Antimicrobial Resistance: Pharmacokinetics‐Pharmacodynamics of Antimicrobial Therapy: It’s Not Just for Mice Anymore

Surgical Antibiotic Prophylaxis Dosing in Adult Patients with Obesity: A Comprehensive Review of Pharmacokinetic and Pharmacodynamic Data

Surgical antibiotic prophylaxis is an important measure to prevent postoperative surgical site infections. Current guideline recommendations do not treat obesity specifically, although it can affect pharmacokinetics and pharmacodynamics. The objective of this review was to synthesize current evidence on the need for obesity-related dosing adjustments in surgical antibiotic prophylaxis. MEDLINE and Cochrane Library were searched for studies investigating antibiotic prophylaxis dosing in surgical patients with obesity. Outcomes of interest were pharmacokinetic parameters such as plasma and interstitial fluid concentrations, area under the concentration time curve in plasma and in interstitial fluid, and other pharmacokinetic measures. Thirty studies investigating cefazolin, cefoxitin, cefuroxime, piperacillin/tazobactam, meropenem, ertapenem, metronidazole, vancomycin, ciprofloxacin, and gentamicin were included in this analysis. Except for metronidazole, cefoxitin, and gentamicin, there is currently no evidence suggesting the need for dosing adjustments.

Population Pharmacokinetics of Meropenem Across the Adult Lifespan

BACKGROUND AND OBJECTIVE

We conducted an opportunistic pharmacokinetic study to evaluate the population pharmacokinetics of meropenem, an antimicrobial commonly used to treat Gram-negative infections in adults of different ages, including older adults, and determined optimal dosing regimens.

METHODS

A total of 99 patients were included. The population pharmacokinetic models used had two compartments: zero-order input and linear elimination. Covariates evaluated included renal function, body size, age, sex, vasopressor use, and frailty, using the Canadian Study of Health and Aging Clinical Frailty score (in patients aged ≥ 65 years). We simulated optimal dosing regimens by renal function and by age group to achieve therapeutic target attainment.

RESULTS

Participants' ages ranged from 20 to 95 years, with an average age of 57.4 years, and 22% (23/103) were aged ≥ 75 years. Creatinine clearance had the greatest impact on the clearance of meropenem. After accounting for renal function and body size, no other covariates resulted in a significant impact on the pharmacokinetics of meropenem. Simulations indicated that patients with normal renal function achieved ≥ 90% target attainment only for organisms with minimum inhibitory concentrations (MICs) ≤ 4 mg/L using the least strict surrogate target of unbound concentration > MIC (fT>MIC) for 40% of the dosing interval. For the conservative target fT>4xMIC for 100% of the dosing interval, extended infusion may be required even for organisms with MICs up to 0.25 mg/L. Patients with renal impairment could achieve ≥ 90% target attainment for more resistant organisms, but extended infusion did not increase the MICs up to which target attainment could be achieved.

CONCLUSIONS

Meropenem dosing should be based on renal function rather than age. For patients without renal impairment, extended infusion may increase the probability of target attainment.

Therapeutic alternatives for sporotrichosis induced by wild-type and non-wild-type Sporothrix schenckii through in vitro and in vivo assessment of enilconazole, isavuconazole, posaconazole, and terbinafine

This study explores the effectiveness of various antifungal drugs in treating sporotrichosis caused by Sporothrix schenckii, especially in non-wild-type (non-WT) strains. The drugs tested include enilconazole (ENIL), isavuconazole (ISA), posaconazole (POS), terbinafine (TER), and itraconazole (ITC). The study involved in vitro and in vivo tests on 10 WT isolates and eight ITC non-WT isolates. Two isolates were assessed using time-kill assays, checkerboard assays, and Galleria mellonella infection models. In vitro studies have shown that all of these drugs were more effective than or equal to ITC against WT and non-WT isolates. No ITC resistance was observed with other azoles. All drugs inhibited fungal growth of WT and non-WT strains within 24 h at all incubations. ENIL and TER showed fungicidal effect against types at over 2x minimum inhibitory concentrations with no regrowth. POS was fungicidal against WT at high concentrations but not against non-WT. ISA was only fungicidal for non-WT. ITC did not exhibit any fungicidal activity. In checkerboard experiments, the combination of POS or ISA with TER showed enhanced activity against WT and non-WT strains, surpassing the combination of ITC with TER. In vivo model experiments demonstrated significantly reduced mortality rates with ENIL, POS, and TER against WT and with ENIL, ISA, POS, and TER against non-WT. The study concludes that monotherapy with ENIL, ISA, POS, and TER, and combinations of POS/TER or ISA/TER, show promise as effective antifungal treatments against S. schenckii, including ITC-non-WT isolates.

Bactericidal versus bacteriostatic antibacterials: clinical significance, differences and synergistic potential in clinical practice

Antibacterial activity can be classified as either bactericidal or bacteriostatic, using methods such as the MBC/MIC ratio and time-kill curves. However, such categorization has proven challenging in clinical practice, as these definitions only apply under specific laboratory conditions, which may differ from clinical settings. Several factors, such as the specific bacteria or infectious medium, can affect the action of antibiotics, with many antibacterials exerting both activities. These definitions have also led to the belief that bactericidal antibacterials are superior to bacteriostatic, especially in more severe cases, such as endocarditis, neutropenia and bacteraemia. Additionally, current dogma dictates against the combination of bactericidal and bacteriostatic antibacterials in clinical practice, due to potential antagonism. This review aimed to assess the differences in antibacterial activity of bactericidal and bacteriostatic antibacterials based on in vitro and in vivo studies and examine their antagonistic or synergistic effects. Our findings show that specific bacteriostatic agents, such as linezolid and tigecycline, are clinically non-inferior to bactericidals in multiple infections, including pneumonia, intra-abdominal infections, and skin and soft tissue infections. Studies also support using several bacteriostatic agents as salvage therapies in severe infections, such as neutropenic fever and endocarditis. Additionally, not all combinations of bacteriostatic and bactericidal agents appear to be antagonistic, with many combinations, such as linezolid and rifampicin, already being used. The findings should be interpreted with caution, as most evidence is from observational studies and there is a need for randomized controlled trials to assess their effectiveness and combinations, especially within the context of rising antimicrobial resistance.

Errors Associated With Medication Administration by a Nurse During Hospitalisation: A Prospective Observational Multicentric Study

AIMS

To explore all medication administration errors (MAEs) throughout the entire process of medication administration by nurses in the inpatient setting, to describe their prevalence, and to analyse associated factors, including deviation from the good practice standards.

BACKGROUND

Worldwide, MAEs are very common and regarded as a serious risk factor to inpatient safety. Nurses assume an essential role in the hospital setting during the administration of medications.

DESIGN

The prospective observational study was carried out in accordance with the STROBE guidance.

METHODS

This study was conducted in four regional hospitals from June to August 2021. MAEs were collected when nurses administered medications to the adult inpatients during the morning, noon, and evening medication rounds at the internal, surgical, and follow-up care departments in each hospital over three consecutive days. Direct observation by the multidisciplinary team was employed. MAEs were classified as major MAEs (from the potentially most serious and common to all drug forms), specific MAEs (specific to a drug form), and procedural MAEs (e.g., patient identification, hygiene standards, or generic drug substitution). Predictors of either major MAE or specific MAE frequency were analysed using the generalised linear model and the decision tree model.

RESULTS

Overall, 58 nurses administering medication to 331 inpatients at 12 departments were observed. In total, 6356 medication administrations were observed, of which 461 comprised major MAEs, 1497 specific MAEs, and 12,045 procedural MAEs. The predictors of the occurrence of major MAEs and specific MAEs were the specific hospital, the nurse's length of practice (less than 2 years), and two procedural MAEs (the unclear prescription and the wrong strength).

CONCLUSIONS

Non-adherence to the standard processes in healthcare facilities for prescribing and administering drugs increased the prevalence of severe MAEs. Determinants of MAE occurrence such as incorrect prescriptions or limited experience of nurses should be considered.

IMPLICATION FOR THE PROFESSION AND PATIENT CARE

The identified determinants of MAE should be considered by hospital stakeholders in their support programs to reduce the level of burden for nurses during medication administration.

PATIENT OR PUBLIC CONTRIBUTION

Neither patients nor public was not involved in the design, data collection, or dissemination plans of this study. The researchers observed nurse care delivery at medical departments acting as passive participants.

Imipenem pharmacokinetics/pharmacodynamics in preclinical hollow fiber model, dose-finding in virtual patients, and clinical evidence of efficacy for Mycobacterium abscessus lung disease

BACKGROUND

Guideline-based therapy (GBT) for Mycobacterium abscessus (Mab) lung disease achieves sputum culture conversion rates (SCC) of 35%. This poor GBT efficacy is mirrored in the hollow fiber system model of Mab (HFS-Mab). While imipenem is part of GBT, biological effect with or without β-lactamase inhibitors, is unproven.

METHODS

We performed imipenem/relebactam minimum inhibitory concentration (MIC) in 122 Mab isolates, and an exposure-response study in the HFS-Mab using human intrapulmonary pharmacokinetics. The % time that concentration persisted above MIC (TMIC) mediating maximal effect in the HFS-Mab was used as the exposure target in 10,000 virtual subjects Monte Carlo experiment (MCE)-based dose-finding. For real-world evidence, we performed a patient, intervention (imipenem), comparison (no β-lactam), and outcome (SCC) (PICO) analysis.

