Intermittent bolus dosing of ceftazidime in critically ill patients

Ceftazidime dosing in obese patients: is it time for more?

INTRODUCTION

Ceftazidime is used for the treatment of many bacterial infections, including severe P. aeruginosa infections. Like other beta-lactams, inter-individual variability in ceftazidime pharmacokinetics has been described. Due to its related pathophysiological modifications, obesity might influence ceftazidime pharmacokinetics.

AREAS COVERED

The objective of this review is to assess the current state of knowledge about the impact of obesity on ceftazidime treatment. A literature search was conducted on PubMed-MEDLINE (2016-2021) to retrieve pharmacokinetic studies published in English, matching the terms 'ceftazidime' AND 'pharmacokinetics.'

EXPERT OPINION

The impact of obesity on pharmacokinetics is generally poorly known, mainly because obese patients are often excluded from clinical studies. However, the published literature clearly shows that obese patients have significantly lower ceftazidime concentrations. This could be explained by increased volume of distribution and clearance. This low exposure represents a major factor of therapeutic failure, potentially fatal for critically ill patients. While further studies would be useful to better assess the magnitude and understanding of this variability, the use of higher doses of ceftazidime is needed in obese patients. Moreover, therapeutic drug monitoring for dose adaptation is of major interest for these patients, as the efficacy of ceftazidime seems to be directly related to its plasma concentration.

Stability of Amoxicillin and Clavulanic Acid in Separate Containers for Administration via a Y-Site

Rationale

With the discovery of new antibiotics diminishing, optimising the administration of existing antibiotics such as amoxicillin-clavulanic acid has become a necessity. At present, the optimal approach for enhancing the effectiveness of time-dependent antibiotics involves extending the time at which antibiotic concentrations are maintained above the minimal inhibitory concentration by prolonging the infusion time. This pharmacodynamic rationale cannot be applied to co-amoxiclav because of poor stability at room temperature. The aim of this study was to establish the shelf-life of amoxicillin and clavulanic acid prepared in separate containers to determine the feasibility of 24-hr continuous infusion therapy.

Methods

A previously developed and validated stability-indicating HPLC method was used to establish the shelf-life of reconstituted amoxicillin and clavulanic acid when prepared in separate containers. Stability at clinical concentration was evaluated at three temperatures. To establish whether there were significant differences at the level of both active ingredients and temperature, results were analysed using analysis of covariance (ANCOVA) to assess differences between the attained slopes of regression.

Results

Data obtained indicated amoxicillin and clavulanic acid stability superior to that previously proposed making it suitable for continuous infusion therapy. Analysis of regression slopes via ANCOVA showed that temperature significantly affected amoxicillin and clavulanic acid stability. Amoxicillin retained 90% of its initial concentration for 80.3 hrs when stored at 4°C, 24.8 hrs at 25°C and 9 hrs when incubated at 37°C. Clavulanic acid retained 90% of its initial concentration for 152 hrs when stored at 4°C, 26 hrs at 25°C and 6.4 hrs when incubated at 37°C.

Conclusion

Amoxicillin and clavulanic acid are suitable for administration via continuous infusion when prepared, stored, and administered in separate containers. Results obtained from this study aid in ameliorating current dosing regimens to optimise antibiotic efficacy; however, more in-depth amoxicillin and clavulanic acid y-site compatibility studies are warranted.

Elevated MICs of Susceptible Anti-Pseudomonal Cephalosporins in Non-Carbapenemase-Producing, Carbapenem-Resistant Pseudomonas aeruginosa: Implications for Dose Optimization

The present study evaluated the in vitro potency of ceftazidime and cefepime amongst carbapenem-resistant Pseudomonas aeruginosa collected as part of a global surveillance program and assessed the pharmacodynamic implications using previously published population pharmacokinetics. When susceptible, MICs resulted at the high end of distribution for both ceftazidime and cefepime, thus 6 g/day was required to achieve optimal pharmacodynamic profiles. These findings should be considered in the clinic and for the application of CLSI susceptibility breakpoints.

Population Pharmacokinetics and Probability of Target Attainment of Different Dosing Regimens of Ceftazidime in Critically Ill Patients with a Proven or Suspected Pseudomonas aeruginosa Infection

Altered pharmacokinetics (PK) of hydrophilic antibiotics in critically ill patients is common, with possible consequences for efficacy and resistance. We aimed to describe ceftazidime population PK in critically ill patients with a proven or suspected Pseudomonas aeruginosa infection and to establish optimal dosing. Blood samples were collected for ceftazidime concentration measurement. A population PK model was constructed, and probability of target attainment (PTA) was assessed for targets 100% T > MIC and 100% T > 4 × MIC in the first 24 h. Ninety-six patients yielded 368 ceftazidime concentrations. In a one-compartment model, variability in ceftazidime clearance (CL) showed association with CVVH. For patients not receiving CVVH, variability in ceftazidime CL was 103.4% and showed positive associations with creatinine clearance and with the comorbidities hematologic malignancy, trauma or head injury, explaining 65.2% of variability. For patients treated for at least 24 h and assuming a worst-case MIC of 8 mg/L, PTA was 77% for 100% T > MIC and 14% for 100% T > 4 × MIC. Patients receiving loading doses before continuous infusion demonstrated higher PTA than patients who did not (100% T > MIC: 95% (n = 65) vs. 13% (n = 15); p < 0.001 and 100% T > 4 × MIC: 20% vs. 0%; p = 0.058). The considerable IIV in ceftazidime PK in ICU patients could largely be explained by renal function, CVVH use and several comorbidities. Critically ill patients are at risk for underexposure to ceftazidime when empirically aiming for the breakpoint MIC for P. aeruginosa. A loading dose is recommended.

[Pharmacokinetic modifications and pharmacokinetic/pharmacodynamic optimization of beta-lactams in ICU]

Pharmacokinetic modifications in critically ill patients and those induced by ICU therapeutics raise a lot of issues about antibiotic dose adaptation. Beta-lactams are anti-infectious widely used in ICU. Frequent beta-lactam underdoses induce a risk of therapeutic failure potentially lethal and of emergence of bacterial resistance. Overdoses expose to a neurotoxic and nephrotoxic risk. Therefore, an understanding of pharmacokinetics modifications appears to be essential. A global pharmacokinetic/pharmacodynamic approach is required, including use of prolonged or continued beta-lactam infusions to optimise probability of pharmacokinetic/pharmacodynamic target attainment. Beta-lactam therapeutic drug monitoring should also be considered. Experts agree to target a free plasma betalactam concentration above four times the MIC of the causative bacteria for 100 % of the dosing interval. Bayesian methods could permit individualized doses adaptations.

