Ertapenem in critically ill patients with early-onset ventilator-associated pneumonia: pharmacokinetics with special consideration of free-drug concentration

Albumin: a comprehensive review and practical guideline for clinical use

PURPOSE

Nowadays, it is largely accepted that albumin should not be used in hypoalbuminemia or for nutritional purpose. The most discussed indication of albumin at present is the resuscitation in shock states, especially distributive shocks such as septic shock. The main evidence-based indication is also liver disease. In this review, we provided updated evidence-based instruction for definite and potential indications of albumin administration in clinical practice, with appropriate dosing and duration.

METHODS

Data collection was carried out until November 2023 by search of electronic databases including PubMed, Google Scholar, Scopus, and Web of Science. GRADE system has been used to determine the quality of evidence and strength of recommendations for each albumin indication.

RESULTS

A total of 165 relevant studies were included in this review. Fluid replacement in plasmapheresis and liver diseases, including hepatorenal syndrome, spontaneous bacterial peritonitis, and large-volume paracentesis, have a moderate to high quality of evidence and a strong recommendation for administering albumin. Moreover, albumin is used as a second-line and adjunctive to crystalloids for fluid resuscitation in hypovolemic shock, sepsis and septic shock, severe burns, toxic epidermal necrolysis, intradialytic hypotension, ovarian hyperstimulation syndrome, major surgery, non-traumatic brain injury, extracorporeal membrane oxygenation, acute respiratory distress syndrome, and severe and refractory edema with hypoalbuminemia has a low to moderate quality of evidence and weak recommendation to use. Also, in modest volume paracentesis, severe hyponatremia in cirrhosis has a low to moderate quality of evidence and a weak recommendation.

CONCLUSION

Albumin administration is most indicated in management of cirrhosis complications. Fluid resuscitation or treatment of severe and refractory edema, especially in patients with hypoalbuminemia and not responding to other treatments, is another rational use for albumin. Implementation of evidence-based guidelines in hospitals can be an effective measure to reduce inappropriate uses of albumin.

Ertapenem Versus Meropenem for the Treatment of Extended Spectrum Beta-Lactamase-Producing Enterobacterales Bacteremia in Critically Ill Patients

BACKGROUND

The preferred carbapenem for treatment of infections caused by extended spectrum beta-lactamase-producing Enterobacterales (ESBL-E) in critically ill patients is debated.

OBJECTIVE

The purpose of this study was to evaluate the difference in clinical failure between ertapenem and meropenem for treatment of ESBL-E bacteremia in critically ill patients. Of concern is ertapenem use in hypoalbuminemia given the potential for higher drug clearance.

METHODS

This retrospective, matched cohort study compared critically ill patients treated with ertapenem or meropenem for ESBL-E bacteremia between October 2016 and August 2022. Patients were matched on age, sex, lowest albumin, and in a 1:2 ratio of ertapenem to meropenem. The primary outcome, clinical failure, was a composite of 30-day mortality, antibiotic escalation, and microbiological failure. Secondary outcomes included all-cause readmission and development of superinfection.

RESULTS

Of 54 patients, 18 received ertapenem and 36 meropenem. Most had a urinary infection source (55.6% vs 41.7%, P = 0.393). There was no difference in clinical failure (50.0% vs 38.9%, P = 0.436). Ertapenem patients had antibiotic escalation more often (33.3% vs 2.8%, P = 0.002). There was no difference in 30-day mortality (11.1% vs 27.8%, P = 0.298), microbiological failure (27.8% vs 11.1%, P = 0.142), all-cause readmission (22.2% vs 13.9%, P = 0.461), or development of superinfection (11.1% vs 13.9%, P = 1.000).

CONCLUSION AND RELEVANCE

There was no difference in clinical failure in a small, retrospective cohort of critically ill patients receiving ertapenem or meropenem for ESBL-E bacteremia. Ertapenem may be appropriate in some critically ill and hypoalbuminemic patients, though additional data are needed.

Developmental Pharmacokinetics of Antibiotics Used in Neonatal ICU: Focus on Preterm Infants

Neonatal Infections are among the most common reasons for admission to the intensive care unit. Neonatal sepsis (NS) significantly contributes to mortality rates. Empiric antibiotic therapy of NS recommended by current international guidelines includes benzylpenicillin, ampicillin/amoxicillin, and aminoglycosides (gentamicin). The rise of antibacterial resistance precipitates the growth of the use of antibiotics of the Watch (second, third, and fourth generations of cephalosporines, carbapenems, macrolides, glycopeptides, rifamycins, fluoroquinolones) and Reserve groups (fifth generation of cephalosporines, oxazolidinones, lipoglycopeptides, fosfomycin), which are associated with a less clinical experience and higher risks of toxic reactions. A proper dosing regimen is essential for effective and safe antibiotic therapy, but its choice in neonates is complicated with high variability in the maturation of organ systems affecting drug absorption, distribution, metabolism, and excretion. Changes in antibiotic pharmacokinetic parameters result in altered efficacy and safety. Population pharmacokinetics can help to prognosis outcomes of antibiotic therapy, but it should be considered that the neonatal population is heterogeneous, and this heterogeneity is mainly determined by gestational and postnatal age. Preterm neonates are common in clinical practice, and due to the different physiology compared to the full terms, constitute a specific neonatal subpopulation. The objective of this review is to summarize the evidence about the developmental changes (specific for preterm and full-term infants, separately) of pharmacokinetic parameters of antibiotics used in neonatal intensive care units.

Hypoalbuminemia and Pharmacokinetics: When the Misunderstanding of a Fundamental Concept Leads to Repeated Errors over Decades

Surprisingly, misinterpretation of the influence of hypoalbuminemia on pharmacokinetics and the clinical effects of drugs seems to be a current problem, even though hypoalbuminemia has no impact on the pharmacologically active exposure. Exceptions to this fact are highly protein-bound anaesthetics with high elimination capacity (i.e., <5 drugs on the market). To assess the frequency of misinterpretation of the influence of hypoalbuminemia on pharmacokinetics and the clinical effects of drugs between 1975 and 2021, a PubMed literature review was conducted. Each paragraph on albumin binding was classified as correct, ambiguous or incorrect, creating two acceptable categories: (1) content without any errors, and (2) content containing some incorrect and/or ambiguous statements. The analyses of these articles showed that fewer than 11% of articles contained no interpretation errors. In order to contain this misinterpretation, several measures are proposed: (1) Make the message accessible to a wide audience by offering a simplified and didactic video representation of the lack of impact of albumin binding to drugs. (2) Precise terminology (unbound/free form/concentration) should be used for highly bound drugs. (3) Unbound/free forms should be systematically quantified for highly plasma protein bound drugs for clinical trials as well as for therapeutic drug monitoring.

Imipenem/cilastatin/relebactam pharmacokinetics in critically ill patients with augmented renal clearance

BACKGROUND

Imipenem and relebactam are predominantly excreted via glomerular filtration. Augmented renal clearance (ARC) is a common syndrome in critically-ill patients with sepsis, and sub-therapeutic antibiotic concentrations are of concern. Herein, we describe the pharmacokinetics of imipenem/relebactam in critically-ill patients with ARC.

METHODS

Infected patients in the ICU with ARC (CLCR ≥ 130 mL/min) received a single dose of imipenem/cilastatin/relebactam 1.25 g as a 30 min infusion. Blood samples were collected over 6 h for concentration determination. Protein binding was assessed by ultrafiltration. An 8 h urine creatinine collection confirmed ARC. Population pharmacokinetic models with and without covariates were fit using the non-parametric adaptive grid algorithm in Pmetrics. A 5000 patient Monte Carlo simulation assessed joint PTA using relebactam fAUC/MIC ≥8 and imipenem ≥40% fT>MIC.

