Plasma and lung concentrations of ceftazidime administered in continuous infusion to critically ill patients with severe nosocomial pneumonia

Rationale and evidence for the use of new beta-lactam/beta-lactamase inhibitor combinations and cefiderocol in critically ill patients

BACKGROUND

Healthcare-associated infections involving Gram-negative bacteria (GNB) with difficult-to-treat resistance (DTR) phenotype are associated with impaired patient-centered outcomes and poses daily therapeutic challenges in most of intensive care units worldwide. Over the recent years, four innovative β-lactam/β-lactamase inhibitor (BL/BLI) combinations (ceftolozane-tazobactam, ceftazidime-avibactam, imipenem-relebactam and meropenem-vaborbactam) and a new siderophore cephalosporin (cefiderocol) have been approved for the treatment of certain DTR-GNB infections. The literature addressing their microbiological spectrum, pharmacokinetics, clinical efficacy and safety was exhaustively audited by our group to support the recent guidelines of the French Intensive Care Society on their utilization in critically ill patients. This narrative review summarizes the available evidence and unanswered questions on these issues.

METHODS

A systematic search for English-language publications in PUBMED and the Cochrane Library database from inception to November 15, 2022.

RESULTS

These drugs have demonstrated relevant clinical success rates and a reduced renal risk in most of severe infections for whom polymyxin- and/or aminoglycoside-based regimen were historically used as last-resort strategies-namely, ceftazidime-avibactam for infections due to Klebsiella pneumoniae carbapenemase (KPC)- or OXA-48-like-producing Enterobacterales, meropenem-vaborbactam for KPC-producing Enterobacterales, ceftazidime-avibactam/aztreonam combination or cefiderocol for metallo-β-lactamase (MBL)-producing Enterobacterales, and ceftolozane-tazobactam, ceftazidime-avibactam and imipenem-relebactam for non-MBL-producing DTR Pseudomonas aeruginosa. However, limited clinical evidence exists in critically ill patients. Extended-infusion scheme (except for imipenem-relebactam) may be indicated for DTR-GNB with high minimal inhibitory concentrations and/or in case of augmented renal clearance. The potential benefit of combining these agents with other antimicrobials remains under-investigated, notably for the most severe presentations. Other important knowledge gaps include pharmacokinetic information in particular situations (e.g., pneumonia, other deep-seated infections, and renal replacement therapy), the hazard of treatment-emergent resistance and possible preventive measures, the safety of high-dose regimen, the potential usefulness of rapid molecular diagnostic tools to rationalize their empirical utilization, and optimal treatment durations. Comparative clinical, ecological, and medico-economic data are needed for infections in whom two or more of these agents exhibit in vitro activity against the causative pathogen.

CONCLUSIONS

New BL/BLI combinations and cefiderocol represent long-awaited options for improving the management of DTR-GNB infections. Several research axes must be explored to better define the positioning and appropriate administration scheme of these drugs in critically ill patients.

Development of Modernized Acinetobacter baumannii Susceptibility Test Interpretive Criteria for Recommended Antimicrobial Agents Using Pharmacometric Approaches

Acinetobacter baumannii-Acinetobacter calcoaceticus complex (referred to herein as A. baumannii) treatment guidelines contain numerous older antimicrobial agents with susceptibility test interpretive criteria (STIC, also known as susceptibility breakpoints) set using only epidemiological data. We utilized a combination of in vitro surveillance data, preclinical murine thigh and lung infection models, population pharmacokinetics, simulation, and pharmacokinetic/pharmacodynamic (PK/PD) target attainment analyses to evaluate A. baumannii STIC for four commonly recommended antimicrobials from different classes (amikacin, ceftazidime, ciprofloxacin, and minocycline). Antimicrobial in vitro surveillance data were based on 1,647 clinical A. baumannii isolates obtained from 109 centers in the United States and Europe. Among these isolates, 5 were selected for evaluation in murine infection models based on fitness and MIC variability. PK and dose-ranging studies were conducted using neutropenic murine thigh and lung infection models The MIC ranges for the 5 isolates evaluated were as follows: amikacin, 2 to 32 μg/mL; ceftazidime, 4 to 16 μg/mL; ciprofloxacin, 0.12 to 2 μg/mL; minocycline, 0.25 to 4 μg/mL. All organisms grew ≥1.5 log10 CFU in both models in untreated controls. Plasma and epithelial lining fluid (ELF) pharmacokinetics for all drugs were determined in mice using liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods. For each isolate, 5 dose levels of each drug were tested individually in the thigh and lung infection model. The inoculum ranged from 7.9 to 8.4 and 6.8 to 7.7 log10 CFU/mL for the lung and thigh models, respectively. PK/PD targets associated with net bacterial stasis and 1- and 2-log10 CFU reductions from baseline were identified for each organism/infection model using Hill-type models. Population pharmacokinetic models for each agent were identified from the literature. Using demographic variables for simulated patients with hospital-acquired or ventilator-associated bacterial pneumonia or urinary tract infections (including acute pyelonephritis) who were administered maximal dosing regimens of each agent, estimates of protein binding, and ELF penetration ratios based on data from the literature, free-drug plasma and total-drug concentration-time profiles were generated, and PK/PD indices by MIC were calculated. Percent probabilities of attaining median and randomly assigned PK/PD targets associated with the above-described endpoints were determined. Recommended susceptible breakpoints for each agent were those representing the highest MIC at which the percent probabilities of achieving PK/PD targets associated with a 1-log10 CFU reduction from baseline approached or were ≥90%. The following susceptible breakpoints for A. baumannii were identified: amikacin, ≤8 μg/mL for pneumonia; ceftazidime, ≤32 and ≤8 μg/mL for pneumonia; ciprofloxacin, ≤1 μg/mL; and minocycline, ≤0.5/≤1 μg/mL which correspond to the standard and high minocycline dosing regimens of 200 mg per day and 200 mg every 12 h, respectively. Implementation of appropriate STIC will help clinicians optimally use the above-described agents and improve the likelihood of successful patient outcomes.

Tissue Penetration of Antimicrobials in Intensive Care Unit Patients: A Systematic Review—Part I

The challenging severity of some infections, especially in critically ill patients, makes the diffusion of antimicrobial drugs within tissues one of the cornerstones of chemotherapy. The knowledge of how antibacterial agents penetrate tissues may come from different sources: preclinical studies in animal models, phase I–III clinical trials and post-registration studies. However, the particular physiopathology of critically ill patients may significantly alter drug pharmacokinetics. Indeed, changes in interstitial volumes (the third space) and/or in glomerular filtration ratio may influence the achievement of bactericidal concentrations in peripheral compartments, while inflammation can alter the systemic distribution of some drugs. On the contrary, other antibacterial agents may reach high and effective concentrations thanks to the increased tissue accumulation of macrophages and neutrophils. Therefore, the present review explores the tissue distribution of beta-lactams and other antimicrobials acting on the cell wall and cytoplasmic membrane of bacteria in critically ill patients. A systematic search of articles was performed according to PRISMA guidelines, and tissue/plasma penetration ratios were collected. Results showed a highly variable passage of drugs within tissues, while large interindividual variability may represent a hurdle which must be overcome to achieve therapeutic concentrations in some compartments. To solve that issue, off-label dosing regimens could represent an effective solution in particular conditions.