Novel Cassette Assay To Quantify the Outer Membrane Permeability of Five β-Lactams Simultaneously in Carbapenem-Resistant Klebsiella pneumoniae and Enterobacter cloacae

Poor penetration through the outer membrane (OM) of Gram-negative bacteria is a major barrier of antibiotic development. While β-lactam antibiotics are commonly used against Klebsiella pneumoniae and Enterobacter cloacae, there are limited data on OM permeability especially in K. pneumoniae Here, we developed a novel cassette assay, which can simultaneously quantify the OM permeability to five β-lactams in carbapenem-resistant K. pneumoniae and E. cloacae Both clinical isolates harbored a blaKPC-2 and several other β-lactamases. The OM permeability of each antibiotic was studied separately ("discrete assay") and simultaneously ("cassette assay") by determining the degradation of extracellular β-lactam concentrations via multiplex liquid chromatography-tandem mass spectrometry analyses. Our K. pneumoniae isolate was polymyxin resistant, whereas the E. cloacae was polymyxin susceptible. Imipenem penetrated the OM at least 7-fold faster than meropenem for both isolates. Imipenem penetrated E. cloacae at least 258-fold faster and K. pneumoniae 150-fold faster compared to aztreonam, cefepime, and ceftazidime. For our β-lactams, OM permeability was substantially higher in the E. cloacae compared to the K. pneumoniae isolate (except for aztreonam). This correlated with a higher OmpC porin production in E. cloacae, as determined by proteomics. The cassette and discrete assays showed comparable results, suggesting limited or no competition during influx through OM porins. This cassette assay allowed us, for the first time, to efficiently quantify the OM permeability of multiple β-lactams in carbapenem-resistant K. pneumoniae and E. cloacae Characterizing the OM permeability presents a critical contribution to combating the antimicrobial resistance crisis and enables us to rationally optimize the use of β-lactam antibiotics.IMPORTANCE Antimicrobial resistance is causing a global human health crisis and is affecting all antibiotic classes. While β-lactams have been commonly used against susceptible isolates of Klebsiella pneumoniae and Enterobacter cloacae, carbapenem-resistant isolates are spreading worldwide and pose substantial clinical challenges. Rapid penetration of β-lactams leads to high drug concentrations at their periplasmic target sites, allowing β-lactams to more completely inactivate their target receptors. Despite this, there are limited tangible data on the permeability of β-lactams through the outer membranes of many Gram-negative pathogens. This study presents a novel, cassette assay, which can simultaneously characterize the permeability of five β-lactams in multidrug-resistant clinical isolates. We show that carbapenems, and especially imipenem, penetrate the outer membrane of K. pneumoniae and E. cloacae substantially faster than noncarbapenem β-lactams. The ability to efficiently characterize the outer membrane permeability is critical to optimize the use of β-lactams and combat carbapenem-resistant isolates.

Dose Selection and Validation for Ceftazidime-Avibactam in Adults with Complicated Intra-abdominal Infections, Complicated Urinary Tract Infections, and Nosocomial Pneumonia

Avibactam is a non-β-lactam β-lactamase inhibitor that has been approved in combination with ceftazidime for the treatment of complicated intra-abdominal infections, complicated urinary tract infections, and nosocomial pneumonia, including ventilator-associated pneumonia. In Europe, ceftazidime-avibactam is also approved for the treatment of Gram-negative infections with limited treatment options. Selection and validation of the ceftazidime-avibactam dosage regimen was guided by an iterative process of population pharmacokinetic (PK) modelling, whereby population PK models for ceftazidime and avibactam were developed using PK data from clinical trials and updated periodically. These models were used in probability of target attainment (PTA) simulations using joint pharmacodynamic (PD) targets for ceftazidime and avibactam derived from preclinical data. Joint PTA was calculated based on the simultaneous achievement of the individual PK/PD targets (50% free time above the ceftazidime-avibactam MIC for ceftazidime and free time above a critical avibactam threshold concentration of 1 mg/liter for avibactam). The joint PTA analyses supported a ceftazidime-avibactam dosage regimen of 2,000 + 500 mg every 8 h by 2-h intravenous infusion for patients with creatinine clearance (CL_CR) >50 ml/min across all approved indications and modified dosage regimens for patients with CL_CR ≤50 ml/min. Subgroup simulations for individual phase 3 patients showed that the dosage regimen was robust, with high target attainment (>95%) against MICs ≤8 mg/liter achieved regardless of older age, obesity, augmented renal clearance, or severity of infection. This review summarizes how the approved ceftazidime-avibactam dosage regimens were developed and validated using PK/PD targets, population PK modeling, and PTA analyses.

Pharmacokinetic and Pharmacodynamic Analysis of Ceftazidime/Avibactam in Critically Ill Patients

BACKGROUND

The pharmacokinetics, especially the volume of distribution (Vd), of ß-lactam antibiotics can be altered in critically ill patients. This can lead to decreased serum concentrations and a reduction in clinical cures. Ceftazidime/avibactam (CZA) is a new antimicrobial agent utilized in critically ill patients although its pharmacokinetics has not been well defined in these patients.

PATIENTS AND METHODS

In this study, the serum concentrations of CZA from adult patients treated in an intensive care unit (ICU) with standard dosing regimens were measured and both pharmacokinetic and pharmacodynamic parameters were computed. The pharmacodynamic analyses included Monte Carlo simulations to determine the probability of target attainment (PTA: free ceftazidime concentrations exceed the minimum inhibitory concentration [MIC] for 50% of the dosing interval; free avibactam concentrations exceed 1 mg/L over the dosing interval) and serum time-kill curves against multi-drug-resistant Enterobacteriaceae susceptible to CZA. Serum concentrations were measured in 10 critically ill patients at two, four, six, and eight hours after multiple doses (infused over two hours) of CZA.

RESULTS

A significant linear relation between creatinine clearance and total body clearance was identified for both ceftazidime (R = 0.91) and avibactam (R = 0.88). The mean clearance, volume of distribution, and half-life for ceftazidime were 6.1 ± 3.8 L/h, 35 ± 10.5 L, and 4.8 ± 2.15 h, respectively. For avibactam, these values were 11.1 ± 6.8 L/h, 50.8 ± 14.3 L, and 4.1 ± 2.1 h, respectively. Ceftazidime/avibactam achieved optimal PTA for bacteria with MICs of 16 mg/L or less. Furthermore, time-kill experiments revealed that serum concentrations of CZA, at each collection time, exhibited bactericidal (≥ 3 log₁₀ CFU/mL reduction) activity against each of the study isolates.

CONCLUSION

In conclusion, our study results suggest that the current dosing regimens of CZA can provide effective antimicrobial activity in ICU patients against CZA-susceptible (MIC ≤8 mg/L) isolates.

Application of Pharmacodynamic Profiling for the Selection of Optimal β-lactam Regimens in a Large University Hospital

BACKGROUND

Infections caused by drug-resistant Gram-negative bacteria (GNB) are increasing worldwide and as a result, the selection of appropriate empiric antibiotics (ATBs) has been made increasingly difficult. The present study aimed to identify optimized dosing regimens of intravenous (IV) ATBs, defined by cumulative fraction response (CFR), against E. coli (EC), K. pneumoniae (KP), P. aeruginosa (PA), and A. baumannii (AB) at 2,300-bed University Hospital.

MATERIALS AND METHODS

The minimum inhibitory concentrations (MIC) of EC, KP, PA, and AB from clinical specimens, 250 each, were determined. Pharmacodynamic profiling using Monte Carlo Simulation was performed for standard, high dosage, and prolonged infusions (PI) of ceftriaxone, cefepime, ceftazidime, imipenem, meropenem, and doripenem. A CFR of ≥90% was targeted as providing a sufficiently high ATB exposure.

RESULTS

When considering the Enterobacteriaceae, the % susceptible for the cephalosporins ranged from 60% for ceftriaxone to 86% for cefepime, as a result only the 2g q8h regimens of ceftazidime and cefepime provided high CFRs. In contrast, all the carbapenems had % susceptible and CFRs ≥90% for EC and KP. While cefepime and ceftazidime demonstrated higher % susceptibility (82-83%) for PA relative to that of the carbapenems (61-69%) only doripenem 2g q8h (4h PI) achieved an optimal CFR (92%) against this organism. Due to the MIC profiles and dismal susceptibilities of AB (16-22%), none of the regimens studied achieved CFRs > 65%.

