Insufficient β-lactam concentrations in the early phase of severe sepsis and septic shock

The Surgical Infection Society Revised Guidelines on the Management of Intra-Abdominal Infection

BACKGROUND

Previous evidence-based guidelines on the management of intra-abdominal infection (IAI) were published by the Surgical Infection Society (SIS) in 1992, 2002, and 2010. At the time the most recent guideline was released, the plan was to update the guideline every five years to ensure the timeliness and appropriateness of the recommendations.

METHODS

Based on the previous guidelines, the task force outlined a number of topics related to the treatment of patients with IAI and then developed key questions on these various topics. All questions were approached using general and specific literature searches, focusing on articles and other information published since 2008. These publications and additional materials published before 2008 were reviewed by the task force as a whole or by individual subgroups as to relevance to individual questions. Recommendations were developed by a process of iterative consensus, with all task force members voting to accept or reject each recommendation. Grading was based on the GRADE (Grades of Recommendation Assessment, Development, and Evaluation) system; the quality of the evidence was graded as high, moderate, or weak, and the strength of the recommendation was graded as strong or weak. Review of the document was performed by members of the SIS who were not on the task force. After responses were made to all critiques, the document was approved as an official guideline of the SIS by the Executive Council.

RESULTS

This guideline summarizes the current recommendations developed by the task force on the treatment of patients who have IAI. Evidence-based recommendations have been made regarding risk assessment in individual patients; source control; the timing, selection, and duration of antimicrobial therapy; and suggested approaches to patients who fail initial therapy. Additional recommendations related to the treatment of pediatric patients with IAI have been included.

SUMMARY

The current recommendations of the SIS regarding the treatment of patients with IAI are provided in this guideline.

Therapeutic drug monitoring of beta-lactam antibiotics - Influence of sample stability on the analysis of piperacillin, meropenem, ceftazidime and flucloxacillin by HPLC-UV

INTRODUCTION

Therapeutic drug monitoring (TDM) is a useful tool to optimize antibiotic therapy. Increasing interest in alternative dosing strategies of beta-lactam antibiotics, e.g. continuous or prolonged infusion, require a feasible analytical method for quantification of these antimicrobial agents. However, pre-analytical issues including sample handling and stability are to be considered to provide valuable analytical results.

METHODS

For the simultaneous determination of piperacillin, meropenem, ceftazidime and flucloxacillin, a high performance liquid chromatography (HPLC) method including protein precipitation was established utilizing ertapenem as internal standard. Long-term stability of stock solutions and plasma samples were monitored. Furthermore, whole blood stability of the analytes in heparinized blood tubes was investigated comparing storage under ambient conditions and 2-8°C.

RESULTS

A calibration range of 5-200μg/ml (piperacillin, ceftazidime, flucloxacillin) and 2-200μg/ml (meropenem) was linear with r²>0.999, precision and inaccuracy were <9% and <11%, respectively. The successfully validated HPLC assay was applied to clinical samples and stability investigations. At -80°C, plasma samples were stable for 9 months (piperacillin, meropenem) or 13 months (ceftazidime, flucloxacillin). Concentrations of the four beta-lactam antibiotics in whole blood tubes were found to remain within specifications for 8h when stored at 2-8°C but not at room temperature.

CONCLUSIONS

The presented method is a rapid and simple option for routine TDM of piperacillin, meropenem, ceftazidime and flucloxacillin. Whereas long-term storage of beta-lactam samples at -80°C is possible for at least 9 months, whole blood tubes are recommended to be kept refrigerated until analysis.

Target attainment with continuous dosing of piperacillin/tazobactam in critical illness: a prospective observational study

Optimal dosing of β-lactam antibiotics in critically ill patients is a challenge given the unpredictable pharmacokinetic profile of this patient population. Several studies have shown intermittent dosing to often yield inadequate drug concentrations. Continuous dosing is an attractive alternative from a pharmacodynamic point of view. This study evaluated whether, during continuous dosing, piperacillin concentrations reached and maintained a pre-defined target in critically ill patients. Adult patients treated with piperacillin by continuous dosing in the intensive care unit of a university medical centre in The Netherlands were prospectively studied. Total and unbound piperacillin concentrations drawn at fixed time points throughout the entire treatment course were determined by liquid chromatography-tandem mass spectrometry. A pharmacokinetic combined target of a piperacillin concentration ≥80 mg/L, reached within 1 h of starting study treatment and maintained throughout the treatment course, was set. Eighteen patients were analysed. The median duration of monitored piperacillin treatment was 60 h (interquartile range, 33-96 h). Of the 18 patients, 5 (27.8%) reached the combined target; 15 (83.3%) reached and maintained a less strict target of >16 mg/L. In this patient cohort, this dosing schedule was insufficient to reach the pre-defined target. Depending on which target is to be met, a larger initial cumulative dose is desirable, combined with therapeutic drug monitoring.

Management of intra-abdominal infections: recommendations by the WSES 2016 consensus conference

This paper reports on the consensus conference on the management of intra-abdominal infections (IAIs) which was held on July 23, 2016, in Dublin, Ireland, as a part of the annual World Society of Emergency Surgery (WSES) meeting. This document covers all aspects of the management of IAIs. The Grading of Recommendations Assessment, Development and Evaluation recommendation is used, and this document represents the executive summary of the consensus conference findings.

Efficacy of nebulized colistin-based therapy without concurrent intravenous colistin for ventilator-associated pneumonia caused by carbapenem-resistant Acinetobacter baumannii

BACKGROUND

Although there have been studies regarding the role of nebulized colistin as adjunctive therapy of ventilator-associated pneumonia (VAP) caused by carbapenem-resistant Acinetobacter baumannii (CRAB), a paucity of information on the efficacy of nebulized colistin as monotherapy is available.

METHODS

We retrospectively reviewed 219 patients with VAP caused by CRAB treated with either intravenous (n=93) or nebulized colistin (n=126), from March 2010 to November 2015. Factors related to clinical failure was assessed using propensity-score-matched analysis.

RESULTS

Of 219 patients, 39 patients from each group (n=78) were matched after covariate adjustment using propensity score. There were no significant differences in baseline characteristics as well as the rates of clinical failure between the propensity-score-matched groups [Odds ratio (OR), 0.48; 95% confidence interval (CI), 0.19-1.19; P=0.11], while a significantly lower rate of acute kidney injury (AKI) during colistin therapy (18% vs. 49%, P=0.004) was observed in nebulized colistin group. In addition, multivariable analysis revealed that nebulized colistin did not significantly alter the rate of clinical failure [adjusted odds ratio (aOR), 0.36; 95% CI, 0.12-1.09; P=0.070]. Instead, medical intensive care unit (ICU) admission (aOR, 7.14; 95% CI, 1.60-32.00; P=0.010), and septic shock (aOR, 3.93; 95% CI, 1.27-12.17; P=0.018) were independent risk factors for clinical failure.