RESULTS

Eight patients with ARC completed the study. A base population pharmacokinetic model with two-compartments fitted the data best. The mean ± SD parameters were: CL, 17.31 ± 5.76 L/h; Vc, 16.15 ± 7.75 L; k12, 1.62 ± 0.99 h-1; and k21, 3.53 ± 3.31 h-1 for imipenem, and 11.51 ± 4.79 L/h, 16.54 ± 7.43 L, 1.59 ± 1.12 h-1, and 2.83 ± 2.91 h-1 for relebactam. Imipenem/cilastatin/relebactam 1.25 g as a 30 min infusion every 6 h achieved 100% and 93% PTA at MICs of 1 and 2 mg/L, respectively.

CONCLUSIONS

Despite enhanced clearance of both imipenem and relebactam, the currently approved dosing regimen for normal renal function was predicted to achieve optimal exposure in critically-ill patients with ARC sufficient to treat most susceptible pathogens.

Thirty-Day Mortality Rates in Patients with Extended-Spectrum β-Lactamase-Producing Enterobacterales Bacteremia Receiving Ertapenem versus Other Carbapenems

Ertapenem is one of the carbapenems recommended for treating extended-spectrum β-lactamase (ESBL)-producing Enterobacterales. However, efficacy data are limited. We compared 30-day mortality rates for patients receiving ertapenem and other carbapenems for treatment of ESBL-producing Enterobacterales bacteremia. A multicenter, retrospective study was performed from January 2013 to December 2020 at three hospitals. Patients who received only members of one group of carbapenems (group 1 or group 2) throughout their treatment for ESBL-producing Escherichia coli or Klebsiella pneumoniae bacteremia were enrolled. To compare 30-day all-cause mortality rates in the two groups, propensity score matching was used to control for selection bias. Subgroup analyses were performed for several subgroups. Secondary outcomes included Clostridioides difficile infection (CDI) and the emergence of multidrug-resistant Gram-negative bacteria within 90 days after initiation of carbapenem treatment. One-to-one propensity score matching yielded 162 pairs of patients from the total of 603 patients included. There was no difference in 30-day mortality rates between ertapenem and the other carbapenems in adjusted analyses (hazard ratio, 0.60 [95% confidence interval [CI], 0.29 to 1.22]) of the propensity score-matched cohorts. A similar result was obtained in a subgroup analysis of patients who suffered severe sepsis or septic shock and those who did not (P = 0.54 for interaction). Emergence of CDI (odds ratio [OR], 0.99 [95% CI, 0.44 to 2.20]) and carbapenem-resistant Enterobacterales (OR, 1.31 [95% CI, 0.51 to 3.53]) did not differ between the two groups. Our study suggests that the efficacy of ertapenem may be comparable to that of the other carbapenems in treatment of ESBL-producing E. coli and K. pneumoniae bacteremia.

Ertapenem Concentrations in Obese Patients Undergoing Surgery

Background: Antimicrobial prophylaxis is a cornerstone to preventing surgical site infections (SSIs). Ertapenem, a carbapenem antibiotic, is commonly used for surgical prophylaxis for many different procedures, including patients undergoing colorectal and other gastrointestinal surgeries. Obesity complicates surgical intervention and increases the risk for SSIs. This study aims to describe the pharmacokinetics of ertapenem for surgical prophylaxis using a population pharmacokinetic model. Patients and Methods: Ten patients were recruited and given a single dose of ertapenem 1 g intravenous over 30 minutes. Plasma samples were obtained at multiple time points over 24 hours and assayed via validated high-performance liquid chromatography (HPLC). Pharmacokinetic analyses were conducted using a population pharmacokinetic analysis to generate pharmacokinetic parameters used in the subsequent 5,000 patient Monte Carlo simulation. The probability of target attainment (PTA) for free drug concentrations remaining above the minimum inhibitory concentration (MIC) for ≥40% was used. Results: The mean maximum plasma concentration and area under the concentration time curve (AUC_0-∞) was 40.7 ± 16.5 and 148.8 ± 28.0, respectively, with a half-life of the terminal portion to be 4.3 ± 0.8 hours. Monte Carlo simulations observed PTAs above 90% for MICs ≤0.25 and ≤0.125 mcg/mL in surgeries up to three and four hours, respectively. Sufficiently high PTAs were not attainable for MICs of ≥0.5 mcg/mL. Conclusions: Ertapenem given as 1 g single dose may be an appropriate candidate for surgical prophylaxis in obese patients undergoing surgeries of four hours or less.

Clinical Outcomes with Ertapenem for Pneumonia in Obese versus Nonobese Patients

The objective of this study was to compare the rate of pneumonia resolution in obese (body mass index [BMI], ≥30 kg/m2) and nonobese (BMI, <30 kg/m2) patients treated with 1 gram ertapenem daily. In this retrospective cohort study, we evaluated patients treated at The Ohio State University Wexner Medical Center between 1 January 2015 and 31 August 2020. Patients were included if they were between 18 and 89 years old and received ertapenem for at least 48 hours for pneumonia treatment. Patients were excluded if they were pregnant, were incarcerated, had renal impairment, received antibiotics with Gram-negative activity for a significant period prior to or in addition to ertapenem, and had other concomitant deep-seated infections. The primary outcome of clinical resolution was defined as meeting any of the following three criteria in order of evaluations: discontinuation of antibiotics by day 8 of therapy, afebrile while on ertapenem in addition to a decrease in white blood cell count, or improvement on chest radiograph at day 7 of therapy. A multivariable logistic regression analysis was performed to examine the association between obesity and clinical resolution, while adjusting for proven confounders. There were 76 nonobese and 65 obese patients included. The median patient BMI was 23.7 kg/m2 (21.0 to 26.9) and 35.0 kg/m2 (32.8 to 39.8) for the nonobese and obese cohorts, respectively. Clinical resolution was achieved in 78% (59/76) of nonobese and 75% (49/65) of obese patients (P = 0.75) without an observed difference in the regression model. Outcomes were similar in obese and nonobese patients treated with 1 gram of ertapenem daily for pneumonia.

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.

Bacterial infections in cirrhosis: Current treatment

Bacterial infections frequently cause decompensating events in cirrhotic patients and are also the most common factor identified for the development of acute-on-chronic liver failure (ACLF). The increase in the prevalence of infections caused by multidrug-resistant (MDR) microorganisms has resulted in the reduced effectiveness of empiric antimicrobial treatment. We conducted a PubMed search from the last 20 years using the Keywords cirrhosis; multidrug-resistant; infections; diagnosis; treatment; prophylaxis; monitoring; sepsis; nutrition and antibiotic resistant. We made a review about bacterial infections among cirrhotic patients; we mainly focus on the description of diagnostic tools; biomarkers; clinical scores for diagnosis and prognosis also; we made an analysis concerning the monitoring of cirrhotic patients with sepsis and finally made some recommendations about the treatment; prophylaxis and prevention.