Intrapulmonary Pharmacokinetic Modeling and Simulation of Cefiderocol, a Parenteral Siderophore Cephalosporin, in Patients With Pneumonia and Healthy Subjects

Cefiderocol is a siderophore cephalosporin for the treatment of infections caused by gram-negative bacteria including carbapenem-resistant strains. The aim of this study was to develop an intrapulmonary pharmacokinetic (PK) model of cefiderocol and assess the PK profile in lungs. An intrapulmonary PK model of cefiderocol was developed using the concentration data in plasma and epithelial lining fluid (ELF) from 7 patients with pneumonia requiring mechanical ventilation and 20 healthy subjects. Subsequently, the model was applied to assess the ELF exposure of 125 patients with nosocomial pneumonia. Monte Carlo simulations were performed to calculate the probability of target attainment for the percentage of time for which free ELF concentrations exceed the minimum inhibitory concentration (MIC) over the dosing interval (%fT>MIC,ELF ). The developed model adequately described ELF concentrations and suggested the delayed distribution in ELF for patients with pneumonia compared to healthy subjects. Lung penetration ratio of cefiderocol in patients with pneumonia was calculated to be 34%, which was 1.4-fold that in healthy subjects. The estimated %fT>MIC,ELF was 100% in most of patients with nosocomial pneumonia, and no PK/pharmacodynamic relationship with %fT>MIC,ELF was found for microbiological or clinical outcome. The probability of target attainment for 100% fT>MIC,ELF was ≥ 99.5% against MICs ≤2 μg/mL and ≥87.0% against MICs ≤4 μg/mL regardless of renal function. The median of simulated ELF trough concentrations at steady state was >4 μg/mL regardless of renal function. These results reveal the adequacy of cefiderocol exposure in plasma and ELF at the recommended dosing regimens adjusted on the basis of renal function in critically ill patients with pneumonia.

Treatment of ventilator-associated pneumonia due to carbapenem-resistant Gram-negative bacteria with novel agents: a contemporary, multidisciplinary ESGCIP perspective

INTRODUCTION

: In the past 15 years, treatment of VAP caused by carbapenem-resistant Gram-negative bacteria (CR-GNB) has represented an intricate challenge for clinicians.

AREAS COVERED

In this perspective article, we discuss the available clinical data about novel agents for the treatment of CR-GNB VAP, together with general PK/PD principles for the treatment of VAP, in the attempt to provide some suggestions for optimizing antimicrobial therapy of CR-GNB VAP in the daily clinical practice.

EXPERT OPINION

Recently, novel BL and BL/BLI combinations have become available that have shown potent in vitro activity against CR-GNB and have attracted much interest as novel, less toxic, and possibly more efficacious options for the treatment of CR-GNB VAP compared with previous standard of care. Besides randomized controlled trials, a good solution to enrich our knowledge on how to use these novel agents at best in the near future, while at the same time remaining adherent to current evidence-based guidelines, is to improve our collaboration to conduct larger multinational observational studies to collect sufficiently large populations treated in real life with those novel agents for which guidelines currently do not provide a recommendation (in favor or against) for certain causative organisms.

Pharmacokinetic evaluation of cefiderocol for the treatment of multidrug resistant Gram-negative infections

INTRODUCTION

Cefiderocol is a siderophore cephalosporin antibiotic and first of its kind approved by the Food and Drug Administration for the treatment of complicated urinary tract infections (cUTI) and hospital-acquired and ventilator-associated bacterial pneumonia (HABP/VABP) in patients 18 years or older caused by susceptible organisms. Cefiderocol's unique mechanism of iron chelation improves Gram-negative membrane penetration as the bacteria's iron uptake mechanism recognizes the chelated iron antibiotic and iron for entry. This also allows for the evasion of cefiderocol from cell entry-related resistance mechanisms.

AREAS COVERED

This review covers the mechanism of action, resistance mechanisms, pharmacokinetics in various patient populations, and pharmacodynamics. Relevant literature evaluating efficacy and safety are discussed.

EXPERT OPINION

Limited treatment options are available for the treatment of carbapenem-resistantorganisms. Clinical trials have demonstrated that cefiderocol is no worse than alternative treatment options for cUTIs and HABP/VABP, but more data are currently available to support the use of beta-lactam beta-lactamase inhibitor agents, where susceptible. Mortality differences demonstrated in patients with pneumonia and bloodstream infections must further be explored and logistical and practical considerations regarding susceptibility testing and use as monotherapy vs. combination therapy must be considered prior to confidently recommending cefiderocol for regular use in systemic infections.

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.

Simulated intravenous versus inhaled tobramycin with and without intravenous ceftazidime evaluated against hypermutable Pseudomonas aeruginosa via a dynamic biofilm model and mechanism-based modeling

Acute exacerbations of chronic respiratory infections in patients with cystic fibrosis are highly challenging due to hypermutable Pseudomonas aeruginosa, biofilm formation and resistance emergence. We aimed to systematically evaluate the effects of intravenous versus inhaled tobramycin with and without intravenous ceftazidime. Two hypermutable P. aeruginosa isolates, CW30 (MIC_CAZ 0.5mg/L, MIC_TOB 2mg/L) and CW8 (MIC_CAZ 2mg/L, MIC_TOB 8mg/L), were investigated for 120h in dynamic in vitro biofilm studies. Treatments were: intravenous ceftazidime 9g/day (33% lung fluid penetration); intravenous tobramycin 10mg/kg 24-hourly (50% lung fluid penetration); inhaled tobramycin 300mg 12-hourly, and both ceftazidime-tobramycin combinations. Total and less-susceptible planktonic and biofilm bacteria were quantified over 120h. Mechanism-based modeling was performed. All monotherapies were ineffective for both isolates, with regrowth of planktonic (≥4.7log₁₀ CFU/mL) and biofilm (>3.8log₁₀ CFU/cm²) bacteria, and resistance amplification by 120h. Both combination treatments demonstrated synergistic or enhanced bacterial killing of planktonic and biofilm bacteria. With the combination simulating tobramycin inhalation, planktonic bacterial counts of the two isolates at 120h were 0.47% and 36% of those for the combination with intravenous tobramycin; for biofilm bacteria the corresponding values were 8.2% and 13%. Combination regimens achieved substantial suppression of resistance of planktonic and biofilm bacteria compared to each antibiotic in monotherapy for both isolates. Mechanism-based modeling well described all planktonic and biofilm counts, and indicated synergy of the combination regimens despite reduced activity of tobramycin in biofilm. Combination regimens of inhaled tobramycin with ceftazidime hold promise to treat acute exacerbations caused by hypermutable P. aeruginosa strains and warrant further investigation.

Penetration of Antibacterial Agents into Pulmonary Epithelial Lining Fluid: An Update

A comprehensive review of drug penetration into pulmonary epithelial lining fluid (ELF) was previously published in 2011. Since then, an extensive number of studies comparing plasma and ELF concentrations of antibacterial agents have been published and are summarized in this review. The majority of the studies included in this review determined ELF concentrations of antibacterial agents using bronchoscopy and bronchoalveolar lavage, and this review focuses on intrapulmonary penetration ratios determined with area under the concentration-time curve from healthy human adult studies or pharmacokinetic modeling of various antibacterial agents. If available, pharmacokinetic/pharmacodynamic parameters determined from preclinical murine infection models that evaluated ELF concentrations are also provided. There are also a limited number of recently published investigations of intrapulmonary penetration in critically ill patients with lower respiratory tract infections, where greater variability in ELF concentrations may exist. The significance of these changes may impact the intrapulmonary penetration in the setting of infection, and further studies relating ELF concentrations to clinical response are needed. Phase I drug development programs now include assessment of initial pharmacodynamic target values for pertinent organisms in animal models, followed by evaluation of antibacterial penetration into the human lung to assist in dosage selection for clinical trials in infected patients. The recent focus has been on β-lactam agents, including those in combination with β-lactamase inhibitors, particularly due to the rise of multidrug-resistant infections. This manifests as a large portion of the review focusing on cephalosporins and carbapenems, with or without β-lactamase inhibitors, in both healthy adult subjects and critically ill patients with lower respiratory tract infections. Further studies are warranted in critically ill patients with lower respiratory tract infections to evaluate the relationship between intrapulmonary penetration and clinical and microbiological outcomes. Our clinical research experience with these studies, along with this literature review, has allowed us to outline key steps in developing and evaluating dosage regimens to treat extracellular bacteria in lower respiratory tract infections.

