Optimizing Pharmacokinetics-Pharmacodynamics of Antimicrobial Management in Patients with Sepsis: A Review

'Real-life' approach to applying PK/PD principles in infectious diseases clinical practice without access to prompt TDM

INTRODUCTION

Infectious disease treatments are transitioning from a one-size-fits-all approach to a more tailored approach. The increasing adoption of therapeutic drug monitoring (TDM) of antimicrobials is a clear example of this trend. Routine antimicrobial TDM in critically ill patients should be mandatory. Unfortunately, nowadays, only expert centers can provide it. Given the crucial nature of the first hours/days for achieving a favorable clinical outcome, empirical antibiotic therapy with an adequate choice of drug, dose and administration modalities is fundamental.

AREAS COVERED

We outline common scenarios encountered in clinical practice, such as in edematous patients, hypoalbuminemia, patients with liver and renal diseases, patients under renal replacement therapy or extracorporeal membrane oxygenation (ECMO), over or under-weight patients, in old adults and cases of infections caused by relatively high minimum inhibitory concentration (MIC) pathogens. Various clinical situations were analyzed with the help of the available literature (PubMed/MEDLINE/Google Scholar and books written by experts in pharmacology and infectious diseases).

EXPERT OPINION

In these different scenarios, we reported common examples of optimizing drug utilization to maximize therapeutic outcomes, reduce incorrect prescriptions and limit the emergence of antimicrobial resistance.

Prolonged Beta-Lactam Infusions in Children: A Systematic Review and Meta-Analysis

OBJECTIVE

To assess whether beta-lactam extended or continuous beta-lactam infusions (EI/CI) improve clinical outcomes in children with proven or suspected bacterial infections.

STUDY DESIGN

We included observational and interventional studies that compared beta-lactam EI or CI with standard infusions in children less than 18 years old, and reported on mortality, hospital or intensive care unit length of stay, microbiological cure, and/or clinical cure. Data sources included PubMed, Medline, EBM Reviews, EMBASE, and CINAHL and were searched from January 1, 1980, to November 3, 2023. Thirteen studies (2945 patients) were included: 5 randomized control trials and 8 observational studies. Indications for antimicrobial therapies and clinical severity varied, ranging from cystic fibrosis exacerbation to critically ill children with bacteriemia.

RESULTS

EI and CI were not associated with a reduction in mortality in randomized control trials (n = 1464; RR 0.93, 95% CI 0.71, 1.21), but were in observational studies (n = 833; RR 0.43, 95% CI 0.19, 0.96). We found no difference in hospital length of stay. Results for clinical and microbiological cures were heterogeneous and reported as narrative review. The included studies were highly heterogeneous, limiting the strength of our findings. The lack of shared definitions for clinical and microbiological cure outcomes precluded analysis.

CONCLUSIONS

EI and CI were not consistently associated with reduced mortality or length of stay in children. Results were conflicting regarding clinical and microbiological cures. More well-designed studies targeting high-risk populations are necessary to determine the efficacy of these alternative dosing strategies.

Central Nervous System Antimicrobial Exposure and Proposed Dosing for Anthrax Meningitis

BACKGROUND

The high mortality of systemic anthrax is likely a consequence of the severe central nervous system inflammation that occurs in anthrax meningitis. Effective treatment of such infections requires, at a minimum, adequate cerebrospinal fluid (CSF) antimicrobial concentrations.

METHODS

We reviewed English medical literature and regulatory documents to extract information on serum and CSF exposures for antimicrobials with in vitro activity against Bacillus anthracis. Using CSF pharmacokinetic exposures and in vitro B. anthracis susceptibility data, we used population pharmacokinetic modeling and Monte Carlo simulations to determine whether a specific antimicrobial dosage would likely achieve effective CSF antimicrobial activity in patients with normal to inflamed meninges (ie, an intact to markedly disrupted blood-brain barrier).

RESULTS

The probability of microbiologic success at achievable antimicrobial dosages was high (≥95%) for ciprofloxacin, levofloxacin (500 mg every 12 hours), meropenem, imipenem/cilastatin, penicillin G, ampicillin, ampicillin/sulbactam, doxycycline, and minocycline; acceptable (90%-95%) for piperacillin/tazobactam and levofloxacin (750 mg every 24 hours); and low (<90%) for vancomycin, amikacin, clindamycin, and linezolid.

