 10 liters, rate constant for distribution of unbound ceftolozane or tazobactam from central to peripheral compartment (Kcp) of 0.46 ± 0.74 and 2.96 ± 8.6 h⁻¹, and rate constant for distribution of unbound ceftolozane or tazobactam from peripheral to central compartment (Kpc) of 0.39 ± 0.37 and 26.5 ± 8.4 h⁻¹. With dosing at 1.5 g and 3.0 g every 8 h (q8h), the fractional target attainment (FTA) against Pseudomonas aeruginosa was ≥85% for directed therapy (MIC ≤ 4 mg/liter). However, for empirical coverage (MIC up to 64 mg/liter), the FTA was 84% with the 1.5-g q8h regimen when creatinine clearance is 180 ml/min/1.73 m², whereas the 3.0-g q8h regimen consistently achieved an FTA of ≥85%. For a target of 40% of time the free drug concentration is above the MIC (40% fT_>MIC), 3g q8h by intermittent infusion is suggested unless a highly susceptible pathogen is present, in which case 1.5-g dosing could be used. If a higher target of 100% fT_>MIC is required, a 1.5-g loading dose plus a 4.5-g continuous infusion may be adequate.

Use of microdialysis for the assessment of fluoroquinolone pharmacokinetics in the clinical practice

Antibacterial drugs, including fluoroquinolones, can exert their therapeutic action only with adequate penetration at the infection site. Multiple factors, such as rate of protein binding, drug liposolubility and organ blood-flow all influence ability of antibiotics to penetrate target tissues. Microdialysis is an in vivo sampling technique that has been successfully applied to measure the distribution of fluoroquinolones in the interstitial fluid of different tissues both in animal studies and clinical setting. Tissue concentrations need to be interpreted within the context of the pathogenesis and causative agents implicated in infections. Integration of microdialysis -derived tissue pharmacokinetics with pharmacodynamic data offers crucial information for correlating exposure with antibacterial effect. This review explores these concepts and provides an overview of tissue concentrations of fluoroquinolones derived from microdialysis studies and explores the therapeutic implications of fluoroquinolone distribution at various target tissues.

A Population Pharmacokinetic Analysis to Study the Effect of Extracorporeal Membrane Oxygenation on Cefepime Disposition in Children

OBJECTIVES

Limited data exist on the effects of extracorporeal membrane oxygenation on pharmacokinetics of cefepime in critically ill pediatric patients. The objective was to describe cefepime disposition in children treated with extracorporeal membrane oxygenation using population pharmacokinetic modeling.

DESIGN

Multicenter, prospective observational study.

SETTING

The pediatric and cardiac ICUs of six sites of the Collaborative Pediatric Critical Care Research Network.

PATIENTS

Seventeen critically ill children (30 d to < 2 yr old) on extracorporeal membrane oxygenation who received cefepime as standard of care between January 4, 2014, and August 24, 2015, were enrolled.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A pharmacokinetic model was developed to evaluate cefepime disposition differences due to extracorporeal membrane oxygenation. A two-compartment model with linear elimination, weight effects on clearance, intercompartmental clearance (Q), central volume of distribution (V1), and peripheral volume of distribution (V2) adequately described the data. The typical value of clearance in this study was 7.1 mL/min (1.9 mL/min/kg) for a patient weighing 5.8 kg. This value decreased by approximately 40% with the addition of renal replacement therapy. The typical value for V1 was 1,170 mL. In the setting of blood transfusions, V1 increased by over two-fold but was reduced with increasing age of the extracorporeal membrane oxygenation circuit oxygenator.

CONCLUSIONS

Cefepime clearance was reduced in pediatric patients treated with extracorporeal membrane oxygenation compared with previously reported values in children not receiving extracorporeal membrane oxygenation. The model demonstrated that the age of the extracorporeal membrane oxygenation circuit oxygenator is inversely correlated to V1. For free cefepime, only 14 of the 19 doses (74%) demonstrated a fT_minimum inhibitory concentration of 16 mg/L, an appropriate target for the treatment of pseudomonal infections, for greater than 70% of the dosing interval. Pediatric patients on extracorporeal membrane oxygenation might benefit from the addition of therapeutic drug monitoring of cefepime to assure appropriate dosing.

Population pharmacokinetics and dosing simulations of ceftazidime in critically ill patients receiving sustained low-efficiency dialysis

Objectives

To describe the population PKs of ceftazidime in critically ill patients receiving sustained low-efficiency dialysis (SLED).

Patients and methods

This study was performed in ICUs of a university hospital. We collected blood samples during three consecutive days of SLED sessions in patients receiving ceftazidime. Concentration versus time curves were analysed using a population PKs approach with Pmetrics ® . Monte Carlo simulation for the first 24 h including a 6 h SLED session was performed with the final model. The fractional target attainment against the MIC of Pseudomonas aeruginosa was executed using targets of 50 and 100% fT  >   MIC .