RESULTS

Imipenem killed 1.32 log10 CFU/mL below day 0 in HFS-Mab. Imipenem target exposure was TMIC=47.9±9.77%. 1g infusion, every 6h, achieved the target in >90% of virtual patients in MCEs. The pharmacokinetics/pharmacodynamics MIC breakpoint was 1mg/L. In PICO analyses, median days-to-SCC were 470 in comparators, 311 for imipenem added on failing regimen, and 37 in newly treated (p=0.049). The odds ratio for SCC when imipenem was part of the initial regimen versus comparators was 12.5 (95% confidence interval: 1.47 to 84.55). Patients on imipenem experienced no treatment-limiting adverse event, while 2/7 comparators did (p=0.0457). Middlebrook 7H9 broth MIC distribution, read at 24 hours, correlated better with patient responses than cation-adjusted Mueller Hinton broth.

CONCLUSION

Imipenem demonstrated biologic effect in the HFS-Mab and in patients. Imipenem/relebactam doses of 1g every 6h are recommended.

Effective, but Safe? Physiologically Based Pharmacokinetic (PBPK)-Modeling-Based Dosing Study of Molnupiravir for Risk Assessment in Pediatric Subpopulations

Despite the end of COVID-19 pandemic, only intravenous remdesivir was approved for treatment of vulnerable pediatric populations. Molnupiravir is effective against viruses beyond SARS-CoV-2 and is orally administrable without CYP-interaction liabilities but has a burden of potential bone or cartilage toxicity, observed at doses exceeding 500 mg/kg/day in rats. Especially, activity of molnupiravir against viruses, such as Ebola, with high fatality rates and no treatment option warrants the exploration of potentially effective but safe doses for pediatric populations, i.e., neonates (0-27 days), infants (1-12 months), and children in early childhood (1-12 years). The bone and cartilage toxicity risk for these populations based on the preclinical results has not been systematically investigated yet. Using physiologically based pharmacokinetic (PBPK) modeling, we developed adult PBPK models for doses ranging from 50 to 1200 mg with minimal parameter optimization because of incorporation of CES1, a carboxylesterase. Therein, CES1 served as the main driver for conversion of molnupiravir to its active metabolite β-d-N4-hydroxycytidine (NHC). By incorporation of the ontogeny of CES1 for pediatric populations, we successfully developed PBPK models for different doses ranging from 10 to 75 mg/kg. For molnupiravir, efficacy is driven by the area under the curve (AUC). To achieve a similar AUC to that seen in adults, a dose of around 28 mg/kg BID was necessary in all three investigated pediatric subpopulations. This dose exceeded the safe dose observed in dogs and was slightly below the toxicity-associated human equivalent dose in rats. In summary, the pediatric PBPK models suggested that an efficacious dose posed a toxicity risk. These data confirmed the contraindication for children <18 years.

Determination of pharmacokinetic-pharmacodynamic cutoff values of oxytetracycline in calves and adult cattle using population pharmacokinetic modeling

Introduction

A harmonized clinical breakpoint for interpreting antimicrobial susceptibility testing of oxytetracycline in cattle is currently lacking in Europe. This study aimed to establish a pharmacokinetic/pharmacodynamic (PK/PD) cutoff to propose clinical breakpoints, facilitating reliable interpretation of antimicrobial susceptibility results in cattle.

Methods

A meta-analysis of oxytetracycline pharmacokinetic data from 69 cattle was conducted, including 1,730 plasma concentration samples from animals administered 20 mg/kg intramuscularly and/or 20 or 40 mg/kg intravenously. A three-compartment model with two absorption phases was selected, incorporating age as a covariate for clearances and distribution volumes. The PK/PD cutoff was defined as the maximum MIC for which the fAUC/MIC index achieves the pharmacodynamic target in 90% of cattle given the standard dosing regimen. The pharmacodynamic index (PDI) target selected was established to 24 h, i.e., the average free plasma concentration of oxytetracycline over the 24-h dosing interval, under steady-state conditions, is equal to the selected MIC.

Results

Simulations indicated a PK/PD cutoff of 2 mg/L in adult cattle and 1 mg/L in calves for intramuscularly administered long-acting products at 20 mg/kg with a 48-hour efficacy duration. The difference is attributed to higher clearance rates in calves.

Discussion

The established PK/PD cutoffs, when used alongside the wild-type bacterial epidemiological cutoff, can aid in setting clinical breakpoints for oxytetracycline, supporting effective antimicrobial therapy in cattle and accounting for age-related pharmacokinetic differences.

Model-informed precision dosing: State of the art and future perspectives

Model-informed precision dosing (MIPD) stands as a significant development in personalized medicine to tailor drug dosing to individual patient characteristics. MIPD moves beyond traditional therapeutic drug monitoring (TDM) by integrating mathematical predictions of dosing and considering patient-specific factors (patient characteristics, drug measurements) as well as different sources of variability. For this purpose, rigorous model qualification is required for the application of MIPD in patients. This review delves into new methods in model selection and validation, also highlighting the role of machine learning in improving MIPD, the utilization of biosensors for real-time monitoring, as well as the potential of models integrating biomarkers for efficacy or toxicity for precision dosing. The clinical evidence of TDM and MIPD is discussed for various medical fields including infection medicine, oncology, transplant medicine, and inflammatory bowel diseases, thereby underscoring the role of pharmacokinetics/pharmacodynamics and specific biomarkers. Further research, particularly randomized clinical trials, is warranted to corroborate the value of MIPD in enhancing patient outcomes and advancing personalized medicine.

Preclinical and clinical studies in the drug development process of European Medicines Agency-approved non-HIV antiviral agents: a narrative review

BACKGROUND

Viral diseases represent a substantial global health challenge, necessitating the urgent development of effective antiviral medications.

OBJECTIVES

This review aims to present a thorough examination of systemic antiviral drugs approved by the European Medicines Agency (EMA) since its founding, excluding those targeting HIV, with a focus on preclinical and clinical studies in the drug development process.

SOURCES

Data was extracted from the European Public Assessment Reports and Summary of Product Characteristics issued by the EMA.

CONTENT

In total, 21 currently approved agents were analysed with a focus on preclinical and clinical studies. The majority of substances have been approved for hepatitis C (38%) and B (19%) followed by influenza and SARS-CoV-2 (14% and 10%, respectively). A smaller subset obtained approval for the indications of hepatitis D, cytomegalovirus, and pox viruses. As for preclinical studies, heterogeneity in the methods used for efficacy studies was observed, which is at least partly explained by the diverse nature of viruses and their hosts and the lack of general guidelines for antiviral pharmacokinetics and pharmacodynamics studies by the EMA. Clinical studies varied in sample sizes, ranging from a few hundred to several thousand patients. Many antiviral agents have a high potential for cytochrome P450 (CYP) and other enzyme interactions, resulting in the need for a high number of drug-drug interaction studies. Special market authorizations are available, including conditional approval for urgently required drugs such as nirmatrelvir/ritonavir for the treatment of COVID-19, and authorization under exceptional circumstances when comprehensive data cannot be provided, as seen with tecovirimat for pox viruses.

IMPLICATIONS

Streamlining the drug development process of antiviral substances and providing more guidelines would be crucial given the ongoing demand for effective treatment options for existing and new viral diseases.

Antibiotic dose optimisation in the critically ill: targets, evidence and future strategies

PURPOSE OF REVIEW

To highlight the recent evidence for antibiotic pharmacokinetics and pharmacodynamics (PK/PD) in enhancing patient outcomes in sepsis and septic shock. We also summarise the limitations of available data and describe future directions for research to support translation of antibiotic dose optimisation to the clinical setting.

RECENT FINDINGS

Sepsis and septic shock are associated with poor outcomes and require antibiotic dose optimisation, mostly due to significantly altered pharmacokinetics. Many studies, including some randomised controlled trials have been conducted to measure the clinical outcome effects of antibiotic dose optimisation interventions including use of therapeutic drug monitoring. Current data support antibiotic dose optimisation for the critically ill. Further investigation is required to evolve more timely and robust precision antibiotic dose optimisation approaches, and to clearly quantify whether any clinical and health-economic benefits support expanded use of this treatment intervention.

SUMMARY

Antibiotic dose optimisation appears to improve outcomes in critically ill patients with sepsis and septic shock, however further research is required to quantify the level of benefit and develop a stronger knowledge of the role of new technologies to facilitate optimised dosing.

Pharmacokinetics of ceftiofur crystalline-free acid in plasma and seminal plasma in beef bulls

The objective of this study was to compare the plasma (PL) and seminal plasma (SP) pharmacokinetic profile of ceftiofur (CEFT) and desuroylceftiofur acetamide (DFCA) after administration of CEFT crystalline-free acid (CCFA) by SC route in two sites of the ear in beef bulls. Four clinically healthy Hereford bulls received a comprehensive physical exam and subsequently a breeding-soundness examination, CBC, and chemistry profile panel. All bulls were diagnosed healthy and satisfactory potential breeders. In one group (n = 2), a single dose of CCFA was administered SC route at the base of the ear (BOE) at a dose of 6.6 mg/kg of body weight. The second group (n = 2) was also administered by SC route in the middle third of the posterior aspect of the ear (MTE). The concentrations of CEFT and DFCA in PL and SP were determined by a high-performance liquid chromatography mass spectrometry (HPLC-MS). Blood and semen samples were collected before the administration of CCFA and at 12, 24, 36, 48, 72, 96, 120, 144, and 168 h after injection. No levels of CEFT were detected in PL and only in 20 of the 40 SP samples (P = 0.0001). The mean level of CEFT in SP was 0.11 % in comparison with the DFCA level. DFCA was found in all PL and SP samples. Therefore, DFCA was chosen to be utilized in the study of the pharmacokinetics parameters both in PL and SP. There were no differences in the mean PL levels of DFCA for the two sites of SC administration between the BOE (102.9 ± 78.9 ng/mL; X ± SD) and to MTE (116.1 ± 70.2 ng/mL; P = 0.58). The mean SP levels of DFCA after administration in the BOE was 857 ± 747 ng/mL, and for the MTE was 549 ± 488 ng/mL without differences between both sites (P = 0.15). The mean level of DFCA in PL was 109.5 ± 74.0 ng/mL, which was lower than the mean SP levels of 695 ± 103 ng/mL (P = 0.001). Moreover, the PL peak DFCA concentration (Cmax) was 229 ± 46 ng/mL at 36.0 ± 29.4 h (Tmax) post-administration. The SP Cmax was 1851 ± 533 ng/mL at 30.0 ± 28.6 h (Tmax) post-administration. The Cmax between PL and SP were distinctive (P = 0.004) without any differences in Tmax between PL and SP (P = 0.60). The terminal half-life for PL DFCA (47.4 ± 29.3 h) was not different than in SP (53.1 ± 23.6 h; P = 0.77). The PL area under the curve concentration time from the first to the last sample (AUC0-last) was 18,984 ± 4841 ng/mL/h, which was significatively smaller compared with 125,677 ± 59,445 ng/mL/h for SP AUC0-last (P = 0.04). The PL mean residence time from the first to the last sample (MRT0-last) was 69.7 ± 15.1 h, and it was similar than for SP of 66.5 ± 7.7 h (P = 0.69). From the present investigation, based in its pharmacokinetic features, it was concluded that CCFA should be an appropriate antibiotic that could be used for the treatment of bull genital infections when its indication is properly outlined. To study the pharmacokinetics of CCFA in SP, DFCA metabolite was appropriated.