Hypothesis of using albumin to improve drug efficacy in cancers accompanied by hypoalbuminemia

A common problem in many cancers is the resistance of some patients to common drugs or relapse. Hypoalbuminemia has been reported in some of resistant cancer patients.This article evaluates the usefulness of albumin in the treatment of drug-resistant cancers with hypoalbuminemia based on available evidences.Rapid metabolism and drug excretion from the body is one of the causes of drug resistance. Albumin is the major plasma protein to which almost all drugs are bound. There is some evidence that increasing drug binding to albumin has beneficial effects on drug efficacy in some cancers and cancer cells. On the other hand, some reports have shown that cancer cells can use albumin as the energy and amino acid source.We have hypothesized that in this particular group of cancers, adding albumin to a treatment regimen could have a beneficial effect on drug efficacy and dosage. In fact, excess albumin can prevent rapid metabolism of drug by increasing the fraction of albumin-bound drug, and can increase drug delivery to cancer cells due to the absorption of drug-albumin complex by cancer cells.

Hypoalbuminemia as Surrogate and Culprit of Infections

Hypoalbuminemia is associated with the acquisition and severity of infectious diseases, and intact innate and adaptive immune responses depend on albumin. Albumin oxidation and breakdown affect interactions with bioactive lipid mediators that play important roles in antimicrobial defense and repair. There is bio-mechanistic plausibility for a causal link between hypoalbuminemia and increased risks of primary and secondary infections. Serum albumin levels have prognostic value for complications in viral, bacterial and fungal infections, and for infectious complications of non-infective chronic conditions. Hypoalbuminemia predicts the development of healthcare-associated infections, particularly with Clostridium difficile. In coronavirus disease 2019, hypoalbuminemia correlates with viral load and degree of acute lung injury and organ dysfunction. Non-oncotic properties of albumin affect the pharmacokinetics and pharmacodynamics of antimicrobials. Low serum albumin is associated with inadequate antimicrobial treatment. Infusion of human albumin solution (HAS) supplements endogenous albumin in patients with cirrhosis of the liver and effectively supported antimicrobial therapy in randomized controlled trials (RCTs). Evidence of the beneficial effects of HAS on infections in hypoalbuminemic patients without cirrhosis is largely observational. Prospective RCTs are underway and, if hypotheses are confirmed, could lead to changes in clinical practice for the management of hypoalbuminemic patients with infections or at risk of infectious complications.

Measurement of Free Plasma Concentrations of Beta-Lactam Antibiotics: An Applicability Study in Intensive Care Unit Patients

BACKGROUND

The antibacterial effect of antibiotics is linked to the free drug concentration. This study investigated the applicability of an ultrafiltration method to determine free plasma concentrations of beta-lactam antibiotics in ICU patients.

METHODS

Eligible patients included adult ICU patients treated with ceftazidime (CAZ), meropenem (MEM), piperacillin (PIP)/tazobactam (TAZ), or flucloxacillin (FXN) by continuous infusion. Up to 2 arterial blood samples were drawn at steady state. Patients could be included more than once if they received another antibiotic. Free drug concentrations were determined by high-performance liquid chromatography with ultraviolet detection after ultrafiltration, using a method that maintained physiological conditions (pH 7.4/37°C). Total drug concentrations were determined to calculate the unbound fraction. In a post-hoc analysis, free concentrations were compared with the target value of 4× the epidemiological cut-off value (ECOFF) for Pseudomonas aeruginosa as a worst-case scenario for empirical therapy with CAZ, MEM or PIP/tazobactam and against methicillin-sensitive Staphylococcus aureus for targeted therapy with FXN.

RESULTS

Fifty different antibiotic treatment periods in 38 patients were evaluated. The concentrations of the antibiotics showed a wide range because of the fixed dosing regimen in a mixed population with variable kidney function. The mean unbound fractions (fu) of CAZ, MEM, and PIP were 102.5%, 98.4%, and 95.7%, with interpatient variability of <6%. The mean fu of FXN was 11.6%, with interpatient variability of 39%. It was observed that 2 of 12 free concentrations of CAZ, 1 of 40 concentrations of MEM, and 11 of 23 concentrations of PIP were below the applied target concentration of 4 × ECOFF for P. aeruginosa. All concentrations of FXN (9 samples from 6 patients) were >8 × ECOFF for methicillin-sensitive Staphylococcus aureus.

CONCLUSIONS

For therapeutic drug monitoring purposes, measuring total or free concentrations of CAZ, MEM, or PIP is seemingly adequate. For highly protein-bound beta-lactams such as FXN, free concentrations should be favored in ICU patients with prevalent hypoalbuminemia.

[Laparostoma-Avoidance and treatment of complications]

The open abdomen (OA) is an established concept for treating severe abdominal diseases. The most frequent reasons for placement of an open abdomen are abdominal sepsis (e.g. from intestinal perforation or anastomotic leakage), severe abdominal organ injury and abdominal compartment syndrome. The pathophysiology is much more complex than the surgeon's eye can see in an OA. The temporary closure of the abdominal wall ensures sufficient drainage of infected ascites, protection of the intestinal loops and conditioning of the abdominal wall in order to be able carry out definitive closure of the abdominal wall at the end of the surgical treatment. Negative peritoneal pressure therapy combined with fascia traction (with or without mesh) is well-established in the management of an open abdomen.

Optimizing therapy of bloodstream infection due to extended-spectrum β-lactamase-producing Enterobacteriaceae

PURPOSE OF REVIEW

Infections due to extended-spectrum β-lactamase-producing Enterobacteriaceae (ESBL-E) are increasing worldwide. Carbapenems are usually regarded as the antibiotics of choice for the treatment of serious ESBL infections. However, because of the alarming emergence or carbapenem resistance, interest in effective alternatives has emerged. The present review summarizes the findings published on the antibiotics currently available for treatment of patients with an ESBL-E bloodstream infection (BSI).

RECENT FINDINGS

Meropenem and imipenem are the drugs recommended for treatment of ESBL BSIs in critically ill patients, and in infections with high bacterial loads or elevated β-lactam minimum inhibitory concentrations. Ertapenem should be reserved for patients with less severe presentations, and should be used at high doses. In milder presentations or BSIs from low-risk sources, other carbapenem-sparing alternatives could be considered: cephamycins, fluoroquinolones, and particularly a β-lactam/β-lactam inhibitor combination (particularly piperacillin/tazobactam). Optimized dosing of piperacillin/tazobactam is recommended (high doses and extended infusion). There are few data on the use of the promising newly available drugs (e.g. ceftolozane/tazobactam, ceftazidime/avibactam, cefiderocol, and plazomicin), and it seems reasonable to reserve them as last-resort drugs.

SUMMARY

Carbapenems should be used in patients with serious infections; alternatives could be used individually, particularly for definitive treatment of patients with milder presentations.

Pharmacokinetic variability of beta-lactams in critically ill patients: A narrative review

The use of antibacterial drugs is very common in critically ill patients and beta-lactam agents are widely used in this context. Critically ill patients show several characteristics (e.g., sepsis, renal impairment or conversely augmented renal clearance, renal replacement therapy) that may alter beta-lactam pharmacokinetics (PK) in comparison with non-critically ill patients. This narrative literature review aims to identify recent studies quantifying the variability of beta-lactams volume of distribution and clearance and to determine its main determinants. Seventy studies published between 2000 and 2018 were retained. Data on volume of distribution and clearance variability were reported for 5 penicillins, 3 beta-lactamase inhibitors, 6 cephalosporins and 4 carbapenems. Data confirm specific changes in PK parameters and important variability of beta-lactam PK in critically ill patients. Renal function, body weight and use of renal replacement therapy are the principal factors influencing PK parameters described in this population. Few studies have directly compared beta-lactam PK in critically ill versus non-critically ill patients. Conclusions are also limited by small study size and sparse PK data in several studies. These results suggest approaches to assess this PK variability in clinical practice. Beta-lactam therapeutic drug monitoring seems to be the best way to deal with this issue.