Results

In total, 211 blood samples of 16 critically ill patients under SLED were collected. SLED treatments were 299.3 (68.4) min in duration. A two-compartment linear population PK model was most appropriate. The mean (SD) CL of ceftazidime on SLED, and off SLED were 5.32 (3.2), 1.06 (1.0) L/h respectively. The PTA for 50% fT  >   MIC for a dose of 1 g intravenously every 8 h was 98%. Assuming a target of 100% fT  >   MIC a dose of 2 g every 12 h covers isolates with MIC ≤8 mg/L with a PTA of 96%.

Conclusion

In critically ill patients receiving SLED, ceftazidime 1 g every 8 h and ceftazidime 2 g every 12 h appear to be sufficient for achieving traditional (50% fT  >   MIC ) and aggressive PD targets (100% fT  >   MIC ) for susceptible isolates (MIC ≤8 mg/L), respectively.

Population Pharmacokinetics of Piperacillin in Nonobese, Obese, and Morbidly Obese Critically Ill Patients

The treatment of infections in critically ill obese and morbidly obese patients is challenging because of the combined physiological changes that result from obesity and critical illness. The aim of this study was to describe the population pharmacokinetics of piperacillin in a cohort of critically ill patients, including obese and morbidly obese patients. Critically ill patients who received piperacillin-tazobactam were classified according to their body mass index (BMI) as nonobese, obese, and morbidly obese. Plasma samples were collected, and piperacillin concentrations were determined by a validated chromatographic method. Population pharmacokinetic analysis and Monte Carlo dosing simulations were performed using Pmetrics software. Thirty-seven critically ill patients (including 12 obese patients and 12 morbidly obese patients) were enrolled. The patients' mean ± standard deviation age, weight, and BMI were 50 ± 15 years, 104 ± 35 kg, and 38.0 ± 15.0 kg/m², respectively. The concentration-time data were best described by a two-compartment linear model. The mean ± SD parameter estimates for the final covariate model were a clearance of 14.0 ± 7.1 liters/h, a volume of distribution of the central compartment of 49.0 ± 19.0 liters, an intercompartmental clearance from the central compartment to the peripheral compartment of 0.9 ± 0.6 liters · h^-1, and an intercompartmental clearance from the peripheral compartment to the central compartment of 2.3 ± 2.8 liters · h^-1 A higher measured creatinine clearance and shorter-duration infusions were associated with a lower likelihood of achieving therapeutic piperacillin exposures in patients in all BMI categories. Piperacillin pharmacokinetics are altered in the presence of obesity and critical illness. As with nonobese patients, prolonged infusions increase the likelihood of achieving therapeutic concentrations.

Uncertainty in Antibiotic Dosing in Critically Ill Neonate and Pediatric Patients: Can Microsampling Provide the Answers?

PURPOSE

With a decreasing supply of antibiotics that are effective against the pathogens that cause sepsis, it is critical that we learn to use currently available antibiotics optimally. Pharmacokinetic studies provide an evidence base from which we can optimize antibiotic dosing. However, these studies are challenging in critically ill neonate and pediatric patients due to the small blood volumes and associated risks and burden to the patient from taking blood. We investigate whether microsampling, that is, obtaining a biologic sample of low volume (<50 μL), can improve opportunities to conduct pharmacokinetic studies.

METHODS

We performed a literature search to find relevant articles using the following search terms: sepsis, critically ill, severe infection, intensive care AND antibiotic, pharmacokinetic, p(a)ediatric, neonate. For microsampling, we performed a search using antibiotics AND dried blood spots OR dried plasma spots OR volumetric absorptive microsampling OR solid-phase microextraction OR capillary microsampling OR microsampling. Databases searched include Web of Knowledge, PubMed, and EMbase.

FINDINGS

Of the 32 antibiotic pharmacokinetic studies performed on critically ill neonate or pediatric patients in this review, most of the authors identified changes to the pharmacokinetic properties in their patient group and recommended either further investigations into this patient population or therapeutic drug monitoring to ensure antibiotic doses are suitable. There remain considerable gaps in knowledge regarding the pharmacokinetic properties of antibiotics in critically ill pediatric patients. Implementing microsampling in an antibiotic pharmacokinetic study is contingent on the properties of the antibiotic, the pathophysiology of the patient (and how this can affect the microsample), and the location of the patient. A validation of the sampling technique is required before implementation.

IMPLICATIONS

Current antibiotic regimens for critically ill neonate and pediatric patients are frequently suboptimal due to a poor understanding of altered pharmacokinetic properties. An assessment of the suitability of microsampling for pharmacokinetic studies in neonate and pediatric patients is recommended before wider use. The method of sampling, as well as the method of bioanalysis, also requires validation to ensure the data obtained reflect the true result.