Assessment of pharmacokinetics-pharmacodynamics to support omadacycline dosing regimens for the treatment of patients with acute bacterial skin and skin structure infections

Pharmacokinetic-pharmacodynamic (PK-PD) relationships for efficacy were evaluated using data from omadacycline-treated patients with acute bacterial skin and skin structure infections (ABSSSI) enrolled in two phase 3 studies. Patients received omadacycline 100 mg intravenously (IV) every 12 hours for two doses, followed by 100 mg IV every 24 hours (q24h), with the option to switch to 300 mg oral (PO) q24h after 3 days or 450 mg PO q24h for two doses, followed by 300 mg PO q24h for a total duration of 7-14 days. Clinical response was evaluated at 48-72 hours [early clinical response (ECR)], end of treatment (EOT), and 7-14 days after EOT. Using a population pharmacokinetic (PK) model and PK data from patients with Staphylococcus aureus at baseline, omadacycline free-drug plasma area under the concentration-time curve (AUC) values were determined, and the relationships between free-drug plasma AUC:MIC ratio and dichotomous efficacy endpoints were evaluated. Using these relationships, the population PK model, simulation, and an omadacycline MIC distribution for S. aureus, mean percent probabilities of response were evaluated. Statistically significant PK--PD relationships were identified for ECR (P = 0.016 and 0.013 for optimized two- and three-group free-drug plasma AUC:MIC ratios, respectively). At an MIC value of 0.5 µg/mL, percent probabilities of model-predicted success for ECR based on the univariable PK-PD relationships using continuous and two-group free-drug plasma AUC:MIC ratio variables were 91.9 and 95.6%, respectively, for the IV-to-PO dosing regimen and 89.3 and 88.4%, respectively, for the PO-only dosing regimen. These data support for omadacycline IV-to-PO and PO-only dosing regimens for ABSSSI and an omadacycline susceptibility breakpoint of 0.5 µg/mL for S. aureus.

Risk Factors Associated with Antibiotic Exposure Variability in Critically Ill Patients: A Systematic Review

(1) Background: Knowledge about the behavior of antibiotics in critically ill patients has been increasing in recent years. Some studies have concluded that a high percentage may be outside the therapeutic range. The most likely cause of this is the pharmacokinetic variability of critically ill patients, but it is not clear which factors have the greatest impact. The aim of this systematic review is to identify risk factors among critically ill patients that may exhibit significant pharmacokinetic alterations, compromising treatment efficacy and safety. (2) Methods: The search included the PubMed, Web of Science, and Embase databases. (3) Results: We identified 246 observational studies and ten clinical trials. The most studied risk factors in the literature were renal function, weight, age, sex, and renal replacement therapy. Risk factors with the greatest impact included renal function, weight, renal replacement therapy, age, protein or albumin levels, and APACHE or SAPS scores. (4) Conclusions: The review allows us to identify which critically ill patients are at a higher risk of not reaching therapeutic targets and helps us to recognize the extensive number of risk factors that have been studied, guiding their inclusion in future studies. It is essential to continue researching, especially in real clinical practice and with clinical outcomes.

The dynamics of Staphylococcal infection and their treatment with antibiotics and bacteriophage in the Galleria mellonella model system

Critical to our understanding of infections and their treatment is the role the innate immune system plays in controlling bacterial pathogens. Nevertheless, many in vivo systems are made or modified such that they do not have an innate immune response. Use of these systems denies the opportunity to examine the synergy between the immune system and antimicrobial agents. In this study we demonstrate that the larva of Galleria mellonella is an effective in vivo model for the study of the population and evolutionary biology of bacterial infections and their treatment. To do this we test three hypotheses concerning the role of the innate immune system during infection. We show: i) sufficiently high densities of bacteria are capable of saturating the innate immune system, ii) bacteriostatic drugs and bacteriophages are as effective as bactericidal antibiotics in preventing mortality and controlling bacterial densities, and iii) minority populations of bacteria resistant to a treating antibiotic will not ascend. Using a highly virulent strain of Staphylococcus aureus and a mathematical computer-simulation model, we further explore how the dynamics of the infection within the short term determine the ultimate infection outcome. We find that excess immune activation in response to high densities of bacteria leads to a strong but short-lived immune response which ultimately results in a high degree of mortality. Overall, our findings illustrate the utility of the G. mellonella model system in conjunction with established in vivo models in studying infectious disease progression and treatment.

Amoxicillin-Clavulanate Breakpoints Against Enterobacterales: Rationale for Revision by the Clinical and Laboratory Standards Institute

Amoxicillin-clavulanate (AMC) is among the most frequently prescribed antibiotics globally. It has broad antibacterial activity against gram-positive, gram-negative, and anaerobic bacteria and has been used to treat infections caused by a broad range of pathogens. AMC breakpoints against Enterobacterales were initially set in the 1980s. However, since that time, increases in antibiotic resistance, advances in pharmacokinetic/pharmacodynamic analyses, and publication of additional clinical data prompted a reassessment by the Clinical and Laboratory Standards Institute (CLSI) Subcommittee on Antimicrobial Susceptibility Testing. Based on this contemporary reappraisal, the CLSI retained the Enterobacterales breakpoints but revised comments regarding dosing associated with use of the AMC breakpoints in the 2022 supplement of M100. This viewpoint provides insight into the CLSI breakpoint reevaluation process and summarizes the data and rationale used to support these revisions to the AMC Enterobacterales breakpoint.

Ceftriaxone Efficacy for Mycobacterium avium Complex Lung Disease in the Hollow Fiber and Translation to Sustained Sputum Culture Conversion in Patients

BACKGROUND

Only 35.6%-50.8% of patients with Mycobacterium avium complex (MAC) pulmonary disease achieve sustained sputum culture conversion (SSCC) on treatment with the azithromycin-ethambutol-rifabutin standard of care (SOC). We tested the efficacy of ceftriaxone, a β-lactam with a lung-to-serum penetration ratio of 12.18-fold.

METHODS

We mimicked lung concentration-time profiles of 7 ceftriaxone once-daily doses for 28 days in the hollow fiber system model of intracellular MAC (HFS-MAC). Monte Carlo experiments were used for dose selection. We also compared once-daily ceftriaxone monotherapy to 3-drug SOC against 5 MAC clinical isolates in HFS-MAC using γ (kill) slopes, and translated to SSCC rates.

RESULTS

Ceftriaxone killed 1.02-3.82 log10 colony-forming units (CFU)/mL, at optimal dose of 2 g once-daily. Ceftriaxone killed all 5 strains below day 0 versus 2 of 5 for SOC. The median γ (95% confidence interval [CI]) was 0.49 (.47-.52) log10 CFU/mL/day for ceftriaxone and 0.38 (.34-.43) log10 CFU/mL/day for SOC. In patients, the SOC was predicted to achieve SSCC rates (CI) of 39.3% (36%-42%) at 6 months. The SOC SSCC was 50% at 8.18 (3.64-27.66) months versus 3.58 (2.20-7.23) months for ceftriaxone, shortening time to SSCC 2.35-fold.

CONCLUSIONS

Ceftriaxone is a promising agent for creation of short-course chemotherapy.

Can we do better with Mylotarg? Model-based assessment of opportunities to improve therapeutic index

Late-stage clinical trial failures increase the overall cost and risk of bringing new drugs to market. Determining the pharmacokinetic (PK) drivers of toxicity and efficacy in preclinical studies and early clinical trials supports quantitative optimization of drug schedule and dose through computational modeling. Additionally, this approach permits prioritization of lead candidates with better PK properties early in development. Mylotarg is an antibody-drug conjugate (ADC) that attained U.S. Food and Drug Administration (FDA) approval under a fractionated dosing schedule after 17 years of clinical trials, including a 10-year period on the market resulting in hundreds of fatal adverse events. Although ADCs are often considered lower risk for toxicity due to their targeted nature, off-target activity and liberated payload can still constrain dosing and drive clinical failure. Under its original schedule, Mylotarg was dosed infrequently at high levels, which is typical for ADCs because of their long half-lives. However, our PK modeling suggests that these regimens increase maximum plasma concentration (Cmax)-related toxicities while producing suboptimal exposures to the target receptor. Our analysis demonstrates that the benefits of dose fractionation for Mylotarg tolerability should have been obvious early in the drug's clinical development and could have curtailed the proliferation of ineffective Phase III studies. We also identify schedules likely to be even more efficacious without compromising on tolerability. Alternatively, a longer-circulating Mylotarg formulation could obviate the need for dose fractionation, allowing superior patient convenience. Early-stage PK optimization through quantitative modeling methods can accelerate clinical development and prevent late-stage failures.