Beta-Lactams Dosing in Critically Ill Patients with Gram-Negative Bacterial Infections: A PK/PD Approach

Beta-lactam antibiotics are often the backbone of treatment for Gram-negative infections in the critically ill. Beta-lactams exhibit time-dependent killing, and their efficacy depends on the percentage of dosing interval that the concentration remains above the minimum inhibitory concentration. The Gram-negative resistance rates of pathogens are increasing in the intensive care unit (ICU), and critically ill patients often possess physiology that makes dosing more challenging. The volume of distribution is usually increased, and drug clearance is variable. Augmented renal clearance and hypermetabolic states increase the clearance of beta-lactams, while acute kidney injury reduces the clearance. To overcome the factors affecting ICU patients and decreasing susceptibilities, dosing strategies involving higher doses, and extended or continuous infusions may be required. In this review, we specifically examined pharmacokinetic models in ICU patients, to determine the desired beta-lactam regimens for clinical breakpoints of Enterobacterales and Pseudomonas aeruginosa, as determined by the European Committee on Antimicrobial Susceptibility Testing. The beta-lactams evaluated included penicillins, cephalosporins, carbapenems, and monobactams. We found that when treating less-susceptible pathogens, especially P. aeruginosa, continuous infusions are frequently needed to achieve the desired pharmacokinetic/pharmacodynamic targets. More studies are needed to determine optimal dosing strategies in the novel beta-lactams.

Outcomes of adult patients in the intensive care unit with Pseudomonas aeruginosa pneumonia who received an active anti-pseudomonal β-lactam: Does "S" equal success in the presence of resistance to other anti-pseudomonal β-lactams?

STUDY OBJECTIVES

The most commonly prescribed antibiotics for patients with hospital-acquired bacterial pneumonia (HABP) and ventilator-associated bacterial pneumonia (VABP) due to Pseudomonas aeruginosa are the conventional anti-pseudomonal β-lactams (APBLs) (ie, ceftazidime, cefepime, meropenem, or piperacillin-tazobactam). Similar resistance mechanisms in P. aeruginosa affect the APBLs, and it is unclear if resistance to one APBL can affect the effectiveness of other APBLs. This exploratory, hypothesis-generating analysis evaluates the impact of APBL resistance among patients in the intensive care unit (ICU) with P. aeruginosa HABP/VABP who initially receive a microbiologically active APBL.

DESIGN

A retrospective cohort [GJ1] [LT2] study.

SETTING

Kaiser Permanente Southern California members (01/01/2011-12/31/2017).

PATIENTS

The study included adult patients admitted to the ICU with a monomicrobial P. aeruginosa HABP/VABP who received a microbiologically active APBL within 2 days of index P. aeruginosa respiratory culture.

INTERVENTION

Patients were stratified by presence of resistance to APBL on index P. aeruginosa (0 vs. ≥1 resistant APBL).

MEASUREMENTS

Primary outcomes were 30-day mortality and discharge to home.

MAIN RESULTS

Overall, 553 patients were included. Thirty-day mortality was 28%, and 32% of patients were discharged home. Eighty-eight patients (16%) had a P. aeruginosa HABP/VABP that was resistant to ≥1 APBL (other than active empiric treatment). Relative to patients with no APBL resistance, patients with resistance to ≥1 APBL had a higher 30-day mortality (adjusted odds ratio (aOR) [95% confidence interval (CI)]: 1.65 [1.02-2.66]) and were less likely to be discharged home (adjusted hazard ratio (aHR) [95% CI]: 0.50 [0.29-0.85]).

CONCLUSION

Further study is needed, but this exploratory analysis suggests that the full APBL susceptibility profile should be considered when selecting therapy for patients with P. aeruginosa HABP/VABP.

Pharmacodynamics of ceftazidime plus tobramycin combination dosage regimens against hypermutable Pseudomonas aeruginosa isolates at simulated epithelial lining fluid concentrations in a dynamic in vitro infection model

OBJECTIVES

Hypermutable Pseudomonas aeruginosa strains are a major challenge in cystic fibrosis. We investigated bacterial killing and resistance emergence for approved ceftazidime and tobramycin regimens, alone and in combination.

METHODS

Pseudomonas aeruginosa PAOΔmutS and six hypermutable clinical isolates were examined using 48-h static concentration time-kill (SCTK) studies (inoculum ~10^7.5 CFU/mL); four strains were also studied in a dynamic in vitro model (IVM) (inoculum ~10⁸ CFU/mL). The IVM simulated concentration-time profiles in epithelial lining fluid following intravenous administration of ceftazidime (3 g/day and 9 g/day continuous infusion), tobramycin (5 mg/kg and 10 mg/kg via 30-min infusion 24-hourly; half-life 3.5 h), and their combinations. Time courses of total and less-susceptible populations were determined.

RESULTS

Ceftazidime plus tobramycin demonstrated synergistic killing in SCTK studies for all strains, although to a lesser extent for ceftazidime-resistant strains. In the IVM, ceftazidime and tobramycin monotherapies provided ≤5.4 and ≤3.4 log₁₀ initial killing, respectively; however, re-growth with resistance occurred by 72 h. Against strains susceptible to one or both antibiotics, high-dose combination regimens provided >6 log₁₀ initial killing, which was generally synergistic from 8-24 h, and marked suppression of re-growth and resistance at 72 h. The time course of bacterial density in the IVM was well described by mechanism-based models, enabling Monte Carlo simulations (MCSs) to predict likely effectiveness of the combination in patients.

CONCLUSION

Results of the IVM and MCS suggested antibacterial effect depends both on the strain's susceptibility and hypermutability. Further investigation of the combination against hypermutable P. aeruginosa strains is warranted.

Intrapulmonary Pharmacokinetics of Cefepime and Enmetazobactam in Healthy Volunteers: Towards New Treatments for Nosocomial Pneumonia

Cefepime-enmetazobactam is a novel β-lactam-β-lactamase inhibitor combination with broad-spectrum antimicrobial activity against a range of multidrug-resistant Enterobacteriaceae This agent is being developed for a range of serious hospital infections. An understanding of the extent of partitioning of β-lactam-β-lactamase inhibitor combinations into the human lung is required to better understand the potential role of cefepime-enmetazobactam for the treatment of nosocomial pneumonia. A total of 20 healthy volunteers were used to study the intrapulmonary pharmacokinetics of a regimen of 2 g cefepime-1 g enmetazobactam every 8 h intravenously (2 g/1 g q8h i.v.). Each volunteer contributed multiple plasma samples and a single epithelial lining fluid (ELF) sample, obtained by bronchoalveolar lavage. Concentrations of cefepime and enmetazobactam were quantified using liquid chromatography-tandem mass spectrometry. The pharmacokinetic data were modeled using a population methodology, and Monte Carlo simulations were performed to assess the attainment of pharmacodynamic targets defined in preclinical models. The concentration-time profiles of both agents in plasma and ELF were similar. The mean ± standard deviation percentage of partitioning of total drug concentrations of cefepime and enmetazobactam between plasma and ELF was 60.59% ± 28.62% and 53.03% ± 21.05%, respectively. Using pharmacodynamic targets for cefepime of greater than the MIC and free enmetazobactam concentrations of >2 mg/liter in ELF of 20% of the dosing interval, a regimen of cefepime-enmetazobactam of 2 g/0.5 g q8h i.v. infused over 2 h resulted in a probability of target attainment of ≥90% for Enterobacteriaceae with cefepime-enmetazobactam MICs of ≤8 mg/liter. This result provides a rationale to further consider cefepime-enmetazobactam for the treatment of nosocomial pneumonia caused by multidrug-resistant Enterobacteriaceae.