What is the effect of obesity on piperacillin and meropenem trough concentrations in critically ill patients?

OBJECTIVES

The objectives of this study were to determine the effects of obesity on unbound trough concentrations and on the achievement of pharmacokinetic (PK)/pharmacodynamic (PD) targets of piperacillin and meropenem in critically ill patients.

METHODS

This study retrospectively analysed therapeutic-drug-monitoring data from ICU databases in Australia, Germany and Spain, as well as from a large PK study. The presence of obesity was defined as a BMI ≥30 kg/m(2), and patients were also categorized based on level of renal function. The presence of obesity was compared with unbound piperacillin and meropenem trough concentrations. We also used logistic regression to describe factors associated with the achievement of the PK/PD targets, an unbound concentration maintained above the MIC breakpoint (100% fT>MIC and 100% fT>4×MIC) of Pseudomonas aeruginosa.

RESULTS

In all, 1400 patients were eligible for inclusion in the study. The median age and weight were 67 years (IQR 52-76 years) and 79 kg (69-90 kg), respectively, and 65% of participants were male. Significantly lower median piperacillin trough concentrations [29.4 mg/L (IQR 17.0-58.0 mg/L)] were found in obese patients compared with non-obese patients [42.0 mg/L (21.5-73.5 mg/L)] (P = 0.001). There was no difference for meropenem trough concentrations [obese 10.3 mg/L (IQR 4.8-16.0 mg/L) versus non-obese 11.0 mg/L (4.3-18.5 mg/L); P = 0.296]. Using logistic regression, we found that the presence of obesity was not associated with achievement of 100% fT>MIC, but the use of prolonged infusion, a creatinine clearance ≤100 mL/min, increasing age and female gender were for various PK/PD targets for both piperacillin and meropenem (P < 0.05).

CONCLUSIONS

This large dataset has shown that the presence of obesity in critically ill patients may affect piperacillin, but not meropenem, unbound trough concentrations.

A Simulation Study Reveals Lack of Pharmacokinetic/Pharmacodynamic Target Attainment in De-escalated Antibiotic Therapy in Critically Ill Patients

De-escalation of empirical antibiotic therapy is often included in antimicrobial stewardship programs in critically ill patients, but differences in target attainment when antibiotics are switched are rarely considered. The primary objective of this study was to compare the fractional target attainments of contemporary dosing of empirical broad-spectrum β-lactam antibiotics and narrower-spectrum antibiotics for a number pathogens for which de-escalation may be considered. The secondary objective was to determine whether alternative dosing strategies improve target attainment. We performed a simulation study using published population pharmacokinetic (PK) studies in critically ill patients for a number of broad-spectrum β-lactam antibiotics and narrower-spectrum antibiotics. Simulations were undertaken using a data set obtained from critically ill patients with sepsis without absolute renal failure (n = 49). The probability of target attainment of antibiotic therapy for different microorganisms for which de-escalation was applied was analyzed. EUCAST MIC distribution data were used to calculate fractional target attainment. The probability that therapeutic exposure will be achieved was lower for the narrower-spectrum antibiotics with conventional dosing than for the broad-spectrum alternatives and could drastically be improved with higher dosages and different modes of administrations. For a selection of microorganisms, the probability that therapeutic exposure will be achieved was overall lower for the narrower-spectrum antibiotics using conventional dosing than for the broad-spectrum antibiotics.

Shortening the course of antibiotic treatment in the intensive care unit

Effective antimicrobial stewardship is an increasingly important concern for healthcare providers globally. Antibiotics are frequently prescribed for patients who develop sepsis in the intensive care unit and traditionally courses are prolonged, with uncertain benefit and probable harm. There is little evidence to support many guidelines recommending between 10 and 14 days, and a number of studies suggest substantially shorter courses of less than 7 days may suffice. Safely reducing course length is likely to depend on a number of preconditions, including thorough eradication of any septic foci; optimization of serum antibiotic concentrations, particularly when there is physiological derangement; and use of novel biomarkers such as procalcitonin. The critical care environment is well suited to this aim as patients are closely monitored. With these measures in place, it is reasonable to believe short antibiotic courses can safely be used for the majority of intensive care infections.

Are standard doses of piperacillin sufficient for critically ill patients with augmented creatinine clearance?

Introduction

The aim of this study was to explore the impact of augmented creatinine clearance and differing minimum inhibitory concentrations (MIC) on piperacillin pharmacokinetic/pharmacodynamic (PK/PD) target attainment (time above MIC (fT_>MIC)) in critically ill patients with sepsis receiving intermittent dosing.