CONCLUSIONS

The pharmacodynamic profiling undertaken in the current study provides insights that allow prescribers to select more appropriate empirical antibiotic regimens for the treatment of infection caused by these common GNB pathogens at this Thai hospital. While higher doses and PI of β-lactams improve exposures against EC, KP and PA, this approach will not sufficiently enhance their potency against AB, thus alternative therapies should be considered for this organism.

Ceftolozane/tazobactam pharmacokinetic/pharmacodynamic-derived dose justification for phase 3 studies in patients with nosocomial pneumonia

Ceftolozane/tazobactam is an antipseudomonal antibacterial approved for the treatment of complicated urinary tract infections (cUTIs) and complicated intra‐abdominal infections (cIAIs) and in phase 3 clinical development for treatment of nosocomial pneumonia. A population pharmacokinetic (PK) model with the plasma‐to‐epithelial lining fluid (ELF) kinetics of ceftolozane/tazobactam was used to justify dosing regimens for patients with nosocomial pneumonia in phase 3 studies. Monte Carlo simulations were performed to determine ceftolozane/tazobactam dosing regimens with a >90% probability of target attainment (PTA) for a range of pharmacokinetic/pharmacodynamic targets at relevant minimum inhibitory concentrations (MICs) for key pathogens in nosocomial pneumonia. With a plasma‐to‐ELF penetration ratio of approximately 50%, as observed from an ELF PK study, a doubling of the current dose regimens for different renal functions that are approved for cUTIs and cIAIs is needed to achieve >90% PTA for nosocomial pneumonia. For example, a 3‐g dose of ceftolozane/tazobactam for nosocomial pneumonia patients with normal renal function is needed to achieve a >90% PTA (actual 98%) for the 1‐log kill target against pathogens with an MIC of ≤8 mg/L in ELF, compared with the 1.5‐g dose approved for cIAIs and cUTIs.

Lung concentrations of ceftazidime administered by continuous versus intermittent infusion in patients with ventilator-associated pneumonia

Ceftazidime is a beta-lactam compound that exerts a time-dependent bactericidal effect. Numerous arguments are in favor of continuous administration of ceftazidime, both for reasons of clinical efficacy and to preserve bacteriological mutation. We report a prospective, single-center, parallel-group, randomized, controlled trial comparing two modes of administration of ceftazidime, namely, continuous administration (loading dose of 20 mg/kg of body weight followed by 60 mg/kg/day) versus intermittent administration (20 mg/kg over 30 min every 8 h) in 34 patients with ventilator-associated pneumonia due to Gram-negative bacilli. The study was performed over 48 h with 13 and 18 assessments of serum ceftazidime in the continuous-infusion group (group A) and the intermittent-fusion group (group B), respectively. Bronchoalveolar lavage (BAL) was performed at steady state in both groups at 44 h to determine ceftazidime levels in the epithelial lining fluid. We chose a predefined threshold of 20 mg/liter for serum concentrations of ceftazidime because of ecological conditions in our center. The median time above 20 mg/liter (T>20 mg) was 100% in group A versus 46% in group B. In group A, 14/17 patients had 100% T>20 mg, versus only 1/17 patients in group B. In the epithelial lining fluid, the median concentration of ceftazidime was 12 mg/liter in group A versus 6 mg/liter in group B. A threshold of 8 mg/liter in the epithelial lining fluid was achieved twice as often in group A as in group B. This study of ceftazidime concentrations in the epithelial lining fluid indicates that continuous infusion presents advantages in terms of pharmacodynamics and predictable efficacy in patients presenting ventilator-associated pneumonia.

Prolonged infusion versus intermittent boluses of β-lactam antibiotics for treatment of acute infections: a meta-analysis

The clinical advantages of prolonged (extended/continuous) infusion remain controversial. Previous studies and reviews have failed to show consistent clinical benefits of extending the infusion time. This meta-analysis sought to determine whether prolonged β-lactam infusions were associated with a reduction in mortality and improvement in clinical success. A search of PubMed, EMBASE and The Cochrane Library for randomised controlled trials (RCTs) and observational studies comparing prolonged infusion with intermittent bolus administration of the same antibiotic in hospitalised adult patients was conducted. Primary outcomes evaluated were mortality and clinical success. A total of 29 studies with 2206 patients (18 RCTs and 11 observational studies) were included in the meta-analysis. Compared with intermittent boluses, use of prolonged infusion appeared to be associated with a significant reduction in mortality [pooled relative risk (RR) = 0.66, 95% confidence interval (CI) 0.53-0.83] and improvement in clinical success (RR = 1.12, 95% CI 1.03-1.21). Statistically significant benefit was supported by non-randomised studies (mortality, RR = 0.57, 95% CI 0.43-0.76; clinical success, RR = 1.34, 95% CI 1.02-1.76) but not by RCTs (mortality, RR = 0.83, 95% CI 0.57-1.21; clinical success, RR = 1.05, 95% CI 0.99-1.12). The positive results from observational studies, especially in the face of increasing antibiotic resistance, serve to justify the imperative need to conduct a large-scale, well-designed, multicentre RCT involving critically ill patients infected with high minimum inhibitory concentration pathogens to clearly substantiate this benefit.

Augmented renal clearance is a common finding with worse clinical outcome in critically ill patients receiving antimicrobial therapy

INTRODUCTION

We describe incidence and patient factors associated with augmented renal clearance (ARC) in adult intensive care unit (ICU) patients.

MATERIALS AND METHODS

A prospective observational study in a mixed cohort of surgical and medical ICU patients receiving antimicrobial therapy at the Ghent University Hospital, Belgium. Kidney function was assessed by the 24-hour creatinine clearance (Ccr); ARC defined as at least one Ccr of >130 mL/min per 1.73 m2. Multivariate logistic regression analysis: to assess variables associated with ARC occurrence. Therapeutic failure (TF): an impaired clinical response and need for alternate antimicrobial therapy.

RESULTS

Of the 128 patients and 599 studied treatment days, ARC was present in 51.6% of the patients. Twelve percent permanently expressed ARC. ARC patients had a median Ccr of 144 mL/min per 1.73 m2 (IQR 98-196). Median serum creatinine concentration on the first day of ARC was 0.54 mg/dL (IQR 0.48-0.69). Patients with ARC were significantly younger (P<.001). Age and male gender were independently associated with ARC whereas the APACHE II score was not. ARC patients had more TF (18 (27.3%) vs. 8 (12.9%); P=.04).

CONCLUSION

ARC was documented in approximately 52% of a mixed ICU patient population receiving antibiotic treatment with worse clinical outcome. Young age and male gender were independently associated with ARC presence.

Current treatment of community-acquired pneumonia

INTRODUCTION

Community-acquired pneumonia (CAP) is a leading cause of morbidity and mortality worldwide. Management decisions regarding site of care, extent of assessment and level of treatment are based primarily on disease severity (outpatient, inpatient and ICU admission). Despite the developments in antibiotic therapy, CAP is still the most common infectious cause of death.

AREAS COVERED

There are several challenges with the management of CAP, from the accurate diagnosis, decisions about place of therapy and the choice of appropriate antibiotics. An extensive literature review of manuscripts, in PubMed, published in the past 10 years has been performed, using combinations of words and terms appropriate to the concepts of CAP, treatment, guidelines and corticoids. Some empirical antimicrobial regimens, such as macrolides, are still being debated; some new antibiotics and adjunctive therapies (corticoids) have recently been tested. This is a review of current recommended antimicrobials regimens, novel approaches and adjunctive drugs for the treatment of CAP.