CONCLUSIONS

Our findings suggest that nebulized colistin-based therapy, even without concurrent administration of intravenous colistin, may be an effective and safe treatment option for VAP caused by CRAB.

Meropenem for treating KPC-producing Klebsiella pneumoniae bloodstream infections: Should we get to the PK/PD root of the paradox?

The objective of this study was to assess the achievement of pharmacokinetic/pharmacodynamic (PK/PD) targets of meropenem (MEM) in critically-ill patients with bloodstream infections (BSI) due to Klebsiella pneumoniae-carbapenemase-producing Klebsiella pneumoniae (KPC-Kp) with MEM minimum inhibitory concentrations (MICs) ≥16 mg/L. Nineteen critically-ill patients with KPC-Kp BSI were given combination therapy including MEM, tigecycline, plus colistin or gentamicin (according to susceptibility testing). MEM was administered as an extended 3-hour infusion of 2 g every 8 hours, or adjusted according to renal function. MEM plasma concentrations were determined by high-performance liquid chromatography. PK/PD targets for MEM were defined as T > 40% 1×MIC and T > 40% 4×MIC. Possible synergisms between MEM and coadministered agents were assessed by time-kill assays based on plasma levels for MEM and on fixed plasma concentrations for the other agents. In none of 19 patients MEM reached any PK/PD target. The actual MEM MICs were 256, 512, and 1024 mg/L in 1, 3, and 15 isolates, respectively. However, theoretically, the PK/PD target of T > 40% 1×MIC could have been achieved in 95%, 68%, 32% and 0% of the isolates for MIC equal to 8, 16, 32, and 64 mg/L, respectively. No synergisms were observed between MEM and coadministered agents. In conclusion, high-dose MEM failed to reach PK/PD targets in 19 patients with BSI due to KPC-Kp with very high MEM MICs. On a theoretical basis, our results suggest a possible usefulness of MEM against resistant blood isolates with MICs up to 32 mg/L.

Population pharmacokinetics of meropenem in elderly patients: dosing simulations based on renal function

OBJECTIVES

The aim of this study was to evaluate different dosage regimens of meropenem in elderly patients in relation with renal function using a population pharmacokinetic (popPK) model.

METHODS

The data of 178 elderly patients treated with meropenem was collected from different sources. A popPK model was developed by using NONMEM® and the influence of different covariates on meropenem CL and V₁ was observed. Monte Carlo dosing simulations were performed at steady state to observe the % T > MIC for targets of 40, 60 and 80% of dosage intervals at different levels of creatinine clearance (CL_CR).

RESULTS

The data was described by a two-compartment model and the values of parameter estimates for CL, V₁, Q and V₂ were 5.27 L/h, 17.2 L, 9.92 L/h and 10.6 L, respectively. The CL_CR, body weight and centre had a significant influence on meropenem CL while no direct influence of age was observed. Extended infusions had pharmacokinetic and pharmacodynamic (PK/PD) breakpoint one dilution greater than corresponding short infusion regimens for each target of % T > MIC.

CONCLUSION

Meropenem CL was significantly lower in the elderly compared to CL reported in younger patients due to the reduced renal function. An extended infusion of 1000 mg q8h can be considered for empirical treatment of infections in elderly patients when CL_CR is ≤ 50 mL/min. A continuous infusion of 3000 mg daily dose is preferred if CL_CR > 50 mL/min. However, a higher daily dose of meropenem would be required for resistant strains (MIC >8 mg/L) of bacteria if CL_CR is >100 mL/min.

Individualized antibiotic strategies

PURPOSE OF REVIEW

Infections are common complications in critically ill patients and are frequently treated with antibiotics. Unfortunately, delivery of optimal therapy is complicated because efficacy of antimicrobials is influenced by the timing of treatment initiation, the use of combination therapy, and the optimization of drug dosing.

RECENT FINDINGS

Early diagnosis of infection is mandatory to provide a rapid and appropriate antibiotic therapy. The presence of less susceptible strains, in particular for hospital-acquired infections, or patients with severe disease, such as the presence of septic shock, may need combination antibiotic therapy. Antibiotic pharmacokinetics, notably volume of distribution and total body clearance, are significantly altered in these critically ill patients and can influence the attainment of adequate circulating levels when standard dosage regimens are administered. Higher dosing should be considered in such patients, although in case of renal impairment and reduced clearance, drug accumulation could also result in some side-effects. Nebulized antibiotics may provide a better clinical response than systemic antibiotics in ventilator-associated pneumonia because of multidrug-resistant pathogens.

SUMMARY

The optimal use of antibiotics in the management of severe infections is an important challenge for ICU physicians. Antimicrobial therapy needs to be individualized according to specific patient characteristics, infecting organisms, and susceptibility patterns.

Population Pharmacokinetics and Pharmacodynamics Modeling To Optimize Dosage Regimens of Sulbactam in Critically Ill Patients with Severe Sepsis Caused by Acinetobacter baumannii

Sulbactam is being considered as an alternative concomitant medication with other effective antibiotics for the treatment of multidrug-resistant (MDR) Acinetobacter baumannii infections. Pathophysiological changes in critically ill patients with severe sepsis, resulting in altered pharmacokinetic (PK) patterns for antibiotics, are important factors in determining therapeutic success. The aims of this study were (i) to examine the population PK parameters and (ii) to assess the probability of target attainment (PTA) for sulbactam in patients with severe sepsis caused by A. baumannii PK studies were carried out following administration of 2 g of sulbactam every 12 h on the 4th day of drug administration in 27 patients, and a Monte Carlo simulation was performed to determine the PTA of achieving 40% exposure time during which the plasma drug concentration remained above the MIC (T_>MIC) and 60% T_>MIC The central and peripheral volumes of distribution were 14.56 and 9.55 liters, respectively, and total clearances of sulbactam were 2.26 liters/h and 7.64 liters/h in patients aged >65 years and ≤65 years, respectively. The high PTAs (≥90%) for targets of 40% T_>MIC and 60% T_>MIC with a MIC of 4 μg/ml were observed when sulbactam was administered by a 4-h infusion of 1 g every 12 h and 1 g every 8 h, respectively. Sulbactam would be an alternative antibiotic option to coadminister with colistin for the treatment of infections caused by MDR A. baumannii However, for pathogens with MICs of >4 μg/ml, higher dosage regimens of sulbactam are required.

Standard dosing of piperacillin and meropenem fail to achieve adequate plasma concentrations in ICU patients

BACKGROUND

Controversies remain regarding optimal dosing and the need for plasma concentration measurements when treating intensive care patients with beta-lactam antibiotics.