Methods

To be eligible for enrolment, critically ill patients with sepsis had to be receiving piperacillin-tazobactam 4.5 g intravenously (IV) by intermittent infusion every 6 hours for presumed or confirmed nosocomial infection without significant renal impairment (defined by a plasma creatinine concentration greater than 171 μmol/L or the need for renal replacement therapy). Over a single dosing interval, blood samples were drawn to determine unbound plasma piperacillin concentrations. Renal function was assessed by measuring creatinine clearance (CL_CR). A population PK model was constructed, and the probability of target attainment (PTA) for 50% and 100% fT_>MIC was calculated for varying MIC and CL_CR values.

Results

In total, 48 patients provided data. Increasing CL_CR values were associated with lower trough plasma piperacillin concentrations (P < 0.01), such that with an MIC of 16 mg/L, 100% fT_>MIC would be achieved in only one-third (n = 16) of patients. Mean piperacillin clearance was approximately 1.5-fold higher than in healthy volunteers and correlated with CL_CR (r = 0.58, P < 0.01). A reduced PTA for all MIC values, when targeting either 50% or 100% fT_>MIC, was noted with increasing CL_CR measures.

Conclusions

Standard intermittent piperacillin-tazobactam dosing is unlikely to achieve optimal piperacillin exposures in a significant proportion of critically ill patients with sepsis, owing to elevated drug clearance. These data suggest that CL_CR can be employed as a useful tool to determine whether piperacillin PK/PD target attainment is likely with a range of MIC values.

Plasma and target-site subcutaneous tissue population pharmacokinetics and dosing simulations of cefazolin in post-trauma critically ill patients

OBJECTIVES

The objective of this study was to describe the population pharmacokinetics of cefazolin in plasma and the interstitial fluid of subcutaneous tissue of post-trauma critically ill patients and provide clinically relevant dosing recommendations that result in optimal concentrations at the target site.

PATIENTS AND METHODS

This was a pharmacokinetic study in a tertiary referral ICU. We recruited 30 post-trauma critically ill adult patients and collected serial total and unbound plasma cefazolin concentrations. Interstitial fluid concentrations were determined using in vivo microdialysis. Population pharmacokinetic analysis and Monte Carlo simulations were undertaken with Pmetrics(®). Fractional target attainment against an MIC distribution for Staphylococcus aureus isolates was calculated.

RESULTS

The mean (SD) age, weight, APACHE II score and CLCR were 37.0 (14.1) years, 86.8 (22.7) kg, 16.9 (5.3) and 163 (44) mL/min, respectively. A three-compartment linear population pharmacokinetic model was most appropriate. Covariates included in the model were CLCR on drug clearance and serum albumin concentration and body weight on the volume of the central compartment. The fractional target attainment for a 1 g intravenous 8-hourly dose for a CLCR of 50 mL/min was 88%, whereas for a patient with a CLCR of 215 mL/min, a dose of 2 g 6-hourly achieved 84% fractional target attainment.

CONCLUSIONS

Clinicians should be mindful of the effects of elevated CLCR and serum albumin concentrations on dosing requirements for post-trauma critically ill patients.

Using skin for drug delivery and diagnosis in the critically ill

Skin offers easy access, convenience and non-invasiveness for drug delivery and diagnosis. In principle, these advantages of skin appear to be attractive for critically ill patients given potential difficulties that may be associated with oral and parenteral access in these patients. However, the profound changes in skin physiology that can be seen in these patients provide a challenge to reliably deliver drugs or provide diagnostic information. Drug delivery through skin may be used to manage burn injury, wounds, infection, trauma and the multisystem complications that rise from these conditions. Local anaesthetics and analgesics can be delivered through skin and may have wide application in critically ill patients. To ensure accurate information, diagnostic tools require validation in the critically ill patient population as information from other patient populations may not be applicable.

Anaerobic metabolism associated with traumatic hemorrhagic shock monitored by microdialysis of muscle tissue is dependent on the levels of hemoglobin and central venous oxygen saturation: a prospective, observational study

Background

Traumatic hemorrhagic shock resulting in tissue hypoxia is a significant cause of morbidity and mortality in polytraumatized patients. Early identification of tissue hypoxia is possible with microdialysis. The aim of this study was to determine the correlation between a marker of tissue hypoxia (L/P; lactate to pyruvate ratio) and selected parameters of systemic oxygen delivery (Hb; hemoglobin) and oxygen extraction (ScvO₂; central venous oxygen saturation). We also investigated the severity of tissue hypoxia over the course of care.

Methods

Adult patients with traumatic hemorrhagic shock were enrolled in this prospective, observational study. Microdialysis of the peripheral muscle tissue was performed. Demographic data and timeline of care were collected. Tissue lactate, pyruvate, glycerol, glucose levels, hemoglobin, serum lactate and oxygen saturation of the central venous blood (ScvO₂) levels were also measured.