CONCLUSIONS

Prompt empiric antimicrobial therapy of patients with suspected or confirmed anthrax meningitis may reduce the high morbidity and mortality. Our data support using several β-lactam-, fluoroquinolone-, and tetracycline-class antimicrobials as first-line and alternative agents for treatment of patients with anthrax meningitis; all should achieve effective microbiologic exposures. Our data suggest antimicrobials that should not be relied on to treat suspected or documented anthrax meningitis. Furthermore, the protein synthesis inhibitors clindamycin and linezolid can decrease toxin production and may be useful components of combination therapy.

A New Dosing Frontier: Retrospective Assessment of Effluent Flow Rates and Residual Renal Function Among Critically Ill Patients Receiving Continuous Renal Replacement Therapy

OBJECTIVES

In 2020, cefiderocol became the first Food and Drug Administration-approved medication with continuous renal replacement therapy (CRRT) dosing recommendations based on effluent flow rates (QE). We aimed to evaluate the magnitude and frequency of factors that may influence these recommendations, that is, QE intrapatient variability and residual renal function.

DESIGN

Retrospective observational cohort study.

SETTING

ICUs within Hartford Hospital (890-bed, acute-care hospital) in Connecticut from 2017 to 2023.

PATIENTS

Adult ICU patients receiving CRRT for greater than 72 hours.

MEASUREMENTS AND MAIN RESULTS

CRRT settings including QE and urine output (UOP) were extracted from the time of CRRT initiation (0 hr) and trends were assessed. To assess the impact on antibiotic dosing, cefiderocol doses were assigned to 0 hour, 24 hours, 48 hours, and 72 hours QE values per product label, and the proportion of antibiotic dose changes required as a result of changes in inpatient's QE was evaluated. Among the 380 ICU patients receiving CRRT for greater than 72 hours, the median (interquartile range) 0 hour QE was 2.96 (2.35-3.29) L/hr. Approximately 9 QE values were documented per patient per 24-hour window. QE changes of greater than 0.75 L/hr were observed in 21.6% of patients over the first 24 hours and in 7.9% (24-48 hr) and 5.8% (48-72 hr) of patients. Approximately 40% of patients had UOP greater than 500 mL at 24 hours post-CRRT initiation. Due to QE changes within 24 hours of CRRT initiation, a potential cefiderocol dose adjustment would have been warranted in 38% of patients (increase of 21.3%; decrease of 16.6%). QE changes were less common after 24 hours, warranting cefiderocol dose adjustments in less than 15% of patients.

CONCLUSIONS

Results highlight the temporal and variable dynamics of QE and prevalence of residual renal function. Data also demonstrate a risk of antibiotic under-dosing in the first 24 hours of CRRT initiation due to increases in QE. For antibiotics with QE-based dosing recommendations, empiric dose escalation may be warranted in the first 24 hours of CRRT initiation.

Optimizing Antibiotic Therapy for Intravenous Drug Users: A Narrative Review Unraveling Pharmacokinetics/Pharmacodynamics Challenges

Intravenous drug users (IVDUs) face heightened susceptibility to life-threatening gram-positive bacterial infections, particularly methicillin-resistant Staphylococcus aureus (MRSA). While the standard antibiotic dosing strategies for special patients, such as obese or critically ill individuals, are known to be inadequate, raising concerns about treatment efficacy, a similar sort of understanding has not been assessed for IVDUs yet. With this in mind, this review examines the pharmacokinetic/pharmacodynamic characteristics of antibiotics commonly used against gram-positive bacteria in IVDUs. Focusing on daptomycin, vancomycin, teicoplanin, aminoglycosides, and the novel lipoglycopeptide dalbavancin, the study reveals significant pharmacokinetic variations in IVDUs, suggesting the need for personalized dosing. Concomitant opioid substitution therapy and other factors, such as malnutrition, contribute to altered pharmacokinetics/pharmacodynamics, emphasizing the importance of targeted therapeutic drug monitoring. Overall, our study calls for increased awareness among clinicians regarding the unique pharmacokinetic/pharmacodynamic challenges in IVDUs and advocates for tailored antibiotic dosing strategies to enhance treatment outcomes in this marginalized population.