METHODS

We studied ICU patients treated with either antibiotic, excluding patients on renal replacement therapy. Antibiotic concentrations were measured at the mid and end of the dosing interval, and repeated after 2-3 days when feasible. Glomerular filtration rate (GFR) was estimated from plasma creatinine and cystatin C, GFR calculated from cystatin C (eGFR) and measured creatinine clearance (CrCl). Measured concentrations were compared to the clinical susceptible breakpoints for Pseudomonas aeruginosa, 16 and 2 mg/l for piperacillin and meropenem respectively.

RESULTS

We analysed 33 and 31 paired samples from 20 and 19 patients treated with piperacillin-tazobactam and meropenem respectively. Antibiotic concentrations at the mid and end of the dosing interval were for piperacillin, 27.0 (14.7-52.9) and 8.6 (2.7-30.3); and for meropenem, 7.5 (4.7-10.2) and 2.4 (1.0-3.5). All values median (interquartile range) and concentrations in mg/l. The percentage of measured concentrations below the breakpoint at the mid and end of the dosing interval were for piperacillin, 27% and 61%; and for meropenem, 6% and 48%. Lower estimates of GFR were associated with higher concentrations but concentrations varied greatly between patients with similar GFR. The correlation with terminal concentration half-life was similar for eGFR and CrCl.

CONCLUSIONS

With standard doses of meropenem and piperacillin-tazobactam, plasma concentrations in ICU patients vary > 10-fold and are suboptimal in a significant percentage of patients. The variation is large also between patients with similar renal function.

Ceftazidime-avibactam for the treatment of complicated intra-abdominal infections

INTRODUCTION

The treatment of complicated intra-abdominal infections (cIAI) is increasingly challenging due to increased resistance of Gram-negative organisms. These multidrug resistant organisms lead to an increase in morbidity and mortality. This has led to renewed interest in use of older β-lactam antibiotics in combination with newer β-lactamase inhibitors. Ceftazidime-avibactam is one of the newest such combination antibiotics, which has been released for treatment of complicated intra-abdominal infections in combination with metronidazole. Areas covered: In this drug evaluation manuscript cIAI along with the chemistry, pharmacodynamics, pharmacokinetics, metabolism and clinical study results of ceftazidime-avibactam are reviewed. Expert opinion: The role of ceftazidime-avibactam in combination with metronidazole in the treatment of cIAI is still to be defined. Patients with cIAI known to be infected with Klebsiella pneumoniae carbapenemase-producing Enterobacteriaceae would be clear candidates for treatment with this agent, as would patients infected with more common types of extended-spectrum β-lactamase producing Gram-negative pathogens if a carbapenem alternative were desired. At present, it is difficult to establish a clear group of patients with cIAI for whom initial empiric therapy with this agent would be warranted.

Clinical outcomes of extended versus intermittent administration of piperacillin/tazobactam for the treatment of hospital-acquired pneumonia: a randomized controlled trial

The purpose of this study was to assess the pharmacokinetic (PK) characteristics, clinical efficiency, and pharmacoeconomic parameters of piperacillin/tazobactam administered by extended infusion (EI) or intermittent infusion (II) in the treatment of hospital-acquired pneumonia (HAP) in critically ill patients with low illness severity in China. Fifty patients completed the study, with 25 patients receiving 4/0.5 g piperacillin/tazobactam over 30 min as the II group and 25 patients receiving 4/0.5 g piperacillin/tazobactam over 3 h every 6 h as the EI group. Drug assay was performed using high-performance liquid chromatography (HPLC). The percentage of the dosing interval for which the free piperacillin concentration (%fT) exceeds the minimum inhibitory concentration (MIC) was calculated. The patients' therapy cost, clinical efficiency, and adverse effects were also recorded. %fT>MIC was about 100, 98.73, and 93.04 % in the EI arm versus 81.48, 53.29, and 42.15 % in the II arm, respectively, when the microorganism responsible for HAP had an MIC of 4, 8, and 16 mg/L. The therapy cost in the EI group was lower than that of the II group ($1351.72 ± 120.39 vs. $1782.04 ± 164.51, p = 0.001). However, the clinical success rate, clinical failure rate, and drug-related adverse events did not significantly differ between groups. EI treatment with piperacillin/tazobactam was a cost-effective approach to the management of HAP, being equally clinically effective to conventional II.

Pharmacokinetic and Pharmacodynamic Principles of Anti-infective Dosing

PURPOSE

An understanding of the pharmacokinetic (PK) and pharmacodynamic (PD) principles that determine response to antimicrobial therapy can provide the clinician with better-informed dosing regimens. Factors influential on antibiotic disposition and clinical outcome are presented, with a focus on the primary site of infection. Techniques to better understand antibiotic PK and optimize PD are acknowledged.

METHODS

PubMed (inception-April 2016) was reviewed for relevant publications assessing antimicrobial exposures within different anatomic locations and clinical outcomes for various infection sites.

FINDINGS

A limited literature base indicates variable penetration of antibiotics to different target sites of infection, with drug solubility and extent of protein binding providing significant PK influences in addition to the major clearing pathway of the agent. PD indices derived from in vitro studies and animal models determine the optimal magnitude and frequency of dosing regimens for patients. PK/PD modeling and simulation has been shown an efficient means of assessing these PD endpoints against a variety of PK determinants, clarifying the unique effects of infection site and patient characteristics to inform the adequacy of a given antibiotic regimen.

IMPLICATIONS

Appreciation of the PK properties of an antibiotic and its PD measure of efficacy can maximize the utility of these life-saving drugs. Unfortunately, clinical data remain limited for a number of infection site-antibiotic exposure relationships. Modeling and simulation can bridge preclinical and patient data for the prescription of optimal antibiotic dosing regimens, consistent with the tenets of personalized medicine.

Simultaneous Determination of Eight β-Lactam Antibiotics, Amoxicillin, Cefazolin, Cefepime, Cefotaxime, Ceftazidime, Cloxacillin, Oxacillin, and Piperacillin, in Human Plasma by Using Ultra-High-Performance Liquid Chromatography with Ultraviolet Detection

A simple and rapid ultra-high-performance liquid chromatography (UHPLC) method using UV detection was developed for the simultaneous determination of eight β-lactam antibiotics in human plasma, including four penicillins, amoxicillin (AMX), cloxacillin (CLX), oxacillin (OXA), and piperacillin (PIP), and four cephalosporins, cefazolin (CFZ), cefepime (FEP), cefotaxime (CTX), and ceftazidime (CAZ). One hundred-microliter samples were spiked with thiopental as an internal standard, and proteins were precipitated by acetonitrile containing 0.1% formic acid. Separation was achieved on a pentafluorophenyl (PFP) column with a mobile phase composed of phosphoric acid (10 mM) and acetonitrile in gradient elution mode at a flow rate of 500 μl/min. Detection was performed at 230 nm for AMX, CLX, OXA, and PIP and 260 nm for CFZ, FEP, CTX, and CAZ. The total analysis time did not exceed 13 min. The method was found to be linear at concentrations ranging from 2 to 100 mg/liter for each compound, and all validation parameters fulfilled international requirements. Between- and within-run accuracy errors ranged from -5.2% to 11.4%, and precision was lower than 14.2%. This simple method requires small-volume samples and can easily be implemented in most clinical laboratories to promote the therapeutic drug monitoring of β-lactam antibiotics. The simultaneous determination of several antibiotics considerably reduces the time to results for clinicians, which may improve treatment efficiency, especially in critically ill patients.