Ceftaroline fosamil as a potential treatment option for Staphylococcus aureus community-acquired pneumonia in adults

Staphylococcus aureus (S. aureus), including methicillin-resistant S. aureus (MRSA), is an important aetiological cause of community-acquired pneumonia (CAP) and associated with significant morbidity and mortality. Empiric therapy for CAP frequently consists of β-lactam monotherapy or β-lactam/macrolide combination therapy. However, such agents are often ineffective against S. aureus and do not reflect the emergence and increasing prevalence of MRSA in the community setting. Ceftaroline fosamil is a fifth-generation parenteral cephalosporin with broad-spectrum activity against Gram-positive pathogens - such as S. aureus (including MRSA), Streptococcus pneumoniae and Streptococcus pyogenes - and typical Gram-negative pathogens, including Haemophilus influenzae and Moraxella catarrhalis. The approval of ceftaroline fosamil in the United States and Europe for the treatment of adults with moderate-to-severe CAP was based on two phase 3 trials (FOCUS 1 and 2), which demonstrated that ceftaroline fosamil was non-inferior to ceftriaxone, a standard empiric treatment for CAP, while exhibiting a comparable safety profile. Although head-to-head trials of ceftaroline fosamil versus comparators against MRSA CAP are lacking, the effectiveness of ceftaroline fosamil in subpopulations of patients not covered by phase 3 trials (e.g. those with MRSA CAP or severe renal impairment) has been demonstrated in the Clinical Assessment Program and Teflaro Utilization Registry (CAPTURE) study. As ineffective empiric therapy is associated with adverse outcomes, including mortality and increased costs, ceftaroline fosamil, with its extended spectrum of activity, is an attractive alternative to standard antibiotic CAP regimens.

Intrapulmonary pharmacokinetics of cefiderocol, a novel siderophore cephalosporin, in healthy adult subjects

BACKGROUND

Cefiderocol, a novel siderophore cephalosporin, has shown potent activity against Gram-negative bacteria, including MDR pathogens. Cefiderocol is under clinical investigation for the treatment of serious Gram-negative infections including nosocomial pneumonia.

OBJECTIVES

This study assessed intrapulmonary penetration after a single intravenous dose of cefiderocol (2000 mg infused over 60 min) in healthy adult males.

MATERIALS AND METHODS

Each subject underwent one bronchoscopy with bronchoalveolar lavage (BAL) to collect BAL fluid (BALF). Fifteen subjects were assigned to one of three collection timepoints (1, 2 or 4 h from start of infusion). Five additional subjects were assigned to a collection timepoint at 6 h, which was added based on concentration data between 1 and 4 h predicting measurable BALF cefiderocol concentrations at 6 h.

RESULTS

Cefiderocol concentrations in plasma, epithelial lining fluid (ELF) and alveolar macrophages (AMs) were calculated for each subject. The ELF concentration of cefiderocol was 13.8, 6.69, 2.78 and 1.38 mg/L at 1, 2, 4 and 6 h after single intravenous dosing, respectively. Over 6 h, geometric mean concentration ratios ranged from 0.0927 to 0.116 for ELF to total plasma and from 0.00496 to 0.104 for AMs to total plasma. AUC ratios of ELF and AMs to plasma were 0.101 and 0.0177 based on total drug in plasma, respectively, and 0.239 and 0.0419 based on free drug in plasma, respectively. There were no major drug-related adverse events.

CONCLUSIONS

Results of this study indicate that cefiderocol penetrates into ELF, and ELF and plasma concentrations appear to be parallel.

Individualising Therapy to Minimize Bacterial Multidrug Resistance

The scourge of antibiotic resistance threatens modern healthcare delivery. A contributing factor to this significant issue may be antibiotic dosing, whereby standard antibiotic regimens are unable to suppress the emergence of antibiotic resistance. This article aims to review the role of pharmacokinetic and pharmacodynamic (PK/PD) measures for optimising antibiotic therapy to minimise resistance emergence. It also seeks to describe the utility of combination antibiotic therapy for suppression of resistance and summarise the role of biomarkers in individualising antibiotic therapy. Scientific journals indexed in PubMed and Web of Science were searched to identify relevant articles and summarise existing evidence. Studies suggest that optimising antibiotic dosing to attain defined PK/PD ratios may limit the emergence of resistance. A maximum aminoglycoside concentration to minimum inhibitory concentration (MIC) ratio of > 20, a fluoroquinolone area under the concentration-time curve to MIC ratio of > 285 and a β-lactam trough concentration of > 6 × MIC are likely required for resistance suppression. In vitro studies demonstrate a clear advantage for some antibiotic combinations. However, clinical evidence is limited, suggesting that the use of combination regimens should be assessed on an individual patient basis. Biomarkers, such as procalcitonin, may help to individualise and reduce the duration of antibiotic treatment, which may minimise antibiotic resistance emergence during therapy. Future studies should translate laboratory-based studies into clinical trials and validate the appropriate clinical PK/PD predictors required for resistance suppression in vivo. Other adjunct strategies, such as biomarker-guided therapy or the use of antibiotic combinations require further investigation.

Pharmacokinetics-pharmacodynamics issues relevant for the clinical use of beta-lactam antibiotics in critically ill patients

Antimicrobials are among the most important and commonly prescribed drugs in the management of critically ill patients and beta-lactams are the most common antibiotic class used. Critically ill patient's pathophysiological factors lead to altered pharmacokinetics and pharmacodynamics of beta-lactams.A comprehensive bibliographic search in PubMed database of all English language articles published from January 2000 to December 2017 was performed, allowing the selection of articles addressing the pharmacokinetics or pharmacodynamics of beta-lactam antibiotics in critically ill patients.In critically ill patients, several factors may increase volume of distribution and enhance renal clearance, inducing high intra- and inter-patient variability in beta-lactam concentration and promoting the risk of antibiotic underdosing. The duration of infusion of beta-lactams has been shown to influence the fT > minimal inhibitory concentration and an improved beta-lactam pharmacodynamics profile may be obtained by longer exposure with more frequent dosing, extended infusions, or continuous infusions.The use of extracorporeal support techniques in the critically ill may further contribute to this problem and we recommend not reducing standard antibiotic dosage since no drug accumulation was found in the available literature and to maintain continuous or prolonged infusion, especially for the treatment of infections caused by multidrug-resistant bacteria.Prediction of outcome based on concentrations in plasma results in overestimation of antimicrobial activity at the site of infection, namely in cerebrospinal fluid and the lung. Therefore, although no studies have assessed clinical outcome, we recommend using higher than standard dosing, preferably with continuous or prolonged infusions, especially when treating less susceptible bacterial strains at these sites, as the pharmacodynamics profile may improve with no apparent increase in toxicity.A therapeutic drug monitoring-guided approach could be particularly useful in critically ill patients in whom achieving target concentrations is more difficult, such as obese patients, immunocompromised patients, those infected by highly resistant bacterial strains, patients with augmented renal clearance, and those undergoing extracorporeal support techniques.