Advancing Precision Medicine: A Review of Innovative In Silico Approaches for Drug Development, Clinical Pharmacology and Personalized Healthcare

The landscape of medical treatments is undergoing a transformative shift. Precision medicine has ushered in a revolutionary era in healthcare by individualizing diagnostics and treatments according to each patient's uniquely evolving health status. This groundbreaking method of tailoring disease prevention and treatment considers individual variations in genes, environments, and lifestyles. The goal of precision medicine is to target the "five rights": the right patient, the right drug, the right time, the right dose, and the right route. In this pursuit, in silico techniques have emerged as an anchor, driving precision medicine forward and making this a realistic and promising avenue for personalized therapies. With the advancements in high-throughput DNA sequencing technologies, genomic data, including genetic variants and their interactions with each other and the environment, can be incorporated into clinical decision-making. Pharmacometrics, gathering pharmacokinetic (PK) and pharmacodynamic (PD) data, and mathematical models further contribute to drug optimization, drug behavior prediction, and drug-drug interaction identification. Digital health, wearables, and computational tools offer continuous monitoring and real-time data collection, enabling treatment adjustments. Furthermore, the incorporation of extensive datasets in computational tools, such as electronic health records (EHRs) and omics data, is also another pathway to acquire meaningful information in this field. Although they are fairly new, machine learning (ML) algorithms and artificial intelligence (AI) techniques are also resources researchers use to analyze big data and develop predictive models. This review explores the interplay of these multiple in silico approaches in advancing precision medicine and fostering individual healthcare. Despite intrinsic challenges, such as ethical considerations, data protection, and the need for more comprehensive research, this marks a new era of patient-centered healthcare. Innovative in silico techniques hold the potential to reshape the future of medicine for generations to come.

Predicting cytokine kinetics during sepsis; a modelling framework from a porcine sepsis model with live Escherichia coli

BACKGROUND

Describing the kinetics of cytokines involved as biomarkers of sepsis progression could help to optimise interventions in septic patients. This work aimed to quantitively characterise the cytokine kinetics upon exposure to live E. coli by developing an in silico model, and to explore predicted cytokine kinetics at different bacterial exposure scenarios.

METHODS

Data from published in vivo studies using a porcine sepsis model were analysed. A model describing the time courses of bacterial dynamics, endotoxin (ETX) release, and the kinetics of TNF and IL-6 was developed. The model structure was extended from a published model that quantifies the ETX-cytokines relationship. An external model evaluation was conducted by applying the model to literature data. Model simulations were performed to explore the sensitivity of the host response towards differences in the input rate of bacteria, while keeping the total bacterial burden constant.

RESULTS

The analysis included 645 observations from 30 animals. The blood bacterial count was well described by a one-compartment model with linear elimination. A scaling factor was estimated to quantify the ETX release by bacteria. The model successfully described the profiles of TNF, and IL-6 without a need to modify the ETX-cytokines model structure. The kinetics of TNF, and IL-6 in the external datasets were well predicted. According to the simulations, the ETX tolerance development results in that low initial input rates of bacteria trigger the lowest cytokine release.

CONCLUSION

The model quantitively described and predicted the cytokine kinetics triggered by E. coli exposure. The host response was found to be sensitive to the bacterial exposure rate given the same total bacterial burden.

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.

Pharmacokinetics of cefmetazole in plasma, peritoneal fluid, peritoneum, and subcutaneous adipose tissue of patients scheduled for lower gastrointestinal surgery: Dosing considerations based on site-specific pharmacodynamic target attainment

INTRODUCTION

Cefmetazole (CMZ) has gained interest as a carbapenem-sparing alternative to the epidemic of extended-spectrum β-lactamase (ESBL)-producing Enterobacterales (ESBL-E). In this study, we investigated the pharmacokinetics (PK) of CMZ in plasma, peritoneal fluid, peritoneum, and subcutaneous adipose tissue to assess the dosing regimen needed to achieve pharmacodynamic (PD) goals at the target site.

METHODS

Patients scheduled for elective lower gastrointestinal surgery were intravenously administered CMZ. Plasma, peritoneal fluid, peritoneum, and subcutaneous adipose tissue samples were collected after CMZ infusion and during the surgery, and CMZ concentrations were measured. The non-compartmental and compartmental PK parameters were estimated and used to evaluate site-specific PD target attainment.