Serum β-lactam concentrations in critically ill patients with cirrhosis: a matched case-control study

BACKGROUND & AIMS

The pharmacokinetics of β-lactam antibiotics have not been well defined in critically ill patients with cirrhosis.

METHODS

We reviewed data from critically ill patients with cirrhosis and matched controls in whom routine therapeutic drug monitoring of two broad-spectrum β-lactam antibiotics (piperacillin/tazobactam and meropenem) had been performed. Serum drug concentrations were measured twice by high-performance liquid chromatography. Antibiotic pharmacokinetics were calculated using a one-compartment model. We considered that therapy was adequate when serum drug concentrations were between 4 and 8 times the minimal inhibitory concentration of Pseudomonas aeruginosa during optimal periods of time for each drug (≥ 50% for piperacillin/tazobactam; ≥ 40% for meropenem).

RESULTS

We studied 38 patients with cirrhosis (16 for piperacillin/tazobactam and 22 for meropenem) and 38 matched controls. Drug dosing was similar in the two groups. The pharmacokinetics analysis showed a lower volume of distribution of meropenem (P = 0.05) and a lower antibiotic clearance of piperacillin/tazobactam (P = 0.009) in patients with cirrhosis than in the matched controls. Patients with cirrhosis were more likely than those without cirrhosis to have excessive serum β-lactam concentrations (P = 0.015), in particular for piperacillin/tazobactam.

CONCLUSIONS

Standard β-lactam antibiotics regimens resulted in excessive serum concentrations in two thirds of the patients with cirrhosis. This was particularly true for piperacillin/tazobactam, probably because of reduced drug clearance.

Pharmacokinetics and pharmacodynamics of meropenem in children with severe infection

This study aimed to describe the pharmacokinetic (PK) characteristics of meropenem in children with severe infections and to assess the pharmacokinetic/pharmacodynamic (PK/PD) profiles of various meropenem dosage regimens in these patients. Fourteen children with severe infections received intravenous (i.v.) bolus doses of meropenem (20 mg/kg/dose) every 8 h (q8h). Serum samples were obtained before and serially after the second dose of meropenem, and a population PK analysis was performed. The final model was used to simulate serum concentration-time profiles with various dosage regimens. The PK/PD target was to achieve a serum meropenem concentration higher than the minimum inhibitory concentration (MIC) of the causative organism (i.e. Pseudomonas aeruginosa and Enterobacteriaceae) for ≥40% of the dosing interval (40%T>MIC). The median age and weight of the children were 6.0 years and 20.0 kg, respectively. Meropenem serum concentration-time profiles were best described by a two-compartmental model with first-order elimination. The simulations showed that the probabilities of target attainment (PTAs) for organisms with an MIC of 1 mg/L were 0.678 and 1.000 following i.v. bolus and 3-h infusion of meropenem (20 mg/kg/dose), respectively. Using a 3-h infusion of a 20 mg/kg/dose, the PTA was 0.999 and 0.765 for organisms with MICs of 4 mg/L and 8 mg/L, respectively. Meropenem given as i.v. bolus doses of 20 mg/kg/dose q8h appeared to be inadequate for PK/PD target attainment for organisms with an MIC of 1 mg/L. The simulations showed that meropenem administration via a 3-h infusion using the same dose improved the PTA.

Advances in antibiotic therapy in the critically ill

Infections occur frequently in critically ill patients and their management can be challenging for various reasons, including delayed diagnosis, difficulties identifying causative microorganisms, and the high prevalence of antibiotic-resistant strains. In this review, we briefly discuss the importance of early infection diagnosis, before considering in more detail some of the key issues related to antibiotic management in these patients, including controversies surrounding use of combination or monotherapy, duration of therapy, and de-escalation. Antibiotic pharmacodynamics and pharmacokinetics, notably volumes of distribution and clearance, can be altered by critical illness and can influence dosing regimens. Dosing decisions in different subgroups of patients, e.g., the obese, are also covered. We also briefly consider ventilator-associated pneumonia and the role of inhaled antibiotics. Finally, we mention antibiotics that are currently being developed and show promise for the future.

The ANTIBIOPERF study: a nationwide cross-sectional survey about practices for β-lactam administration and therapeutic drug monitoring among critically ill patients in France

Our objective was to assess current practices about the administration (intermittent, extended, or continuous infusions) and therapeutic drug monitoring (TDM) of β-lactam antibiotics and vancomycin in France. We conducted a nationwide cross-sectional survey in May-August 2015, using an online questionnaire, sent as an e-mail link to infectious disease specialists and intensive care specialists through national mailing lists. We used clinical vignettes of critically ill patients to assess physicians' practices about administration and TDM practices for amoxicillin, cloxacillin, piperacillin/tazobactam, cefotaxime, ceftazidime, cefepime, meropenem and vancomycin. In all, 507 physicians participated (507/1200, response rate 42%). TDM was rarely available for β-lactams (from 16.5% (81/490) for cloxacillin to 30% (145/490) for ceftazidime), whereas vancomycin TDM was available in 97% (477/490) of the cases. In the clinical vignettes, ceftazidime and piperacillin/tazobactam were the β-lactams administered most frequently by extended or continuous infusions (76% (336/440) and 57% (252/444), respectively). Gaps in knowledge about the duration of stability of intravenous β-lactams were common (correct answers ranged from 8% (35/432) for cloxacillin to 33% (146/438) for ceftazidime). Most physicians (77%, 339/442) were convinced of the value of extended or continuous infusions for β-lactams in critically ill patients, but 48% (211/442) did not have access to practical guidelines. Our survey found that most infectious disease and intensive care specialists are favourable to optimized administration of β-lactams in critically ill patients. But the lack of guidelines and limited TDM availability for β-lactams in hospitals are potential barriers to its implementation.