Pharmacokinetic-Pharmacodynamic Evaluation of Ertapenem for Patients with Hospital-Acquired or Ventilator-Associated Bacterial Pneumonia

Ertapenem provides activity against many pathogens commonly associated with hospital-acquired and ventilator-associated bacterial pneumoniae (HABP and VABP, respectively), including methicillin-susceptible Staphylococcus aureus and numerous Gram-negative pathogens with one major gap in coverage, Pseudomonas aeruginosa Pharmacokinetic-pharmacodynamic (PK-PD) target attainment analyses were conducted to evaluate ertapenem against the most prevalent Enterobacteriaceae causing HABP/VABP. The objective of these analyses was to provide dose selection support for and demonstrate the appropriateness of ertapenem to empirically treat patients with HABP/VABP when administered with murepavadin, a novel targeted antimicrobial exhibiting a highly specific spectrum of activity against P. aeruginosa A previously developed population pharmacokinetic model, a total-drug epithelial lining fluid (ELF) to free-drug serum penetration ratio, contemporary in vitro surveillance data for ertapenem against Enterobacteriaceae, and percentage of the dosing interval for which drug concentrations exceed the MIC value (%T>MIC) targets associated with efficacy were used to conduct Monte Carlo simulations for five ertapenem regimens administered over short or prolonged durations of infusion. Overall total-drug ELF percent probabilities of PK-PD target attainment based on a %T>MIC target of 35% among simulated patients with HABP/VABP arising from Enterobacteriaceae based on pathogen prevalence data for nosocomial pneumonia ranged from 89.1 to 92.7% for all five ertapenem regimens evaluated. Total-drug ELF percent probabilities of PK-PD target attainment ranged from 99.8 to 100%, 97.9 to 100%, 10.6 to 74.1%, and 0 to 1.50% at MIC values of 0.06, 0.12, 1, and 4 μg/ml, respectively (MIC₉₀ values for Escherichia coli, Serratia marcescens, Enterobacter species, and Klebsiella pneumoniae, respectively). Results of these analyses provide support for the evaluation of ertapenem in combination with murepavadin for the treatment of patients with HABP/VABP.

Population pharmacokinetics and probability of target attainment of ertapenem administered by subcutaneous or intravenous route in patients with bone and joint infection

Background

Ertapenem is a therapeutic option in patients with Gram-negative bone and joint infection (BJI). The subcutaneous (sc) route of administration is convenient in the outpatient setting and has shown favourable pharmacokinetics (PK), but available data on ertapenem are limited.

Objectives

To perform population PK analysis and pharmacokinetic/pharmacodynamic (PK/PD) simulation of ertapenem administered by the intravenous (iv) or sc route to patients with BJI.

Patients and methods

This was a retrospective analysis of PK data collected in patients with BJI who received iv or sc ertapenem. Measured ertapenem concentrations were analysed with a non-parametric population approach. Then, simulations were performed based on the final model to investigate the influence of ertapenem route of administration, dosage and renal function on the probability of achieving a pharmacodynamic (PD) target, defined as the percentage of time for which free plasma concentrations of ertapenem remained above the MIC (fT>MIC) of 40%.

Results

Forty-six PK profiles (13 with iv and 33 with sc ertapenem) with a total of 133 concentrations from 31 subjects were available for the analysis. A two-compartment model with linear sc absorption and linear elimination best fitted the data. Creatinine clearance was found to significantly influence ertapenem plasma clearance. Simulations showed that twice daily dosing, sc administration and renal impairment were associated with an increase in fT>MIC and target attainment.

Conclusions

Our results indicate that 1 g of ertapenem administered twice daily, by the iv or sc route, may optimize ertapenem exposure and achievement of PK/PD targets in patients with BJI.

Population Pharmacokinetic Analyses for Ertapenem in Subjects with a Wide Range of Body Sizes

Despite a number of studies reporting that ertapenem pharmacokinetic parameters differ considerably in obese patients from those in healthy volunteers, functions describing the relationships between this agent's pharmacokinetics and indicators of body size have not been developed. The aim of this analysis was to develop an ertapenem population pharmacokinetic model using data from a previously described study in normal-weight, obese, and morbidly obese healthy volunteers. A single ertapenem 1-g dose administered intravenously was evaluated in 30 subjects within different body mass index (BMI) categories. The population pharmacokinetic model was developed using the first-order conditional estimation method with interaction (FOCE-I) algorithm within NONMEM. The ability of age, sex, renal function, and various body size measures (total body weight, height, body mass index, ideal body weight, fat-free mass, and body surface area [BSA]) to explain a portion of the interindividual variability on select pharmacokinetic parameters was explored using stepwise forward selection (α = 0.01) and backward elimination (α = 0.001). The data were best described using a linear three-compartment model with total body weight as a covariate on clearance (CL = 1.79 · [weight/95.90]^0.278) and BSA as a covariate on central volume (Vc = 4.76 · [BSA/2.06]^1.86). After accounting for fixed effects, the estimated interindividual variability was very low (<10% for all clearance and volume terms). Goodness-of-fit diagnostics indicated a precise and unbiased fit to the data. Using the developed population pharmacokinetic model and simulation, reliable estimates of ertapenem serum exposures, which can be utilized to evaluate various dosing regimens in subjects with a wide range of body sizes, are expected.

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.

New paradigm for rapid achievement of appropriate therapy in special populations: coupling antibiotic dose optimization rapid microbiological methods

INTRODUCTION

Some special patient populations (e.g. critically ill, burns, hematological malignancy, post-major surgery, post-major trauma) have characteristics that lead to higher rates of failure and mortality associated with infection. Choice of effective antibiotics and optimized doses are challenging in these patients that are commonly infected by multidrug-resistant pathogens. Areas covered: A review of the importance of diagnosis and the place of newer microbiological methods (e.g. whole-genome sequencing) to ensure rapid transition from empiric to directed antibiotic therapy is provided. The effects of pathophysiological changes on antibiotic pharmacokinetics are also provided. Expert opinion: Product information dosing regimens do not address the pharmacokinetic alterations that can occur in special patient populations and increase the likelihood of therapeutic failure and the emergence of bacterial resistance. Altered dosing approaches, supplemented with the use of dosing software and therapeutic drug monitoring, may be needed to ensure optimal antibiotic exposure and better therapeutic outcomes in these patients with severe infection. Dose optimization needs to be coupled with advanced microbiological techniques that enable rapid microbiological identification and characterization of resistance mechanism to ensure that maximally effective directed therapy can be chosen.

Pharmacokinetics of Antibiotics in Sub-Saharan African Patient Populations: A Systematic Review

BACKGROUND

In sub-Saharan Africa (SSA), severe febrile illness accounts for a large majority of medical admissions. SSA patients may also suffer from cachexia and organ dysfunction resulting from tuberculosis, hepatitis B, and hypertension. It is hard to tell how these conditions influence the pharmacokinetics (PK) of antibiotics in this population. The aim of this systematic review was to summarize antibiotic PK data of SSA adult patient populations to clarify whether inappropriate drug concentrations that may also lead to antimicrobial resistance are likely to occur.

