Determining β-lactam exposure threshold to suppress resistance development in Gram-negative bacteria

Beta-Lactam Antibiotic Concentrations and the Acquisition of Multi-Drug Resistant Bacteria in Critically Ill Patients

Antimicrobial resistance (AMR) is a worldwide healthcare emergency. Whether insufficient beta-lactam antibiotic concentrations can be associated with AMR emergence remains controversial. This is a retrospective single-center cohort study including patients admitted to the intensive care unit of a tertiary university hospital from 2009 to 2014, who required a broad-spectrum beta-lactam antibiotic and had at least one therapeutic drug monitoring (TDM). Patients were categorized as having inadequate drug levels if the trough concentration (Cmin) fell below the clinical breakpoint for Pseudomonas aeruginosa. AMR was defined according to breakpoints recommended by the European Committee on Antimicrobial Susceptibility Testing (EUCAST) using the disk diffusion method. A total of 444 patients (male sex, n = 313, 71%; female sex, n = 131, 29%; mean age 58 ± 15 years) were enrolled in the study. Patients received piperacillin/tazobactam (n = 168), ceftazidime/cefepime (n = 58) or meropenem (n = 218); among them, 65 (15%) had insufficient drug levels. Nine of these 65 (13.8%) patients with insufficient antibiotic levels acquired at least one pathogen with AMR within 15 days of TDM, when compared to 84/379 (22%) in the other group (OR 0.56 [95%CI 0.27-1.19]; p = 0.13). In a multivariable competing-risk analysis including male gender, APACHE score on admission, previous colonization by other MDR bacteria, urinary catheter, central venous catheter, mechanical ventilation, previous hospitalization and previous surgery, insufficient antibiotic levels were not associated with AMR acquisition (sHR 0.84 [95% CI 0.42-1.68]). Similar results were found when a higher threshold was used to define insufficient drug levels (Cmin < 4 times the clinical breakpoint). In conclusion, insufficient beta-lactam levels were not independently associated with AMR acquisition. Future prospective studies are needed to evaluate better the relationship between low drug levels and antibiotic resistance acquisition.

Urinary Biomarkers and Attainment of Cefepime Therapeutic Targets in Critically Ill Children

BACKGROUND

Critically ill children are at risk for subtherapeutic antibiotic concentrations. The frequency of target attainment and risk factors for subtherapeutic concentrations of cefepime in children have not been extensively studied.

METHODS

We performed an observational study in critically ill children receiving a new prescription of standard dosing of cefepime for suspected sepsis (≥2 systemic inflammatory response syndrome criteria within 48 hours of cefepime start). Three plasma cefepime concentrations were measured at steady state and, a urine sample was collected prior to pharmacokinetics (PK) sampling for measurement of urinary biomarkers. Bayesian analysis determined cefepime PK for each individual, and simulations were used to estimate time above minimum inhibitory concentration (fT > MIC) for 8 µg/mL (breakpoint for Pseudomonas). Clinical factors and urinary biomarkers were compared between patients who did and did not achieve 100% fT > MIC. Correlations between covariates and cefepime PK parameters, as well as optimal cut points to identify <100% fT > MIC, were evaluated.

RESULTS

Twenty-one subjects were enrolled and PK sampling occurred after a median of 5 doses (range, 3-9); 43% of children achieved 100% fT > MIC for an MIC of 8 µg/mL. Younger age and lower urinary biomarkers (neutrophil gelatinase-associated lipocalin and kidney injury molecule-1) were significantly associated with failure to attain 100% fT > 8 µg/mL. Urinary neutrophil gelatinase-associated lipocalin (<122.1-ng/mg creatinine) best identified individuals who failed to attain this putative target (positive predictive value, 91.7%).

CONCLUSIONS

A large proportion of critically ill children failed to attain target concentrations for empiric treatment of Pseudomonas aeruginosa with cefepime. Urinary biomarkers may be a noninvasive means to identify those at higher risk for increased cefepime clearance and subtherapeutic concentrations.

Difficult-to-Treat Pseudomonas aeruginosa Infections in Critically Ill Patients: A Comprehensive Review and Treatment Proposal

The management of infections caused by difficult-to-treat Pseudomonas aeruginosa in critically ill patients poses a significant challenge. Optimal antibiotic therapy is crucial for patient prognosis, yet the numerous resistance mechanisms of P. aeruginosa, which may even combine, complicate the selection of an appropriate antibiotic. In this review, we examine the epidemiology, resistance mechanisms, risk factors, and available and future therapeutic options, as well as strategies for treatment optimization. Finally, we propose a treatment algorithm to facilitate decision making based on the resistance patterns specific to each Intensive Care Unit.

Translating PK-PD principles into improved methodology for clinical trials which compare intermittent with prolonged infusion of beta-lactam antibiotics

Based on the fact that beta-lactam antibiotics demonstrate time-dependent killing, different dosing strategies have been implemented to increase the time that free (f) (unbound) antibiotic concentrations remain above the Minimal Inhibitory Concentration (MIC), including prolonged and continuous infusion. Multiple studies have been performed that compared continuous with traditional intermittent infusion to improve outcomes in patients with severe sepsis and/or septic shock. These studies have yielded inconsistent results for patients as measured by clinical response to treatment and mortality due to heterogeneity of included patients, pathogens, dosing strategies and the absence of Therapeutic Drug Monitoring (TDM). The MERCY and BLING III studies failed to show a difference in mortality between patients randomized to receive continuous and intermittent infusion of beta-lactam antibiotics.
 A deeper understanding of pharmacokinetic (PK) and pharmacodynamic (PD) mechanisms that occur in critically ill patients should guide us in dose optimization and improvement in methodology for future clinical trials.

Rapid Design of Combination Antimicrobial Therapy against Acinetobacter baumannii

Treatment of serious bacterial infections with antimicrobial agents, such as antibiotics, is a major clinical challenge, because of growing bacterial resistance to multiple agents. Combination therapy (i.e. combined dosing of more than one agent) is often used for the purpose, but its systematic design remains a challenge. To address this, we recently reported a method to mathematically model bacterial response to antimicrobial agents, and to use this model for systematic design of clinically relevant combination therapy. The method relies on (a) longitudinal data of bacterial load, estimated from optical density measurements during time-kill experiments in an automated instrument, and (b) use of these data to fit a mathematical model for combination therapy design. In this work, we studied an application of the proposed method to (a) an important bacterial pathogen (Acinetobacter baumannii) and (b) two cases of antibiotic combinations (ceftazidime / amikacin and ceftazidime / avibactam) in synchronous and asynchronous dosing, not otherwise studied to date. Following the proposed method, optical density based data of bacterial load under antibiotic exposure for 20 h were used to calibrate the mathematical model and subsequently predict outcomes of various dosing regimens with clinically relevant pharmacokinetics. Representative predictions by the mathematical model were tested in vitro in a hollow fiber infection model over 120 h. Test outcomes validated these predictions. Collectively, this study both provides guidance for design of A. baumannii infection treatments with the agents studied and underscores the broader applicability of the proposed method for design of clinically relevant combination therapy.

Improving pharmacokinetic/pharmacodynamic outcomes of antimicrobial therapy for pneumonia in the ICU

INTRODUCTION

Pneumonia remains a significant global health challenge due to its high prevalence and mortality rate, and challenging treatment. This review explores the best strategies to optimize the antibiotic therapy for pneumonia in critically ill patients, focusing on pharmacokinetics, pharmacodynamics, and therapeutic data.

AREAS COVERED

A review of scientific publications on severe pneumonia highlights the challenges of optimizing antibiotic use to improve lung diffusion, bacterial killing, and achieving PK/PD targets, emphasizing the need to understand microbiological epidemiology and MIC breakpoints. Key strategies like nebulization, therapeutic drug monitoring, and emerging technologies such as ELF TDM and nanomaterial-based drug delivery systems are essential for optimizing PK/PD outcomes and addressing antimicrobial resistance.

EXPERT OPINION

Improving our understanding of pulmonary pharmacokinetics and optimizing their tissue diffusion are instrumental for achieving precision antibiotic therapy for severe pneumonia. By addressing current limitations and embracing interdisciplinary collaboration, we can pave the way for more efficient personalized approaches in infectious disease management.

Piperacillin-tazobactam vs. carbapenems for treating hospitalized patients with ESBL-producing Enterobacterales bloodstream infections: A systematic review and meta-analysis

OBJECTIVES

To meta-analyse the clinical efficacy of piperacillin-tazobactam vs. carbapenems for treating hospitalized patients affected by extended-spectrum beta-lactamase (ESBL)-producing Enterobacterales bloodstream infections (BSIs).

METHODS

Two authors independently searched PubMed-MEDLINE and Scopus database up to January 17, 2024, to retrieve randomized controlled trials (RCTs) or observational studies comparing piperacillin-tazobactam vs. carbapenems for the management of hospitalized patients with ESBL-BSIs. Data were independently extracted by the two authors, and the quality of included studies was independently assessed according to ROB 2.0 or ROBINS-I tools. Mortality rate was selected as primary outcome. Meta-analysis was performed by pooling odds ratios (ORs) retrieved from studies providing adjustment for confounders using a random-effects model with the inverse variance method.

RESULTS

After screening 3,418 articles, 10 studies were meta-analysed (one RCT and nine retrospective observational studies; N = 1,962). Mortality rate did not significantly differ between treatment with piperacillin-tazobactam vs. carbapenems (N = 6; OR: 1.41; 95% CI: 0.96-2.07; I² = 23.6%). The findings were consistent also in subgroup analyses assessing patients receiving empirical therapy (N = 5; OR: 1.36; 95% CI: 0.99-1.85), or patients having in ≥50% of cases urinary/biliary tract as the primary BSI source (N = 2; OR: 1.26; 95% CI: 0.84-1.89). Conversely, the mortality rate was significantly higher with piperacillin-tazobactam only among patients having in <50% of cases urinary/biliary tract as the primary source of BSI (N = 3; OR: 2.02; 95% CI: 1.00-4.07).