EXPERT OPINION

Effective management of CAP requires risk stratification of patients by severity and proper place of therapy. Additional therapeutic interventions along with antibiotics may help to improve outcome in patients with CAP, especially in severe CAP.

Meropenem and piperacillin/tazobactam prescribing in critically ill patients: does augmented renal clearance affect pharmacokinetic/pharmacodynamic target attainment when extended infusions are used?

Background

Correct antibiotic dosing remains a challenge for the clinician. The aim of this study was to assess the influence of augmented renal clearance on pharmacokinetic/pharmacodynamic target attainment in critically ill patients receiving meropenem or piperacillin/tazobactam, administered as an extended infusion.

Methods

This was a prospective, observational, pharmacokinetic study executed at the medical and surgical intensive care unit at a large academic medical center. Elegible patients were adult patients without renal dysfunction receiving meropenem or piperacillin/tazobactam as an extended infusion. Serial blood samples were collected to describe the antibiotic pharmacokinetics. Urine samples were taken from a 24-hour collection to measure creatinine clearance. Relevant data were drawn from the electronic patient file and the intensive care information system.

Results

We obtained data from 61 patients and observed extensive pharmacokinetic variability. Forty-eight percent of the patients did not achieve the desired pharmacokinetic/pharmacodynamic target (100% fT_>MIC), of which almost 80% had a measured creatinine clearance >130 mL/min. Multivariate logistic regression demonstrated that high creatinine clearance was an independent predictor of not achieving the pharmacokinetic/pharmacodynamic target. Seven out of nineteen patients (37%) displaying a creatinine clearance >130 mL/min did not achieve the minimum pharmacokinetic/pharmacodynamic target of 50% fT_>MIC.

Conclusions

In this large patient cohort, we observed significant variability in pharmacokinetic/pharmacodynamic target attainment in critically ill patients. A large proportion of the patients without renal dysfunction, most of whom displayed a creatinine clearance >130 mL/min, did not achieve the desired pharmacokinetic/pharmacodynamic target, even with the use of alternative administration methods. Consequently, these patients may be at risk for treatment failure without dose up-titration.

Pharmacodynamic profiling of antimicrobials against Gram-negative respiratory isolates from Canadian hospitals

BACKGROUND

With diminishing antimicrobial potency, the choice of effective empirical therapy has become more challenging. Thus, the pharmacodynamic evaluation of potential therapies is essential to identify optimal agents, doses and administration strategies.

METHODS

Monte Carlo simulation was conducted for standard and/or prolonged infusion regimens of cefepime, ceftazidime, ceftriaxone, ciprofloxacin, doripenem, ertapenem, meropenem and piperacillin/tazobactam. Minimum inhibitory concentrations were obtained for Escherichia coli (n=64 respiratory isolates), Enterobacter cloacae (n=53), Klebsiella pneumoniae (n=75) and Pseudomonas aeruginosa (n=273) throughout Canada. The cumulative fraction of response (CFR) was calculated using bactericidal targets for each regimen against each species. A CFR ≥90% was defined as optimal.

RESULTS

All cefepime, doripenem, ertapenem and meropenem regimens achieved optimal exposures against Enterobacteriaceae, whereas target attainment was organism and dose dependent for the other agents. Prolonged infusion doripenem and meropenem 1 g and 2 g every 8 h, along with standard infusion doripenem and meropenem 2 g every 8 h, were the only regimens to attain optimal exposures against P aeruginosa. Ciprofloxacin had the lowest CFR against P aeruginosa, followed by cefepime. Among the P aeruginosa isolates collected in the intensive care unit (ICU) compared with the wards, differences of 0.5% to 10% were noted in favour of non-ICU isolates for all agents; however, marked differences (10% to 15%) in CFR were observed for ciprofloxacin in favour of ICU isolates.

CONCLUSION

Standard dosing of cefepime, doripenem, ertapenem and meropenem has a high likelihood of obtaining optimal pharmacodynamic indexes against these Enterobacteriaceae. For P aeruginosa, aggressive treatment with high-dose and/or prolonged infusion regimens are likely required to address the elevated resistance rates of respiratory isolates from Canada.

Continuous beta-lactam infusion in critically ill patients: the clinical evidence

There is controversy over whether traditional intermittent bolus dosing or continuous infusion of beta-lactam antibiotics is preferable in critically ill patients. No significant difference between these two dosing strategies in terms of patient outcomes has been shown yet. This is despite compelling in vitro and in vivo pharmacokinetic/pharmacodynamic (PK/PD) data. A lack of significance in clinical outcome studies may be due to several methodological flaws potentially masking the benefits of continuous infusion observed in preclinical studies. In this review, we explore the methodological shortcomings of the published clinical studies and describe the criteria that should be considered for performing a definitive clinical trial. We found that most trials utilized inconsistent antibiotic doses and recruited only small numbers of heterogeneous patient groups. The results of these trials suggest that continuous infusion of beta-lactam antibiotics may have variable efficacy in different patient groups. Patients who may benefit from continuous infusion are critically ill patients with a high level of illness severity. Thus, future trials should test the potential clinical advantages of continuous infusion in this patient population. To further ascertain whether benefits of continuous infusion in critically ill patients do exist, a large-scale, prospective, multinational trial with a robust design is required.

Does Beta-lactam Pharmacokinetic Variability in Critically Ill Patients Justify Therapeutic Drug Monitoring? A Systematic Review

The pharmacokinetics of beta-lactam antibiotics in intensive care patients may be profoundly altered due to the dynamic, unpredictable pathophysiological changes that occur in critical illness. For many drugs, significant increases in the volume of distribution and/or variability in drug clearance are common. When “standard” beta-lactam doses are used, such pharmacokinetic changes can result in subtherapeutic plasma concentrations, treatment failure, and the development of antibiotic resistance. Emerging data support the use of beta-lactam therapeutic drug monitoring (TDM) and individualized dosing to ensure the achievement of pharmacodynamic targets associated with rapid bacterial killing and optimal clinical outcomes. The purpose of this work was to describe the pharmacokinetic variability of beta-lactams in the critically ill and to discuss the potential utility of TDM to optimize antibiotic therapy through a structured literature review of all relevant publications between 1946 and October 2011. Only a few studies have reported the utility of TDM as a tool to improve beta-lactam dosing in critically ill patients. Moreover, there is little agreement between studies on the pharmacodynamic targets required to optimize antibiotic therapy. The impact of TDM on important clinical outcomes also remains to be established. Whereas TDM may be theoretically rational, clinical studies to assess utility in the clinical setting are urgently required.

Appropriate antibiotic dosage levels in the treatment of severe sepsis and septic shock

Antibiotic treatment of critically ill patients remains a significant challenge. Optimal antibacterial strategy should achieve therapeutic drug concentration in the blood as well as the infected site. Achieving therapeutic drug concentrations is particularly difficult when infections are caused by some pathogens, such as Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus (MRSA) and Gram-negative rods, because of their low susceptibility to antimicrobials. In sepsis, pharmacokinetics (PKs) of antibiotics are profoundly altered and may result in inadequate drug concentrations, even when recommended regimens are used, which potentially contribute to increased mortality and spread of resistance. The wide inter-individual PK variability observed in septic patients strongly limits the a priori prediction of the optimal dose that should be administered. Higher than standard dosages are necessary for the drugs, such as β-lactams, aminoglycosides, and glycopeptides, that are commonly used as first-line therapy in these patients to maximize their antibacterial activity. However, the benefit of reaching adequate drug concentrations on clinical outcome needs to be further determined.