METHODS

An electronic search was conducted in Ovid MEDLINE, Embase, and the African Index Medicus collecting studies from 1946 to May 2016. Reviewers independently selected studies reporting outcome data on volume of distribution (V), clearance, and half-life. Relevant information was abstracted and quality assessed.

RESULTS

Twelve studies were selected, addressing 6 antibiotic classes. There were 6 studies on fluoroquinolones and 1 on β-lactam antibiotics. Nine out of 12 originated from South Africa and 6 of those dealt with intensive care unit (ICU) populations. The quality of most studies was low. Studies on amikacin, teicoplanin, and ertapenem (n = 4) displayed a pattern of a large V with low drug concentrations. Fluoroquinolone PK changes were less prominent and more diverse whereas the probability of pharmacodynamic target attainment was low for the treatment of tuberculosis in South Africa. Interindividual variability of V was high for 10/12 studies.

CONCLUSIONS

Antibiotic PK data of SSA adult patient populations are scarce, but disease-induced inappropriate drug concentrations do occur. Data from non-ICU, severely ill patients, and β-lactam data are particularly lacking, whereas β-lactam antibiotics are commonly used, and typically vulnerable to disease-induced PK changes. Studies investigating the PK and pharmacodynamics of β-lactam antibiotics in severely ill, adult SSA patient populations are needed to improve local antibiotic dosing strategies.

Treatment of Infections Caused by Extended-Spectrum-Beta-Lactamase-, AmpC-, and Carbapenemase-Producing Enterobacteriaceae

Therapy of invasive infections due to multidrug-resistant Enterobacteriaceae (MDR-E) is challenging, and some of the few active drugs are not available in many countries. For extended-spectrum β-lactamase and AmpC producers, carbapenems are the drugs of choice, but alternatives are needed because the rate of carbapenem resistance is rising. Potential active drugs include classic and newer β-lactam-β-lactamase inhibitor combinations, cephamycins, temocillin, aminoglycosides, tigecycline, fosfomycin, and, rarely, fluoroquinolones or trimethoprim-sulfamethoxazole. These drugs might be considered in some specific situations. AmpC producers are resistant to cephamycins, but cefepime is an option. In the case of carbapenemase-producing Enterobacteriaceae (CPE), only some "second-line" drugs, such as polymyxins, tigecycline, aminoglycosides, and fosfomycin, may be active; double carbapenems can also be considered in specific situations. Combination therapy is associated with better outcomes for high-risk patients, such as those in septic shock or with pneumonia. Ceftazidime-avibactam was recently approved and is active against KPC and OXA-48 producers; the available experience is scarce but promising, although development of resistance is a concern. New drugs active against some CPE isolates are in different stages of development, including meropenem-vaborbactam, imipenem-relebactam, plazomicin, cefiderocol, eravacycline, and aztreonam-avibactam. Overall, therapy of MDR-E infection must be individualized according to the susceptibility profile, type, and severity of infection and the features of the patient.

The effects of major burn related pathophysiological changes on the pharmacokinetics and pharmacodynamics of drug use: An appraisal utilizing antibiotics

Patients suffering major burn injury represent a unique population of critically ill patients. Widespread skin and tissue damage causes release of systemic inflammatory mediators that promote endothelial leak, extravascular fluid shifts, and cardiovascular derangement. This phase is characterized by relative intra-vascular hypovolaemia and poor peripheral perfusion. Large volume intravenous fluid resuscitation is generally required. The patients' clinical course is then typically complicated by ongoing inflammation, protein catabolism, and marked haemodynamic perturbation. At all times, drug distribution, metabolism, and elimination are grossly distorted. For hydrophilic agents, changes in volume of distribution and clearance are marked, resulting in potentially sub-optimal drug exposure. In the case of antibiotics, this may then promote treatment failure, or the development of bacterial drug resistance. As such, empirical dose selection and pharmaceutical development must consider these features, with the application of strategies that attempt to counter the unique pharmacokinetic changes encountered in this setting.

Sterilizing Effect of Ertapenem-Clavulanate in a Hollow-Fiber Model of Tuberculosis and Implications on Clinical Dosing

Carbapenems are now being explored for treatment of multidrug-resistant tuberculosis (MDR-TB), especially in conjunction with clavulanate. Clinical use is constrained by the need for multiple parenteral doses per day and the lack of knowledge of the optimal dose for sterilizing effect. Our objective was to identify the ertapenem exposure associated with optimal sterilizing effect and then design a once-a-day dose for clinical use. We utilized the hollow-fiber system model of tuberculosis in a 28-day exposure-response study of 8 different ertapenem doses in combination with clavulanate. The systems were sampled at predetermined time points to verify the concentration-time profile and identify the total bacterial burden. Inhibitory sigmoid maximum-effect (E_max) modeling was used to identify the relationship between total bacterial burden and the drug exposure and to identify optimal exposures. Contrary to the literature, ertapenem-clavulanate combination demonstrated good microbial kill and sterilizing effect. In a dose fractionation hollow-fiber study, efficacy was linked to percentage of the 24-h dosing interval of ertapenem concentration persisting above MIC (%T_MIC). We performed 10,000 MDR-TB patient computer-aided clinical trial simulations, based on Monte Carlo methods, to identify the doses and schedule that would achieve or exceed a %T_MIC of ≥40%. We identified an intravenous dosage of 2 g once per day as achieving the target in 96% of patients. An ertapenem susceptibility breakpoint MIC of 2 mg/liter was identified for that dose. An ertapenem dosage of 2 g once daily is the most suitable to be tested in a phase II study of sterilizing effect in MDR-TB patients.

Therapeutic drug monitoring in the past 40 years of the Journal of Antimicrobial Chemotherapy

Since the Journal of Antimicrobial Chemotherapy was first published in 1975, papers addressing therapeutic drug monitoring (TDM) have been a regular feature. Initially they focused on laboratory aspects of drug concentration measurement then they changed more to the application of TDM in a clinical setting. Over its history, the Journal has provided its readership with the latest technological and scientific advances in TDM and has helped to drive changes in TDM that have directly impacted on patient care. These have varied from improvement in the quality of antimicrobial measurements through better identification of dosage regimens and TDM targets that help predict outcome and adverse events. Despite these advances in our understanding of the science and practice of TDM, there remain many areas of uncertainty. As we move into the next 40 years, it is clear that the Journal will continue to provide the readership with the latest science and opinion in this important area.

Pharmacokinetic Modeling and Limited Sampling Strategies Based on Healthy Volunteers for Monitoring of Ertapenem in Patients with Multidrug-Resistant Tuberculosis

Ertapenem is a broad-spectrum carbapenem antibiotic whose activity against Mycobacterium tuberculosis is being explored. Carbapenems have antibacterial activity when the plasma concentration exceeds the MIC at least 40% of the time (40% T_MIC). To assess the 40% T_MIC in multidrug-resistant tuberculosis (MDR-TB) patients, a limited sampling strategy was developed using a population pharmacokinetic model based on data for healthy volunteers. A two-compartment population pharmacokinetic model was developed with data for 42 healthy volunteers using an iterative two-stage Bayesian method. External validation was performed by Bayesian fitting of the model developed with data for volunteers to the data for individual MDR-TB patients (in which the fitted values of the area under the concentration-time curve from 0 to 24 h [AUC_{0-24, fit} values] were used) using the population model developed for volunteers as a prior. A Monte Carlo simulation (n = 1,000) was used to evaluate limited sampling strategies. Additionally, the 40% T_MIC with the free fraction (f 40% T_MIC) of ertapenem in MDR-TB patients was estimated with the population pharmacokinetic model. The population pharmacokinetic model that was developed was shown to overestimate the area under the concentration-time curve from 0 to 24 h (AUC_0-24) in MDR-TB patients by 6.8% (range, -17.2 to 30.7%). The best-performing limited sampling strategy, which had a time restriction of 0 to 6 h, was found to be sampling at 1 and 5 h (r² = 0.78, mean prediction error = -0.33%, root mean square error = 5.5%). Drug exposure was overestimated by a mean percentage of 4.2% (range, -15.2 to 23.6%). When a free fraction of 5% was considered and the MIC was set at 0.5 mg/liter, the minimum f 40% T_MIC would have been exceeded in 9 out of 12 patients. A population pharmacokinetic model and limited sampling strategy, developed using data from healthy volunteers, were shown to be adequate to predict ertapenem exposure in MDR-TB patients.