CONCLUSIONS

This meta-analysis showed that, after performing appropriate adjustments for confounders, mortality and clinical outcome in patients having ESBL-producing Enterobacterales BSIs did not significantly differ among those receiving piperacillin-tazobactam compared to those receiving carbapenems.

Clinical pharmacokinetics of antimicrobials in critical care: a narrative review

INTRODUCTION

The management of critically ill septic patients presents considerable challenges due to multifaceted physiological alterations. Rapid changes such as fluid shifts, hyperdynamic states, and altered renal clearance often require special attention for better clinical outcomes. Vital organ dysfunction, with or without MODS, often necessitates supportive management like RRT, ventilatory support, and ECMO. These interventions can significantly affect the PK/PD of administered antimicrobials, complicating effective treatment.

AREA COVERED

Patient-specific parameters such as age, weight, and comorbid illnesses (e.g. cystic fibrosis, burns, and immunocompromised states) are critical determinants of antimicrobial pharmacokinetics. Understanding PK/PD determinants is crucial for developing optimized dosing regimens that enhance therapeutic efficacy and minimize toxicity in critically ill patients.

EXPERT OPINION

Incorporating pharmacometrics approaches in dose optimization can significantly improve patient outcomes. This review focuses on the nuances of PK/PD for optimized antimicrobial dosing in critically ill septic patients, emphasizing the importance of individualized treatment plans to address the complex and dynamic needs of this patient population. The adoption of these advanced pharmacokinetic and pharmacodynamic principles into clinical practice is essential for advancing patient care and optimizing therapeutic outcomes in critically ill patients.

Pharmacokinetic/pharmacodynamic issues for optimizing treatment with beta-lactams of Gram-negative infections in critically ill orthotopic liver transplant recipients: a comprehensive review

Orthotopic liver transplant (OLT) represents the standard of care for managing patients affected by end-stage and life-threatening liver diseases. Although a significant improvement in surgical techniques, immunosuppressant regimens, and prompt identification of early post-transplant complications resulted in better clinical outcome and survival in OLT recipients, the occurrence of early bacterial infections still represents a remarkable cause of morbidity and mortality. In this scenario, beta-lactams are the most frequent antimicrobials used in critical OLT recipients. The aim of this narrative review was to provide a comprehensive overview of the pathophysiological issues potentially affecting the pharmacokinetics of beta-lactams and to identify potential strategies for maximizing the likelihood of attaining adequate pharmacokinetic/pharmacodynamic (PK/PD) targets of beta-lactams in critically ill OLT recipients. A literature search was carried out on PubMed-MEDLINE database (until 31st March 2024) in order to retrieve clinical trials, real-world observational evidence, and/or case series/reports evaluating the PK/PD of traditional and novel beta-lactams in settings potentially involving critically ill OLT recipients. Retrieved evidence were categorized according to the concepts of the so-called "antimicrobial therapy puzzle", specifically assessing a) beta-lactam PK/PD features, with specific regard to aggressive PK/PD target attainment; b) site of infection, with specific regard to beta-lactam penetration in the lung, ascitic fluid, and bile; and c) pathophysiological alterations, focusing mainly on those specifically associated with OLT. Overall, several research gaps still exist in assessing the PK behavior of beta-lactams in critical OLT recipients. The impact of specific OLT-associated pathophysiological alterations on the attainment of optimal PK/PD targets may represent an important field in which further studies are warranted. Assessing the relationship between aggressive beta-lactam PK/PD target attainment and clinical outcome in critical OLT recipients will represent a major challenge in the next future.

Impact of attaining aggressive vs. conservative PK/PD target on the clinical efficacy of beta-lactams for the treatment of Gram-negative infections in the critically ill patients: a systematic review and meta-analysis

BACKGROUND

To perform a systematic review with meta-analysis with the dual intent of assessing the impact of attaining aggressive vs. conservative beta-lactams PK/PD target on the clinical efficacy for treating Gram-negative infections in critical patients, and of identifying predictive factors of failure in attaining aggressive PK/PD targets.

METHODS

Two authors independently searched PubMed-MEDLINE and Scopus database from inception to 23rd December 2023, to retrieve studies comparing the impact of attaining aggressive vs. conservative PK/PD targets on clinical efficacy of beta-lactams. Independent predictive factors of failure in attaining aggressive PK/PD targets were also assessed. Aggressive PK/PD target was considered a100%fT>4xMIC, and clinical cure rate was selected as primary outcome. Meta-analysis was performed by pooling odds ratios (ORs) extrapolated from studies providing adjustment for confounders using a random-effects model with inverse variance method.

RESULTS

A total of 20,364 articles were screened, and 21 observational studies were included in the meta-analysis (N = 4833; 2193 aggressive vs. 2640 conservative PK/PD target). Attaining aggressive PK/PD target was significantly associated with higher clinical cure rate (OR 1.69; 95% CI 1.15-2.49) and lower risk of beta-lactam resistance development (OR 0.06; 95% CI 0.01-0.29). Male gender, body mass index > 30 kg/m2, augmented renal clearance and MIC above the clinical breakpoint emerged as significant independent predictors of failure in attaining aggressive PK/PD targets, whereas prolonged/continuous infusion administration of beta-lactams resulted as protective factor. The risk of bias was moderate in 19 studies and severe in the other 2.

CONCLUSIONS

Attaining aggressive beta-lactams PK/PD targets provided significant clinical benefits in critical patients. Our analysis could be useful to stratify patients at high-risk of failure in attaining aggressive PK/PD targets.

Comparative Impact of an Optimized PK/PD Target Attainment of Piperacillin-Tazobactam vs. Meropenem on the Trend over Time of SOFA Score and Inflammatory Biomarkers in Critically Ill Patients Receiving Continuous Infusion Monotherapy for Treating Documented Gram-Negative BSIs and/or VAP

(1) Background: The advantage of using carbapenems over beta-lactam/beta-lactamase inhibitor combinations in critically ill septic patients still remains a debated issue. We aimed to assess the comparative impact of an optimized pharmacokinetic/pharmacodynamic (PK/PD) target attainment of piperacillin-tazobactam vs. meropenem on the trend over time of both Sequential Organ Failure Assessment (SOFA) score and inflammatory biomarkers in critically ill patients receiving continuous infusion (CI) monotherapy with piperacillin-tazobactam or meropenem for treating documented Gram-negative bloodstream infections (BSI) and/or ventilator-associated pneumonia (VAP). (2) Methods: We performed a retrospective observational study comparing critically ill patients receiving targeted treatment with CI meropenem monotherapy for documented Gram-negative BSIs or VAP with a historical cohort of critical patients receiving CI piperacillin-tazobactam monotherapy. Patients included in the two groups were admitted to the general and post-transplant intensive care unit in the period July 2021-September 2023 and fulfilled the same inclusion criteria. The delta values of the SOFA score between the baseline of meropenem or piperacillin-tazobactam treatment and those at 48-h (delta 48-h SOFA score) or at 7-days (delta 7-days SOFA) were selected as primary outcomes. Delta 48-h and 7-days C-reactive protein (CRP) and procalcitonin (PCT), microbiological eradication, resistance occurrence, clinical cure, multi-drug resistant colonization at 90-day, ICU, and 30-day mortality rate were selected as secondary outcomes. Univariate analysis comparing primary and secondary outcomes between critically ill patients receiving CI monotherapy with piperacillin-tazobactam vs. meropenem was carried out. (3) Results: Overall, 32 critically ill patients receiving CI meropenem monotherapy were compared with a historical cohort of 43 cases receiving CI piperacillin-tazobactam monotherapy. No significant differences in terms of demographics and clinical features emerged at baseline between the two groups. Optimal PK/PD target was attained in 83.7% and 100.0% of patients receiving piperacillin-tazobactam and meropenem, respectively. No significant differences were observed between groups in terms of median values of delta 48-h SOFA (0 points vs. 1 point; p = 0.89) and median delta 7-days SOFA (2 points vs. 1 point; p = 0.43). Similarly, no significant differences were found between patients receiving piperacillin-tazobactam vs. meropenem for any of the secondary outcomes. (4) Conclusion: Our findings may support the contention that in critically ill patients with documented Gram-negative BSIs and/or VAP, the decreases in the SOFA score and in the inflammatory biomarkers serum levels achievable with CI piperacillin-tazobactam monotherapy at 48-h and at 7-days may be of similar extent and as effective as to those achievable with CI meropenem monotherapy provided that optimization on real-time by means of a TDM-based expert clinical pharmacological advice program is granted.

Safety and effectiveness of fifth generation cephalosporins for the treatment of methicillin-resistant staphylococcus aureus bloodstream infections: a narrative review exploring past, present, and future

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infection (BSI) is a major issue in healthcare, since it is often associated with endocarditis or deep site foci. Relevant morbidity and mortality associated with MRSA-BSIs forced the development of new antibiotic strategies; in particular, this review will focus the attention on fifth-generation cephalosporins (ceftaroline/ceftobiprole), that are the only ß-lactams active against MRSA.

AREAS COVERED

The review discusses the available randomized controlled trials and real-world observational studies conducted on safety and effectiveness of ceftaroline/ceftobiprole for the treatment of MRSA-BSIs. Finally, a proposal of MRSA-BSI treatment flowchart, based on fifth-generation cephalosporins, is described.

EXPERT OPINION

The use of anti-MRSA cephalosporins is an acceptable choice either in monotherapy or combination therapy for the treatment of MRSA-BSIs due to their relevant effectiveness and safety. Particularly, their use may be advisable in combination therapy in case of severe infections (including endocarditis or persistent bacteriemia) or in monotherapy in subjects at higher risk of drugs-induced toxicity with older regimens. On the contrary, caution should be taken in case of suspected/ascertained central nervous system infections due to inconsistent data regarding penetration of these drugs in cerebrospinal fluid and brain tissues.