Antibiotics in critically ill patients: a systematic review of the pharmacokinetics of β-lactams

INTRODUCTION

Several reports have shown marked heterogeneity of antibiotic pharmacokinetics (PK) in patients admitted to ICUs, which might potentially affect outcomes. Therefore, the pharmacodynamic (PD) parameter of the efficacy of β-lactam antibiotics, that is, the time that its concentration is above the bacteria minimal inhibitory concentration (T > MIC), cannot be safely extrapolated from data derived from the PK of healthy volunteers.

METHODS

We performed a full review of published studies addressing the PK of intravenous β-lactam antibiotics given to infected ICU patients. Study selection comprised a comprehensive bibliographic search of the PubMed database and bibliographic references in relevant reviews from January 1966 to December 2010. We selected only English-language articles reporting studies addressing β-lactam antibiotics that had been described in at least five previously published studies. Studies of the PK of patients undergoing renal replacement therapy were excluded.

RESULTS

A total of 57 studies addressing six different β-lactam antibiotics (meropenem, imipenem, piperacillin, cefpirome, cefepime and ceftazidime) were selected. Significant PK heterogeneity was noted, with a broad, more than twofold variation both of volume of distribution and of drug clearance (Cl). The correlation of antibiotic Cl with creatinine clearance was usually reported. Consequently, in ICU patients, β-lactam antibiotic half-life and T > MIC were virtually unpredictable, especially in those patients with normal renal function. A better PD profile was usually obtained by prolonged or even continuous infusion. Tissue penetration was also found to be compromised in critically ill patients with septic shock.

CONCLUSIONS

The PK of β-lactam antibiotics are heterogeneous and largely unpredictable in ICU patients. Consequently, the dosing of antibiotics should be supported by PK concepts, including data derived from studies of the PK of ICU patients and therapeutic drug monitoring.

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

Background

Critical illness, mediated by trauma or sepsis, can lead to physiological changes that alter the pharmacokinetics of antibiotics and may result in sub-therapeutic concentrations at the sites of infection. The first aim of this project is to identify the clinical characteristics of critically ill patients with significant trauma that have been recently admitted to ICU that may predict the dosing requirements for the antibiotic, cefazolin. The second aim of this is to identify the clinical characteristics of critically ill patients with sepsis that may predict the dosing requirements for the combination antibiotic, piperacillin-tazobactam.

Methods/Design

This is an observational pharmacokinetic study of patients with trauma (cefazolin) or with sepsis (piperacillin-tazobactam). Participants will have samples from blood and urine, collected at different intervals. Patients will also have a microdialysis catheter inserted into subcutaneous tissue to measure interstitial fluid penetration of the antibiotic. Participants will be administered sinistrin, indocyanine green and sodium bromide as well as have cardiac output monitoring performed and tetrapolar bioimpedance to determine physiological changes resulting from pathology. Analysis of samples will be performed using validated liquid chromatography tandem mass-spectrometry. Pharmacokinetic analysis will be performed using non-linear mixed effects modeling to determine individual and population pharmacokinetic parameters of antibiotics.

Discussion

The study will describe cefazolin and piperacillin-tazobactam concentrations in plasma and the interstitial fluid of tissues in trauma and sepsis patients respectively. The results of this study will guide clinicians to effectively dose these antibiotics in order to maximize the concentration of antibiotics in the interstitial fluid of tissues.

Analytical validation of microdialysis analyzer for monitoring glucose, lactate and pyruvate in cerebral microdialysates

BACKGROUND

Cerebral microdialysis is a valuable tool for neurochemical monitoring of acute brain injury. We performed an independent analytical validation of glucose, lactate and pyruvate methods on the new ISCUS(flex) new analyzer developed by CMA Microdialysis.

METHODS

Evaluation of analytical parameters included limit of detection, limit of quantification, linearity, intra- and inter-assay imprecision expressed as the coefficient of variation (CV), recovery, inter-sample and inter-reagent contamination, drug and bilirubin interferences, sample stability, method comparison.

RESULTS

Linearity ranges were 0.1-25 mmol/L, 0.2-12 mmol/L and 19-1500 μmol/L for glucose, lactate and pyruvate respectively. For critical threshold, intra- and inter-assay CVs were 3.1/4.5% for glucose (1 mmol/L), 3.5/4% for lactate (4 mmol/L) and 3.3/4.3% for pyruvate (100 μmol/L). Inter-assay CVs for lactate/pyruvate (LPR) and lactate/glucose (LGR) ratios were 5.9% and 6.0% respectively. For glucose, lactate, pyruvate, LPR and LGR, the reference change values (RCV) were 20%, 26%, 20%, 27% and 28% respectively. Practically, variations below 27% between two successive LPR values could not be interpreted as significant.

CONCLUSION

These data prove that ISCUS(flex) has the qualities required for clinical application in neuro-intensive care. Correct clinical interpretation of data need the implementation of a strict quality control program and strong cooperation between clinicians and biologists.

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

Introduction

Altered pharmacokinetics (PK) in critically ill patients can result in insufficient serum β-lactam concentrations when standard dosages are administered. Previous studies on β-lactam PK have generally excluded the most severely ill patients, or were conducted during the steady-state period of treatment. The aim of our study was to determine whether the first dose of piperacillin-tazobactam, ceftazidime, cefepime, and meropenem would result in adequate serum drug concentrations in patients with severe sepsis and septic shock.

Methods

Open, prospective, multicenter study in four Belgian intensive care units. All consecutive patients with a diagnosis of severe sepsis or septic shock, in whom treatment with the study drugs was indicated, were included. Serum concentrations of the antibiotics were determined by high-pressure liquid chromatography (HPLC) before and 1, 1.5, 4.5 and 6 or 8 hours after administration.

Results

80 patients were treated with piperacillin-tazobactam (n = 27), ceftazidime (n = 18), cefepime (n = 19) or meropenem (n = 16). Serum concentrations remained above 4 times the minimal inhibitory concentration (T > 4 × MIC), corresponding to the clinical breakpoint for Pseudomonas aeruginosa defined by the European Committee on Antimicrobial Susceptibility Testing (EUCAST), for 57% of the dosage interval for meropenem (target MIC = 8 μg/mL), 45% for ceftazidime (MIC = 32 μg/mL), 34% for cefepime (MIC = 32 μg/mL), and 33% for piperacillin-tazobactam (MIC = 64 μg/mL). The number of patients who attained the target PK profile was 12/16 for meropenem (75%), 5/18 for ceftazidime (28%), 3/19 (16%) for cefepime, and 12/27 (44%) for piperacillin-tazobactam.

Conclusions

Serum concentrations of the antibiotic after the first dose were acceptable only for meropenem. Standard dosage regimens for piperacillin-tazobactam, ceftazidime and cefepime may, therefore, be insufficient to empirically cover less susceptible pathogens in the early phase of severe sepsis and septic shock.