Results

The L/P ratio trend may react to changes in systemic hemoglobin levels with a delay of 7 to 10 hours, particularly when systemic hemoglobin levels are increased by transfusion. Decrease in tissue L/P ratio may react to increase in ScvO₂ with a delay of up to 10 hours, and such a decrease may signify elimination of tissue hypoxia after transfusion. We also observed changes in the L/P trend in the 13 hours preceding a change in the hemoglobin level. Fluid administration, which is routinely used as a first-line treatment of hypovolemic shock, can cause hemodilution and decreased hemoglobin. When ScvO₂ decreases, increase in L/P ratio may precede the ScvO₂ trend by 10 or 11 hours. An increase in the L/P ratio is an early warning sign of insufficient tissue oxygenation and should lead to intensive observation of hemoglobin levels, ScvO₂ and other hemodynamic parameters. Patients who were treated more rapidly had lower maximal L/P values and a lower degree of tissue ischemia.

Conclusion

The L/P ratio is useful to identify tissue ischemia and can estimate the effectiveness of fluid resuscitation. An increase in the L/P ratio is an early warning sign of inadequate tissue oxygenation and should lead to more detailed hemodynamic and laboratory monitoring. This information cannot usually be obtained from global markers.

New dosing strategies for an old antibiotic: pharmacodynamics of front-loaded regimens of colistin at simulated pharmacokinetics in patients with kidney or liver disease

Increasing evidence suggests that colistin monotherapy is suboptimal at currently recommended doses. We hypothesized that front-loading provides an improved dosing strategy for polymyxin antibiotics to maximize killing and minimize total exposure. Here, we utilized an in vitro pharmacodynamic model to examine the impact of front-loaded colistin regimens against a high bacterial density (10(8) CFU/ml) of Pseudomonas aeruginosa. The pharmacokinetics were simulated for patients with hepatic (half-life [t1/2] of 3.2 h) or renal (t1/2 of 14.8 h) disease. Front-loaded regimens (n=5) demonstrated improvement in bacterial killing, with reduced overall free drug areas under the concentration-time curve (fAUC) compared to those with traditional dosing regimens (n=14) with various dosing frequencies (every 12 h [q12h] and q24h). In the renal failure simulations, front-loaded regimens at lower exposures (fAUC of 143 mg · h/liter) obtained killing activity similar to that of traditional regimens (fAUC of 268 mg · h/liter), with an ∼97% reduction in the area under the viable count curve over 48 h. In hepatic failure simulations, front-loaded regimens yielded rapid initial killing by up to 7 log10 within 2 h, but considerable regrowth occurred for both front-loaded and traditional regimens. No regimen eradicated the high bacterial inoculum of P. aeruginosa. The current study, which utilizes an in vitro pharmacodynamic infection model, demonstrates the potential benefits of front-loading strategies for polymyxins simulating differential pharmacokinetics in patients with hepatic and renal failure at a range of doses. Our findings may have important clinical implications, as front-loading polymyxins as a part of a combination regimen may be a viable strategy for aggressive treatment of high-bacterial-burden infections.

Pharmacokinetic behavior presents drug therapy challenges

There are conditions that cause a substantial change in drug clearance to such a degree that how a specific drug is managed to optimize drug response and minimize drug toxicity presents a challenge. This review will focus on recent literature (within the past 5 years) that evaluates pathophysiologic and genetic conditions and drug interactions which can change drug clearance to the magnitude that response is affected. Situations discussed that cause an increase in drug clearance will include: augmented renal clearance in critically ill patients; ultrafast drug metabolism caused by gene duplication; and enzyme induction interactions caused by rifampin. Situations discussed that result in a reduction in clearance will include: multiple organ failure in critically ill, patients with non-functioning CYP2D6 and CYP2C8/9 alleles, and CYP3A4 drug interactions with erythromycin and clarithromycin. In each case evaluated clearance is changed to the magnitude such that managing drug therapy can be difficult.

Approaches for dosage individualisation in critically ill patients

INTRODUCTION

Pharmacokinetic variability in critically ill patients is the result of the overlapping of multiple pathophysiological and clinical factors. Unpredictable exposure from standard dosage regimens may influence the outcome of treatment. Therefore, strategies for dosage individualisation are recommended in this setting.

AREAS COVERED

The authors focus on several approaches for dosage individualisation that have been developed, ranging from the well-established therapeutic drug monitoring (TDM) up to the innovative application of pharmacogenomics criteria. Furthermore, the authors summarise the specific population pharmacokinetic models for different drugs developed for critically ill patients to improve the initial dosage selection and the Bayesian forecasting of serum concentrations. The authors also consider the use of Monte Carlo simulation for the selection of dosage strategies.