Individualized, dynamic, and full-course vancomycin dosing prediction: a study on the customized dose model

Purpose

The single-point trough-based therapeutic drug monitoring (TDM) and Bayesian forecasting approaches are still limited in individualized and dynamic vancomycin delivery. Until recently, there has not yet been enough focus on the direct integration of pharmacokinetic/pharmacodynamic (PK/PD) and TDM to construct a customized dose model (CDM) for vancomycin to achieve individualized, dynamic, and full-course dose prediction from empirical to follow-up treatment. This study sought to establish CDM for vancomycin, test its performance and superiority in clinical efficacy prediction, formulate a CDM-driven full-course dosage prediction strategy to overcome the above challenge, and predict the empirical vancomycin dosages for six Staphylococci populations and four strains in patients with various creatinine clearance rates (CLcr).

Methods

The PK/PD and concentration models derived from our earlier research were used to establish CDM. The receiver operating characteristic (ROC) curve, with the area under ROC curve (AUCR) as the primary endpoint, for 21 retrospective cases was applied to test the performance and superiority of CDM in clinical efficacy prediction by comparison to the current frequently-used dose model (FDM). A model with an AUCR of at least 0.8 was considered acceptable. Based on the availability of TDM, the strategy of CDM-driven individualized, dynamic, and full-course dose prediction for vancomycin therapy was formulated. Based on the CDM, Monte Carlo simulation was used to predict the empirical vancomycin dosages for the target populations and bacteria.

Results

Four CDMs and the strategy of CDM-driven individualized, dynamic, and full-course dose prediction for vancomycin therapy from empirical to follow-up treatment were constructed. Compared with FDM, CDM showed a greater AUCR value (0.807 vs. 0.688) in clinical efficacy prediction. The empirical vancomycin dosages for six Staphylococci populations and four strains in patients with various CLcr were predicted.

Conclusion

CDM is a competitive individualized dose model. It compensates for the drawbacks of the existing TDM technology and Bayesian forecasting and offers a straightforward and useful supplemental approach for individualized and dynamic vancomycin delivery. Through mathematical modeling of the vancomycin dosage, this study achieved the goal of predicting doses individually, dynamically, and throughout, thus promoting "mathematical knowledge transfer and application" and also providing reference for quantitative and personalized research on similar drugs.

Development and Quality Control of a Population Pharmacokinetic Model Library for Caspofungin

BACKGROUND

Caspofungin is an echinocandin antifungal agent commonly used as the first-line therapy for invasive candidiasis, salvage therapy for invasive aspergillosis, and empirical therapy for presumed fungal infections. Pharmacokinetic (PK) variabilities and suboptimal exposure have been reported for caspofungin, increasing the risk of insufficient efficacy.

OBJECTIVE

This work aimed to develop a caspofungin population pharmacokinetic (popPK) library and demonstrate its utility by assessing the probability of target attainment across diverse settings.

METHODS

We established a caspofungin popPK model library following a rigorous literature review, re-implementing selected models in R with rxode2. Quality control procedures included a comparison of different studies and assessing covariate impacts. Model libraries were primarily used to perform Monte Carlo simulations to estimate target attainment and guide personalized dosing in Candida infections.

RESULTS

A total of 13 models, one- or two-compartment models, were included. The most significant covariates were body size (weight and body surface area), liver function, and albumin level. The results show that children and adults showed considerable differences in pharmacokinetics. For C. albicans and C. parapsilosis, none of the populations achieved a PTA of ≥90% at their respective susceptible MIC values. In contrast, for C. glabrata, 70% of the adult studies reached a PTA of ≥90%, while all pediatric studies achieved the same PTA level.

CONCLUSION

At the recommended dosage, adult patients showed notably lower exposure to caspofungin compared to pediatric patients. Considering body size, liver function, and serum albumin is crucial when determining caspofungin dosage regimens. Furthermore, further research is required to comprehensively understand the pharmacokinetics of caspofungin in pediatric patients.

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.

Predicted efficacy and tolerance of different dosage regimens of benzylpenicillin in horses based on a pharmacokinetic study with three IM formulations and one IV formulation

Introduction

Benzylpenicillin (BP) is a first-line antibiotic in horses but there are discrepancies between manufacturers and literature recommendations regarding dosing regimen. Objectives of this study were to evaluate pharmacokinetics and local tolerance of four different formulations of BP in adult horses, and to suggest optimized dosing regimen according to the formulation.

Methods

A cross-over design was used in 3 phases for the intramuscular injection of three different products: procaine BP alone, procaine BP/ benzathine BP combination or penethamate hydriodide were administered IM in the gluteal muscles of 6 horses for 3 days. Single IV administration of sodium BP was performed to the same horses with a dose of 22,000 IU BP/kg bwt 39 weeks after last IM injection. BP plasma concentrations were determined by UPLC assay coupled with mass spectrometry and a PK/PD analysis was conducted to predict the efficacy of various dosing regimens by estimating values of the fT>MIC index for different minimum inhibitory concentrations (MIC). Tolerance at the site of IM injection was monitored by creatine kinase activity quantified with a validated chemistry system and clinical scorings.

Results and discussion

Except one neurological reaction following one administration of penethamate hydriodide, the tolerance was good. Procaine BP alone, procaine BP/benzathine BP combination or penethamate hydriodide intramuscular administrations at a dosage of 22,000 IU BP/kg bwt q24h for 5 days would yield plasma concentrations that should be effective against bacteria with MIC of ≤0.256, 0.125 or 0.064 mg/L respectively. Of all the tested treatments, the use of a sodium BP by IV Constant Rate Infusion (CRI) for 10 hours a day was deemed to be the most efficient. All the formulations tested in this study are adequate to treat infections with susceptible Streptococcus equi.

Pharmacokinetics/pharmacodynamics cut-off determination for fosfomycin using Monte Carlo simulation in healthy horses

Fosfomycin (FOM) is an approved veterinary medicinal product for large animals in Japan, but Clinical breakpoint (CBP) for antimicrobial susceptibility test (AST) is not defined for animals. This study aimed at conducting a pharmacokinetics/pharmacodynamics (PK/PD) analysis to determine the PK/PD cutoff for the CBP in horses. Drug concentrations following single intravenous administration (IV) of 20 mg/kg body weight (BW) FOM in nine horses were measured using liquid chromatography/mass spectrometry. The data were modelled using a nonlinear mixed-effects model, followed by Monte Carlo simulations. A 90% probability of target attainment for a PK/PD target of the ratio of Area Under the free plasma concentration-time curve divided by the minimal inhibitory concentration (MIC) >24 hr was set as PK/PD cut-off. The PK/PD cutoff for FOM 20 mg/kg BW q12 hr IV was estimated with the MIC value of ≤16.0 mg/L, and this regimen was considered effective against E. coli (MIC90; 16.0 mg/L) in healthy horses based on the MIC90 values of the wild population. Owing to the relevance of FOM to human health, veterinarians should use q 12 hr FOM 20 mg /kg against E. coli infections with an MIC <16 µg/mL, as suggested by our PK/PD cutoff after AST.

Population pharmacokinetics and humanized dosage regimens matching the peak, area, trough, and range of amikacin plasma concentrations in immune-competent murine bloodstream and lung infection models

Amikacin is an FDA-approved aminoglycoside antibiotic that is commonly used. However, validated dosage regimens that achieve clinically relevant exposure profiles in mice are lacking. We aimed to design and validate humanized dosage regimens for amikacin in immune-competent murine bloodstream and lung infection models of Acinetobacter baumannii. Plasma and lung epithelial lining fluid (ELF) concentrations after single subcutaneous doses of 1.37, 13.7, and 137 mg/kg of body weight were simultaneously modeled via population pharmacokinetics. Then, humanized amikacin dosage regimens in mice were designed and prospectively validated to match the peak, area, trough, and range of plasma concentration profiles in critically ill patients (clinical dose: 25-30 mg/kg of body weight). The pharmacokinetics of amikacin were linear, with a clearance of 9.93 mL/h in both infection models after a single dose. However, the volume of distribution differed between models, resulting in an elimination half-life of 48 min for the bloodstream and 36 min for the lung model. The drug exposure in ELF was 72.7% compared to that in plasma. After multiple q6h dosing, clearance decreased by ~80% from the first (7.35 mL/h) to the last two dosing intervals (~1.50 mL/h) in the bloodstream model. Likewise, clearance decreased by 41% from 7.44 to 4.39 mL/h in the lung model. The humanized dosage regimens were 117 mg/kg of body weight/day in mice [administered in four fractions 6 h apart (q6h): 61.9%, 18.6%, 11.3%, and 8.21% of total dose] for the bloodstream and 96.7 mg/kg of body weight/day (given q6h as 65.1%, 16.9%, 10.5%, and 7.41%) for the lung model. These validated humanized dosage regimens and population pharmacokinetic models support translational studies with clinically relevant amikacin exposure profiles.