Antimicrobial Stewardship in the Intensive Care Unit: A Focus on Potential Pitfalls

Patients in the intensive care unit (ICU) have many risk factors for resistant pathogens such as prolonged length of stay, frequent and broad-spectrum antimicrobial therapy, presence of foreign materials, and proximity with other patients. However, of the risk factors associated with acquisition of resistant pathogens, inappropriate use of antimicrobial agents has been the most implicated. Thus, many health care institutions have adopted antimicrobial stewardship programs (ASPs) as a mechanism to ensure more appropriate antimicrobial use. ASPs can have a significant impact in the ICU, leading to improved antimicrobial use and resistance patterns and decreased infection rates and costs, due to the inherent nature of infections encountered and high and often inappropriate antibiotic utilization in this setting. However, certain challenges exist for ASPs in the ICU including issues with infrastructure and personnel, information technology, the core ASP strategy, patient-specific factors, conversion of intravenous to oral therapy, and dose optimization. The combination of comprehensive infection control (IC) and effective antimicrobial stewardship can prevent the emergence of resistance among microorganisms and may decrease the negative consequences associated with antimicrobial misuse.

Population pharmacokinetics of ceftazidime in intensive care unit patients: influence of glomerular filtration rate, mechanical ventilation, and reason for admission

The aim of this study was to develop a population-pharmacokinetic model of ceftazidime in intensive care unit patients to include the influence of patients' characteristics on the pharmacokinetics. Forty-nine patients for model building and 23 patients for validation were included in a randomized study. They received ceftazidime at 2 g three times a day or as 6 g per day continuously. A NONMEM pharmacokinetic model was constructed, and the influences of covariates were studied. The model was validated by a comparison of the predicted and observed concentrations. A final model was elaborated from the whole population. Total clearance (CL) was significantly correlated with the glomerular filtration rate (GFR) calculated by modification of the diet in renal disease (MDRD), the central volume of distribution (V1) with intubation, and the peripheral volume of distribution (V2) with the reason for admission. The mean pharmacokinetic parameters were as follows: CL, 5.48 liters/h, 40%; V1, 10.48 liters, 34%; V2, 32.12 liters, 59%; total volume, 42.60 liters, 45%; and intercompartmental clearance, 16.19 liters/h, 42%. In the polytrauma population (mechanically ventilated), the time above the MIC at steady state never corresponds to 100% for discontinuous administration, and the target concentration of five times the MIC was reached with a 6-g/day dose only for patients with an MDRD of <150 ml/min. We showed that the GFR-MDRD, mechanical ventilation, and the reason for admission may influence the achieved concentrations of ceftazidime. Our model allows the a priori dosing to be adjusted to the individual patient.

Comparison of 2002–2006 OPTAMA Programs for US Hospitals: Focus on Gram-Negative Resistance

Background:

Resistance among gram-negative bacteria is increasing within the US.

Objective:

To determine pharmacodynamic target attainment rates for 10 antimicrobials against selected gram-negative bacilli and compare these results with previous Optimizing Pharmacodynamic Target Attainment Using the MYSTIC Antibiogram (OPTAMA) assessments.

Methods:

A 5000-patient Monte Carlo simulation using data from population pharmacokinetic studies was employed to estimate the pharmacokinetic profiles for standard and/or prolonged infusion (PI) regimens of cefepime, ceftazidime, ceftriaxone, ciprofloxacin, ertapenem, imipenem, levofloxacin, meropenem, piperacillin–tazobactam, and tigecycline. Minimum inhibitory concentration data were obtained from intensive care units of 15 US hospitals participating in the 2006 MYSTIC (Meropenem Yearly Susceptibility Test Information Collection) study for 640 Escherichia coli, 618 Klebsiella spp., and 606 Pseudomonas aeruginosa isolates. Cumulative fraction of response (CFR) was calculated using pharmacodynamic targets for each antibiotic and compared with results from the 2002 and 2004 OPTAMA studies.

Results:

Against E. coli, CFRs greater than 92% were maintained for all regimens except the fluoroquinolones (CFR range 69.4–72%), which showed a 7% decrease compared with 2004. The presence of Klebsiella spp. producing KPC-type carbapenemases with associated multidrug resistance resulted in a 7% or greater drop in CFR of standard regimens relative to 2004. Despite these resistant phenotypes, high-dose PI regimens (2 g every 8 hours as 3-hour PI) of cefepime and meropenem achieved CFRs of 97% and 95.8%, respectively. Excluding 3 KPC-harboring hospitals resulted in CFR increases to greater than 98% for carbapenems and cefepime and greater than 88% for all other agents tested, except tigecycline. Against P. aeruginosa, the fluoroquinolones had the lowest CFR (55.8–63.9%), followed by imipenem (74.6-80.4%). The most predictable activity was seen with cefepime 2 g every 12 hours or higher (>90%), ceftazidime 2 g every 8 hours (97.9%), and meropenem 1-2 g every 8 hours (86.7–92.6%). Use of PI for piperacillin-tazobactam and meropenem increased CFRs by 6% and 4%, respectively, over standard infusions.

Conclusions:

Relative to previous years, an increase in resistance was noted among gram-negative bacilli to common antibiotics, resulting in disproportionate decreases in pharmacodynamic target attainment. The use of PI for β-lactams may help to overcome these decreases.

A pharmacodynamic simulation to assess tigecycline efficacy for hospital-acquired pneumonia compared with other common intravenous antibiotics

A pharmacodynamic model was used to generate supportive data comparing tigecycline with other broad-spectrum agents against pathogens implicated in hospital-acquired pneumonia (HAP). A 5000 patient Monte Carlo simulation determined the probability of target attainment (PTA) of tigecycline (+/- ceftazidime) compared with imipenem, levofloxacin, and piperacillin/tazobactam (+/- vancomycin). PTA was calculated over MICs of current Gram-positive and Gram-negative bacteria collected from worldwide surveillance and weighted by the expected prevalence of these pathogens causing HAP. For monotherapy, the weighted PTA was imipenem (78.2%), piperacillin/tazobactam (73.3%), tigecycline (62.9%), and levofloxacin (62.5%). By pathogen PTA was greatest for tigecycline against Gram-positives, and ceftazidime or imipenem against Gram-negatives. Combination therapy increased PTA to 88.6%, 85.5%, 80.6%, and 69.8% for tigecycline, imipenem, piperacillin/tazobactam, and levofloxacin, respectively. Based on contemporary resistance data, tigecycline plus ceftazidime is predicted to achieve its pharmacodynamic targets similarly to combination therapy with imipenem plus vancomycin for the treatment of patients with HAP.

Continuous infusion of beta-lactam antibiotics in severe infections: a review of its role

Continuous infusion of beta-lactam antibiotics has been widely promoted to optimise their time-dependent activity. Increasing evidence is emerging suggesting potential benefits in patient populations with altered pathophysiology, such as seriously ill patients. From a pharmacokinetic viewpoint, much information supports higher trough concentrations of beta-lactam antibiotics when administered by continuous infusion. This advantage of continuous infusion translates into a superior ability to achieve pharmacodynamic targets, particularly when the minimum inhibitory concentration (MIC) of the pathogen is >or=4 mg/L. One drawback of continuous infusion may be limited physicochemical stability. This issue exists particularly for carbapenem antibiotics whereby prolonged infusions (i.e. >3h) can be used to improve the time above the MIC compared with conventional bolus dosing. Few studies have examined clinical outcomes of bolus and continuous dosing of beta-lactam antibiotics in seriously ill patients. No statistically significant differences have been shown for: mortality; time to normalisation of leukocytosis or pyrexia; or duration of mechanical ventilation, intensive care unit stay or hospital stay. Some evidence suggests improved clinical cure and resolution of illness with continuous infusion in seriously ill patients. Pharmacoeconomic advantages of continuous infusion of beta-lactam antibiotics are well characterised. Available data suggest that seriously ill patients with severe infections requiring significant antibiotic courses (>or=4 days) may be the subgroup that will achieve better outcomes with continuous infusion.