EXPERT OPINION

Pharmacokinetic/pharmacodynamics (PK/PD) modelling and dosage individualisation methods based on mathematical and statistical criteria will contribute in improving pharmacologic treatment in critically ill patients. Moreover, substantial effort will be necessary to integrate pharmacogenomics criteria into critical care practice. The lack of availability of target biomarkers for dosage adjustment emphasizes the value of TDM which allows a large part of treatment outcome variability to be controlled.

The clinical relevance of plasma protein binding changes

Controversy reigns as to how protein binding changes alter the time course of unbound drug concentrations in patients. Given that the unbound concentration is responsible for drug efficacy and potential drug toxicity, this area is of significant interest to clinicians and academics worldwide. The present uncertainty means that many questions relating to this area exist, including "How important is protein binding?", "Is protein binding always constant?", "Do pH and temperature changes alter binding?" and "How do protein binding changes affect dosing requirements?". In this paper, we seek to address these questions and consider the data associated with altered pharmacokinetics in the presence of changes in protein binding and the clinical consequences that these may have on therapy, using examples from the critical care area. The published literature consistently indicates that a change in the protein binding and unbound concentrations of some drugs are common in certain specific patient groups such as the critically ill. Changes in pharmacokinetic parameters, including clearance and apparent volume of distribution (V(d)), may be dramatic. Drugs with high protein binding, high intrinsic clearance (e.g. clearance by glomerular filtration) and where dosing is not titrated to effect are most likely to be affected in a clinical context. Drugs such as highly protein bound antibacterials with multiple half-lives within a dosing interval and that have some level of renal clearance, such as ertapenem, teicoplanin, ceftriaxone and flucloxacillin, are commonly affected. In response to these challenges, clinicians need to adapt dosing regimens rationally based on the pharmacokinetic/pharmacodynamic characteristics of the drug. We propose that further pharmacokinetic modelling-based research is required to enable the design of robust dosing regimens for drugs affected by altered protein binding.

The ECMO PK Project: an incremental research approach to advance understanding of the pharmacokinetic alterations and improve patient outcomes during extracorporeal membrane oxygenation

Background

Extracorporeal membrane oxygenation (ECMO) is a supportive therapy and its success depends on optimal drug therapy along with other supportive care. Emerging evidence suggests significant interactions between the drug and the device resulting in altered pharmacokinetics (PK) of vital drugs which may be further complicated by the PK changes that occur in the context of critical illness. Such PK alterations are complex and challenging to investigate in critically ill patients on ECMO and necessitate mechanistic research. The aim of this project is to investigate each of circuit, drug and critical illness factors that affect drug PK during ECMO.

Methods/design

An incremental research plan that encompasses ex vivo experiments for drug stability testing in fresh human and ovine whole blood, ex vivo drug disposition studies in standard and modified adult ECMO circuits primed with fresh human or ovine whole blood, PK studies in healthy and critically ill ovine models of ECMO with appropriate non ECMO controls and an international mutli-centre clinical population PK study will be utilised to comprehensively define the PK alterations that occur in the presence of ECMO. Novel drug assays that will allow quantification of multiple drugs in small volumes of plasma will also be developed. Mixed-effects regression models will be used to estimate the drug loss over time in ex vivo studies. Data from animal and clinical studies will be analysed using non-linear mixed-effects models. This will lead to generation of PK data that enables the development evidence based guidelines for antibiotic, sedative and analgesic drug therapy during ECMO.

Discussion

Systematic research that integrates both mechanistic and clinical research is desirable when investigating the complex area of pharmacokinetic alterations during ECMO. The above research approach will provide an advanced mechanistic understanding of PK during ECMO. The clinical study when complete will result in development robust guidelines for prescription of 18 commonly used antibiotic, sedative and analgesic drugs used in ECMO patients. This research may also pave the way for further refinements in circuitry, drug chemistry and drug prescriptions during ECMO.

Trial registration

ACTRN12612000559819.

Augmented renal clearance in septic and traumatized patients with normal plasma creatinine concentrations: identifying at-risk patients

Introduction

Improved methods to optimize drug dosing in the critically ill are urgently needed. Traditional prescribing culture involves recognition of factors that mandate dose reduction (such as renal impairment), although optimizing drug exposure, through more frequent or augmented dosing, represents an evolving strategy. Elevated creatinine clearance (CL_CR) has been associated with sub-therapeutic antibacterial concentrations in the critically ill, a concept termed augmented renal clearance (ARC). We aimed to determine the prevalence of ARC in a cohort of septic and traumatized critically ill patients, while also examining demographic, physiological and illness severity characteristics that may help identify this phenomenon.