Dosing of Ertapenem in an Extreme Obesity: A Case Report of 250 kg Patient

Limited available data for dosing in obesity of the medicines used in this case are discussed, with the emphasis on ertapenem. The case illustrates the difficulties in dosing medicines to morbidly overweight patients. The number of such patients is increasing but data on adequate doses of medicines are scarce. We demonstrate that ertapenem 1,5 g i.v. once daily provided adequate drug exposure for susceptible bacteria in a 250 kg patient with normal renal function. The case suggests the usefulness of therapeutic drug monitoring of antibiotics, especially in critically ill patients.

Population Pharmacokinetics and Target Attainment of Ertapenem in Plasma and Tissue Assessed via Microdialysis in Morbidly Obese Patients after Laparoscopic Visceral Surgery

Ertapenem provides broad-spectrum activity against many pathogens, and its use is relevant for the prophylaxis and treatment of infections in morbidly obese patients undergoing surgery. However, its pharmacokinetics and tissue penetration in these patients are not well defined. We assessed the population pharmacokinetics and target attainment for ertapenem in the plasma, subcutaneous tissue, and peritoneal fluid of morbidly obese patients. Six female patients (body mass index, 43.7 to 55.9 kg/m²) received 1,000 mg ertapenem as 15-min infusions at 0 and 26 h. On day 2, the unbound ertapenem concentrations in plasma, subcutaneous tissue, and peritoneal fluid were measured by microdialysis; total plasma concentrations were additionally quantified. The probability of attaining a target of an unbound ertapenem concentration above the MIC for at least 40% of the dosing interval was predicted via Monte Carlo simulations. The population pharmacokinetic model contained two disposition compartments and simultaneously described all concentrations. For unbound ertapenem, total clearance was 12.3 liters/h (coefficient of variation, 21.6% for between-patient variability) and the volume of distribution at steady state was 57.8 liters in patients with a 53-kg fat-free mass. The area under the concentration-time curve (AUC) for ertapenem was 49% lower in subcutaneous tissue and 25% lower in peritoneal fluid than the unbound AUC in plasma. Tissue penetration was rapid (equilibration half-life, <15 min) and was variable in subcutaneous tissue. Short-term ertapenem infusions (1,000 mg every 24 h) achieved robust (>90%) target attainment probabilities for MICs of up to 1 mg/liter in plasma, 0.25 to 0.5 mg/liter in subcutaneous tissue, and 0.5 mg/liter in peritoneal fluid. Ertapenem presents an attractive choice for many pathogens relevant to morbidly obese patients undergoing surgery. (This study has been registered at ClinicalTrials.gov under identifier NCT01407965.).

Animal models in the pharmacokinetic/pharmacodynamic evaluation of antimicrobial agents

Animal infection models in the pharmacokinetic/pharmacodynamic (PK/PD) evaluation of antimicrobial therapy serve an important role in preclinical assessments of new antibiotics, dosing optimization for those that are clinically approved, and setting or confirming susceptibility breakpoints. The goal of animal model studies is to mimic the infectious diseases seen in humans to allow for robust PK/PD studies to find the optimal drug exposures that lead to therapeutic success. The PK/PD index and target drug exposures obtained in validated animal infection models are critical components in optimizing dosing regimen design in order to maximize efficacy while minimize the cost and duration of clinical trials. This review outlines the key components in animal infection models which have been used extensively in antibiotic discovery and development including PK/PD analyses.

The use and risks of antibiotics in critically ill patients

INTRODUCTION

The altered pathophysiology in critically ill patients presents a unique challenge in both the diagnosis of infection and the appropriate prescription of antibiotics. In this context, the importance of effective and timely treatment needs to be weighed against the individual and community harms associated with antibiotic collateral damage and antibiotic resistance.

AREAS COVERED

We evaluate the principles of antibiotic use in critically ill patients, including dose optimisation, use of combination antibiotic therapy, therapeutic drug monitoring, appropriate antibiotic therapy duration, de-escalation, and utilisation of sepsis biomarkers. We also describe the potential risks associated with antibiotic therapy including antibiotic resistance, delayed treatment, treatment failure, and collateral damage.

EXPERT OPINION

Prescribing teams must be aware of the impact of critical illness on their patients and tailor antibiotic therapy appropriately to prevent the significant harms associated with suboptimal antibiotic administration.

Ertapenem for the treatment of bloodstream infections due to ESBL-producing Enterobacteriaceae: a multinational pre-registered cohort study

OBJECTIVES

Data about the efficacy of ertapenem for the treatment of bloodstream infections (BSI) due to ESBL-producing Enterobacteriaceae (ESBL-E) are limited. We compared the clinical efficacy of ertapenem and other carbapenems in monomicrobial BSI due to ESBL-E.

METHODS

A multinational retrospective cohort study (INCREMENT project) was performed (ClinicalTrials.gov identifier: NCT01764490). Patients given monotherapy with ertapenem or other carbapenems were compared. Empirical and targeted therapies were analysed. Propensity scores were used to control for confounding; sensitivity analyses were performed in subgroups. The outcome variables were cure/improvement rate at day 14 and all-cause 30 day mortality.

RESULTS

The empirical therapy cohort (ETC) and the targeted therapy cohort (TTC) included 195 and 509 patients, respectively. Cure/improvement rates were 90.6% with ertapenem and 75.5% with other carbapenems (P = 0.06) in the ETC and 89.8% and 82.6% (P = 0.02) in the TTC, respectively; 30 day mortality rates were 3.1% and 23.3% (P = 0.01) in the ETC and 9.3% and 17.1% (P = 0.01) in the TTC, respectively. Adjusted ORs (95% CI) for cure/improvement with empirical and targeted ertapenem were 1.87 (0.24-20.08; P = 0.58) and 1.04 (0.44-2.50; P = 0.92), respectively. For the propensity-matched cohorts it was 1.18 (0.43-3.29; P = 0.74). Regarding 30 day mortality, the adjusted HR (95% CI) for targeted ertapenem was 0.93 (0.43-2.03; P = 0.86) and for the propensity-matched cohorts it was 1.05 (0.46-2.44; P = 0.90). Sensitivity analyses were consistent except for patients with severe sepsis/septic shock, which showed a non-significant trend favouring other carbapenems.

CONCLUSIONS

Ertapenem appears as effective as other carbapenems for empirical and targeted therapy of BSI due to ESBL-E, but further studies are needed for patients with severe sepsis/septic shock.