Reevaluation of current susceptibility breakpoints for Gram-negative rods based on pharmacodynamic assessment

Although pharmacodynamic (PD) modeling is now being considered for decision support for susceptibility breakpoint determination against Gram-negative bacteria, these PD-derived breakpoints should be verified using a clinically applicable population of organisms. In this analysis, a 5000-patient Monte Carlo simulation was used to determine PD breakpoints, the highest 2-fold MIC in which the probability of bactericidal target attainment (PTA) remained > or = 90%. Percent susceptibilities for 639 Pseudomonas aeruginosa, 103 Acinetobacter baumannii, 705 Escherichia coli, and 418 Klebsiella spp. collected during the 2004 Meropenem Yearly Susceptibility Test Information Collection surveillance study were then defined according to the PD-derived breakpoint (%S(PD)) and compared with the current Clinical Laboratory Standards Institute (CLSI)-defined breakpoints (%S(CLSI)). %S(PD) and %S(CLSI) were compared with the bactericidal PTA for each pathogen population to determine the degree of agreement. Resulting PD breakpoints were drug and dose dependent; moreover, values were commonly 2 to 4 MIC dilutions lower than CLSI breakpoints. Overall, %S(PD) more closely agreed with the PTA for the tested beta-lactam and fluoroquinolone dosing regimens. In contrast, %S(CLSI) overestimated PTA for many dosing regimens, especially against Pseudomonas: piperacillin/tazobactam 4.5 g qid (+9.7%), ciprofloxacin 0.4 g bid (+13.7%) and 0.4 g tid (+9.3%), and levofloxacin 0.5 g every 24 h (+22.4%) and 0.75 g every 24 h (+9.9%). Differences were most pronounced against the nonfermenting Gram-negative bacteria and were not observed among the Enterobacteriaceae. As a result, a new method of breakpoint classification is proposed, which is dosing regimen and pathogen specific, and is designed to denote isolates as susceptible only if target bactericidal exposures are achievable with the dosing regimen selected.

Pharmacodynamic Target Attainment of Six β-Lactams and Two Fluoroquinolones AgainstPseudomonas aeruginosa,Acinetobacter baumannii,Escherichia coli, andKlebsiellaSpecies Collected from United States Intensive Care Units in 2004

STUDY OBJECTIVE

To determine the likelihood that antibiotic regimens achieve bactericidal pharmacodynamic exposures against common nosocomial pathogens.

DESIGN

Pharmacodynamic Monte Carlo simulation model.

DATA SOURCE

Microbiologic data generated from isolates from the 14 centers in the United States in the 2004 Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) surveillance study.

PATIENTS

Five thousand simulated patients with infection.

MEASUREMENTS AND MAIN RESULTS

Pharmacokinetic profiles of the patients were simulated to determine the bactericidal cumulative fraction of response (CFR) for commonly used intravenous regimens of cefepime, ceftazidime, ceftriaxone, ciprofloxacin, imipenem, levofloxacin, meropenem, and piperacillin-tazobactam against Pseudomonas aeruginosa, Acinetobacter baumannii, Escherichia coli, and Klebsiella species. Ciprofloxacin and levofloxacin had CFRs among the lowest of all drugs against all pathogens, especially P. aeruginosa (40.4-65.5%) and A. baumannii (43.6-48.2%). The low CFR of about 78% against E. coli with these two agents was of particular concern. Among the beta-lactams, only high-dose cefepime and ceftazidime regimens achieved CFRs of greater than 90% against P. aeruginosa, followed by cefepime 2 g every 12 hours and the carbapenems (86.3-89.7%). No regimen achieved an optimum CFR for A. baumannii. All beta-lactam regimens achieved a greater-than-90% likelihood of having bactericidal CFRs against Enterobacteriaceae.

CONCLUSION

Because of the continual evolution of resistance among gram-negative bacteria in the United States, reevaluation of optimum dosing strategies for beta-lactam and fluoroquinolone antibiotics is necessary.

Continuous versus intermittent intravenous administration of antibacterials with time-dependent action: a systematic review of pharmacokinetic and pharmacodynamic parameters

We performed a systematic review of randomised clinical trials to evaluate the comparative pharmacokinetic and pharmacodynamic properties of the continuous versus intermittent mode of intravenous administration of various antibacterials. Data were identified from PubMed (January 1950 to January 2005), Current Contents, the Cochrane central register of controlled trials, and references from relevant articles and reviews. Seventeen randomised clinical trials comparing continuous with intermittent intravenous administration of the same antibacterial regimen and examining the pharmacokinetic and pharmacodynamic properties were included in this systematic review. We reviewed data regarding the clinical setting, number of participants, antibacterial agents and dosages used, as well as maximum serum concentration (Cmax), trough serum concentration (Cmin), steady-state or plateau serum concentration (Css), area under the concentration-time curve (AUC), time above the minimum inhibitory concentration (MIC) [T>MIC], AUC: MIC, elimination rate constant, elimination half-life, volume of distribution and systematic clearance. The mean Cmax of the intermittently administered antibacterials was higher compared with Css achieved by the continuous infusion of the same antibacterial in all eligible studies (Cmax was on average 5.5 times higher than Css, range 1.9-11.2). Css was on average 5.8 times higher than the Cmin of the intermittently administered antibacterials (range 1.2-15.6). In three of six studies the length of time that the drug concentration was above the MIC of the responsible pathogens was longer in patients receiving the antibacterials continuously. In conclusion, the reviewed data suggest that the continuous intravenous infusion of antibacterials with time-dependent bacterial killing seems to be superior than the intermittent intravenous administration, from a pharmacodynamic point of view, at least when treating bacteria with high MIC values for the studied antibacterials.

Trough serum concentrations of β-lactam antibiotics in cancer patients: inappropriateness of conventional schedules to pharmacokinetic/pharmacodynamic properties of β-lactams

Serum concentrations of beta-lactams that continuously exceed the minimum inhibitory concentration may improve therapeutic outcomes for immunosuppressed patients. The trough serum levels of ceftazidime (CAZ), cefepime (FEP) or imipenem (IMP) were prospectively determined on days 1 and 3 of treatment in cancer patients. Seventy-eight episodes of suspected infection were analysed. Trough serum levels were higher than 4 mg/L in 62%, 24% and 0% of cases in the CAZ, FEP and IMP groups, respectively, and were higher than 20 mg/L in 24% of cases in the CAZ group compared with 0% both in the FEP and IMP groups. For suspected infectious episodes in cancer patients, the traditional intermittent regimen of beta-lactams does not appear to be appropriate for the pharmacokinetic/pharmacodynamic properties of these antibiotics.

Comparison of pharmacodynamic target attainment between healthy subjects and patients for ceftazidime and meropenem

STUDY OBJECTIVE

To compare the pharmacodynamics of two beta-lactams--ceftazidime and meropenem--in healthy subjects versus patients.

DESIGN

Monte Carlo simulation based on published pharmacokinetic studies.

SUBJECTS

One hundred and ninety-seven participants (75 healthy volunteers and 122 patients) from published pharmacokinetic studies of ceftazidime or meropenem.