Pharmacokinetic drug evaluation of avibactam + ceftazidime for the treatment of hospital-acquired pneumonia

INTRODUCTION

Ceftazidime-avibactam (CAZ-AVI) is a combination of a third-generation cephalosporin and a non-β-lactam, β-lactamase inhibitor, recently approved for urinary tract infections and complicated abdominal infections. Moreover, it represents a treatment option for patients with hospital acquired pneumonia (HAP), especially when caused by multidrug-resistant (MDR) bacteria. Areas covered: The review focuses on the pharmacokinetics (PK) of CAZ-AVI in HAP and on preclinical and clinical studies evaluating PK/pharmacodynamics (PD) in this field. Expert opinion: In vitro and in vivo data about PK/PD of CAZ-AVI confirm that penetration of CAZ-AVI in the epithelial lining fluid (ELF) represents approximately 30% of the plasma concentrations. Clinical studies documented that CAZ-AVI 2000 mg/500 mg every 8 h is the optimal dose regimen to achieve the PK/PD target attainment in patients with HAP. Thus, CAZ-AVI could represent an option both to treat HAP caused by Gram-negative bacilli (GNB) displaying resistance to most of the antibiotics and to reduce the use of carbapenems, limiting the onset of resistance profiles among GNB. Additional information about specific patients populations, such as critically-ill subjects or pediatric patients, are needed for a more individualized use of CAZ-AVI.

Antibiotic dosing for multidrug-resistant pathogen pneumonia

PURPOSE OF REVIEW

Nosocomial pneumonia caused by multidrug-resistant pathogens is increasing in the ICU, and these infections are negatively associated with patient outcomes. Optimization of antibiotic dosing has been suggested as a key intervention to improve clinical outcomes in patients with nosocomial pneumonia. This review describes the recent pharmacokinetic/pharmacodynamic data relevant to antibiotic dosing for nosocomial pneumonia caused by multidrug-resistant pathogens.

RECENT FINDINGS

Optimal antibiotic treatment is challenging in critically ill patients with nosocomial pneumonia; most dosing guidelines do not consider the altered physiology and illness severity associated with severe lung infections. Antibiotic dosing can be guided by plasma drug concentrations, which do not reflect the concentrations at the site of infection. The application of aggressive dosing regimens, in accordance to the antibiotic's pharmacokinetic/pharmacodynamic characteristics, may be required to ensure rapid and effective drug exposure in infected lung tissues.

SUMMARY

Conventional antibiotic dosing increases the likelihood of therapeutic failure in critically ill patients with nosocomial pneumonia. Alternative dosing strategies, which exploit the pharmacokinetic/pharmacodynamic properties of an antibiotic, should be strongly considered to ensure optimal antibiotic exposure and better therapeutic outcomes in these patients.

Considerations for effect site pharmacokinetics to estimate drug exposure: concentrations of antibiotics in the lung

Bronchoalveolar lavage (BAL) and microdialysis have become the most reliable and relevant methods for measuring lung concentrations of antibiotics, with the majority of BAL studies involving either healthy adult subjects or patients undergoing diagnostic bronchoscopy. Emphasis on the amount of drug that reaches the site of infection is increasingly recognized as necessary to determine whether a dose selection will translate to good clinical outcomes in the treatment of patients with pneumonia. Observed concentrations and/or parameters of exposure (e.g. area-under-the-curve) need to be incorporated with pharmacokinetic-pharmacodynamic indices so that rational dose selection can be identified for specific pathogens and types of pneumonic infection (community-acquired vs hospital-acquired bacterial pneumonia, including ventilator-associated bacterial pneumonia). Although having measured plasma or lung concentration-time data from critically ill patients to incorporate into pharmacokinetic-pharmacodynamic models is very unlikely during drug development, it is essential that altered distribution, augmented renal clearance, and renal or hepatic dysfunction should be considered. Notably, the number of published studies involving microdialysis and intrapulmonary penetration of antibiotics has been limited and mainly involve beta-lactam agents, levofloxacin, and fosfomycin. Opportunities to measure in high-resolution effect site spatial pharmacokinetics (e.g. with MALDI-MSI or PET imaging) and in vivo continuous drug concentrations (e.g. with aptamer-based probes) now exist. Going forward these studies could be incorporated into antibiotic development programs for pneumonia in order to further increase the probability of candidate success.

Pharmacokinetics and Dosing of Ceftobiprole Medocaril for the Treatment of Hospital- and Community-Acquired Pneumonia in Different Patient Populations

Hospital-acquired pneumonia (HAP) and community-acquired pneumonia (CAP) are among the most common infections treated in the hospital setting, and together they place a significant burden on healthcare systems. Successful management of HAP and CAP depends on rapid initiation of empirical antibiotic therapy with broad-spectrum antibiotics. Ceftobiprole is a new-generation, broad-spectrum cephalosporin antibiotic for the treatment of HAP (excluding ventilator-associated pneumonia) and CAP. It displays potent in vitro activity against a broad range of pathogens important in pneumonia. This review summarizes the pharmacokinetic profile of ceftobiprole, and considers the pharmacokinetic parameters and pharmacodynamics underlying the choice of dosing regimen. Ceftobiprole shows linear pharmacokinetics after single and multiple doses and is eliminated predominantly through the kidneys. Ceftobiprole is administered as a 500 mg intravenous infusion over 2 h every 8 h, and steady-state concentrations are reached on the first day of dosing. Dose adjustment is recommended for patients with moderate or severe renal impairment and for those with end-stage renal disease. Extending the infusion time of ceftobiprole to 4 h is recommended to optimize drug exposure in critically ill patients with augmented renal clearance. However, there is no need for dose adjustments based on age, sex or ethnicity, or for patients with severe obesity. Population pharmacokinetic modelling and Monte Carlo simulations were used to determine the optimal dosing regimen for ceftobiprole in special patient populations, including paediatric patients. Future studies of ceftobiprole in patients with HAP and CAP would be of interest.

The role of infection models and PK/PD modelling for optimising care of critically ill patients with severe infections

Critically ill patients with severe infections are at high risk of suboptimal antimicrobial dosing. The pharmacokinetics (PK) and pharmacodynamics (PD) of antimicrobials in these patients differ significantly from the patient groups from whose data the conventional dosing regimens were developed. Use of such regimens often results in inadequate antimicrobial concentrations at the site of infection and is associated with poor patient outcomes. In this article, we describe the potential of in vitro and in vivo infection models, clinical pharmacokinetic data and pharmacokinetic/pharmacodynamic models to guide the design of more effective antimicrobial dosing regimens. Individualised dosing, based on population PK models and patient factors (e.g. renal function and weight) known to influence antimicrobial PK, increases the probability of achieving therapeutic drug exposures while at the same time avoiding toxic concentrations. When therapeutic drug monitoring (TDM) is applied, early dose adaptation to the needs of the individual patient is possible. TDM is likely to be of particular importance for infected critically ill patients, where profound PK changes are present and prompt appropriate antibiotic therapy is crucial. In the light of the continued high mortality rates in critically ill patients with severe infections, a paradigm shift to refined dosing strategies for antimicrobials is warranted to enhance the probability of achieving drug concentrations that increase the likelihood of clinical success.