Could an Optimized Joint Pharmacokinetic/Pharmacodynamic Target Attainment of Continuous Infusion Piperacillin-Tazobactam Be a Valuable Innovative Approach for Maximizing the Effectiveness of Monotherapy Even in the Treatment of Critically Ill Patients with Documented Extended-Spectrum Beta-Lactamase-Producing Enterobacterales Bloodstream Infections and/or Ventilator-Associated Pneumonia?

(1) Background: Piperacillin-tazobactam represents the first-line option for treating infections caused by full- or multi-susceptible Enterobacterales and/or Pseudomonas aeruginosa in critically ill patients. Several studies reported that attaining aggressive pharmacokinetic/pharmacodynamic (PK/PD) targets with beta-lactams is associated with an improved microbiological/clinical outcome. We aimed to assess the relationship between the joint PK/PD target attainment of continuous infusion (CI) piperacillin-tazobactam and the microbiological/clinical outcome of documented Gram-negative bloodstream infections (BSI) and/or ventilator-associated pneumonia (VAP) of critically ill patients treated with CI piperacillin-tazobactam monotherapy. (2) Methods: Critically ill patients admitted to the general and post-transplant intensive care unit in the period July 2021-September 2023 treated with CI piperacillin-tazobactam monotherapy optimized by means of a real-time therapeutic drug monitoring (TDM)-guided expert clinical pharmacological advice (ECPA) program for documented Gram-negative BSIs and/or VAP were retrospectively retrieved. Steady-state plasma concentrations (Css) of piperacillin and of tazobactam were measured, and the free fractions (f) were calculated according to respective plasma protein binding. The joint PK/PD target was defined as optimal whenever both the piperacillin fCss/MIC ratio was >4 and the tazobactam fCss/target concentration (CT) ratio was > 1 (quasi-optimal or suboptimal whenever only one or none of the two weas achieved, respectively). Multivariate logistic regression analysis was performed for testing variables potentially associated with microbiological outcome. (3) Results: Overall, 43 critically ill patients (median age 69 years; male 58.1%; median SOFA score at baseline 8) treated with CI piperacillin-tazobactam monotherapy were included. Optimal joint PK/PD target was attained in 36 cases (83.7%). At multivariate analysis, optimal attaining of joint PK/PD target was protective against microbiological failure (OR 0.03; 95%CI 0.003-0.27; p = 0.002), whereas quasi-optimal/suboptimal emerged as the only independent predictor of microbiological failure (OR 37.2; 95%CI 3.66-377.86; p = 0.002). (4) Conclusion: Optimized joint PK/PD target attainment of CI piperacillin-tazobactam could represent a valuable strategy for maximizing microbiological outcome in critically ill patients with documented Gram-negative BSI and/or VAP, even when sustained by extended-spectrum beta-lactamase (ESBL)-producing Enterobacterales. In this scenario, implementing a real-time TDM-guided ECPA program may be helpful in preventing failure in attaining optimal joint PK/PD targets among critically ill patients. Larger prospective studies are warranted to confirm our findings.

Role of a Real-Time TDM-Based Expert Clinical Pharmacological Advice Program in Optimizing the Early Pharmacokinetic/Pharmacodynamic Target Attainment of Continuous Infusion Beta-Lactams among Orthotopic Liver Transplant Recipients with Documented or Suspected Gram-Negative Infections

(1) Objectives: To describe the attainment of optimal pharmacokinetic/pharmacodynamic (PK/PD) targets in orthotopic liver transplant (OLT) recipients treated with continuous infusion (CI) beta-lactams optimized using a real-time therapeutic drug monitoring (TDM)-guided expert clinical pharmacological advice (ECPA) program during the early post-surgical period. (2) Methods: OLT recipients admitted to the post-transplant intensive care unit over the period of July 2021-September 2023, receiving empirical or targeted therapy with CI meropenem, piperacillin-tazobactam, meropenem-vaborbactam, or ceftazidime-avibactam optimized using a real-time TDM-guided ECPA program, were retrospectively retrieved. Steady-state beta-lactam (BL) and/or beta-lactamase inhibitor (BLI) plasma concentrations (Css) were measured, and the Css/MIC ratio was selected as the best PK/PD target for beta-lactam efficacy. The PK/PD target of meropenem was defined as being optimal when attaining a fCss/MIC ratio > 4. The joint PK/PD target of the BL/BLI combinations (namely piperacillin-tazobactam, ceftazidime-avibactam, and meropenem-vaborbactam) was defined as being optimal when the fCss/MIC ratio > 4 of the BL and the fCss/target concentration (CT) ratio > 1 of tazobactam or avibactam, or the fAUC/CT ratio > 24 of vaborbactam were simultaneously attained. Multivariate logistic regression analysis was performed for testing potential variables that were associated with a failure in attaining early (i.e., at first TDM assessment) optimal PK/PD targets. (3) Results: Overall, 77 critically ill OLT recipients (median age, 57 years; male, 63.6%; median MELD score at transplantation, 17 points) receiving a total of 100 beta-lactam treatment courses, were included. Beta-lactam therapy was targeted in 43% of cases. Beta-lactam dosing adjustments were provided in 76 out of 100 first TDM assessments (76.0%; 69.0% decreases and 7.0% increases), and overall, in 134 out of 245 total ECPAs (54.7%). Optimal PK/PD target was attained early in 88% of treatment courses, and throughout beta-lactam therapy in 89% of cases. Augmented renal clearance (ARC; OR 7.64; 95%CI 1.32-44.13) and MIC values above the EUCAST clinical breakpoint (OR 91.55; 95%CI 7.12-1177.12) emerged as independent predictors of failure in attaining early optimal beta-lactam PK/PD targets. (4) Conclusion: A real-time TDM-guided ECPA program allowed for the attainment of optimal beta-lactam PK/PD targets in approximately 90% of critically ill OLT recipients treated with CI beta-lactams during the early post-transplant period. OLT recipients having ARC or being affected by pathogens with MIC values above the EUCAST clinical breakpoint were at high risk for failure in attaining early optimal beta-lactam PK/PD targets. Larger prospective studies are warranted for confirming our findings.

Relationship Between Real-time TDM-guided Pharmacodynamic Target Attainment of Continuous Infusion Beta-lactam Monotherapy and Microbiologic Outcome in the Treatment of Critically Ill Children With Severe Documented Gram-negative Infections

OBJECTIVES

To explore the relationship between real-time therapeutic drug monitoring (TDM)-guided pharmacodynamic target attainment of continuous infusion (CI) beta-lactam monotherapy and microbiological outcome in the treatment of critically ill children with severe documented Gram-negative infections.

METHODS

Observational, monocentric, retrospective study of critically ill patients receiving CI piperacillin-tazobactam, ceftazidime, or meropenem in monotherapy for documented Gram-negative infections optimized by means of a real-time TDM-guided strategy. Average steady-state beta-lactam concentrations (C ss ) were calculated for each patient, and the beta-lactam C ss /minimum inhibitory concentration (MIC) ratio was selected as a pharmacodynamic parameter of efficacy. The C ss /MIC ratio was defined as optimal if ≥4, quasi-optimal if between 1 and 4, and suboptimal if <1. The relationship between C ss /MIC and microbiological outcome was assessed.

RESULTS

Forty-six TDM assessments were carried out in 21 patients [median age 2 (interquartile range: 1-8) years]. C ss /MIC ratios were optimal in 76.2% of cases. Patients with optimal C ss /MIC ratios had both a significantly higher microbiological eradication rate (75.0% vs. 0.0%; P = 0.006) and lower resistance development rate (25.0% vs. 80.0%; P = 0.047) than those with quasi-optimal or suboptimal C ss /MIC ratios. Quasi-optimal/suboptimal C ss /MIC ratio occurred more frequently when patients had infections caused by pathogens with MIC values above the European Committee on Antimicrobial Susceptibility Testing clinical breakpoint (100.0% vs. 6.3%; P < 0.001).

CONCLUSIONS

Real-time TDM-guided pharmacodynamic target attainment of CI beta-lactam monotherapy allowed to maximize treatment efficacy in most critically ill children with severe Gram-negative infections. Attaining early optimal C ss /MIC ratios of CI beta-lactams could be a key determinant associated with microbiologic eradication during the treatment of Gram-negative infections. Larger prospective studies are warranted for confirming our findings.

Cefepime Daily Exposure and the Associated Impact on the Change in Sequential Organ Failure Assessment Scores and Vasopressors Requirement in Critically Ill Patients Using Repeated-Measures Mixed-Effect Modeling

IMPORTANCE

Sepsis and septic shock are major healthcare problems that need early and appropriate management.

OBJECTIVES

To evaluate the association of daily cefepime pharmacokinetic/pharmacodynamic (PK/PD) parameters with change in Sequential Organ Failure Assessment (SOFA) score and vasopressors requirement.

DESIGN SETTING AND PARTICIPANTS

This is a retrospective study. Adult ICU patients who received cefepime for Gram-negative pneumonia or bloodstream infection (BSI) and had cefepime concentrations measured were included. Daily cefepime exposure was generated and PK/PD parameters calculated for patients. Repeated-measures mixed-effect modeling was used to evaluate the impact of PK/PD on the outcomes.

MAIN OUTCOMES AND MEASURES

Change in daily SOFA score and vasopressors requirement.