RESULTS

A total of 38 plasma, 27 peritoneal fluid, 36 peritoneum, and 38 subcutaneous adipose tissue samples were collected from 10 patients. The non-compartmental PK analysis revealed the ratios of the mean area under the drug concentration-time curve (AUC_0-3.5 h) of peritoneal fluid-to-plasma, peritoneum-to-plasma, and subcutaneous adipose tissue-to-plasma were 0.60, 0.36, and 0.11, respectively. The site-specific PD target attainment analyses based on the breakpoints for ESBL-E per the Japanese surgical site infection (SSI) surveillance (MIC₉₀ = 8 mg/L) revealed that 2 g CMZ every 3.5 h achieved desired bactericidal effect at all sites and 2 g CMZ every 6 h achieved PD goals at peritoneum and peritoneal fluid.

CONCLUSION

These findings clarify the PK of CMZ in abdominal tissues and could help decide optimal dosing regimens to treat intra-abdominal infection and prophylaxis of SSI.

Pharmacokinetic parameters over time during sepsis and the association of target attainment and outcomes in critically ill children and young adults receiving ceftriaxone

INTRODUCTION

Early sepsis results in pharmacokinetic (PK) changes due to physiologic alterations. PK changes can lead to suboptimal drug target attainment, risking inadequate coverage from antibiotics like ceftriaxone. Little is known about how ceftriaxone PK and target attainment quantitatively change over time in patients with sepsis or the association between target attainment and outcomes in critically ill children and young adults.

METHODS

A retrospective analysis of a prospective study was conducted in a single-center pediatric intensive care unit. Septic patients given at least one ceftriaxone dose (commonly as 50 mg/kg every 12 h) and who had blood obtained in both the first 48 h of therapy (early) and afterwards (late) were included. Normalized clearance and central volume were estimated and compared in both sepsis phases. We evaluated target attainment, defined as concentrations above 1× or 4× the minimum inhibitory concentration (MIC) for 100% of dosing intervals, and investigated the association between target attainment and clinical outcomes.

RESULTS

Fifty-five septic patients (median age: 7.5 years) were included. Normalized clearance and central volume were similar in both phases (6.18 ± 1.48 L/h/70 kg early vs. 6.10 ± 1.61 L/h/70 kg late, p = 0.60; 26.6 [IQR 22.3, 31.3] L/70 kg early vs. 24.5 [IQR 22.0, 29.4] L/70 kg late, p = 0.18). Individual percent differences in normalized clearance and central volume between sepsis phases ranged from -39% to 276% and -51% to 212% (reference, late sepsis), respectively. Fewer patients attained the 1× MIC target in late sepsis (82% late vs. 96% early, p = 0.013), which was associated with transition to once daily dosing, typically done due to transfer from the pediatric intensive care unit (PICU) to a lower acuity unit. Failure to attain either target in late sepsis was associated with antibiotic broadening.

CONCLUSION

Ceftriaxone PK parameters were similar between early and late sepsis, but there were large individual differences. Fewer patients attained MIC targets in late sepsis and all who did not attain the less stringent target received once daily dosing during this period. The failure to attain targets in late sepsis was associated with antibiotic broadening and could be an area for antibiotic stewardship intervention.

Comparison of the pharmacokinetics of continuous and intermittent infusions of ampicillin-sulbactam in dogs with septic peritonitis

OBJECTIVE

To evaluate the time-course of ampicillin-sulbactam and percentage of time that its concentration is above a given MIC (T% > MIC) in dogs with septic peritonitis when delivered as either a continuous infusion (CI) or intermittent infusion (II).

ANIMALS

11 dogs with septic peritonitis.

PROCEDURES

Dogs were randomized to receive ampicillin-sulbactam as either CI or II. Continuous infusions were delivered as a 50 mg/kg bolus IV followed by a rate of 0.1 mg/kg/min. Intermittent infusions were administered as 50 mg/kg IV q8h. Serum ampicillin-sulbactam concentrations were measured at hours 0, 1, 6, and every 12 hours after until patients were transitioned to an oral antimicrobial equivalent. All other care was at the discretion of the attending clinician. Statistical analysis was used to determine each patient's percentage of time T% > MIC for 4 MIC breakpoints (0.25, 1.25, 8, and 16 µg/mL).