Penetration of Ceftaroline into the Epithelial Lining Fluid of Healthy Adult Subjects

Ceftaroline, the active metabolite of the prodrug ceftaroline fosamil, is a cephalosporin with bactericidal activity against Gram-positive organisms, including methicillin-resistant Staphylococcus aureus (MRSA). This study aimed to (i) evaluate ceftaroline concentrations in human plasma and epithelial lining fluid (ELF) and (ii) develop a population pharmacokinetic (PK) model for plasma and ELF to be used in PK/pharmacodynamic (PD) target attainment simulations. Ceftaroline concentrations in ELF and plasma at steady state (day 4) were measured in healthy adult subjects for two dosages: 600 mg every 12 h (q12h) and 600 mg every 8 h (q8h). Both were well tolerated with no serious adverse events. The penetration of free ceftaroline into ELF, assuming 20% protein binding in plasma and no protein binding in ELF, was ≈23%. The population PK model utilized a two-compartment model for both ceftaroline fosamil and ceftaroline. Goodness-of-fit criteria revealed the model was consistent with observed data and no systematic bias remained. At 600 mg q12h and a MIC of 1 mg/liter, 98.1% of simulated patients would be expected to achieve a target free drug concentration above the MIC (fT>MIC) in plasma of 42%, and in ELF 81.7% would be expected to achieve a target fT>MIC of 17%; at 600 mg q8h, 100% were predicted to achieve an fT>MIC in plasma of 42% and 94.7% to achieve an fT>MIC of 17% in ELF. The literature and data suggest the 600 mg q12h dose is adequate for MICs of ≤1 mg/liter. There is a need for clinical data in patients with MRSA pneumonia and data to correlate PK/PD relationships in ELF with clinical outcomes.

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.

Prolonged versus Intermittent Infusion of β-Lactams for the Treatment of Nosocomial Pneumonia: A Meta-Analysis

BACKGROUND

The primary objective of this meta-analysis is aimed at determining whether β-lactams prolonged infusion in patients with nosocomial pneumonia (NP) results in higher cure rate and improved mortality compared to intermittent infusion.

MATERIALS AND METHODS

Relevant studies were identified from searches of MEDLINE, EMBASE, and CENTRAL from inception to September 1st, 2015. All published articles which evaluated the outcome of extended/continuous infusion of antimicrobial therapy versus intermittent infusion therapy in the treatment of NP were reviewed.

RESULTS

A total of ten studies were included in the analysis involving 1,051 cases of NP. Prolonged infusion of β-lactams was associated with higher clinical cure rate (OR 2.45, 95% CI, 1.12, 5.37) compared to intermittent infusion. However, there was no significant difference in mortality (OR 0.85, 95% CI 0.63-1.15) between the two groups. Subgroup analysis for β-lactam subclasses and for severity of illness showed comparable outcomes.

CONCLUSION

The limited data available suggest that reduced clinical failure rates when using prolonged infusions of β-lactam antibiotics in critically ill patients with NP. More detailed studies are needed to determine the impact of such strategy on mortality in this patient population.

The β-Lactams Strike Back: Ceftazidime-Avibactam

Gram-negative resistance has reached a crucial point, with emergence of pathogens resistant to most or all available antibiotics. Ceftazidime-avibactam is a newly approved agent combining ceftazidime and a novel β-lactamase inhibitor with activity against multidrug-resistant gram-negative bacteria. Avibactam has increased potency and expanded spectrum of inhibition of class A and C β-lactamases relative to available β-lactamase inhibitors, including extended-spectrum β-lactamases, AmpC, and Klebsiella pneumoniae carbapenemase (KPC) enzymes. Avibactam expands ceftazidime's spectrum of activity to include many ceftazidime- and carbapenem-resistant Enterobacteriaceae and Pseudomonas aeruginosa. Early clinical data indicate that ceftazidime-avibactam is effective and well tolerated in patients with complicated urinary tract infections (cUTIs) and complicated intraabdominal infections (cIAI). In a phase II trial of patients with cUTIs, ceftazidime-avibactam produced similar rates of clinical and microbiologic success compared with imipenem-cilastatin (70.5% and 71.4% microbiologic success rates, respectively). Likewise, patients receiving ceftazidime-avibactam plus metronidazole in a phase II study of patients with cIAI had similar response rates to those receiving meropenem (91.2% and 93.4% clinical success rates, respectively). Based on available in vitro, in vivo, and phase II trial data, as well as preliminary phase III trial results in ceftazidime-resistant, gram-negative cUTI and cIAI, ceftazidime-avibactam received U.S. Food and Drug Administration approval for treatment of cUTI, including pyelonephritis, and cIAI, in combination with metronidazole, in adult patients with limited or no alternative treatment options. The approved dosage, ceftazidime 2 g-avibactam 0.5 g administered as a 2-hour infusion every 8 hours, was selected based on pharmacodynamic analysis and available clinical data. This dosage is under further investigation in patients with cUTI, cIAI, and nosocomial or ventilator-associated pneumonia. The current body of evidence suggests that ceftazidime-avibactam is a promising addition to our therapeutic armamentarium with potential to answer an urgent unmet medical need. Further data in highly resistant gram-negative infections, particularly those caused by KPC-producing Enterobacteriaceae, are needed. As it is introduced into clinical use, careful stewardship and rational use are essential to preserve ceftazidime-avibactam's potential utility.

Phase 1 study assessing the steady-state concentration of ceftazidime and avibactam in plasma and epithelial lining fluid following two dosing regimens

OBJECTIVES

The aim of this Phase 1, open-label study (NCT01395420) was to measure and compare concentrations of ceftazidime and avibactam in bronchial epithelial lining fluid (ELF) and plasma, following administration of two different dosing regimens in healthy subjects.

PATIENTS AND METHODS

Healthy volunteers received 2000 mg of ceftazidime + 500 mg of avibactam (n = 22) or 3000 mg of ceftazidime + 1000 mg of avibactam (n = 21), administered intravenously every 8 h for 3 days (total of nine doses). Bronchoscopy with bronchoalveolar lavage was performed once per subject, 2, 4, 6 or 8 h after the last infusion. Pharmacokinetic parameters were estimated from individual plasma concentrations and the composite ELF concentration-time profile. Safety was assessed.

RESULTS

Forty-three subjects received treatment (2000 mg of ceftazidime + 500 mg of avibactam, n = 22; 3000 mg of ceftazidime + 1000 mg of avibactam, n = 21). Plasma and ELF concentrations increased dose-proportionally for both drugs, with 1.5- and 2-fold increases in AUCτ, for respective components. Ceftazidime Cmax and AUCτ in ELF were ∼ 23%-26% and 31%-32% of plasma exposure. Avibactam Cmax and AUCτ in ELF were ∼ 28%-35% and 32%-35% of plasma exposure. ELF and plasma elimination were similar for both drugs. No serious adverse events were observed.

CONCLUSIONS

Both ceftazidime and avibactam penetrated dose-proportionally into ELF, with ELF exposure to both drugs ∼ 30% of plasma exposure.