RESULTS

A total of 394 and 207 patients were included in the SOFA and vasopressors analyses, respectively. The mean (±sd) age was 55 years (19) and weight 81 kg (29). For the change in SOFA score, daily SOFA score, mechanical ventilation, renal replacement therapy, and number of vasopressors were included. In the vasopressors analysis, daily SOFA score, day of therapy, and hydrocortisone dose were significant covariates in the final model. Achieving cefepime concentrations above the minimum inhibitory concentration (MIC) (T>MIC) for 100% of the dosing interval was associated with 0.006 µg/kg/min decrease in norepinephrine-equivalent dose. Cefepime PK/PD did not have an impact on the daily change in SOFA score.

CONCLUSIONS AND RELEVANCE

Achieving 100% T>MIC was associated with negligible decrease in vasopressors requirement in ICU patients with Gram-negative pneumonia and BSI. There was no impact on the change in SOFA score.

Real-Time TDM-Based Expert Clinical Pharmacological Advice Program for Attaining Aggressive Pharmacokinetic/Pharmacodynamic Target of Continuous Infusion Meropenem in the Treatment of Critically Ill Patients with Documented Gram-Negative Infections Undergoing Continuous Veno-Venous Hemodiafiltration

(1) Objectives: to describe the pharmacokinetic/pharmacodynamic (PK/PD) profile of continuous infusion (CI) meropenem in critical patients with documented Gram-negative infections undergoing continuous veno-venous hemodiafiltration (CVVHDF) and to assess the relationship with microbiological outcome. (2) Methods: Data were retrospectively retrieved for patients admitted to the general and the post-transplant intensive care units in the period October 2022-May 2023 who underwent CVVHDF during treatment with CI meropenem optimized by means of a real-time therapeutic drug monitoring (TDM)-based expert clinical pharmacological advice (ECPA) program for documented Gram-negative infections. Steady-state meropenem plasma concentrations were measured, and the free fractions (fCss) were calculated. Meropenem total clearance (CLtot) was calculated at each TDM assessment, and the impact of CVVHDF dose intensity and of residual diuresis on CLtot was investigated by means of linear regression. Optimal meropenem PK/PD target attainment was defined as an fCss/MIC ratio > 4. The relationship between meropenem PK/PD target attainment and microbiological outcome was assessed. (3) Results: A total of 24 critical patients (median age 68 years; male 62.5%) with documented Gram-negative infections were included. Median (IQR) meropenem fCss was 19.9 mg/L (17.4-28.0 mg/L). Median (IQR) CLtot was 3.89 L/h (3.28-5.29 L/h), and median (IQR) CVVHDF dose intensity was 37.4 mL/kg/h (33.8-44.6 mL/kg/h). Meropenem dosing adjustments were provided in 20 out of 24 first TDM assessments (83.3%, all decreases) and overall in 26 out of the 51 total ECPA cases (51.0%). Meropenem PK/PD target attainment was always optimal, and microbiological eradication was achieved in 90.5% of assessable cases. (4) Conclusion: the real-time TDM-guided ECPA program was useful in attaining aggressive PK/PD targeting with CI meropenem in critically ill patients undergoing high-intensity CVVHDF and allowed microbiological eradication in most cases with dosing regimens ranging between 125 and 500 mg q6h over 6 h.

The clinical application of beta-lactam antibiotic therapeutic drug monitoring in the critical care setting

Critically ill patients have increased variability in beta-lactam antibiotic (beta-lactam) exposure due to alterations in their volume of distribution and elimination. Therapeutic drug monitoring (TDM) of beta-lactams, as a dose optimization and individualization tool, has been recommended to overcome this variability in exposure. Despite its potential benefit, only a few centres worldwide perform beta-lactam TDM. An important reason for the low uptake is that the evidence for clinical benefits of beta-lactam TDM is not well established. TDM also requires the availability of specific infrastructure, knowledge and expertise. Observational studies and systematic reviews have demonstrated that TDM leads to an improvement in achieving target concentrations, a reduction in potentially toxic concentrations and improvement of clinical and microbiological outcomes. However, a small number of randomized controlled trials have not shown a mortality benefit. Opportunities for improved study design are apparent, as existing studies are limited by their inclusion of heterogeneous patient populations, including patients that may not even have infection, small sample size, variability in the types of beta-lactams included, infections caused by highly susceptible bacteria, and varied sampling, analytical and dosing algorithm methods. Here we review the fundamentals of beta-lactam TDM in critically ill patients, the existing clinical evidence and the practical aspects involved in beta-lactam TDM implementation.

Cefepime pharmacokinetics in critically ill children and young adults undergoing continuous kidney replacement therapy

OBJECTIVES

Cefepime is an antibiotic commonly used to treat sepsis and is cleared by renal excretion. Cefepime dosing requires adjustment in patients with decreased kidney function and in those receiving continuous kidney replacement therapy (CKRT). We aimed to characterize cefepime PK in a diverse cohort of critically ill paediatric patients on CKRT.

METHODS

Patients were identified from an ongoing pharmacokinetic/pharmacodynamic (PK/PD) study of beta-lactam antibiotics, and were included if they had received at least two cefepime doses in the ICU and were on CKRT for at least 24 h. PK parameters were estimated using MwPharm++ with Bayesian estimation and a paediatric population PK model. Target attainment was assessed as time of free cefepime concentrations above minimum inhibitory concentration (fT > 1× or 4 × MIC).

RESULTS

Seven patients were included in the study (ages 2 to 20 years). CKRT indications included liver failure (n = 1), renal failure (n = 4) and fluid overload (n = 2). Total effluent flow rates ranged from 1833 to 3115 (mean 2603) mL/1.73 m2/h, while clearance was 2.11-3.70 (mean 3.0) L/h/70 kg. Effluent flows were lower, but clearance and fT > MIC were similar to paediatric data published previously. Using Pseudomonas aeruginosa MIC breakpoints, all patients had 100% of dosing interval above MIC, but only one had 100% of dosing interval above 4× MIC.

CONCLUSIONS

Since most patients failed to attain stringent targets of 100% fT > 4×  MIC, model-informed precision dosing may benefit such patients.

Pharmacokinetic/Pharmacodynamic Target Attainment of Continuous Infusion Piperacillin-Tazobactam or Meropenem and Microbiological Outcome among Urologic Patients with Documented Gram-Negative Infections

(1) Objectives: To describe the relationship between pharmacokinetic/pharmacodynamic (PK/PD) target attainment of continuous infusion (CI) piperacillin-tazobactam or meropenem monotherapy and microbiological outcome in a case series of urological patients with documented Gram-negative infections. (2) Methods: Patients admitted to the urology ward who were treated with CI piperacillin-tazobactam or meropenem monotherapy for documented Gram-negative infections and underwent real-time therapeutic drug monitoring (TDM)-guided expert clinical pharmacological advice (ECPA) program from June 2021 to May 2023 were retrospectively retrieved. Average steady-state (Css) piperacillin-tazobactam and meropenem concentrations were determined, and the free fractions (fCss) were calculated. Optimal PK/PD target attainments were defined as an fCss/MIC ratio >4 for CI meropenem and an fCss/MIC ratio of piperacillin >4 coupled with an fCss/CT ratio for tazobactam >1 for piperacillin-tazobactam (joint PK/PD target). The relationship between beta-lactam PK/PD targets and microbiological outcome was explored. (3) Results: Sixteen urologic patients with documented Gram-negative infections (62.5% complicated urinary tract infections (cUTI)) had 30 TDM-guided ECPAs. At first TDM assessment, beta-lactam dosing adjustments were recommended in 11 out of 16 cases (68.75%, of which 62.5% decreases and 6.25% increases). Overall, beta-lactam dosing adjustments were recommended in 14 out of 30 ECPAs (46.6%). Beta-lactam PK/PD target attainments were optimal in 100.0% of cases. Microbiological failure occurred in two patients, both developing beta-lactam resistance. (4) Conclusion: A TDM-guided ECPA program may allow for optimizing beta-lactam treatment in urologic patients with documented Gram-negative infections, ensuring microbiological eradication in most cases.

Optimizing the Use of Beta-Lactam Antibiotics in Clinical Practice: A Test of Time

Despite their limitations, the pharmacokinetics (PK) and pharmacodynamics (PD) indices form the basis for our current understanding regarding antibiotic development, selection, and dose optimization. Application of PK-PD in medicine has been associated with better clinical outcome, suppression of resistance, and optimization of antibiotic consumption. Beta-lactam antibiotics remain the cornerstone for empirical and directed therapy in many patients. The percentage of time of the dosing interval that the free (unbound) drug concentration remains above the minimal inhibitory concentration (MIC) (%fT > MIC) has been considered the PK-PD index that best predicts the relationship between antibiotic exposure and killing for the beta-lactam antibiotics. Time dependence of beta-lactam antibiotics has its origin in the acylation process of the serine active site of penicillin-binding proteins, which subsequently results in bacteriostatic and bactericidal effects during the dosing interval. To enhance the likelihood of target attainment, higher doses, and prolonged infusion strategies, with/or without loading doses, have been applied to compensate for subtherapeutic levels of antibiotics related to PK-PD changes, especially in the early phase of severe sepsis. To minimize resistance and maximize clinical outcome, empirical therapy with a meropenem loading dose followed by high-dose-prolonged infusion should be considered in patients with high inoculum infections presenting as severe (Gram negative) sepsis. Subsequent de-escalation and dosing of beta-lactam antibiotics should be considered as an individualized dynamic process that requires dose adjustments throughout the time course of the disease process mediated by clinical parameters that indirectly assess PK-PD alterations.

Therapeutic drug monitoring of carbapenem antibiotics in critically ill patients: an overview of principles, recommended dosing regimens, and clinical outcomes

INTRODUCTION

The importance of antibiotic treatment for sepsis in critically ill septic patients is well established. Consistently achieving the dose of antibiotics required to optimally kill bacteria, minimize the development of resistance, and avoid toxicity is challenging. The increasing understanding of the pharmacokinetic and pharmacodynamic (PK/PD) characteristics of antibiotics, and the effects of critical illness on key PK/PD parameters, is gradually re-shaping how antibiotics are dosed in critically ill patients.