Methods

This prospective observational study was performed in a 30-bed tertiary level, university affiliated, adult intensive care unit. Consecutive traumatized and septic critically ill patients, receiving antibacterial therapy, with a plasma creatinine concentration ≤110 μmol/L, were eligible for enrolment. Pulse contour analysis (Vigileo / Flo Trac^® system, Edwards Lifesciences, Irvine, CA, USA), was used to provide continuous cardiac index (CI) assessment over a single six-hour dosing interval. Urinary CL_CR measures were obtained concurrently.

Results

Seventy-one patients contributed data (sepsis n = 43, multi-trauma n = 28). Overall, 57.7% of the cohort manifested ARC, although there was a greater prevalence in trauma (85.7% versus 39.5%, P <0.001). In all patients, a weak correlation was noted between CI and CL_CR (r = 0.346, P = 0.003). This was mostly driven by septic patients (r = 0.508, P = 0.001), as no correlation (r = -0.012, P = 0.951) was identified in trauma. Those manifesting ARC were younger (P <0.001), male (P = 0.012), with lower acute physiology and chronic health evaluation (APACHE) II (P= 0.008) and modified sequential organ failure assessment (SOFA) scores (P = 0.013), and higher cardiac indices (P = 0.013). In multivariate analysis, age ≤50 years, trauma, and a modified SOFA score ≤4, were identified as significant risk factors. These had greater utility in predicting ARC, compared with CI assessment alone.

Conclusions

Diagnosis, illness severity and age, are likely to significantly influence renal drug elimination in the critically ill, and must be regularly considered in future study design and daily prescribing practice.

See related commentary by De Waele and Carlier, http://ccforum.com/content/17/2/130

ASAP ECMO: Antibiotic, Sedative and Analgesic Pharmacokinetics during Extracorporeal Membrane Oxygenation: a multi-centre study to optimise drug therapy during ECMO

Background

Given the expanding scope of extracorporeal membrane oxygenation (ECMO) and its variable impact on drug pharmacokinetics as observed in neonatal studies, it is imperative that the effects of the device on the drugs commonly prescribed in the intensive care unit (ICU) are further investigated. Currently, there are no data to confirm the appropriateness of standard drug dosing in adult patients on ECMO. Ineffective drug regimens in these critically ill patients can seriously worsen patient outcomes. This study was designed to describe the pharmacokinetics of the commonly used antibiotic, analgesic and sedative drugs in adult patients receiving ECMO.

Methods/Design

This is a multi-centre, open-label, descriptive pharmacokinetic (PK) study. Eligible patients will be adults treated with ECMO for severe cardiac and/or respiratory failure at five Intensive Care Units in Australia and New Zealand. Patients will receive the study drugs as part of their routine management. Blood samples will be taken from indwelling catheters to investigate plasma concentrations of several antibiotics (ceftriaxone, meropenem, vancomycin, ciprofloxacin, gentamicin, piperacillin-tazobactum, ticarcillin-clavulunate, linezolid, fluconazole, voriconazole, caspofungin, oseltamivir), sedatives and analgesics (midazolam, morphine, fentanyl, propofol, dexmedetomidine, thiopentone). The PK of each drug will be characterised to determine the variability of PK in these patients and to develop dosing guidelines for prescription during ECMO.

Discussion

The evidence-based dosing algorithms generated from this analysis can be evaluated in later clinical studies. This knowledge is vitally important for optimising pharmacotherapy in these most severely ill patients to maximise the opportunity for therapeutic success and minimise the risk of therapeutic failure.

Trial registration

ACTRN12612000559819

Continuous infusion of piperacillin/tazobactam in septic critically ill patients--a multicenter propensity matched analysis

The clinical efficacy of continuous infusion of piperacillin/tazobactam in critically ill patients with microbiologically documented infections is currently unknown. We conducted a retrospective multicenter cohort study in 7 Portuguese intensive care units (ICU). We included 569 critically ill adult patients with a documented infection and treated with piperacillin/tazobactam admitted to one of the participating ICU between 2006 and 2010. We successfully matched 173 pairs of patients according to whether they received continuous or conventional intermittent dosing of piperacillin/tazobactam, using a propensity score to adjust for confounding variables. The majority of patients received 16g/day of piperacillin plus 2g/day of tazobactam. The 28-day mortality rate was 28.3% in both groups (p = 1.0). The ICU and in-hospital mortality were also similar either in those receiving continuous infusion or intermittent dosing (23.7% vs. 20.2%, p = 0.512 and 41.6% vs. 40.5%, p = 0.913, respectively). In the subgroup of patients with a Simplified Acute Physiology Score (SAPS) II>42, the 28-day mortality rate was lower in the continuous infusion group (31.4% vs. 35.2%) although not reaching significance (p = 0.66). We concluded that the clinical efficacy of piperacillin/tazobactam in this heterogeneous group of critically ill patients infected with susceptible bacteria was independent of its mode of administration, either continuous infusion or intermittent dosing.