Therapeutic drug monitoring of anti-infective agents in critically ill patients

Initial adequate anti-infective therapy is associated with significantly improved clinical outcomes for patients with severe infections. However, in critically ill patients, several pathophysiological and/or iatrogenic factors may affect the pharmacokinetics of anti-infective agents leading to suboptimal drug exposure, in particular during the early phase of therapy. Therapeutic drug monitoring (TDM) may assist to overcome this problem. We discuss the available evidence on the use of TDM in critically ill patient populations for a number of anti-infective agents, including aminoglycosides, β-lactams, glycopeptides, antifungals and antivirals. Also, we present the available evidence on the practices of anti-infective TDM and describe the potential utility of TDM to improve treatment outcome in critically ill patients with severe infections. For aminoglycosides, glycopeptides and voriconazole, beneficial effects of TDM have been established on both drug effectiveness and potential side effects. However, for other drugs, therapeutic ranges need to be further defined to optimize treatment prescription in this setting.

Piperacillin concentration in relation to therapeutic range in critically ill patients--a prospective observational study

BACKGROUND

Piperacillin levels after standard dosing have been shown frequently to be subtherapeutic, especially when renal clearance was augmented. Here, we aimed to determine if piperacillin was in its therapeutic range in a typically heterogeneous intensive care unit patient group, and also to describe target attainment dependent on daily dosage, creatinine clearance, and renal replacement therapy (RRT).

METHODS

Sixty patients with severe infections were included in this monocentric prospective observational study. Patients received 4.5 g of piperacillin-tazobactam two to three times daily by intermittent infusion depending on renal function according to clinical guidelines. Over 4 days, multiple serum samples (median per patient, 29; in total, 1627) were obtained to determine total piperacillin concentrations using ultra-high-performance liquid chromatography/tandem mass spectrometry.

RESULTS

A high heterogeneity of patient characteristics was observed (e.g., on day 1: creatinine clearance 2-233 mL/min and ten patients on RRT). Piperacillin trough levels showed inter-individual variation from 123 to >1785-fold on different study days. Each day, approximately 50% and 60% of the patients had piperacillin levels below the target ranges 1 and 2, respectively [defined for the calculated unbound piperacillin fraction according to the literature as 100% time above MIC (100%fT > MIC) (target range 1) and ≥ 50%fT > 4 × MIC (target range 2); MIC = 16 mg/L]. Whereas only the minority of patients who received piperacillin-tazobactam three times daily (TID) reached target 1 (38% on day 1), most patients who received piperacillin-tazobactam only twice daily (BID) because of severely impaired renal function reached this target (100% on day 1). Patients with RRT had significant higher percentages of fT > MIC. Zero percent, 55% and 100% of patients without RRT who received antibiotics TID reached target 1 when creatinine clearance was > 65 mL/min, 30-65 mL/min and < 30 mL/min, respectively. In patients with causative strains only sensitive to piperacillin-tazobactam of all antibiotics given to the patient, piperacillin levels negatively correlated with CRP concentrations of day 4 (p < 0.05).

CONCLUSIONS

A dosage of 4.5 g piperacillin-tazobactam TID seems to be frequently insufficient in critically ill patients, and also in patients where renal function is mildly to moderately impaired. For these patients, prescription of 4.5 g piperacillin-tazobactam four times daily could be considered.

TRIAL REGISTRATION

Clinicaltrials.gov NCT01793012. Registered 24 January 2013.

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

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

Pseudomonas aeruginosa ventilator-associated pneumonia management

Ventilator-associated pneumonia is the most common infection in intensive care unit patients associated with high morbidity rates and elevated economic costs; Pseudomonas aeruginosa is one of the most frequent bacteria linked with this entity, with a high attributable mortality despite adequate treatment that is increased in the presence of multiresistant strains, a situation that is becoming more common in intensive care units. In this manuscript, we review the current management of ventilator-associated pneumonia due to P. aeruginosa, the most recent antipseudomonal agents, and new adjunctive therapies that are shifting the way we treat these infections. We support early initiation of broad-spectrum antipseudomonal antibiotics in present, followed by culture-guided monotherapy de-escalation when susceptibilities are available. Future management should be directed at blocking virulence; the role of alternative strategies such as new antibiotics, nebulized treatments, and vaccines is promising.

Personalised beta-lactam therapy: basic principles and practical approach

Bacterial infections are potentially life-threatening diseases requiring effective antibiotic treatment right from the outset to achieve a favourable prognosis. Therapeutic success depends on the susceptibility of the bacterial pathogen, determined by the minimum inhibitory concentration (MIC), and the concentration of the antibiotic at the focus of infection, which is influenced by drug metabolism and pharmacokinetic (PK) factors. Beta-lactams are time-dependent antibiotics. Bacterial killing correlates with the duration of the drug concentration above the MIC of the pathogen. Critical illness is associated with major PK changes. This may lead to unexpected drug concentrations and unpredictable dose requirements differing significantly from standard dosages. Emerging dosing strategies are therefore based on PK/pharmacodynamic (PD) principles. Therapeutic drug monitoring (TDM) is increasingly playing a key role in antibiotic treatment optimisation in general and in beta-lactam therapy, in particular, notably in severely ill patients. Furthermore, evidence of the superiority of continuous beta-lactam infusions over shorter administration regimens is growing. Target drug concentrations have to be defined, considering MIC values especially in pathogens with limited susceptibility. For reliable TDM results, correct pre-analytical sample handling is indispensable. Personalised, TDM-guided therapy currently offers the most promising approach to assuring that beta-lactam treatment is effective, especially in critically ill patients.

Doripenem Treatment during Continuous Renal Replacement Therapy

Doripenem is a broad-spectrum parenteral carbapenem with enhanced activity against Pseudomonas aeruginosa. While the initial dosing recommendation for renally competent patients and patients undergoing continuous renal replacement therapy (cRRT) was 500 mg every 8 h (q8h), the dose for renally competent patients was updated to 1 g q8h in June 2012. There are no updated data for the dosing of patients on continuous renal replacement therapy. The original dosing regimen for cRRT patients was based on nonseptic patients, while newer publications chose comparatively low target concentrations for a carbapenem. Thus, there is an urgent need for updated recommendations for dosing during cRRT. In the trial presented here, we included 13 oliguric septic patients undergoing cRRT in an intensive care setting. Five patients each were treated with hemodiafiltration or hemodialysis, while three patients received hemofiltration treatment. All patients received 1 g doripenem every 8 h. Doripenem concentrations in the plasma and ultrafiltrate were measured over 48 h. The mean hemofilter clearance was 36.53 ml/min, and the mean volume of distribution was 59.26 liters. The steady-state trough levels were found at 8.5 mg/liter, with no considerable accumulation. Based on pharmacokinetic and pharmacodynamic considerations, we propose a regimen of 1 g q8h, which may be combined with a loading dose of 1.5 to 2 g for critically ill patients. (This study has been registered with EudraCT under registration no. 2009-018010-18 and at ClinicalTrials.gov under registration no. NCT02018939.).