AREAS COVERED

The PK/PD characteristics of commonly used carbapenem antibiotics, the principles of the application of therapeutic drug monitoring (TDM), and current as well as future methods of utilizing TDM to optimally devise dosing regimens will be reviewed. The limitations and evidence-base supporting the use of carbapenem TDM to improve outcomes in critically ill patients will be examined.

EXPERT OPINION

It is important to understand the principles of TDM in order to correctly inform dosing regimens. Although the concept of TDM is attractive, and the ability to utilize PK software to optimize dosing in the near future is expected to rapidly increase clinicians' ability to meet pre-defined PK/PD targets more accurately, current evidence provides only limited support for the use of TDM to guide carbapenem dosing in critically ill patients.

The expert clinical pharmacological advice program for tailoring on real-time antimicrobial therapies with emerging TDM candidates in special populations: how the ugly duckling turned into a swan

INTRODUCTION

The growing spread of infections caused by multidrug-resistant pathogens makes the need of tailoring antimicrobial therapies by means of a 'patient-centered' approach fundamental. In this scenario, therapeutic drug monitoring (TDM) of emerging antimicrobial candidates may be a valuable approach, but expert interpretation of TDM results should be granted for making them more clinically useful. The MD Clinical Pharmacologist may take over this task since this specialist may couple PK/PD expertise on drugs with a medical background and may provide expert interpretation of TDM results of antimicrobials for tailoring therapy on real-time in each single patient based on specific both drug/pathogen issues and patient issues.

AREAS COVERED

This article aims to highlight the main key-points and organizational aspects for implementing a successful TDM-based expert clinical pharmacological advice (ECPA) program for tailoring antimicrobial therapies on real-time in different hospitalized patient special populations.

EXPERT OPINION

TDM-based ECPA programs lead by the MD Clinical Pharmacologist may represent a way forward for maximizing clinical efficacy and for minimizing the risk of resistance developments and/or toxicity of antimicrobials. Stakeholders should be aware of the fact that this innovative approach may be cost-effective.

Population Pharmacokinetics and Dosing Optimization of Ceftazidime in Term Asphyxiated Neonates during Controlled Therapeutic Hypothermia

Ceftazidime is an antibiotic commonly used to treat bacterial infections in term neonates undergoing controlled therapeutic hypothermia (TH) for hypoxic-ischemic encephalopathy after perinatal asphyxia. We aimed to describe the population pharmacokinetics (PK) of ceftazidime in asphyxiated neonates during hypothermia, rewarming, and normothermia and propose a population-based rational dosing regimen with optimal PK/pharmacodynamic (PD) target attainment. Data were collected in the PharmaCool prospective observational multicenter study. A population PK model was constructed, and the probability of target attainment (PTA) was assessed during all phases of controlled TH using targets of 100% of the time that the concentration in the blood exceeds the MIC (T>MIC) (for efficacy purposes and 100% T>4×MIC and 100% T>5×MIC to prevent resistance). A total of 35 patients with 338 ceftazidime concentrations were included. An allometrically scaled one-compartment model with postnatal age and body temperature as covariates on clearance was constructed. For a typical patient receiving the current dose of 100 mg/kg of body weight/day in 2 doses and assuming a worst-case MIC of 8 mg/L for Pseudomonas aeruginosa, the PTA was 99.7% for 100% T>MIC during hypothermia (33.7°C; postnatal age [PNA] of 2 days). The PTA decreased to 87.7% for 100% T>MIC during normothermia (36.7°C; PNA of 5 days). Therefore, a dosing regimen of 100 mg/kg/day in 2 doses during hypothermia and rewarming and 150 mg/kg/day in 3 doses during the following normothermic phase is advised. Higher-dosing regimens (150 mg/kg/day in 3 doses during hypothermia and 200 mg/kg/day in 4 doses during normothermia) could be considered when achievements of 100% T>4×MIC and 100% T>5×MIC are desired.

Beta-Lactam Dose Optimisation in the Intensive Care Unit: Targets, Therapeutic Drug Monitoring and Toxicity

Beta-lactams are an important family of antibiotics used to treat infections and are commonly used in critically ill patients. Optimal use of these drugs in the intensive care unit (ICU) is important because of the serious complications from sepsis. Target beta-lactam antibiotic exposures may be chosen using fundamental principles of beta-lactam activity derived from pre-clinical and clinical studies, although the debate regarding optimal beta-lactam exposure targets is ongoing. Attainment of target exposures in the ICU requires overcoming significant pharmacokinetic (PK) and pharmacodynamic (PD) challenges. For beta-lactam drugs, the use of therapeutic drug monitoring (TDM) to confirm if the desired exposure targets are achieved has shown promise, but further data are required to determine if improvement in infection-related outcomes can be achieved. Additionally, beta-lactam TDM may be useful where a relationship exists between supratherapeutic antibiotic exposure and drug adverse effects. An ideal beta-lactam TDM service should endeavor to efficiently sample and report results in identified at-risk patients in a timely manner. Consensus beta-lactam PK/PD targets associated with optimal patient outcomes are lacking and should be a focus for future research.

A Systematic Review on Antimicrobial Pharmacokinetic Differences between Asian and Non-Asian Adult Populations

While the relevance of inter-ethnic differences to the pharmacokinetic variabilities of antimicrobials has been reported in studies recruiting healthy subjects, differences in antimicrobial pharmacokinetics between Asian and non-Asian patients with severe pathologic conditions require further investigation. For the purpose of describing the potential differences in antimicrobial pharmacokinetics between Asian and non-Asian populations, a systematic review was performed using six journal databases and six theses/dissertation databases (PROSPERO record CRD42018090054). The pharmacokinetic data of healthy volunteers and non-critically ill and critically ill patients were reviewed. Thirty studies on meropenem, imipenem, doripenem, linezolid, and vancomycin were included in the final descriptive summaries. In studies recruiting hospitalised patients, inconsistent differences in the volume of distribution (V_d) and drug clearance (CL) of the studied antimicrobials between Asian and non-Asian patients were observed. Additionally, factors other than ethnicity, such as demographic (e.g., age) or clinical (e.g., sepsis) factors, were suggested to better characterise these pharmacokinetic differences. Inconsistent differences in pharmacokinetic parameters between Asian and non-Asian subjects/patients may suggest that ethnicity is not an important predictor to characterise interindividual pharmacokinetic differences between meropenem, imipenem, doripenem, linezolid, and vancomycin. Therefore, the dosing regimens of these antimicrobials should be adjusted according to patients' demographic or clinical characteristics that can better describe pharmacokinetic differences.

A novel method to evaluate ceftazidime/avibactam therapy in patients with carbapenemase-producing Enterobactericeae (CPE) bloodstream infections

INTRODUCTION

This study reports experience managing eight patients with bloodstream infections treated with a continuous infusion of ceftazidime-avibactam.

METHODS

Patients who were treated for documented CPE BSIs susceptible to CAZ-AVI and who underwent real-time therapeutic drug monitoring were retrospectively assessed. Ceftazidime MICs were assessed in presence of increasing concentrations of avibactam by the broth microdilution method. An inhibitory sigmoid Emax model was used to characterize ceftazidime MIC reduction as a function of avibactam concentration, and the MICi was derived by conditioning the best-fit model using steady-state avibactam concentrations (Css). Ceftazidime fCss/MICi ratio was calculated for each patient and correlated to microbiological outcome.

RESULTS

By adopting the innovative concept of effective MIC with an inhibitor (MICi), a trend towards higher microbiological failure and resistance development was found in patients with a lower ceftazidime fCss/MICi ratio (2/3 vs. 0/5).

CONCLUSION

Assessment of changes in the ceftazidime MIC in relation to increasing avibactam concentration could represent a more robust pharmacokinetic/pharmacodynamic method for predicting microbiological failure given beta-lactam/beta-lactamase inhibitor combinations.

Beta-lactam target attainment and associated outcomes in patients with bloodstream infections

OBJECTIVES

To evaluate the association between early and cumulative beta-lactam pharmacokinetic/pharmacodynamic (PK/PD) parameters and therapy outcomes in bloodstream infection (BSI).

METHODS

Adult patients who received cefepime, meropenem, or piperacillin/tazobactam for BSI and had concentrations measured were included. Beta-lactam exposure was generated and the time that free concentration remained above the minimum inhibitory concentration (fT_>MIC) and four multiples of MIC (fT_>4 × MIC) were calculated for times 0-24 h and 0-7 days of therapy. Multiple regression analysis was performed to evaluate the impact of PK/PD on microbiological and clinical outcomes.

RESULTS

A total of 204 patients and 213 BSI episodes were included. The mean age was 58 years and weight 83 kg. Age, Sequential Organ Failure Assessment (SOFA) score, haemodialysis, Pitt bacteraemia score, and hours of empiric antibiotic therapy were significantly associated with certain outcomes and retained in the final model. In multiple regression analysis, fT_>4 × MIC at 0-24 h and 0-7 days was a significant predictor of negative blood culture on day 7 (P=0.0161 and 0.0068, respectively). In the time-to-event analysis, patients who achieved 100% fT_>4 × MIC at 0-24 h and 0-7 days had a shorter time to negative blood culture compared with those who did not (log-rank P=0.0004 and 0.0014, respectively). No significant associations were identified between PK/PD parameters and other outcomes, including improvement in symptoms at day 7 and 30-day mortality.

CONCLUSION

Early and cumulative achievement of fT_>4 × MIC was a significant predictor of microbiological outcome in patients with BSI.