RESULTS

No dogs experienced adverse events related to ampicillin-sulbactam administration. Both CI and II maintained a T% > MIC of 100% of MIC 0.25 µg/mL and MIC 1.25 µg/mL. The CI group maintained a higher T% > MIC for MIC 8 µg/mL and MIC 16 µg/mL; however, these differences did not reach statistical significance (P = .15 and P = .12, respectively).

CLINICAL RELEVANCE

This study could not demonstrate that ampicillin-sulbactam CI maintains a greater T% > MIC in dogs with septic peritonitis than II; however, marginal differences were noted at higher antimicrobial breakpoints. While these data support the use of antimicrobial CI in septic and critically ill patients, additional prospective trials are needed to fully define the optimal doses and the associated clinical responses.

β-lactam precision dosing in critically ill children: Current state and knowledge gaps

There has been emerging interest in implementing therapeutic drug monitoring and model-informed precision dosing of β-lactam antibiotics in critically ill patients, including children. Despite a position paper endorsed by multiple international societies that support these efforts in critically ill adults, implementation of β-lactam precision dosing has not been widely adopted. In this review, we highlight what is known about β-lactam antibiotic pharmacokinetics and pharmacodynamics in critically ill children. We also define the knowledge gaps that present barriers to acceptance and implementation of precision dosing of β-lactam antibiotics in critically ill children: a lack of consensus on which subpopulations would benefit most from precision dosing and the uncertainty of how precision dosing changes outcomes. We conclude with opportunities for further research to close these knowledge gaps.

The OBTAINS study: A nationwide cross-sectional survey on the implementation of extended or continuous infusion of β-lactams and vancomycin among neonatal sepsis patients in China

Background: Dosing strategies of β-lactams and vancomycin should be optimized according to pharmacokinetic/pharmacodynamic principles. However, there is no available data indicating the implementation of extended infusion (EI) or continuous infusion (CI) administration in the management of neonatal sepsis. Methods: A nationwide cross-sectional survey was conducted and the pediatricians from 31 provinces in China were enrolled. A multidisciplinary team created the questionnaire, which had three sections and a total of 21 questions with open- and closed-ended responses. The survey was then conducted using an internet platform in an anonymous way. The data was eventually gathered, compiled, and examined. To identify the risk factors associated with the implementation of EI/CI, logistic regression was carried out. Results: A total of 1501 respondents answered the questionnaires. The implementation of EI/CI of β-lactams and vancomycin were only available to one-third of the respondents, and the prolonged strategy was primarily supported by guidelines (71.25%) and advice from medical specialists (55.18%). A significant fraction (72.94%-94.71%) lacked a strong understanding of the infusions' stability. Additionally, it was discovered that more frequent MDT discussions about antibiotic use and the appropriate time pediatricians worked in the neonatal ward were associated with an increase in the use of the EI/CI strategy. Conclusion: The EI/CI strategy in neonatal sepsis was not well recognized in China, and it is necessary to establish a solid MDT team with regularly collaborates. In the near future, guidelines regarding prolonged infusion management in neonatal sepsis should be developed.

Antimicrobial Therapy in Pediatric Sepsis: What Is the Best Strategy?

Pediatric sepsis is a relevant cause of morbidity and mortality in this age group. Children are affected differently in high and low-income countries. Antibiotics are crucial for the treatment of sepsis, but indiscriminate use can increase resistance worldwide. The choice of a correct empiric therapy takes into consideration the site of infection, local epidemiology, host comorbidities and recent antibiotic exposure. Antibiotics should be administered in the first hour for patients with septic shock, and always intravenously or via intraosseous access. Culture results and clinical improvement will guide de-escalation and length of treatment. New diagnostic methods can help improve the prescription of adequate treatment. Prevention of sepsis includes vaccination and prevention of healthcare-associated infections. More research and education for awareness of sepsis is needed to improve care.