Population pharmacokinetics of piperacillin in the early phase of septic shock: does standard dosing result in therapeutic plasma concentrations?

Antibiotic dosing in septic shock patients poses a challenge for clinicians due to the pharmacokinetic (PK) variability seen in this patient population. Piperacillin-tazobactam is often used for empirical treatment, and initial appropriate dosing is crucial for reducing mortality. Accordingly, we determined the pharmacokinetic profile of piperacillin (4 g) every 8 h, during the third consecutive dosing interval, in 15 patients treated empirically for septic shock. We developed a population pharmacokinetic model to assess empirical dosing and to simulate alternative dosing regimens and modes of administration. Time above the MIC (T>MIC) predicted for each patient was evaluated against clinical breakpoint MIC for Pseudomonas aeruginosa (16 mg/liter). Pharmacokinetic-pharmacodynamic (PK/PD) targets evaluated were 50% fT>4×MIC and 100% fT>MIC. A population PK model was developed using NONMEM, and data were best described by a two-compartment model. Central and intercompartmental clearances were 3.6 liters/h (relative standard error [RSE], 15.7%) and 6.58 liters/h (RSE, 16.4%), respectively, and central and peripheral volumes were 7.3 liters (RSE, 11.8%) and 3.9 liters (RSE, 9.7%), respectively. Piperacillin plasma concentrations varied considerably between patients and were associated with levels of plasma creatinine. Patients with impaired renal function were more likely to achieve predefined PK/PD targets than were patients with preserved or augmented renal function. Simulations of alternative dosing regimens showed that frequent intermittent bolus dosing as well as dosing by extended and continuous infusion increases the probability of attaining therapeutic plasma concentrations. For septic shock patients with preserved or augmented renal function, dose increment or prolonged infusion of the drug needs to be considered. (This study has been registered at ClinicalTrials.gov under registration no. NCT02306928.).

Population pharmacokinetics and dosing simulations of cefepime in septic shock patients receiving continuous renal replacement therapy

The aim of this study was to describe the population pharmacokinetics of cefepime in septic shock patients requiring continuous renal replacement therapy and to determine whether current or alternative dosing regimens can achieve PK/PD targets. In this observational PK study, 62 samples from 13 patients were analysed using non-linear mixed-effects modelling. Different dosing regimens were evaluated using Monte Carlo simulations with ultrafiltration flow rates (UFRs) of 1000, 1500 and 2000 mL/h. The probability of target attainment was calculated against a conservative (60% T(>MIC)) and a higher PK/PD target (100% T(>MIC)) against an MIC of 8 mg/L, the clinical susceptibility breakpoint for Pseudomonas aeruginosa. A one-compartment model with between-subject variability (BSV) on clearance and volume of distribution (V(d)) described the data adequately. UFR was supported as a covariate on both parameters. Typical values for clearance and V(d) were 4.4L/h (BSV 37%) and 40.9L (BSV 20%), respectively. Dosing simulations showed failure to achieve both a conservative and a higher PK/PD target using a dose of 1g q12h for patients treated with a high UFR (≥1500 mL/h). The dose of 2g q8h or 1g q6h leads to optimal target attainment for high UFR. One gram q8h is optimal for low UFR (≤1000 mL/h). We found important variability in PK parameters. Dosing simulations show that a dose of 2g q8h or 1g q6h is needed to ensure rapid achievement of adequate levels if the UFR is ≥1500 mL/h and 1g q8h for low UFR (≤1000 mL/h).

Empiric antimicrobial therapy in severe sepsis and septic shock: optimizing pathogen clearance

Mortality and morbidity in severe sepsis and septic shock remain high despite significant advances in critical care. Efforts to improve outcome in septic conditions have focused on targeted, quantitative resuscitation strategies utilizing intravenous fluids, vasopressors, inotropes, and blood transfusions to correct disease-associated circulatory dysfunction driven by immune-mediated systemic inflammation. This review explores an alternate paradigm of septic shock in which microbial burden is identified as the key driver of mortality and progression to irreversible shock. We propose that clinical outcomes in severe sepsis and septic shock hinge upon the optimized selection, dosing, and delivery of highly potent antimicrobial therapy.

Mutagenesis of the CTX-M-type ESBL-is MIC-guided treatment according to the new EUCAST recommendations a safe approach?

OBJECTIVES

Spurred by the latest EUCAST and CLSI recommendation to adjust antibiotic therapy on the basis of MICs instead of resistance mechanisms, we aimed to investigate the ability of CTX-M-1 and CTX-M-14 to achieve ceftazidime resistance under selective conditions.

METHODS

We exposed Escherichia coli transconjugants bearing natural plasmids that express CTX-M-1, CTX-M-14 or CTX-M-15 to various selective culture conditions and tracked their growth and mutational frequencies. For selected mutants we analysed the sequences of the bla CTX-M genes, determined the altered MICs of cefotaxime, cefepime, ceftazidime and meropenem, and measured the efflux properties and the changes in transcriptional levels of bla CTX-M genes.

RESULTS

The CTX-M-1- and CTX-M-14-bearing clones switched from ceftazidime-susceptible to ceftazidime-resistant phenotypes under selective conditions within 24 h. However, no mutations within the bla CTX-M genes were found, and the efflux was unlikely to be involved in the increased ceftazidime MICs. In CTX-M-1-bearing clones bla CTX-M-1 expression was 19-fold increased under ceftazidime-selective conditions but there was a high variance within the clones. Reasons for increased ceftazidime MICs of CTX-M-bearing clones remain unclear but might be the increased enzymatic activity or other intrachromosomal mutations.

CONCLUSIONS

It can be speculated that different strategies to survive under selective conditions can be adopted by E. coli, thereby establishing an optimal mechanism with the lowest energy demand for each transconjugant. Based on our in vitro findings, we cannot fully recommend the use of ceftazidime, particularly in critically ill patients with infections due to ESBL producers, regardless of susceptibility to ceftazidime.

A multicenter study on the effect of continuous hemodiafiltration intensity on antibiotic pharmacokinetics

Introduction

Continuous renal replacement therapy (CRRT) may alter antibiotic pharmacokinetics and increase the risk of incorrect dosing. In a nested cohort within a large randomized controlled trial, we assessed the effect of higher (40 mL/kg per hour) and lower (25 mL/kg per hour) intensity CRRT on antibiotic pharmacokinetics.

Methods

We collected serial blood samples to measure ciprofloxacin, meropenem, piperacillin-tazobactam, and vancomycin levels. We calculated extracorporeal clearance (CL), systemic CL, and volume of distribution (Vd) by non-linear mixed-effects modelling. We assessed the influence of CRRT intensity and other patient factors on antibiotic pharmacokinetics.