Jumping into the future: overcoming pharmacokinetic/pharmacodynamic hurdles to optimize the treatment of severe difficult to treat-Gram-negative infections with novel beta-lactams

INTRODUCTION

The choice of best therapeutic strategy for difficult-to-treat resistance (DTR) Gram-negative infections currently represents an unmet clinical need.

AREAS COVERED

This review provides a critical reappraisal of real-world evidence supporting the role of pharmacokinetic/pharmacodynamic (PK/PD) optimization of novel beta-lactams in the management of DTR Gram-negative infections. The aim was to focus on prolonged and/or continuous infusion administration, penetration rates into deep-seated infections, and maximization of PK/PD targets in special renal patient populations. Retrieved findings were applied to the three most critical clinical scenarios of Gram-negative resistance phenotypes (i.e. carbapenem-resistant Enterobacterales; difficult-to-treat resistant Pseudomonas aeruginosa, and carbapenem-resistant Acinetobacter baumannii).

EXPERT OPINION

Several studies supported the role of PK/PD optimization of beta-lactams in the management of DTR Gram-negative infections for both maximizing clinical efficacy and preventing resistance emergence. Optimizing antimicrobial therapy with novel beta-lactams based on the so called 'antimicrobial therapy puzzle' PK/PD concepts may represent a definitive jump into the future toward a personalized patient management of DTR Gram negative infections. Establishing a dedicated and coordinated multidisciplinary team and implementing a real-time TDM-guided personalized antimicrobial exposure optimization of novel beta-lactams based on expert clinical pharmacological interpretation, could represent crucial cornerstones for the proper management of DTR Gram-negative infections.

Optimizing Clinical Outcomes Through Rational Dosing Strategies: Roles of Pharmacokinetic/Pharmacodynamic Modeling Tools

Significant progress in previous decades has led to several methodologies developed to facilitate the design of optimal antimicrobial dosing. In this review, we highlight common pharmacokinetic/pharmacodynamic (PKPD) modeling techniques and their roles in guiding rational dosing regimen design. In the early drug development phases, dose fractionation studies identify the PKPD index most closely associated with bacterial killing. Once discerned, this index is linked to clinical efficacy end points, and classification and regression tree analysis can be used to define the PKPD target goal. Monte Carlo simulations integrate PKPD and microbiological data to identify dosing strategies with a high probability of achieving the established PKPD target. Results then determine dosing regimens to investigate and/or validate the findings of randomized controlled trials. Further improvements in PKPD modeling could lead to an era of precision dosing and personalized therapeutics.

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

OBJECTIVE

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

DATA SOURCES

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

STUDY SELECTION AND DATA EXTRACTION

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

DATA SYNTHESIS

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

CONCLUSION

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

Optimizing Meropenem in Highly Resistant Klebsiella pneumoniae Environments: Population Pharmacokinetics and Dosing Simulations in Critically Ill Patients

Critically ill patients are characterized by substantial pathophysiological changes that alter the pharmacokinetics (PK) of hydrophilic antibiotics, including carbapenems. Meropenem is a key antibiotic for multidrug-resistant Gram-negative bacilli, and such pathophysiological alterations can worsen treatment outcomes. This study aimed to determine the population PK of meropenem and to propose optimized dosing regimens for the treatment of multidrug-resistant Klebsiella pneumoniae in critically ill patients. Two plasma samples were collected from eligible patients over a dosing interval. Nonparametric population PK modeling was performed using Pmetrics. Monte Carlo simulations were applied to different dosing regimens to determine the probability of target attainment and the cumulative fraction of response, taking into account the local MIC distribution for K. pneumoniae. The targets of 40% and 100% for the fraction of time that free drug concentrations remained above the MIC (ƒT>MIC) were tested, as suggested for critically ill patients. A one-compartment PK model using data from 27 patients showed high interindividual variability. Significant PK covariates were the 8-h creatinine clearance for meropenem and the presence of an indwelling catheter for pleural, abdominal, or cerebrospinal fluid drainage for the meropenem volume of distribution. The target 100% ƒT>MIC for K. pneumoniae, with a MIC of ≤2 mg/liter, could be attained by the use of a continuous infusion of 2.0 g/day. Meropenem therapy in critically ill patients could be optimized for K. pneumoniae isolates with an MIC of ≤2 mg/liter by using a continuous infusion in settings with more than 50% isolates have a MIC of ≥32mg/L.

Pharmacodynamic evaluation of intermittent versus extended and continuous infusions of piperacillin/tazobactam in a hollow-fibre infection model against Escherichia coli clinical isolates

OBJECTIVES

To compare the bacterial killing and emergence of resistance of intermittent versus prolonged (extended and continuous infusions) infusion dosing regimens of piperacillin/tazobactam against two Escherichia coli clinical isolates in a dynamic hollow-fibre infection model (HFIM).

METHODS

Three piperacillin/tazobactam dosing regimens (4/0.5 g 8 hourly as 0.5 and 4 h infusions and 12/1.5 g/24 h continuous infusion) against a ceftriaxone-susceptible, non-ESBL-producing E. coli 44 (Ec44, MIC 2 mg/L) and six piperacillin/tazobactam dosing regimens (4/0.5 g 8 hourly as 0.5 and 4 h infusions and 12/1.5 g/24 h continuous infusion; 4/0.5 g 6 hourly as 0.5 and 3 h infusions and 16/2 g/24 h continuous infusion) were simulated against a ceftriaxone-resistant, AmpC- and ESBL-producing E. coli 50 (Ec50, MIC 8 mg/L) in a HFIM over 7 days (initial inoculum ∼107 cfu/mL). Total and less-susceptible subpopulations and MICs were determined.

RESULTS

All simulated dosing regimens against Ec44 exhibited 4 log10 of bacterial killing over 8 h without regrowth and resistance emergence throughout the experiment. For Ec50, there was the initial bacterial killing of 4 log10 followed by regrowth to 1011 cfu/mL within 24 h against all simulated dosing regimens, and the MICs for resistant subpopulations exceeded 256 mg/L at 72 h.

CONCLUSIONS

Our study suggests that, for critically ill patients, conventional intermittent infusion, or prolonged infusions of piperacillin/tazobactam may suppress resistant subpopulations of non-ESBL-producing E. coli clinical isolates. However, intermittent, or prolonged infusions may not suppress the resistant subpopulations of AmpC- and ESBL-producing E. coli clinical isolates. More studies are required to confirm these findings.

Binding of temocillin to plasma proteins in vitro and in vivo: the importance of plasma protein levels in different populations and of co-medications

BACKGROUND

Temocillin plasma protein binding (PPB) in healthy individuals is reported to be ∼85% but had not been studied in patients.

OBJECTIVES

To obtain normative data on temocillin PPB in patients in relation to infection and impact of co-medications widely used in ICU.

METHODS

Plasma was obtained from healthy individuals (Group #1), non-ICU patients with UTI (Group #2), ICU patients with suspected/confirmed ventriculitis (Group #3) or with sepsis/septic shock (Group #4). Total and unbound temocillin concentrations were measured in spiked samples from temocillin-naive donors (in vitro) or in plasma from temocillin-treated subjects (in vivo). The impact of diluting plasma, using pharmaceutical albumin, or adding drugs potentially competing for PPB was tested in spiked samples. Data were analysed using a modified Hill-Langmuir equation taking ligand depletion into account.

RESULTS

Temocillin PPB was saturable in all groups, both in vitro and in vivo. Maximal binding capacity (Bmax) was 1.2-2-fold lower in patients. At 20 and 200 mg/L (total concentrations), the unbound fraction reached 12%-29%, 23%-42% and 32%-52% in Groups #2, #3, #4. The unbound fraction was inversely correlated with albumin and C-reactive protein concentrations. Binding to albumin was 2-3-fold lower than in plasma and non-saturable. Drugs with high PPB but active at lower molar concentrations than temocillin caused minimal displacement, while fluconazole (low PPB but similar plasma concentrations to temocillin) increased up to 2-fold its unbound fraction.

CONCLUSIONS

Temocillin PPB is saturable, 2-4-fold lowered in infected patients in relation to disease severity (ICU admission, hypoalbuminaemia, inflammation) and only partially reproducible with albumin. Competition with other drugs must be considered for therapeutic concentrations to be meaningful.

Using Machine Learning To Define the Impact of Beta-Lactam Early and Cumulative Target Attainment on Outcomes in Intensive Care Unit Patients with Hospital-Acquired and Ventilator-Associated Pneumonia

Hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) are the most common intensive care unit (ICU) infections. We aimed to evaluate the association of early and cumulative beta-lactam pharmacokinetic/pharmacodynamic (PK/PD) parameters with therapy outcomes in pneumonia. Adult ICU patients who received cefepime, meropenem, or piperacillin-tazobactam for HAP or VAP and had its concentration measured were included. Beta-lactam exposure was generated for every patient for the entire duration of therapy, and the time free concentration remained above the MIC (fT_>MIC) and the time free concentration remained above four multiples of the MIC (fT_>4×MIC) were calculated for time frames of 0 to 24 h, 0 to 10 days, and day 0 to end of therapy. Regression analyses and machine learning were performed to evaluate the impact of PK/PD on therapy outcomes. A total of 735 patients and 840 HAP/VAP episodes (47% HAP) were included. The mean age was 56 years, and the mean weight was 80 kg. Sequential organ failure assessment (SOFA), hemodialysis, age, and weight were significantly associated with the clinical outcomes and kept in the final model. In the full cohort including all pneumonia episodes, PK/PD parameters at different time windows were associated with a favorable composite outcome, clinical cure, and mechanical ventilation (MV)-free days. In patients who had positive cultures and reported MICs, almost all PK/PD parameters were significant predictors of therapy outcomes. In the machine learning analysis, PK/PD parameters ranked high and were the primary overall predictors of clinical cure. Early target attainment and cumulative target attainment have a great impact on pneumonia outcomes. Beta-lactam exposure should be optimized early and maintained through therapy duration.