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.

A comparison of pulse contour wave analysis and ultrasonic cardiac output monitoring in the critically ill

Cardiac output (CO) is a key determinant of major organ blood flow and solute delivery to drug eliminating organs. As such, CO assessment is a key covariate in understanding altered drug handling in the critically ill. Newer minimally-invasive devices are providing unique platforms for such an application, although comparison data are currently lacking. In this study we evaluated the Vigileo (Edwards Lifesciences, Irvine, CA, USA) and USCOM (USCOM Ltd, Sydney, NSW) devices in 62 critically ill patients requiring antibacterial therapy. The mean COVigileo and COUSCOM for the first paired measurements were 8.20±2.65 l/minute and 6.84±2.57 l/minute respectively (P <0.001). A significant correlation was evident in all patients (r=0.537, P <0.001) although the recorded bias was large (1.36±2.51 l/minute, limits of agreement -3.6 to±6.3 l/minute). The overall percentage error was 65%. There was an improved correlation in those admitted with sepsis (r=0.639, P <0.001), compared to trauma (r=0.373, P=0.066), although bias, precision and percentage error were similar in both subgroups. In 54 patients a second paired assessment was obtained at three hours. A weak, although significant correlation (r=0.377, P=0.005) was observed suggesting that gross trends over time were similar. In conclusion, our findings demonstrate poor agreement between these techniques suggesting that these devices are not simply interchangeable when assessing CO in a research or clinical setting.

Ceftazidime dosage regimen in intensive care unit patients: from a population pharmacokinetic approach to clinical practice via Monte Carlo simulations

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

The large variability in drug pharmacokinetic disposition has already been described in ICU patients leading to important variations in drugs concentrations. The usual recommended dosage of ceftazidime is not adapted for all ICU situations and ceftazidime should be monitored closely. New recommendations have to be given for some specific cases.

WHAT THIS STUDY ADDS

Our results propose individual therapeutic drug monitoring taking into account: For the patient: the reason of admission in the ICU, the mechanical ventilation status and the creatinine clearance calculated by the modified diet in renal disease (MDRD). • For the antibiotics: the lung distribution, the minimal inhibitory concentration (MIC) of the strain to eradicate and the potential toxicity. AIM To predict the ceftazidime dosage regimen as a function of the glomerular filtration rate expressed by the modification of the diet in renal disease (MDRD), reason for admission and mechanical ventilation in intensive care unit (ICU) patients to treat Pseudomonas aeruginosa pneumonia.

METHOD

A published and qualified population pharmacokinetic model was used to perform Monte Carlo simulations of ceftazidime concentrations. The serum target of 40-100 mg l(-1) was defined based on the minimal inhibitory concentration (MIC), the European break point (EBP), the pulmonary drug diffusion and toxicity. The recommended dosage regimens were based on the maximum percentile of the patients with simulated steady state concentrations reaching the target.

RESULTS

Steady-state was reached at 72 h whatever the MDRD. The simulations of serum concentrations generated higher percentiles of the population reaching the target after continuous administration. We recommend a 4 g continuous dose after the usual 2 g loading dose for patients with MDRD from 10 to 30 ml min(-1) , 6 g for MDRD between 40 and 80 ml min(-1) , 8 g for MDRD from 90 to 110 ml min(-1) , 10 g for MDRD from 120 to 190 ml min(-1) and 12 g day(-1) for patients with MDRD higher than 200 ml min(-1) .

CONCLUSION

Our study demonstrated that in ICU patients for a given MDRD, steady-state takes longer to reach in polytrauma patients than in patients with medical or post surgery reasons for admission. Continuous infusion ensures that a higher percentage of patients reaches the target than the same dose given by discontinuous administration and this only depends on MDRD.

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.

Dosing of medications in morbidly obese patients in the intensive care unit setting

OBJECTIVE

To derive recommendations for the dosing of commonly used medications in the morbidly obese patient in the ICU.

DATA SOURCES

Articles were obtained through computerized searches involving MEDLINE. The bibliographies of retrieved publications and textbooks were reviewed for additional references.

STUDY SELECTION

All studies involving the pharmacokinetics or pharmacodynamics of medications in obese subjects or patients.

DATA EXTRACTION

The emphasis was on studies involving morbidly obese patients but, in the absence of such data, investigations involving lesser forms of obesity were extracted.

DATA SYNTHESIS

There is a paucity of data upon which to make recommendations for dosing commonly used medications in the morbidly obese patient in the ICU, although recommendations were provided based on the available information.

CONCLUSIONS

There is clearly a need for more investigations involving dosing regimens of medications in the morbidly obese population. Until such studies are available, the clinician must try to derive the best dosing regimens for medications based on the limited pharmacokinetic data available for some agents and clinical judgement.