Beta-Lactams Therapeutic Monitoring in Septic Children-What Target Are We Aiming for? A Scoping Review

The antimicrobial therapy of sepsis and septic shock should be individualized based on pharmacokinetic/pharmacodynamic (PK/PD) parameters to deliver effective and timely treatment of life-threatening infections. We conducted a literature scoping review to identify therapeutic targets of beta-lactam antibiotics in septic pediatric patients and the strategies that have been applied to overcome sepsis-related altered pharmacokinetics and increase target attainment against susceptible pathogens. A systematic search was conducted in the MEDLINE, EMBASE and Web of Science databases to select studies conducted since 2010 with therapeutic monitoring data of beta-lactams in septic children. Last searches were performed on 02 September 2021. Two independent authors selected the studies and extracted the data. A narrative and qualitative approach was used to summarize the findings. Out of the 118 identified articles, 21 met the eligibility criteria. Population pharmacokinetic modeling was performed in 12 studies, while nine studies reported data from bedside monitoring of beta-lactams. Most studies were conducted in the United States of America (n = 9) and France (n = 5) and reported PK/PD data of amoxicillin, ampicillin, azlocillin, aztreonam, cefazolin, cefepime, cefotaxime, ceftaroline, ceftazidime, doripenem, meropenem and piperacillin/tazobactam. Therapeutic targets ranged from to 40% fT> MIC to 100% fT> 6 × MIC. Prolonging the infusion time and frequency were most described strategies to increase target attainment. Monitoring beta-lactam serum concentrations in clinical practice may potentially maximize therapeutic target attainment. Further studies are required to define the therapeutic target associated with the best clinical outcomes.

Optimizing Antimicrobial Drug Dosing in Critically Ill Patients

A fundamental step in the successful management of sepsis and septic shock is early empiric antimicrobial therapy. However, for this to be effective, several decisions must be addressed simultaneously: (1) antimicrobial choices should be adequate, covering the most probable pathogens; (2) they should be administered in the appropriate dose, (3) by the correct route, and (4) using the correct mode of administration to achieve successful concentration at the infection site. In critically ill patients, antimicrobial dosing is a common challenge and a frequent source of errors, since these patients present deranged pharmacokinetics, namely increased volume of distribution and altered drug clearance, which either increased or decreased. Moreover, the clinical condition of these patients changes markedly over time, either improving or deteriorating. The consequent impact on drug pharmacokinetics further complicates the selection of correct drug schedules and dosing during the course of therapy. In recent years, the knowledge of pharmacokinetics and pharmacodynamics, drug dosing, therapeutic drug monitoring, and antimicrobial resistance in the critically ill patients has greatly improved, fostering strategies to optimize therapeutic efficacy and to reduce toxicity and adverse events. Nonetheless, delivering adequate and appropriate antimicrobial therapy is still a challenge, since pathogen resistance continues to rise, and new therapeutic agents remain scarce. We aim to review the available literature to assess the challenges, impact, and tools to optimize individualization of antimicrobial dosing to maximize exposure and effectiveness in critically ill patients.

Quantification of Ceftaroline in Human Plasma Using High-Performance Liquid Chromatography with Ultraviolet Detection: Application to Pharmacokinetic Studies

This study was conducted to develop a rapid, simple and reproducible method for the quantification of ceftaroline in plasma samples by high-performance liquid chromatography with ultraviolet detection (HPLC-UV). Sample processing consisted of methanol precipitation and then, after centrifugation, the supernatant was injected into the HPLC system, working in isocratic mode. Ceftaroline was detected at 238 nm at a short acquisition time (less than 5 min). The calibration curve was linear over the concentration range from 0.25 to 40 µg/mL, and the method appeared to be selective, precise and accurate. Ceftaroline in plasma samples was stable at -80 °C for at least 3 months. The method was successfully applied to characterize the pharmacokinetic profile of ceftaroline in two critically ill patients and to evaluate whether the pharmacokinetic/pharmacodynamic (PK/PD) target was reached or not with the dose regimen administered.

The Role of PK/PD Analysis in the Development and Evaluation of Antimicrobials

Pharmacokinetic/pharmacodynamic (PK/PD) analysis has proved to be very useful to establish rational dosage regimens of antimicrobial agents in human and veterinary medicine. Actually, PK/PD studies are included in the European Medicines Agency (EMA) guidelines for the evaluation of medicinal products. The PK/PD approach implies the use of in vitro, ex vivo, and in vivo models, as well as mathematical models to describe the relationship between the kinetics and the dynamic to determine the optimal dosing regimens of antimicrobials, but also to establish susceptibility breakpoints, and prevention of resistance. The final goal is to optimize therapy in order to maximize efficacy and minimize side effects and emergence of resistance. In this review, we revise the PK/PD principles and the models to investigate the relationship between the PK and the PD of antibiotics. Additionally, we highlight the outstanding role of the PK/PD analysis at different levels, from the development and evaluation of new antibiotics to the optimization of the dosage regimens of currently available drugs, both for human and animal use.