Hospital-Based Antimicrobial Stewardship Programs Used in Low- and Middle-Income Countries: A Scoping Review

The burden of antimicrobial resistance (AMR) is considerable in many low- and middle-income countries (LMICs), and it is important to describe the antimicrobial stewardship program (ASP) activities found in these countries and report their impact. Importantly, as these programs target prescribing behavior, the factors influencing prescription of antimicrobials must also be taken into account. This scoping review aimed to (1) describe hospital-based ASP activities, (2) report methods used to measure the impact of ASPs, and (3) explore factors influencing antimicrobial prescribing behavior in LMICs. PubMed was searched from database inception until April 2021. Factors influencing antimicrobial prescribing behavior were canvassed using the Capability-Opportunity-Motivation and Behavior framework. Most of ASP studies in LMICs were predominantly conducted in tertiary care and university-based hospitals. Audit of antimicrobial prescriptions with feedback and restrictive-based strategies was the main reported activity. Total antimicrobial consumption was the main method used to measure the impact of ASPs. Positive outcomes were observed for both clinical and microbiological outcomes; however, these were measured from nonrandomized controlled trials. Dominant factors identified through the behavioral framework were a limited awareness of AMR as a local problem, a perception that overprescription of antimicrobials had limited consequences and was mainly driven by a motivation to help improve patient outcomes. In addition, antimicrobial prescribing practices were largely influenced by existing hierarchy among prescribers. Our scoping review suggests that LMICs need to evaluate antimicrobial appropriateness as an added measure to assess impact. Furthermore, improvements in the access of microbiology and diagnostic facilities and ensuring ASP champions are recruited from senior prescribers will positively influence antimicrobial prescribing behavior, helping improve stewardship of antimicrobials in these countries.

Therapeutic Strategies for Emerging Multidrug-Resistant Pseudomonas aeruginosa

Multidrug-resistant (MDR) and extensively drug-resistant (XDR) Pseudomonas aeruginosa isolates are frequent causes of serious nosocomial infections that may compromise the selection of antimicrobial therapy. The goal of this review is to summarize recent epidemiologic, microbiologic, and clinical data pertinent to the therapeutic management of patients with infections caused by MDR/XDR-P. aeruginosa. Historically, conventional antipseudomonal β-lactam antibiotics have been used for the empiric treatment of MDR/XDR-P. aeruginosa. Owing to the remarkable capacity of P. aeruginosa to confer resistance via multiple mechanisms, these traditional therapies are often rendered ineffective. To increase the likelihood of administering empiric antipseudomonal therapy with in vitro activity, a second agent from a different antibiotic class is often administered concomitantly with a traditional antipseudomonal β-lactam. However, combination therapy may pose an increased risk of antibiotic toxicity and secondary infection, notably, Clostridioides difficile. Multiple novel agents that demonstrate in vitro activity against MDR-P. aeruginosa (e.g., β-lactam/β-lactamase inhibitor combinations and cefiderocol) have been recently granted US Food and Drug Administration (FDA) approval and are promising additions to the antipseudomonal armamentarium. Even so, comparative clinical data pertaining to these novel agents is sparse, and concerns surrounding the scarcity of antibiotics active against refractory MDR/XDR-P. aeruginosa necessitates continued assessment of alternative therapies. This is particularly important in patients with cystic fibrosis (CF) who may be chronically colonized and suffer from recurrent infections and disease exacerbations due in part to limited efficacious antipseudomonal agents. Bacteriophages represent a promising candidate for combatting recurrent and refractory infections with their ability to target specific host bacteria and circumvent traditional mechanisms of antibiotic resistance seen in MDR/XDR-P. aeruginosa. Future goals for the management of these infections include increased comparator clinical data of novel agents to determine in what scenario certain agents may be preferred over others. Until then, appropriate treatment of these infections requires a thorough evaluation of patient- and infection-specific factors to guide empiric and definitive therapeutic decisions.

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.

Interplay between Klebsiella pneumoniae producing KPC-31 and KPC-3 under treatment with high dosage meropenem: a case report

The objective was to study ceftazidime-avibactam resistant and susceptible Klebsiella pneumoniae isolated from a patient admitted to the Policlinico Umberto I of Rome for SARS-CoV2. Data on the evolution of patient's conditions, antimicrobial therapies, and microbiological data were collected. Whole-genome sequencing performed by Illumina and Nanopore sequencing methods were used to type the strains. During the hospitalization, a SARS-CoV2-infected patient was colonized by a KPC-producing K. pneumoniae strain and empirically treated with ceftazidime-avibactam (CZA) when presenting spiking fever symptoms. Successively, ST2502 CZA-resistant strain producing the KPC-31 variant gave a pulmonary infection to the patient. The infection was treated with high doses of meropenem. The KPC-31-producing strain disappeared but the patient remained colonized by a KPC-3-producing K. pneumoniae strain. An interplay between highly conserved KPC-31- and KPC-3-producing ST2502 strains occurred in the SARS-CoV2 patient during the hospitalization, selected by CZA and carbapenem treatments, respectively.

Ceftolozane/tazobactam for refractory P. aeruginosa endocarditis: A case report and pharmacokinetic analysis

We describe a case of a 48 years old male with left sided endocarditis and septic emboli secondary to a Pseudomonas aeruginosa strain that developed resistance to other β-lactam antibiotics during therapy resulting in prolonged bacteremia. Blood cultures sterilized within 1 day of initiating ceftolozane/tazobactam 3 g every 8 hours in combination with ciprofloxacin. Steady state free ceftolozane plasma Cmax and Cmin concentrations were calculated to be 122.2μg/mL and 24.3μg/mL, respectively. The multidrug-resistant strain harbored chromosomal β-lactamases OXA-486 and PDC-3, mutations in ampD and dacB predicted to lead to ampC over-expression, and mutations in OprD predicted to decrease outer membrane permeability. Following completion of a 42 day course and aortic valve replacement, the patient was deemed clinically cured without recurrence of infection at follow up 2 years later. To our knowledge, this is the first reported case to measure ceftolozane concentrations during the treatment of endocarditis which supports dose optimization approaches of severe endovascular disease due to multidrug resistant pathogens.

Impact of Maximizing Css/MIC Ratio on Efficacy of Continuous Infusion Meropenem Against Documented Gram-Negative Infections in Critically Ill Patients and Population Pharmacokinetic/Pharmacodynamic Analysis to Support Treatment Optimization

Introduction: optimal treatment of Gram-negative infections in critically ill patients is challenged by changing pathophysiological conditions, reduced antimicrobial susceptibility and limited therapeutic options. The aim of this study was to assess the impact of maximizing Css/MIC ratio on efficacy of continuous infusion (CI) meropenem in treating documented Gram-negative infections in critically ill patients and to perform a population pharmacokinetic/pharmacodynamic analysis to support treatment optimization.

Materials and Methods: Classification and regression tree (CART) analysis was used to identify whether a cutoff of steady-state meropenem concentration (Css)-to-minimum inhibitory concentration (MIC) (Css/MIC) ratio correlated with favorable clinical outcome. A non-parametric approach with Pmetrics was used for pharmacokinetic analysis and covariate evaluation. The probability of target attainment (PTA) of the identified Css/MIC ratio was calculated by means of Monte Carlo simulations. Cumulative fraction of response (CFRs) were calculated against common Enterobacterales, P. aeruginosa and A. baumannii as well.

Results: a total of 74 patients with 183 meropenem Css were included. CART analysis identified a Css/MIC ratio ≥4.63 as cutoff value significantly associated with favorable clinical outcomes. Multivariate regression analysis confirmed the association [OR (95%CI): 20.440 (2.063–202.522); p < 0.01]. Creatinine clearance (CL_CR) was the only covariate associated with meropenem clearance. Monte Carlo simulations showed that, across different classes of renal function, dosages of meropenem ranging between 0.5 and 2 g q6h over 6 h (namely by CI) may grant PTAs of Css/MIC ratios ≥4.63 against susceptible pathogens with an MIC up to the EUCAST clinical breakpoint of 2 mg/L. The CFRs achievable with these dosages were very high (>90%) against Enterobacterales across all the classes of renal function and against P. aeruginosa among patients with CL_CR < 30 ml/min/1.73 m², and quite lower against A. baumannii.

Discussion: our findings suggest that Css/MIC ratio ≥4.63 may be considered the pharmacodynamic target useful at maximizing the efficacy of CI meropenem in the treatment of Gram-negative infections in critically ill patients. Dosages ranging between 0.5 g q6h and 2 g q6h by CI may maximize the probability of favorable clinical outcome against meropenem-susceptible Gram-negative pathogens among critically ill patients having different degrees of renal function.

SIMULTANEOUS IN VITRO SIMULATION OF MULTIPLE ANTIMICROBIAL AGENTS WITH DIFFERENT ELIMINATION HALF-LIVES IN A PRE-CLINICAL INFECTION MODEL

Combination therapy for treatment of multi-drug resistant bacterial infections is becoming common. In vitro testing of drug combinations under realistic pharmacokinetic conditions is needed before a corresponding combination is eventually put into clinical use. The current standard for design of such in vitro simulations for drugs with different half-lives is heuristic and limited to two drugs. To address that void, we develop a rigorous design method suitable for an arbitrary number of N drugs with different half-lives. The method developed offers substantial flexibility and produces novel designs even for two drugs. Explicit design equations are rigorously developed and are suitable for immediate use by experimenters. These equations were used in experimental verification using a combination of three antibiotics with distinctly different half-lives. In addition to antibiotics, the method is applicable to any anti-infective or anti-cancer drugs with distinct elimination pharmacokinetics.