Pharmacokinetics and penetration of ceftazidime and avibactam into epithelial lining fluid in thigh- and lung-infected mice

Ceftazidime and the β-lactamase inhibitor avibactam constitute a new, potentially highly active combination in the battle against extended-spectrum-β-lactamase (ESBL)-producing bacteria. To determine possible clinical use, it is important to know the pharmacokinetic profiles of the compounds related to each other in plasma and the different compartments of infection in experimentally infected animals and in humans. We used a neutropenic murine thigh infection model and lung infection model to study pharmacokinetics in plasma and epithelial lining fluid (ELF). Mice were infected with ca. 10(6) CFU of Pseudomonas aeruginosa intramuscularly into the thigh or intranasally to cause pneumonia and were given 8 different (single) subcutaneous doses of ceftazidime and avibactam in various combined concentrations, ranging from 1 to 128 mg/kg of body weight in 2-fold increases. Concomitant samples of serum and bronchoalveolar lavage fluid were taken at up to 12 time points until 6 h after administration. Pharmacokinetics of both compounds were linear and dose proportional in plasma and ELF and were independent of the infection type, with estimated half-lives (standard deviations [SD]) in plasma of ceftazidime of 0.28 (0.02) h and of avibactam of 0.24 (0.04) h and volumes of distribution of 0.80 (0.14) and 1.18 (0.34) liters/kg. The ELF-plasma (area under the concentration-time curve [AUC]) ratios (standard errors [SE]) were 0.24 (0.03) for total ceftazidime and 0.27 (0.03) for unbound ceftazidime; for avibactam, the ratios were 0.20 (0.02) and 0.22 (0.02), respectively. No pharmacokinetic interaction between ceftazidime and avibactam was observed. Ceftazidime and avibactam showed linear plasma pharmacokinetics that were independent of the dose combinations used or the infection site in mice. Assuming pharmacokinetic similarity in humans, this indicates that similar dose ratios of ceftazidime and avibactam could be used for different types and sites of infection.

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.

Measuring drug distribution in the critically ill patient

Critically ill patients often present with a combination of disease states and comorbid conditions that progress over a clinical course. This can manifest in physiological changes, such as fluid shifts, alterations in protein binding, and acid-base balance issues, which may in turn alter a drug's distribution, potentially towards or away from its site of action. It's vital that these factors are examined for drugs used in critical illness in varying disease states, acute and chronic in nature. Several methods have been used to study the variations in target site penetration, but few provide a feasible option to reliably measure active drug concentrations at the site of action over time. This review examines these techniques, their merits and shortcomings, generally and as they relate to use in critically ill.

Community-acquired pneumonia: identification and evaluation of nonresponders

Community acquired pneumonia (CAP) is a relevant public health problem, constituting an important cause of morbidity and mortality. It accounts for a significant number of adult hospital admissions and a large number of those patients ultimately die, especially the population who needed mechanical ventilation or vasopressor support. Thus, early identification of CAP patients and its rapid and appropriate treatment are important features with impact on hospital resource consumption and overall mortality. Although CAP diagnosis may sometimes be straightforward, the diagnostic criteria commonly used are highly sensitive but largely unspecific. Biomarkers and microbiological documentation may be useful but have important limitations. Evaluation of clinical response is also critical especially to identify patients who fail to respond to initial treatment since these patients have a high risk of in-hospital death. However, the criteria of definition of non-response in CAP are largely empirical and frequently markedly diverse between different studies. In this review, we aim to identify criteria defining nonresponse in CAP and the pitfalls associated with this diagnosis. We also aim to overview the main causes of treatment failure especially in severe CAP and the possible strategies to identify and reassess non-responders trying to change the dismal prognosis associated with this condition.

Individualised antibiotic dosing for patients who are critically ill: challenges and potential solutions

Infections in critically ill patients are associated with persistently poor clinical outcomes. These patients have severely altered and variable antibiotic pharmacokinetics and are infected by less susceptible pathogens. Antibiotic dosing that does not account for these features is likely to result in suboptimum outcomes. In this Review, we explore the challenges related to patients and pathogens that contribute to inadequate antibiotic dosing and discuss how to implement a process for individualised antibiotic therapy that increases the accuracy of dosing and optimises care for critically ill patients. To improve antibiotic dosing, any physiological changes in patients that could alter antibiotic concentrations should first be established; such changes include altered fluid status, changes in serum albumin concentrations and renal and hepatic function, and microvascular failure. Second, antibiotic susceptibility of pathogens should be confirmed with microbiological techniques. Data for bacterial susceptibility could then be combined with measured data for antibiotic concentrations (when available) in clinical dosing software, which uses pharmacokinetic/pharmacodynamic derived models from critically ill patients to predict accurately the dosing needs for individual patients. Individualisation of dosing could optimise antibiotic exposure and maximise effectiveness.

Clinical pharmacodynamics of antipseudomonal cephalosporins in patients with ventilator-associated pneumonia

Advanced-generation cephalosporins are frequently used for empirical coverage of ventilator-associated pneumonia (VAP) due to their activity against a broad spectrum of Gram-positive and Gram-negative aerobic bacteria, including Pseudomonas aeruginosa and Enterobacteriaceae. Providing optimal antibiotic exposure is essential to achieving successful response in patients with VAP. We evaluated exposures of two antipseudomonal cephalosporins, ceftazidime and cefepime, in patients with VAP due to Gram-negative bacilli to identify the pharmacodynamic parameter predictive of microbiological success. Population pharmacokinetic models were used to estimate individual free drug exposures. Pharmacodynamic indices were determined for each patient using the baseline Gram-negative bacilli with the highest drug MIC. Classification and regression tree analysis was utilized to partition exposure breakpoints, and multivariate logistic regression was conducted to identify predictors of microbiological success. A total of 73 patients (18 receiving ceftazidime therapy and 55 receiving cefepime therapy) were included. MICs ranged widely from 0.047 to 96 μg/ml. The microbiological success rate was 58.9%. Predictive breakpoints were identified for all pharmacodynamic parameters, including a serum fT>MIC greater than 53% (P=0.02). When controlling for APACHE II (odds ratio [OR], 1.01; 95% confidence interval, 0.93 to 1.09; P=0.85) and combination therapy (OR, 0.74; 95% confidence interval, 0.25 to 2.19; P=0.59), achieving a greater than 53% fT>MIC remained a significant predictor of success (OR, 10.3; 95% confidence interval, 1.1 to 92.3; P=0.04). In patients with VAP due to Gram-negative bacilli, serum exposure of greater than 53% fT>MIC was found to be a significant predictor of favorable microbiological response for antipseudomonal cephalosporins. These data are useful when determining dosing regimens for cephalosporin agents under development for pneumonia.

Efficacies of ceftazidime-avibactam and ceftazidime against Pseudomonas aeruginosa in a murine lung infection model

This study aimed to determine the efficacy of human-simulated plasma exposures of 2 g ceftazidime plus 0.5 g avibactam every 8 h administered as a 2-h infusion or a ceftazidime regimen that produced a specific epithelial lining fluid (ELF) percentage of the dosing interval in which serum free drug concentrations remain above the MIC (fT>MIC) against 28 Pseudomonas aeruginosa isolates within a neutropenic murine pneumonia model and to assess the impact of host infection on pulmonary pharmacokinetics. The fT>MIC was calculated as the mean and upper end of the 95% confidence limit. Against the 28 P. aeruginosa strains used, the ceftazidime-avibactam MICs were 4 to 64 μg/ml, and those of ceftazidime were 8 to >128 μg/ml. The change in log10 CFU after 24 h of treatment was analyzed relative to that of 0-h controls. Pharmacokinetic studies in serum and ELF were conducted using ceftazidime-avibactam in infected and uninfected mice. Humanized ceftazidime-avibactam doses resulted in significant exposures in the lung, producing reductions of >1 log10 CFU against P. aeruginosa with ceftazidime-avibactam MICs of ≤32 μg/ml (ELF upper 95% confidence limit for fT>MIC [ELF fT>MIC] of ≥19%), except for one isolate with a ceftazidime-avibactam MIC of 16 μg/ml. No efficacy was observed against the isolate with a ceftazidime-avibactam MIC of 64 μg/ml (ELF fT>MIC of 0%). Bacterial reductions were observed with ceftazidime against isolates with ceftazidime MICs of 32 μg/ml (ELF fT>MIC of ≥12%), variable efficacy at ceftazidime MICs of 64 μg/ml (ELF fT>MIC of ≥0%), and no activity at a ceftazidime MIC of 128 μg/ml, where the ELF fT>MIC was 0%. ELF fT>MICs were similar between infected and uninfected mice. Ceftazidime-avibactam was effective against P. aeruginosa, with MICs of up to 32 μg/ml with an ELF fT>MIC of ≥19%. The data suggest the potential utility of ceftazidime-avibactam for treatment of lung infections caused by P. aeruginosa.