Results

We studied 24 patients who provided 179 pairs of samples. Extracorporeal CL increased with higher-intensity CRRT but the increase was significant for vancomycin only (mean 28 versus 22 mL/minute; P = 0.0003). At any given prescribed CRRT effluent rate, extracorporeal CL of individual antibiotics varied widely, and the effluent-to-plasma concentration ratio decreased with increasing effluent flow. Overall, systemic CL varied to a greater extent than Vd, particularly for meropenem, piperacillin, and tazobactam, and large intra-individual differences were also observed. CRRT dose did not influence overall (systemic) CL, Vd, or half-life. The proportion of systemic CL due to CRRT varied widely and was high in some cases.

Conclusions

In patients receiving CRRT, there is great variability in antibiotic pharmacokinetics, which complicates an empiric approach to dosing and suggests the need for therapeutic drug monitoring. More research is required to investigate the apparent relative decrease in clearance at higher CRRT effluent rates.

Trial registration

ClinicalTrials.gov NCT00221013. Registered 14 September 2005.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-0818-8) contains supplementary material, which is available to authorized users.

Population pharmacokinetics and Monte Carlo dosing simulations of meropenem during the early phase of severe sepsis and septic shock in critically ill patients in intensive care units

Pathophysiological changes during the early phase of severe sepsis and septic shock in critically ill patients, resulting in altered pharmacokinetic (PK) patterns for antibiotics, are important factors influencing therapeutic success. The aims of this study were (i) to reveal the population PK parameters and (ii) to assess the probability of target attainment (PTA) for meropenem. The PK studies were carried out following administration of 1 g of meropenem every 8 h during the first 24 h of severe sepsis and septic shock in nine patients, and a Monte Carlo simulation was performed to determine the PTA of achieving 40% exposure time during which the free plasma drug concentration remains above the MIC (fT>MIC) and 80% fT>MIC. The volume of distribution (V) and total clearance (CL) of meropenem in these patients were 23.7 liters and 7.82 liters/h, respectively. For pathogens with MICs of 4 μg/ml, the PTAs of 40% fT>MIC following administration of meropenem as a 1-h infusion of 1 g every 8 h and a 4-h infusion of 0.5 g every 8 h were 92.52% and 90.29%, respectively. For pathogens with MICs of 2 μg/ml in immunocompromised hosts, the PTAs of 80% fT>MIC following administration of 1-h and 4-h infusions of 2 g of meropenem every 8 h were 84.32% and 94.72%, respectively. These findings indicated that the V of meropenem was greater and the CL of meropenem was lower than the values obtained in a previous study with healthy subjects. The maximum recommended dose, i.e., 2 g of meropenem every 8 h, may be required for treatment of life-threatening infections in this patient population.

Antimicrobial dosing in critically ill patients with sepsis-induced acute kidney injury

Severe sepsis often leads to multiple organ dysfunction syndromes (MODS) with acute kidney injury (AKI). AKI affects approximately, 35% of Intensive Care Unit patients, and most of these are due to sepsis. Mortality rate of sepsis-induced AKI is high. Inappropriate use of antimicrobials may be responsible for higher therapeutic failure, mortality rates, costs and toxicity as well as the emergence of resistance. Antimicrobial treatment is particularly difficult due to altered pharmacokinetic profile, dynamic changes in patient's clinical status and, in many cases, need for renal replacement therapy. This article aims to describe the appropriate antimicrobial dosing and reviews the factors contributing to the difficulties in establishing precise guidelines for antimicrobial dosing in sepsis-induced AKI patients.

SEARCH STRATEGY

Text material was collected by systematic search in PubMed, Google (1978-2013) for original articles.

Quantification of piperacillin, tazobactam, cefepime, meropenem, ciprofloxacin and linezolid in serum using an isotope dilution UHPLC-MS/MS method with semi-automated sample preparation

Recent studies have demonstrated highly variable blood concentrations of piperacillin, tazobactam, cefepime, meropenem, ciprofloxacin and linezolid in critically ill patients with a high incidence of sub-therapeutic levels. Consequently, therapeutic drug monitoring (TDM) of these antibiotics has to be considered, requiring robust and reliable routine analytical methods. The aim of the present work was to develop and validate a multi-analyte ultra high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method for the simultaneous quantification of the above mentioned antibiotics.

Sample preparation included a manual protein precipitation step followed by two-dimensional ultra high performance liquid chromatography (2D-UHPLC). Corresponding stable isotope-labeled substances were used as internal standards for all of the analytes, with the exception of tazobactam. The injected sample volume was 7 μL. The run time was 5.0 min.

Inaccuracy was ≤8% and imprecision coefficient of variation (CV) was <9% for all analytes. Only minor matrix effects and negligible carry-over was observed. The method was found to be robust during the validation period.

We were able to develop a reliable 2D-UHPLC-MS/MS method addressing analytes with highly heterogeneous physico-chemical properties. The novel assay may be an efficient tool for an optimized process workflow in clinical laboratories for important antibiotics in regards to TDM.

Antibiotics and extracorporeal circulation--one size does not fit all

Dosing of antibiotics in critically ill patients is a significant challenge. The increasing number of patients undergoing extracorporeal membrane oxygenation further complicates the issue due to inflammatory activation and to drug sequestration in the circuit. Since patients receiving extracorporeal membrane oxygenation commonly face severe infections, appropriate antibiotic selection and correct dosing is of paramount importance to improve survival. Therapeutic drug monitoring (whenever available) or population pharmacokinetics, based on readily available clinical and laboratory data, should help tailor antibiotic dosing to the individual patient.

Initial dosing regimen of vancomycin to achieve early therapeutic plasma concentration in critically ill patients with MRSA infection based on APACHE II score

It is essential to assure the efficacy of antimicrobials at the initial phase of therapy. However, increasing the volume of distribution (Vd) of hydrophilic antimicrobials in critically ill patients leads to reduced antimicrobial concentration in plasma and tissue, which may adversely affect the efficacy of that therapy. The aim of the present study was to establish a theoretical methodology for setting an appropriate level for initial vancomycin therapy in individual patients based on Acute Physiology and Chronic Health Evaluation (APACHE) II score. We obtained data from patients who received intravenous vancomycin for a suspected or definitively diagnosed Gram-positive bacterial infection within 72 h after admission to the intensive care unit. The Vd and elimination half-life (t 1/2) of vancomycin values were calculated using the Bayesian method, and we investigated the relationship between them and APACHE II score. There were significant correlations between APACHE II scores and Vd/actual body weight (ABW), as well as t 1/2 (r = 0.58, p < 0.05 and r = 0.74, p < 0.01, respectively). Our results suggested that the Vd and t 1/2 of vancomycin could be estimated using the following regression equations using APACHE II score.[Formula: see text] [Formula: see text]We found that APACHE II score was a useful index for predicting the Vd and t 1/2 of vancomycin, and used that to establish an initial vancomycin dosing regimen comprised of initial dose and administration interval for individual patients.