A descriptive case series of pharmacokinetic/pharmacodynamic target attainment and microbiological outcome in critically ill patients with documented severe extensively drug-resistant Acinetobacter baumannii bloodstream infection and/or ventilator-associated pneumonia treated with cefiderocol

OBJECTIVES

The aim of this study was to explore the relationship between cefiderocol pharmacokinetic/pharmacodynamic (PK/PD) target attainment and microbiological outcome in critically ill patients affected by extensively drug-resistant Acinetobacter baumannii (XDR-AB) bloodstream infection (BSI) and/or ventilator-associated pneumonia (VAP).

METHODS

Patients who received compassionate use of cefiderocol to treat documented XDR-AB infections at the intensive care unit of the IRCCS Azienda Ospedaliero-Universitaria of Bologna and who underwent therapeutic drug monitoring (TDM) from 15 March 2021 to 30 April 2021 were retrospectively assessed. Cefiderocol trough concentration (Cmin) was determined at steady-state, and the free fraction (fCmin) was calculated according to a plasma protein binding of 58%. The fCmin/MIC ratio was selected as a pharmacodynamic parameter of cefiderocol efficacy and was defined as optimal if ≥4, quasi-optimal if between 1 and 4, and suboptimal if <1. The association between fCmin/MIC and microbiological outcome was assessed.

RESULTS

A total of 13 patients treated with cefiderocol for the management of XDR-AB infections (6 BSI plus VAP, 5 VAP and 2 BSI) were retrieved. fCmin/MIC ratios were suboptimal in 3 cases (23%) and quasi-optimal or optimal in 5 cases each (38%). Microbiological failure occurred in seven cases (54%; six with VAP and one with VAP plus BSI). Microbiological failure occurred in 80% of patients with suboptimal fCmin/MIC compared with 29% of those achieving optimal or quasi-optimal fCmin/MIC ratio.

CONCLUSION

Suboptimal attainment of PK/PD targets of cefiderocol may lead to microbiological failure of treatment with cefiderocol of critically ill patients affected by XDR-AB VAP.

Pseudomonas aeruginosa Susceptibility in Spain: Antimicrobial Activity and Resistance Suppression Evaluation by PK/PD Analysis

Pseudomonas aeruginosa remains one of the major causes of healthcare-associated infection in Europe; in 2019, 12.5% of invasive isolates of P. aeruginosa in Spain presented combined resistance to ≥3 antimicrobial groups. The Spanish nationwide survey on P. aeruginosa antimicrobial resistance mechanisms and molecular epidemiology was published in 2019. Based on the information from this survey, the objective of this work was to analyze the overall antimicrobial activity of the antipseudomonal antibiotics considering pharmacokinetic/pharmacodynamic (PK/PD) analysis. The role of PK/PD to prevent or minimize resistance emergence was also evaluated. A 10,000-subject Monte Carlo simulation was executed to calculate the probability of target attainment (PTA) and the cumulative fraction of response (CFR) considering the minimum inhibitory concentration (MIC) distribution of bacteria isolated in ICU or medical wards, and distinguishing between sample types (respiratory and non-respiratory). Ceftazidime/avibactam followed by ceftolozane/tazobactam and colistin, categorized as the Reserve by the Access, Watch, Reserve (AWaRe) classification of the World Health Organization, were the most active antimicrobials, with differences depending on the admission service, sample type, and dose regimen. Discrepancies between EUCAST-susceptibility breakpoints for P. aeruginosa and those estimated by PK/PD analysis were detected. Only standard doses of ceftazidime/avibactam and ceftolozane/tazobactam provided drug concentrations associated with resistance suppression.

Assessment of a PK/PD Target of Continuous Infusion Beta-Lactams Useful for Preventing Microbiological Failure and/or Resistance Development in Critically Ill Patients Affected by Documented Gram-Negative Infections

BACKGROUND

Emerging data suggest that more aggressive beta-lactam PK/PD targets could minimize the occurrence of microbiological failure and/or resistance development. This study aims to assess whether a PK/PD target threshold of continuous infusion (CI) beta-lactams may be useful in preventing microbiological failure and/or resistance development in critically ill patients affected by documented Gram-negative infections.

METHODS

Patients admitted to intensive care units from December 2020 to July 2021 receiving continuous infusion beta-lactams for documented Gram-negative infections and having at least one therapeutic drug monitoring in the first 72 h of treatment were included. A receiver operating characteristic (ROC) curve analysis was performed using the ratio between steady-state concentration and minimum inhibitory concentration (C_ss/MIC) ratio as the test variable and occurrence of microbiological failure as the state variable. Area under the curve (AUC) and 95% confidence interval (CI) were calculated. Independent risk factors for the occurrence of microbiological failure were investigated using logistic regression.

RESULTS

Overall, 116 patients were included. Microbiological failure occurred in 26 cases (22.4%). A C_ss/MIC ratio ≤ 5 was identified as PK/PD target cut-off with sensitivity of 80.8% (CI 60.6-93.4%) and specificity of 90.5% (CI 74.2-94.4%), and with an AUC of 0.868 (95%CI 0.793-0.924; p < 0.001). At multivariate regression, independent predictors of microbiological failure were C_ss/MIC ratio ≤ 5 (odds ratio [OR] 34.54; 95%CI 7.45-160.11; p < 0.001) and Pseudomonas aeruginosa infection (OR 4.79; 95%CI 1.11-20.79; p = 0.036).

CONCLUSIONS

Early targeting of CI beta-lactams at C_ss/MIC ratio > 5 during the treatment of documented Gram-negative infections may be helpful in preventing microbiological failure and/or resistance development in critically ill patients.

Applying cefepime population pharmacokinetics on critically ill patients receiving continuous renal replacement therapy

Patients admitted to the intensive care unit (ICU) may need continuous renal replacement therapy (CRRT) due to acute kidney injury or worsening of underlying chronic kidney disease. This will affect their antimicrobial exposure and may have a significant impact on the treatment. We aim to develop a cefepime pharmacokinetic (PK) model in CRRT ICU patients and generate the posterior predictions for a group and assess their therapy outcomes. Adult patients, admitted to the ICU, received cefepime, and had its concentration measured while on CRRT were included from three different datasets. In two datasets, samples were collected from the predialyzer, postdialyzer ports, and effluent fluid at different times within the same dosing interval. The third dataset had only cefepime plasma concentration measured as part of clinical service. Patients' demographics, cefepime regimens and concentration, CRRT parameters, and therapy outcomes were recorded. NPAG was used for population PK and posterior predictions. A total of 125 patients were included. Cefepime was described by a five-compartment model, and the CRRT flow rates described the rates of cefepime transfer between compartments. The posterior predictions were generated for the third dataset and the median (range) fT_>MIC was 100% (27%-100%) and fT_>4×MIC was 64% (0%-100%). The mortality rate was 53%. There was no difference in target attainment in terms of clinical cure and 30-day mortality. This model can be used as a precision dosing tool in CRRT patients. Future studies may address other PK/PD targets in a larger population.

Suboptimal drug exposure leads to selection of different subpopulations of ceftazidime-avibactam-resistant Klebsiella pneumoniae carbapenemase-producing Klebsiella pneumoniae in a critically ill patient

OBJECTIVES

Ceftazidime-avibactam (CAZ-AVI) is a promising novel agent with activity against carbapenem-resistant Enterobacteriaceae. Here, we describe the dynamic evolution of a Klebsiella pneumoniae carbapenemase-producing Klebsiella pneumoniae (KPC-Kp) infection in a critically ill patient treated with CAZ-AVI-tigecycline combination therapy.

METHODS

Whole-genome sequencing was performed on longitudinal intrapatient KPC-Kp strains isolated from different sites during CAZ-AVI treatment. The pharmacokinetic/pharmacodynamic (PK/PD) analysis was performed on the basis of therapeutic drug monitoring of ceftazidime.

RESULTS

The development of resistance due to mutations in the blaKPC gene was observed in KPC-Kp strains isolated from bronchoalveolar lavage and blood during CAZ-AVI treatment. PK/PD analysis demonstrated that during the first days of treatment CAZ- AVI blood exposure was suboptimal (steady-state concentration/minimum inhibitory concentration ratio 2.85). Of note, the low antibiotic pressure may have selected hybrid subpopulations harboring bla_KPC-3 and T243M mutation in KPC-Kp isolated from bronchoalveolar lavage and D179Y mutation in those isolated from blood.

CONCLUSION

These results suggest the high adaptability of KPC to CAZ-AVI due to the rapid evolution of resistance and highlight the importance of identifying the optimal PK/PD target to prevent such an event from occurring again in a critically ill patient with pneumonia due to KPC-Kp.

Experimental Validation of a Mathematical Framework to Simulate Antibiotics with Distinct Half-Lives Concurrently in an In Vitro Model

Antimicrobial resistance has been steadily increasing in prevalence, and combination therapy is commonly used to treat infections due to multidrug resistant bacteria. Under certain circumstances, combination therapy of three or more drugs may be necessary, which makes it necessary to simulate the pharmacokinetic profiles of more than two drugs concurrently in vitro. Recently, a general theoretical framework was developed to simulate three drugs with distinctly different half-lives. The objective of the study was to experimentally validate the theoretical model. Clinically relevant exposures of meropenem, ceftazidime, and ceftriaxone were simulated concurrently in a hollow-fiber infection model, with the corresponding half-lives of 1, 2.5, and 8 h, respectively. Serial samples were obtained over 24 h and drug concentrations were assayed using validated LC-MS/MS methods. A one-compartment model with zero-order input was used to characterize the observed concentration-time profiles. The experimentally observed half-lives corresponding to exponential decline of all three drugs were in good agreement with the respective values anticipated at the experiment design stage. These results were reproducible when the experiment was repeated on a different day. The validated benchtop setup can be used as a more flexible preclinical tool to explore the effectiveness of various drug combinations against multidrug resistant bacteria.

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

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