Delivering antibiotics to the lungs of patients with ventilator-associated pneumonia: an update

Ventilator-associated pneumonia is a serious hospital-acquired infection, with 20-70% crude mortality and 10-40% estimated attributable mortality. Insufficient antibiotic concentrations at the infection site when these drugs are given intravenously may lead to poor outcomes, particularly when difficult-to-treat pathogens are responsible; for example, Pseudomonas aeruginosa, extended spectrum beta lactamase-producing Gram-negative bacilli, Acinetobacter spp. and/or methicillin-resistant Staphylococcus aureus. Direct drug delivery to the infection site via aerosolization combined with intravenous administration achieves concentrations exceeding MICs of the pathogens, even those with impaired susceptibility. Experimental and recent clinical results demonstrated our markedly improved ability to deliver aerosolized antibiotics to the lung with new-generation devices, for example, vibrating-mesh nebulizers. Convincing clinical data from a large randomized trial are still lacking to support the routine administration of aerosolized antibiotics to treat ventilator-associated pneumonia, even though some small-randomized trials' observations are encouraging.

Ceftazidime for respiratory infections

INTRODUCTION

Ceftazidime is a third-generation cephalosporin that has activity against Gram-negative bacilli, including Pseudomonas aeruginosa. The increasing prevalence of antimicrobial resistance and the limited number of antimicrobial agents in development have necessitated a review of the current status of treatments involving ceftazidime.

AREAS COVERED

This review focuses on studies examining the in vitro antibacterial activity of ceftazidime against recent clinical isolates and recent randomized controlled trials studying the clinical efficacy of ceftazidime, and discusses strategies for the optimal use of ceftazidime for treating respiratory tract infections, mainly hospital-acquired pneumonia (HAP).

EXPERT OPINION

Although ceftazidime remains an important option for HAP treatment, its role as an effective antimicrobial agent has been compromised by the sharp increase in resistance rates over the last decade, especially in P. aeruginosa and Acinetobacter baumannii. To maintain or improve the clinical use of ceftazidime in patients with severe HAP, it will be essential to gain a thorough understanding of local resistance patterns, reserve ceftazidime use when pathogens are susceptible to other third-generation cephalosporins, optimize ceftazidime therapy using prolonged or continuous infusion, determine the effectiveness of the combination of ceftazidime with inhibitors of broad-spectrum β-lactamases and role of combination therapy for P. aeruginosa infections, and judiciously use antimicrobial agents through individualization of antimicrobial therapy for HAP.

Continuous infusion of antibiotics in the critically ill: The new holy grail for beta-lactams and vancomycin?

The alarming global rise of antimicrobial resistance combined with the lack of new antimicrobial agents has led to a renewed interest in optimization of our current antibiotics. Continuous infusion (CI) of time-dependent antibiotics has certain theoretical advantages toward efficacy based on pharmacokinetic/pharmacodynamic principles. We reviewed the available clinical studies concerning continuous infusion of beta-lactam antibiotics and vancomycin in critically ill patients. We conclude that CI of beta-lactam antibiotics is not necessarily more advantageous for all patients. Continuous infusion is only likely to have clinical benefits in subpopulations of patients where intermittent infusion is unable to achieve an adequate time above the minimal inhibitory concentration (T > MIC). For example, in patients with infections caused by organisms with elevated MICs, patients with altered pharmacokinetics (such as the critically ill) and possibly also immunocompromised patients. For vancomycin CI can be chosen, not always for better clinical efficacy, but because it is practical, cheaper, associated with less AUC_24h (area under the curve >24 h)-variability, and easier to monitor.

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

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

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

WHAT THIS STUDY ADDS

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

METHOD

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

RESULTS

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

CONCLUSION

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

Penetration of anti-infective agents into pulmonary epithelial lining fluid: focus on antibacterial agents

The exposure-response relationship of anti-infective agents at the site of infection is currently being re-examined. Epithelial lining fluid (ELF) has been suggested as the site (compartment) of antimicrobial activity against lung infections caused by extracellular pathogens. There have been an extensive number of studies conducted during the past 20 years to determine drug penetration into ELF and to compare plasma and ELF concentrations of anti-infective agents. The majority of these studies estimated ELF drug concentrations by the method of urea dilution and involved either healthy adult subjects or patients undergoing diagnostic bronchoscopy. Antibacterial agents such as macrolides, ketolides, newer fluoroquinolones and oxazolidinones have ELF to plasma concentration ratios of >1. In comparison, β-lactams, aminoglycosides and glycopeptides have ELF to plasma concentration ratios of ≤1. Potential explanations (e.g. drug transporters, overestimation of the ELF volume, lysis of cells) for why these differences in ELF penetration occur among antibacterial classes need further investigation. The relationship between ELF concentrations and clinical outcomes has been under-studied. In vitro pharmacodynamic models, using simulated ELF and plasma concentrations, have been used to examine the eradication rates of resistant and susceptible pathogens and to explain why selected anti-infective agents (e.g. those with ELF to plasma concentration ratios of >1) are less likely to be associated with clinical treatment failures. Population pharmacokinetic modelling and Monte Carlo simulations have recently been used and permit ELF and plasma concentrations to be evaluated with regard to achievement of target attainment rates. These mathematical modelling techniques have also allowed further examination of drug doses and differences in the time courses of ELF and plasma concentrations as potential explanations for clinical and microbiological effects seen in clinical trials. Further studies are warranted in patients with lower respiratory tract infections to confirm and explore the relationships between ELF concentrations, clinical and microbiological outcomes, and pharmacodynamic parameters.

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.

What are the properties that make an antibiotic acceptable for therapy of community-acquired pneumonia?

The factors associated with identifying an appropriate dose and schedule of an antimicrobial agent for treatment of hospitalized, seriously ill patients with pneumonia are straightforward. Information is required about the potency of the agent for typical pathogens likely to be encountered with pneumonia. It is helpful to understand the utility of the agent against pathogens that express resistance to older antimicrobial agents. The agent must be able to gain access to the site of infection at the dose and schedule chosen and at concentrations high enough to attain microbiologically effective targets [e.g. 1 or 2 log(10) (cfu/g) bacterial cell kill, accounting for between-patient variability]. Finally, therapeutic concentrations should be attained quickly at the primary site of infection to optimize clinical outcomes. When considering all of these factors, it is expected that ceftaroline fosamil will be a valuable addition to the therapeutic armamentarium for management of community-acquired pneumonia.