Population Pharmacokinetics and Outcomes of Critically Ill Pediatric Patients Treated with Intravenous Colistin at Higher Than Recommended Doses

Limited pharmacokinetic (PK) data suggest that currently recommended pediatric dosages of colistimethate sodium (CMS) by the Food and Drug Administration and European Medicines Agency may lead to suboptimal exposure, resulting in plasma colistin concentrations that are frequently <2 mg/liter. We conducted a population PK study in 17 critically ill patients 3 months to 13.75 years (median, 3.3 years) old who received CMS for infections caused by carbapenem-resistant Gram-negative bacteria. CMS was dosed at 200,000 IU/kg/day (6.6 mg colistin base activity [CBA]/kg/day; 6 patients), 300,000 IU/kg/day (9.9 mg CBA/kg/day; 10 patients), and 350,000 IU/kg/day (11.6 mg CBA/kg/day; 1 patient). Plasma colistin concentrations were determined using ultraperformance liquid chromatography combined with electrospray ionization-tandem mass spectrometry. Colistin PK was described by a one-compartment disposition model, including creatinine clearance, body weight, and the presence or absence of systemic inflammatory response syndrome (SIRS) as covariates (P < 0.05 for each). The average colistin plasma steady-state concentration (C_ss,avg) ranged from 1.11 to 8.47 mg/liter (median, 2.92 mg/liter). Ten patients had C_ss,avg of ≥2 mg/liter. The presence of SIRS was associated with decreased apparent clearance of colistin (47.8% of that without SIRS). The relationship between the number of milligrams of CBA per day needed to achieve each 1 mg/liter of plasma colistin C_ss,avg and creatinine clearance (in milliliters per minute) was described by linear regression with different slopes for patients with and without SIRS. Nephrotoxicity, probably unrelated to colistin, was observed in one patient. In conclusion, administration of CMS at the above doses improved exposure and was well tolerated. Apparent clearance of colistin was influenced by creatinine clearance and the presence or absence of SIRS.

New β-Lactam-β-Lactamase Inhibitor Combinations

The limited armamentarium against drug-resistant Gram-negative bacilli has led to the development of several novel β-lactam-β-lactamase inhibitor combinations (BLBLIs). In this review, we summarize their spectrum of in vitro activities, mechanisms of resistance, and pharmacokinetic-pharmacodynamic (PK-PD) characteristics. A summary of available clinical data is provided per drug. Four approved BLBLIs are discussed in detail. All are options for treating multidrug-resistant (MDR) Enterobacterales and Pseudomonas aeruginosa Ceftazidime-avibactam is a potential drug for treating Enterobacterales producing extended-spectrum β-lactamase (ESBL), Klebsiella pneumoniae carbapenemase (KPC), AmpC, and some class D β-lactamases (OXA-48) in addition to carbapenem-resistant Pseudomonas aeruginosa Ceftolozane-tazobactam is a treatment option mainly for carbapenem-resistant P. aeruginosa (non-carbapenemase producing), with some activity against ESBL-producing Enterobacterales Meropenem-vaborbactam has emerged as treatment option for Enterobacterales producing ESBL, KPC, or AmpC, with similar activity as meropenem against P. aeruginosa Imipenem-relebactam has documented activity against Enterobacterales producing ESBL, KPC, and AmpC, with the combination having some additional activity against P. aeruginosa relative to imipenem. None of these drugs present in vitro activity against Enterobacterales or P. aeruginosa producing metallo-β-lactamase (MBL) or against carbapenemase-producing Acinetobacter baumannii Clinical data regarding the use of these drugs to treat MDR bacteria are limited and rely mostly on nonrandomized studies. An overview on eight BLBLIs in development is also provided. These drugs provide various levels of in vitro coverage of carbapenem-resistant Enterobacterales, with several drugs presenting in vitro activity against MBLs (cefepime-zidebactam, aztreonam-avibactam, meropenem-nacubactam, and cefepime-taniborbactam). Among these drugs, some also present in vitro activity against carbapenem-resistant P. aeruginosa (cefepime-zidebactam and cefepime-taniborbactam) and A. baumannii (cefepime-zidebactam and sulbactam-durlobactam).