Investigation of clindamycin concentrations in human plasma and jawbone tissue in patients with osteonecrosis of the jaw: A prospective trial

The aim of this study was to investigate the jawbone concentration of clindamycin (CLI) in patients with an osteonecrosis of the jaw (ONJ). Patients with medication-related ONJ (MRONJ) and osteoradionecrosis (ORN) with an antibiotic treatment with CLI were included. Plasma, vital and necrotic bone samples were collected. Plasma and jawbone samples were analyzed by liquid chromatography-tandem mass spectrometry. Patients with MRONJ exhibited a mean plasma CLI concentration of 9.6 μg/mL (SD ± 3.6 μg/mL) and mean concentrations of 2.3 μg/g CLI (SD ± 1.4 μg/g) and 2.1 μg/g CLI (SD ± 2.4 μg/g) in vital and necrotic bone samples, without statistical significance (p = 0.79). In patients with ORN, mean concentration in plasma was 12.0 μg/mL (SD ± 2.6 μg/mL), in vital bone 2.1 μg/g (SD ± 1.5 μg/g), and in necrotic bone 1.7 μg/g (SD ± 1.2 μg/g). Vital and necrotic bone concentrations did not differ significantly (p = 0.88). The results demonstrate that CLI concentrations are considerably lower than in plasma, but sufficient for most bacteria present in ONJ. Within the limitations of the study, it seems that CLI is a relevant alternative to other antibiotics in the treatment of ONJ because it reaches adequate concentrations in jawbone.

Relationship between Target Time above Minimum Inhibitory Concentration Achievement Rate of Meropenem Using Monte Carlo Simulation and In-Hospital Survival in Patients with Pseudomonas aeruginosa Bacteremia

Pseudomonas aeruginosa bacteremia is associated with a high mortality rate, and meropenem (MEPM) is commonly used to treat it. However, the relationship between the time above the minimum inhibitory concentration (fT>MIC) of MEPM and its therapeutic efficacy in P. aeruginosa bacteremia has not been explored. This study aimed to investigate this relationship by defining the target % fT>MIC of MEPM as 75%. The retrospective study spanned 14 years and included hospitalized patients treated with MEPM for P. aeruginosa bacteremia. Monte Carlo simulation was used to calculate the probability of target attainment (PTA) for each patient, and the threshold for a PTA of 75% fT>MIC associated with in-hospital survival was determined using receiver operating characteristic (ROC) curves. The ROC curve-derived PTA associated with improved in-hospital survival was 65.0%, a significant finding in multivariate logistic regression analysis adjusted for patient background factors (odds ratio: 20.49, 95% confidence interval: 3.02-245.23, p = 0.005). This result suggests a dosing regimen that achieves a PTA of at least 65% when the target fT>MIC of MEPM for treating P. aeruginosa bacteremia is defined as 75%.

Aerosolized delivery of ESKAPE pathogens for murine pneumonia models

Murine pneumonia models for ESKAPE pathogens serve to evaluate novel antibacterials or to investigate immunological responses. The majority of published models uses intranasal or to a limited extent the intratracheal instillation to challenge animals. In this study, we propose the aerosol delivery of pathogens using a nebulizer. Aerosol delivery typically results in homogeneous distribution of the inoculum in the lungs because of lower particle size. This is of particular importance when compounds are assessed for their pharmacokinetic and pharmacodynamic (PK/PD) relationships as it allows to conduct several analysis with the same sample material. Moreover, aerosol delivery has the advantage that it mimics the 'natural route' of respiratory infection. In this short and concise study, we show that aerosol delivery of pathogens resulted in a sustained bacterial burden in the neutropenic lung infection model for five pathogens tested, whereas it gave a similar result in immunocompetent mice for three out of five pathogens. Moreover, a substantial bacterial burden in the lungs was already achieved 2 h post inhalation. Hence, this study constitutes a viable alternative for intranasal administration and a refinement of murine pneumonia models for PK/PD assessments of novel antibacterial compounds allowing to study multiple readouts with the same sample material.

Translational PK/PD for the Development of Novel Antibiotics-A Drug Developer's Perspective

Antibiotic development traditionally involved large Phase 3 programs, preceded by Phase 2 studies. Recognizing the high unmet medical need for new antibiotics and, in some cases, challenges to conducting large clinical trials, regulators created a streamlined clinical development pathway in which a lean clinical efficacy dataset is complemented by nonclinical data as supportive evidence of efficacy. In this context, translational Pharmacokinetic/Pharmacodynamic (PK/PD) plays a key role and is a major contributor to a "robust" nonclinical package. The classical PK/PD index approach, proven successful for established classes of antibiotics, is at the core of recent antibiotic approvals and the current antibacterial PK/PD guidelines by regulators. Nevertheless, in the case of novel antibiotics with a novel Mechanism of Action (MoA), there is no prior experience with the PK/PD index approach as the basis for translating nonclinical efficacy to clinical outcome, and additional nonclinical studies and PK/PD analyses might be considered to increase confidence. In this review, we discuss the value and limitations of the classical PK/PD approach and present potential risk mitigation activities, including the introduction of a semi-mechanism-based PK/PD modeling approach. We propose a general nonclinical PK/PD package from which drug developers might choose the studies most relevant for each individual candidate in order to build up a "robust" nonclinical PK/PD understanding.

Development and validation of a rabbit model of Pseudomonas aeruginosa non-ventilated pneumonia for preclinical drug development

Background

New drugs targeting antimicrobial resistant pathogens, including Pseudomonas aeruginosa, have been challenging to evaluate in clinical trials, particularly for the non-ventilated hospital-acquired pneumonia and ventilator-associated pneumonia indications. Development of new antibacterial drugs is facilitated by preclinical animal models that could predict clinical efficacy in patients with these infections.

Methods

We report here an FDA-funded study to develop a rabbit model of non-ventilated pneumonia with Pseudomonas aeruginosa by determining the extent to which the natural history of animal disease reproduced human pathophysiology and conducting validation studies to evaluate whether humanized dosing regimens of two antibiotics, meropenem and tobramycin, can halt or reverse disease progression.

Results

In a rabbit model of non-ventilated pneumonia, endobronchial challenge with live P. aeruginosa strain 6206, but not with UV-killed Pa6206, caused acute respiratory distress syndrome, as evidenced by acute lung inflammation, pulmonary edema, hemorrhage, severe hypoxemia, hyperlactatemia, neutropenia, thrombocytopenia, and hypoglycemia, which preceded respiratory failure and death. Pa6206 increased >100-fold in the lungs and then disseminated from there to infect distal organs, including spleen and kidneys. At 5 h post-infection, 67% of Pa6206-challenged rabbits had PaO2 <60 mmHg, corresponding to a clinical cut-off when oxygen therapy would be required. When administered at 5 h post-infection, humanized dosing regimens of tobramycin and meropenem reduced mortality to 17-33%, compared to 100% for saline-treated rabbits (P<0.001 by log-rank tests). For meropenem which exhibits time-dependent bactericidal activity, rabbits treated with a humanized meropenem dosing regimen of 80 mg/kg q2h for 24 h achieved 100% T>MIC, resulting in 75% microbiological clearance rate of Pa6206 from the lungs. For tobramycin which exhibits concentration-dependent killing, rabbits treated with a humanized tobramycin dosing regimen of 8 mg/kg q8h for 24 h achieved Cmax/MIC of 9.8 ± 1.4 at 60 min post-dose, resulting in 50% lung microbiological clearance rate. In contrast, rabbits treated with a single tobramycin dose of 2.5 mg/kg had Cmax/MIC of 7.8 ± 0.8 and 8% (1/12) microbiological clearance rate, indicating that this rabbit model can detect dose-response effects.

Conclusion

The rabbit model may be used to help predict clinical efficacy of new antibacterial drugs for the treatment of non-ventilated P. aeruginosa pneumonia.

Pharmacokinetic/pharmacodynamic analysis of cephalothin after intramuscular administration in Thoroughbred horses

A pharmacokinetic/pharmacodynamic (PK/PD) approach was used to determine a dosage regimen of cephalothin (CET) after intramuscular (IM) administration in horses. CET plasma concentrations were measured in eight horses after a single IM administration of 11 mg/kg bwt of CET. The data were modeled using a nonlinear mixed-effect model, and the probability of target attainment (PTA) of the PK/PD target was calculated for 5,000 horses generated by Monte Carlo simulations. IM administrations of CET at 11 mg/kg bwt q 8 hr and q 6 hr achieved a PTA of 90% against the MIC90 of S. zooepidemicus and S. aureus, respectively, and were considered to be effective dosage regimens. The total dose for the IM administration recommended in this study was lower than that for intravenous (IV) administration in previous studies.

Pharmacokinetics, Safety, and Tolerability of Imipenem/Cilastatin/Relebactam in Children with Confirmed or Suspected Gram-Negative Bacterial Infections: A Phase 1b, Open-Label, Single-Dose Clinical Trial

Imipenem/cilastatin/relebactam is approved for the treatment of serious gram-negative bacterial infections in adults. This study assessed the pharmacokinetics (PK), safety, and tolerability of a single dose of imipenem/cilastatin/relebactam (with a fixed 2:1 ratio of imipenem/cilastatin to relebactam, and with a maximum dose of 15 mg/kg imipenem and 15 mg/kg cilastatin [≤500 mg imipenem and ≤500 mg cilastatin] and 7.5 mg/kg relebactam [≤250 mg relebactam]) in children with confirmed/suspected gram-negative bacterial infections receiving standard-of-care antibacterial therapy. In this phase 1, noncomparative study (ClinicalTrials.gov identifier, NCT03230916), PK parameters from 46 children were analyzed using both population modeling and noncompartmental analysis. The PK/pharmacodynamic (PD) target for imipenem was percent time of the dosing interval that unbound plasma concentration exceeded the minimum inhibitory concentration (%fT>MIC) of ≥30% (MIC = 2 mcg/mL). For relebactam, the PK/PD target was a free drug area under the plasma concentration-time curve (AUC) normalized to MIC (at 2 mcg/mL) of ≥8.0 (equivalent to an AUC from time zero extrapolated to infinity of ≥20.52 mcg·h/mL). Safety was assessed up to 14 days after drug infusion. For imipenem, the ranges for the geometric mean %fT>MIC and maximum concentration (Cmax ) across age cohorts were 56.5%-93.7% and 32.2-38.2 mcg/mL, respectively. For relebactam, the ranges of the geometric mean Cmax and AUC from 0 to 6 hours across age cohorts were 16.9-21.3 mcg/mL and 26.1-55.3 mcg·h/mL, respectively. In total, 8/46 (17%) children experienced ≥1 adverse events (AEs) and 2/46 (4%) children experienced nonserious AEs that were deemed drug related by the investigator. Imipenem and relebactam exceeded plasma PK/PD targets; single doses of imipenem/cilastatin/relebactam were well tolerated with no significant safety concerns identified. These results informed imipenem/cilastatin/relebactam dose selection for further pediatric clinical evaluation.