Pharmacokinetic considerations and dosing strategies of antibiotics in the critically ill patient

The treatment of sepsis remains a significant challenge and is the cause of high mortality and morbidity. The pathophysiological alterations that are associated with sepsis can complicate drug dosing. Critical care patients often have capillary leak, increased cardiac output and altered protein levels which can have profound effects on the volume of distribution (Vd) and clearance (Cl) of antibacterial agents, both of which may affect the pharmacokinetics (PK) / pharmacodynamics (PD) of the drug. Along with antibacterial factors such as the hydrophilicity and its kill characteristics and the susceptibility and site of action of the microorganism, different dosing and administration strategies may be needed for the different drug classes. In conclusion, developing dosing and administration regimes of antibacterials that adhere to PK/PD principles increase antibacterial exposure. Tailoring therapy to the individual patient combined with TDM may contribute to improved clinical efficacy and contain the spread of resistance.

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

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

Antibiotic Dosing in Patients With Acute Kidney Injury: "Enough But Not Too Much"

Increasing evidence suggests that antibiotic dosing in critically ill patients with acute kidney injury (AKI) often does not achieve pharmacodynamic goals, and the continued high mortality rate due to infectious causes appears to confirm these findings. Although there are compelling reasons why clinicians should use more aggressive antibiotic dosing, particularly in patients receiving aggressive renal replacement therapies, concerns for toxicity associated with higher doses are real. The presence of multisystem organ failure and polypharmacy predispose these patients to drug toxicity. This article examines the pharmacokinetic and pharmacodynamic consequences of critical illness, AKI, and renal replacement therapy and describes potential solutions to help clinicians give "enough but not too much" in these very complicated patients.

Association between hypoalbuminemia and mortality among subjects treated with ertapenem versus other carbapenems: prospective cohort study

The aim of this study was to determine whether ertapenem, being highly protein bound, is less effective than other carbapenems in the presence of hypoalbuminemia. In a prospective cohort study, we included adults with clinically and microbiologically documented infections caused by carbapenem-susceptible Enterobacteriaceae who were hospitalized in a tertiary medical center from March 2010 to September 2012. We tested whether hypoalbuminemia (serum albumin <2.5 g/dL) had a larger effect on 30-day mortality in subjects treated with ertapenem compared to those treated with meropenem or imipenem (I/M). Logistic regression analysis was used to identify independent risk factors for death including the carbapenem drug and the interaction between albumin and the carbapenem. Of 279 individual subjects included, 173 were treated with ertapenem and 106 with I/M. The odds ratio (OR) for 30-day mortality with hypoalbuminemia was 4.6 (95% confidence interval (CI) 2.1-10.1) among subjects with ertapenem versus 1.2 (95% CI 0.5-2.70) with I/M (p = 0.02 for difference between groups). In the regression model, the interaction between carbapenem type and albumin levels was significant (p = 0.03); for ertapenem lower albumin levels were associated with increased 30-day mortality (OR 2.45, 95% CI 1.19-5.05), while for I/M the change was not significant (OR 0.67, 95% CI 0.31-1.41). The model suggests that the risk of death for ertapenem-treated subjects quintupled when albumin was 2 g/dL compared to 4 g/dL. Hypoalbuminemia was associated with mortality significantly more among subjects treated with ertapenem compared to subjects treated with I/M. The effectiveness of current dosing schemes of ertapenem in subjects with significant hypoalbuminemia should be revisited.

High-dose continuous oxacillin infusion results in achievement of pharmacokinetics targets in critically ill patients with deep sternal wound infections following cardiac surgery

Knowledge regarding antimicrobial therapy strategies in deep sternal wound infections (DSWI) following cardiac surgery is limited. Therefore, we aimed to determine the steady-state plasma and mediastinal concentrations of oxacillin administered by continuous infusion in critically ill patients with DSWI and to compare these concentrations with the susceptibility of staphylococci recovered. A continuous infusion of oxacillin (150 to 200 mg/kg of body weight/24 h) was administered after a loading dose (50 mg/kg). Plasma and mediastinal concentrations of total and unbound oxacillin were determined 4 h after the loading dose (H4) and then at day 1 (H24) and day 2 (H48). Twelve patients were included. Nine patients exhibited bacteremia, 5 were in septic shock, 8 were positive for Staphylococcus aureus, and 4 were positive for coagulase-negative staphylococci. The median MIC (first to third interquartile range) was 0.25 (0.24 to 0.41) mg/liter. Median plasma concentrations of total and unbound oxacillin at H4, H24, and H48 were, respectively, 64.4 (41.4 to 78.5) and 20.4 (12.4 to 30.4) mg/liter, 56.9 (31.4 to 80.6) and 21.7 (6.5 to 27.3) mg/liter, and 57.5 (32.2 to 85.1) and 20 (14.3 to 35.7) mg/liter. The median mediastinal concentrations of total and unbound oxacillin at H4, H24, and H48 were, respectively, 2.3 (0.7 to 25.9) and 0.9 (<0.5 to 15) mg/liter, 29.1 (19.7 to 38.2) and 12.6 (5.9 to 19.8) mg/liter, and 31.6 (14.9 to 42.9) and 17.1 (6.7 to 26.7) mg/liter. High-dose oxacillin delivered by continuous infusion is a valuable strategy to achieve our pharmacokinetic target (4× MIC) at the site of action at H24. But concerns remain in cases of higher MICs, emphasizing the need for clinicians to obtain the MICs for the bacteria and to monitor oxacillin concentrations, especially the unbound forms, at the target site.

Beta-lactam dosing in critically ill patients with septic shock and continuous renal replacement therapy

Although early and appropriate antibiotic therapy remains the most important intervention for successful treatment of septic shock, data guiding optimization of beta-lactam prescription in critically ill patients prescribed with continuous renal replacement therapy (CRRT) are still limited. Being small hydrophilic molecules, beta-lactams are likely to be cleared by CRRT to a significant extent. As a result, additional variability may be introduced to the per se variable antibiotic concentrations in critically ill patients. This article aims to describe the current clinical scenario for beta-lactam dosing in critically ill patients with septic shock and CRRT, to highlight the sources of variability among the different studies that reduce extrapolation to clinical practice, and to identify the opportunities for future research and improvement in this field. Three frequently prescribed beta-lactams (meropenem, piperacillin and ceftriaxone) were chosen for review. Our findings showed that present dosing recommendations are based on studies with drawbacks limiting their applicability in the clinical setting. In general, current antibiotic dosing regimens for CRRT follow a one-size-fits-all fashion despite emerging clinical data suggesting that drug clearance is partially dependent on CRRT modality and intensity. Moreover, some studies pool data from heterogeneous populations with CRRT that may exhibit different pharmacokinetics (for example, admission diagnoses different to septic shock, such as trauma), which also limit their extrapolation to critically ill patients with septic shock. Finally, there is still no consensus regarding the %T_>MIC (percentage of dosing interval when concentration of the antibiotic is above the minimum inhibitory concentration of the pathogen) value that should be chosen as the pharmacodynamic target for antibiotic therapy in patients with septic shock and CRRT. For empirically optimized dosing, during the first day a loading dose is required to compensate the increased volume of distribution, regardless of impaired organ function. An additional loading dose may be required when CRRT is initiated due to steady-state equilibrium breakage driven by clearance variation. From day 2, dosing must be adjusted to CRRT settings and residual renal function. Therapeutic drug monitoring of beta-lactams may be regarded as a useful tool to daily individualize dosing and to ensure optimal antibiotic exposure.