MEASUREMENTS AND MAIN RESULTS

Data on total body clearance and volume of distribution for ceftazidime and meropenem in healthy subjects and patients were obtained from published studies. Monte Carlo simulations were performed based on the pharmacokinetics from each study for ceftazidime 1000 mg every 8 hours and meropenem 1000 mg every 8 hours against isolates of Escherichia coli , Klebsiella pneumoniae , Acinetobacter baumannii , and Pseudomonas aeruginosa collected from North and South America. We calculated the likelihood of obtaining bactericidal exposures (50% time above the minimum inhibitory concentration [MIC] for ceftazidime and 40% time above the MIC for meropenem) for each combination of pharmacokinetic study data and MIC distribution. Linear regression was used to compare target attainments for healthy subjects versus patients. Only three drug-pathogen combinations differed in target attainment between healthy subjects and patients: ceftazidime against P. aeruginosa in North America and meropenem against E. coli and P. aeruginosa in South America. The regression line of target attainment for patients versus healthy subjects had a slope of 1.04 (95% confidence interval [CI] 0.983-1.093) and a y intercept of -3.73 (95% CI -8.265-0.827, r2 = 0.992). The beta values for slope and intercept did not differ to a statistically significant extent between the regression line and the line of identity (p=0.264).

CONCLUSION

The pharmacodynamic target attainment calculated with healthy subject pharmacokinetic data was predictive of patient target target attainment for ceftazidime and meropenem.

Continuous versus intermittent intravenous administration of antibiotics: a meta-analysis of randomised controlled trials

Intermittent intravenous administration of antibiotics is the first-line approach in the management of severe infections worldwide. However, the potential benefits of alternate modes of administration of antibiotics, including continuous intravenous infusion, deserve further evaluation. We did a meta-analysis of randomised controlled trials comparing continuous intravenous infusion with intermittent intravenous administration of the same antibiotic regimen. Nine randomised controlled trials studying beta-lactams, aminoglycosides, and vancomycin were included. Clinical failure was lower, although without statistical significance, in patients receiving continuous infusion of antibiotics (pooled OR 0.73, 95% CI 0.53-1.01); the difference was statistically significant in a subset of randomised controlled trials that used the same total daily antibiotic dose for both intervention arms (0.70, 0.50-0.98, fixed and random effects models). Regarding mortality and nephrotoxicity, no differences were found (mortality 0.89, 0.48-1.64; nephrotoxicity 0.91, 0.56-1.47). In conclusion, the data suggest that the administration of the same total antibiotic dose by continuous intravenous infusion may be more efficient, with regard to clinical effectiveness, compared with the intermittent mode. In an era of gradually increasing resistance among most pathogens, the potential advantages of continuous intravenous administration of antibiotics on several clinical outcomes should be further investigated.

A retrospective analysis using Monte Carlo simulation to evaluate recommended ceftazidime dosing regimens in healthy volunteers, patients with cystic fibrosis, and patients in the intensive care unit

BACKGROUND

Over the past decades, the relationship between the pharmacokinetic (PK) properties of antibiotics, MICs, and clinical effects has been increasingly well understood. Interpatient variability in the PK profile, however, has only recently been recognized as a major factor in predicting the outcome in individual patients and establishing breakpoints for clinical susceptibility. Most predictions to date have used data from healthy volunteers.

OBJECTIVE

The purpose of this study was to perform Monte Carlo simulations of the PK/pharmacodynamic relationships of ceftazidime to assess whether the probability of target attainment (PTA) differed significantly between 3 distinct populations. To that end, population PK models of ceftazidime were developed for the 3 populations.

METHODS

Serum concentration-time data from earlier studies in healthy volunteers (n = 8), patients with cystic fibrosis (CF) (n = 17), and patients in the intensive care unit (ICU) (n = 6) were used to obtain population PK parameter estimates and covariance matrices using the nonparametric adaptive grid program. The PTA for each group was obtained using 10,000 patient simulations for dosing regimens of 1000 and 2000 mg q8h over a range of MICs and percentages of time that concentrations of unbound drug remained above the MIC (%T > MIC).

RESULTS

The relationship between the MIC and the population mean %T > MIC, as well as the PTA profiles, differed markedly between the 3 groups as a result of both differences and variations in V(d) and Cl. Breakpoints based on a 100% PTA for a %T > MIC of 60% were < or = 4, 0.5, and 0.5 mg/L in healthy volunteers, patients with CF, and patients in the ICU, respectively. However, when PTA values between 90% and 100% were reevaluated and differences in clinical dosing regimens were accounted for, the resulting breakpoints were identical in the 3 groups.

CONCLUSIONS

PK parameter estimates for ceftazidime based on data from a small group of healthy volunteers resulted in a clinical susceptibility breakpoint comparable to those for patients with CF and patients in the ICU. Based on the study findings, this breakpoint would be < or = 4 mg/L. Patients suspected of having unusually high rates of clearance should be monitored closely.

Antibiotic pharmacokinetic and pharmacodynamic considerations in critical illness

BACKGROUND

Many factors over which there may be little control may influence the response of a patient to therapy. However, therapy with antibiotics can be readily optimised.

DISCUSSION

Concentration-dependent agents such as aminoglycosides appear effective and to entail fewer side effects when given in large, infrequent doses. There is also evidence that time-dependent antibiotics often fail to reach adequate concentrations throughout the treatment period. To date no randomised controlled prospective trial has demonstrated improvement in clinical outcome following infusion rather than intermittent boluses of time-dependent antibiotics. Critical illness alters antibiotic pharmacokinetics principally through increases in volume of distribution. Other than glycopeptides and aminoglycosides, antibiotic blood concentrations are rarely monitored and therefore adequate concentrations can only be inferred from clinical response.

CONCLUSIONS

Failure to respond within the first few days of empirical treatment may be due to antibiotic resistance or inadequate doses. Therefore the same rigor should be applied to achieving adequate antibiotic concentrations as is applied to inotropes, which are titrated to achieve predetermined physiological targets.

Cefepime versus cefpirome: the importance of creatinine clearance

Standard dosage recommendations for beta-lactam antibiotics can result in very low drug levels in intensive care (IC) patients without renal dysfunction. We compared the pharmacokinetics of two fourth-generation cephalosporins, cefepime and cefpirome, and examined the relationship of drug clearance (CL) to creatinine clearance (CL(CR)). Two separate but similar pharmacokinetic studies (which used 2 g twice daily for each antibiotic) were conducted. Blood was sampled after an initial and a subsequent antibiotic dose. Drug plasma concentrations were measured, and pharmacokinetic analyses were conducted and compared. The pharmacokinetics of cefepime and cefpirome are similar in IC patients. Any differences in drug CL can largely be attributed to differences in CL(CR). Despite normal plasma creatinine concentrations, 54% of patients' antibiotic concentrations were less than the minimum inhibitory concentration (MIC) (4 mg/L) for >20% of the dosing interval. Thirty-four percent of patients had CL(CR) >144 mL/min (20% higher than the expected maximum of 120 mL/min). Only CL(CR) was an independent predictor of antibiotic CL. Time above MIC was predicted only by CL(CR). Some IC patients have a very large CL(CR), which results in very low levels of studied antibiotics. Either shortening the dosage interval or using continuous infusions would prevent low levels and keep troughs above the MIC for longer periods. In view of the lack of bedside measurement of cephalosporin levels, we suggest that more frequent use be made of CL(CR) to allow prediction of small concentrations clinically.

IMPLICATIONS

Some intensive care patients have very large creatinine clearances that result in very low levels of fourth-generation cephalosporins. Serum levels of these antibiotics need to be maintained (time > minimum inhibitory concentration is important). Because routine measurements of cephalosporin levels are generally unavailable, we suggest that more frequent use be made of creatinine clearances to allow prediction of low levels and, hence, alterations in dosing.