Breaking Down the Breakpoints: Rationale for the 2022 Clinical and Laboratory Standards Institute Revised Piperacillin-Tazobactam Breakpoints Against Enterobacterales

Piperacillin-tazobactam (PTZ) is one of the most common antibiotics administered to hospitalized patients. Its broad activity against gram-negative, gram-positive, and anaerobic pathogens; efficacy in clinical trials across diverse infection types and patient populations; and generally favorable toxicity profile make it a particularly appealing antibiotic agent. PTZ susceptibility interpretive criteria (ie, breakpoints) for the Enterobacterales were initially established in 1992, as the drug was undergoing approval by the US Food and Drug Administration. In the ensuing 30 years, changes in the molecular epidemiology of the Enterobacterales and its impact on PTZ susceptibility testing, mounting pharmacokinetic/pharmacodynamic data generated from sophisticated techniques such as population pharmacokinetic modeling and Monte Carlo simulation, and disturbing safety signals in a large clinical trial prompted the Clinical Laboratory and Standards Institute (CLSI) to review available evidence to determine the need for revision of the PTZ breakpoints for Enterobacterales. After an extensive literature review and formal voting process, the susceptibility criteria were revised in the 2022 CLSI M100 document to the following: ≤8/4 µg/mL (susceptible), 16/4 µg/mL (susceptible dose-dependent), and ≥32/4 µg/mL (resistant). Herein, we provide a brief overview of the CLSI process of antibiotic breakpoint revisions and elaborate on the available data that ultimately led to the decision to revise the PTZ breakpoints.

In vivo Pharmacokinetic/Pharmacodynamic Analysis of the Efficacy of the Cefepime/Nacubactam Combination Against β-Lactamase-Producing Enterobacterales based on the Instantaneous MIC Concept

PURPOSE

Nacubactam (NAC) is a novel diazabicyclooctane β-lactamase inhibitor used in combination with cefepime (CFPM). In this study, we aimed to determine the target pharmacokinetics (PK) and pharmacodynamics (PD) values of CFPM/NAC in mice infected with β-lactamase-producing Enterobacterales, such as the carbapenemase-producing Enterobacterales.

METHODS

Three strains of β-lactamase-producing Enterobacterales, Klebsiella pneumoniae MSC 21444, Escherichia coli MSC 20662, and K. pneumoniae ATCC BAA-1898, were used for checkerboard assays and fractionation studies and dose-range studies. A PK study was performed in neutropenic mice. Additionally, PK/PD analysis was performed based on the instantaneous minimum inhibitory concentration (MICi) concept.

RESULTS

Checkerboard measurements revealed that higher NAC concentrations decreased the CFPM MIC in a concentration-dependent manner. In all tested strains, fT > MICi calculated from the PK experiments showed a high correlation with the mean change in the bacterial count of thigh-infected mice in the in vivo PD study, suggesting that fT > MICi is an optimal PK/PD parameter for monitoring the CFPM/NAC combination. The target fT > MICi values for CFPM/NAC to achieve a bacteriostatic effect, 1-log10-kill, and 2-log10-kill values were 30, 49, and 94%, respectively.

CONCLUSIONS

Our results indicate that fT > MICi is a PK/PD parameter is suitable for monitoring the CFPM/NAC combination. The minimum target value for achieving a static effect against β-lactamase-producing Enterobacterales is 30%.

In vitro and ex vivo antibacterial activity of levofloxacin against Pasteurella multocida and Escherichia coli isolated from rabbits (Oryctolagus cuniculus) - A preliminary study

Levofloxacin veterinary formulations are available in Argentina, China and India for the use in dogs, cattle, pig and sheep, but not currently in the rabbit. Only the extra-label use in rabbits is possible. Levofloxacin is not labelled for veterinary use in the EU or the USA. The activity of levofloxacin against rabbit pathogens Pasteurella multocida (P. multocida) and Escherichia coli (E. coli) was evaluated. Minimum inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were determined in broth and serum for 10 P. multocida isolates and 5 E. coli isolates from rabbits. One isolate of each bacterial species was used for the time-killing curve study in vitro and ex vivo. In vitro AUC24 /MIC ratios were used for building the inhibitory pharmacodynamic Imax model. The P. multocida MIC were 0.008-0.5 μg/mL, MBC - 0.015-0.5 μg/mL. Escherichia coli MIC was 0.008-0.03 μg/mL and MBC - 0.03-0.25 μg/mL. Bacterial counts were reduced to the limit of detection after 24 h with levofloxacin concentrations of 2 MIC and higher. All serum samples from rabbits treated with levofloxacin eliminated the bacteria within 24 h. AUC24 /MIC ratios for bacteriostatic, bactericidal and bacterial elimination effects for P. multocida and E. coli isolates were 21, 29 and 75 h and 27, 32 and 60 h, respectively. Proposed daily doses against P. multocida (MIC = 0.015 μg/mL) and E. coli (MIC = 0.03 μg/mL) isolates were calculated as ≤0.91 and ≤1.43 mg/kg, respectively. Fluoroquinolones are categorized by WHO as 'highest priority critically important antimicrobials'. Considering the increasing importance of antimicrobial stewardship, antimicrobials from a lower importance category that are active against the isolate of interest should be used in preference to fluoroquinolones. Fluoroquinolone use in veterinary medicine should be based on antimicrobial susceptibility testing in order to mitigate the risk to public health and prevent the spread of bacterial resistance.

Neutropenic Rat Thigh Infection Model for Evaluation of the Pharmacokinetics/Pharmacodynamics of Anti-Infectives

The neutropenic mouse infection model is extensively used to characterize the pharmacokinetics/pharmacodynamics (PK/PD) of anti-infective agents. However, it is difficult to evaluate agents following intravenous (i.v.) infusions using this model. Furthermore, in many drug discovery programs, lead identification and optimization is performed in rats, and pharmacology is performed in mice. Alternative models of infection are needed for robust predictions of PK/PD in humans. The rat is an alternative model of infection which can overcome the shortcomings of the mouse model. However, the rat neutropenic thigh infection (NTI) model has not been adequately characterized for evaluation of the PK/PD of anti-infectives. The aim of this study was to characterize the PK/PD of ciprofloxacin against bacterial pathogens in a rat NTI model. We studied the PK/PD relationships of ciprofloxacin against wild-type Escherichia coli, Acinetobacter baumannii, Pseudomonas aeruginosa, and Klebsiella pneumoniae in neutropenic Wistar rats following administration of 10, 30, and 100 mg/kg as single intravenous boluses and 30- and 60-min infusions. The PK/PD of ciprofloxacin against all four pathogens was AUC/MIC dependent and independent of the duration of administration at 10, 30, and 100 mg/kg. At human-equivalent rat doses, the PK/PD targets of ciprofloxacin achieved in rats for microbiological cure were similar to those reported in human patients. The neutropenic rat thigh infection model can be used to evaluate anti-infective agents intended to be administered as infusions in the clinic, and it complements the mouse model, increasing the robustness of PK/PD predictions in humans. IMPORTANCE Many antibiotics are administered as intravenous infusions in the clinic, especially in intensive care units. Anti-infective drug discovery companies develop clinical candidates that are intended to be administered as i.v. infusions in the clinic. However, there are no well-characterized models with which they can evaluate the PK/PD of the candidates following i.v. infusions. The neutropenic rat thigh infection model reported in this study helps in evaluating anti-infective agents that are intended to be administered as i.v. infusions in the clinic. The rat model is useful for simulating the clinical conditions for i.v. infusions for treatment of infections, such as acute bacterial skin and skin structure, lung, and urinary tract infections. This model is predictive of efficacy in humans and can serve as an additional confirmatory model, along with the mouse model, for determining the proof of concept and for making robust predictions of efficacy in humans.

Therapeutic drug monitoring-guided dosing for pediatric cystic fibrosis patients: recent advances and future outlooks

INTRODUCTION

Medicine use in children with cystic fibrosis (CF) is complicated by inconsistent pharmacokinetics at variance with the general population, a lack of research into this and its effects on clinical outcomes. In the absence of established dose regimens, therapeutic drug monitoring (TDM) is a clinically relevant tool to optimize drug exposure and maximize therapeutic effect by the bedside. In clinical practice though, use of this is variable and limited by a lack of expert recommendations.

AREAS COVERED

We aimed to review the use of TDM in children with CF to summarize recent developments, current recommendations, and opportunities for future directions. We searched PubMed for relevant publications using the broad search terms "cystic fibrosis" in combination with the specific terms "therapeutic drug monitoring (TDM)" and "children." Further searches were undertaken using the name of identified drugs combined with the term "TDM."

EXPERT OPINION

Further research into the use of Bayesian forecasting and the relationship between exposure and response is required to personalize dosing, with the opportunity for the development of expert recommendations in children with CF. Use of noninvasive methods of TDM has the potential to improve accessibility to TDM in this cohort.

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.