Pulmonary penetration of piperacillin and tazobactam in critically ill patients

Pulmonary infections in critically ill patients are common and are associated with high morbidity and mortality. Piperacillin–tazobactam is a frequently used therapy in critically ill patients with pulmonary infection. Antibiotic concentrations in the lung reflect target‐site antibiotic concentrations in patients with pneumonia. The aim of this study was to assess the plasma and intrapulmonary pharmacokinetics (PK) of piperacillin–tazobactam in critically ill patients administered standard piperacillin–tazobactam regimens. A population PK model was developed to describe plasma and intrapulmonary piperacillin and tazobactam concentrations. The probability of piperacillin exposures reaching pharmacodynamic end points and the impact of pulmonary permeability on piperacillin and tazobactam pulmonary penetration was explored. The median piperacillin and tazobactam pulmonary penetration ratios were 49.3 and 121.2%, respectively. Pulmonary piperacillin and tazobactam concentrations were unpredictable and negatively correlated with pulmonary permeability. Current piperacillin–tazobactam regimens may be insufficient to treat pneumonia caused by piperacillin–tazobactam–susceptible organisms in some critically ill patients.

Clinical Pharmacology & Therapeutics (2014); 96 4, 438–448. doi:10.1038/clpt.2014.131

How severe is antibiotic pharmacokinetic variability in critically ill patients and what can be done about it?

The pharmacokinetics (PK) of antimicrobial agents administered to critically ill patients exhibit marked variability. This variability results from pathophysiological changes that occur in critically ill patients. Changes in volume of distribution, clearance, and tissue penetration all affect the drug concentrations at the site of infection. PK-pharmacodynamic indices (fCmax:MIC; AUC0-24:MIC; fT>MIC; fCmin:MIC) for both antimicrobial effect and suppression of emergence of resistance are described for many antimicrobial drugs. Changing the regimen by which antimicrobial drugs are delivered can help overcome the PK variability and optimise target attainment. This will deliver optimised antimicrobial chemotherapy to individual critically ill patients. Delivery of β-lactams antimicrobial agents by infusions, rather than bolus dosing, is effective at increasing the duration of the dosing interval that the drug concentration is above the MIC. Therapeutic drug monitoring, utilising population PK mathematical models with Bayesian estimation, can also be used to optimise regimens following measurement of plasma drug concentrations. Clinical trials are required to establish if patient outcomes can be improved by implementing these techniques.

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.

Pharmacokinetics of ertapenem in critically ill patients receiving continuous venovenous hemodialysis or hemodiafiltration

This study characterizes the pharmacokinetics of ertapenem, a carbapenem antibiotic, in critically ill adult subjects receiving continuous renal replacement therapy (CRRT). Eight critically ill patients with suspected/known Gram-negative infections receiving continuous venovenous hemodialysis (CVVHD) or continuous venovenous hemodiafiltration (CVVHDF) and ertapenem were enrolled. One gram of ertapenem was infused over 30 min. Predialyzer blood samples were drawn with the first dose of ertapenem from the hemodialysis tubing at time zero, 30 min, and 1, 2, 4, 8, 12, 18, and 24 h after the start of the ertapenem infusion. Effluent was collected at the same time points. Ertapenem total serum, unbound serum, and effluent concentrations from all eight subjects were used simultaneously to perform a population compartmental pharmacokinetic modeling procedure using NONMEM. Monte Carlo simulations were performed to evaluate the ability of several ertapenem dosing regimens (500 mg once daily, 750 mg once daily, 500 mg twice daily, and 1,000 mg once daily) to obtain effective unbound serum concentrations above 0.5, 1, and 2 μg/ml. For our simulated patients, all regimens produced unbound ertapenem concentrations above 2 μg/ml for 40% of the dosing interval for at least 96% of simulated patients. (This study has been registered at ClinicalTrials.gov under registration no. NCT00877370.).

Pharmacokinetics and pharmacodynamics of antimicrobial drugs in intensive care unit patients

Inappropriate use of antimicrobial drugs is responsible for therapeutic failures, increased mortality rates, and the emergence of resistance. Antimicrobial activity is determined by intrinsic pharmacokinetics/pharmacodynamics concepts. In critically ill patients, an inappropriate dosing regimen can be caused by the inability of an antimicrobial drug to reach adequate concentrations at the infection site owing to alterations in the drug's pharmacokinetics caused by pathophysiological changes. Understanding these concepts and changes in PK-PD parameters that occur in intensive care unit patients is crucial for the optimization of antimicrobial therapy in these patients.

Effect of experimentally induced hypovolemia on ertapenem tissue distribution using microdialysis in rats

Hypovolemia is a common event in critical care patients that may affect drug distribution and elimination. In order to better understand this issue the effect of hypovolemia on the plasma protein binding and tissue distribution of ertapenem was investigated in rats using microdialysis. Microdialysis probes were inserted into the jugular vein and hind leg muscle. Ertapenem recoveries in muscle and blood were determined in each rat by retrodialysis by drug before drug administration. Hypovolemia was induced in 6 rats by removing 40% of the initial blood volume over 30 min. Ertapenem was infused intravenously at a dose of 40 mg kg(-1) over 30 min, and microdialysis samples were collected for 310 min. The unbound concentration profiles in muscle and blood were virtually superimposed in both groups except at early time points. The ratios of the area under the concentration-time curve (AUC) for tissue to the AUC for blood were 0.7±0.2 and 0.8±0.2 for control and hypovolemic rats, respectively. Hypovolemia induced a 40% decrease in the clearance of ertapenem, with no statistically significant alteration of its volume of distribution. This study showed that ertapenem elimination was altered in hypovolemic rats, probably due to decreased renal blood flow, but its distribution characteristics were not. Unbound concentrations of ertapenem in blood and muscle were always virtually identical.

Efficacy of single-dose antibiotic against early-onset pneumonia in comatose patients who are ventilated

BACKGROUND

Comatose patients present a high risk of early-onset ventilator-associated pneumonia (EO-VAP) for which antibiotic prophylaxis has been proposed. Comatose patients were studied to evaluate the efficacy of a single-dose of antibiotic prophylaxis at intubation against EO-VAP.

METHODS

A prospective cohort of comatose patients (Glasgow Coma Score ≤ 8) who were admitted in 2009-2010 and administered a single-dose of antibiotic within 4 h of intubation was compared with comatose patients (admitted ≥ 4 h after intubation in 2009-2010 or admitted in 2007-2008) who did not receive antibiotic prophylaxis. We analyzed the incidence of EO-VAP, late-onset VAP, and ventilator-associated tracheobronchitis in both groups. Propensity scores for receiving antibiotic prophylaxis were derived on the basis of patients' characteristics (eg, age and severity) to assess its impact on EO-VAP development.

RESULTS

We included 129 patients (71 in the prophylaxis group and 58 in the control group). The global incidence of VAP and incidence of EO-VAP were lower in the prophylaxis group: 10.8 vs 28.4 episodes/1,000 days on mechanical ventilation (P = .015) and 4.4 vs 23.1 episodes/1,000 days on mechanical ventilation (P = .02), respectively. The incidence of late-onset VAP did not differ. The prophylaxis group tended toward lower incidence of ventilator-associated tracheobronchitis (15.5% vs 25.9%, P = .14). No differences in mortality were found between groups. The propensity-score regression analysis confirmed that a single dose of antibiotic prophylaxis was independently associated with lower incidence of EO-VAP (OR, 0.11; 95% CI, 0.02-0.58; P = .009).

CONCLUSIONS

A single dose of antibiotic prophylaxis at intubation might lower the incidence of EO-VAP. However, a randomized clinical trial should be conducted to confirm our findings.