β-Lactam pharmacokinetics during extracorporeal membrane oxygenation therapy: A case-control study

Most adult patients receiving extracorporeal membrane oxygenation (ECMO) require antibiotic therapy, however the pharmacokinetics of β-lactams have not been well studied in these conditions. In this study, data from all patients receiving ECMO support and meropenem (MEM) or piperacillin/tazobactam (TZP) were reviewed. Drug concentrations were measured 2h after the start of a 30-min infusion and just before the subsequent dose. Therapeutic drug monitoring (TDM) results in ECMO patients were matched with those in non-ECMO patients for (i) drug regimen, (ii) renal function, (iii) total body weight, (iv) severity of organ dysfunction and (v) age. Drug concentrations were considered adequate if they remained 4-8× the clinical MIC breakpoint for Pseudomonas aeruginosa for 50% (TZP) or 40% (MEM) of the dosing interval. A total of 41 TDM results (27 MEM; 14 TZP) were obtained in 26 ECMO patients, with 41 matched controls. There were no significant differences in serum concentrations or pharmacokinetic parameters between ECMO and non-ECMO patients, including Vd [0.38 (0.27-0.68) vs. 0.46 (0.33-0.79)L/kg; P=0.37], half-life [2.6 (1.8-4.4) vs. 2.9 (1.7-3.7)h; P=0.96] and clearance [132 (66-200) vs. 141 (93-197)mL/min; P=0.52]. The proportion of insufficient (13/41 vs. 12/41), adequate (15/41 vs. 19/41) and excessive (13/41 vs. 10/41) drug concentrations was similar in ECMO and non-ECMO patients. Achievement of target concentrations of these β-lactams was poor in ECMO and non-ECMO patients. The influence of ECMO on MEM and TZP pharmacokinetics does not appear to be significant.

How do we use therapeutic drug monitoring to improve outcomes from severe infections in critically ill patients?

High mortality and morbidity rates associated with severe infections in the critically ill continue to be a significant issue for the healthcare system. In view of the diverse and unique pharmacokinetic profile of drugs in this patient population, there is increasing use of therapeutic drug monitoring (TDM) in attempt to optimize the exposure of antibiotics, improve clinical outcome and minimize the emergence of antibiotic resistance. Despite this, a beneficial clinical outcome for TDM of antibiotics has only been demonstrated for aminoglycosides in a general hospital patient population. Clinical outcome studies for other antibiotics remain elusive. Further, there is significant variability among institutions with respect to the practice of TDM including the selection of patients, sampling time for concentration monitoring, methodologies of antibiotic assay, selection of PK/PD targets as well as dose optimisation strategies. The aim of this paper is to review the available evidence relating to practices of antibiotic TDM, and describe how TDM can be applied to potentially improve outcomes from severe infections in the critically ill.

Temocillin (6 g daily) in critically ill patients: continuous infusion versus three times daily administration

OBJECTIVES

The growing incidence of infections caused by Enterobacteriaceae producing ESBLs has led to increased use of carbapenems. Temocillin, which resists most β-lactamases, may be a useful alternative. The aim of this study was to assess the pharmacokinetics and target attainment rates of 6 g of temocillin daily divided into three administrations every 8 h (three times daily) or administered by continuous infusion in critically ill patients.

PATIENTS AND METHODS

This was a prospective, two-centre, randomized, controlled study in patients with intra-abdominal or lower respiratory tract infections caused by Enterobacteriaceae.

RESULTS

Thirty-two patients were included and analysed for clinical efficacy, and pharmacokinetics were measured in 29 of them. Four patients undergoing continuous veno-venous haemofiltration (CVVH) were analysed separately. Mean, median and range of percentages of the dosing interval during which the free drug concentration remained >16 mg/L were 76.4, 98 and 18.7-98.9 in patients treated three times daily and 98.9, 89.7 and 36.4-99.9 in patients with continuous infusion, respectively. Clinical cure rates were 79% and 93% in each of these groups, respectively (not significant). Patients with CVVH received a daily dose of 750 mg given by continuous infusion and had a mean free drug concentration of only 13.8 ± 1.9 mg/L. No adverse event attributable to temocillin was observed.

CONCLUSIONS

Temocillin (6 g daily) given by continuous infusion allows a larger proportion of critically ill patients to have free drug serum concentrations covering infections caused by Enterobacteriaceae with an MIC of 16 mg/L compared with administration three times daily. Clinical efficacy compared with carbapenems in documented severe infections needs to be further studied.

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.

The challenges of multiple organ dysfunction syndrome and extra-corporeal circuits for drug delivery in critically ill patients

The multiple organ dysfunction syndrome (MODS) is characterized by more than one organ system failing, especially during critical illness. MODS is the leading cause of morbidity and mortality in current ICU practice; moreover, multiple organ dysfunction, especially liver and kidneys, may significantly affect the pharmacokinetics (PKs) of different drugs that are currently administered in critically ill patients. These PK alterations may either result in insufficient drug concentrations to achieve the desired effects or in blood and tissue accumulation, with the development of serious adverse events. The use of extra-corporeal circuits, such as extracorporeal membrane oxygenation (ECMO) and continuous renal replacement therapy (CRRT), may further contribute to PKs changes in this patients' population. In this review, we have described the main PK changes occurring in all these conditions and how drug concentrations may potentially be affected. The lack of prospective studies on large cohorts of patients makes impossible any specific recommendation on drug regimen adjustment in ICU patients. Nevertheless, the clinicians should be aware of these abnormalities in order to better understand some unexpected therapeutic issues occurring in such patients.

The effect of pathophysiology on pharmacokinetics in the critically ill patient--concepts appraised by the example of antimicrobial agents

Critically ill patients are at high risk for development of life-threatening infection leading to sepsis and multiple organ failure. Adequate antimicrobial therapy is pivotal for optimizing the chances of survival. However, efficient dosing is problematic because pathophysiological changes associated with critical illness impact on pharmacokinetics of mainly hydrophilic antimicrobials. Concentrations of hydrophilic antimicrobials may be increased because of decreased renal clearance due to acute kidney injury. Alternatively, antimicrobial concentrations may be decreased because of increased volume of distribution and augmented renal clearance provoked by systemic inflammatory response syndrome, capillary leak, decreased protein binding and administration of intravenous fluids and inotropes. Often multiple conditions that may influence pharmacokinetics are present at the same time thereby excessively complicating the prediction of adequate concentrations. In general, conditions leading to underdosing are predominant. Yet, since prediction of serum concentrations remains difficult, therapeutic drug monitoring for individual fine-tuning of antimicrobial therapy seems the way forward.