Antimicrobial Efficacy Evaluations of Metronidazole against Clostridioides difficile Infection using Fecal Pharmacokinetic and Pharmacodynamic Analyses

OBJECTIVES

The pharmacokinetics/pharmacodynamics (PK/PD) characteristics of metronidazole (MNZ) in Clostridioides difficile infection (CDI) remain unclear. We aimed to determine the PK/PD characteristics of MNZ using a fecal PK/PD analysis model.

METHODS

Susceptibility testing, time-kill studies, and post-antibiotic effect (PAE) measurements were performed to evaluate in vitro PD profiles. MNZ was subcutaneously administered to mice infected with C. difficile ATCC® 43255 to evaluate in vivo PK and PD profiles, followed by determining fecal PK/PD indices with target value.

RESULTS

MNZ exerted concentration-dependent bactericidal activities with minimum inhibitory concentration (MIC) and PAE being 0.79 µg/mL and 4.8 h, respectively, against C. difficile ATCC® 43255. The reduction in vegetative cells in feces and treatment outcomes were most closely correlated with the ratio of the area under the fecal drug concentration-time curve from 0 to 24 h to the MIC (fecal AUC24/MIC). The target value of fecal AUC24/MIC to achieve a 1 log10 reduction in vegetative cells was 188. Upon meeting the target value, high survival rates (94.5%) and low clinical sickness score grading (5.2) were achieved in the CDI mouse models.

CONCLUSIONS

The PK/PD index and its target value of MNZ for CDI treatment was fecal AUC24/MIC ≥ 188. These findings may contribute to the effective clinical use of MNZ.

Relebactam restores susceptibility of resistant Pseudomonas aeruginosa and Enterobacterales and enhances imipenem activity against chromosomal AmpC-producing species: analysis of global SMART 2018-2020

BACKGROUND

Carbapenem-resistant bacteria are an increasing problem in clinical practice; thus, it is important to identify β-lactamase inhibitors (e.g., relebactam) that can restore carbapenem susceptibility. We report analyses of relebactam enhancement of imipenem activity against both imipenem-nonsusceptible (NS) and imipenem-susceptible (S) Pseudomonas aeruginosa and Enterobacterales. Gram-negative bacterial isolates were collected for the ongoing Study for Monitoring Antimicrobial Resistance Trends global surveillance program. Clinical and Laboratory Standards Institute-defined broth microdilution minimum inhibitory concentrations (MIC) were used to determine the imipenem and imipenem/relebactam antibacterial susceptibilities of P. aeruginosa and Enterobacterales isolates.

RESULTS

Between 2018 and 2020, 36.2% of P. aeruginosa (N = 23,073) and 8.2% of Enterobacterales (N = 91,769) isolates were imipenem-NS. Relebactam restored imipenem susceptibility in 64.1% and 49.4% of imipenem-NS P. aeruginosa and Enterobacterales isolates, respectively. Restoration of susceptibility was largely observed among K. pneumoniae carbapenemase-producing Enterobacterales and carbapenemase-negative P. aeruginosa. Relebactam also caused a lowering of imipenem MIC among imipenem-S P. aeruginosa and Enterobacterales isolates from chromosomal Ambler class C β-lactamase (AmpC)-producing species. For both imipenem-NS and imipenem-S P. aeruginosa isolates, relebactam reduced the imipenem MIC mode from 16 μg/mL to 1 μg/mL and from 2 μg/mL to 0.5 μg/mL, respectively, compared with imipenem alone.

CONCLUSIONS

Relebactam restored imipenem susceptibility among nonsusceptible isolates of P. aeruginosa and Enterobacterales and enhanced imipenem susceptibility among susceptible isolates of P. aeruginosa and isolates from Enterobacterales species that can produce chromosomal AmpC. The reduced imipenem modal MIC values with relebactam may result in a higher probability of target attainment in patients.

In Vivo Pharmacodynamic Profile of EVER206, a Novel Polymyxin Antimicrobial, against Gram-Negative Bacteria in the Murine Thigh Infection Model

The objective was to determine the magnitude of the EVER206 free-plasma area under the concentration time curve (fAUC)/MIC target associated with bacteriostasis and 1-log10 kill against clinically relevant Gram-negative bacteria in the murine thigh model. Twenty-seven clinical isolates (Pseudomonas aeruginosa, n = 10; Escherichia coli, n = 9; Klebsiella pneumoniae, n = 5; Enterobacter cloacae, n = 2; and Klebsiella aerogenes, n = 1) were tested. Mice were pretreated with cyclophosphamide (induce neutropenia) and uranyl nitrate (increase the exposure of test compound through predictable renal dysfunction). Two hours postinoculation, five doses of EVER206 were administered subcutaneously. EVER206 pharmacokinetics were determined in infected mice. Data were fit using maximum effect (Emax) models to elucidate the fAUC/MIC targets for stasis and 1-log10 bacterial kill (reported as mean [range] by species). EVER206 MICs (mg/L) ranged from 0.25 to 2 mg/L (P. aeruginosa), 0.06 to 2 mg/L (E. coli), 0.06 to 0.125 mg/L (E. cloacae), 0.06 mg/L (K. aerogenes), and 0.06 to 2 mg/L (K. pneumoniae). In vivo, the mean 0-h baseline bacterial burden was 5.57 ± 0.39 log10 CFU/thigh. Stasis was achieved in 9/10 P. aeruginosa (fAUC/MIC, 88.13 [50.33 to 129.74]), 9/9 E. coli (fAUC/MIC, 112.84 [19.19 to 279.38]), 2/2 E. cloacae (fAUC/MIC, 259.28 [124.08 to 394.47]), 0/1 K. aerogenes, and 4/5 K. pneumoniae (fAUC/MIC, 99.26 [62.3 to 144.43]) isolates tested. 1-log10 kill was achieved in 9/10 for P. aeruginosa (fAUC/MIC, 106.43 [55.22 to 152.08]), 3/9 for E. coli (fAUC/MIC, 258.96 [74.08 to 559.4]), and 1/2 for E. cloacae (fAUC/MIC, 255.33). Using the murine thigh model, the fAUC/MIC targets of EVER206 were assessed across a broad MIC distribution. Integrating these data with microbiologic and clinical exposure data will aid in determining the clinical dose of EVER206.

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.

Antimicrobial Activity of Gepotidacin Tested against Escherichia coli and Staphylococcus saprophyticus Isolates Causing Urinary Tract Infections in Medical Centers Worldwide (2019 to 2020)

The in vitro activities of gepotidacin and comparator agents against 3,560 Escherichia coli and 344 Staphylococcus saprophyticus collected from female (81.1%) and male (18.9%) patients with urinary tract infections (UTIs) in a global prospective surveillance program in 2019 to 2020 were determined. Isolates collected from 92 medical centers in 25 countries, including the United States, Europe, Latin America, and Japan, were tested for susceptibility by reference methods in a central monitoring laboratory. Gepotidacin inhibited 98.0% (3,488/3,560 isolates) of E. coli and 100% (344/344 isolates) of S. saprophyticus at gepotidacin concentrations of ≤4 μg/mL and ≤0.25 μg/mL, respectively. This activity was largely unaffected with isolates that demonstrated resistance phenotypes to other oral standard-of-care antibiotics, including amoxicillin-clavulanic acid, cephalosporins, fluoroquinolones, fosfomycin, nitrofurantoin, and trimethoprim-sulfamethoxazole. Gepotidacin also inhibited 94.3% (581/616 isolates) of E. coli isolates with an extended-spectrum β-lactamase-producing phenotype, 97.2% (1,085/1,129 isolates) of E. coli isolates resistant to ciprofloxacin, 96.1% (874/899) of E. coli isolates resistant to trimethoprim-sulfamethoxazole, and 96.3% (235/244 isolates) of multidrug-resistant E. coli isolates at gepotidacin concentrations of ≤4 μg/mL. In summary, gepotidacin demonstrated potent activity against a large collection of contemporary UTI E. coli and S. saprophyticus strains collected from patients worldwide. These data support the further clinical development of gepotidacin as a potential treatment option for patients with uncomplicated UTIs.

ADME, Pharmacokinetic Scaling, Pharmacodynamic and Prediction of Human Dose and Regimen of Novel Antiviral Drugs

The search for new drugs is an extremely time-consuming and expensive endeavour. Much of that time and money go into generating predictive human pharmacokinetic profiles from preclinical efficacy and safety animal data. These pharmacokinetic profiles are used to prioritize or minimize the attrition at later stages of the drug discovery process. In the area of antiviral drug research, these pharmacokinetic profiles are equally important for the optimization, estimation of half-life, determination of effective dose, and dosing regimen, in humans. In this article we have highlighted three important aspects of these profiles. First, the impact of plasma protein binding on two primary pharmacokinetic parameters-volume of distribution and clearance. Second, interdependence of primary parameters on unbound fraction of the drug. Third, the ability to extrapolate human pharmacokinetic parameters and concentration time profiles from animal profiles.

All Roads Lead to Rome: Enhancing the Probability of Target Attainment with Different Pharmacokinetic/Pharmacodynamic Modelling Approaches

In light of rising antimicrobial resistance and a decreasing number of antibiotics with novel modes of action, it is of utmost importance to accelerate development of novel treatment options. One aspect of acceleration is to understand pharmacokinetics (PK) and pharmacodynamics (PD) of drugs and to assess the probability of target attainment (PTA). Several in vitro and in vivo methods are deployed to determine these parameters, such as time-kill-curves, hollow-fiber infection models or animal models. However, to date the use of in silico methods to predict PK/PD and PTA is increasing. Since there is not just one way to perform the in silico analysis, we embarked on reviewing for which indications and how PK and PK/PD models as well as PTA analysis has been used to contribute to the understanding of the PK and PD of a drug. Therefore, we examined four recent examples in more detail, namely ceftazidime-avibactam, omadacycline, gepotidacin and zoliflodacin as well as cefiderocol. Whereas the first two compound classes mainly relied on the ‘classical’ development path and PK/PD was only deployed after approval, cefiderocol highly profited from in silico techniques that led to its approval. Finally, this review shall highlight current developments and possibilities to accelerate drug development, especially for anti-infectives.

Phenotypes, genotypes and breakpoints: an assessment of β-lactam/β-lactamase inhibitor combinations against OXA-48

BACKGROUND

Two of the three recently approved β-lactam agent (BL)/β-lactamase inhibitor (BLI) combinations have higher CLSI susceptibility breakpoints (ceftazidime/avibactam 8 mg/L; meropenem/vaborbactam 4 mg/L) compared with the BL alone (ceftazidime 4 mg/L; meropenem 1 mg/L). This can lead to a therapeutic grey area on susceptibility reports depending on resistance mechanism. For instance, a meropenem-resistant OXA-48 isolate (MIC 4 mg/L) may appear as meropenem/vaborbactam-susceptible (MIC 4 mg/L) despite vaborbactam's lack of OXA-48 inhibitory activity.

METHODS

OXA-48-positive (n = 51) and OXA-48-negative (KPC, n = 5; Klebsiella pneumoniae wild-type, n = 1) Enterobacterales were utilized. Susceptibility tests (broth microdilution) were conducted with ceftazidime/avibactam, imipenem/relebactam and meropenem/vaborbactam, as well as their respective BL partner. Antimicrobial activity of all six agents was evaluated in the murine neutropenic thigh model using clinically relevant exposures. Efficacy was assessed as the change in bacterial growth at 24 h, compared with 0 h controls.

RESULTS

On average, the three BL/BLI agents resulted in robust bacteria killing among OXA-48-negative isolates. Among OXA-48-positive isolates, poor in vivo activity with imipenem/relebactam was concordant with its resistant phenotypic profile. Variable meropenem/vaborbactam activity was observed among isolates with a 'susceptible' MIC of 4 mg/L. Only 30% (7/23) of isolates at meropenem/vaborbactam MICs of 2 and 4 mg/L met the ≥1-log bacterial reduction threshold predictive of clinical efficacy in serious infections. In contrast, ceftazidime/avibactam resulted in marked bacterial density reduction across the range of MICs, and 96% (49/51) of isolates exceeded the ≥1-log bacterial reduction threshold.

CONCLUSIONS

Data demonstrate that current imipenem/relebactam and ceftazidime/avibactam CLSI breakpoints are appropriate. Data also suggest that higher meropenem/vaborbactam breakpoints relative to meropenem can translate to potentially poor clinical outcomes in patients infected with OXA-48-harbouring isolates.

Pharmacokinetic/Pharmacodynamic Index Linked to In Vivo Efficacy of the Ampicillin-Ceftriaxone Combination against Enterococcus faecalis

Combination therapy with ampicillin plus ceftriaxone (AMP+CRO) is the first-line therapy for treating severe infections due to Enterococcus faecalis. However, the pharmacokinetic/pharmacodynamic (PK/PD) index linked to the in vivo efficacy of the combination is not yet defined, hindering dose optimization in the clinic. Because classical PK/PD indices are not directly applicable to antimicrobial combinations, two novel indices were tested in the optimized murine model of infection by E. faecalis to delineate the potentiation of AMP by CRO: the time above the CRO threshold (T_>threshold) and the time above the AMP instantaneous MIC (T_>MICi). The potential clinical relevance was evaluated by simulating human doses of AMP and CRO. Hill's equation fitted well the exposure-response data in terms of T_>threshold, with a CRO threshold of 1 mg/L. The required exposures were 46%, 49%, and 52% for stasis and 1- and 2-log₁₀ killing, respectively. Human ceftriaxone doses of 2 g every 12 h (q12h) would reach the target in >90% of strains with thresholds ≤64 mg/L. The AMP T_>MICi index also fitted well, and the required exposures were 37%, 41%, and 46% for stasis and 1- and 2-log₁₀ killing, respectively. In humans, the addition of CRO would allow use of lower AMP doses to reach the same T_>MICi and to treat strains with higher MICs. This is the first report of the PK/PD indices and required magnitudes linked to AMP+CRO against E. faecalis; these results can be used as the basis to guide the design of clinical trials to improve combined therapy against enterococci.

Development of an optimized and practical pharmacokinetics/pharmacodynamics analysis method for aztreonam/nacubactam against carbapenemase-producing K. pneumoniae

BACKGROUND

Nacubactam, a new β-lactamase inhibitor with antibacterial activity, is being developed as a single drug to be co-administered with cefepime or aztreonam. However, determining pharmacokinetics/pharmacodynamics (PK/PD) parameters in β-lactam/β-lactamase inhibitor combinations remains challenging. We aimed to establish a practical PK/PD analysis method for aztreonam/nacubactam that incorporates instantaneous MIC (MICi).

METHODS

Based on chequerboard MIC measurements, MICi of aztreonam against carbapenemase-producing Klebsiella pneumoniae in the presence of nacubactam was simulated.

RESULTS

The mean change in the bacterial count of thigh-infected mice in an in vivo PD study was plotted based on %fT>MICi and analysed using the inhibitory effect sigmoid Imax model. fT>MICi calculated from the PK experiments showed a high correlation with the in vivo bactericidal effect, suggesting that fT>MICi is the optimal PK/PD parameter for aztreonam/nacubactam. The target values of fT>MICi achieving growth inhibition, 1 log10 kill and 2 log10 kill, were 22, 38% and 75%, respectively.

CONCLUSIONS

The PK/PD analysis method proposed in this study is promising for determining practical PK/PD parameters in combination therapy. In addition, this is the first report of aztreonam/nacubactam showing a potent in vivo therapeutic effect against NDM-producing K. pneumoniae.

A liquid chromatography-tandem mass spectrometry method for the quantification of ampicillin/sulbactam and clindamycin in jawbone, plasma, and platelet-rich fibrin: Application to patients with osteonecrosis of the jaw

Ampicillin in combination with sulbactam is a widely used drug choice for infection prophylaxis, especially in oral and maxillofacial surgery. Clindamycin serves as an alternative in patients with known allergy to β-lactam antibiotics. To ensure effective prophylaxis, it is important to achieve sufficiently high concentrations of active antibiotic substances in the tissues affected by the surgery. To this end, a LC-MS/MS method was developed and validated that allows the quantification of ampicillin, sulbactam and clindamycin in jawbone, plasma, and so-called platelet-rich fibrin (PRF). Validation was performed in accordance with the European Medicines Agency guidelines for bioanalytical method validation. For all matrices, sample processing was carried out by protein precipitation with acetonitrile or methanol 80%, containing the isotope labelled internal standards (IS) of the three drugs. Analytes were separated on a pentaflourophenyl column at 20 °C using gradient elution. Furthermore, detection was accomplished by electrospray ionisation in positive-ion mode (ampicillin, clindamycin and corresponding IS) and negative-ion mode (sulbactam and corresponding IS) in combination with multiple reaction monitoring. Depending on the analyte and the matrix under investigation, calibration curves ranged from 0.14 to 59.8 µg/g (jawbone - ampicillin), 2.0-1000 µg/mL (plasma - ampicillin), and 1.0-495 µg/mL (PRF - ampicillin). All analytes fulfilled the requirements of the guideline regarding sensitivity, linearity, selectivity, carryover, within-run and between run accuracy and precision, matrix effect and extraction recovery in all matrices. The method was successfully applied to measure concentrations of ampicillin, sulbactam and clindamycin in real-life samples obtained in routine clinical practice.

Dose selection for a phase III study evaluating gepotidacin (GSK2140944) in the treatment of uncomplicated urogenital gonorrhoea

BACKGROUND

Gepotidacin is a novel, first-in-class triazaacenaphthylene antibiotic that inhibits bacterial DNA replication by a distinct mechanism of action and is active against most strains of Neisseria gonorrhoeae (N. gonorrhoeae). Phase II data suggested higher exposures were needed for efficacy and to suppress resistance development. A translational approach using in vitro pharmacokinetic/pharmacodynamic (PK/PD) and clinical data was used to select a gepotidacin dose for a phase III study. In this narrative review of previously shown data, we summarise how a translational approach based on in vitro PK/PD and population PK modelling and simulation data was undertaken to select a dosing regimen for the ongoing phase III gepotidacin study in participants with uncomplicated urogenital gonorrhoea.

METHODS

For dose selection, prior in vitro minimum inhibitory concentrations (MICs) and PK/PD data were available. PK modelling was conducted to determine a dose that would limit plasma concentrations to less than 14 µg/mL (as concentrations above this are associated with QT prolongation and effects associated with acetylcholinesterase inhibition) while maintaining ≥90% probability of target attainment (PTA) for efficacy and resistance suppression against N. gonorrhoeae isolates with gepotidacin MICs ≤1 µg/mL.

RESULTS

Two 3000 mg gepotidacin doses, administered 10-12 hours apart, resulted in PTA of ≥97.5% and ≥91.7% for gepotidacin MICs ≤1 µg/mL for the ratio of the area under the free drug plasma concentration-time curve over 24 hours to the MIC (fAUC_0-24/MIC) efficacy, and resistance suppression targets of 40 and 46, respectively, but limited the occurrence of maximum plasma concentrations ≥14 µg/mL.

CONCLUSIONS

Two gepotidacin 3000 mg oral doses 10-12 hours apart provide ~2-fold higher systemic exposures, increase efficacy for higher gepotidacin MIC N. gonorrhoeae isolates, reduce resistance potential and limit plasma concentrations of potential safety concern, compared with higher doses.